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Shifting Climate States of the Polar Regions (SHIFTS)

Bakke, Jostein 1

1 University of Bergen

SHIFTS is a five year research program (2011-2016) aiming to produce high resolution climate reconstructions covering the Holocene time epoch from the two polar regions. Few approaches in palaeoscience have the potential to portray the spatial, temporal, and scalar expression of climate variability more accurately than the history of alpine glaciers worldwide. They are an underused resource in solving the puzzle of the Holocene drivers of global climate. However, it is only continuous reconstructions of glacier fluctuations that can be precisely correlated to other palaeoclimatic archives and records of forcing that will enhance our understanding of decadal and multidecadal climate variability. Our approach is based on the study of lake sediments in distal glacier-fed lakes mirroring the relationship between changes in sediment transfer rates from alpine glaciers and the size of the glacier and the changing glacier mass turnover gradient, which is driven by accumulation rates in winter and ablation-season temperatures.

Karlén (1976) originally suggested that glacial erosion and its associated rock-flour production provide a record of Holocene glacial fluctuations. Based on this concept, many studies have used the organic content of lacustrine sediments (measured by loss-on-ignition), sediment grain size, bulk sediment density, and magnetic susceptibility as proxies for the amount of glacial erosion, and thus glacial activity. However, it is now clear that this simple approach outlined by Karlén needs to be supported by other methods. In order to portray the variability of glaciers at the timescale of the Holocene, it is necessary to integrate multiple methods for dating moraines (e.g. cosmogenic 10Be dating of moraine surface boulders and lichenometry) and multi-proxy analyses of sediments from distal glacial-fed lakes. The downstream lake sediments will be linked to glacier activity through a novel methodology that integrates physical properties (grain size, density, organic content, water content), geochemical properties (elements analyzed at high resolution with XRF scanner), and different magnetic properties (e.g. magnetic susceptibility, paramagnetic susceptibility, diamagnetic susceptibility, ferromagnetic susceptibility, natural remanent magnetisation) in combination with multiple dating techniques including radiocarbon dating, 210Pb dating, palaeosecular variations (PSV) and Relative PaleoIntensity (RPI), and identification of tephra layers. The SHIFTS project applies a suite of multi proxy analyses to the sedimentary records, with the aim of describing the relationship between glacier sizes and different physical properties and geochemical variability in distal glacial-fed lakes. The new glacier reconstructions provided by SHIFTS will be validated against recent instrumental climate data and glacier mass-balance measurements at a regional scale. Based on this, rigorous error estimates for the proxy records will be generated. These are essential for defining the scale of natural variability and for the data output. Information on winter climate can be extracted from reconstructed glaciers combined with an independent proxy for contemporaneous summer temperature (e.g. pollen or chironomids).

In SHIFTS we aim to establish an integrated, coherent, targeted effort to reconstruct past shifts in the major polar atmospheric circulation systems such as the Southern Annular Mode (SAM) and the Northern Annular Mode (NAM) using novel approaches involving integrated reconstructions of past glacier variability in the two hemispheres. The understanding of natural variability achieved in SHIFTS will improve attribution and prediction of recent and future warming in polar regions and will be ground breaking for constraining the potential for natural cycles to amplify or dampen anthropogenically forced changes. We hope that the development of a novel methodological approach and the application of this in polar regions where palaeoclimatic data with high resolution are scarce, will provide new insight into the puzzle of Holocene climate variability. SHIFTS will integrate specialist knowledge from different researchers and research fields. Once the methodology has been established and calibrated, the approach can be widely used in palaeoclimatic investigations, not only in distal glacial-fed lakes but also in non-glacial lakes in order to verify the sedimentary proxies used for climate reconstructions e.g. from pollen data. Hopefully the methodological approaches developed in SHIFTS will set a new standard for analyses of sediments from lakes worldwide.

So far we have done fieldwork in three out of four regions during the two first years of the project and are currently planning an expedition to Kerguelen during the fall 2013. At South Georgia, Southern Ocean we have cored seven lakes and we have sampled two moraine systems for analyses of cosmogenic samples in order to build a robust and well dated Holocene moraine chronology. Two coring campaigns have been complete, the first one was during the International Polar Year in 2008 were we surveyed a lot of lake systems and the last one was in 2012 completing the lake coring program under the SHIFTS umbrella. One of the reconstructions are finalized and presented in this poster. The Hodges glacier is now melted away for the first time during the entire Holocene as a response to the warming that has taken place over this region during the latest decades. In general the glacial history of South Georgia is a story about retreating glaciers interrupted by some large glacial advance bracketed between 8.5-8k yr BP, 6-5.5k yr BP, 2-1.5k yr BP and during the “Litte Ice Age”. In Arctic Norway we have cored seven lakes in three different areas and sampled one moraine system containing Late-Glacial and Holocene moraines. Two of these records are finalized and are presented in this poster. Two others are in progress and will be based on both lake sediments and direct dating with exposure dating. During the fall of 2012 we assembled a Norwegian – US coring team for a two weeks coring campaign at Svalbard. We set of in a 55feet long sailing yacht overloaded with equipment along the west coast of Svalbard. During this campaign we cored lakes at the Mitra Peninsula and at the Island Amsterdamøya. At Amsterdamøya we cored the northernmost lake system in the world at 79oN. This lake is assumed to be located outside the Last Glacial maximum ice sheet covering Svalbard and the Barents Sea.

The SHIFTS project aims to provide a new avenue for understanding how bi-polar climates varied during the Holocene, through the application of new methods for reconstructing primary features of atmospheric circulation and variability. Based on the wide spectrum of analyses that is planned in the proposal the project will in any case be able to refine our understanding of past climates in polar regions.

*SHIFTS project members; Jostein Bakke, Hella Wittmeier, Lea Toska Oppedal, Willem van der Bilt, Marthe Gjerde, Sædis Olafdottir, Anne E. Bjune, Kristian Vasskog, Reidar Løvlie, Øyvind Paasche, Ray Bradley, Billy D´Andrea, Gerald Haug, Torgeir Røthe, Arild Sunde Rinnan, Thea Eeg and Sunniva Vatne





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