A Synthesis of Year-Round Interdisciplinary Mooring Measurements in the Bering Strait (1990-2014) and the RUSALCA Years (2004-2011) Woodgate, R. A., Stafford, K. M., & Prahl, F. G. (2015). A Synthesis of Year-round Interdisciplinary Mooring Measurements in the Bering Strait (1990-2014) and the RUSALCA years (2004-2011). Oceanography, 28(3), 46-67. doi:10.5670/oceanog.2015.57 10.5670/oceanog.2015.57 Oceanography Society Version of Record http://cdss.library.oregonstate.edu/sa-termsofuse RUSSIAN-AMERICAN LONG-TERM CENSUS OF THE ARCTIC A Synthesis of Year-Round Interdisciplinary Mooring Measurements in the Bering Strait (1990–2014) and the RUSALCA Years (2004–2011) By Rebecca A. Woodgate, Kathleen M. Stafford, and Fredrick G. Prahl Brightness Temperature (°C) 0 5 10 15 20 July 18, 2013, Landsat brightness temperature image of the Bering Strait, with the Russian coast on the left and the Alaskan coast on the right. The northward flow of water forms cold eddies behind the two islands (Big Diomede and Little Diomede) in the center of the strait. Between the islands and the Alaskan coast, a vortex chain of small eddies is cast off Fairway Rock, just south of the strait (Lavrova et al., 2002). Image from http://landsat.usgs.gov, with thanks to R. Lindsay 46 Oceanography | Vol.28, No.3 ABSTRACT. The flow through the Bering Strait, the only Pacific-Arctic oceanic a region that provides ~50% of the US gateway, has dramatic local, regional, and global impacts. Advanced year-round fish catch (Sigler et al., 2010). North of moored technology quantifies challengingly large temporal (subdaily, seasonal, and the Bering Strait, the throughflow dom- interannual) and spatial variability in the ~85 km wide, two-channel strait. The typically inates the properties and residence time northward flow, intensified seasonally in the ~10–20 km wide, warm, fresh, nutrient- of waters in the Chukchi Sea (Woodgate poor Alaskan Coastal Current (ACC) in the east, is otherwise generally homogeneous et al., 2005b), which is in turn one of the in velocity throughout the strait, although with higher salinities and nutrients and lower most productive areas of the world ocean temperatures in the west. Velocity and water properties respond rapidly (including (Grebmeier et al., 2006a). In the Arctic flow reversals) to local wind, likely causing most of the strait’s approximately two-layer proper, waters of the throughflow (often summer structure (by “spilling” the ACC) and winter water-column homogenization. referred to in the Arctic as Pacific waters, We identify island-trapped eddy zones in the central strait; changes in sea-ice properties since the Bering Strait is the sole source of (season mean thicknesses from <1 m to >2 m); and increases in annual mean volume, Pacific water to the Arctic) are an import- heat, and freshwater fluxes from 2001 to present (2013). Tantalizing first results from ant source of nutrients for Arctic ecosys- year-round bio-optics, nitrate, and ocean acidification sensors indicate significant tems (Walsh et al., 1997); act as a trigger seasonal and spatial change, possibly driven by the spring bloom. Moored acoustic for the melt back of Arctic sea ice in sum- recorders show large interannual variability in sub-Arctic whale occurrence, related mer (Woodgate et al., 2010b); and provide perhaps to water property changes. Substantial daily variability demonstrates the about one-third of the freshwater enter- dangers of interpreting section data and the necessity for year-round interdisciplinary ing the Arctic (Aagaard and Carmack, time-series measurements. 1989). The throughflow also provides a conduit for contaminants into the Arctic WELCOME TO THE the rich ecosystem just north of the strait Ocean (Macdonald et al., 2003). PACIFIC GATEWAY TO in the Chukchi Sea. In present times, as Pacific waters are found through- THE ARCTIC OCEAN summer Arctic sea-ice cover is dramat- out roughly half the area of the upper The western Arctic landmass has been ically decreasing (Stroeve et al., 2007, (shallower than ~100 m) Arctic Ocean home to native communities of humans 2014), a new Arctic rush is taking place, (Jones and Anderson, 1986; Steele et al., for 10,000–20,000 years (Hoffecker and with the Bering Strait offering the gate- 2004), where they likely influence west- Elias, 2003). Deglaciation ~15,000– way for trans-Arctic shipping and access ern Arctic sea-ice retreat in two opposing 10,000 years ago led to a rise in sea level to the natural resources being revealed ways (Francis et al., 2005; Shimada et al., and the opening of the oceanic channel by the retreating ice. 2006; Woodgate et al., 2010b)—the sum- we now call the Bering Strait, likely sta- Besides its role as a geographical bar- mer Pacific water provides a subsurface bilizing world climate (Dyke et al., 1996; rier, the narrow (~85 km wide), shal- source of heat to the sea ice in winter, and Hoffecker and Elias, 2003; De Boer and low (~50 m deep) Bering Strait plays