sm2: yamal region trw analysis - university of east anglia · figure yt07 – a) tree indices for...

12
08/04/2013 Page 1 of 12 SM2: Yamal Region TRW Analysis YT1. Raw measurement data (Table YT1, YT2) YT2. Inter-group common signal (Figures YT01 to YT04) YT3. Khadytla site problem (Figures YT05-YT08) YT4. Multiple RCS curves (Figures YT09-YT14) YT1 Raw Measurement Data Yamal Trees The CE portion of the Yamal data set of 2002 (Hantemirov and Shiyatov) consisted of 265 sub-fossil samples and a selection of 17 living-tree samples from 5 sites across the region. Further work by Russian scientists has resulted in living-tree samples from several more sites and many more sub-fossil samples. Where multiple cores existed, these were averaged to produce mean-tree series for all trees. Those modern samples which were less than 40 years old were removed from the chronology because they were outside the age range of the sub- fossil samples (all placed in file “young.rwl”). The file “yml-old.raw” is made up of a few samples from the sites with insufficient samples to consider separately. Only a few trees from the two earliest living-tree sites had been digitised and crossdated and these trees are in the “yml-old.raw” file. The current data set (yml-all.raw) which we use here has samples from 473 sub-fossil trees and 142 living trees and includes sub-fossil samples with rings in the period 500 B.C. to present though we only advise use of the resulting chronology from 1 CE. All initial crossdating of samples was carried out by Rashit Hantemirov and Stepan Shiyatov at the Institute of Plant and Animal Ecology, Ural Division of the Russian Academy of Sciences, Ekaterinburg though this dating was subsequently re-examined as a prelude to the work described here. Crossdating reports (...Corr.prn) and statistical reports of trees (...Stats.prn) are available at http://www.cru.uea.ac.uk/cru/papers/briffa2013qsr/ . Khadytla Site In 1991, Fritz Schweingruber (W.S.L.) and a Russian team flew by helicopter to the valley Khadyta River (Southern Yamal) where samples were collected first from all located sub- fossil wood. Subsequently, a search of the local forest area was made in an attempt to locate suitable living larch trees from which to extract increment cores. As the river valley was covered with dense forest and tall bushes, it proved difficult to find a suitable place to land the helicopter. Finally a site was found, but the trees in this nearby forest were not considered ideal for dendroclimatic analysis. This stand was located on the sandy shore of river, where the depth of permafrost is more than 2 m. In such conditions the trees developed a deep root system. Where the sand bank of the river had migrated away, a thick layer of moss developed, and the permafrost was much closer to the surface (up to 20-30 cm) and the roots of trees could be observed within the frozen ground. The trees at this location have reduced growth and appear to be dying. Despite this, a set of modern samples from 18 trees was taken from this site “Khad.raw” (Schweingruber and Briffa 1996). However, we consider that the chronology produced from this site is not suitable for dendroclimatic analysis. These data were included in the analysis described in Briffa and Melvin (2009). This analysis amounted to a sensitivity study, testing the robustness of the Yamal chronology as previously published. The work showed that the Khadytla data were anomalous in terms of 20 th century growth trend. However, specifically to demonstrate the robustness of the Yamal chronology signal, a version of the Yamal chronology was constructed that did contain the Khadytla data. This was not substantively different from the previous RCS version. Nevertheless, the site report (and statistical evidence) demonstrating the anomalous “signal” in the Khadytla data lead us to omit them from the new Yamal chronology constructed here (see SM5 for details).

