Coastal Alaska Research Articles

Canada, British Columbia, Graham Island, Gulf of Alaska Coast

Canada, British Columbia, Graham Island, Gulf of Alaska Coast

Behaviors of the Yukon River Sediment Plume in the Bering Sea: Relations to Glacier-Melt Discharge and Sediment Load

Sediment plumes, released to the Bering Sea from the delta front of the Yukon River, Alaska, are initiated mainly by glacier-melt sediment runoffs in the glacierized regions of the Yukon River drainage basin. The surface sediment plumes are extended around the fan-shaped Yukon River delta, which is followed by the northwestward dispersion. During continuous measurements of the Yukon River discharge and sediment load, behaviors of the sediment plumes were explored by shipboard and coastal observations in the Bering Sea. At the high river sediment load of ca. 2500 kg/s, the plume partially plunged into the sea bottom layer. The plunging probably originated in the nepheloid-layer formation from the flocculation of river-suspended sediment, of which more than 90% wt. is silt and clay (grain size d < 63 μm). In order to numerically obtain the area of the surface sediment plumes, a satellite image analysis was performed by using three near-infrared bands in MODIS/Aqua or MODIS/Terra. The plume area was significantly correlated (R2 = 0.735, p < 0.01) to the sediment load averaged for the two days with time lags of 20 days and 21 days to the date of a certain satellite image. Hence, the dispersion of plume-suspended sediment appears to be controlled by the sediment runoff events in the Yukon River rather than the northward “Alaskan Coastal Water”.

Lichen-based critical loads for deposition of nitrogen and sulfur in US forests

Critical loads are thresholds of atmospheric deposition below which harmful ecological effects do not occur. Because lichens are sensitive to atmospheric deposition, lichen-based critical loads can foreshadow changes of other forest processes. Here, we derive critical loads of nitrogen (N) and sulfur (S) deposition for continental US and coastal Alaskan forests, based on nationally consistent lichen community surveys at 8855 sites. Across the eastern and western US ranges of 459 lichen species, each species' realized optimum was the N or S atmospheric deposition value at which it most frequently occurred. The mean of optima for all species at a site, weighted by their abundances, was defined as a community “airscore” indicative of species’ collective responses to atmospheric deposition. To determine critical loads for adverse community compositional shifts, we then modeled changes in airscores as a function of deposition, climate and forest habitat predictors in nonparametric multiplicative regression. Critical loads, indicative of initial shifts from pollution-sensitive toward pollution-tolerant species, occurred at 1.5 kg N ha−1 y−1 and 2.7 kg S ha−1 y−1. Importantly, these critical loads remain constant under any climate regime nationwide, suggesting both simplicity and nationwide applicability. Our models predict that preventing excess N deposition of just 0.2–2.0 kg ha−1 y−1 in the next century could offset the detrimental effects of predicted climate warming on lichen communities. Because excess deposition and climate warming both harm the most ecologically influential species, keeping conditions below critical loads would sustain both forest ecosystem functioning and climate resilience.

Landfast ice properties over the Beaufort Sea region in 2000–2019 from MODIS and Canadian Ice Service data

Two decades (2000–2019) of the landfast ice properties in the Beaufort Sea region in the Canadian Arctic were analyzed at 250 m spatial resolution from two sources: (1) monthly maps derived at the Canada Centre for Remote Sensing from the Moderate Resolution Imaging Spectroradiometer clear-sky satellite image composites; and (2) Canadian Ice Service charts. Detailed comparisons have been conducted for the landfast ice spatial extent, the water depth at, and the distance to the outer seaward edge from the coast in four sub-regions: (1) Alaska coast; (2) Barter Island to Herschel Island; (3) Mackenzie Bay; and (4) Richards Island to Cape Bathurst. The results from both sources demonstrate good agreement. The average spatial extent for the entire region over the April–June period is 48.5 (±5.0) × 103 km2 from Canadian Ice Service data versus 45.1 (±6.1) × 103 km2 from satellite data used in this study (7.0% difference). The correlation coefficient for April–June is 0.73 (p = 2.91 × 10−4). The long-term linear trends of the April–June spatial extent since 2000 demonstrated statistically significant decline: −4.45 (±1.69) × 103 km2/decade and −4.73 (±2.17) × 103 km2/decade from Canadian Ice Service and satellite data, respectively. The landfast ice in the Beaufort Sea region showed the general tendency for an earlier break-up, later onset, and longer ice-free period. The break-up date has decreased by 7.6 days/decade in the Mackenzie Bay region. The western part of the study area did not demonstrate statistically significant changes since 2000.

