Reconstructing Sea Surface Temperature in Southwest Greenland Using Long-lived Coralline Algal Buildups

Siobhan Williams1, Jochen Halfar2, Thomas Zack3, Martin Blicher4, Thomas Juul Pedersen4 and Andreas Kronz5, (1)University of Toronto, Earth Sciences, Toronto, ON, Canada, (2)University of Toronto, Chemical & Physical Sciences, Toronto, ON, Canada, (3)University of Gothenburg, Earth Sciences, Gothenburg, Sweden, (4)Greenland Institute of Natural Resources, Nuuk, Greenland, (5)Georg-August-Universität Göttingen, GZG, Abteilung Geochemie, Göttingen, Germany
Abstract:
Accurate instrumental sea surface temperature data only extends back to the 1850’s. However, in more remote locations data exist only for the last few decades. This leaves a significant gap in our knowledge of past climate, so proxy data are required to provide extended time series of past climate data. Long-lived coralline algae have previously been used as a proxy for temperature, and unlike other more established proxies corallines can thrive in harsh environments, including the Arctic Ocean, and can help fill the gaps in our knowledge of past environmental conditions in these areas at annual and subannual resolution. The coralline alga Clathromorphum compactum has clear annual growth increments, similar to tree rings, in a skeleton of CaCO3. Here we analyze C. compactum specimens collected alive in Godthåbsfjord, Greenland in summer 2013. Mg/Ca ratios were analyzed in the algal skeleton in order to reconstruct past temperatures. Calibration samples collected near a water temperature and salinity monitoring site in Godthåbsfjord showed a tight coupling between monthly resolved Mg/Ca and temperature from 2005 to 2012 (R2 = 0.4, p < 0.001) and were used to derive the following Mg/Ca – temperature relationship: T (°C) = 135.64 Mg/Ca − 7.59. Using this calibration we reconstructed a 120 year monthly-resolved temperature record of the outer Godthåbsfjord using a long-lived specimen of C. compactum. There are strong spatial correlations between Mg/Ca ratios and SST in the Irminger Sea (R2 = 0.4, p < 0.001), confirming the consistent influence of an oceanic signature in Godthåbsfjord, rather than that of glacial runoff from the Greenland Ice Sheet. There is also a strong relationship between Atlantic Multidecadal Oscillation (AMO) and coralline algal temperatures. When AMO is in a warm phase Irminger Sea water has a greater influence on Godthåbsfjord, and when AMO is in a cool phase the correlations between algal temperatures are Irminger Sea temperatures are lower.
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