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Autonomous underwater vehicles (AUVs) or gliders are increasingly being used with acoustic telemetry to elucidate fish movements while collecting simultaneous environmental data. We assessed the utility of an AUV equipped with an integrated acoustic receiver to detect Pacific herring (Clupea pallasii) in Prince William Sound, AK, USA. A range test evaluated the effect of glider flight characteristics and environmental conditions on the detection efficiency of transmitters at varying depths. While distance from transmitters was the strongest predictor of detections, glider depth had a variable effect on detection efficiency which depended on transmitter depth and dive orientation. The detection efficiency of the glider-mounted acoustic receiver was less affected by wind speed and water level than that of stationary acoustic receivers deployed within the study area. The AUV also performed repeated, adaptive transects in an area of ∼630 km2 area and detected 30 Pacific herring transmitters without a priori knowledge of their locations. Of these herring transmitters, 14 were presumed shed after repeated detections within the same area, and 2 were detected at multiple locations. This study is the first to demonstrate that glider-mounted acoustic receivers have high detection efficiency for transmitters at varying depths and can detect movements of migratory forage fish in large search areas.

Palmer Deep Canyon is one of the biological hotspots associated with deep bathymetric features along the Western Antarctic Peninsula. The upwelling of nutrient-rich Upper Circumpolar Deep Water to ...

We analyzed velocity and hydrographic data from 23 moorings in the northeast Chukchi Sea from 2011 to 2014. In most years the eastern side of Hanna Shoal was strongly stratified year-round, while weakly stratified regions prevailed on the shelf south and west of the Shoal. Stratification differences cause differential vertical mixing rates, which in conjunction with advection of different bottom water properties resulted in seasonally-varying along-isobath density gradients. In agreement with numerical models, we find that bottom waters flow anticyclonically around the Shoal. Whereas most of the shelf responded barotropically to wind-forcing, there was a strong baroclinic component to the flow field northeast of Hanna Shoal, resulting in no net vertically-integrated transport on average. In contrast there is a net eastward transport from west of the Shoal, which implies convergence north of the Shoal. Convergence and along-isobath density gradients may foster cross-shelf exchange north of Hanna Shoal. Modal analyses indicate that the shelf south of the Shoal and Barrow Canyon responded coherently to local and remote winds, whereas the wind-current response around Hanna Shoal was less coherent. Barotropic topographic waves, of ~3-day period, were generated episodically northeast of the Shoal and propagate clockwise around Hanna Shoal, but are blocked from entering Barrow Canyon and are possibly scattered by the horizontally sheared flow and converging isobaths on the western side of the Shoal. Analysis of water properties on the western side of Hanna Shoal suggests that these include contributions from the western and southern portions of the Chukchi Sea.

We measured northeastern Chukchi Sea surface currents using high-frequency radar systems (HFR) during the ice-free periods of August to October from 2010–2014. We analyzed these data, along with regional winds, using Self-Organizing Maps (SOM) to develop a set of surface current-wind patterns. Temporal changes in the SOM patterns consist predominantly of two patterns comprising northeastward and southwestward surface currents. A third pattern represents a transitional stage established during the onset of strong northeasterly winds. These patterns are analogous to the first two eigenmodes of an empirical orthogonal function analysis of the HFR data. The first principal component (PC1) is significantly correlated (∼0.8) to that of the winds and is directly related to the time series of SOM-derived patterns. The sign of PC1 changes when the speed of local northeasterly winds exceeds ∼6 m s−1, at which point the northeastward surface currents reverse to the southwest. This finding agrees with previous models and observations that suggest this wind threshold is needed to overcome the pressure gradient between the Pacific and Arctic Oceans. The transitional stage is characterized by alongshore currents bifurcating in the vicinity of Icy Cape and wind-driven Ekman currents north of 71.5°N. Its development is a manifestation of interactions amongst the poleward pressure gradient, wind stress, and geostrophic flow due to the coastal setdown.

