Functional Pattern of Benthic Epifauna in the Chukchi Borderland, Arctic Deep Sea

Assessment of Arctic deep-sea ecosystem functioning is currently an urgent task considering that ongoing sea-ice reduction opens opportunities for resource exploitation of yet understudied deep-sea regions. We used Biological Trait Analysis to evaluate ecosystem functioning and test if common paradigms for deep-sea fauna apply to benthic epifauna of the deep-sea Arctic Chukchi Borderland (CBL). We also investigated the influence of environmental factors on the functional structure of the epifauna. The analysis was performed for 106 taxa collected with a beam trawl and a Remotely Operated Vehicle from 486 to 2610 m depth. The most common trait modalities were small-medium size, mobile, benthic direct and lecithotrophic larval development, and predatory feeding, which mostly supports the current view of epifauna in the global deep sea. Functional composition of epifauna differed between two depth strata (486–1059 m and 1882–2610 m), with depth and sediment carbon content explaining most of the functional variability. Proportional abundances of the modalities free-living, swimming, suspension feeders, opportunists/scavengers, internal fertilization and globulose were higher at deep stations. Functional redundancy (FR) was also higher there compared to the mid-depth stations, suggesting adaptation of fauna to the more homogeneous deep environment by fewer and shared traits. Mid-depth stations represented higher functional variability in terms of both trait modality composition and functional diversity, indicating more variable resource use in the more heterogeneous habitat. Food input correlated positively with the proportional abundance of the modalities tube-dwelling, sessile and deposit feeding. Areas with drop stones were associated with higher proportional abundance of the modalities attached, upright, and predators. Comparatively low FR may render the heterogeneous mid-depth area of the CBL vulnerable to disturbance through the risk of loss of functions. Across the study area, high occurrence of taxa with low dispersal ability among adult and larval life stages may prevent rapid adaptation to changes, reduce ability to recolonize and escape perturbation.

Whither the Chukchi Slope Current?

Recent measurements and modeling indicate that roughly half of the Pacific-origin water exiting the Chukchi Sea shelf through Barrow Canyon forms a westward-flowing current known as the Chukchi Slope Current (CSC), yet the trajectory and fate of this current is presently unknown. In this study, through the combined use of shipboard velocity data and information from five profiling floats deployed as quasi-Lagrangian particles, we delve further into the trajectory and the fate of the CSC. During the period of observation, from early September to early October 2018, the CSC progressed far to the north into the Chukchi Borderland. The northward excursion is believed to result from the current negotiating Hanna Canyon on the Chukchi slope, consistent with potential vorticity dynamics. The volume transport of the CSC, calculated using a set of shipboard transects, decreased from approximately 2 Sv (1 Sv ≡ 106 m3 s−1) to near zero over a period of 4 days. This variation can be explained by a concomitant change in the wind stress curl over the Chukchi shelf from positive to negative. After turning northward, the CSC was disrupted and four of the five floats veered offshore, with one of the floats permanently leaving the current. It is hypothesized that the observed disruption was due to an anticyclonic eddy interacting with the CSC, which has been observed previously. These results demonstrate that, at times, the CSC can get entrained into the Beaufort Gyre.

Latitudinal Distributions and Controls of Bacterial Community Composition during the Summer of 2017 in Western Arctic Surface Waters (from the Bering Strait to the Chukchi Borderland)

The western Arctic Ocean is experiencing some of the most rapid environmental changes in the Arctic. However, little is known about the microbial community response to these changes. Employing observations from the summer of 2017, this study investigated latitudinal variations in bacterial community composition in surface waters between the Bering Strait and Chukchi Borderland and the factors driving the changes. Results indicate three distinctive communities. Southern Chukchi bacterial communities are associated with nutrient rich conditions, including genera such as Sulfitobacter, whereas the northern Chukchi bacterial community is dominated by SAR clades, Flavobacterium, Paraglaciecola, and Polaribacter genera associated with low nutrients and sea ice conditions. The frontal region, located on the boundary between the southern and northern Chukchi, is a transition zone with intermediate physical and biogeochemical properties; however, bacterial communities differed markedly from those found to the north and south. In the transition zone, Sphingomonas, with as yet undetermined ecological characteristics, are relatively abundant. Latitudinal distributions in bacterial community composition are mainly attributed to physical and biogeochemical characteristics, suggesting that these communities are susceptible to Arctic environmental changes. These findings provide a foundation to improve understanding of bacterial community variations in response to a rapidly changing Arctic Ocean.