Upload: others

Post on 26-Mar-2020

3 views

Category:

Documents


0 download

TRANSCRIPT

Page 1: SM2: Yamal Region TRW Analysis - University of East Anglia · Figure YT07 – a) Tree indices for the Yamal chronology (black) were created using two-curve signal-free RCS using all

08/04/2013 Page 1 of 12

SM2: Yamal Region TRW Analysis

YT1. Raw measurement data (Table YT1, YT2)

YT2. Inter-group common signal (Figures YT01 to YT04)

YT3. Khadytla site problem (Figures YT05-YT08)

YT4. Multiple RCS curves (Figures YT09-YT14)

YT1 Raw Measurement Data

Yamal Trees

The CE portion of the Yamal data set of 2002 (Hantemirov and Shiyatov) consisted of 265

sub-fossil samples and a selection of 17 living-tree samples from 5 sites across the region.

Further work by Russian scientists has resulted in living-tree samples from several more sites

and many more sub-fossil samples. Where multiple cores existed, these were averaged to

produce mean-tree series for all trees. Those modern samples which were less than 40 years

old were removed from the chronology because they were outside the age range of the sub-

fossil samples (all placed in file “young.rwl”). The file “yml-old.raw” is made up of a few

samples from the sites with insufficient samples to consider separately. Only a few trees from

the two earliest living-tree sites had been digitised and crossdated and these trees are in the

“yml-old.raw” file. The current data set (yml-all.raw) which we use here has samples from

473 sub-fossil trees and 142 living trees and includes sub-fossil samples with rings in the

period 500 B.C. to present though we only advise use of the resulting chronology from 1 CE.

All initial crossdating of samples was carried out by Rashit Hantemirov and Stepan Shiyatov

at the Institute of Plant and Animal Ecology, Ural Division of the Russian Academy of

Sciences, Ekaterinburg though this dating was subsequently re-examined as a prelude to the

work described here. Crossdating reports (...Corr.prn) and statistical reports of trees

(...Stats.prn) are available at http://www.cru.uea.ac.uk/cru/papers/briffa2013qsr/.

Khadytla Site

In 1991, Fritz Schweingruber (W.S.L.) and a Russian team flew by helicopter to the valley

Khadyta River (Southern Yamal) where samples were collected first from all located sub-

fossil wood. Subsequently, a search of the local forest area was made in an attempt to locate

suitable living larch trees from which to extract increment cores. As the river valley was

covered with dense forest and tall bushes, it proved difficult to find a suitable place to land

the helicopter. Finally a site was found, but the trees in this nearby forest were not considered

ideal for dendroclimatic analysis. This stand was located on the sandy shore of river, where

the depth of permafrost is more than 2 m. In such conditions the trees developed a deep root

system. Where the sand bank of the river had migrated away, a thick layer of moss developed,

and the permafrost was much closer to the surface (up to 20-30 cm) and the roots of trees

could be observed within the frozen ground. The trees at this location have reduced growth

and appear to be dying. Despite this, a set of modern samples from 18 trees was taken from

this site “Khad.raw” (Schweingruber and Briffa 1996). However, we consider that the

chronology produced from this site is not suitable for dendroclimatic analysis. These data

were included in the analysis described in Briffa and Melvin (2009). This analysis amounted

to a sensitivity study, testing the robustness of the Yamal chronology as previously published.

The work showed that the Khadytla data were anomalous in terms of 20th

century growth

trend. However, specifically to demonstrate the robustness of the Yamal chronology signal, a

version of the Yamal chronology was constructed that did contain the Khadytla data. This

was not substantively different from the previous RCS version. Nevertheless, the site report

(and statistical evidence) demonstrating the anomalous “signal” in the Khadytla data lead us

to omit them from the new Yamal chronology constructed here (see SM5 for details).

Page 2: SM2: Yamal Region TRW Analysis - University of East Anglia · Figure YT07 – a) Tree indices for the Yamal chronology (black) were created using two-curve signal-free RCS using all

08/04/2013 Page 2 of 12

Table YT1. Some details of the sites/sub-groups of Yamal data explored in this analysis:

altitude (m.a.s.l.), coordinates (degrees and minutes), start and end year and species (LASI is

Larix sibirica Ledeb.).

