Retreat of the cold halocline layer in the Arctic Ocean

Abstract

Abstract. We present a comparison of Arctic Ocean hydrographic data sets from the 1990s, with a focus on changes in the upper few hundred meters of the Eurasian Basin. The most recent observations discussed here were collected during the spring 1995 Scientific Ice Expedition (SCICEX'95), the second in a series of scientific cruises to the Arctic Ocean aboard U.S. Navy nuclear submarines. Although the 1990s have seen an abundance of synoptic cruises to the Arctic, this was the only one to take place in winter/spring conditions. Other data considered here were collected during the first SCICEX cruise in summer 1993 (SCICEX'93) and during an icebreaker cruise to the Eurasian Basin in summer 1991 (Oden'91). A new Russian-American winter climatology is also used as a reference. These comparisons reveal that the Eurasian Basin "cold halocline layer" has retreated during the 1990s to cover significantly less area than in previous years. Specifically, we find a retreat from the Amundsen Basin back into the Makarov Basin; the latter is the only region with a true cold halocline layer during SCICEX'95. Changes are also seen in other halocline types and in the Atlantic Water layer heat content and depth. Since the cold halocline layer insulates the surface layer (and thus the overlying sea ice) from the heat contained in the Atlantic Water layer, this should have profound effects on the surface energy and mass balance of sea ice in this region. Using a simple mixing model, we calculate maximum iceocean heat fluxes of 1-3 W m -2 in the Eurasian Basin, where during SCICEX'95 the surface layer lay in direct contact with the underlying Atlantic Water layer. The overall cause of water mass changes in the 1990s might have been a shift in the atmospheric wind forcing and resulting sea ice motion during the late 1980s, which we speculate influenced the location where fresh shelf waters flow into the deeper basins of the Arctic Ocean. Finally, we discuss two different mechanisms that have been proposed for cold halocline water formation, and we propose a compromise that best fits these data.

Liquid export of Arctic freshwater components through the Fram Strait 1998–2011

“…Meteoric water peaked around 2005/2008, related to enhanced levels of meteoric water in the Transpolar Drift following the eastward diversion of meteoric water from the Siberian shelves during the 1990s (Steele and Boyd, 1998). The most Pacific Water was found in 1998 and none in 2004 and 2005.…”

“…The pathways of freshwater in the Arctic Ocean and their arrival in the Fram Strait are related to both the large-scale atmospheric circulation influencing upper ocean currents and hydrography (Proshutinksy and Johnson, 1997;Steele and Boyd, 1998;Zhang et al, 2003;Häkkinen and Proshutinsky, 2004;Dukhovskoy et al, 2006), and regional processes governing the storage and release of liquid freshwater.…”

Origin of freshwater and polynya water in the Arctic Ocean halocline in summer 2007

“…In the 1990s a decline in the extent of the Beaufort Gyre, and thereby a shift of the Transpolar Drift toward the North American side over the central Arctic Ocean (e.g., Morison et al, 2006), resulted in a thinning of the Arctic Ocean halocline (Steele and Boyd, 1998). Accordingly, the PO*-based assessment by Schlosser et al (2002) (Fig.…”

“…Below the surface mixed layer there is a strong and cold halocline, which is largely maintained by waters from the shelf seas (Aagaard et al, 1981) as well as convective offshore processes (Steele and Boyd, 1998). About 10 % of the world's river discharge is released onto the Arctic shelf areas.…”

Plio-Pleistocene trends in ice rafted debris on the Lomonosov Ridge

“…Of paramount interest are variations in the form, intensity and permanence of sea ice cover, which have a profound impact on the earth's albedo and global thermohaline circulation (Thiede, 1991;Aagaard and Carmack, 1994). Observational records and modeling results highlight the strong interplay between hydrologic processes in the Arctic Ocean, namely changes in the freshwater budget, and exchange with both the Pacific and Atlantic Oceans, emphasizing their role as primary controls on modern sea ice stability (Steele and Boyd, 1998;Zhang et al, 1998;Shimada et al, 2006). On geologic timescales, changes in oceanic exchange pathways, water properties and flux rates are critical parameters impacting the evolution of ice in the Arctic Ocean, and as in other ocean basins require marine sediment records to decipher their history.…”