We used shipboard and towed CTD, current meter, and satellite-tracked drifter data to examine the hydrographic structure in the northeastern Chukchi Sea in August–September of 2011, 2012, and 2013. In all years the densest winter water was around and east of Hanna Shoal. In 2012 and 2013, a ~ 15 m deep layer of cold, dilute meltwater overlaid the dense water north of the shelf region between ~ 71.2 and ~ 71.5°N. A front extends from the southwest side of Hanna Shoal toward the head of Barrow Canyon, separated meltwaters from warmer, saltier Bering Sea Summer Waters to the south. Stratification was stronger and the surface density variances in the meso- and sub-mesoscale range were higher north of the front than to the south. No meltwater or surface fronts were present in 2011 due to a very early ice retreat. Differences in summer ice cover may be due to differences in the amount of grounded ice atop Hanna Shoal associated with the previous winter’s regional ice drift. Along the north side of Hanna Shoal the model-predicted clockwise barotropic flow carrying waters from the western side of the Shoal appears to converge with a counterclockwise, baroclinic flow on the northeast side. The baroclinic tendency is confined to the upper 30 m and can include waters transported from the shelfbreak. The inferred zonal convergence implies that north of the Shoal: a) near-surface waters are a mixture of waters from the western and eastern Chukchi Sea and b) the cross-isobath pressure gradient collapses thereby facilitating leakage of upper layer waters northward across the shelf.

Antarctic krill, Euphausia superba , is a highly abundant and ecologically important zooplankton species in the Southern Ocean. Regions of elevated Antarctic krill biomass exist around Antarctica, often as a result of the concentrating effect of bathymetry and ocean currents. Such areas are considered biological hotspots and are key foraging grounds for numerous top predators in the region. A hotspot of Antarctic krill biomass exists off the southern extent of Anvers Island, Western Antarctic Peninsula, and supports a population of Adelie penguins that feed almost exclusively on it, as well as numerous other top predators. We investigated the spatio-temporal variability in Antarctic krill biomass and aggregation structure over four consecutive summer seasons, identifying environmental factors that were responsible. We identified three distinct krill aggregation types (Large-dense, Small-close and Small-sparse), and found that the relative proportion of each type to total aggregation numbers varied significantly between survey days. Large-dense aggregations occurred more frequently when westerly winds predominated and when the local mixed tide was in the diurnal regime. Small-close aggregations were also more frequent during diurnal tides and were negatively correlated with phytoplankton biomass. Small-sparse aggregations, on the other hand, were more prevalent when the mixed tide was in the semi-diurnal phase. We suggest that, under certain conditions (i.e. diurnal tides and westerly winds), the biological hotspot in the nearshore waters off Palmer Station, Anvers Island, functions as a zone of accumulation, concentrating krill biomass. Our findings provide important information on the dynamics of Antarctic krill at the local scale.

The physical mechanisms that maintain and deliver phytoplankton and Antarctic krill biomass, potentially increasing prey availability to predators, are not well known. The short surface ocean residence times of 1-2 days over Palmer Deep is in conflict with the prevailing hypotheses that local growth support phytoplankton at the base of the food web in these biological hotspots. Instead, the implication is that horizontal dynamics are likely more important to maintaining these biological hotspots than local upwelling. However, coincident measures of phytoplankton, prey fields, and predator locations in their advective context have not been made to establish the ecological importance of horizontal flow. To better understand these important mechanisms, we are deploying a purpose built integrated polar observatory consisting of high frequency radar, coordinated gliders, small boat surveys, and moorings. This integrated polar observatory will enable us to simultaneously sample across the entire food web from the phytoplankton and prey fields to the top predators to understand the ocean features that support life in these polar systems. For the first time in this region, we will: 1) integrate sensors and technologies to simultaneously map phytoplankton blooms, krill aggregations, and top predator foraging relative to dynamic ocean features; 2) integrate these observations with a high-resolution (1.5 km) 3-D dynamic model simulation of the entire WAP coastal ocean to generalize our field measurements to other known hotspots along the WAP through simulation, and to determine which physical mechanisms lead to the maintenance of these hotspots.

