Abstract
Abstract. The importance of Antarctic sea ice and Southern Ocean warming has come into the focus of polar research during the last couple of decades. Especially around West Antarctica, where warm water masses approach the continent and where sea ice has declined, the distribution and evolution of sea ice play a critical role in the stability of nearby ice shelves. Organic geochemical analyses of marine seafloor surface sediments from the Antarctic continental margin allow an evaluation of the applicability of biomarker-based sea-ice and ocean temperature reconstructions in these climate-sensitive areas. We analysed highly branched isoprenoids (HBIs), such as the sea-ice proxy IPSO25 and phytoplankton-derived HBI-trienes, as well as phytosterols and isoprenoidal glycerol dialkyl glycerol tetraethers (GDGTs), which are established tools for the assessment of primary productivity and ocean temperatures respectively. The combination of IPSO25 with a phytoplankton marker (i.e. the PIPSO25 index) permits semi-quantitative sea-ice reconstructions and avoids misleading over- or underestimations of sea-ice cover. Comparisons of the PIPSO25-based sea-ice distribution patterns and TEX86L- and RI-OH′-derived ocean temperatures with (1) sea-ice concentrations obtained from satellite observations and (2) instrument measurements of sea surface and subsurface temperatures corroborate the general capability of these proxies to determine oceanic key variables properly. This is further supported by model data. We also highlight specific aspects and limitations that need to be taken into account for the interpretation of such biomarker data and discuss the potential of IPSO25 as an indicator for the former occurrence of platelet ice and/or the export of ice-shelf water.
Highlights
One of the key components of the global climate system, influencing major atmospheric and oceanic processes, is floating on the ocean’s surface at high latitudes – sea ice (Thomas, 2017)
We first present and discuss the biomarker data generated for this study from north (Antarctic Peninsula) to south (Amundsen and Weddell seas) and draw conclusions about the environmental settings deduced from the data set
In regard to the phytoplankton-derived biomarkers, we focus on the significance of highly branched isoprenoids (HBIs) Z-triene and brassicasterol, because the HBI E-triene and dinosterol data, which are presented in the Supplement (Fig. S1), show very similar patterns
Summary
One of the key components of the global climate system, influencing major atmospheric and oceanic processes, is floating on the ocean’s surface at high latitudes – sea ice (Thomas, 2017). Southern Ocean sea ice is one of the most strongly changing features of the Earth’s surface, as it experiences considerable seasonal variability with the sea-ice extent decreasing from a maximum of 20 × 106 km in September to a minimum of 4 × 106 km in March (Arrigo et al, 1997; Zwally, 1983). The Larsen A and B ice shelves on the east coast of the Antarctic Peninsula collapsed in 1995 and 2002 respectively These collapses were triggered by the loss of a sea-ice buffer, which enabled an increased flexure of the iceshelf margins by ocean swell (Massom et al, 2018). The disintegration of ice shelves reduces the buttressing effect that they exert on ice grounded further upstream, which can lead to partial or total loss of the ice in the catchments of the affected glaciers and, raise global sea level considerably (3.4 to 4.4 m in case of a total West Antarctic Ice Sheet collapse) (Fretwell et al, 2013; Jenkins et al, 2018; Pritchard et al, 2012; Vaughan, 2008)
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