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Holocene climate and atmospheric circulation changes in northern Fennoscandia: Interpretations from lacustrine oxygen isotope records
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis investigates how variations in the oxygen isotopic composition of lake waters in northern Fennoscandia are recorded in lake sediment archives, especially diatoms, and how these variations can be used to infer past changes in climate and atmospheric circulation. Results from analyses of the oxygen isotopic composition of lake water samples (δ18Olakew) collected between 2001 and 2006 show that δ18O of northern Fennoscandian lakes is mainly controlled by the isotopic composition of the precipitation (δ18Op). Changes in local δ18Op depend on variations in ambient air temperature and changes in atmospheric circulation that lead to changes in moisture source, vapour transport efficiency, or winter to summer precipitation distribution. This study demonstrates that the amount of isotopic variation in lake water δ18O is determined by a combination of the original δ18Olakew, the amount and timing of the snowmelt, the amount of seasonally specific precipitation and groundwater, any evaporation effects, and lake water residence time. The fact that the same isotope shifts have been detected in various δ18Olakew proxies, derived from hydrologically different lakes, suggests that these records reflect regional atmospheric circulation changes. The results indicate that diatom biogenic silica isotope (δ18Odiatom) records can provide important information about changes in atmospheric circulation that can help explain temperature and precipitation changes during the Holocene. The reconstructed long-term Holocene decreasing δ18Op trend was likely forced by a shift from strong zonal westerly airflow (relatively high δ18Op) in the early Holocene to a more meridional flow pattern (relatively low δ18Op). The large δ18Olakew depletion recorded in the δ18O records around ca. 500 cal yr BP (AD 1450) may be due to a shift to more intense meridional airflow over northern Fennoscandia resulting in an increasing proportion of winter precipitation from the north or southeast. This climate shift probably marks the onset of the so-called Little Ice Age in this region.

Place, publisher, year, edition, pages
Stockholm: Department of Physical Geography and Quaternary Geology, Stockholm University , 2009. , 30 p.
Series
Dissertations from the Department of Physical Geography and Quaternary Geology, ISSN 1653-7211 ; 18
Keyword [en]
oxygen isotope, diatom silica, lake sediment, atmospheric circulation, North Atlantic Oscillation, northern Fennoscandia, The Holocene, Little Ice Age
National Category
Physical Geography
Research subject
Physical Geography
Identifiers
URN: urn:nbn:se:su:diva-29343ISBN: 978-91-7155-904-3 (print)OAI: oai:DiVA.org:su-29343DiVA: diva2:232861
Public defence
2009-10-02, De Geersalen, Geovetenskapens hus, Svante Arrhenius väg 14, Stockholm, 13:00 (English)
Opponent
Supervisors
Note
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: In press. Paper 2: Submitted. Paper 5: In progress.Available from: 2009-09-10 Created: 2009-08-24 Last updated: 2010-04-22Bibliographically approved
List of papers
1. Stable oxygen and hydrogen isotopes in sub-Arctic lake wateras from northern Sweden
Open this publication in new window or tab >>Stable oxygen and hydrogen isotopes in sub-Arctic lake wateras from northern Sweden
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2009 (English)In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 376, 143-151 p.Article in journal (Refereed) Published
Abstract [en]

Lakes in sub-Arctic regions have the potential of retaining many different aspects of water isotope composition in their sediments which can be used for palaeoclimate reconstruction. It is therefore important to understand the modern isotope hydrology of these lakes. Here we discuss the significance of variations in water isotope composition of a series of lakes located in north-west Swedish Lapland. Climate in this region is forced by changes in the North Atlantic which renders it an interesting area for climate reconstructions. We compare δ18Olake and δ2Hlake collected between 2001 and 2006 and show that the lakes in this sub-Arctic region are currently mainly recharged by shallow groundwater and precipitation which undergoes little subsequent evaporation, and that the d18O and δ2H composition of input to the majority of the lakes varies on a seasonal basis between winter precipitation (and spring thaw) and summer precipitation. Seasonal variations in the isotopic composition of the lake waters are larger in lakes with short residence times (<6 months), which react faster to seasonal changes in the precipitation, compared to lakes with longer residence times (>6 months), which retain an isotopic signal closer to that of annual mean precipitation. Lake waters also show a range of isotope values between sites due to catchment elevation and timing of snow melt. The lake water data collected in this study was supported by isotope data from lake waters, streams and ground waters from1995 to 2000 reported in other studies.

