Abstract
Coinciding with global warming, Arctic sea ice has rapidly decreased during the last four decades and climate scenarios suggest that sea ice may completely disappear during summer within the next about 50–100 years. Here we produce Arctic sea ice biomarker proxy records for the penultimate glacial (Marine Isotope Stage 6) and the subsequent last interglacial (Marine Isotope Stage 5e). The latter is a time interval when the high latitudes were significantly warmer than today. We document that even under such warmer climate conditions, sea ice existed in the central Arctic Ocean during summer, whereas sea ice was significantly reduced along the Barents Sea continental margin influenced by Atlantic Water inflow. Our proxy reconstruction of the last interglacial sea ice cover is supported by climate simulations, although some proxy data/model inconsistencies still exist. During late Marine Isotope Stage 6, polynya-type conditions occurred off the major ice sheets along the northern Barents and East Siberian continental margins, contradicting a giant Marine Isotope Stage 6 ice shelf that covered the entire Arctic Ocean.
Highlights
Coinciding with global warming, Arctic sea ice has rapidly decreased during the last four decades and climate scenarios suggest that sea ice may completely disappear during summer within the about 50–100 years
Based on a proxy reconstruction, ice-free summers occurred during a late Miocene warm climate with simulated atmospheric CO2 concentrations of 450 ppm[8], a value we might reach in the near future
Based on proxy records from ice, terrestrial and marine archives, the last interglacial (LIG) is characterized by an atmospheric CO2 concentration of about 290 ppm, i.e., similar to the pre-industrial (PI) value[13], mean air temperatures in Northeast Siberia that were about 9 °C higher than today[14], air temperatures above the Greenland NEEM ice core site of about 8 ± 4 °C above the mean of the past millennium[15], North Atlantic sea-surface temperatures of about 2 °C higher than the modern (PI) temperatures[12, 16], and a global sea level 5–9 m above the present sea level[17]
Summary
Coinciding with global warming, Arctic sea ice has rapidly decreased during the last four decades and climate scenarios suggest that sea ice may completely disappear during summer within the about 50–100 years. For older glacial and interglacial intervals such as MIS 6 and MIS 5, no such biomarker data of the central Arctic Ocean sea ice cover are available so far For these time intervals, reconstructions of past sea ice conditions are mainly restricted to continental margin sites and, even more important, only based on indirect proxies such as, for example, foraminifera, dinoflagellates, and ostracodes[42,43,44,45,46,47,48]
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