Mapping recent sea ice conditions in the Barents Sea using the proxy biomarker IP25: implications for palaeo sea ice reconstructions

Abstract

An analysis of the sea ice proxy IP25 and the open water phytoplankton indicator brassicasterol has been carried out for 93 surface sediments collected from the Barents Sea and some additional data from previous studies have been included to augment the analysis further. Consistent with a specific and selective sea ice diatom origin for IP25, this biomarker was identified in virtually all sediments from seasonally ice-covered locations, but was absent from the majority of sites beyond the maximum sea ice extent (MSIE) for the period 1983–2002. In contrast, brassicasterol was detected in virtually all sediments from the region and concentrations were not at all associated with the MSIE. Instead, more localised regions of brassicasterol concentrations were identified and these likely reflect different influences on production and deposition. When the IP25 and brassicasterol concentrations were combined together in the form of the previously proposed PBIP25 index, the aforementioned association between IP25 occurrence and the MSIE was clarified further and, in addition, provided more detailed descriptions of sea ice cover. In particular, PBIP25 data indicated seasonal sea ice or marginal ice zone conditions for the region of the Barents Sea within the MSIE according to previously defined PBIP25 ranges. We also amalgamated the biomarker data from the current study with those derived previously by Müller et al. (2011) and compared these larger datasets with satellite-derived mean spring sea ice concentrations. Significantly, although the correlation between the combined IP25 concentration dataset with the satellite data was very similar to that reported previously by Müller et al. (2011), the corresponding correlation using the PBIP25 values was poorer with the larger dataset and some possible reasons for this are discussed. Finally, in a small number of cases, IP25 was identified in sediments somewhat distal from the MSIE, and it is hypothesised that the occurrence of IP25 in these sediments results from allochthonous input following sediment advection between shelf and trough environments. This is the first reported example that provides evidence for the allochthonous input of IP25 into marine sediments and it is recommended that this should be considered carefully when carrying out palaeo sea ice reconstructions based on the occurrence of this biomarker in the future.