Along the Western Antarctic Peninsula, ecological hotspots are spatially coherent with submarine canyons and have persisted for millennia. Palmer Deep Canyon, a representative hotspot, is known to have higher phytoplankton biomass than the surrounding non-canyon regions. The physical mechanisms that maintain and deliver phytoplankton and Antarctic krill biomass, potentially increasing prey availability to predators, are not well known. To better understand these important mechanisms, we deployed a purpose built integrated polar observatory consisting of high frequency radar, coordinated gliders, and moorings. The gliders identified a depth dependent influence of the underlying canyon bathymetry on physical and biological variability. A series of simulated particle release experiments in the HF radar current maps were used to estimate surface residence time and connectivity across the canyon. With an average residence time of 2 days, our analysis indicates that the elevated phytoplankton biomass over the central canyon is transported into and out of the hotspot on time scales much shorter than the observed phytoplankton growth rate, suggesting that the canyon may not act as an incubator of phytoplankton productivity as previously suggested. It may instead serve more as a conveyor belt of phytoplankton biomass produced elsewhere, continually replenishing the phytoplankton biomass for the local krill community, which in turn supports numerous top predators.

Discovering the predictors of foraging locations can be challenging, and is often the critical missing piece for interpreting the ecological significance of observed movement patterns of predators. This is especially true in dynamic coastal marine systems, where planktonic food resources are diffuse and must be either physically or biologically concentrated to support upper trophic levels. In the Western Antarctic Peninsula, recent climate change has created new foraging sympatry between Adélie (Pygoscelis adeliae) and gentoo (P. papua) penguins in a known biological hotspot near Palmer Deep canyon. We used this recent sympatry as an opportunity to investigate how dynamic local oceanographic features affect aspects of the foraging ecology of these two species. Simulated particle trajectories from measured surface currents were used to investigate the co-occurrence of convergent ocean features and penguin foraging locations. Adélie penguin diving activity was restricted to the upper mixed layer, while gentoo penguins often foraged much deeper than the mixed layer, suggesting that Adélie penguins may be more responsive to dynamic surface convergent features compared to gentoo penguins. We found that, despite large differences in diving and foraging behavior, both shallow-diving Adélie and deeper-diving gentoo penguins strongly selected for surface convergent features. Furthermore, there was no difference in selectivity for shallow- versus deep-diving gentoo penguins. Our results suggest that these two mesopredators are selecting surface convergent features, however, how these surface signals are related to subsurface prey fields is unknown.

Although Arctic marine ecosystems are changing rapidly, year-round monitoring is currently very limited and presents multiple challenges unique to this region. The Chukchi Ecosystem Observatory (CEO) described here uses new sensor technologies to meet needs for continuous, high-resolution, and year-round observations across all levels of the ecosystem in the biologically productive and seasonally ice-covered Chukchi Sea off the northwest coast of Alaska. This mooring array records a broad suite of variables that facilitate observations, yielding better understanding of physical, chemical, and biological couplings, phenologies, and the overall state of this Arctic shelf marine ecosystem. While cold temperatures and 8 months of sea ice cover present challenging conditions for the operation of the CEO, this extreme environment also serves as a rigorous test bed for innovative ecosystem monitoring strategies. Here, we present data from the 2015–2016 CEO deployments that provide new perspectives on the seasonal evolution of sea ice, water column structure, and physical properties, annual cycles in nitrate, dissolved oxygen, phytoplankton blooms, and export, zooplankton abundance and vertical migration, the occurrence of Arctic cod, and vocalizations of marine mammals such as bearded seals. These integrated ecosystem observations are being combined with ship-based observations and modeling to produce a time series that documents biological community responses to changing seasonal sea ice and water temperatures while establishing a scientific basis for ecosystem management.

Although Arctic marine ecosystems are changing rapidly, year-round monitoring is currently very limited and presents multiple challenges unique to this region. The Chukchi Ecosystem Observatory (CEO) described here uses new sensor technologies to meet needs for continuous, high resolution, and year-round observations across all levels of the ecosystem in the biologically productive and seasonally ice-covered Chukchi Sea off the northwest coast of Alaska. This mooring array records a broad suite of parameters that facilitate observations, yielding better understanding of physical, chemical and biological couplings, phenologies, and the overall state of this Arctic shelf marine ecosystem. While cold temperatures and eight months of sea ice cover present challenging conditions for the operation of the CEO, this extreme environment also serves as a rigorous test bed for innovative ecosystem monitoring strategies. Here, we present data from the 2015–16 CEO deployments that provide new perspectives on the seasonal evolution of sea ice, water column structure and physical properties, annual cycles in nitrate, dissolved oxygen, phytoplankton blooms and export, zooplankton abundance and vertical migration, the occurrence of Arctic cod, and vocalizations of marine mammals such as bearded seals. These integrated ecosystem observations are being combined with ship-based observations and modeling to produce a time-series that documents biological community responses to changing seasonal sea ice and water temperatures while establishing a scientific basis for ecosystem management.

