The annual heat balance of the surface 100 meters of the northwest Gulf of Alaska shelf

Thesis (M.S.) University of Alaska Fairbanks, 1980Oceanographic and meteorologic data collected from 1970 to 1978 on the northern Gulf of Alaska shelf are used to compute monthly heat budgets within the surface 100 m for a composite year. During months of net heat gain, radiation is the primary source. Latent and sensible heat transfer dominate during months of net heat loss. Persistent downwelling is the second most important route for heat loss. During winter, alongshore advection is the principal contributor of heat to this region. Cross-shelf advection and diffusion of heat are of minor importance throughout the year and generally counter each other. The prevalence of onshore Ekman transport explains the cross-shelf variation in the annual amplitude of heat content and the differential propagation rates of surface temperature anomalies to greater depths. No significant linear relationships were determined between anomalies of surface heat transfer and sea surface temperature. Several hypotheses are presented to explain this result

The impact of spatial wind variations on freshwater transport by the Alaska Coastal Current

The Alaska Coastal Current (ACC) is located in a region with prevailing downwelling-favorable winds, flows over a long stretch of coastline (over 2000 km), and is driven by multiple sources of freshwater discharge totaling 24000 m3 s–1 along its length. Using the Regional Ocean Modeling System (ROMS) we attempt to determine how spatially variable winds affect the downstream transport of freshwater along a long coastline with nearly continuous sources of freshwater. The model domain represents a fraction of the ACC region and periodic boundary conditions are applied to allow propagation of the buoyant flow from upstream. The model is forced by multiple freshwater sources in the central part of the domain and by both constant and spatially-varying, predominantly downwelling-favorable, winds. Freshwater flux gain in the coastal current (as opposed to spreading offshore) is calculated by taking a 30-day averaged difference between freshwater fluxes at the downstream and upstream edges of the buoyancy forcing region. Model runs are split into two categories: relatively high gains (50 – 60% of total discharge) were observed under moderate wind stress (∼0.05 Pa) or no wind conditions while lower gains (35– 45%) were observed under light average wind stresses (∼0.025 Pa), especially when wind varied alongshore. The offshore freshwater transport is eddy-driven and is enhanced in the areas of converging wind forcing. Eddy generation is associated with the wind-induced deepening of the buoyant layer near the coast. When the surface boundary layer is thin under light wind conditions, this deepening translates into enhanced vertical shear of the alongshore current through the thermal wind balance. Reversal of alongshore wind to upwelling-favorable wind effectively blocks the downstream freshwater transport and spreads the buoyant layer offshore

On the Nature of Winter Cooling and the Recent Temperature Shift on the Northern Gulf of Alaska Shelf

[1] In spring 2006 and 2007, northern Gulf of Alaska (GOA) shelf waters were ∼1.5°C below average throughout the similar to ∼250 m deep shelf and the salinity-dependent winter stratification was anomalously weak due to above (below) average surface (bottom) salinities. Spring 2007 and 2008 temperatures were also similar to ∼-1.5°C below average, but the anomalies were confined to the upper 100 m due to moderate salt stratification. Shelf temperatures in these 2 years were among the lowest observed since the early 1970s, thus interrupting an approximately 30-year warming trend. We examined winter cooling processes using historical conductivity-temperature-depth (CTD) profiles and mooring data from hydrographic station GAK1. The 2006 and 2007 cooling was associated with anomalously strong atmospheric heat loss in November 2006 and March 2007 and below-average fall runoff, which weakened winter stratification and allowed the late cooling to penetrate throughout the water column. In 2007 and 2008, early winter cooling was weak, fall runoff large, and stratification moderate at 100 m so that spring temperature anomalies were trapped to the upper 100 m. Analysis of the 40 year GAK1 CTD record indicates that winter averaged air-sea heat flux and salinity stratification anomalies explain 81% of the variation in deep (100-250 m) GOA temperatures. Although the timing and magnitude of winter runoff influences the shelf temperature distribution, temperature anomalies are a consequence of three-dimensional circulation and mixing processes. These involve the complex, but poorly understood, interplay among the air-sea heat flux; the ocean heat flux convergences; the stabilizing influence of runoff; and the destabilizing effects of cooling, vertical mixing, and the wind-driven cross-shelf buoyancy flux

