holocene glacier fluctuations in south america and antarctica
TRANSCRIPT
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7/21/2019 Holocene Glacier Fluctuations in South America and Antarctica
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Quaternary ScienceReviews Vo l. 7, pp. 185-1 98, 1988. 0277-3791/88 0,00 + .50
Printed in Great Britain. All rights reserved. Copyright (~) 1988 Pergamo n Press plc
H O L O C E N E G L A C I E R F L U C T U A T I O N S I N S O U T H A M E R I C A A N D A N T A R C T I C A
C h a l m e r s M . C l a p p e r t o n
Department of Geography University of Aberdeen Aberdeen A B 9 2UF Scotland U.K.
a n d
D a v i d E . S u g d e n
Department of Geography University of Edinburgh Edinburgh EH 8 9XP Scotland U.K .
G l a c i a l g e o l o g ic e v i d e n c e in d i c a t e s t h a t g la c i e r s t h r o u g h o u t t h e A n d e s a n d A n t a r c t i c a f l u c t u a t e d d u r i n g t h e H o l o c e n e .
R a d i o c a r b o n d a t i n g a n d o t h e r a g e d e t e r m i n a t i o n s s u g g e s t t h a t g l a c i e r s re a d v a n c e d s i g n i fi c a n tl y o n ly d u r i n g t h e l a s t 5 k a ,
r e a c h i n g p o s i ti o n s f r o m s e v e r a l 1 0 0 m t o a f e w k i l o m e t r e s b e y o n d t h e i r p r e s e n t l i m i t s . I n S o u t h A m e r i c a t e n u o u s e v i d e n c e f r o m
r a d i o c a r b o n d a t e s , w i t h d e n d r o c h r o n o l o g i c a l d a t a a n d e n v i r o n m e n t a l i n t e r p r e t a ti o n s f r o m p o l l e n a n a l y se s i n d ic a t e f o u r m a i n
p e r i o d s o f N e o g l a c i a l a d v a n c e , c u l m i n a t in g 5 0 0 0 - 4 00 0 B P , 3 0 0 0 - 2 0 0 0 B P , 1 3 00 -1 0 00 B P , a n d 1 5 t h - l a t e 1 9 th c e n t u r i e s ; s m a l le r
a d v a n c e s m a y h a v e o c c u r r e d a t c a . 8 4 0 0 B P , c a . 7 5 0 0 B P , a n d c a . 6 3 00 B P . T h e m e a g r e d a t a a r e c o n s i s te n t i n in d i c a t in g b r o a d
s y n c h r o n y t h r o u g h o u t t h e A n d e s d u r i n g t h e l a s t 5 k a , s u g g e s t i n g re s p o n s e t o g l o b a l c li m a t i c c h a n g e s . A n o m a l i e s e x i st i n
P a t a g o n i a w h e r e s o m e t i d e - w a t e r g l a c ie r s re a c h e d t h e i r m a x i m a l H o l o c e n e l i m i ts r e c e n t l y t h i s c e n tu r y .
T h e b r o a d s p e c t r u m o f d i ff e r i n g A n t a r c t i c e n v i r o n m e n t s p r o d u c e s i n t e r e s t in g c o n t r a s ts . S o m e l o c a l g la c i e rs in t h e M c M u r d o
S o u n d a r e a o f t h e E a s t A n t a r c t i c c o n t i n e n t a r e m o r e e x t e n s i v e n o w t h a n d u r i n g t h e g l o b a l g l a c ia l m a x i m u m c a . 1 8 k a B P , w h e n
t h e y w e r e s t a r v e d o f p r e c ip i t a t io n . C o n s i s t e n t a g r e e m e n t a m o n g 1 4 r a d i o c a r b o n d a t e s f r o m t h e S o u t h S h e t l a n d I s l an d s i n d i c a te s
t w o m a i n H o l o c e n e g l a c i e r a d v a n c e s , t h e m o s t e x t e n s i v e ( 2 - 3 k m ) p e a k i n g i n t h e 1 2 t h c e n t u r y , t h e o t h e r c u l m i n a t i n g i n t h e
1 8 t h - 1 9 t h c e n t u r y . G l a c i e r s in S o u t h G e o r g i a r e a c h e d t h e i r m o s t a d v a n c e d H o l o c e n e l i m i ts b e f o r e 2 2 00 B P . M o r a i n e F j o r d
g l a c i e r , w h i c h c u l m i n a t e d a s a 6 k m a d v a n c e b e t w e e n 1 4 6 0 - 1 7 0 0 r a d i o c a r b o n B P , m a y h a v e l a g g e d 4 0 0 -6 5 0 y e a r s b e h i n d t h e
c l i m a t ic f o rc i n g b e c a u s e i t c o u l d o n l y a d v a n c e i n it s d e e p - w a t e r f j o r d b y b u i l d i n g a m o r a i n e b a n k . S m a l l e r a d v a n c e s i n S o u t h
Georg ia cu lmina ted in the 17 th-19 th cen tur i es and dur ing the 1920s -30s .
T h e r e i s n o f i r m e v i d e n c e o f g l a c i e r a d v a n c e s b e f o r e 3 k a B P i n t h e S o u t h e r n O c e a n - s u b - A n t a r c t i c d o m a i n , b u t b r o a d
s y n c h r o n y i n g l a c ie r a d v a n c e s d u r i n g t h e l a s t c a . 3 0 00 y e a r s a p p e a r s t o h a v e o c c u r r e d t h r o u g h o u t t h e A n d e s - A n t a r c t i c t r a n s e c t .
C a u t i o n i s r e q u i r e d i n t h e i n t e r p r e t a t i o n a n d c o r r e l a t io n o f m o r a i n e s a s s o c i a t e d w i th c a l v i n g g l a c ie r s a n d o f t h o s e w i t h p o o r l y
cons t r a ined da t ing .
I N T R O D U C T I O N
T hi s r e v i e w c ons ide r s t he e v ide nc e f o r Holoc e ne
g la c ie r f luc tua t i ons a long a un iqu e l a nd- ba se d t r a nse c t
f rom equa tor ia l to po lar la t itudes Fig. 1) . I t assesses
the va l i d i t y o f da t a g ive n i n a num be r o f pa pe r s
suppor t i ng a m ode l o f a t l e a s t f our m a jor g l a c i e r
a dva nc e s i n t he Ande s . D i f f i c u l t i e s e nc oun te r e d i n
ide n t i f y ing a nd da t i ng e qu iva l e n t Holoc e ne g l a c i e r
a d v a n c e s o n t h e A n t a r c t i c c o n t i n e n t a n d o n s u b -
Anta r c t i c i s la nds a r e d i sc usse d p r io r t o a n ove r v i e w of
t h e e n t i re A n d e a n - A n t a r c t i c t r a n se c t in a n a t t e m p t t o
d i sc e r n a ny sync hr ony o r l a c k o f sync hr ony in t he
e m e r g in g c hr ono log i e s .
S O U T H A M E R I C A
Gonz a l e z et al. 1965), Och seniu s 1980), and Th ou re t
a nd va n de r Ha m m e n 1981). T he e a r li e s t a dva nc e
a ppe a r s t o h a ve be e n a t c a . 8400 BP in Pa t a gon ia
R6th l i sbe r ge r , 1987) , bu t t he r e g iona l e x t e n t a nd
c l im a t i c s i gn i f i c a nc e o f t h i s e ve n t r e m a in obsc ur e .
Po l l e n a na lyses o f r a d ioc a r bon- da t e d pe a t c o r e s ha ve
suggested cold c l imat ic spe l l s a t ca . 7500 BP, shor t ly
be f or e 6050 BP , a nd 6 - - 5 ka BP Cla pp e r ton , 1983).
T he se i n f e r e nc e s a r e suppor t e d by t he r a d ioc a r bon
da t ing o f o r ga n i c m a te r i a l i nc or po r a t e d w i th in l a t e ra l
m or a ine s i n the t r op ic a l An de s R6th l i sbe r ge r , 1987) .
M o s t g l a c i e r a d v a n c e s i n t h e e a r l y - m i d H o l o c e n e
a ppe a r t o ha ve be e n r e l a t i ve ly sm a l l a nd im ply t ha t
m os t Ande a n g l a c i e r s a t t ha t t im e m a y ha ve be e n
s im i la r in s i z e , o r sm a l l e r, c o m p a r e d w i th t hose o f t he
pr e se n t da y .
Early-Mid Holocene
I t i s ve r y l i ke ly t ha t m os t g l a c i e r s i n t he Ande s
wi thdr e w wi th in t he i r l a t e - g l a c i a l l im i t s dur ing t he
p e r i o d o f H o l o c e n e w a r m t h t h a t p e a k e d c a. 9 4 0 0 -8 6 0 0
BP He usse r a nd S t r e e t e r , 1980): som e sm a l l i c ef i elds
a nd g l a c i e r sys t e m s m a y ha ve d i sa ppe a r e d e n t i r e ly .
A l th oug h the r e a r e f e w s t r a ti g r a ph i c a l a nd m or ph o-
log i c a l da t a sugge s t i ng t ha t g l a c i e r s e xpa nde d o r r e -
d e v e l o p e d d u r i n g t h e n e x t f o u r m i l l e n n i a , e a r l y - m i d
Holoc e ne a dva nc e s ha ve be e n i de n t i f i e d by R6th l i s -
be r ge r 1987) a nd i n f e r r e d f r om po l l e n s tud i e s by
Late H olocene Neoglaciation
T h e r e i s a g r o w i n g b o d y o f e v i d e n c e t h a t A n d e a n
g la ci e rs e xp a nde d o n se ve r a l oc c a s ions dur ing t he l a st
5 k a , t h e t i m e p e r i o d c o n v e n t i o n a l ly k n o w n a s N e o -
g l a c i a t i on . T he m ode l f o r Ne ogla c i a t i on i n t he Ande s
de r ive s f r om the e x t e ns ive wor k o f J .H . M e r c e r i n
Pa t a gon ia . H i s sc h e m e of t h r e e g l a c ia l a dva nc e s pe a k-
ing 4600- 4200 B P , 2700- 2000 BP , a nd A .D . 1600- 1850
M e r c e r , 1965) ha s be e n r e in f o r c e d a nd r e pe a t e d i n a
nu mb er of pap ers M ercer , 1968, 1970, 1976, 1982).
C l a p p e r t o n 1 98 3) e x t e n d e d t h is s c h e m e t o e n c o m p a s s
185
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186 C M C l a p p e rt o n an d D E S u g d e n
0
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EL ALTAR
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~ C O R O I L E R A B I . A N C A
HUA$CARAN
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Mendoz a
TRONADOR ._ ~
r , ~ ' ) ~
4 o S
H IEt .O PATAGON IC O N OR TE
5 H IEL O
P A T A G O N I C O S U N
8 K M
I S C A L E
t : 3 2 M
~ HIELO
PATAGONICO
SUUR
~ 5 0
AN TAI~ C TIC ,~ ~ ~ ~ ~ ' N G GEOR
C ON VER GENC E 6 0 ISL A N D R N T A R C T / C
I S L A N D S ~ * P ~ G E O R G I A ~ \
S O U T H S H E T L A N D ~ - 1= MORAINE
L I V I N G S T O N I S L A N D ~ ' ~ ~ ~ - F
G E O Na E V l S O U N O ~ ~ O
H A L L E Y B A Y
ROSS SEA
I
M C M . . . SOUND ~_~ta~ NT RCTIC
F I G 1 L o c a t i o n m a p s h o w i n g
the ent i re Andean mountain sys tem, observing that
data from Colombia and Peru in part i cu lar appear to
conf irm that g lac iers in the central and northern A nde s
had a l so advanced dur ing the same three Neoglac ia l
t ime per iods ; an addi t ional s tage was sugges ted for the
8 t h - 9 t h c e n t u ri e s A . D . A l t h o u g h t h e s c h e m e i s b a s e d
on rather meagre data , no ev idence has ye t been found
to warrant a major m odi f i cat ion , and so i t is used here
as a framework for d i scuss ing Neoglac ia l g lac ier f luc -
tuat ions in South America .
