Theme: natural conditions and natural resources of the united

THEME: NATURAL CONDITIONS AND NATURAL RESOURCES OF THE UNITED
STATES

Plan

1. 
   Environmental Conditions and Natural Resources in the U.S. Arctic
   
2. 
   Environment & Natural Resources
   
3. 
   Average temperature difference (°F) from 20th-century average in the contiguous US
   
4. 
   

2 Environmental Conditions and Natural Resources in the U.S. Arctic
The components of the Arctic system interact with each other in a complex, evolving pattern. This chapter provides an overview of the physical and biological ocean processes and environments of the Bering Strait and the Chukchi and Beaufort Seas. This is important for understanding current conditions, but also for understanding trends, changes, and future data needs. This knowledge is essential to support safe operations in the Arctic marine environment; to guide oil spill prevention, response, and restoration; and to prioritize sampling and monitoring needs.
The chapter begins with a discussion of the physical environment: ocean, marine weather, sea ice, and coastal characteristics and processes—conditions that would be encountered in the event of an oil spill in Arctic waters. A discussion of Arctic ecosystems follows, with an emphasis on biological information that would be important for oil spill response, including monitoring approaches and data needs for incorporation into spill trajectory models or ecosystem models. A final section discusses current research and monitoring as well as additional needs to advance understanding of the Arctic system.
OCEAN PROCESSES AND CHARACTERISTICS
Three principal branches of Pacific origin water (Alaska Coastal Water, Bering Shelf Water, and Anadyr Water; Figure 2.1) enter the Bering Strait and circulate through the Chukchi and Beaufort Seas. The northward transport of water through the Bering Strait is principally driven by large-scale sea level differences between the Pacific and Arctic Oceans, and opposes the prevailing winds; variability in the currents is predominantly wind driven (Weingartner et al., 2005). The summer retreat of ice in this sector of the Arctic has been linked in part to warm Bering Strait inflows and flow pathways (Woodgate et al., 2010).
Water properties in the Chukchi Sea are set by processes of sea ice melt and growth, winds, and inflows of river water and Pacific Ocean via the Bering Strait, as well as from the East Siberian Sea. Transport of water from the Chukchi and shelf regions to the deep Canada Basin takes place mainly through the Barrow and Herald canyons (Weingartner et al., 2005). Currents that flow eastward along the Beaufort Sea continental slope generate eddies that can propagate into the basin interior,
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Suggested Citation:"2 Environmental Conditions and Natural Resources in the U.S. Arctic." Transportation Research Board and National Research Council. 2014. Responding to Oil Spills in the U.S. Arctic Marine Environment. Washington, DC: The National Academies Press. doi: 10.17226/18625.×
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Figure 2.1 Water masses and sea ice extent in Bering Strait and Chukchi and Beaufort Seas. SOURCE: Grebmeier (2012).

and surface wind forcing can also drive water offshore (e.g., Pickart et al., 2005). Transport pathways, seasonal evolution, and mixing of the water masses are outlined in Weingartner et al. (2013b) and references therein.
Weingartner et al. (2005) found that mean flows over the Chukchi shelf are generally less than 10 km/day except in Barrow Canyon, where maximum current speeds can briefly reach 85 km/day. Elsewhere in the Chukchi Sea, maximum currents are between approximately 25 and 40 km/day. The mean flow is north-northeastward over the central Chukchi shelf, opposite to the mean winds. Weingartner et al. (2013a) examined in detail winds and water properties over the central portion of the northeastern Chukchi Sea shelf (40-45 m depth) in summer and fall 2008-2010. They showed that temperature and salinity properties can vary significantly over only a few tens of to a hundred kilometers. Along the shoreline of the Beaufort Sea in open water or loose ice conditions (July to mid-October), surface currents are predominantly wind driven (speeds typically exceed 8 km/day and maximum currents can reach almost 80 km/day, while in winter under fast ice, currents are weak—less than ~2.5 km/day—and forced predominantly by tides) (Okkonen and Weingartner, 2003). Of utmost importance to oil spill response is the rapid variability of the wind-forced surface ocean circulation. High-frequency radar systems in the Chukchi Sea, which map surface ocean cur-
Page 27
Suggested Citation:"2 Environmental Conditions and Natural Resources in the U.S. Arctic." Transportation Research Board and National Research Council. 2014. Responding to Oil Spills in the U.S. Arctic Marine Environment. Washington, DC: The National Academies Press. doi: 10.17226/18625.×
Save
Cancel
rents, indicate complex flow patterns that can reverse direction in a matter of hours and can vary significantly in both magnitude (0-85 km/day) and direction over spatial scales of less than 10 km.
The Arctic Ocean is strongly stratified, with a fresh, low-density mixed layer up to 40 m deep in the Beaufort Sea. In the summer, very fresh, warm mixed layers only a few meters deep are observed in parts of the Chukchi and Beaufort Seas (e.g., Toole et al., 2010; Weingartner et al., 2013b). This stratification has important implications for the pathways and fate of spilled oil. In the Deepwater Horizon spill, oil plumes rising through the stratified ocean water column spread out at some level of neutral buoyancy and became trapped at depth (Socolofsky et al., 2011). The impact of the strong Arctic Ocean stratification on the subsurface evolution of spilled oil, particularly when surfactants are used (e.g., Adalsteinsson et al., 2013), is an important response planning consideration, as oil that is trapped at depth will not be transported by surface circulation. For this reason, there is a need for characterization and monitoring of Beaufort and Chukchi subsurface circulation, which can be as complex as the surface flow and can be in opposing directions (e.g., Weingartner et al., 1998; Proshutinsky et al., 2009; Morison et al., 2012).
Contaminants residing either in the surface or in the subsurface ocean are subject to redistribution by coastal ocean upwelling and downwelling events; such events have been well studied in the Beaufort Sea (see Williams et al., 2006; Schulze and Pickart, 2012; Pickart et al., 2013). Strong easterly winds have been observed to bring warm, salty deep water to shallow depths along the Beaufort Sea continental slope, with increased frequency of upwelling events in the absence of concentrated pack ice (Pickart et al., 2009). Similarly, downwelling events forced by westerly winds cause the descent of near-surface waters along the coast (Dunton et al., 2006).