This award supports the continuation of the aerial hydrographic surveys component of the North Pole Environmental Observatory (NPEO) as part of the Arctic Observing Network (AON) and the Study of Environmental Arctic Change (SEARCH). During the annual aerial hydrographic surveys a number of tasks will be completed: (1) conductivity/salinity, temperature, dissolved oxygen and nutrient profiles will be measured in the water column; (2) water samples will be retrieved and returned to the laboratory for analysis of a variety of tracers [salinity, Ba, alkalinity, dissolved oxygen, nutrients, delta O-18]; and (3) a variety of ice-based drifting instruments will be deployed for other AON projects, including ice mass balance buoys, ice-tethered profilers and atmospheric pressure buoys. The "Intellectual Merit" of NPEO rests on its foundation of successfully tracking change in the air-ice-ocean system since 2000, and obtaining data that will help to answer the question "have a combination of long-term trends and decadal variability driven the Arctic Ocean to the brink of a new seasonal ice regime?" The "Broader Impacts" of NPEO center on enabling the scientific efforts of other investigators, and educating the public about environmental change in the Arctic. NPEO improves the scientific infrastructure by providing scientific data, developing new observational methods, and providing operational field support to other Arctic researchers. NPEO continues to take advantage of the cachet that the North Pole provides for generating many avenues for informal education and outreach. NPEO maintains a Web site, participates in various talks and demonstrations at the annual Polar Science Weekend at Seattle's Pacific Science Center, and will sponsor a booth at the SACNAS (Society for Advancement of Chicanos/Latinos and Native Americans in Science) conference aimed at broadening participation of under-represented groups in careers in environmental science.
In September, 2012, sea ice in the Arctic reached a record minimum extent: 3.4 million km2, nearly 0.8 million km2 less than the previous record set in 2007. While the rapid decrease in minimum sea-ice extent, measured accurately by satellite since 1979, is an obvious manifestation of Arctic change, less well known but perhaps at least as significant, are changes in the Arctic Ocean thermohaline structure. Starting in 2003 a new technology, the ice-tethered profiler (ITP-- www.whoi.edu/itp/) has provided year-round data on upper ocean (~700 m) temperature and salinity structure at numerous locations scattered about the Arctic, with relatively dense sampling in the Canada Basin. A late winter aerial survey performed in March-April, 2008, as part of the International Polar Year established that relative to the late 20th century, liquid fresh water had increased dramatically in the Canada Basin, substantially altering the surface circulation patterns of the Beaufort Gyre, a large counterclockwise rotating feature occupying much of the area north of the Beaufort and Chukchi Seas. The addition of substantial fresh water from both ice melt and continental runoff in the Beaufort Gyre has raised sea level near its center, increasing the sea-surface slope and the associated surface geostrophic currents. Work performed with partial support from this grant (0856214) analyzed time series of dynamic surface height in the Canada Basin, finding that in the years since the IPY survey (i.e., from 2008 through 2011), fresh water has continued to accumulate in the Beaufort Gyre, and that on its periphery, particularly north of the Beaufort and Chukchi shelf breaks, geostrophic currents are now 5-6 times as intense as indicated by a dynamic topography inferred from climatological data accumulated during the last century (McPhee, 2013, in press, J. Climate and references therein, see www.mcpheeresearch.com/publications.html). The increased currents have changed ice drift patterns in a way that prevents old ice advecting from the north on the eastern side of the Gyre from collecting near its center, as it has in the past. Now the ice appears instead to get caught up in the rapid peripheral currents north of the Beaufort Shelf and swept into the western part of the Basin. Here, the combination of northward currents and anticyclonic summer winds clears the ice much earlier than in the past, and insolation heats the upper ocean to temperatures well above freezing. In the past few years, very little of the old ice entering this region survives the summer, and indeed, most old ice (more than 1 or 2 years old) is now gone from the Canada Basin. An analysis of late summer NCEP-CFSR winds in the Canada Basin from 1981 to 2011 shows that over that time there has been a significant increasing trend in (negative) wind-stress curl, indicating volume convergence of near surface water (typically quite fresh) toward the center of the Beaufort Gyre. Locally, this leads to downwelling at the base of the surface mixed layer, and increased sea-surface elevation. A plausible mechanism driving this convergence is enhanced late summer anticyclonic atmospheric pressure associated with the increased surface temperature gradients. If this hypothesis holds, there may be a positive feedback associated with the Beaufort Gyre currents, as ice produced during winter is advected southward in the eastern Basin, keeping it mainly ice covered during summer, while northward advection in the west opens the upper ocean to rapid heating near summer solstice. This may account for the continuing sequestration of fresh water in the Beaufort Gyre and its associated intensification of surface geostrophic currents.
