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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 satellite‐derived phytoplankton source function, we construct a time series of carbon supply to the bottom of Barrow Canyon.

 

Environmental conditions in the Chukchi Sea are changing rapidly and may alter the abundance and distribution of marine species and their benthic prey. We used a metabarcoding approach to identify potentially important prey taxa from Pacific walrus (Odobenus rosmarus divergens) fecal samples (n= 87). Bivalvia was the most dominant class of prey (66% of all normalized counts) and occurred in 98% of the samples. Polychaeta and Gastropoda occurred in 70% and 62% of the samples, respectively. The remaining nine invertebrate classes comprised <21% of all normalized counts. The common occurrence of these three prey classes is consistent with examinations of walrus stomach contents. Despite these consistencies, biases in the metabarcoding approach to determine diet from feces have been highlighted in other studies and require further study, in addition to biases that may have arisen from our opportunistic sampling. However, this noninvasive approach provides accurate identification of prey taxa from degraded samples and could yield much‐needed information on shifts in walrus diet in a rapidly changing Arctic.

 

Massive declines in sea ice cover and widespread warming seawaters across the Pacific Arctic region over the past several decades have resulted in profound shifts in marine ecosystems that have cascaded throughout all trophic levels. The Distributed Biological Observatory (DBO) provides sampling infrastructure for a latitudinal gradient of biological “hotspot” regions across the Pacific Arctic region, with eight sites spanning the northern Bering, Chukchi, and Beaufort Seas. The purpose of this study is two-fold: (a) to provide an assessment of satellite-based environmental variables for the eight DBO sites (including sea surface temperature (SST), sea ice concentration, annual sea ice persistence and the timing of sea ice breakup/formation, chlorophyll- a concentrations, primary productivity, and photosynthetically available radiation (PAR)) as well as their trends across the 2003–2020 time period; and (b) to assess the importance of sea ice presence/open water for influencing primary productivity across the region and for the eight DBO sites in particular. While we observe significant trends in SST, sea ice, and chlorophyll- a /primary productivity throughout the year, the most significant and synoptic trends for the DBO sites have been those during late summer and autumn (warming SST during October/November, later shifts in the timing of sea ice formation, and increases in chlorophyll- a /primary productivity during August/September). Those DBO sites where significant increases in annual primary productivity over the 2003–2020 time period have been observed include DBO1 in the Bering Sea (37.7 g C/m 2 /year/decade), DBO3 in the Chukchi Sea (48.0 g C/m 2 /year/decade), and DBO8 in the Beaufort Sea (38.8 g C/m 2 /year/decade). The length of the open water season explains the variance of annual primary productivity most strongly for sites DBO3 (74%), DBO4 in the Chukchi Sea (79%), and DBO6 in the Beaufort Sea (78%), with DBO3 influenced most strongly with each day of additional increased open water (3.8 g C/m 2 /year per day). These synoptic satellite-based observations across the suite of DBO sites will provide the legacy groundwork necessary to track additional and inevitable future physical and biological change across the region in response to ongoing climate warming. 

Abstract I describe my path through a series of opportunities that provided stepping stones from childhood years in the landlocked US Midwest to a 45-year-long career focused on cetacean behaviour and ecology. My early interest in the ocean and dolphins led me to switch from majoring in journalism to biology during my undergraduate years. While pursuing a master’s degree focused on bioacoustics, I was employed as a contract scientist with the US Navy’s marine mammal laboratory. During 20 years there, my work ranged from dolphin calling behaviour to marine mammal distribution in Alaskan waters, culminating in a Ph.D. dissertation on cetacean habitats in the Alaskan Arctic. Subsequently, I enjoyed a 20-year career with the US NOAA National Marine Fisheries Service. There, I developed and advanced the idea that marine mammals can act as sentinels of ocean variability. To interpret the messages that marine mammals convey about the ocean, we must broaden science discourse to include Indigenous Knowledge and lessons from the experiences of people whose livelihoods depend on the sea. My advice to students and young professionals is to follow your passion while seeking the perspectives of colleagues from a variety of disciplines and people from all cultures and backgrounds. Coupled with a healthy dose of luck, this approach worked for me. 

