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Observing Pacific Water Inflow to the Arctic in Winter

OCCI/Arctic Research Initiative
2007 Funded Project


Abstract

Although the importance of the Arctic in global climate change is widely recognized, a critical component of the Arctic system has been largely overlooked: The inflow of Pacific Water and its role in maintaining the Arctic halocline. In particular, there is a need to understand the processes by which Pacific Water flowing through the Bering Strait is modified in the shallow ChukchiSea and then transported to the western Arctic basin. The transport most important to halocline properties is that which occurs in winter beneath ice cover. This process establishes hydrographic conditions in the upper 200 m of the Arctic basin that determine the relative influence of Pacific and Atlantic water, and may profoundly affect the thickness and extent of Arctic sea ice. The narrow passage between Point Barrow, Alaska, and the flank of Barrow

Canyon is a critical “choke point” of the system, where a significant portion of the Pacific Water inflow is concentrated subsequent to modification by shelf processes, but prior to exchange with Arctic waters. We propose to obtain high-resolution hydrographic transects across this choke point in winter, using an autonomous underwater vehicle called REMUS. Summer transects obtained in 2005 show that the capabilities of REMUS are well suited to the study, although improvements to vehicle navigation and the development of a through-ice launch and recovery system will be necessary to operate successfully in winter. The result of this project will be spatially-resolved observations of Pacific Water properties just prior to entering the Arctic basin and the first direct measurement of Pacific Water transport into the western Arctic in winter.

Background

The Arctic is thought to be particularly sensitive to climate change, and there are indications that measurable changes are already occurring (Overpeck et al., 2005; Lindsay and Zhang, 2005). Although the importance of the Arctic within the global climate system is widely recognized, a critical component of the Arctic circulation has been largely overlooked: The role of Pacific Water in maintaining the halocline in the western Arctic. The halocline is a region of relatively uniform, cold (near the freezing point) temperatures and increasing salinity extending from about 30-200 m depth that separates warmer, more saline Atlantic water from the surface mixed layer. In particular, there is a need to understand the processes by which Pacific Water flowing through the Bering Strait is modified in the shallow ChukchiSea and then transported to the western Arctic basin (Fig. 1). The transport most important to halocline properties is that which occurs in winter beneath ice cover. The narrow passage between Point Barrow, Alaska, and the flank of Barrow Canyon is a critical “choke point” of the system, where a substantial portion of the Pacific Water inflow is concentrated (Winsor and Chapman, 2004; Spall, submitted).Observations there in winter would characterize Pacific Water subsequent to modification by shelf processes, but prior to exchange with Arctic waters. Although some parts of the Pacific Water inflow system are presently being monitored (e.g. Bering Strait, Beaufort Gyre), and important observations in the northern Chukchi Sea have been reported (Weingartner et al., 2005), the transport of winter-transformed Pacific Water into the western Arctic along the coastal pathway has never been measured. We propose to obtain the first high-resolution hydrographic transects across the choke point of this pathway, using an autonomous underwater vehicle (AUV) operating beneath the ice in winter.

Last updated: September 14, 2010