F i r s t Ne o g l a ci a l a d v an c e: 5 4 k a B P
Morphological ev idence of g lac ier advances ear l i er
than those of recent centur ies i s be l i eved to be mos t
p l a c e s m e n t i o n e d i n t h e t e x t
obvious in some parts of Patagonia where lateral and
terminal moraines bear ing mature vegetat ion contras t
wi th younger , sparse ly vegetated moraines . The
val id i ty of ev idence that these moraines were formed
by g lac ier advances dur ing 5- 4 ka BP i s worthy of
e x a m i n a t i o n . F o r e x a m p l e , i m m e n s e p i e d m o n t l o b e s
d e v e l o p e d o n t h e n o r t h e a s t e r n s i d e o f t h e H i e l o
Patagonico Norte where the Gualas , San Rafae l , and
San Q uint in o ut l e t g lac iers advanced 15 km, 10 km,
and 2 km, respect ive ly , beyon d the ir present l imi ts
Fig . 2) . The age of the consp icuous moraines front ing
these g lac iers i s imprec i se ly known. A near-basal
sample of organic s ed iments taken from a ket t l e pond
on the outermos t moraine at Glac iar San Rafae l gave a
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Holocene Glacier Fluctuations in South America and Antarctica 187
FIG. 2a. M ap of the main Patagonian icefields, Hielo Patagonico Norte and H ielo Patagonico Sur, showing ocation of glaciers
referred to in the tex t.
. . . . . .. . . . . .. 1 9 t h C . M OR / ~
- - - - F I R S T N E O
P A C / F / C O C ~ W
0 I ~ K M
FIG. 2b. G laciers and N eoglacial morain es in the L aguna de San Rafael area, Patagonia (Chile) (after Heusser, 1960).
r a d i o c a r b o n a g e o f 36 1 0 + 4 0 0 B P ( l a te r r e c a l c u l a t e d
t o 3 7 4 0 + 4 0 0 B P - - M e r c e r , 1 9 8 2 , p . 3 8 ) . H e u s s e r
( 1 9 6 0 ) o r i g i n a l l y e s t i m a t e d t h e m o r a i n e t o b e c a . 4 0 00
y e a r s o l d , b u t t h e d a t a c l e a rl y g iv e o n l y a n u p p e r
l im i t in g a g e a n d t h e f e a t u r e c o u l d b e v e r y m u c h o l d e r .
A l o w e r l i m i ti n g a g e w a s a s s u m e d f r o m a s o - c a l l e d
i n t e r f lu c t u a t i o n a l s e c t io n w h e r e s i lt y p e a t o v e r l a i n b y
8 5 c m o f t il l g a v e a r a d i o c a r b o n a g e o f 6 8 5 0 + 2 0 0 B P
( H e u s s e r , 1 9 6 0 ). S i n c e t h e s i t e is w i t h i n t h e g l a c i e r s
1 9 t h c e n t u r y m o r a i n e l i m i t s , t h e o v e r l y i n g t il l c o u l d b e
n o m o r e t h a n 1 0 0 y e a r s o l d , a n d o n e i m p l i c a t i o n is t h a t
G l a c i a r S an R a f a e l m a y n o t h a v e a d v a n c e d f u r t h e r t h a n
i t s 1 9 t h c e n t u r y l i m i t s f o r m o r e t h a n 7 0 0 0 y e a r s . T h u s ,
t h e o l d e r m o r a i n e s e n c l o s i n g L a g u n a S a n R a f a e l c o u l d
b e l a t e - g l a c i a l i n a g e , a s s u s p e c t e d b y M u l l e r ( 1 9 6 0 ).
D o u b t c o n c e r n i n g t h e N e o g l a c i a l h i s t o r y o f G l a c i a r S a n
R a f a e l is c o m p o u n d e d b y t h e a b s e n c e o f a n y e v i d e n c e
f o r a n e x p a n s i o n a b o u t 3 - 2 k a B P s o t h a t M e r c e r s
i n t e r p r e t a t i o n t h a t t h e S a n R a f a e l m o r a i n e s i n d i c a t e a n
a d v a n c e p e a k i n g 4 7 0 0 - 4 2 0 0 B P w i l l r e m a i n e q u i v o c a l
u n t il f u r t h e r d a t a a r e f o u n d .
R a d i o c a r b o n d a t e s f r o m t h e v i c i n it y o f o t h e r g l a c i er s
i n P a t a g o n i a g i v e n o m o r e t h a n u p p e r l i m i ti n g a g e s f o r
t h e m o r a i n e s w i t h w h i c h t h e y a r e a s s o c i a t e d ( T a b l e 1 ) .
T h e s t r o n g e s t e v i d e n c e f o r a g la c i e r a d v a n c e 5 - 4 k a B P
c o m e s f r o m o n l y o n e s i t e , a t G l a c i a r S a n L o r e n z o E s t e
( F i g . 2 ) , w h e r e a s m a l l t r e e w a s a p p a r e n t l y k i l l e d w h e n
a n i c e - d a m m e d l a k e d e v e l o p e d a s th e g l a c ie r a d v a n c e d
a n d f o r m e d i ts o u t e r m o s t N e o g l a c i a l e n d m o r a i n e . T h e
r a d i o c a r b o n a g e o f t h e t r e e i s 4 5 9 0 + 1 15 B P ( M e r c e r ,
1 9 68 ). E v e n t h is e v i d e n c e b e c o m e s d o u b t f u l i f t h e t r e e
d i e d f o r o t h e r r e a s o n s .
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188 C M Clapper ton and D E Sugden
O u t s i d e P a t a g o n i a o n l y m e a g r e e v i d e n c e s u p p o r t s a
g l ac i er a d v a n c e a t c a . 5 - 4 k a B P . I t c o m e s f r o m P e r u ,
w h e r e r a d i o c a r b o n d a t e s ( T a b l e 1 ) w e r e d e r i v e d f r o m
o r g a n i c m a t e r i a l i n t e r b e d d e d w i t h i n s u p e r p o s e d
m o r a i n e s ( m o r a i n e s f o r m e d b y r e p e a t e d g l ac i er a d -
v a n c e s t o ro u g h l y t h e s a m e p o s i t i o n ) p e r i o d i c a l l y
b u ry i n g so i ls a n d v e g e t a t i o n ( c . f . R r t h l i s b e rg e r a n d
S c h n e e b e l i , 1 97 9) . Tw o o f t h e d a t e s f ro m t h e C o rd i l l e r a
B l a n c a a r e f r o m s o il s d e v e l o p e d o n u n d e r l y in g m o r a i n e
p re -d a t i n g c a . 3 5 0 0 -3 6 0 0 B P (C l a p p e r t o n , 1 9 8 3) . Th e
m o r a i n i c m a t e r i a l c o u l d t h e r e f o r e b e a s s o c i a t e d w i t h a n
a d v a n c e b e t w e e n 5 k a a n d 4 k a B P , b u t t h is r e m a i n s
u n c e r t a i n i n t h e a b s e n c e o f l o w e r b r a c k e t i n g d a t e s . T h e
t h ir d d a t e is f r o m p e a t i n t e r b e d d e d w i t h c o a r s e o u t w a s h
s e d i m e n t s d o w n s t r e a m f r o m t h e l a r g e d e b r i s - c o v e r e d
s u p e r p o s e d m o r a i n e o f C h o p i c a l q u i g l a c i e r e a s t o f
H u a s c a ra n i n t h e C o rd i l l e r a B l a n c a (F i g . 1 ) . Th e s i t e
l ie s in s i d e m o ra i n e l im i t s n o w j u d g e d t o b e o f l a te -
g l a ci a l a g e o n t h e b a s i s o f t h e a m o u n t o f s n o w l i n e
l o w e r i n g t h e y in d i c a t e . Tw o i n t e rp r e t a t i o n s o f t h e p e a t
b e d a r e p o s s i b le . O n e i s t h a t t h e p e a t b e c a m e b u r i e d b y
o u t w a s h f ro m a N e o g l a c i a l a d v a n c e s h o r t l y a f t e r c a .
4 3 00 B P ; t h e o t h e r i s t h a t p e a t d e v e l o p e d o n o u t w a s h
f r o m a N e o g l a c i a l a d v a n c e t h a t c u l m i n a t e d s o m e t i m e
b e fo re c a . 4 3 0 0 B P .
I t i s c lear tha t g lac ia l -geo log ic ev idence fo r a
N e o g l a c i al a d v a n c e c a . 5 - 4 k a B P i n S o u t h A m e r i c a i s
i n c o n c l u s i v e . N e v e r t h e l e s s , t h e e v i d e n c e , t h o u g h
t e n u o u s , i s s u f f i c ie n t l y c o n s i s t e n t a n d p e r s u a s i v e t o
s u p p o r t a w o r k i n g h y p o t h e si s , b u t m a n y m o r e d a t a a r e
r e q u i r e d t o t e s t i t . W e a k t h o u g h t h e g l a c i a l e v i d e n c e
m a y b e , e n v i r o n m e n t a l i n t e r p r e t a ti o n s f r o m p o l l e n
a n a l y s e s a t s i t e s a s f a r a p a r t a s C o l o m b i a a n d s o u t h e rn
C h i l e a r e c o n s i s t e n t i n s u g g e s t in g a c l i m a t i c r e v e r s a l t o
c o o l e r , m o i s t e r c o n d i t i o n s d u r i n g t h e i n te rv a l 5 - 4 k a
B P ( T h o u r e t a n d v a n d e r H a m m e n , 1 98 1; H e u s s e r ,
1984 ; He uss er and S t ree te r , 1980). C l ima t ica l ly
s e n s i t i v e g l a c i e r s m a y r e a s o n a b l y b e e x p e c t e d t o h a v e
a d v a n c e d i n t h e c o n d i t i o n s d e d u c e d f o r C h i l e a n P a t a -
g o n ia w h e r e m e a n a n n u a l t e m p e r a t u r e m a y h a v e
d r o p p e d b y 2 C a n d m e a n a n n u a l p r e c i p i ta t i o n r o s e b y
3000 mm (Heusser and S t ree te r , 1980 , F ig . 2 , p . 1346) .
Second Neog lac ia l advance: 3 2 ka BP
Ev i d e n c e fo r a d i s t i n c t i v e N e o g l a c i a l a d v a n c e c u l -
m i n a t i n g 3 -2 k a B P i n S o u t h A m e r i c a i s a l s o h i g h ly
u n c e r t a in , t h e o n l y d a t a c o m i n g f r o m P a t a g o n i a , P e r u ,
a n d E c u a d o r ( T a b l e 1 ). A p p a r e n t c o n f i r m a t io n o f a
2 7 0 0 - 2 0 0 0 B P a d v a n c e h a s b e e n a r g u e d f r o m a s it e
c l o s e t o G l a c i a r U p s a l a , a l a rg e o u t l e t f r o m t h e e a s t e rn
s i d e o f H i e l o P a t a g o n i c o S u r i n A r g e n t i n a ( M e r c e r ,
1965, 1976 , 1982) . A log em be dd ed in ti l l s eem ing ly
a s s o c ia t e d w i t h a 1 0 k m r e a d v a n c e m o r a i n e ( P e a r s o n 1 )
g a v e a r a d i o c a rb o n a g e o f c a . 2 3 0 0 B P , i m p l y i n g t h a t
the g lac ie r reached i t s l imi t sho r t ly a f te r th i s da te .