Palmer Deep canyon along the central West Antarctic Peninsula is known to have higher phytoplankton biomass than the surrounding non-canyon regions, but the circulation mechanisms that transport and locally concentrate phytoplankton and Antarctic krill, potentially increasing prey availability to upper-trophic-level predators such as penguins and cetaceans, are currently unknown. We deployed a three-site high-frequency radar network that provided hourly surface circulation maps over the Palmer Deep hotspot. A series of particle release experiments were used to estimate surface residence time and connectivity across the canyon. The majority of residence times fell between 1.0 and 3.5 days, with a mean of 2 days and a maximum of 5 days. We found a highly significant negative relationship between wind speed and residence time. Our residence time analysis indicates that the elevated phytoplankton biomass over the central canyon is transported into and out of the hotspot on time scales much shorter than the observed phytoplankton growth rate, suggesting that the canyon may not act as an incubator of phytoplankton productivity as previously suggested. It may instead serve more as a conveyor belt of phytoplankton biomass produced elsewhere, continually replenishing the phytoplankton biomass for the local Antarctic krill community, which in turn supports numerous top predators. This article is part of the theme issue ‘The marine system of the West Antarctic Peninsula: status and strategy for progress in a region of rapid change’.

Increased maritime activities and rapid environmental change pose significant hazards, both natural and technological, to Arctic maritime operators and coastal communities. Currently, U.S. and foreign research activities account for more than half of the sustained hazard-relevant observations in the U.S. maritime Arctic, but hazard assessment and emergency response are hampered by a lack of dedicated hazard monitoring installations in the Arctic. In the present study, we consider a number of different sustained environmental observations associated with research into atmosphere-ice-ocean processes, and discuss how they can help support the toolkit of emergency responders. Building on a case study at Utqiaġvik (Barrow), Alaska, we investigate potential hazards in the seasonally ice-covered coastal zone. Guided by recent incidents requiring emergency response, we analyze data from coastal radar and other observing assets, such as an ice mass balance site and oceanographic moorings, in order to outline a framework for coastal maritime hazard assessments that builds on diverse observing systems infrastructure. This approach links Arctic system science research to operational information needs in the context of the development of a Common Operational Picture (COP) for Maritime Domain Awareness (MDA) relevant for Arctic coastal and offshore regions. A COP in these regions needs to consider threats not typically part of the classic MDA framework, including sea ice or slow-onset hazards. An environmental security and MDA testbed is proposed for northern Alaska, building on research and community assets to help guide a hybrid research-operational framework that supports effective emergency response in Arctic regions.

Summer and fall hydrographic sections in the northeastern Chukchi Sea frequently capture 5–20 m thick intrapycnocline lenses or horizontal plumes of warm, moderately salty summer Bering Sea Water flowing northward from Bering Strait. These features occur within the shallow (~20 m depth) pycnocline separating cold, dilute, surface meltwater from near-freezing, salty, winter-formed waters beneath the pycnocline. An idealized numerical model suggests that the features arise from eddies and meanders generated by instability of the surface front separating meltwater from Bering Sea Water. Warm Bering Sea Water is transported across the front and into the pycnocline by the cross-frontal velocities associated with the instabilities. The accompanying lateral eddy heat fluxes may be important both in summer for promoting ice melt and in fall by delaying the onset of ice formation over portions of this shelf. Lateral heat flux magnitudes depend upon the stratification of the Bering Sea Water.