a the winter Pacific water below forms a Nof, 2004) and leading eventually to the remarkably large role in local and global protective layer between the sea ice and development of a maritime culture in climate. It is the only conduit for ocean the warmer Atlantic waters deeper in the the region at least 3,500 years ago (for waters between the Pacific and the Arctic Arctic water column (for a brief review of overview, see Fitzhugh, in press). Ever Oceans. Although the flow through the Arctic Ocean circulation, see Woodgate, since the first explorers passed through strait is modest in global terms (~0.8 Sv; 2013). The nutrients brought into the the Bering Strait (Semyon Dezhnyov in Roach et al., 1995; 1 Sv = 1 Sverdrup = Arctic by the Pacific waters fuel Arctic 1648; Cossack Chief Ermak before 1650; 106 m3 s–1) compared to the Gulf Stream ecosystems and biological productivity Vitus Bering in 1728; see, e.g., Black, (between 30–85 Sv; e.g., Pickard and also in the areas where they exit the Arctic 2004), nations have realized the poten- Emery, 1990), the impact of the Bering Ocean (Jones et al., 2003), especially the tial for this narrow channel as a gate- Strait throughflow is substantial—locally, polynya regions of the Canadian Arctic way to Arctic riches. The western Arctic in the Arctic, and globally. By providing Archipelago (e.g., Tremblay et al., 2002). whaling boom (1848–1908) saw a dra- a northward exit, the flow through the Via its contribution to Arctic fresh- matic increase in shipping through the strait has an important draining influ- water outflow, the influence of the strait (one ship in 1848; over 220 ships in ence on the Bering Sea shelf to the south Bering Strait is also felt in the Atlantic 1852; Bockstoce, 1986), eager to exploit (Stabeno et al., 1999; Zhang et al., 2012), Ocean, with implications for global Oceanography | September 2015 47 climate stability. Modeling studies (see, being accessible currently only by aircraft the islands. As discussed below, coastal e.g., Wadley and Bigg, 2002, for a review) or by sea, although increasingly in recent currents are found on both the US and suggest the throughflow can influence the years, plans for a tunnel or a bridge across Russian coasts, and there are indications path of the Gulf Stream and the Atlantic the strait are frequently mooted, despite of trapped circulations around and near Overturning Circulation, and paleo stud- the lack of infrastructure on either side the islands (Woodgate and the RUSALCA ies attribute modern climate stability of the strait. Even access by sea is com- 2011 Science Team, 2011; Raymond- to the balancing influence of the Bering plex, as the nearest deep water port is Yakoubian et al., 2014; author Woodgate Strait throughflow (De Boer and Nof, Dutch Harbor in the Aleutian Chain and colleagues, unpublished data). 2004; Hu et al., 2007). some 1,300 km south of the strait, while The 1867 US-Russian convention line The remarkably broad impacts of the closer port of Nome (220 km south- also runs through the Chukchi Sea and the Bering Strait throughflow drive the east of the Bering Strait) takes only the center of the strait between the two desire to quantify and explain its prop- smaller vessels and is vulnerable to clo- islands at 168°58'37''W (Figure 1), mean- erties, both for local and global envi- sure in bad weather. ing that Exclusive Economic Zone (EEZ) ronmental and climate studies and to In winter (from approximately permission (US or Russian) is required to anticipate the impacts and challenges of November/December to May/June), sea work in all regions of the strait. economic growth in the region. In this ice (and in places landfast ice) may Observations of the flow from explor- article, we address the observational block the strait (Torgerson and Stringer, ers stretch back as far as 1728 (Coachman challenges of the strait and the interdis- 1985; Travers, 2012; author Woodgate and Aagaard, 1966), where most, but not ciplinary progress that has been made and Cynthia Travers, University of all, expeditions reported northward flow. in recent decades, especially since the Washington, unpublished data), hinder- Scientific measurements from the strait, advent of the US-Russian RUSALCA ing shipping but promoting sea-ice-based although sparse in space and time, are (Russian-American Long-term Census hunting and travel between the main- reported as early as 1937 in the Russian of the Arctic) program in 2004. Drawing land and the islands. As discussed below, literature (for discussion, see Shtokman, on mooring, satellite, and hydrographic ice keels may be >20 m (Richard Moritz, 1957). Although we appear to lack access data, we summarize our current best University of Washington, unpublished to the full details of the Russian research understanding of the oceanography of data), endangering upper water column from this era, it is clear that authors such as the strait, starting with the underlying moored instrumentation.