Ex a m i n a t i o n o f t h e o r i g i n a l f ie l d d e s c r i p t io n s u g g e s t s
t h a t t h e e v i d e n c e c o u l d b e e q u i v o c a l . F o r e x a m p l e ,
M e rc e r ( 1 9 6 5, p . 4 0 4 ) r e f e r r e d t o a 6 m c l if f c u t i n d r if t
w h i c h s h o w s a m a rk e d d i s c o n t i n u i ty b e t w e e n c l a y - r ic h
d r i ft b e l o w 5 m a n d d r i f t w i t h l e s s c l a y a b o v e . T h e 2 3 0 0
y e a r -o l d l o g w a s e m b e d d e d i n t h e l o w e r d r if t . S i n c e t h e
s i t e l i e s a l s o w i t h i n l i m i t s o f a s e c o n d r e a d v a n c e
m o ra i n e ( P e a r s o n 2 ) b e l i e v e d , o n t h e b a s i s o f t r e e - r i n g
s t u d i e s , t o h a v e fo rm e d c a . A .D . 1 60 0 , th e i m p l i c a t i o n is
t h a t o n l y t h e u p p e r c l a y - i m p o v e r i s h e d d r i f t w a s d e -
p o s i t e d b y t h e y o u n g e r a d v a n c e . S u c h a n i n t e r p r e t a ti o n
i s p l a u s i b l e b u t n o t c o n c l u s iv e . B o t h d r i f t s c o u l d b e
a s s o c i a t e d w i t h t h e A .D . 1 6 00 a d v a n c e , t h e l o w e r b e i n g
basa l t i l l and the upper an ab la t ion t i l l . The s t ronges t
e v i d e n c e f a v o u r i n g M e rc e r s i n t e rp r e t a t i o n i s t h a t t h e
e m b e d d e d l o g w a s w e l l p r e s e r v e d , w i t h b a r k a t t a c h e d ,
a n d t h u s w a s p r o b a b l y b u r i e d n e a r w h e r e i t g r e w b y th e
i c e a d v a n c i n g p a s t t h i s p o i n t a b o u t 3 5 0 B C (M e rc e r ,
1965 , p . 404) . Th is sugges t s tha t the log i s un l ike ly to
h a v e b e e n l y i n g a ro u n d o n t h e s u r f a c e fo r 2 0 0 0 y e a r s
f ro m d e a t h u n t i l i n c o rp o ra t i o n i n a n A .D . 1 60 0 a d v a n c e .
N e v e r t h e l e s s , c o n s i d e r a b l e u n c e r t a i n t y s u r r o u n d s t h e
N e o g l a c i a l h i s t o ry o f t h is a r e a . I f G l a c i a r U p s a l a
r e a d v a n c e d 1 0 k m s h o r t l y a f t e r 2 3 0 0 B P a n d 8 k m i n
A .D . 1 60 0, w h y i s t h e r e n o e v i d e n c e o f a n e a r l ie r
N e o g l a c i a l r e a d v a n c e ? T h e P e r u v i a n d a t a f o r a n a d -
v a n c e c u l m i n a t i n g 2 7 0 0 -2 0 0 0 B P a r e a s u n c e r t a i n a s
t h o s e fo r t h e e a r l i e r p e r i o d . A t o n e s i t e i n t h e
C o rd i l l e r a B l a n c a , R r t h l i s b e rg e r ( 1 9 8 7 ) h a s r a d i o -
c a rb o n -d a t e d s o i l s , b r a c k e t i n g a t i l l , b u r i e d w i t h i n
s u p e rp o s e d m o ra i n e s . Th e s o i ls h a v e a g e s o f c a . 3 5 0 0
a n d c a . 2 k a B P . Th e t i l l c o u l d h a v e b e e n d e p o s i t e d b y
a r e a d v a n c e b e t w e e n 2 7 0 0 a nd 2 k a B P , b u t e q u a l l y
m a y b e a s s o c i a t e d w i t h a n a d v a n c e p e a k i n g s h o r t l y
a f t e r c a . 3 50 0 B P . Th e r a d i o c a rb o n a g e o f c a . 2 2 0 0 B P
fo r b a s a l p e a t o v e r l y i n g l a rg e b l o c k s d e p o s i t e d b y a n
a d v a n c e o f t h e E l A l t a r c a l d e r a g l a c ie r i n Ec u a d o r (F i g .
1 ) g i v e s o n l y a m i n i m a l a g e fo r t h e d e p o s i t (C l a p p e r t o n ,
1986).
A l t h o u g h p a l y n o l o g i c a l w o r k i n C o l o m b i a ( T h o u r e t
a n d v a n d e r H a m m e n , 1 98 1 ) su g g e s t s t h a t a b r i e f s p e ll
o f c o l d cl i m a te o c c u r r e d d u r i ng t h e m i l l en i u m 3 - 2 k a
B P , c o n c l u s i v e e v i d e n c e o f s y n c h ro n o u s g l a c i e r r e -
a d v a n c e s t h r o u g h o u t t h e A n d e s f o r t h is p e r i o d h a s y e t
t o b e d e m o n s t r a t e d . Ex i s t i n g d a t a a r e c o n s i s t e n t a n d
sugges t ive , bu t s t i l l equ ivoca l .
Third Neog lac ia l advance: 1300 1000 BP
P a l y n o l o g i c a l e v i d e n c e s u g g e s t s t h a t t h e i n t e rv a l
2 0 0 0 - 1 3 0 0 B P w a s a m i l d er p e r i o d p r o b a b l y c h a r a c -
t e r i s e d b y r e d u c e d g l a c i e r s , b u t t e n u o u s e v i d e n c e fo r
r e n e w e d g l a c i a l e x p a n s i o n d u r i n g t h e fo l l o w i n g 3 0 0
y e a r s e x is t s i n P e r u a n d P a t a g o n i a . T h e m o s t p e r s u a s i v e
d a t a a r e f r o m t h e C o r d i l l e ra B l a n c a , P e r u , w h e r e t r e e s
r o o t e d i n an o l d e r N e o g l a c i a l m o r a i n e w e r e o v e r r i d d e n
d u r i n g a r e a d v a n c e p e a k i n g s o m e t i m e a f t e r c a . 1 3 2 5 B P
( T a b l e 1 ) . H o w e v e r , m u c h m o r e e v i d e n c e is r e q u i r e d
b e f o r e i t c a n b e d e c i d e d w h e t h e r o r n o t g l a c i e r
e x p a n s i o n o c c u r r e d t h r o u g h o u t t h e A n d e s .
Fourth Neoglacial advance: 12th 19th centuries
Th e re i s g ro w i n g e v i d e n c e t h a t g l a c i e r s i n t h e
N o r t h e r n H e m i s p h e r e h a v e f l u c t u a t e d i n e x te n t d u r in g
a t l e a s t t h e l a s t 1 3 0 0 y e a r s (P o r t e r , 1 98 6 ). A d v a n c e s i n
e a r l y M e d i e v a l t i m e s w e r e s e p a r a t e d b y a n i n t e r v a l o f
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r e la t iv e w a r m t h e x t e n d i n g fr o m c a . A . D . 1 09 0 t o A . D .
1 2 3 0 , b e f o r e t h e o n s e t o f t h e L i t t l e I c e A g e . A n d e a n
g l a c i e r s ma y a l s o h a v e a d v a n c e d d u r i n g s i m i l a r t i me
p e r i o d s . R 6 t h l i s b e r g e r ( 19 8 7) i d e n t i f i e d t w o t o t h r e e
p h a s e s o f e x p a n s i o n b e t w e e n 1 7 0 0 - 1 0 5 0 B P , t h e
g r e a t e s t a d v a n c e o c c u r r i n g a t ca . 1 1 00 BP . T h e s e w e r e
f o l lo w e d b y tw o a d v a n c e s b e t w e e n 9 0 0 - 5 0 0 B P a n d b y
a d v a n c e s d u r i n g t h e l a s t t h r e e c e n t u r i e s . R i n g s t u d i e s o f
t r e e s o n r e c e n t m o r a i n e s i n P a t a g o n i a l e d M e r c e r
(1965 , 1970) to conc lude tha t d i f fe ren t g lac i e rs rea che d
t h e i r m a x i ma l l im i t s a t d i f f e r e n t t i me s d u r i n g t h e 1 7 t h,
1 8 t h a n d 1 9 t h c e n t u r i e s . L e s s p r e c i s e d a t a f r o m t h e
m o r e n o r t h e r n A n d e s s u g ge s t t h a t m o s t g l a c ie r s w e r e
b e g i n n i n g t o r e c e d e f r o m n e a r - m a x i m a l p o s i t i o n s b y
t h e l a s t t w o d e c a d e s o f t h e 1 9 t h c e n t u r y ( C l a p p e r t o n ,
1983).
South American glaciers in the 20th century
A p a r t f r o m a f e w n o t a b l e e x c e p t i o n s , m o s t A n d e a n
g l a c i e r s h a v e r e c e d e d d r a ma t i c a l l y f r o m e n l a r g e d p o s -
i t i o n s i n t h e mi d - l a t e 1 9 t h c e n t u r y . Ph o t o g r a p h i c
r e c o r d s i n p la c e s s h o w m a r k e d s h r i n k a g e b y t h e 1 92 0s
( Br o g g i , 1 9 4 3 ; O p p e n h e i m a n d Sp a n n , 1 9 4 6 ) , b u t t h e
p e r i o d o f m o s t r a p i d r e c e s s i o n s e e m s t o h a v e b e e n
b e t w e e n t h e e a r l y 1 93 0s a n d t h e e a r l y 1 9 6 0 s . W o o d
( 19 70 ) e s t i m a t e d t h a t C o l o m b i a n g l a c i e rs d e c r e a s e d i n
e x t e n t b y o n e - t h i r d b e t w e e n 1 9 3 9 a n d 1 9 69 , w h i le
Br o g g i (1 94 3) a n d O p p e n h e i m a n d Sp a n n ( 1 94 6) n o t e d
a c o n s i d e r a b l e r i s e i n t h e s n o w l i n e o f ma n y Pe r u v i a n
g lac ie rs . The on ly repor t o f a reversa l i n th i s t rend i s a
r a t h e r d u b i o u s o b s e r v a t i o n b y Br o g g i ( 19 43 , p . 6 6 ) ,
b a s e d o n s ma l l - s c a l e ma p e v i d e n c e , t h a t t h e s n o w l i n e
o n H u a s c a r a n d e s c e n d e d 1 50 m s o m e t i m e b e t w e e n
1 90 9 a n d 1 9 3 2 . T h e v e r t ic a l r is e o f t h e s n o w l i n e i n t h e
P i c o Bo l i v a r a r e a , V e n e z u e l a , h a s b e e n e s t i ma t e d a t
6 m p e r y e a r f o r t h e p e r i o d 1 8 8 5 -1 9 7 2 ( Sc h u b e r t ,
1 9 7 2 ) , l e a d i n g t o t h e c o mp l e t e d i s a p p e a r a n c e o f ma n y
s ma l l g l a c i e r s a n d p e r e n n i a l s n o w f i e l d s . H a s t e n r a t h
( 19 81 ) r e p o r t e d s i m i l a r e f f e c t s i n t h e E c u a d o r i a n A n d e s
where su rv iv ing g lac ie rs ex i s t on ly on vo lcan ic mass i f s
r i s ing above 5000 m.
W h e r e a s m o s t g l a c i e r s i n t h e c e n t r a l a n d n o r t h e r n
A n d e s b e h a v e n o r m a l l y u n l e ss a ff e c t e d b y v ol c a ni c
a c t i v i t y , i t i s c l e a r t h a t s o me i n t h e s o u t h e r n A n d e s ,
f r o m 4 1 l a t. s o u t h w a r d s , e x h i b i t a n o m a l o u s b e h a v i o u r
b e c a u s e o f th e i r i n t e r n a l d y n a m i c s o r c o n d i t i o n s i n th e i r
c a t c h me n t s . Fo r e x a mp l e , s o me g l a c i e r s i n t h e c e n t r a l
A n d e s o f A r g e n t i n a h a v e e x p e r i e n c e d r a p i d a d v a n c e s
o v e r s e v e r a l h u n d r e d m e t r e s , e n c o u r a g i n g th e o p i n io n
t h a t t h e y a r e p e r i o d i c a l l y s u r g i n g g l a c i e r s . E x a mp l e s
i n c lu d e t h e F r i a s g la c i er o n M o u n t T r o n a d o r ( R a b a s s a
et al.
1 97 9) , t h e L a g u n a a n d P l o m o g l a c i er s i n t h e R i o
M e n d o z a b a s i n ( Co b o s a n d B o n i n s e g n a , 1 9 8 3 ; E s p iz f i,
1 9 8 6 ) a n d M t . A c o n c a g u a w h e r e t h e A t u e l g l a c i e r
su rged 600 m in 1985-86 . I t i s a l so ev iden t tha t some
w a t e r - t e r mi n a t i n g g l a c i e r s f l u c t u a t e o u t o f p h a s e w i t h
a d j a c e n t g l a c i e r s , n o t a b l e e x a mp l e s i n c l u d i n g t h e
M o r e n o g l a c i e r ( L a g o A r g e n t i n o ) a n d G l a c i a r B r u g g e n
( F i o r d o E y r e ) w h i c h a r e e a s t e r n a n d w e s t e r n o u t l e t s
f r o m t h e H i e l o Pa t a g o n i c o Su r , r e s p e c t i v e l y ( F i g. 2 ) .
