Seasonal variation of the Beaufort shelfbreak jet and its relationship to Arctic cetacean occurrence

Abstract

Using mooring time series from September 2008 to August 2012, together with ancillary atmospheric and satellite data sets, we quantify the seasonal variations of the shelfbreak jet in the Alaskan Beaufort Sea and explore connections to the occurrences of bowhead and beluga whales. Wind patterns during the 4 year study period are different from the long‐term climatological conditions that the springtime peak in easterly winds shifted from May to June and the autumn peak was limited to October instead of extending farther into the fall. These changes were primarily due to the behavior of the two regional atmospheric centers of action, the Aleutian Low and Beaufort High. The volume transport of the shelfbreak jet, which peaks in the summer, was decomposed into a background (weak wind) component and a wind‐driven component. The wind‐driven component is correlated to the Pt. Barrow, AK alongcoast wind speed record although a more accurate prediction is obtained when considering the ice thickness at the mooring site. An upwelling index reveals that wind‐driven upwelling is enhanced in June and October when storms are stronger and longer‐lasting. The seasonal variation of Arctic cetacean occurrence is dominated by the eastward migration in spring, dictated by pack‐ice patterns, and westward migration in fall, coincident with the autumn peak in shelfbreak upwelling intensity.

Short commentary on marine productivity at Arctic shelf breaks: upwelling, advection and vertical mixing

“…This argument was reinforced by a number of studies conducted in the Pacific Arctic (Williams et al, 2006;Schulze and Pickart, 2012;Spall et al, 2014;Arrigo et al, 2014;Lin et al, 2016), which directly extended earlier direct observations of shelf break upwelling dating back to at least the 1980s (e.g. Aagaard et al, 1981).…”

“…5 illustrates how only roughly 2 % of all summer days through the last 30 years can be considered upwellingfavourable using a very generous criterion for what constitutes "upwelling-favourable", and even this is assuming that the local topography would allow for this kind of upwelling. (Again, note the difference to the Beaufort shelf where winds are very upwelling-favourable also in June; see Lin et al, 2016.) There might still be storms that make deeper waters spill onto the shelf by Ekman pumping alone, but these also have a tendency to occur more frequently in the winter season (see also Lind and Ingvaldsen, 2012).…”

Water Mass Evolution and Circulation of the Northeastern Chukchi Sea in Summer: Implications for Nutrient Distributions

“…The data were subsequently quality controlled by removing outliers and interpolating over small gaps (see Pickart et al, , for details). These data have been widely used in studies of the northern Chukchi Sea and western Alaskan Beaufort Sea (e.g., Lin, Pickart, et al, , Lin, Pickart, Moore, et al, ; Li et al, ; Pickart et al, ). (3) Reanalysis wind: In order to calculate wind stress curl over shelf, we used the European Center for Medium‐Range Weather Forecasts (ECMWF) ERA‐Interim reanalysis 10‐m wind data (Berrisford et al, ).…”

The Chukchi slope current

“…Our analysis also includes a fresher water mass that is composed of fluvial, precipitation, and ice melt contributions; this water mass is labelled "meltwater" to be consistent with the literature (e.g. Gong and Pickart, 2016;Lin et al, 2016). We note that these water mass boundaries are not precise and should be considered as guidelines, since the characteristics of the Pacific water change from year to year (e.g.…”