Independent validation of downscaled climate estimates from a coastal Alaska watershed using local historical weather journals.

Downscaling coarse global and regional climate models allows researchers to access weather and climate data at finer temporal and spatial resolution, but there remains a need to compare these models with empirical data sources to assess model accuracy. Here, we validate a widely used software for generating North American downscaled climate data, ClimateNA, with a novel empirical data source, 20th century weather journals kept by Admiralty Island, Alaska homesteader, Allen Hasselborg. Using Hasselborg’s journals, we calculated monthly precipitation and monthly mean of the maximum daily air temperature across the years 1926 to 1954 and compared these to ClimateNA data generated from the Hasselborg homestead location and adjacent areas. To demonstrate the utility and potential implications of this validation for other disciplines such as hydrology, we used an established regression equation to generate time series of 95% low duration flow estimates for the month of August using mean annual precipitation from ClimateNA predictions and Hasselborg data. Across 279 months, we found strong correlation between modeled and observed measurements of monthly precipitation (ρ = 0.74) and monthly mean of the maximum daily air temperature (ρ = 0.98). Monthly precipitation residuals (calculated as ClimateNA data - Hasselborg data) generally demonstrated heteroscedasticity around zero, but a negative trend in residual values starting during the last decade of observations may have been due to a shift to the cold-phase Pacific Decadal Oscillation. Air temperature residuals demonstrated a consistent but small positive bias, with ClimateNA tending to overestimate air temperature relative to Hasselborg’s journals. The degree of correlation between weather patterns observed at the Hasselborg homestead site and ClimateNA data extracted from spatial grid cells across the region varied by wet and dry climate years. Monthly precipitation from both data sources tended to be more similar across a larger area during wet years (mean ρ across grid cells = 0.73) compared to dry years (mean ρ across grid cells = 0.65). The time series of annual 95% low duration flow estimates for the month of August generated using ClimateNA and Hasselborg data were moderately correlated (ρ = 0.55). Our analysis supports previous research in other regions which also found ClimateNA to be a robust source for past climate data estimates.

Multiscale variations in Arctic sea ice motion and links to atmospheric and oceanic conditions

Abstract. Arctic sea ice drift motion affects the global material balance, energy exchange and climate change and seriously affects the navigational safety of ships along certain channels. Due to the Arctic's special geographical location and harsh natural conditions, observations and broad understanding of the Arctic sea ice motion are very limited. In this study, sea ice motion data released by the National Snow and Ice Data Center (NSIDC) were used to analyze the climatological, spatial and temporal characteristics of the Arctic sea ice drift from 1979 to 2018 and to understand the multiscale variation characteristics of the three major Arctic sea ice drift patterns. The empirical orthogonal function (EOF) analysis method was used to extract the three main sea ice drift patterns, which are the anticyclonic sea ice drift circulation pattern on the scale of the Arctic basin, the average sea ice transport pattern from the Arctic Ocean to the Fram Strait, and the transport pattern moving ice between the Kara Sea (KS) and the northern coast of Alaska. By using the ensemble empirical mode decomposition (EEMD) method, each temporal coefficient series extracted by the EOF method was decomposed into multiple timescale sequences. We found that the three major drift patterns have four significant interannual variation periods of approximately 1, 2, 4 and 8 years. Furthermore, the second pattern has a significant interdecadal variation characteristic with a period of approximately 19 years, while the other two patterns have no significant interdecadal variation characteristics. Combined with the atmospheric and oceanic geophysical variables, the results of the correlation analysis show that the first EOF sea ice drift pattern is mainly related to atmospheric environmental factors, the second pattern is related to the joint action of atmospheric and oceanic factors, and the third pattern is mainly related to oceanic factors. Our study suggests that the ocean environment also has a strong correlation with sea ice movement. Especially for some sea ice transport patterns, the correlation even exceeds atmospheric forcing.

