Sea-ice dynamics in an Arctic coastal polynya during the past 6500 years

Abstract

The production of high-salinity brines during 9 sea-ice freezing in circum-arctic coastal polynyas is 10 thought to be part of northern deep water formation as it 11 supplies additional dense waters to the Atlantic meridional 12 overturning circulation system. To better predict the effect 13 of possible future summer ice-free conditions in the Arctic 14 Ocean on global climate, it is important to improve our 15 understanding of how climate change has affected sea-ice 16 and brine formation, and thus finally dense water formation 17 during the past. Here, we show temporal coherence 18 between sea-ice conditions in a key Arctic polynya (Stor-19 fjorden, Svalbard) and patterns of deep water convection in 20 the neighbouring Nordic Seas over the last 6500 years. A 21 period of frequent sea-ice melting and freezing between 6.5 22 and 2.8 ka BP coincided with enhanced deep water 23 renewal, while near-permanent sea-ice cover and low brine 24 rejection after 2.8 ka BP likely reduced the overflow of 25 high-salinity shelf waters, concomitant with a gradual slow 26 down of deep water convection in the Nordic Seas, which 27 occurred along with a regional expansion in sea-ice and 28 surface water freshening. The Storfjorden polynya sea-ice 29 factory restarted at *0.5 ka BP, coincident with renewed 30 deep water penetration to the Arctic and climate amelioration over Svalbard. The identified synergy between Arctic polynya sea-ice conditions and deep water convection during the present interglacial is an indication of the potential consequences for ocean ventilation during states with permanent sea-ice cover or future Arctic icefree conditions.

Multiproxy evidence of the Neoglacial expansion of Atlantic Water to eastern Svalbard

“…4). Previous studies reported a decrease in the concentration of benthic foraminifera in Storfjorden at that time, which was attributed to the presence of extensive ice cover (Rasmussen and Thomsen, 2015;Knies et al, 2017). The dominant components of the ST_1.5 foraminiferal assemblage were C. reniforme and M. barleeanum (Fig.…”

“…The period after 0.5 cal ka BP Modern-like conditions were established in Storfjorden at ∼ 0.5 cal ka BP (Knies et al, 2017). The ST_1.5 record displayed a decrease in SAR compared to the preceding period, a decreasing 0-63 µm fraction and low IRD delivery (Fig.…”

“…In contrast, Rasmussen and Thomsen (2015) suggested glacial advance, followed by intensive ice rafting and meltwater delivery to Storfjorden at that time. According to Knies et al (2017), inner Storfjorden was covered by densely packed sea ice between ∼ 2.8 and 0.5 cal ka BP. Therefore, the decreasing IRD in the ST_1.5 core may result from the presence of a sea ice cover that reduced iceberg rafting, while the majority of coarse-grained material settled in the proximity to the glacial fronts.…”

“…6, 7). All these taxa have recently been observed in the fjords of Svalbard and Novaya Zemlya (e.g., Gooday et al, 2005;Majewski et al, 2005;Sabbattini et al, 2007;Pawłowska et al, 2014;Korsun and Hald, 1998;Korsun et al, 1995). Cylindrogullmia and Micrometula are dependent on the presence of fresh phytodetritus (Alve, 2010).…”

“…Conversely, the colder phases of the Neoglacial were characterized by heavy and densely packed sea ice, resulting in limited productivity (Knies et al, 2017). The presence of T. antarctica sequences and the disappearance of T. hispida (Fig.…”