Physical Controls on the Macrofaunal Benthic Biomass in Barrow Canyon, Chukchi Sea

Abstract

The Chukchi Sea is one of the most productive regions of the Arctic Ocean (Springer & McRoy, 1993), in part because of the high levels of nutrients advected through the Bering Strait (Grebmeier, Bluhm, et al., 2015). Furthermore, due to the recent decline in sea ice cover and higher percentage of thin first-year ice, light levels have increased which has led to even larger levels of annual production (Arrigo & van Dijken, 2011). Since the Chukchi shelf is an export-dominated regime, the large amount of carbon that reaches the seafloor supports robust levels of benthic activity (Grebmeier, Bluhm, et al., 2015). This in turn influences benthic-feeding higher trophic species such as walrus, whales, and sea birds (Grebmeier, Cooper, et al., 2006).The levels of benthic macrofaunal biomass vary regionally across the Chukchi shelf, with several well-defined "hot spots" (Figure 1). The broad area of enhanced biomass northwest of Bering Strait is associated with particularly high levels of nitrate that are advected into the region with the Anadyr water (Fang Abstract A region of exceptionally high macrofaunal benthic biomass exists in Barrow Canyon, implying a carbon export process that is locally concentrated. Here we offer an explanation for this benthic "hotspot" using shipboard data together with a set of dynamical equations. Repeat occupations of the Distributed Biological Observatory transect in Barrow Canyon reveal that when the northward flow is strong and the density front in the canyon is sharp, plumes of fluorescence and oxygen extend from the pycnocline to the seafloor in the vicinity of the hotspot. By solving the quasi-geostrophic omega equation with an analytical flow field fashioned after the observations, we diagnose the vertical velocity in the canyon. This reveals that, as the along stream flow converges into the canyon, it drives a secondary circulation cell with strong downwelling on the cyclonic side of the northward flow. The downwelling quickly advects material from the pycnocline to the seafloor in a vertical plume analogous to those seen in the observations. The plume occurs only when the phytoplankton reside in the pycnocline, since the near-surface vertical velocity is weak, also consistent with the observations. Using a wind-based proxy to represent the strength of the northward flow and hence the pumping, in conjunction with a satellitederived phytoplankton source function, we construct a time series of carbon supply to the bottom of Barrow Canyon.

Changes in gray whale phenology and distribution related to prey variability and ocean biophysics in the northern Bering and eastern Chukchi seas

“…have extended their distribution northward with warming seawater [53]. Of note, DBO5 stations in Barrow Canyon do not show increased bottom water temperatures, likely due to its dynamic nature and the seasonally variable water masses reported there [54]. Finally, increasing bottom water salinity since 2019 in DBO2 is perhaps indicative of a stronger Anadyr water signal at depth that may also influence nutrient availability to surface waters by mixing upward of AW after storm events.…”

Upwelling of Atlantic Water in Barrow Canyon, Chukchi Sea

“…The 10-m wind data were obtained from the meteorological station at Utqiaġvik, Alaska (magenta star in Figure 1b). The data well represent the regional wind condition in the vicinity of Barrow Canyon (Pickart et al, 2019(Pickart et al, , 2021. The data have been quality controlled and interpolated onto an hourly interval (see Pickart, Schulze, et al, 2013 for the details).…”

“…Pickart et al. (2021) revealed that the flow accelerates as converging into the canyon, resulting in a strong downwelling on this cyclonic side (northwestern side) of the flow. The downwelling feeds the biological processes to the seabed and thus contributes a benthic “hotspot” in the Barrow Canyon.…”

A comprehensive satellite-based assessment across the Pacific Arctic Distributed Biological Observatory shows widespread late-season sea surface warming and sea ice declines with significant influences on primary productivity

“…These observations are particularly important given the extensive environmental changes observed throughout the region over the past few decades. Numerous recent studies have illustrated the importance of climate warming for ecosystem dynamics throughout the DBO sites [38][39][40][41][42][43]. While there have been recent satellite- Basemap datasets from Natural Earth [49] and ESRI [50].…”