millennial-scale dynamics of continental peatlands in western canada: pattern, controls and climate...
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Millennial-scale Dynamics of Millennial-scale Dynamics of Continental Peatlands in Western Continental Peatlands in Western
Canada: Canada: Pattern, Controls and Climate Pattern, Controls and Climate
ConnectionConnectionZicheng Yu
Lehigh UniversityBethlehem, Pennsylvania
QUEST Workshop on CH4 & Wetlands
14-16 June 2004, Bristol, UK
AcknowledgementsAcknowledgements
Dale Vitt, Kel Wieder, Merritt Turetsky, Dave Beilman, Ilka Bauer, Mike Apps, Celina Campbell, and Ian Campbell for sharing slides, data and ideas.
Climate Change Action Fund (Canada) and National Science Foundation (US) for funding.
Outline of TalkOutline of Talk
Overview of continental peatlands
in western Canada
Accumulation pattern & trajectories
Possible climate & global C cycle
connections
Conclusions
Permafrost peatlands
Open fens
Treed fens
Bogs (treed)
Peatland Types in Western CanadaPeatland Types in Western Canada
Total peatland area = 365,160 km2 (21% landbase)
63% fens28% permafrost bogs9% non-permafrost bogs
% Cover
Vitt et al. (2000)
Peatland Distribution
Non
perm
afro
stbo
gs
Perm
afro
stbo
gs
Tree
d fe
nsSh
rubb
y fe
nsO
pen
fens
-
nonp
atte
rned
Ope
n fe
ns -
patte
rned
C S
tora
ge
(Pg
)
ArcticSubarcticMontaneHigh borealMid-borealParkland
0
2
4
6
8
10
12
14
Total = 48 Pg
Vitt et al. (2000)
Peatland Carbon Storage
Fens are more important C pool and have larger area than bogs in continental Canadian peatlands, as well as bigger CH4 emitters,
but we know much less about these ecosystems than bogs in general
Outline of TalkOutline of Talk
Overview of continental peatlands
in western Canada
Accumulation pattern & trajectories
Possible climate & global C cycle
connections
Conclusions
Because:Observed pattern Infer & understand the processes Projecting future dynamics/trajectories
Time (ka)
Cu
mu
lati
ve M
ass
(g. c
m-2)
Exponential
Linear
Logarithmic
0 4 8 12
0
20
40
60
100
120
80
Why accumulation pattern matters?
(Concave)
(Convex)
Draved Mose, Denmark(data from Aaby & Tauber, 1975)
Age (calendar year BP)
0 1000 2000 3000 4000 5000 6000 7000
Cumulative peat mass (g/cm
2) 0
5
10
15
20
25
Concave Pattern from Oceanic BogsConcave Pattern from Oceanic Bogs
(assuming constant PAR and decay)
“apparent” C accumulation rate
Study Sites
Basal dates from ~80 paludified peatlands
5 sites with hi-resolution peat core analysis
Loss-on-Ignition from Upper Pinto Loss-on-Ignition from Upper Pinto FenFen
Yu et al. 2003
1-cm LOI
n=20 dates
also,
2-cm macro
2-cm isotopes
Peat Depth-Age Curve: Convex at Peat Depth-Age Curve: Convex at UPFUPF
Yu et al. 2003
Opposite to well-documented “concave” pattern
UPF: Convex Pattern
Age (cal yr BP)
0 1000 2000 3000 4000 5000 6000
Cumulative Peat Mass (g/cm
2)
0
10
20
30
What Does This Indicate?What Does This Indicate?
Causes?
• decreasing peat-addition rates from acrotelm, and/or
• increasing catotelm decomposition rate
A Simple Extended ModelA Simple Extended Model
Followed the suggestion by Clymo (2000; Quebec Meeting),
Mepdt
dM tb ** * α−= −
,
where M = cumulative peat mass; p = eventual PAR;
α
= catotelm decomposition rate; and b = PAR coefficient.This equation has an analytical solution,
)(*)( ** ttb eeb
pM α
α−− −
−=
.