Project Plowshare: The Peaceful Use of Nuclear Explosives in Cold War America

Project Plowshare: The Peaceful Use of Nuclear Explosives in Cold War America

New species of deep-sea Antipatharians from the North Pacific (Cnidaria: Anthozoa: Antipatharia), Part 2.

Five new species of deep-sea antipatharian corals are described from the North Pacific primarily collected off the coast of Alaska and on adjacent seamounts. All the species are referred to the family Schizopathidae. Described as new are: Alternatipathes mirabilis, Bathypathes ptiloides, Bathypathes tiburonae, Bathypathes alaskensis, and Parantipathes pluma. Illustrations of the type material of Bathypathes patula, B. patula var. plenispina and B. tenuis are provided for comparative proposes. Bathypathes patula var. plenispina is here recognized as a species distinct from B. patula, and B. tenuis is considered incertae sedis due to the poor condition of the type material.

Water mass distribution in the northern Bering and southern Chukchi seas using light absorption of chromophoric dissolved organic matter

The northern Bering Sea (NBS) and southern Chukchi Sea (SCS) contain several water masses with different characteristics that have been conventionally classified using temperature and salinity data. However, recent warming and sea ice decline can change these water properties, which suggests that classifying water masses using temperature–salinity diagrams could be problematic for this region. We used the light absorption coefficient of chromophoric dissolved organic matter (CDOM), aCDOM, as an alternative way to classify water masses. The aCDOM spectra of several water depths were measured in the NBS, the Gulf of Anadyr included, and SCS in July 2017 and 2018, and August 2018. Optical parameters that indicate CDOM quantity and quality, aCDOM(350) and spectral slopes (S275–295 and S350–400), were calculated for each sample; water masses were classified using cluster analysis. When surface waters in the NBS and SCS are classified on the basis of the conventional method using a temperature–salinity diagram, they are mistakenly identified as Alaskan Coastal Water because of warmer temperatures. However, our cluster analysis using CDOM parameters evenly classified seven water masses with reasonable distributions. A water mass with the highest aCDOM(350) and lowest S275–295 was found along the coast of the Gulf of Anadyr and Alaska mainland, which suggests that freshwater originates from the Anadyr and Yukon rivers and is transported by the Anadyr Current and Alaskan Coastal Current, respectively. A CDOM-based water mass with high S275–295, indicating CDOM degradation by ultraviolet radiation, was present at the sea surface. A water mass with low S275–295 was found at deeper water depths and river mouths. These results suggest that classification with CDOM parameters is consistent with geographical features. In addition, we recognized a water mass with high nitrate concentrations, which is likely Anadyr Water that originates in the region from the Bering Slope to the Gulf of Anadyr. Overall, this study reveals that water mass classification using CDOM parameters is useful in coastal sea areas in which water mass mixing is complex.

Staying close to home: Ecological constraints on space use and range fidelity in a mountain ungulate.

Understanding patterns of animal space use and range fidelity has important implications for species and habitat conservation. For species that live in highly seasonal environments, such as mountain goats (Oreamnos americanus), spatial use patterns are expected to vary in relation to seasonal changes in environmental conditions and sex‐ or age‐specific selection pressures. To address hypotheses about sex, age, and seasonality influence on space‐use ecology, we collected GPS location data from 263 radio‐collared mountain goats (males, n = 140; females, n = 123) in coastal Alaska during 2005–2016. Location data were analyzed to derive seasonal and sex‐specific fixed‐kernel home range estimates and to quantify the degree of seasonal range and utilization distribution overlap. Overall, we determined that home range size was smallest during winter, expanded coincident with the onset of green‐up and parturition, and was largest during summer. Home range size of males and females did not differ significantly during winter, but females had larger home ranges than males during summer, a relationship that was switched during the mating season. Pairwise comparisons involving individual females across subsequent years indicated home ranges were significantly smaller during years when they gave birth to offspring. Mountain goats exhibited a strong degree of range fidelity, and 99% (n = 138) of individual animals returned to their previous year's seasonal range with an average annual Bhattacharyya's affinity utilization distribution overlap index of 68%. Similarity of seasonal home range utilization distributions varied in relation to sex and season in some respects. Home range overlap was highest during the summer vegetation growing season, particularly among females. These findings advance our understanding about how environmental variation and sex‐ and age‐related reproductive constraints influence space use and range fidelity among alpine ungulates. Documentation of the high degree of range fidelity among mountain goats has important conservation implications in landscapes increasingly altered by anthropogenic activities.