Bowhead Whales Along the Chukotka Coast in Autumn

Bowhead whales (Balaena mysticetus) were seen in autumn 1992 and 1993 only along the northern coast of Chukotka, Russia, although an extensive area of the Chukchi Sea was searched during ship cruises. Single-day counts for 76 and 50 bowheads were made on 1 October 1992 and 3 October 1993, respectively, with only a few whales seen on other days. Whales seen between Cape Schmidt and Cape Vankarem on 1 October 1992 appeared to be feeding, but there was no means to detect or sample subsurface forage that year. On 3 October 1993, bowheads appeared to be feeding in an area where a 5 m x 8 km patch of zooplankton was identified, via acoustics, at 25-30 m in water 35 m deep. A vertical-tow sample near the patch indicated the euphausiid Thysanoessa rachii, a common bowhead prey species, was abundant in the water column. The location of the zooplankton patch corresponded with a sharp salinity (proxy density) gradient. In addition, whale distribution coincided with a surface thermal boundary, identified by satellite-borne Advanced Very High Resolution Radiometer (AVHRR) imagery. The confinement of bowhead sightings to the northern coast of Chukotka in 1992-93 corresponds to reports from autumn surveys in 1979, 1980 and 1990, while the association of whales with physical oceanographic fronts is similar to findings from a study of bowhead feeding areas in the southern Beaufort Sea. These observations suggest that the Chukotka coast may be an important feeding or staging area for the Bering Sea stock and that oceanographic patterns influencing whale occurrence may be identifiable from standard oceanographic measurements.Key words: bowhead whale, Balaena mysticetus, migration, Chukchi Sea, Bering Sea, Chukotka, Thysanoessa rachii, satellite imagery, AVHRRDurant l'automne de 1992 et celui de 1993, on n'a pu observer de baleines boréales (Balaena mysticetus) que le long de la côte nord de Chukotka (Russie), bien que des recherches aient eu lieu dans une zone étendue de la mer des Tchouktches lors de croisières en bateau. Des comptages de 76 et 50 baleines boréales ont été obtenus respectivement le 1er octobre 1992 et le 3 octobre 1993, alors qu'on n'en a observé que quelques-unes les autres jours. Les baleines observées entre Cape Schmidt et Cape Vankarem le 1er octobre 1992 semblaient être en train de s'alimenter, mais on ne disposait pas de moyens pour détecter le genre de nourriture sous la surface, ni pour en prélever un échantillon cette année-là. Le 3 octobre 1993, les baleines semblaient s'alimenter là où une plaque de zooplancton de 5 m x 8 km avait été identifiée par méthode acoustique entre 25 et 30 m de profondeur, dans une zone de 35 m de fond. Un échantillon prélevé par hâlage vertical près de la plaque a indiqué que l'euphausiacé Thysanoessa rachii, une proie courante de la baleine boréale, était abondant dans la colonne d'eau. L'emplacement de la plaque de zooplancton correspondait à un fort gradient de salinité (approximation par la densité). De plus, la distribution des baleines coïncidait avec une limite thermique de surface identifiée au moyen de l'imagerie par radiomètre perfectionné à très haute résolution, transporté par satellite. Le confinement des observations de baleines à la côte nord de Chukotka en 1992-93 correspond aux rapports des relevés d'automne de 1979, 1980 et 1990, tandis que l'association des baleines à des fronts physiques océanographiques cadre avec les résultats d'une étude des zones d'alimentation de la baleine boréale dans le sud de la mer de Beaufort. Ces observations suggèrent que la côte de Chukotka pourrait être une importante zone d'alimentation ou de rassemblement pour la population de la mer de Béring, et que les caractéristiques océanographiques qui influencent la présence des baleines pourraient être identifiables à partir des mesures océanographiques courantes.Mots clés: baleine boréale, Balaena mysticetus, migration, mer des Tchouktches, mer de Béring, Chukotka, Thysanoessa rachii, imagerie par satellite, radiomètre perfectionné à très haute résolutio

An Independent Review of USGS Circular 1370: An Evaluation of the Science Needs to Inform Decisions on Outer Continental Shelf Energy Development in the Chukchi and Beaufort Seas, Alaska

