The Canada Basin, 1989–1995: Upstream events and far‐field effects of the Barents Sea

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Abstract
The effects of upstream events on southern Canada Basin waters were examined using physical and geochemical data collected at one location between 1989 and 1995. These events included Atlantic layer warming, relocation of the Atlantic/Pacific water mass boundary, and increased ventilation of boundary current waters. Early signals of change in the Canada Basin first appeared in 1993 along the continental margin and by 1995 were evident in the basin interior and farther downstream. Differences in physical and geochemical properties (nutrients, oxygen, 129I, and CFCs) were observed between 150 and 1600 m of the water column. By 1995 the boundary between Pacific‐ and Atlantic‐origin water was shallower and Atlantic‐origin water occupied more of the Canada Basin water column. Atlantic‐origin lower halocline water was colder and more ventilated, Fram Strait Branch water was colder, fresher, and more ventilated, and Barents Sea Branch water was warmer, fresher, more ventilated, and occupied a larger volume of the water column than in previous years. Water mass analysis showed that the composition of Atlantic‐origin water in the Canada Basin in 1995 included 20% more water from the Barents Sea. Two related events upstream appear to be the source of this change: an atmospheric regime shift in 1989 that increased cyclonic circulation, a transition unprecedented within the latter half of the 20th century in magnitude, geographic reach, and apparent oceanographic impacts, and a large volume of dense water flowed from the Barents Sea to the Arctic Ocean between 1988 and 1989. These two phenomena illustrate the close relationship between atmospheric and oceanic events whose combined influence was evident 6 years later and 5100 km downstream in the Canada Basin at depths >1000 m.

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