Formation of Hybrid Computational Structure for the Analysis of Critical Control Scenarios in Biocybernetics

We have considered methods of computational modeling of rapid processes in ecosystems and events of changes with extreme amplitude of abundance. For biocybernetics, the phenomena of degradation of the commercial population in the form of a sudden collapse for specialists and an explosive increase in the number of a new species after invasion — outbreaks are of the type predicted with difficulties. We have developed and ecologically substantiated a method for modeling a group of rapid phenomena, including the calculation of threshold states and transient modes. Algorithmically implemented computational structure, which describes spontaneous modes of rapid transformations in ecodynamics based on the internal properties of biosystems. New model is based on the formalization of threshold effects in regulation of reproduction, included as additional functionals in the basic hybrid structure for research in scenario experiments. Computational scenario is obtained for a generalized description of the extreme population process. We have considered the situation of the collapse of the commercial population with a quota-regulated harvest on the example of the king crab Paralithodes camtschaticus near the coast of Alaska. In the simulation scenario of the crab collapse, we took into account the logic of expert management of the level of exploitation of biological resources. The resulting control scenarios using the iterative model use bifurcations and the loss of the invariance property by the attractor. Modeling with the expert logic of fishery management revealed the characteristic signs of the dynamics of crab collapse and predicted important stages in the process of degradation of exploited biological resources.

Inherent tolerance of extreme seasonal variability in light and salinity in an Arctic endemic kelp (Laminaria solidungula).

The kelp Laminaria solidungula is an important foundation species in the circumpolar Arctic. One of the largest populations of L.solidungula in the Beaufort Sea occurs in Stefansson Sound, off the north coast of Alaska. We surveyed kelp populations in the Stefansson Sound Boulder Patch and found that inshore sites in close proximity (3.5km) to river input and increased turbidity exhibited lower sporophyte densities (0.36±0.44·m-2 ) than more offshore sites (>7km) to the west (0.72±0.48·m-2 ) and east (4.72±1.51 · m-2 ). We performed culture experiments to examine the possible combined effects of salinity and light on microscopic sporophyte production. Gametophytes cultured in the low salinity treatment (10) were unable to produce sporophytes regardless of light level. The highest light level tested (40µmol photons·m-2 ·s-1 ) produced the greatest sporophyte densities (0.037±0.08·mm-2 ) at a salinity of 30. Subsequent experimental work on the effect of salinity on microscopic stages revealed that haploid stages were not capable of producing sporophytes at a salinity of 10, but 3-month-old microscopic sporophytes were able to persist in the lower (10 and 20) salinity treatments. Although L.solidungula sporophytes have apparently acclimated to extreme salinity (<5-33) and light variations, the vulnerability of haploid microscopic stages to reduced salinity has the potential to affect future populations as the timing and magnitude of freshwater input to the Arctic Ocean changes.