Reviews the U.S. Geological Survey's findings and recommendations on Alaska's Arctic Ocean, including geology, ecology and subsistence, effect of climate change on, and impact of oil spills. Makes recommendations for data management and other issues

Mollusks in the Northeastern Chukchi Sea

Infaunal and epifaunal mollusks of the northeastern Chukchi Sea were sampled and 139 molluscan taxa were identified. The pattern of spatial distribution of molluscan species was determined by cluster analysis, which resulted in six infaunal and five epifaunal station groups. Species characterizing various faunal groups are defined. Stepwise multiple discriminant analysis was applied to correlate benthic biological associations with environmental variables. Delineation of infaunal groups was mainly due to percentage of sand and bottom salinity, while epifaunal groups were separated by percent gravel and bottom temperature. An increase in abundance and biomass of infaunal mollusks occurred adjacent to and north and northwest of an identified bottom front between the Bering Shelf and Resident Chukchi Water and Alaska Coastal Water. Epifaunal molluscan abundance and biomass were highest near the coast. Mollusks, especially smaller species and the juvenile stages of larger species, represent a food resource for bottom-feeding predators in the study area.Key words: Chukchi Sea, mollusk, benthic, infauna, epifauna, bottom front, bottom-feeding predators, cluster analysis, discriminant analysisOn a fait un échantillonnage des mollusques de l'endofaune et de l'épifaune du nord-est de la mer des Tchouktches et on a identifié 139 taxons de mollusques. On a déterminé le schéma de répartition géographique des espèces de mollusques au moyen d'une analyse typologique, qui a donné six groupes de stations dans l'endofaune et cinq dans l'épifaune. On définit des espèces caractéristiques des divers groupes fauniques. On a appliqué une analyse discriminante multiple séquentielle pour corréler les associations biologiques du benthos aux variables de l'environnement. La délimitation des groupes de l'endofaune était due en grande partie au taux de sable et de salinité au fond, tandis que les groupes de l'épifaune étaient répartis en fonction du taux de gravier et de température au fond. Une augmentation dans la quantité et la biomasse des mollusques de l'endofaune apparaissait près du nord et du nord-ouest d'un front de fond compris entre le plateau continental, les eaux non brassées de la mer des Tchouktches et les eaux côtières de l'Alaska. C'est près de la côte qu'on retrouvait l'abondance et la biomasse maximales des mollusques de l'épifaune. Les mollusques, surtout ceux des petites espèces et ceux des grandes espèces qui étaient au stade juvénile, représentaient une source alimentaire pour les prédateurs benthiques vivant dans la zone d'étude.Mots clés : mer des Tchouktches, mollusque, benthique, enfofaune, épifaune, front au fond, prédateurs benthiques, analyse typologique, analyse discriminant

A refined model for spinning dust radiation

We present a comprehensive treatment of the spectrum of electric dipole emission from spinning dust grains, updating the commonly used model of Draine and Lazarian. Grain angular velocity distributions are computed using the Fokker-Planck equation; we revisit the drift and diffusion coefficients for the major torques on the grain, including collisions, grain-plasma interactions, and infrared emission. We use updated grain optical properties and size distributions. The theoretical formalism is implemented in the companion code, SPDUST, which is publicly available. The effect of some environmental and grain parameters on the emissivity is shown and analysed.Comment: Minor corrections. Matches the MNRAS published version (except for a typo in Eq.(74) corrected here). The companion code, SPDUST, can be downloaded from http://www.tapir.caltech.edu/~yacine/spdust/spdust.htm

The Northeast Pacific GLOBEC Program: Coastal Gulf of Alaska

(First Paragraph) The Gulf of Alaska (GOA) continental shelf encompasses approximately 370,000 km2, or about 13% of the U.S. continental shell and supports a rich and diverse marine ecosystem including some of the largest commercial fisheries in the U.S. Exclusive Economic Zone. Of particular economic importance is the salmon fishery, which was worth on the order of $170 million (landed value) in 2000 accrued from a catch of over 100 million fish. However, there is considerable variability on both interannual and longer time scales in harvest and recruitment success to this and other GOA fisheries. Of recent interest are compelling indications that abundances of salmon, other fish species, and zooplankton vary on decadal scales in association with North Pacific basin-scale climate changes (Beamish, 1995; Mantua et al., 1997; Roemmich and McGowan, 1995; Brodeur et al., 1996; Francis et al., 1998; Anderson and Piatt, 1999; Hollowed et al., 2001)