T h e M o r e n o g l ac i e r a d v a n c e d 1 k m b e t w e e n 1 8 99 a n d
1 9 6 6 ( Me r c e r , 1 9 6 8 ) a n d G l a c i a r B r u g g e n a d v a n c e d
1 0 k m b e t w e e n 1 9 4 5 a n d 1 9 8 3 t o r e a c h i ts m a x i m a l
N e o g l a c i a l p o s i t io n ( J . H . M e r c e r ,
pers. commun.
1 98 7) . T h e r e a s o n w h y t h e s e g l a c i e rs h a v e a d v a n c e d i n
r e c e n t ti me s w h i l e mo s t o t h e r s h a v e b e e n i n r e c e s s i o n is
n o t y e t u n d e r s t o o d , b u t p a r t o f t h e e x p l a n a t i o n m a y
r e s t o n t h e p a r t i c u l a r d y n a m i c s o f t h e s e c a l v i n g g la c i e rs
a n d t h e t o p o g r a p h y o f t h e i r b a s i n s . Su c h d i f f e r e n t i a l
b e h a v i o u r o f g l a c ie r s in So u t h A me r i c a , p a r t i c u l a r l y in
P a t a g o n i a w h e r e t h e m o s t c o m p r e h e n s i v e m o d e l o f
H o l o c e n e g l a c i e r f l u c t u a t i o n s h a s b e e n d e r i v e d
( M e r c e r , 1 98 2) , mu s t c l e a r l y b e t a k e n i n t o a c c o u n t i n
a s s e s s i n g t h e s t r e n g t h o f t h e e v i d e n c e p r e s e n t e d i n
s u p p o r t o f g l a c i e r fl u c t u a t i o n s d u r i n g N e o g l a c i a t i o n .
A s s u m i n g t h a t m a n y A n d e a n g l a c i e r s h a v e r e -
a d v a n c e d t o s i m i l a r l i m i t s o n t h r e e o r f o u r o c c a s i o n s
d u r i n g t h e H o l o c e n e , a d e p r e s s i o n o f th e i r e q u i l ib r i u m
l i n e a l t i t u d e ( E L A ) b y a s i m i l a r a mo u n t e a c h t i me i s
s u g g e s t e d . N o e s t i m a t i o n h a s b e e n m a d e f o r E L A
d e p r e s s i o n i n Pa t a g o n i a , b u t c a l c u l a t i o n s f o r t h e
t r o p i c a l A n d e s s u g g e s t a l o w e r i n g o f c a . 2 0 0 - 3 0 0 m
(Clapper ton , 1986) .
T H
A N T A R C T I C
T h e r e c o r d o f N e o g l a c i a l g l a c i e r f l u c t u a t i o n s i n
A n t a r c t i c a a n d s u r r o u n d i n g a r e a s i s d if f ic u l t t o u n r a v e l
f o r t h r e e r e a s o n s . F i r s t , t h e r e c o r d i s s p a r s e b e c a u s e
t h e r e a r e f e w n u n a t a k s o r o a s e s p r o t ru d i n g t h r o u g h t h e
i c e s h e e t w i t h a g l a c i a l- g e o l og i c r e c o r d a v a i l a b l e f o r
s t u d y . Se c o n d , m o s t A n t a r c t i c g l a c ie r s a c h i e v e t h e b u l k
o f t h e i r a b l a t i o n b y c a l v i n g . T h i s me a n s t h a t t h e y a r e
r e l a t i v e l y i n s e n s i t i v e t o t e mp e r a t u r e f l u c t u a t i o n s a n d
a r e t h u s u n l i k e l y t o r e s p o n d s e n s it i v el y t o c l i ma t i c
c h a n g e a s d o mo s t o t h e r g l a c i e r s i n t h e w o r l d . I n s t e a d ,
t h e y r e s p o n d m a i n l y to c h a n g e s i n a c c u m u l a t i o n w h ic h
af fec t s i ce th i ckness and g round ing l ines , t o cyc l i ca l
var i a t ions in ca lv ing ac t iv i ty and to changes in re l a t ive
s e a l e v e l ; t h e s ma l l e r a l p i n e g l a c ie r s in m a r i t i me a r e a s
ma y n e v e r t h e l e s s f l u c t u a t e w i t h c l i ma t e . T h i r d , t h e
l a r g e s i z e o f t h e A n t a r c t i c i c e s h e e t me a n s t h a t i t s
r e s p o n s e t o c l i ma t i c fo r c i n g ma y f o l lo w a l a g o f s e v e r a l
t h o u s a n d y e a r s . T o g e t h e r , t h e s e p r o b l e m s p r e s e n t
c o n s i d e r a b l e d i f fi c u l ty i n i n t e g r a t i n g H o l o c e n e g l a c i e r
f l u c t u a t io n s i n A n t a r c t i c a w i t h a w o r l d w i d e f r a me w o r k .
T h i s p a r t o f t h e r e v i e w c o n s i d e r s g l a c ie r s so u t h o f t h e
A n t a r c t i c Co n v e r g e n c e ( F i g . 1 ). S i n c e a l l o f th i s r e g i o n
i s n o t s t r i ct l y A n t a r c t i c a , t h e d i s cu s s io n f o c u s e s o n t h e
f o l l o w i n g g e o g r a p h i c a l a r e a s ; E a s t A n t a r c t i c a , W e s t
A n t a r c t i c a , s u b - A n t a r c t i c i s l a n d s a n d So u t h G e o r g i a
( S o u t h e r n O c e a n ) .
East Antarctica
T h e r e a r e t h r e e ma i n l o c a l i t i e s i n E a s t A n t a r c t i c a
w h e r e N e o g l a c i a l g l a c i e r a d v a n c e s h a v e b e e n r e c o g -
n i s e d . T h e f i rs t i s i n t h e M c M u r d o D r y V a l l e y s ( F ig . 1 )
w h e r e n u m e r o u s r a d i o c a r b o n d a t e s r e v e a l t h a t l o c a l
g l ac ie r s h a v e e x p a n d e d f r o m a m i n i m a l e x t e n t d u r i n g
t h e l a s t g la c i a t io n 1 8 k a B P a n d r e a c h e d a m a x i ma l
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C M Clapperton and D E Sugden
e x t e n t s o m e t i m e i n t h e H o l o c e n e ( S t u iv e r e t a l . , 1981).
Th e i n t e rp r e t a t i o n i s b a s e d o n c ro s s - c u tt i n g m o ra i n e
re l a t i o n s h i p s (D e n t o n
e t a l . ,
1971) . Dur ing the l as t
g l a c i a l m a x i m u m , g l a c i e r i c e i n t h e R o s s S e a b u i l t u p
a n d p u s h e d i n t o t h e s e a w a rd e n d o f t h e v a l l e y s , l e a v i n g
a c l e a r u p p e r l im i t o f ti ll o f t e n u n i n t e r ru p t e d b y l o c a l
a l p i n e g l a c i e r s . F o l l o w i n g d e g l a c i a t i o n a n d t h e w i t h -
d ra w a l o f g l a c i e r i c e f ro m t h e R o s s S e a , t h e a l p i n e
g l a c ie r s a d v a n c e d , l o c a l l y o v e r t h e R o s s S e a d r i f t. S o m e
o f t h e s e g l a c i e r s a r e c u r r e n t l y a t t h e i r m o s t a d v a n c e d
H o l o c e n e po s i ti o n s - - f o r e x a m p l e , C a n a d a , C o m m o n -
w e a l t h , H o b b s , a n d W a l c o t t G l a c i e r s ( S t u i v e r
e t a l . ,
1 9 8 1 ) . W h i l e i t i s t r u e t h a t m o s t g l a c i e r s n o u t s o c c u p y
t h e i r m a x i m a l H o l o c e n e p o s i t i o n s , t h e s a m e i s n o t t r u e
o f m a n y g l a c i e r l a t e r a l m a rg i n s . S o m e l a t e r a l m a rg i n s
a r e b o r d e r e d b y s m a l l i c e - c o r e d m o r a i n e s w h i c h p a s s
b e n e a t h t h e g l a c i e r t o w a rd s i t s s n o u t . A t S u e s s a n d
G a r w o o d g l a c i e r s , t h e s e m o r a i n e s h a v e b e e n r a d i o -
c a rb o n d a t e d t o a b o u t 2 9 0 0 B P , s u g g e s t i n g th a t t h e i r
m a x i m a l H o l o c e n e w i d t h o c c u r r e d a t t h a t t im e . F o l l o w -
i n g r e c e s s i o n a n d t h in n i n g , s u b s e q u e n t r e j u v e n a t i o n l e d
t o i c e f l o w i n g m o re r a p i d l y d o w n t h e g l a c i e r s ' c e n t r e -
l i n e s , t h e r e b y o v e r r i d i n g i c e - c o re d m o ra i n e s a t t h e
g l a c i e r s n o u t s b u t n o t a t t h e l a t e r a l m a rg i n s (D e n t o n
and Wi l son , 1982) . In the Dry Val leys , cu r ren t ly r i s ing
l a k e le v e ls a c c o m p a n y w a r m i n g s u m m e r t e m p e r a t u r e s ;
s i n c e 1 7 r a d i o c a rb o n d a t e s i n d i c a t e h i g h l e v e l s f o r La k e
V a n d a a t 2 - 3 k a B P , w a r m e r c l i m a t i c c o n d i t i o n s a r e
i n f e r r e d fo r t h a t ~ e r i o d . Th e re i s n o e v i d e n c e fo r L i t t le
i c e A g e c o o l i n g i n t h e D ry V a l l e y s a n d t h e p o s s i b i l i t y
r e m a i n s t h a t t h e l a s t f e w c e n t u r i e s m a y h a v e b e e n
w a r m e r t h a n n o w (G . H .
D e n t o n p e r s . c o m m u n . ,
1987).
Th u s t w o p e r i o d s o f N e o g l a c i a l c o o li n g i n S o u t h
A m e r i c a m a y c o i n c i d e w it h t w o p e r i o d s o f w a r m i n g i n
t h e D r y V a l l e y s . Th e c a u s e o f t h is a n o m a l y i s u n k n o w n
b u t m a y r e f l e c t s o m e l o c a l c l i m a t i c c o n d i t i o n .
In te res t ing ly , a s imi la r expans ion o f a lp ine g lac ie rs
o c c u r r e d d u r i n g a t l e a s t t h e l a s t t h r e e p r e v i o u s i n t e r -
g l a c i a t i o n s (H e n d y
e t a l . ,
1 97 9) . P ro b a b l y t h e a d v a n c e
a n d r e t r e a t o f t h e a l p i n e g l ac i er s i n th e M c M u r d o D r y
V a l l e y s r e f le c t v a r i a t i o n s i n p r e c i p i t a t i o n (D o r t , 1 97 0) .
D u r i n g g l a c i a t i o n s t h e p r e c i p i t a t i o n -b e a r i n g w i n d s a r e
b l o c k e d f r o m t h e D r y V a l l e y s b y g r o u n d e d i c e i n t h e
R o s s S e a a n d t h e a l p i n e g l a c i e rs r e t r e a t . D u r i n g
i n t e rg la c i a t io n s t h e p r e c i p i t a t i o n i n c r e a s e s a n d t h e l o c a l
g l a c ie r s a d v a n c e . I n t h is c a s e p r e c i p i t a t i o n c h a n g e s
o v e r r i d e t h e e f f e c t o f t e m p e r a t u r e c h a n g e s w h i c h w o u l d
b e e x p e c t e d t o o p e ra t e i n t h e o p p o s i t e d i r e c t i o n ,
A n o t h e r l o c a t i o n i n E a s t A n t a r c t i c a w i t h r e p o r t s o f
N e o g l a c i a l g l a c i e r f l u c t u a t i o n s o c c u r s i n t h e V e s t fo l d
H i l l s (F i g . 1 ) w h e re t h e r e i s t e n u o u s e v i d e n c e o f a n i c e
a d v a n c e a b o u t 3 k a B P ( Z h a n g , 1 98 5; A d a m s o n a n d
Pickard , 1986) .