Incursion of Alaska Coastal Water as a mechanism promoting small phytoplankton in the western Arctic Ocean

The inflow of Alaska Coastal Water (ACW) acts as a source of heat and freshwater for the Arctic Ocean, and contributes to ecosystem succession as well as phytoplankton change. To explore the mechanisms and patterns of the phytoplankton composition in response to the ACW, diagnostic pigments and environmental parameters were analyzed along three similar transects from shelf to basin in the Arctic Ocean during summer in 2008–2016. The results showed that the incursion of the ACW reduced the chlorophyll a (Chl a) concentration in the shelf areas, but favored phytoplankton growth in basin areas, especially that of small prasinophytes and chrysophytes. A possible explanation is the change in nutrient status, because during its northward flow, the ACW dissipates heat and receives nutrients from the surrounding cold water. The concentrations of Prasino and Chl b (the diagnostic pigments of prasinophytes) increase from barely detected in 2008 to higher than 15 ng/dm3 (Prasino) and 65 ng/dm3 (Chl b) respectively in 2014 and 2016, which occurred synchronously with presence of ACW and an increase in subsurface nitrate reservoirs. These findings indicate that the incursion of the ACW brings nutrients into subsurface basin layers, which could favor the growth of small phytoplankton in the western Arctic Ocean.

Exploring GPS Observations of Postseismic Deformation Following the 2012 MW7.8 Haida Gwaii and 2013 MW7.5 Craig, Alaska Earthquakes: Implications for Viscoelastic Earth Structure

AbstractThe Queen Charlotte‐Fairweather Fault (QC‐FF) system off the coast of British Columbia and southeast Alaska is a highly active dextral strike‐slip plate boundary that accommodates ∼50 mm/yr of relative motion between the Pacific and North America plates. Nine MW ≥ 6.7 earthquakes have occurred along the QC‐FF system since 1910, including a MS(G‐R)8.1 event in 1949. Two recent earthquakes, the October 28, 2012 Haida Gwaii (MW7.8) and January 5, 2013 Craig, Alaska (MW7.5) events, produced postseismic transient deformation that was recorded in the motions of 25 nearby continuous Global Positioning System (cGPS) stations. Here, we use 5+ yr of cGPS measurements to characterize the underlying mechanisms of postseismic deformation and to constrain the viscosity structure of the upper mantle surrounding the QC‐FF. We construct forward models of viscoelastic deformation driven by coseismic stress changes from these two earthquakes and explore a large set of laterally heterogeneous viscosity structures that incorporate a relatively weak back‐arc domain; we then evaluate each model based on its fit to the postseismic signals in our cGPS data. In determining best‐fit model structures, we additionally incorporate the effects of afterslip following the 2012 event. Our results indicate the occurrence of a combination of temporally decaying afterslip and vigorous viscoelastic relaxation of the mantle asthenosphere. In addition, our best‐fit viscosity structure (transient viscosity of 1.4–2.0 × 1018 Pa s; steady‐state viscosity of 1019 Pa s) is consistent with the range of upper mantle viscosities determined in previous studies of glacial isostatic rebound and postseismic deformation.

Virtual cultural landscapes: Geospatial visualizations of past environments

AbstractRecent advances in spatial and remote sensing technology have led to new methods in archaeological site identification and reconstruction, allowing archaeologists to investigate landscapes and sites on multiple scales. These remotely conducted surveys create virtual cultural landscapes and seascapes that archaeologists and the public interact with and experience, often better than traditional maps. Our study examines landscape reconstruction and archaeological site classifications from a phenomenological and human behavioural ecology (HBE) perspective. HBE aims to reconstruct how humans interacted with these places as part of their active and passive decision making. Through temporal reconstructions, archaeologists and others can experience and interpret past landscapes and subtle changes in cultural land‐ and seascapes. Here, we evaluate the use of remotely sensed data (lidar, satellite imagery, sonar, radar, etc.) for developing virtual cultural landscapes while also incorporating Indigenous perspectives. Our study compares two vastly different landscapes and perspectives: a seascape in coastal Alaska, USA, and a neotropical jungle in Belize, Central America. By incorporating ethnographic accounts, oral histories, Indigenous traditional knowledge and community engagement, archaeologists can develop new tools to understand decisions made in the past, especially pertaining to settlement selection and resource procurement. These virtual reconstructions become cognitive images of a possible place that the observer experiences. Virtual cultural landscapes allow archaeologists to reproduce landscapes that may otherwise be invisible and present them to different publics. These processes elucidate how landscapes changed over time based on human behaviours while simultaneously allowing archaeologists to engage with Indigenous communities and the public in the protection of prehistoric and historic sites and sacred spaces through cultural heritage management.

