Southern Ocean sea surface temperatures over the last 200,000 years

  • Post published:November 1, 2021
Southern Ocean sea surface temperatures over the last 200,000 years

To help improve projections of future ice sheet melting and sea level rise, we sometimes study past warm periods. One of these past warm periods is the last interglacial (LIG: ∼130 to 115 thousand years before present), which was likely a couple of degrees warmer than present. To better understand ice sheet response to warming during the LIG, we need reliable climate reconstructions from Antarctica and the surrounding Southern Ocean. Marine sediment cores are a valuable archive in this respect, since the remains of plankton preserved in these cores provide proxies for sea surface temperature changes over hundreds of thousands of years. However, sea surface temperature reconstructions from plankton have many challenges, including sparse data and the uncertain influences of factors other than temperature. To increase confidence in Southern Ocean temperature reconstructions, we have reviewed the available proxies and their respective calibrations, and made some recommendations for which proxies we consider the most reliable in this region. We then follow those recommendations and reconstruct Southern Ocean sea surface temperature over the last 200,000 years, including the last interglacial warm period. Although our new reconstruction still shows considerable variability in temperature changes between the available sites, this variability should now better reflect real geographic variability, with less influence from reconstruction errors. On average, we find that Southern Ocean sea surface temperatures reached 1.6 ± 1.1 °C warmer than present during the last interglacial. In contrast, cooling during the last two ice ages reached about −3.6 ± 1.0 °C. Even though last interglacial warming was quite modest, previous studies have suggested this led to several metres of sea level rise (perhaps 5 to 9 m). The next part of our project will focus on how much of this past sea level rise might have been contributed by the Antarctic Ice Sheet, which will help us to project Antarctica’s sea level contribution under future climate warming. 

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