File Site Name Alt North East Start End Species

Yml-sub.rwl Yamal 30 6720 7000 -764 1984 LASI

TNL.rwl Tanlovayakha 25 6723 6916 1686 1999 LASI

KHAD.raw1 Khadytayakha

1 15 6712 6950 1782 1990 LASI

HDT.rwl Khadytayakha 20 6710 6955 1626 2000 LASI

CCC.rwl Yadayakhodyyakha 30 6726 7048 1824 2005 LASI

PM0.rwl Yadayakhodyyakha 30 6726 7049 1823 2005 LASI

PVX.rwl Yadayakhodyyakha 30 6726 7049 1909 2005 LASI

YX0.rwl Yadayakhodyyakha 30 6726 7049 1886 2005 LASI

YAD.raw Yadayakhodyyakha 30 6726 7050 1803 1996 LASI

POR.raw Portsayakha 30 6725 7058 1580 1994 LASI

JAH.raw Yadayakhodyyakha 25 6723 7100 1573 1991 LASI

Notes:

1. The KHAD.raw data from Khadytayakha is called Khadytla here (following Fritz

Schweingruber and to distinguish it from HDT.raw), but it has also been called “Khadyta

River”.

2. CCC, PM0, PVX, YX0 and YAD are plots located close to each other. POR, HDT and

TNL are larger areas and the coordinates given are approximately the site centre.

Table YT2 – Basic statistics for Yamal sub-groups:

Indices created by standardising with a 30-year high-pass spline.

Corr - the mean correlation of each index series with the chronology (excluding that series).

Rbar - the mean inter index-series correlation.

MnRaw - the mean value of TRW measurements for the site.

Name File Trees Start End Years Rings Corr RBar MnRaw

CCC ccc.rwl 12 1824 2005 182 1328 0.81 0.71 1.016

HDT hdt.rwl 17 1626 2000 375 3929 0.81 0.70 0.601

JAH jahm.raw 23 1573 1991 419 4243 0.79 0.66 0.634

KHA khad.raw 18 1782 1990 209 2368 0.84 0.72 0.683

PM0 pm0.rwl 12 1823 2005 183 943 0.82 0.71 0.849

POR por.raw 12 1580 1994 415 3503 0.80 0.69 0.466

PVX pvx.rwl 12 1909 2005 97 902 0.81 0.69 1.127

TNL tnl.rwl 21 1686 1999 314 3087 0.80 0.68 0.879

YAD yad.raw 10 1803 1996 194 1338 0.76 0.67 0.880

YX0 yx0.rwl 9 1886 2005 120 794 0.80 0.71 0.796

Old yml-old.raw 14 1628 2003 376 2929 0.75 0.60 0.500

SUB yml-sub.rwl 473 -764 1984 2749 71235 0.78 0.63 0.636

ALL yml-all.raw 633 -764 2005 2770 96599 0.78 0.62 0.649

young.rwl 15 1968 2005 38 412 0.61 0.44 1.475

Page 3: SM2: Yamal Region TRW Analysis - University of East Anglia · Figure YT07 – a) Tree indices for the Yamal chronology (black) were created using two-curve signal-free RCS using all

08/04/2013 Page 3 of 12

YT2 Inter-site common signal

Figure YT01 – To examine the consistency of the medium to high frequency signal in the

sub-sets of data the raw data were standardised using a 100-year high-pass spline, signal-free

standardisation. High-pass filtered chronologies for each site are shown (a). The same data

after filtering with a low-pass 10-year spline are shown in b). Thick lines show sample

counts >3. A high degree of medium to high frequency common variability is apparent

between all sub-groups.

Figure YT02 – As for YT01 above but using signal-free RCS, each site processed

independently. The low-frequency signal is noisy and less consistent, partly because sample

counts at each site are low and secondly, because the overall slope of each of these

chronologies is poorly defined (see Briffa and Melvin 2011 for detailed discussion). The

means of each chronology will be 1.0, independently of the common forcing over the life of

each chronology. Chronologies are shown smoothed with a 20-year spline.