Comparison of picoeukaryote community structures and their environmental relationships between summer and autumn in the southern Chukchi Sea.

Picoeukaryotes constitute an important component of the living biomass of oceanic communities and play major roles in biogeochemical cycles. There are very few studies on picoeukaryotes found in the Chukchi Sea. This work shows the relationship between community distribution and composition of picoeukaryotes residing in water masses and physicochemical factors in the southern Chukchi Sea studied in both midsummer (July) and early autumn (September), 2012. Illumina 18S V4 rDNA metabarcoding were used as the main tool. In July, Mamiellophyceae, Dinophyceae, and Trebouxiophyceae were the main microbial classes, with Micromonas, Prasinoderma, Telonema, Amoebophrya, Bathycoccus, Picomonas, and Bolidomonas representing the main genera. In September, Trebouxiophyceae surpassed Dinophyceae and was the second main microbial class, with Micromonas, Prasinoderma, Bathycoccus, Bolidomonas, Telonema, Choricystis, and Diaphanoeca representing the main genera. Water mass was the primary factor determining the community composition and diversity of picoeukaryotes. Abundance of Bathycoccus was found to be highly correlated with Alaskan Coastal Water and that of Prasinoderma, Bolidomonas, and Diaphanoeca with Bering Seawater. Nitrate and phosphate content of water in midsummer and dissolved oxygen (DO) and temperature in early autumn were the main factors that shaped the abundance of the picoeukaryote community.

Characteristics of terrigenous components of Amerasian Arctic Ocean surface sediments: Implications for reconstructing provenance and transport modes

We investigated the petrographic composition of coarse-grained clasts (>250 μm) in 117 core-top sediment samples from the western Arctic Ocean (the Amerasian Basin, Chukchi Sea, Alaskan/Beaufort margin and East Siberian Sea). Combined with analyses of bulk sediment mineralogy and grain size, we use the results to elucidate the terrigenous clastic sediment distribution patterns and transport modes in four different regions: (1) In the Chukchi Sea, the Bering Strait Inflow (BSI) contributes most of the sediments, with an additional terrigenous clastic contribution from Northern Alaska and Eastern Siberia. The highest coarse clastic content and a northward-fining of the grain-size distributions are attributed to the winnowing by the BSI. (2) In the Alaskan margin, terrigenous clasts are enriched in sea ice/anchor ice-transported quartz-rich sediments from Northern Alaska, and in addition the Alaska Coastal Current (ACC) contributes sediments originating from the Yukon River. Coarse-grained sediments accumulate near offshore Alaska with the finer fractions being transported further into the Chukchi Sea Shelf. (3) In the East Siberian Sea, coarse clasts are sparse and even absent in most study sites. Combined with the results of previous studies, we conclude that the terrigenous components are derived from the Laptev Sea and the adjacent Siberian Platform. They are transported by the Siberian Coastal Current and sea ice. (4) In the Canada Basin, terrigenous clasts are characterized by carbonate and quartz-rich sediments derived from the Canadian Arctic Archipelago (CAA). Sediments incorporated in sea ice/anchor ice drift from the CAA to the Beaufort Sea, where they combine with sediments from the Mackenzie River and are then transported into the Canada Basin by the Beaufort Gyre. Sediments and grain size in northern and southern Canada Basin also involve the early Holocene iceberg-entrained IRD from CAA and winnowing/nepheloid transported mica from marginal areas, respectively.

