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Holocene climate change in high latitudes recorded by stable isotopes in peat
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
2010 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

A key to the understanding of natural and human induced climate variations is to reconstruct past changes from different environments. No outstanding method for general use has been pinpointed, instead, a need of multi-proxy studies is often stressed and the reconstructions are under constant improvement by new techniques. The aim of my PhD project is to test a relatively new method, stable carbon and oxygen isotopes isolated from single moss species, and develop climate reconstructions based on them. The main interest is to implement the method in records from northern peatlands where permafrost conditions prevail, and contribute to the discussion about the warming Arctic.

The first part of the Licentiate thesis is a method study about the variation of stable carbon and oxygen isotope ratios in different moss plant components. Modern isotopic values were calibrated against instrumental climate records from the study region in west-central Canada. The impact of peat decay on proxies was investigated by colorimetric and chemical (C/N) methods. The results indicate that the isotope signal is well preserved in peat that started to accumulate c. 6000 years ago. Furthermore, statistical analyses imply that the variation of stable carbon isotope ratios in Sphagnum fuscum is significantly correlated to the variation of summer temperatures.

A temperature reconstruction was developed in the second part of the thesis, based on stable carbon isotope ratios. Wet/dry periods were derived from the stable oxygen isotope record, macrofossil analysis, and the peat humification record. The results were compared with other proxy records from the vicinity of the study area. The main climate periods, such as The Mediaeval Warm Period and The Little Ice Age were registered in the temperature record. The amplitude of the temperature change was similar to especially those in chironomid based reconstructions, showing c. 6.5±1°C variation in July temperatures during the past 6.2 ka.

Place, publisher, year, edition, pages
Stockholm: Department of Physical Geography and Quaternary Geology, Stockholm University , 2010.
Keyword [en]
-
National Category
Geology
Research subject
Quarternary Geology
Identifiers
URN: urn:nbn:se:su:diva-43380OAI: oai:DiVA.org:su-43380DiVA: diva2:356118
Presentation
2010-04-23, Institutionen för naturgeografi och kvartärgeologi, Svante Arrhenius väg 8, Stockholm, 11:23 (English)
Opponent
Supervisors
Projects
Holocene climate and environmental change in high latitudes as recorded by stable isotopes in peat deposits
Available from: 2010-10-19 Created: 2010-10-11 Last updated: 2012-04-10Bibliographically approved
List of papers
1. Stable carbon and oxygen isotopes in Sphagnum fuscum peat from subarctic Canada: implications for palaeoclimate studies
Open this publication in new window or tab >>Stable carbon and oxygen isotopes in Sphagnum fuscum peat from subarctic Canada: implications for palaeoclimate studies
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2010 (English)In: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 270, no 1-4, 216-226 p.Article in journal (Refereed) Published
Abstract [en]

Stable carbon and oxygen isotope ratios in single plant components in Sphagnum peat have a good potential to reveal environmental changes in peat archives. Two peat profiles, covering the past ~6000 years, and a Sphagnum hummock from a discontinuous permafrost area in west central Canada were studied in order to evaluate the effect of decomposition rate on isotope records and to assess which plant components are most suitable for climate reconstructions. The stable isotope values from the most recently forming Sphagnum tissues were compared with observational climate data to study the impact of variations in temperature and precipitation on the peat isotopes. Our results show that there is high correlation between δ13C values in α-cellulose isolated from Sphagnum fuscum stems and summer temperatures, whereas δ18O in the plant tissues is controlled by several factors, such as summer precipitation, summer temperature and evaporation. According to our results, decomposition as derived from C/N values and colorimetry does not seem to affect the oxygen and carbon isotope values of α-cellulose from Sphagnum fuscum peat significantly. There is, however, a (quasi-) constant offset between the isotope values of branches and stems and between whole plant material and  α-cellulose, which makes it crucial to select single moss-fractions when past climate and environmental changes are to be derived from the isotope record.

Keyword
Sphagnum peat, stable isotopes, Canadian subarctic, climate change, peat decomposition
National Category
Geology
Research subject
Quarternary Geology
Identifiers
urn:nbn:se:su:diva-43378 (URN)10.1016/j.chemgeo.2009.12.001 (DOI)000274989800019 ()
Projects
Holocene climate and environmental change in high latitudes as recorded by stable isotopes in peat deposits
Available from: 2010-10-11 Created: 2010-10-11 Last updated: 2017-12-12Bibliographically approved
2. Long-term climate variability in continental subarctic Canada: A 6200-year record derived from stable isotopes in peat
Open this publication in new window or tab >>Long-term climate variability in continental subarctic Canada: A 6200-year record derived from stable isotopes in peat
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2010 (English)In: Palaeogeography, Palaeoclimatology, Palaeoecology, ISSN 0031-0182, E-ISSN 1872-616X, Vol. 298, no 3, 235-246 p.Article in journal (Refereed) Published
Abstract [en]

The rapid warming of arctic regions during recent decades has been recorded by instrumental monitoring, but the natural climate variability in the past is still sparsely reconstructed across many areas. We have reconstructed past climate changes in subarctic west-central Canada. Stable carbon and oxygen isotope ratios (δ13C, δ18O) were derived from a single Sphagnum fuscum plant component; α-cellulose isolated from stems. Periods of warmer and cooler conditions identified in this region, described in terms of a “Mediaeval Climatic Anomaly” and “Little Ice Age” were registered in the temperature reconstruction based on the δ13C record. Some conclusions could be drawn about wet/dry shifts during the same time interval from the δ18O record, humification indices and the macrofossil analysis. The results were compared with other proxy data from the vicinity of the study area. The amplitude of the temperature change was similar to that in chironomid based reconstructions, showing c. 6.5±2.3°C variability in July temperatures during the past 6.2 ka.

Keyword
stable isotopes, subarctic, Sphagnum, climate reconstruction
National Category
Geology
Research subject
Quarternary Geology
Identifiers
urn:nbn:se:su:diva-48254 (URN)10.1016/j.palaeo.2010.09.029 (DOI)
Projects
Holocene climate and environmental change in high latitudes as recorded by stable isotopes in peat deposits
Available from: 2010-12-06 Created: 2010-12-06 Last updated: 2017-12-12Bibliographically approved

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