The role of Arctic Ocean freshwater during the past 200 ky

Abstract

As part of the hydrologic cycle, the freshwater system plays a pivotal role for the Arctic Ocean. It maintains the strong stratification in the upper waters and fosters the formation of sea ice on the circum-Arctic shelves from where the ice is being exported toward Fram Strait and into the Nordic Seas. Recent projections of climate change under the greenhouse effect predict severe changes for the hydrologic cycle in the Arctic. This manuscript reviews the current knowledge of past changes in freshwater fluxes to and from the Arctic Ocean and their possible impact on ocean circulation and climate outside the Arctic during the past 200,000 years. It becomes evident that abrupt and large-volume discharges into the Arctic Ocean during times of major climate transitions were capable of disturbing the global ocean circulation and triggering further climate change, e.g., at the onset of the Younger Dryas cold event. During sea-level rise in the Holocene, a connection between the increasing areas available for sea ice formation, the position of the ice margin in the ice export area (the Fram Strait) and the deepwater convection in the Greenland Sea is suggested. Further work is needed to investigate the effects of other catastrophic freshwater discharges from previously ice-dammed lakes in northern Eurasia during the Weichselian and Saalian glaciations. Events like the 8.2 ka and the Younger Dryas, which were associated with flooding and routing of glacial meltwaters and had a significant effect on climate, could serve as a template to better validate the impact of similar occurrences in the past. To date, the actual influence of the earlier events on ocean circulation and climate remains elusive.

Modern planktic foraminifers in the high-latitude ocean

“…Higher than modern sea surface temperatures (SSTs) during the last interglacial maximum (MIS 5.5), about 125 thousand years (125 ka) ago, were accompanied by reduced ice volume and corresponding sea level rise (e.g., Kopp et al, 2009;Rohling et al, 2014). Freshening of polar surface waters has been observed along with past and modern climate warming and sea ice retreat (e.g., Haas et al, 2008;Spielhagen and Bauch, 2015;Haumann et al, 2016). Climate model projections indicate an asymmetric warming between the Arctic and Southern Ocean, with an early response in the Arctic and a delayed response in the Southern Ocean: Northern polar regions are projected by modeling studies to be subjected to warming mostly through persistent Atlantic Meridional Overturning, also referred to as polar amplification (e.g., Manabe and Stouffer, 1980;Manabe et al, 1991;Meehl et al, 2007).…”

The Role of the Russian Shelf in Seasonal and Interannual Variability of Arctic Sea Surface Salinity and Freshwater Content

“…While the Arctic's FWV decreased in the initial years to 71,220 km 3 in 1985, it has subsequently sustained an increase, reaching a maximum of 90,450 km 3 in 2018. On average, the Arctic Ocean's FWV has been reported to be roughly 84,000 km 3 when using a reference salinity of 34.8 psu (Serreze et al., 2006; Spielhagen & Bauch, 2015). Here, ORAS5 shows a comparable FWV of 80,763 km 3 (Table 1), with the Russian Shelf contributing ∼16% and the BG ∼23%.…”

“…Ahmed et al (2020) reported that the annual discharge over the years 1980-2009 from the Ob, Lena, and Yenisei Rivers increased by 10.3, 40.6, and 23.7 km 3 per decade respectively. Arctic shelves also tend to favor polynyas where ice grows and an excess of saline water is left behind (Spielhagen & Bauch, 2015). Both factors contribute greatly to seasonal and interannual variability.…”

The Late Mesozoic‐Cenozoic Arctic Ocean Climate and Sea Ice History: A Challenge for Past and Future Scientific Ocean Drilling

“…Inflow of Pacific Waters through Bering Strait and export of ice and low‐saline waters through Fram Strait are indicated. Gray arrows mark the average surface water circulation within the Beaufort Gyre and the Transpolar Drift and red arrows the places of sinking water masses (Spielhagen & Bauch, , supplemented; based on data from EWG, ).…”