Modern seasonal variability and deglacial/Holocene change of central Arctic Ocean sea-ice cover: New insights from biomarker proxy records

Abstract

Keywords:Arctic Ocean sea ice biomarker IP 25 Younger Dryas sediment trap a b s t r a c t For the reconstruction of sea-ice variability, a biomarker approach which is based on (1) the determination of sea-ice diatom-specific highly-branched isoprenoid (IP 25 ) and (2) the coupling of phytoplankton biomarkers and IP 25 has been used. For the first time, such a data set was obtained from an array of two sediment traps deployed at the southern Lomonosov Ridge in the central Arctic Ocean at water depth of 150 m and 1550 m and recording the seasonal variability of sea ice cover in 1995/1996. These data indicate a predominantly permanent sea ice cover at the trap location between November 1995 and June 1996, an ice-edge situation with increased phytoplankton productivity and sea-ice algae input in July/ August 1996, and the start of new-ice formation in late September. The record of modern sea-ice variability is then used to better interpret data from sediment core PS2458-4 recovered at the Laptev Sea continental slope close to the interception with Lomonosov Ridge and recording the post-glacial to Holocene change in sea-ice cover.Based on IP 25 and phytoplankton biomarker data from Core PS2458-4, minimum sea-ice cover was reconstructed for the Bølling/Allerød warm interval between about 14.5 and 13 calendar kyr BP, followed by a rapid and distinct increase in sea-ice cover at about 12.8 calendar kyr BP. This sea-ice event was directly preceded by a dramatic freshwater event and a collapse of phytoplankton productivity, having started about 100 years earlier. These data are the first direct evidence that enhanced freshwater flux caused enhanced sea-ice formation in the Arctic at the beginning of the Younger Dryas. In combination with a contemporaneous, abrupt and very prominent freshwater/meltwater pulse in the Yermak Plateau/ Fram Strait area these data may furthermore support the hypothesis that strongly enhanced freshwater (and ice) export from the Arctic into the North Atlantic could have played an important trigger role for the onset of the Younger Dryas cold reversal. During the Early Holocene, sea-ice cover steadily increased again (ice-edge situation), reaching modern sea-ice conditions (more or less permanent sea-ice cover) probably at about 7-8 calendar kyr BP.

Source identification of the Arctic sea ice proxy IP25

“…Previous studies based on the analysis of IP 25 in sea ice and sediments have shown a consistent abundance relationship between these two structural homologues indicating a common source at least within the Arctic 12,24,33,34 . Our data not only confirm this source association but, the similarity of the C 25:2 /IP 25 ratio in producers (2.3 ± 0.8) to that found in sea ice and sediments 12,24,33,34 , implies a close link between the source and Arctic sedimentary signatures of these two biomarkers. As such, a significant formation of IP 25 over C 25:2 (or vice versa) in sea ice or differential degradation of either biomarker in situ, seems unlikely.…”

Atlantic Water advection vs. glacier dynamics in northern Spitsbergen since early deglaciation

“…This cold reversal was most likely initiated by a massive glacial lake drainage into the Arctic Ocean that reduced the Atlantic Meridional Overturning Circulation (Broecker, 2006;Broecker et al, 1989;Fahl and Stein, 2012;Murton et al, 2010;Stein et al, 2012;Tarasov and Peltier, 2005). Nonetheless, the influence of AW is seen at numerous locations around Svalbard, at least during the early YD and possibly temporarily (e.g.…”

“…Brassicasterol and dinosterol were quantified as trimethylsilyl ethers using the molecular ions m/z 470 and m/z 500, respectively, in relation to the molecular ion m/z 464 of cholesterol-D 6 . For more details about the quantification of IP 25 as well as the sterols, see Fahl and Stein (2012). Accumulation rates of sea ice and phytoplankton biomarkers (IP 25 and brassicasterol, respectively) were calculated following Eq.…”

Sea ice dynamics influence halogen deposition to Svalbard

“…The occurrence of floating ice could be revealed by the presence of ice-rafted debris (Lisitzin, 2002), while sea ice-related palaeo-productivity can be inferred from the sedimented remains of microscopic organisms and other biomarkers (Cronin et al, 2008). Recently, the determination of highly branched isoprenoids (IP 25 ) in specific sea ice diatoms have been proposed to describe the past sea ice variability (Vare et al, 2009;Fahl and Stein, 2012). Coastal records also help to understand the past dynamics of sea ice, producing a clear signal both in coastal sediment and landforms (Polyak et al, 2010).…”