W e s t A n t a r c t i c a
A s e c o n d a r e a w i t h e v i d e n c e o f N e o g l a c i a l g l a c ie r
f l u c tu a t io n s i s A l e x a n d e r I s la n d a n d G e o r g e V I S o u n d
a t t h e b a s e o f t h e A n t a r c t i c P e n i n s u l a (F i g. 1 ) , a c o a s t a l
m a r i t im e l o c a t io n w i t h a m e a n a n n u a l t e m p e r a t u r e o f
a b o u t - 9 C . T h e c h r o n o l o g y is c o n s t r a in e d b y ra d i o -
c a rb o n a n d a m i n o a c i d a s s a y s o f b a rn a c l e s B a t h y l a s m a
c o r o l l i f o r r n e )
i n c o rp o ra t e d w i t h i n m o ra i n e s . Th e r e -
s u it s s u gg e s t th a t G e o r g e V I I c e s h e l f d i s a p p e a r e d i n th e
m i d d l e H o l o c e n e a b o u t 6 5 0 0 B P a n d r e f o r m e d s u b -
s e q u e n t l y (C l a p p e r t o n a n d S u g d e n , 1 98 2 ). C ro s s -
c u t t i n g m o ra i n e s s h o w t h a t s m a l l l o c a l g l a c i e r s a d -
v a n c e d s o m e h u n d r e d s o f m e t r e s b e y o n d t h e i r p r e s e n t
l im i t s b o t h a t t h e t i m e o f ic e s h e l f d i s a p p e a ra n c e a n d
a f t e r i t s r e c o n s t i t u t i o n . L i t t l e c a n b e s a i d a b o u t t h e
e n v i ro n m e n t a l s i g n if i c a n c e o f th e s e f l u c t u a t io n s u n t i l
t h e r e i s a m u c h f i rm e r c h ro n o l o g i c a l f r a m e w o rk .
P o s s i b l y t h e e a r l i e r a d v a n c e o f t h e l o c a l g la c i e r s
r e f l e c t e d a n i n c r e a s e i n p r e c i p i t a t i o n d u e t o t h e
d i s a p p e a r a n c e o f G e o r g e V I I c e sh e l f, b u t i t c o u ld
e q u a l ly h a v e b e e n d u e t o t h e o n s e t o f N e o g l a ci a t io n .
S u b - A n t a r c t i c I s l a n d s a n d S o u t h G e o r g i a
A l t h o u g h t h e r e a r e f r e q u e n t r e f e r e n c e s t o r e l i c t
m o ra i n e s i n f ro n t o f gl a c i er s in s u b -A n t a r c t i c a a n d t h e
S o u t h e r n O c e a n , o n l y tw o i s l an d g ro u p s c o n t a i n s u f-
f i c i e n t r a d i o c a rb o n d a t e s t o fo rm t h e b a s i s o f a
H o l o c e n e g l a c ie r c h r o n o l o g y - - t h e S o u t h S h e t l a n d
I s l a n d s (6 1 -6 3 3 0 ' S ) a n d S o u t h G e o rg i a (5 4 -5 5 S ) .
B o t h i s l a n d g ro u p s b o rd e r t h e S c o t i a S e a a n d l i e i n t h e
b e l t o f w e s t e r ly w e a t h e r s y s te m s w h i c h d o m i n a t e t h e s e
l a ti t ud e s . T h e m e a n a n n u a l t e m p e r a t u r e i n t h e S o u t h
S h e t l a n d I s l a n d s is a b o u t - 2 C a n d p r e c i p i t a t i o n
a v e ra g e s 4 0 0 -6 0 0 m m . M o s t o f t h e i s la n d a r e a i s
c o v e re d b y g l a c i e r s , b u t i c e - f r e e p e n i n s u l a s o n t h e
e a s t e rn s i d e o f L i v i n g s t o n I s l a n d a n d K i n g G e o rg e
I s l a n d b e a r e v i d e n c e o f a f o rm e r i c e c o v e r . I n S o u t h
G e o r g i a t h e m e a n a n n u a l t e m p e r a t u r e a t se a le v e l o n
t h e n o r t h e a s t c o a s t i s 1 . 8 C a n d t h e m e a n a n n u a l
p rec ip i t a t ion i s 1393 mm (Sm i th , 1960). Ice covers 58
o f t h e i s la n d , m o s t l y o n t h e w i n d w a rd s o u t h w e s t e rn
s i d e . B o t h i s l a n d g ro u p s w e re s u b m e rg e d b y ic e c a p s
t h a t e x t e n d e d o f f s h o re d u r i n g t h e l a s t g l a c i a t i o n
(C l a p p e r t o n 1 9 7 1 ; J o h n a n d S u g d e n , 1 9 7 1 ; S u g d e n a n d
J o h n , 1 9 7 3 ; S u g d e n a n d C l a p p e r t o n , 1 9 7 7 ; C l a p p e r t o n
e t a l . , 1 9 78 ). G l a c i e r s h a d w i t h d ra w n c l o s e t o t h e i r
p r e s e n t l im i t s a t l e a s t b y 9 7 0 0 B P i n S o u t h G e o rg i a a n d
b y 9 k a B P i n t h e S o u t h S h e t l a n d I s l a n d s. S i n c e t h e n
t h e r e h a v e b e e n t w o t o t h r e e m a i n a d v a n c e s , o n e i n
w h i c h g l a c i e r s e x t e n d e d a f e w k i l o m e t r e s d o w n - f j o r d
a n d o t h e r s w h e re g l a c i e r s w e re o n l y s l i g h t l y m o re
e x t e n s i v e t h a n t o d a y . Th e t i m i n g o f t h e s e a d v a n c e s i s
d i f f e r e n t i n e a c h i s l a n d g ro u p a n d r e q u i r e s s e p a ra t e
d i scuss ion .
S o u t h S h e t l a n d I s l a n d s
M o ra i n e l im i t s o f t h e m a i n f j o rd a d v a n c e i n t h e
S o u t h S h e t l a n d I s l a n d s c o i n c i d e w i t h a r a i s e d b e a c h a t
c a . 6 m (v a ry i n g l o c a ll y b e t w e e n 5 a n d 7 .5 m ) , a n d
r e p r e s e n t a n a d v a n c e o f 2 - 3 k m i n s e v e r a l f j o r d s , e . g .,
i n b r a n c h e s o f A d m i r a l t y B a y , P o t t e r C o v e a n d M a r i a n
C o v e o n K in g G e o r g e I s l a n d a n d in Y a n k e e H a r b o u r
o n G re e n w i c h I s l a n d (S u g d e n a n d J o h n , 1 9 7 3 ) . I n a l l
c a s e s t h e h i g h e s t b e a c h c o i n c i d e n t w i t h t h e m o ra i n e l ie s
a t c a . 6 m w h i l e m u c h h i g h e r r a i s e d b e a c h e s o c c u r
i m m e d i a t e l y o u t s i d e , e . g . a t 4 1 m i n P o t t e r C o v e r (F i g .
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191
3). The moraines dearly represent a readvance rather
than a recessional still-stand because the glaciers
overrode and entr ained beach sediments and deposited
till over early Holocene shell-bearing marine deposits
(Potter Cover). Because the sea was unable to pen-
etrate within the moraine limits and form beaches at
equivalent and lower altitudes, the glaciers must have
been at the site of the te rminal moraines while the 6 m
beach formed. This suggests that when glaciers stood
at the moraine limits relative sea level was 6 m lower
than now. Within the fjords there is another moraine
linked with a raised beach at 2.5-3 m. This beach is
present outside the moraine but not within it. The
moraine indicates an advance of 0.25-1 km beyond the
present glacier margins. Organic remains associated
with the raised beach series allow the two moraines to
be dated. Altoge ther, several workers have obtained 14
radiocarbon dates from penguin, seal, whale, and
seaweed remains (Table 2). A problem relating to
radiocarbon dates on marine animals in the Antarctic is
the significant depletion in radiocarbon activity in the
sea which leads to falsely old dates relative to the
terrestrial time scale (Broecker, 1963). Harkness
(1979) and Gordon (1987) have cons idered the prob lem
in the West Antarctic seas and on the basis of dates on
marine organisms which died this century suggest that a
correction factor of 750 years may apply widely in
Antarctica. However, there appear to be regional
variations in radiocarbon activity and in an attempt to
derive its value for the South Shetland Islands an
approximate value of 850 years was estimated from
dates on four modem whale and seal bones (Table 2,
bottom). This figure should be regarded as no more
than a provisional guide, however, and the corrected
dates could easily differ by more than 100 years either
way.
If the same correction factor is used for all the
marine-based dates, then the overall pattern of the 14
radiocarbon ages is remarkably consistent (Fig. 3).
Beaches above 6 m range in age from 1680 to 5800 yr
BP, being progressively older with increasing altitude.
Four dates suggest that the 6 m beach formed ca.
510-800 14C years BP, while three others suggest the
3 m beach formed ca. 200-360 14C years BP. One o f the
dates for the 6 m beach is from a tree trunk
N o t h o -
f a g u s a n t a r c t i c a - -
Southern Beech) and requires no
correction, yet it corresponds well with the corrected
whalebone dates associated with the same beach.
Bearing in mind the number of different workers and
laboratories involved and the variety of different
materials used, the consistency of the pattern is
striking. If the high-precision calibration curves derived
by Stuiver and Pearson (1986) are applied to the last
seven radiocarbon dates, using a one sigma range, then
a first approximation of the calendar age span of the
6 m beach would be late 13th-early 16th centuries
A.D. This implies that the 2-3 km glacier readvance
associated with the beach culminated at some time
close to this period. On a similar basis, the 3 m beach
and the glacier readvance of 250-1000 m would have an
approximate calendar age most probably in the range of
the 15th-17th centuries A.D.
The chronology based on radiocarbon dating of
raised beaches is supported by independent licheno-
metric dating of moraines on both Livingston Island
and King George Island. Using
R h i z o c a r p o n g e o -
g r a p h i c u m thalli calibrated by measurements on a
sealer s hut thought to have been built about 1820-
1825, Curl (1980) gave a minimum age of ca. A.D. 1720
to recent moraines at False Bay and Elephant Point on
Livingston Island. In addition, Birkenmajer (1981)
used the same growth curve to approximate a minimum
age of A.D. 1240 for a moraine contemporaneous with
the 6 m beach in front of Ferrar Glacier, King George
Island. Again this agrees with the raised-beach chronol-
ogy. Birkenmajer also used lichenometry to derive
minimal ages for two other mora ines as A.D. 1780 and
A.D. 1825. Somewhat later limiting dates of A.D. 1837
lSm 3760 - 3 8508 .C. ( ~710 - 580 0 8 .P. )
' 0 O 0 O 0 0 0 ( 2 O M es )
G l a c J e ~ ~ t 0 m (232 Dates-21 )B'C (19 / '3 - 227'18.P. )
x ~ 1 2 4 0 A . D .
~ _ _ - i L ichen ) 7 .6 r n 270 A.D. ( 1aS0 B.P. )
4 L ~'~ O O I Date )
6 n l 1215 - 1510A.0. ( )
10
802
B+P.
O O O O O O O ~ O O O O O O ( 4 0 s t u )
~ 1 7 2 0 A , O .
~ y ' ~ , ~ ( U c h e n )
IP / 3rn 1450 -180 0 A.D. ( 208 - 360 B.P. )
0 0 0 0 0 0 0 0 0 0 0 ' 0 0 ~ 0 0 ~ 0 0 O 0 ( 3 D ~ II II I l
t 8 r n
O O O O O O O O O O O 'O ~ - - O O O O O O O O O O O ~O O ~ PresentBeach
Distance down - f jord
Moraine ~ Raised beach
F I G . 3 . S c h e m a t i c d i a g r a m s h o w i n g t h e r e l a ti o n s h i p o f H o l o c e n e g l a c i e r r e a d v a n c e m o r a i n e s w i t h r a d i o c a r b o n d a t e d r a i s e d
be a c he s South She t l a nd I s l a nds An ta rc t i c a .