Page 4: SM2: Yamal Region TRW Analysis - University of East Anglia · Figure YT07 – a) Tree indices for the Yamal chronology (black) were created using two-curve signal-free RCS using all

08/04/2013 Page 4 of 12

Figure YT03 - The various site data sets were combined into one set and standardised using

one-curve signal-free RCS. Sub-chronologies are shown here for each site (a), and also

shown filtered with a low-pass 20-year spline for display (b). Thick lines show sample

counts >3. There is a much wider spread of values when the low-frequency is retained

(compare with YT01). For each chronology the slopes are better constrained (than was the

case in YT02b) because the inclusion of sub-fossil data and because the means are set relative

to the average of all trees. In YT02b POR looks anomalous in the 20th

century while KHA

appears to be consistent with the other series. In YT03b POR fits reasonably well while KHA

exhibits an anomalous decrease (relative to the other sites) in the late 20th

century (see later

Figures).

Figure YT04 –Sample counts by ring age (a) and by calendar year (b) for each site/group.

The sub-fossil numbers are frequently outside the plotted area because of large sample counts.

Thick lines show sample counts >3.

Page 5: SM2: Yamal Region TRW Analysis - University of East Anglia · Figure YT07 – a) Tree indices for the Yamal chronology (black) were created using two-curve signal-free RCS using all

08/04/2013 Page 5 of 12

YT3 Khadytla site problem and justification for removal of these data

Figure YT05 - The RCS curves for each site (mean of signal-free measurements by ring age

smoothed using an age related spline) are plotted for trees standardised using signal-free RCS

using separate sites (a), one-curve RCS for all trees (b), and two-curve RCS for all trees (c).

Thick lines show sample counts >3. The CCC (green) chronology, consisting of cohorts of

young (about 75 years) and older (about 150 years) trees, appears anomalous when processed

separately (YT05a) but when processed with all the other trees is not especially unusual. The

Khadytla trees (red) show up as having an anomalous slope in Figures (b) and (c) relative to

all the other sites. In Figure (a) the slope problem will have been mitigated by the removal of

the slope of the chronology (built from living trees) from each individual tree (see Briffa and

Melvin 2011, Figure 5.2 and associated explanation).

Page 6: SM2: Yamal Region TRW Analysis - University of East Anglia · Figure YT07 – a) Tree indices for the Yamal chronology (black) were created using two-curve signal-free RCS using all

08/04/2013 Page 6 of 12

Figure YT06 – Chronologies created from sub-groups of Yamal data (see Table YT1 for site

details) using one-curve RCS separately on each site (a). These site data were also pooled

into one data set and standardised using either one-curve signal-free RCS (b) or two-curve

signal-free RCS (c). Thick lines show sample counts >3. The tree indices for each sub-group

were then averaged together to produce separate sub-chronologies. All chronologies were

smoothed with a 20-year spline for display. The recent spread of the site chronologies is

smaller for two-curve RCS than for one-curve RCS.

Page 7: SM2: Yamal Region TRW Analysis - University of East Anglia · Figure YT07 – a) Tree indices for the Yamal chronology (black) were created using two-curve signal-free RCS using all

08/04/2013 Page 7 of 12

Figure YT07 – a) Tree indices for the Yamal chronology (black) were created using two-

curve signal-free RCS using all the Yamal raw measurement data, including those from the

Khadytla site. A separate Khadytla sub chronology (red) was created by averaging the indices

from the Khadytla trees. The common high-frequency signal can be seen in both sets of trees.