Abstract A 15-year time-series of data on benthic community response to rapid climate change at a biomass ‘hotspot’ in the northern Bering Sea, Alaska, provides an exceptional opportunity to evaluate naturally occurring molluscan dead-shell assemblages as ecological archives. We find that, at five middle-shelf stations censused annually from 2000 to 2014, dead-shell assemblages collected in 2014 are dominated by obligate deposit-feeding Nuculanidae bivalves as opposed to the other families in that guild or the facultative deposit-feeding Tellinidae that dominate the most recent living bivalve assemblages, thus correctly detecting the location and direction of known ecological changes. However, live–dead contrast is significant where the bivalve biomass and abundance has declined over time, and muted where bivalve abundances, and therefore shell input, increased, underscoring the general danger of assuming constant shell input. We also find that proportional abundance-based measures are best suited for detecting benthic response to climate change. Combined with preliminary results from shell age-dating, these results indicate that dead-shell assemblages provide a short-lived but compositionally faithful ecological memory well-suited for detecting recent site- and habitat-level ecological change under cold-water conditions. With marine regime change suspected to now be underway throughout the Arctic, molluscan dead-shell assemblages should become an integral part of efforts to detect transitioning regions. 

A large volume of freshwater is incorporated in the relatively fresh (salinity ~32–33) Pacific Ocean waters that are transported north through the Bering Strait relative to deep Atlantic salinity in the Arctic Ocean (salinity ~34.8). These freshened waters help maintain the halocline that separates cold Arctic surface waters from warmer Arctic Ocean waters at depth. The stable oxygen isotope composition of the Bering Sea contribution to the upper Arctic Ocean halocline was established as early as the late 1980’s as having a δ 18 O V - SMOW value of approximately -1.1‰. More recent data indicates a shift to an isotopic composition that is more depleted in 18 O (mean δ 18 O value ~-1.5‰). This shift is supported by a data synthesis of >1400 water samples (salinity from 32.5 to 33.5) from the northern Bering and Chukchi seas, from the years 1987–2020, which show significant year-to-year, seasonal and regional variability. This change in the oxygen isotope composition of water in the upper halocline is consistent with observations of added freshwater in the Canada Basin, and mooring-based estimates of increased freshwater inflows through Bering Strait. Here, we use this isotopic time-series as an independent means of estimating freshwater flux changes through the Bering Strait. We employed a simple end-member mixing model that requires that the volume of freshwater (including runoff and other meteoric water, but not sea ice melt) flowing through Bering Strait has increased by ~40% over the past two decades to account for a change in the isotopic composition of the 33.1 salinity water from a δ 18 O value of approximately -1.1‰ to a mean of -1.5‰. This freshwater flux change is comparable with independent published measurements made from mooring arrays in the Bering Strait (freshwater fluxes rising from 2000–2500 km 3 in 2001 to 3000–3500 km 3 in 2011). 

Declines in seasonal sea ice in polar regions have stimulated projections of how primary production has shifted in response to greater light penetration over a longer open water season. Despite the limitations of remotely sensed observations in an often cloudy environment, remote sensing data provide strong indications that surface chlorophyll biomass has increased (since 2000) as sea ice has declined in the Pacific Arctic region. We present here shipboard measurements of chlorophyll-a that have been made annually in July since 2000 from the Distributed Biological Observatory (DBO) stations in the Bering Strait region. This time series as well as shipboard observations made in other months since the late 1980s implicate complexities that intrude on a simple expectation that, as open water periods increase, the production and biomass of phytoplankton will increase predictably. These shipboard observations indicate that there have not been sharp increases in chlorophyll-a, for either maxima observed in the water column or integrated over the whole water column, at the DBO stations over a time-series extending for as long as 20 years coinciding with seasonal sea ice declines. On the other hand, biomass may be increasing in other months: we provide a shipboard confirmation of a fall bloom in October as wind mixing introduced nutrients back into the upper water column. The productive DBO stations may be at a high enough production already that additional enhancements in chlorophyll-a biomass should not be expected, but our time-series record does not exclude the possibility that additional enhanced production may be present in other areas outside the DBO station grid. These findings may also reflect limitations imposed by nutrient cycling and water column structure. The increasing freshwater component of waters flowing through the Bering Strait is likely associated with increased stratification that limits the potential change in biological production associated with decreases in seasonal sea ice persistence. 