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192
C M Clapperton and D E Sugden
a n d A . D . 1 8 80 w e r e d e r i v e d f r o m l i c h e n o m e t r y f o r t w o
m o ra i n e s c l o s e t o t h e i c e c a p o n S i g n y I s l a n d i n t h e
S o u t h O rk n e y I s l a n d s (L i n d s a y , 1 9 7 3 ) . C o n s i d e r i n g t h e
u n c e r t a i n t i e s i n v o l v e d in b o t h a p p ro a c h e s t o d a t i n g , t h e
a g r e e m e n t b e t w e e n t h e t w o i s e n c o u r a g i n g a n d t w o
i m p o r t a n t c o n c l u s i o n s m a y b e m a d e w i t h s o m e d e g r e e
o f c o n f i d e n c e . O n e i s th a t t h e l a rg e s t g la c i al a d v a n c e i n
t h e S o u t h S h e t l a n d I s l a n d s d u r i n g t h e l a s t 9 k a c u l m i -
n a t e d b e t w e e n t h e l a t e 1 3 t h a n d t h e e a r l y 1 6 th c e n t u r i e s
A . D . , p o s s ib l y c o r r e s p o n d i n g w i t h t h e e a r l y p a r t o f t h e
L i t t l e I c e A g e (A .D . 1 2 5 0 -1 5 0 0 ) ; t h e o t h e r i s t h a t a le s s
e x t e n s i v e a d v a n c e ( o r a d v a n c e s ) o c c u r r e d s o m e t i m e
b e t w e e n t h e 1 5 t h an d 1 9 t h c e nt u r i e s A . D . , c o r r e s p o n d -
i n g w i t h t h e l a t e r L i t t l e I c e A g e (A .D . 1 5 5 0 -1 8 5 0 ) .
South Georgia
I n S o u t h G e o r g i a e v i d e n c e o f H o l o c e n e g l a c ie r
a d v a n c e s i s d e m o n s t r a t e d b y a r c u a t e m o r a i n i c r i d g e s
e x t e n d i n g b e y o n d m o s t g l a c ie r s o n t h e l e e n o r t h e a s t e rn
s i d e o f t h e i s l a n d (F i g . 4 ) . Th e m o ra i n e s a r e d i s -
t i n g u i s h e d f ro m g l a c i a l d e p o s i t s o u t s i d e t h e i r l i m i t s b y
f r e s h n e s s o f f o rm , c o n t i n u i t y , a s s o c i a t i o n w i t h s e a l e v e l
c l o s e t o t h e p r e s e n t , t h e p r e s e n c e o f b o u l d e r s o n t h e i r
t o p s , a n d b y t h e l a c k o f ir o n s t a in i n g . S o m e f j o rd
g l a c i e r s , s u c h a s t h o s e t e rm i n a t i n g i n M o ra i n e F j o rd
( F ig . 5 ) a n d A n t a r c t i c a B a y , a d v a n c e d m o r e t h a n 6 k m
a n d p ro d u c e d m o ra i n i c r i d g e s o v e r 3 0 m h i g h , w h i l e
l a n d -b a s e d g l a c i e r s a d v a n c e d o n l y s e v e ra l t e n s o r
h u n d r e d s o f m e t r e s a n d p r o d u c e d r i d g e s g e n e r al l y le s s
t h a n 5 m h i g h . W i t h i n t h e c l e a r o u t e r m o ra i n e l i m i t a r e
t w o o t h e r m o ra i n e s u s u a l l y o c c u r r i n g w i t h i n a f e w
h u n d re d m e t r e s o f t h e p r e s e n t g l ac i e r m a rg i n s . I n
c o n t r a s t t o t h e o u t e r m o ra i n e w h i c h i s w e l l -v e g e t a t e d ,
t h e i n n e r m o r a i n e s a r e p o o r l y v e g e t a t e d , b l o c k y a n d , i n
t h e c a s e o f s o m e i n n e rm o s t r i d g e s , i c e - c o re d a n d
u n s t a b le . T w o s e t s o f i n n e r m o r a i n e s h a v e b e e n
m a p p e d a r o u n d t h e m a r g in s o f m a n y S o u t h G e o r g i a n
g l a c i e r s (C l a p p e r t o n , 1 9 7 1 ; C l a p p e r t o n a n d S u g d e n ,
1980).
Th e m o s t e x t e n s i v e H o l o c e n e m o ra i n e i s t i g h t l y
d a t e d i n M o r a i n e F j o r d ( F ig . 4 ) w h e r e a s e r i e s o f t h r e e
t o fo u r l o b a t e t e rm i n a l r i d g e s 3 -5 m h i g h fo rm s u p e r -
f i ci a l t o p o g ra p h y o n a m a s s i v e a c c u m u l a t i o n o f ti ll
m o re t h a n 3 5 m t h ic k . O n t h e e a s t e r n s i d e o f t h e f j o rd
m o u t h , a n a c t i v e l y e ro d i n g s e a c l if f 8 m h i g h e x p o s e s
3 -5 m o f ti ll w h i c h c o v e r s a l a y e r o f p l a n t r e m a i n s
( c o m p r e s s e d
caena
s t e m s ) o v e r l y i n g a t h i n o rg a n i c
s o il . Th i s, i n t u rn , h a d d e v e l o p e d o n a l o w e r ti ll , t h e
b a s e o f w h ic h is n o t e x p o s e d . R a d i o c a r b o n d a t e s o f
1 7 00 + 5 0 a n d 2 0 0 0 + 5 0 B P w e re o b t a i n e d fo r t h e
p l a n t a n d s o i l m a t e r i a l , r e s p e c t i v e l y , s u g g e s t in g t h a t t h e
l a st g la c ie r a d v a n c e t o t h e m o u t h o f M o r a i n e F j o r d
o c c u r r e d s h o r t l y a f t e r c a . 1 7 0 0 y e a r s a g o . U p p e r
b ra c k e t i n g d a t e s fo r g l a c i e r r e c e s s i o n w e re o b t a i n e d
f r o m b a s a l p e a t o v e r l y in g o u t w a s h o n t h e e a s t e r n s i d e
o f t h e m o r a i n e a n d f r o m b a s a l o r g a n ic s e d i m e n t s i n a
k e t t le p o n d j u s t in s id e t h e e n d m o r a i n e o n t h e w e s t e r n
s i d e o f t h e f j o rd (F i g . 6 ) . Th e s e g a v e r a d i o c a rb o n d a t e s
o f 1000 + 50 and 1460 + 60 BP , respec t ive ly , sugges t -
i n g t h a t t h e M o r a i n e F j o r d g l a c i e r p r o b a b l y r e c e d e d
f r o m t h e m o r a i n e c o m p l e x s o m e t i m e b e f o r e 1 00 0 B P .
S i n c e t h e d a t e d s o i l i s o n l y a t h i n s k e l e t a l l a y e r , t h e
g l a ci a l s e d i m e n t s o n w h i c h i t is d e v e l o p e d p o s s i b l y d a t e
f ro m a n e a r l i e r H o l o c e n e a d v a n c e . S u c h a n o p i n i o n i s
s u p p o r t e d b y t h e f a c t t h a t p e a t u p t o 3 m t h i c k a n d
6 0 0 0 - 9 0 0 0 y e a r s o l d c o v e r s g r o u n d i m m e d i a t e l y o u t -
s i d e t h e m o ra i n e l im i t . F u r t h e r m o re , t h e m o ra i n e i s a
m a s s i v e c o m p l e x o f f o u r m a j o r r i d g e s s u g g e st i n g t h a t i t
m a y b e a c o m p o s i t e f e a t u r e c o n s t r u c t e d b y s e v e r a l
a d v a n c e s t o a p p r o x i m a t e l y t h e s a m e p o i n t , a p l a c e
w h e re a r o c k t h r e s h o l d c ro s s e s t h e f j o rd a s it w i d e n s
a b ru p t l y i n t o C u m b e r l a n d B a y (F i g . 4 ) . Th u s , a l t h o u g h
ra d i o c a rb o n d a t i n g c o n f i rm s t h a t t h e l a s t a d v a n c e i n
M o ra i n e F j o rd c u l m i n a t e d s h o r t l y a f t e r c a . 1 70 0 B P ,
a d v a n c e s m a y a l s o h a v e o c c u r r e d e a r l i e r a n d l a t e r i n
t h e H o l o c e n e .
Th re e o t h e r r a d i o c a rb o n d a t e s c l o s e t o t h i s a g e r a n g e
c o m e f r o m a d j a c e n t g l a ci er s . T w o a r e f r o m b a s a l p e a ts
i m m e d i a t e l y o u t s i d e a n d i n s i d e e q u i v a l e n t m o ra i n e s i n
t h e H a m b e r g L a k e s v a l l e y w h e r e a d i s tr i b u ta r y l o b e o f
t h e M o r a i n e F j o r d g l a c i e r s y s t e m a d v a n c e d t o f o r m
t h re e w e l l -d e f i n e d a r c u a t e r i d g e s (F i g . 7 ) . Th e o u t e r
a n d i n n e r p e a t s g a v e d a t e s o f 2 2 1 0 + 5 0 a n d 9 5 0 + 5 0
B P , r e s p e c t i v e l y . Th e o t h e r s i t e i s i n D o r i s B a y s o m e
2 5 k m t o t h e s o u t h e a s t w h e r e w e l l - v e g e t a te d m o r a i n e s
t e r m i n a t e a t t h e c o a s t a p p r o x i m a t e l y 1 .7 k m f r o m
N a c h t i g a l g l a c i e r (F i g . 4 ) . B a s a l p e a t d u g f ro m a k e t t l e
h o l l o w c a . 4 0 0 m i n s id e t h e m o ra i n e l i m it g a v e a
r a d i o c a r b o n a g e o f 2 0 1 2 + 4 5 B P ( C l a p p e r t o n a n d
Sugden , 1980) . Th is i s a l imi t ing da te fo r an advance o f
N a c h t i g a l g l a c i e r r e a c h i n g i t s f u r t h e s t N e o g l a c i a l e x t e n t
s o m e t i m e b e f o r e c a. 2 k a B P . N e a r t h e e a s t e r n s i d e o f
N o r d e n s k j r l d g l ac i e r, w h i c h c a l v e s i n t o w a t e r o v e r
2 0 0 m d e e p i n C u m b e r l a n d E a s t B a y , a m e l t w a t e r
s t r e a m h a d i n 1 9 82 e x p o s e d a 6 c m t h i c k b e d o f p e a t
e x t e n d i n g 1 0 m a w a y f ro m b e n e a t h t h e g l a c i e r s l a n d -
b a s e d t e rm i n u s . Th e p e a t r e s t s o n t il l, is c o m p a c t e d ,
a n d i s p a r t l y c o v e re d b y f r e s h l y d e p o s i t e d t i l l ; t h e p e a t
a l s o e x is t s a s l a rg e b l o c k s i n th e i n n e rm o s t m o ra i n e .
R a d i o c a rb o n d a t e s o f 2 23 0 + 7 0 a n d 3 3 3 0 + 1 20 B P
w e r e o b t a i n e d f o r t h e t o p a n d b o t t o m
in situ
l a y e r s
r e s p e c t i v e l y , s u g g e s t i n g i c e - f r e e c o n d i t i o n s a t t h e s i t e
b e t w e e n c a l e n d a r a g e s 2 1 22 - 2 3 3 4 a n d 3 3 9 5 - 2 6 8 9 B P
(G o rd o n , 1 98 7) . Th i s s u g g e s t s t h a t i f N o rd e n s k j r l d
g l a c i er a d v a n c e d i n r e s p o n s e t o a n e a r l y N e o g l a c i a l ( s a y
2 7 0 0 -2 2 0 0 B P ) c l im a t i c d e t e r i o r a t i o n , p o s s i b l y e x t e n d -
i n g as f a r a s t h e o u t e rm o s t i n n e r m o ra i n e , i t l a g g e d
s e v e ra l h u n d re d y e a r s b e h i n d t h e fo r c i n g , s i m i l a r t o
M o ra i n e F j o rd g l a c i e r .
