Abstract
Abstract. Organic geochemical and micropaleontological analyses of surface sediments collected in the southern Drake Passage and the Bransfield Strait, Western Antarctic Peninsula, enable a proxy-based reconstruction of recent sea ice conditions in this climate-sensitive area. We study the distribution of the sea ice biomarker IPSO25, and biomarkers of open marine environments such as more unsaturated highly branched isoprenoid alkenes and phytosterols. Comparison of the sedimentary distribution of these biomarker lipids with sea ice data obtained from satellite observations and diatom-based sea ice estimates provide for an evaluation of the suitability of these biomarkers to reflect recent sea surface conditions. The distribution of IPSO25 supports earlier suggestions that the source diatom seems to be common in near-coastal environments characterized by annually recurring sea ice cover, while the distribution of the other biomarkers is highly variable. Offsets between sea ice estimates deduced from the abundance of biomarkers and satellite-based sea ice data are attributed to the different time intervals recorded within the sediments and the instrumental records from the study area, which experienced rapid environmental changes during the past 100 years. To distinguish areas characterized by permanently ice-free conditions, seasonal sea ice cover and extended sea ice cover, we apply the concept of the PIP25 index from the Arctic Ocean to our data and introduce the term PIPSO25 as a potential sea ice proxy. While the trends in PIPSO25 are generally consistent with satellite sea ice data and winter sea ice concentrations in the study area estimated by diatom transfer functions, more studies on the environmental significance of IPSO25 as a Southern Ocean sea ice proxy are needed before this biomarker can be applied for semi-quantitative sea ice reconstructions.
Highlights
In the last century, the Western Antarctic Peninsula (WAP) has undergone a rapid warming of the atmosphere of 3.7 ± 1 ◦C, which exceeds several times the average global warming (Pachauri et al, 2014; Vaughan et al, 2003)
We especially focus on the applicability of these biomarkers for reconstructing sea ice conditions and integrate information derived from satellite observations and diatom-based sea ice estimations
We further discuss the possible approach of a sea ice index phytoplankton-IPSO25 index (PIPSO25) by analogy with the Arctic sea ice index PIP25 (Müller et al, 2011)
Summary
The Western Antarctic Peninsula (WAP) has undergone a rapid warming of the atmosphere of 3.7 ± 1 ◦C, which exceeds several times the average global warming (Pachauri et al, 2014; Vaughan et al, 2003). Since the start of satellite-based sea ice observations, a slight increase in total Antarctic sea ice extent has been documented, which contrasts with the significant decrease in sea ice in Western Antarctica, especially around the WAP (Hobbs et al, 2016). For an improved understanding of the oceanic and atmospheric feedback mechanisms associated with the observed changes in sea ice coverage, reconstructions of past sea ice conditions in climate-sensitive areas such as the WAP are of increasing importance.
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