Ocean surface conditions during Holocene Thermal Maximum in Kongsfjorden, Svalbard, and its relevance for understanding modern warming in the region

Abstract

The Holocene Thermal Maximum (HTM) is a significant warm period of the Holocene epoch, occurring between 11 and 6 ka BP. Here we present a multidecadal-to-centennial scale resolution diatom-based quantitative reconstruction of August Sea surface temperature (aSST) from Kongsfjorden, Svalbard for the regional HTM period between 10.5 and 7.5 ka BP. We find highly variable and moderately warm surface conditions with periods of colder aSST and/or seasonal sea ice presence. Based on the reconstruction, we infer that the variability of local surface conditions during HTM was mainly influenced by insolation and glacier/sea ice melt along with changes in the proximity of oceanic frontal zones, while influence of Atlantic Water at the surface was limited. The reconstructed aSST of 3.7 °C on average for the reconstructed part of the HTM period and 4.2 °C for its warmest interval between 10.5 and 10.1 ka BP are comparable within the method uncertainty to summer sea surface temperatures observed in the area today. We further present the evidence that the diatom assemblages are preserved in the sedimentary sequence for the first time in the record during the HTM and then re-emerge only in the core top sediments, suggesting some similarity in the environmental conditions in Kongsfjorden between the modern period and the HTM.