Decreased sea ice cover in the northern Bering Sea has altered annual phytoplankton phenology owing to an expansion of open water duration and its impact on ocean stratification. Limitations of satellite remote sensing such as the inability to detect bloom activity throughout the water column, under ice, and in cloudy conditions dictate the need for shipboard based measurements to provide more information on bloom dynamics. In this study, we adapted remote sensing land cover classification techniques to provide a new means to determine bloom stage from shipboard samples. Specifically, we used multiyear satellite time series of chlorophyll a to determine whether in-situ blooms were actively growing or mature (i.e., past-peak) at the time of field sampling. Field observations of chlorophyll a and pheophytin (degraded and oxidized chlorophyll products) were used to calculate pheophytin proportions, i.e., (Pheophytin/(Chlorophyll a + Pheophytin)) and empirically determine whether the bloom was growing or mature based on remotely sensed bloom stages. Data collected at 13 north Bering Sea stations each July from 2013–2019 supported a pheophytin proportion of 28% as the best empirical threshold to distinguish a growing vs. mature bloom stage. One outcome was that low vs. high sea ice years resulted in significantly different pheophytin proportions in July; in years with low winter-to-spring ice, more blooms with growing status were observed, compared to later stage, more mature blooms following springs with abundant seasonal sea ice. The detection of growing blooms in July following low ice years suggests that changes in the timing of the spring bloom triggers cascading effects on mid-summer production. 

Changes in gray whale ( Eschrichtius robustus ) phenology and distribution are related to observed and hypothesized prey availability, bottom water temperature, salinity, sea ice persistence, integrated water column and sediment chlorophyll a , and patterns of wind-driven biophysical forcing in the northern Bering and eastern Chukchi seas. This portion of the Pacific Arctic includes four Distributed Biological Observatory (DBO) sampling regions. In the Bering Strait area, passive acoustic data showed marked declines in gray whale calling activity coincident with unprecedented wintertime sea ice loss there in 2017–2019, although some whales were seen there during DBO cruises in those years. In the northern Bering Sea, sightings during DBO cruises show changes in gray whale distribution coincident with a shrinking field of infaunal amphipods, with a significant decrease in prey abundance (r = -0.314, p<0.05) observed in the DBO 2 region over the 2010–2019 period. In the eastern Chukchi Sea, sightings during broad scale aerial surveys show that gray whale distribution is associated with localized areas of high infaunal crustacean abundance. Although infaunal crustacean prey abundance was unchanged in DBO regions 3, 4 and 5, a mid-decade shift in gray whale distribution corresponded to both: (i) a localized increase in infaunal prey abundance in DBO regions 4 and 5, and (ii) a correlation of whale relative abundance with wind patterns that can influence epi-benthic and pelagic prey availability. Specifically, in the northeastern Chukchi Sea, increased sighting rates (whales/km) associated with an ~110 km (60 nm) offshore shift in distribution was positively correlated with large scale and local wind patterns conducive to increased availability of krill. In the southern Chukchi Sea, gray whale distribution clustered in all years near an amphipod-krill ‘hotspot’ associated with a 50-60m deep trough. We discuss potential impacts of observed and inferred prey shifts on gray whale nutrition in the context of an ongoing unusual gray whale mortality event. To conclude, we use the conceptual Arctic Marine Pulses (AMP) model to frame hypotheses that may guide future research on whales in the Pacific Arctic marine ecosystem.