Coupled wind-forced controls of the Bering–Chukchi shelf circulation and the Bering Strait throughflow: Ekman transport, continental shelf waves, and variations of the Pacific–Arctic sea surface height gradient

AbstractWe develop a conceptual model of the closely co-dependent Bering shelf, Bering Strait, and Chukchi shelf circulation fields by evaluating the effects of wind stress over the North Pacific and western Arctic using atmospheric reanalyses, current meter observations, satellite-based sea surface height (SSH) measurements, hydrographic profiles, and numerical model integrations. This conceptual model suggests Bering Strait transport anomalies are primarily set by the longitudinal location of the Aleutian Low, which drives oppositely signed anomalies at synoptic and annual time scales. Synoptic time scale variations in shelf currents result from local wind forcing and remotely generated continental shelf waves, whereas annual variations are driven by basin scale adjustments to wind stress that alter the magnitude of the along-strait (meridional) pressure gradient. In particular, we show that storms centered over the Bering Sea excite continental shelf waves on the eastern Bering shelf that carry northward velocity anomalies northward through Bering Strait and along the Chukchi coast. The integrated effect of these storms tends to decrease the northward Bering Strait transport at annual to decadal time scales by imposing cyclonic wind stress curl over the Aleutian Basin and the Western Subarctic Gyre. Ekman suction then increases the water column density through isopycnal uplift, thereby decreasing the dynamic height, sea surface height, and along-strait pressure gradient. Storms displaced eastward over the Gulf of Alaska generate an opposite set of Bering shelf and Aleutian Basin responses. While Ekman pumping controls Canada Basin dynamic heights (Proshutinsky et al., 2002), we do not find evidence for a strong relation between Beaufort Gyre sea surface height variations and the annually averaged Bering Strait throughflow. Over the western Chukchi and East Siberian seas easterly winds promote coastal divergence, which also increases the along-strait pressure head, as well as generates shelf waves that impinge upon Bering Strait from the northwest

The St. Lawrence polynya and the Bering shelf circulation : new observations and a model comparison

Author Posting. © American Geophysical Union, 2006. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 111 (2006): C09023, doi:10.1029/2005JC003268.Using 14 year-long instrumented moorings deployed south of St. Lawrence Island, along with oceanographic drifters, we investigate the circulation over the central Bering shelf and the role of polynyas in forming and disseminating saline waters over the shelf. We focus also on evaluating the Gawarkiewicz and Chapman [1995] model of eddy production within coastal polynyas. Principal results include: 1) The northern central shelf near-surface waters exhibit westward flow carrying low-salinity waters from the Alaskan coast in fall and early winter, with consequences for water mass formation and biological production. 2) Within the St. Lawrence polynya, the freshening effect of winter advection is about half as large as the salting effect of surface brine flux resulting from freezing. 3) Brine production over the Bering shelf occurs primarily offshore, rather than within coastal polynyas, even though ice production per unit area is much larger within the polynyas. 4) We find little evidence for the geostrophic flow adjustment predicted by recent polynya models. 5) In contrast to the theoretical prediction that dense water from the polynya is carried offshore by eddies, we find negligible cross-shelf eddy density fluxes within and surrounding the polynya and very low levels of eddy energy that decreased from fall to winter, even though dense water accumulated within the polynya and large cross-shore density gradients developed. 6) It is possible that dense polynya water was advected downstream of our array before appreciable eddy fluxes materialized.This work was supported by National Science Foundation grant OCE9730697 to the University of Alaska and grant OCE9730823 to the University of Washington. S. M. acknowledges the support of the National Science Foundation under OCE9811097 and of NASA under grant NNG04GM69G. The University of Hamburg contributions were funded by the Bundesminister für Bildung und Wissenschaft. Funding for the drifter deployment was made possible by the North Pacific Research Board, grant NPMRI T2130. Manuscript preparation was additionally supported by Office of Naval Research grants N00014-99-1-0345 and N00014-02-1-0305 to the University of Washington