Keyword
Stable isotopes, 18O/16O, 2H/H, surface waters, Sub-Arctic lakes, Northern Sweden
National Category
Physical Geography
Identifiers
urn:nbn:se:su:diva-37521 (URN)10.1016/j.hydrol.2009.07.021 (DOI)000270759400014 ()
Available from: 2010-04-22 Created: 2010-03-09 Last updated: 2017-12-12Bibliographically approved
2. High-resolution diatom d18O records from two sub-Arctic high-altitude lakes in the Swedish Scandes
Open this publication in new window or tab >>High-resolution diatom d18O records from two sub-Arctic high-altitude lakes in the Swedish Scandes
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(English)In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417Article in journal (Refereed) Submitted
Abstract [en]

Waters from high altitude alpine lakes are mainly recharged by meteoric water. Because of seasonal variations in precipitation and temperature, and relatively short hydraulic residence times, most high altitude lakes have lake water isotopic compositions (δ18Olake) that fluctuate due to seasonality in water balance processes. Input from snowmelt, in particular, has a significant role in determining lake water d18O. Here we compare two high resolution δ18Odiatom records from lake sediments in the Swedish Scandes with instrumental data from the last century obtained from nearby meteorological stations. The time period AD 1900 to AD 1990 is characterized by an increase in winter precipitation and high winter/summer precipitation ratios and this is recorded in δ18Odiatom as decreasing trends. Lowest δ18Odiatom values and highest amount of winter precipitation are found around AD 1990 when the winter North Atlantic Oscillation index was above +2. We conclude that for the last 150 years the main factor affecting the δ18Odiatom signal in these sub-Arctic high altitude lakes with short residence times has been changes in amount of winter precipitation and that δ18Odiatom derived from high altitude lakes in the Swedish Scandes can be used as a winter precipitation proxy.

Keyword
oxygen isotopes, high altitude lakes, diatom silica, winter precipitation, North Atlantic Oscillation
National Category
Physical Geography
Identifiers
urn:nbn:se:su:diva-29439 (URN)
Available from: 2009-08-27 Created: 2009-08-27 Last updated: 2017-12-13Bibliographically approved
3. Diatom oxygen isotopes in pro-galcial lake sediments from northern Sweden: A 5000 year record of atmospheric circulation.
Open this publication in new window or tab >>Diatom oxygen isotopes in pro-galcial lake sediments from northern Sweden: A 5000 year record of atmospheric circulation.
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2004 (English)In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 23, no 7-8, 851-859 p.Article in journal (Refereed) Published
Abstract [en]

We use a pro-glacial oxygen isotope record of diatom silica (δ18Odiatom) and a sedimentary proxy for glacier flutuations to determine centennial-millennial scale climate change during the last 5000 yeras in northern Sweden. We show that the lake water isotopic composition åredominantly reflects the isotopic composition of the precipitation. Superimposed on a general depletion trend of 3.5‰ over the past 5000 years we found that the isotopic composition of precipitation became depleted (> 1‰ excursions) during four occasions centered at 4400, 3000, 2000 and, after 1200 cal yr BP. Climate simultaneously sustained a positive glacier mass balance, taht caused the catchment glacier to advance. A peristan cgange in the atmopheric circulation pattern could potentially have caused the registered chnages in the δ18Odiatom because different air masses hold characteristics δ18O signatures of their precipitation. The glacier mass balance primarily responds to the influence of summer temperature on ablation. We suggest that the most likely cause for the recorded chnages in both these proxies is a steadily increasing but fluctuating dominance of colder and δ18O depleted air masses from the north/northeast during the past 5000 years. Theδ18Odiatom depletion and glacier events all occur at times of relative ice-rafted-debris maxima in the North Atlanic, consistent with cold conditions and changes in surface wind directions. Our results confirm that changes towards a predominace of north/northeasterly winds occured at these time intervals.

Keyword
pro-glacial, lake sediment, diatom silica, oxygen isotopes
National Category
Physical Geography
Identifiers
urn:nbn:se:su:diva-29432 (URN)10.1016/j.quascirev.2003.06.009 (DOI)
Available from: 2009-08-27 Created: 2009-08-27 Last updated: 2017-12-13Bibliographically approved
4. North Atlantic region atmospheric circulation dynamics inferred from a late-Holocene lacustrine carbonate isotope record, northern Swedish Lapland
Open this publication in new window or tab >>North Atlantic region atmospheric circulation dynamics inferred from a late-Holocene lacustrine carbonate isotope record, northern Swedish Lapland
2007 (English)In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 17, no 7, 867–873- p.Article in journal (Refereed) Published
Abstract [en]

The first high-resolution record of climate variation based on the oxygen and carbon isotope composition of authigenic carbonate for northern Scandinavia is presented. Modern lake-water isotope data indicate that controls on its oxygen and hydrogen (δ18O<sub>w</sub> and δD<sub>w</sub>) composition are unlikely to be evaporation or temperature, and its variations must therefore reflect changes in, or at the source of, precipitation. Substantial and persistent changes of the isotopic composition of the precipitation are required to change the mean annual isotope composition of lake surface water. For this reason we argue that the recorded changes were significant and that the recurrence of such changes would greatly affect future regional climate conditions in the North Atlantic region. Oxygen isotope (δ<sup>18</sup>O) minima occurring at ~ 200, 500, 1300, 1600 and at 2900 cal. yr BP all coincide with major peaks in North Atlantic ice rafted debris deposition. We suggest that the depletion events in δ<sup>18</sup>O cycles recorded in several lakes in northern Swedish Lapland are caused by the same climatic shifts as those noted in the North Atlantic marine records. This is because changes of atmospheric circulation pattern and the lower ocean and atmospheric temperatures associated with the IRD events help to explain why 18O depletion of precipitation occurred during these events. Our findings indicate that the recorded changes in North Atlantic ice drift and surface hydrography are coupled to changes in atmospheric circulation. 