T h e y o u n g e r m o r a i n e s a r e m o s t c l os e ly d a t e d a t
N o r d e n s k j r l d g l a c ie r w h e r e C l a p p e r t o n ( 1 9 71 ) m a p p e d
t h re e r i d g e s 2 - 5 m h i g h o n t h e w e s t e rn s i d e . Th e
o u t e r m o s t m o r a i n e l ie s n o m o r e t h a n c a . 8 00 m f r o m
the g lac ie r marg in . In 1968 the innermos t r idge was s t i l l
i c e - c o r e d a n d m a y h a v e f o r m e d d u r i n g a n a d v a n c e
c u l m i n a t i n g a b o u t 1 9 5 7 (H a y w a rd , 1 9 8 3 ) . I t h a d b e -
c o m e m u c h l o w e r ( 1 - 2 m ) a n d i c e - fr e e b y 1 98 5. T h e
t w o o u t e r r i d g e s h a v e a s p a r s e b u t s t a b l e v e g e t a t i o n
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x x x L A T E G L A C I A L M O R A I N E
. . . . . N E O G L A C I A L M O R A I N E
- - - 2 0 t h c . M O R A I N E
P E A K S O V E R 2 0 0 0 m ( ~
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F I G . 4 . M a p o f t h e C u m b e r l a n d E a s t B a y a r e a S o u t h G e o r g i a s h o w i n g N e o g l a c i a l m o r a i n e s a n d s o m e r a d i o c a r b o n d a t e d si t e s.
F I G . 5 . H a m b e r g a n d H a r k e r g l a c ie r s c a lv i n g in t o M o r a i n e F j o r d S o u t h G e o r g i a . M o r a i n e s a n d t r i m f i n e s m a r k t h e f o r m e r
e x t e n t o f t h e s e g l a c i e r s d u r i n g t h e L i t t l e I c e A g e .
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194 C.M. Clapperton and D.E. Sugden
FIG. 6. N eoglacial moraine complex at the mouth o f Moraine Fjord, South G eorgia, which may hav e been deposited by mo re
than on e glacier readvance. Radiocarbon dates bracket one readvance between ca. 1700 and ca. 1460 BP.
FIG. 7. Neoglacialmoraines m H amberg Lakes V alley, South Georgia, probable equivalents of those in Moraine Fjord (Fig. 6).
Younger m oraines are contiguous -~th the g lacier and older till is in the foreground.
c o v e r , b u t t h e s e a w a r d e n d o f th e i n n e r o n e i s l a r g e ly
c o m p o s e d o f b e a c h s h i n g le r i c h in s e al r e m a i n s a n d
w h a l e b o n e , a p p a r e n t l y b u l l d o z e d b y a r e a d v a n e e o f t h e
l a n d - b a s e d w e s t e r n e d g e o f th e g l a c i er . A r a d i o c a r b o n
a g e o f 1 5 40 + 7 0 B P o b t a i n e d f r o m a w h a l e b o n e g iv e s
a c o r r e c t e d c a l e n d a r a g e o f A D 1 2 6 5 - 1 3 8 0 , s u g g e st i n g
t h a t t h e r e a d v a n c e m a y h a v e c u l m i n a t e d i n t h e e a r ly
1 4 t h c e n t u r y . T h i s a p p e a r s t o c o r r e s p o n d r e a s o n a b l y
w e l l w i t h t h e a d v a n c e i d e n t i f i e d i n th e S o u t h S h e t l a n d
I sl an d S. E q u i v a l e n t m o r a i n e s m a p p e d a t o t h e r g l a c ie r s
o n S o u t h G e o r g i a h a v e a s i m i l a r v e g e t a t i o n c o v e r a n d
d e g r e e o f r e l a ti v e w e a t h e r i n g ( C l a p p e r t o n , 1 9 7 1 ),
s u g g e s t i n g t h a t t h e 1 3 t h - 1 4 t h c e n t u r i e s a d v a n c e m a y
h a v e b e e n w i d e s p r e a d o n t h e i s l a n d .
S i n c e S o u t h G e o r g i a w a s n o t c o n t i n u o u s l y in h a b i t e d
u n t i l t h e l a n d - b a s e d w h a l i n g i n d u s t r y b e g a n i n 1 9 0 4 ,
t h e r e a r e f e w h i s t o r i c a l r e c o r d s w i t h w h i c h t o a s se s s t h e
b e h a v i o u r o f t h e i s l a n d s g l a c ie r s b e t w e e n t h e 1 7 t h a n d
2 0 t h c e n tu r i e s . H o w e v e r , t h e t o p o f a 1 5 c m p e a t l a y e r
b u r i e d b y 6 0 c m o f t i ll , a p p r o x i m a t e l y 5 0 m f r o m t h e
t e r m i n u s o f H e a n e y G l a c i e r ( F ig . 4 ) , g a v e a r ad i o -
c a r b o n a g e o f 1 5 5 + 4 5 B P . C a l i b r a t i o n t o c a l e n d a r
y e a r s , f o l l o w i n g S t u i v e r a n d P e a r s o n ( 1 9 8 6 ) , i n d i c a t e s
t h a t t h e p e a t c o u l d d a t e f r o m A . D . 1 6 9 0, A . D . 1 7 30 , o r
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H o l o c e n e G l a c i er F l u c t u a ti o n s i n S o u t h A m e r i c a a n d A n t a r c t ic a
195
A . D . 1 82 0; a l l t h a t m a y b e c o n c l u d e d f r o m t h e s i te is
t h a t H e a n e y g l a c ie r r e a d v a n c e d a s h o r t d i s ta n c e s o m e -
t i m e a f t e r t h e e n d o f t h e 1 7 th c e n t u r y .
G l a c i e r f l u c t u a t i o n s o n So u t h G e o r g i a d u r i n g t h e
2 0 th c e n t u r y a r e i m p r e c i s e ly k n o w n , b u t a s t u d y b a s e d
o n p h o t o g r a p h i c a n d s u r v e y i n g r e c o r d s h a s r e c e n t l y
b e e n m a d e b y H a y w a r d 1 98 3) . H e t e n t a t iv e l y c o n -
e l u d e d t h a t t h e r e w a s a n a d v a n c e d u r i n g t h e f i r s t
d e c a d e o f t h e 2 0 t h c e n t u r y , w i t h a m a x i m u m a b o u t
1 9 1 0 . T h i s w a s f o l l o w e d b y a s h o r t p e r i o d o f r e t r e a t
b e f o r e a r a p i d a d v a n c e o f m a n y g l a c i e r s r e a c h e d a
m a x i m u m i n t h e l a t e 1 92 0s , w i th s o me g l a c ie r s mo s t l y
t h e t i d e w a t e r o n e s ) c o n t i n u i n g u n t i l t h e e a r l y 1 9 3 0s , a s
Sm i t h 1 96 0) h a d n o t e d e a r l i e r . S lo w r e t r e a t c o n t i n u i n g
un t i l t he l a t e 1940s was fo l lowed by a shor t , rap id
a d v a n c e c u l mi n a t i n g a r o u n d 1 9 5 6 . Mo s t g l a c i e r s h a v e
s l ow l y r e c e d e d s i n c e th e n , a p a r t f r o m s o m e s e a - c a lv i n g
g l a c i e r s w h i c h a r e p r e s e n t l y c l o s e t o t h e i r g r e a t e s t
e x t e n t o f r e c e n t t i m e s . T h e t r e n d s r e c o g n i s e d b y
H a y w a r d 1 98 3, p p . 5 5 - 5 6 ) a p p e a r t o c o r r e s p o n d w e l l
w i t h t h o s e n o t e d f o r t h e N o r t h e r n H e m i s p h e r e P o r t e r ,
1986).
D I S C U S S I O N
A s t u d y o f t h e mo r a i n e r e c o r d o f a l p i n e g l a c i e r s i n
t h e N o r t h e r n H e m i s p h e r e l e d D e n t o n a n d K a d d n
1 97 3) t o p r o p o s e t h a t m i n o r c l i ma t i c v a r i a t i o n s w i t h
co ld in t e rva l s peak ing wi th a per iod ic i ty o f ca . 2500
y e a r s , w e r e s u p e r i m p o s e d o n l o n g e r - t e r m t r e n d s s u c h
a s t h e H o l o c e n e w a r mi n g . Su b s e q u e n t a n a l y s e s o f 8 1s 0
o s c i ll a ti o n s in t w o G r e e n l a n d i c e c o r e s d e t e c t e d a 2 5 5 0
y e a r p e r i o d i c i t y t h a t i s b e l i e v e d t o r e a s o n a b l y ma t c h
t h e H o l o c e n e g l a c i e r r e c o r d o f t h e p a s t 8 5 0 0 y e a r s
D a n s g a a r d e t a l . 1 9 8 4 ) . D e n t o n e t a l . 1986) con-
e l u d e d t h a t v a r i a t i o n s i n s o l a r a c t i v i t y a r e t h e mo s t
p r o b a b l e c a u s e o f s u c h p e r i o d i c s h o r t - t e r m c l i ma t i c
f l u c t u a t i o n s . T h u s i t ma y r e a s o n a b l y b e e x p e c t e d t h a t
g l a c i e r s i n t h e S o u t h e r n H e m i s p h e r e w o u l d h a v e
f l u c t u a te d s y n c h r o n o u s l y w i t h t h o s e i n t h e N o r t h e r n
H e mi s p h e r e . O n e c u r i o u s in c o n s i s t e n c y i n t h e d is -
c u s s i o n o f D e n t o n e t a l . 1986, p . 20-21) arises ,
h o w e v e r , w h e n t h e 2 5 5 0 - y e a r p e r i o d i c it y is c o m p a r e d
w i t h t h e i r i m p r o v e d s c h e m a t i c d i a g r a m o f p u l s e s o f
g lac ie r ac t iv i ty in Scand inav ia , p resen ted as F ig . 7
D e n t o n e t a l . 1986 , p . 19 ) . The f igure cap t ion
h i g h l i g h t s ma j o r a d v a n c e s d u r i n g t h e L i t t l e I c e A g e
i . e . 1 0 0 - 7 0 0 c a l e n d a r y e a r s a g o ) , 1 9 0 0 - 32 0 0 BP ,
4 4 0 0 -4 8 0 0 B P , a n d 7 3 0 0- 7 6 00 B P ; d e a f l y a n a n o m a l y
e x i st s b e t w e e n a d v a n c e s b e g i n n i n g a t 3 2 00 BP a n d
4800 BP, a gap o f 1600 years ra ther than 2550 years .
F u r t h e r m o r e , n o t o n l y d o e s t h e s c h e m a t i c d i a g r a m
i n d ic a t e t h r e e s m a l l e r ad v a n c e s o f u n k n o w n e x t e n t b u t
a l s o s h o w s t h a t t w o o f t h e m a i n a d v a n c e s w e r e
i n t e r r u p t e d b y s i g n i f i c a n t w a r m p u l s e s . Su c h i n c o n -
s i st e n c ie s r e d u c e c o n f i d e n c e i n t h e v a l i d it y o f a s o l a r -
f o r c e d 2 5 0 0 - y ea r c y c l e a n d s u g g e s t a c a u s a l me c h a n i s m
w i t h l e s s re g u l a r i t y . Pu l s e s o f v o l c a n i s m, f o r e x a m p l e ,
w o u l d b e o n e a p p r o p r i a t e a l t e r n a t i v e t o s o l a r f o r c i n g ,
p a r t i c u l a r l y i n v i e w o f t h e i n f l u e n c e o f e r u p t i o n s o n
g l a ci e r fl u c tu a t io n s i n t h e N o r t h e r n H e m i s p h e r e d u r i n g
the l as t 200 yea rs Po r t e r , 1981 , 1986).
T h e i d e n t i f ic a t i o n a n d d a t i n g o f g l a c i e r f lu c t u a t i o n s
a l o n g a me r i d i o n a l tr a n s e c t s u c h a s t h a t a f f o r d e d b y t h e
A n d e s , t h e W e s t A n t a r c t ic p e n in s u l a , a n d i n t e r v e n in g
i s la n d g r o u p s i s c l e a r l y c r u c i a l t o e s t a b li s h in g s y n c h r o n y
o r n o n - s y n c h r o n y b e t w e e n h e m i s p h e r e s a n d t o t e s ti n g
t h e 2 5 5 0 - y e a r p e r i o d i c i t y m o d e l f o r t h e H o l o c e n e .