Additional data on morphology and distribution of Melitoides valida (Shoemaker, 1955) (Amphipoda, Melitidae)

The genus Melitoides Gurjanova, 1934 (Amphipoda, Melitidae) includes three species from the Arctic and northwestern Pacific: Melitoides makarovi Gurjanova, 1934, M. valida (Shoemaker, 1955), and M. kawaii Labay, 2014. M. makarovi and M. kawaii only were recorded until recently in the seas of the Russian Far East. Only two specimens of M. valida were found once near the Arctic coast of Alaska; therefore, the morphological description of the species was incomplete, which led to difficulties with its generic identification. For the first time, M. valida was found in the seas of the Russian Far East in September 2018 on the shelf of the Sea of Okhotsk, near the North-Eastern Sakhalin Island at the depth of 29 m on the sand bottom. Detailed re-description of the species was carried out using optical and electronic scanning microscopes by the Coleman protocol. The material collected is stored at the Crustacea collection of the Zoological Museum of Far Eastern Federal University (Vladivostok). The specimen from the Sea of Okhotsk is identical to the specimens of the type series from the Arctic coast of Alaska in the form of dorsal carination (with several teeth on posterior margin of pleon segments 2, 3 and urosomites 1, 2), in the structure of pereopods 1–7, especially in the form of propodus of pereopods 2 (palm with distinct posterior-distal tooth, as well as with three large and one small obtuse palmar teeth). M. valida description has been substantially supplemented, and information on its range has been expanded.

An empirical Bayesian approach to incorporate directional movement information from a forage fish into the Arnason-Schwarz mark-recapture model

BackgroundOver the past two decades, various species of forage fish have been successfully implanted with miniaturized acoustic transmitters and subsequently monitored using stationary acoustic receivers. When acoustic receivers are configured in an array, information related to fish direction can potentially be determined, depending upon the number and relative orientation of the acoustic receivers. However, it can be difficult to incorporate directional information into frequentist mark-recapture methods. Here we show how an empirical Bayesian approach can be used to develop a model that incorporates directional movement information into the Arnason-Schwarz modeling framework to describe survival and migration patterns of a Pacific herring (Clupea pallasii) population in coastal Alaska, USA.MethodsWe acoustic-tagged 326 adult Pacific herring during April 2017 and 2018 while on their spawning grounds in Prince William Sound Alaska, USA. To monitor their movements, stationary acoustic receivers were deployed at strategic locations throughout the Sound. Receivers located at the major entrances to the Gulf of Alaska were arranged in parallel arrays to determine the directional movements of the fish. Informative priors were used to incorporate the directional information recorded at the entrance arrays into the model.ResultsA seasonal migratory pattern was found at one of Prince William Sound’s major entrances to the Gulf of Alaska. At this entrance, fish tended to enter the Gulf of Alaska during spring and summer after spawning and return to Prince William Sound during the fall and winter. Fish mortality was higher during spring and summer than fall and winter in both Prince William Sound and the Gulf of Alaska.ConclusionsAn empirical Bayesian modeling approach can be used to extend the Arnason-Schwarz modeling framework to incorporate directional information from acoustic arrays to estimate survival and characterize the timing and direction of migratory movements of forage fish.

Observational Study on the Variability of Mixed Layer Depth in the Bering Sea and the Chukchi Sea in the Summer of 2019

Abstract. Based on the high-resolution CTD data from 58 stations in the Bering Sea and the Chukchi Sea in the summer of 2019, the mixed layer depth (MLD) was obtained according to the density difference threshold method. It was verified that the MLD could be estimated more accurately by using a criterion of 0.125 kg/m3 in this region. The MLD in the Bering Sea basin was larger than that in the Bering Sea shelf, and both of them were smaller than that in the Bering Sea slope. The MLD increased northward both in the Chukchi Sea shelf and the Chukchi Sea slope. The farther northward, the greater the difference between the MLD calculated from temperature (MLDt) and the MLD calculated from density (MLDd) was, and the more important the role of salinity was in determining the MLD. The larger MLD (refer to MLDd specifically) in the Bering Sea slope might be due to the enhancement of mixing caused by the Bering Slope Current (BSC) and eddies. The horizontal advection of the Bering Sea Anadyr Water and the Alaska Coastal Water in the Bering Sea shelf led to the shallower MLD in the central transition zone. The northward increase of the MLD in the Chukchi Sea might be related to the low-salinity seawater resulting from the melting of sea ice in summer. The spatial variation of MLD was more closely related to the surface momentum flux than the sea surface buoyancy flux, and the wave had little effect.