This study investigates the applicability of the optimal interpolation (OI) method proposed by Kim et al. for estimating ocean surface currents from high-frequency radar (HFR) in the northeastern Chukchi Sea, where HFR siting is dictated by power availability rather than optimal locations. Although the OI technique improves data coverage when compared to the conventional unweighted least squares fit (UWLS) method, biased solutions can emerge. The quality of the HFR velocity estimates derived by OI is controlled by three factors: 1) the number of available incorporating radials (AR), 2) the ratio of the incorporating radials from multiple contributing site locations [ratio of overlapping radial velocities (ROR) or radar geometry], and 3) the positive definiteness [condition number (CN)] of the correlation matrix. Operationally, ROR does not require knowledge of the angle covariance matrix used to compute the geometric dilution of precision (GDOP) in the UWLS method and can be computed before site selection to optimize coverage or after data processing to assess data quality when applying the OI method. The Kim et al. method is extended to examine sensitivities to data gaps in the radial distribution and the effects on OI estimates.

Fjords along the western Antarctic Peninsula contain rich marine ecosystems and tidewater glaciers potentially sensitive to ocean change, but much is unknown about the physical oceanography of these fjords. This paper presents a comprehensive description of the physical environment of Andvord Bay, a glacial fjord located in the Gerlache Strait on the northern end of the Peninsula. Measurements were collected as part of the FjordEco program between November 2015 and March 2017, including during three research cruises and from a number of fixed installations (sub-surface moorings, time lapse cameras, and automatic weather stations). Andvord Bay is located just north of a sill in the Gerlache Strait. This sill inhibits the direct influence of warm Upper Circumpolar Deep Water from the shelf, and deep waters in the fjord are therefore relatively cold. As a result, glaciers in Andvord Bay are not subject to the substantial ocean-driven retreat observed farther south on the Peninsula. Instead, mass flux from the glaciers occurs mainly through calving. The influence of meltwater in Andvord Bay is small compared to glacial fjords in the Arctic and in the South Shetland Islands, although summer freshening is evident in the fjord near-surface layer, likely as a result of glacial inputs. The combination of surface freshening and the absence of strong mean wind forcing in the fjord results in salinity stratification extending well into the euphotic zone, providing advantageous conditions for phytoplankton blooms. Andvord Bay is generally dynamically quiet compared to the ambient ocean, with the exception of during local katabatic wind events. Exchange with the Gerlache Strait is weak, although the deep waters of the fjord are replenished on an annual scale through slow lateral exchange with the outside. In addition, deep convection may play a role in ventilating subsurface waters in winter.

The Palmer Deep submarine canyon on the Western Antarctic Peninsula provides a conduit for upwelling of relatively warm, nutrient rich waters which enhance local primary production and support a food web productive enough to sustain a large top predator biomass. In an analysis of ten years of satellite-tagged penguins, showed that circulation features associated with tidal flows may be a key driver of nearshore predator distributions. During diurnal tides, the penguins feed close to their breeding colonies and during semi-diurnal tides, the penguins make foraging trips to the more distant regions of Palmer Deep. It is hypothesized that convergent features act to concentrate primary producers and aggregate schools of krill that influence the behavior of predator species. The initial results from a six month deployment of a High Frequency Radar network in Palmer Deep are presented in an attempt to characterize and quantify convergent features. During a three month period from January through March 2015, we conducted in situ sampling consisting of multiple underwater glider deployments, small boat acoustic surveys of Antarctic krill, and penguin ARGOS-linked satellite telemetry and time-depth recorders (TDRs). The combination of real-time surface current maps with adaptive in situ sampling introduces High Frequency Radar to the Antarctic in a way that allows us to rigorously and efficiently test the influence of local tidal processes on top predator foraging ecology

Project CONVERGE, funded by the National Science Foundation Office of Polar Programs, is deploying a coordinated ocean observing network to better understand ecological connections along the Western Antarctic Peninsula (WAP). Partners from Rutgers University, the University of Alaska, Fairbanks (UAF), Oregon State University, the University of Delaware, and the Polar Oceans Research Group deployed a multiplatform-observing network that includes gliders, animal telemetry, active acoustics for zooplankton distributions, and CODAR High Frequency Radar (HFR). The three-site network was deployed in November of 2014 and provided hourly surface current maps through the following austral summer. This study targets data collected between January and February 2015. Here we focus on Palmer Deep eddy and the tidal currents as they transition from diurnal to semi-diurnal regimes throughout the study period. These data are helping us better understand the links between alternating tidal regimes and the foraging behavior of the local Adelie penguin populations. This analysis has further implications for future research as the region goes through dramatic climate change.