Yu et al. 2003
Age (cal BP)0 1000 2000 3000 4000 5000 6000
0
10
20
30
40
50
60
Age (cal BP)0 1000 2000 3000 4000 5000 6000
Peat Mass (g/cm
2)
0
10
20
30
40
50
60
+50% Decay
-50% Decay
-50% PAR
+50% PAR
Sensitivity to Changes in Decay & Sensitivity to Changes in Decay & PARPAR
Yu et al. 2003
Change in PAR
Age (cal BP)0 2000 4000 6000
Peat-Addition Rate (g m
-2yr
-1)
0
50
100
150
200
250PAR modifier = exp[-b*t]
Time (years)
0 2000 4000 6000
PAR Modifier
0.0
0.2
0.4
0.6
0.8
1.0
b=0.00037 yr-1
0.000185 yr-1
(-50% b)
0.000555 yr-1
(+50% b)
Change in PAR over TimeChange in PAR over Time
191.8 g m-2 yr-1
26.0 g m-2 yr-1
Yu et al. 2003
PAR decrease from initial 192 to eventual 26 g/m2/yr could explain the observed pattern
Summary ISummary I The model suggests that unidirectional decrease
of PAR from 192 to 26 g m-2 yr-1 over that 5400-yr period at UPF could result in the observed convex pattern.
Autogenic drying trend resulted from fen height growth gradually isolates peat surface from water and nutrient sources, causing decreased production, especially for water-demanding rich fen species - esp. in moisture-limiting continental regions.
This analysis indicates that continental peatlands with convex pattern may reach their growth limit sooner than previous model predicts.
Convex Pattern @ Other Sites IConvex Pattern @ Other Sites I
(Kubiw et al. 1989)
Western Canada:
Slave Lake Bog (Kurry & Vitt 1996)
Southwestern Finland:
Pesansuo raised bog (Ikonen, 1993)
Western Siberia:
Salym-Yugan Mire (Turunen et al. 2001)
Convex Pattern @ Other Sites IIConvex Pattern @ Other Sites II
Convex Pattern from Regional SitesConvex Pattern from Regional Sites
(Yu & Vitt, in prep)
Outline of TalkOutline of Talk
Overview of continental peatlands
in western Canada
Accumulation pattern & trajectories
Possible climate & global C cycle
connections
Conclusions
Climate Proxy from Climate Proxy from UPFUPF
(Yu et al. 2003)
UPFW. Canada
(Yu et al. 2003)
Global Climate & C Cycle Connections?
Yu et al. 2003Bond et al. 2001
Indermuhle et al.
1999
Chappellaz et al.1997
Brook et al. 2000
Summary IISummary II Peat accumulation in western Canada shows
sensitive response to Holocene climate variability at millennial time scale.
Peatland carbon dynamics may connect to change in atmospheric CO2 concentrations (Peatlands in western Canada contain ~50 Pg C, which is equivalent to ~25 ppm CO2 if all remained in the atmosphere).
Are there similar pattern in other peatlands of northern latitudes?
Pervasive Climate Controls of Peatland Pervasive Climate Controls of Peatland DynamicsDynamics
A thawed bog shows similar millennial-scale variations
Patuanak Bog (internal lawn)
Connection of Siberian Peatland Initiations and Atmospheric CH4
N = ~200
Smith et al. 2004
Bill Ruddiman’s hypothesis: CO2 increase since 8 ka:
caused by deforestation; CH4 increase since 5 ka:
caused by rice cultivation
Allogenic and Autogenic Controls of Allogenic and Autogenic Controls of Peatland Dynamics: a conceptual modelPeatland Dynamics: a conceptual model
Yu et al. 2003
Autogenic dryingClimate wettingClimate fluctuations
• The different accumulation pattern observed in continental peatlands suggests these peatlands follow different trajectories historically and may respond to climate change differently (compared to well-studied bogs);
• Continental peatlands appear to show sensitive responses to subtle millennial-scale moisture changes during the Holocene;
• Fens seem to be more variable in C accumulation and more sensitive (less self-regulating) to climate variations than bogs;
• Northern peatlands might have had detectable impacts on atmospheric CO2 and CH4 concentrations during the Holocene.
ConclusionsConclusions
• Develop scaling-up models to take advantage of detailed inventory results from western Canada or other regions for regional CH4 emission estimates by peatland types (as a validating tool for global model?);
• Confirm the extent of past climate – peatland – global C cycle connections, particularly using multiple proxies from paired lake-peatland approach (lakes for independent climate reconstructions);
• Understand implications of permafrost (intact, thawing, and thawed) peatlands (and fen-bog transition) for CH4 emission/budget – permafrost is one of the biggest surprises to come in peatland C dynamics;
• Integrate/reconcile down-core paleo data with present-day instrumental C flux measurements.
SuggestionsSuggestions