T a b l e 4 p r e s e n t s a s u m ma r y o f g l a c i e r a d v a n c e s
s u g g e s t e d f o r t h e t r a n s e c t , f r o m w h i c h s e v e r a l i s s u e s
ar i se .
O n e i s s u e c o n c e r n s u n c e r t a i n t y i n i n t e r p r e t i n g t h e
s i g n a l f r o m a l p i n e g l a c i e r s i n E a s t A n t a r c t i c a w h e r e
f l u c t u a t i o n s ma y b e f o r c e d mo r e b y l o c a l c l i ma t i c
cond i t ions than by g loba l var i a t ions ; bu t the poss ib i l i t y
t h a t t h e a d v a n c e c u l mi n a t i n g b e f o r e 2 9 00 BP w a s a
r e s p o n s e t o N e o g l a c i a l c o o l i n g c a n n o t y e t b e d i s -
mi s s e d , s i n c e t h e r e s p o n s e t i me o f s u c h c o l d g l a c ie r s to
c h a n g i n g c li ma t i c p a r a me t e r s i s n o t w e l l k n o w n . E q u a l
u n c e r t a i n t y s u r r o u n d s t h e me a n i n g o f g l a c i e r f l u c -
t u a t io n s o n A l e x a n d e r Is l a n d a n d a d j a c e n t p a r t s o f t h e
W e s t A n t a r c t i c p e n i n s u l a , w h e r e s ma l l - s c a l e a d v a n c e s
o f l o c a l a l p i n e g l a c i e r s ma y b e p a r t l y l i n k e d w i t h t h e
e x t e n t o f s h e l f a n d s e a i c e .
A s e c o n d p u z z l e i s w h y o u t l e t g l a ci e r s f r o m t h e So u t h
Sh e t l a n d i c e c a p s r e a c h e d t h e i r g r e a t e s t H o l o c e n e
T A B L E 4 . M a i n p h a s e s o f c l i m a t ic f l u c t u a ti o n a s d e d u c e d f r o m g l a c i e r o s c il l a ti o n s a n d e n v i r o n m e n t a l i n d i c a to r s f o r t h e
A n d e s - A n t a r c t i c t r a n s e c t . P l a c e s w h e r e t h e e v i d e n c e h a s b e e n o b t a i n e d a r e i n d i c a t e d ; t h e n a t u r e o f t h e e v i d e n c e i s d i s c u s s e d i n
the text. Trop = Tropical; Pata = Patagonia
Period of cold: Period of wan, th:
glaciers advan ce BP) glaciers withdrawn BP) Place
9 4 0 0 -8 6 0 0 S o u t h e r n A n d e s , S o u t h G e o r g i a
c a . 8 4 0 0 P a t a A n d e s
c a . 8 0 0 0 T r o p A n d e s
c a . 7 5 0 0 T r o p A n d e s o n l y
B e f o r e c a . 6 5 0 0 G e o r g e V I S o u n d
c a . 6 3 0 0 - 60 0 0 T r o p A n d e s
c a . 5 0 0 0 - 4 8 0 0 S o u t h G e o r g i a
c a . 5 2 0 0 P a t a A n d e s
c a . 4 7 0 0 - 42 0 0 T r o p P a t a A n d e s , S o u t h G e o r g i a ?
c a . 3 3 3 0 - 2 2 3 0 S o u t h G e o r g i a
c a . 3 2 0 0 T r o p A n d e s , E . A n t a r c t i c a
c a . 2 7 0 0 - 20 0 0 T r o p P a t a A n d e s , S o u t h G e o r g i a
c a . 1 2 t h c e n t u r y - e a r l y 2 0 t h c e n t u r y A l l A n d e s , S o u t h G e o r g i a , S u b - A n t a r c t i c i s l a n d s
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196 C.M. Clapperton and D .E . Sugden
e x t e n t so m e t i m e a b o u t 8 0 0 B P . R a i s e d b e a c h e s o u t s id e
m o ra i n e l im i t s c o n t i g u o u s w i t h t h e 6 m b e a c h a r e
c o n s i s t e n t l y h i g h e r a n d o l d e r t h a n c a . 1 7 0 0 B P b u t d o
n o t s e e m t o b e l i n k e d w i t h m o r a i n e s . O n e p o s s i b l e
e x p l a n a t i o n i s t h a t o l d e r m o ra i n e s a n d e q u i v a l e n t
b e a c h e s (h i g h e r t h a n 6 m ) fo rm e r l y e x i s t e d i n t h e b a y s
b u t w e r e r e m o v e d b y a m o r e e x t e n s i v e a d v a n c e
p e a k i n g a t c a . 4 0 0 - 8 0 0 B P . T h e h i g h e r e l e v a t i o n o f t h e
o l d e r b e a c h e s o u t s i d e t h e 8 0 0 y e a r m o ra i n e l i m i t i s
e x p l a i n e d b y c o n t in u i n g i s o s t a t i c r e c o v e ry ( a n d p o s s i b l y
tec ton ic up l i f t ) o f the i s l ands s ince the l as t g lac ia t ion
m a x i m u m . B e c a u s e u p l i f t c o n s t a n t l y r e d u c e d w a t e r
d e p t h a t t h e c a l v i n g g l a c i e r t e rm i n i , t h e g l a c i e r s a r e
m o r e l i k e l y t o h a v e a d v a n c e d f u r t h e r r e c e n t l y t h a n
fo rm e r l y . Th i s i s c l e a r l y a h y p o t h e s i s t h a t r e q u i r e s
t e s t i n g s i n c e i t i m p l i e s t h a t t h e H o l o c e n e e x t e n t o f
g l a c i e r s i n t h e S o u t h S h e t l a n d I s l a n d s i s c o n t ro l l e d
m o re b y r e l a t i v e s e a l e v e l t h a n b y c l i m a t i c p a r a m e t e r s ,
a l t h o u g h t h e s e p r e s u m a b l y m a y a l s o fo r c e g l a c i e r
a d v a n c e s .
A t h i r d p r o b l e m c o n c e r n s S o u t h G e o r g i a , w h e r e t h e
m a x i m u m H o l o c e n e e x t e n t o f g l ac i er s a p p e a r s t o h a v e
p e a k e d s h o r t l y b e fo re c a . 2 2 0 0 B P . S i n c e fl u c t u a t i o n s
o f g l ac i e r s o n t h e i s l a n d d u r i n g t h e 2 0 t h c e n t u ry ( a s
d e s c r i b e d b y H a y w a rd , 1 98 3) c l o s e l y m a t c h t h o s e i n th e
N o r t h e rn H e m i s p h e re (P o r t e r , 1 9 86 , F ig .~ 1 , p . 3 0 ) , i t
m i g h t b e e x p e c t e d t h a t f l u c t u a t i o n s e a r l i e r i n t h e
H o l o c e n e w o u l d a l s o h a v e c o r r e s p o n d e d w i t h t h o s e i n
E u r o p e . T h e g la c ia l g e ol o g ic re c o r d o n S o u t h G e o r g i a
i s s ti ll i n c o m p l e t e l y k n o w n a n d l a c k s t h e d a t i n g c o n t ro l
n e c e s s a ry t o p e rm i t a r i g o ro u s c o m p a r i s o n w i t h t h e
N o r t h e r n H e m i s p h e r e , b u t s o m e s u p p o r t in g d a t a a r e
e m e r g i n g f r o m t h e p a l a e o e c o l o g i c a l r e c o r d . F o r
e x a m p l e , a n a l y s e s o f v a r ia t i o n s i n p o ll e n , v e g e t a t i o n
m a c ro fo s s i l s , d i a t o m s , a n d i n o rg a n i c s e d i m e n t c o n t e n t
i n c o re s f ro m l a k e s a n d b o g s s u g g e s t (w i th r a d i o c a rb o n
d a t in g ) a p e r i o d o f m i d - H o l o c e n e w a r m t h p e a k i n g
b e t w e e n 5 6 0 0 a n d 4 8 0 0 B P f o l l o w e d b y a tr e n d t o w a r d s
c o o li n g ; p r o n o u n c e d e n v i r o n m e n t a l d e t e r i o r a ti o n is
r e g i st e r e d b e t w e e n 2 7 0 0 a n d 2 1 0 0 B P a n d d u r i n g t h e
l a st 1 0 0 0 y e a r s b y d i s ru p t i o n o f t h e f r a g i l e v e g e t a t i o n
c o v e r a n d b y h i g h e r i n p u t o f i n o rg a n i c s e d i m e n t t o
l a k e s a n d b o g s ( C l a p p e r t o n e t a l . , i n p r e s s . A re l a t e d
p r o b l e m e m e r g i n g f r o m S o u t h G e o r g i a i s t h a t f j o r d
g l a c i e r s a r e u n re l i a b l e fo r t h e p r e c i s e d a t i n g o f
c l i m a t i c a l l y - fo r c e d a d v a n c e s s i n c e t h e i r r e s p o n s e m a y
l a g b y s e v e r a l h u n d r e d y e a r s . D e s p i t e t h i s p r o b l e m ,
h o w e v e r , c a l c u l a t i o n s o f a p e rm i s s i b l e c a l v i n g r a t e a t
M o ra i n e F j o rd g l a c i e r a n d e s t i m a t i o n o f it s r a t e o f
a d v a n c e o n a m o ra i n e b a n k s u g g e s t s t h a t i t s r a d i o -
c a r b o n - d a t e d H o l o c e n e a d v a n c e o f 1 4 6 0 - 1 7 0 0 B P w a s
a d e l a y e d r e s p o n s e t o t h e p u l s e o f g l o b a l g l a c i e r
e x p a n s i o n a t 2 2 0 0 - 3 2 0 0 B P ( C l a p p e r t o n e t a l . , 1987).
T e m p e r a t u r e d e p r e s s i o n i n S o u t h G e o r g i a , e s t i m a t e d
f r o m E L A s c a l c u l a t e d f o r t h e e a r l y N e o g l a c i a l a n d
L i t t l e I c e A g e p e r i o d s , a m o u n t t o c a . I C a n d 0 .5 C
r e s p e c ti v e ly , a n d c o r r e s p o n d w e l l w i th t h o s e e s t i m a t e d
f o r t h e N o r t h e r n H e m i s p h e r e ( P o r t e r , 1 9 86 ).
A fo u r t h i s s u e c o n c e rn s t h e r e l i a b i l it y o f t h e d a t a
f r o m S o u t h A m e r i c a . A l t h o u g h t h e s e q u e n c e o f g l ac i er
f l u c t u a t i o n s d u r i n g t h e N e o g l a c i a l i n P a t a g o n i a
p r o p o s e d b y M e r c e r ( 19 7 6) c o r r e s p o n d s w e l l w i t h t h a t
e m e r g i n g f o r S c a n d i n a v i a a n d t h e E u r o p e a n A l p s
( D e n t o n
e t a l . ,
1986 ; Rb th l i sbe rge r , 1987) , much o f it is
b a s e d o n r a d i o c a rb o n d a t e s t h a t g iv e o n l y m i n i m a l a g e s
f o r th e m o r a i n e s w i t h w h ic h t h e y a r e a s s o c i a te d . O t h e r
r a d i o c a rb o n d a t e s a r e f ro m s o i l o r t r e e s b u r i e d i n
l a t e r a l m o ra i n e s w h e re g l a c i e r t h i c k e n i n g c o u l d h a v e
b e e n c a u s e d b y v a r i a ti o n s i n t h e l o c a l c a t c h m e n t r a t h e r
t h a n b y re g i o n a l c l im a t i c c h a n g e . A l s o , m u c h o f
M e r c e r s d a t a c o m e f r o m c a lv i ng g l a c ie r s w h i c h m a y
f l u c t u a t e i n p o s i t i o n b e c a u s e o f t h e i r d y n a m i c s i n
a d d i t i o n t o c l i m a t i c f o r c i n g . O n e p ro b l e m i n P a t a g o n i a
t h a t h a s n o t y e t b e e n a d d re s s e d i s w h y o u t l e t g l a c ie r s
f ro m t h e n o r t h e rn a n d s o u t h e rn i c e f i e l d s r e a c h e d t h e i r
m a x i m a l H o l o c e n e