However, a large reduction in growth rate of the Khadytla trees after 1950 relative to the

overall Yamal chronology (which includes the Khadytla trees) is clearly shown. Individual

series of tree indices for the Khadytla trees, after 30-year low-pass smoothing, are plotted in

(b). These show a decline in many trees after 1950. The Khadytla site data appear anomalous

with respect to all the other Yamal tree data used here, possibly because it is not located next

to the river (see YT08 and http://www.cru.uea.ac.uk/cru/people/briffa/yamal2009/). The

Khadytla data were removed from consideration in subsequent analysis.

Page 8: SM2: Yamal Region TRW Analysis - University of East Anglia · Figure YT07 – a) Tree indices for the Yamal chronology (black) were created using two-curve signal-free RCS using all

08/04/2013 Page 8 of 12

Figure YT08 – Photograph of the trees at the Khadytla site ( sampled by Fritz

Schweingruber) in 1991. These trees look unhealthy. Some of the trees on this site were

dying and some were depressed likely because of changes to the permafrost layer.

Page 9: SM2: Yamal Region TRW Analysis - University of East Anglia · Figure YT07 – a) Tree indices for the Yamal chronology (black) were created using two-curve signal-free RCS using all

08/04/2013 Page 9 of 12

YT4 Multiple RCS curves

Figure YT09 - The site data (henceforth omitting the Khadytla site measurements) were

combined into one data set and alternatively standardised using one-curve signal-free RCS (a)

and two-curve signal-free RCS (b). The raw data for each site were averaged together to

produce mean-ring width by age curves and these were smoothed with a 20-year spline for

display. Thick lines show sample counts >3. Distribution of site RCS curves shows little

difference between one and two RCS curve chronologies.

Figure YT10 - The site data were combined into one data set (yml-all.raw) and standardised

using one-curve signal-free RCS (a) and two-curve signal-free RCS (b). The tree indices for

each site were averaged together to produce site sub-chronologies and these were smoothed

with a 20-year spline for display. Thick lines show sample counts >3. The spread of the

recent site chronologies is smaller using two-curve RCS.

Page 10: SM2: Yamal Region TRW Analysis - University of East Anglia · Figure YT07 – a) Tree indices for the Yamal chronology (black) were created using two-curve signal-free RCS using all

08/04/2013 Page 10 of 12

Figure YT11 - The site data were combined into one data set (yml-all.raw) and standardised

using one-curve signal-free RCS. The tree indices for each site were averaged together to

produce site chronologies (a) and these chronologies were rescaled to have the same mean

over their full length as the count-weighted mean of the chronology over their common

period (b). Chronologies were smoothed with a 20-year spline for display and thick lines

show sample counts >3.

Page 11: SM2: Yamal Region TRW Analysis - University of East Anglia · Figure YT07 – a) Tree indices for the Yamal chronology (black) were created using two-curve signal-free RCS using all

08/04/2013 Page 11 of 12

Figure YT12 – as for Figure YT11 but created using two-curve signal-free RCS. Rescaling

makes little difference when using two RCS curves.

Figure YT13– as for Figure YT10 but created using three-curve signal-free RCS. Again

rescaling makes little difference when using three RCS curves.

Page 12: SM2: Yamal Region TRW Analysis - University of East Anglia · Figure YT07 – a) Tree indices for the Yamal chronology (black) were created using two-curve signal-free RCS using all

08/04/2013 Page 12 of 12

Figure YT14 - The Yamal data (yml-all.raw) were standardised using three-curve signal-free

RCS (compare these results with those shown for two-curve RCS in Figure 4 of the main

text). Mean ring-width by age (a) is plotted for the three separate RCS curves and the average

of all values. The three separate chronologies by growth rate (b) each have a mean of

approximately 1.0 and show that these independent chronologies generally produce the same

common signal over time, with the exception that chronology sections with lower sample

counts (below 8 shown by thin lines) are less reliable. Chronologies were also created (c)

after rescaling each series of tree indices to have the overall mean value that it would have

had if a single RCS curve had been used. The three chronologies reflect the relative overall

growth rates of the trees. Chronologies were smoothed with a 50-year spline for display

purposes.