Keyword
Oxygen isotopes, carbonate lake sediments, atmospheric circulation dynamics, North Atlantic IRD, late Holocene, northern Sweden
Identifiers
urn:nbn:se:su:diva-20556 (URN)000251541400001 ()
Available from: 2008-01-09 Created: 2008-01-09 Last updated: 2017-12-13Bibliographically approved
5. Two diatom oxygen isotope records from Naimakka in northern Fennoscandia: implications for Holocene palaeohydrology and atmospheric circulation dynamics
Open this publication in new window or tab >>Two diatom oxygen isotope records from Naimakka in northern Fennoscandia: implications for Holocene palaeohydrology and atmospheric circulation dynamics
(English)Manuscript (preprint) (Other academic)
Abstract [en]

This study present past changes in lake water oxygen isotope composition (δ18Olakew) calculated from diatom oxygen isotope composition (δ18Odiatom) from two lake sediment records. The two sediment sequences (9500 and 2800 years) are from open-basin lakes, although with different hydrologies, and are located close to a meteorological station in Naimakka, Northern Fennoscandia. The isotope composition of lake waters was analysed to determine the modern regional hydrological setting. Our results show that changes in the isotope composition of precipitation (δ18Op) is the primary forcing mechanism decreasing or increasing the δ18Olakew values in both lakes. Changes in the isotope signals are interpreted as reflecting regional variations in atmospheric circulation and climatic seasonality. δ18Odiatom from Lake Keitjoru, covering the last 9500 years, shows a depletion trend of 1.3‰ from c. 8000 until around 1500 cal yr BP. This decrease is thought to be due to a long term decrease in the influence of a zonal airflow (strong westerlies, relatively high δ18Op) over Fennoscandia in favor of an increasing proportion of colder meridional airflow (weak westerlies, lower δ18Op) from the north. A synchronous shift to lower δ18O values was recorded in Lake Keitjoru and lake Oikojärvi around 700-600 cal yr BP (~AD 1250-1350), a time when European climate deteriorated into the “Little Ice Age”. We argue that a circulation pattern dominated by meridional airflow, with reduced westerlies over Northern Fennoscandia and high amounts of winter precipitation from southeast or north, replaced a zonal atmospheric circulation pattern at this time. The δ18Odiatom minima c. 400 and 50 cal yr BP (~AD 1550 and AD 1900) is likely also a response to shifts in circulation, which is also seen in lower summer temperatures at that time recorded in tree-rings and from pollen data. The fact that the same isotope shifts have been detected in δ18O records from hydrological different lakes lends support to our conclusion that these records reflect variations in atmospheric circulation pattern.

Keyword
oxygen isotopes, diatom biogenic silica, atmospheric circulation, Holocene, northern Fennoscandia, North Atlantic Oscillation
National Category
Physical Geography
Identifiers
urn:nbn:se:su:diva-29440 (URN)
Available from: 2009-08-27 Created: 2009-08-27 Last updated: 2010-04-22Bibliographically approved
6. Reconstructing past atmosperic circulation changes using oxygen isotopes in lake sediments from Sweden
Open this publication in new window or tab >>Reconstructing past atmosperic circulation changes using oxygen isotopes in lake sediments from Sweden
2010 (English)In: Climate of the Past, ISSN 1814-9324, E-ISSN 1814-9332, Vol. 6, no 1, 49-62 p.Article in journal (Refereed) Published
Abstract [en]

Here we use lake sediment studies from Sweden to illustrate how Holocene-aged oxygen isotope records from lakes located in different hydrological settings, can provide information about climate change. In particular changes in precipitation, atmospheric circulation and water balance. We highlight the importance of understanding the present lake hydrology, and the relationship between climate variables and the oxygen isotopic composition of precipitation (d18Op)and lake waters (d18Olakewater) for interpretation of the oxygen isotopic record from the sediments (d18O). Both precipitation reconstructions from northern Sweden and water balance reconstructions from south and central Sweden show that the atmospheric circulation changed from zonal to a more meridional airflow over the Holocene. Superimposed on this Holocene trend are δ18Op minima resembling intervals of the negative phase of the North Atlantic Oscillation (NAO), thus suggesting that the climate of Northern Europe is strongly influenced by atmospheric and oceanic circulation changes over the North Atlantic.

National Category
Physical Geography
Research subject
Physical Geography
Identifiers
urn:nbn:se:su:diva-36854 (URN)10.5194/cp-6-49-2010 (DOI)000274994500004 ()
Note
First published in Climate of the Past (CP) Discussions, special issue, 5, 1609–1644.Available from: 2010-01-27 Created: 2010-01-27 Last updated: 2017-12-12Bibliographically approved

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