Satellite and hydrographic observations of eddy‐induced shelf‐slope exchange in the northwestern Gulf of Alaska

Okkonen, Stephen R.; Weingartner, Thomas J.; Danielson, Seth L.; Musgrave, David; Schmidt, G. M.

doi:10.1029/2002jc001342

Cited by 105 publications

(78 citation statements)

References 22 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Offshore fluxes are regularly observed in the Mid-Atlantic Bight off the northeastern United States [e.g., Joyce et al (1992) and SST imagery] and in the Gulf of Mexico (Vukovich and Waddell 1991;Frolov et al 2004). These are only two locations of many-along the East Australian shelf (Olson 1991), the Gulf of Alaska (Okkonen et al 2003), the Antarctic shelf (Stewart and Thompson 2015), and so on-where the process might be important.…”

Section: Introductionmentioning

confidence: 99%

Offshore Transport of Shelf Water by Deep-Ocean Eddies

Cherian

Brink

2016

Journal of Physical Oceanography

View full text Add to dashboard Cite

At continental margins, energetic deep-ocean eddies can transport shelf water offshore in filaments that wrap around the eddy. One example is that of Gulf Stream warm-core rings interacting with the Mid-Atlantic Bight shelf. The rate at which shelf water is exported in these filaments is a major unknown in regional budgets of volume, heat, and salt. This unknown transport is constrained using a series of idealized primitive equation numerical experiments wherein a surface-intensified anticyclonic eddy interacts with idealized shelf-slope topography. There is no shelfbreak front in these experiments, and shelf water is tracked using a passive tracer. When anticyclones interact with shelf-slope topography, they suffer apparent intrusions of shelf-slope water, resulting in a subsurface maximum in offshore transport. The simulations help construct an approximate model for the filament of exported water that originates inshore of any given isobath. This model is then used to derive an expression for the total volume of shelf-slope water transported by the eddy across that isobath. The transport scales with water depth, radius, and azimuthal velocity scale of the eddy. The resulting expression can be used with satellite-derived eddy properties to estimate approximate real-world transports ignoring the presence of a shelfbreak front. The expression assumes that the eddy's edge is at the shelf break, a condition not always satisfied by real eddies.

show abstract

Section: Introductionmentioning

confidence: 99%

Offshore Transport of Shelf Water by Deep-Ocean Eddies

Cherian

Brink

2016

Journal of Physical Oceanography

View full text Add to dashboard Cite

show abstract

“…Despite the reduced concentrations of chlorophyll in the western regions, sea lions from the CAI increased, perhaps a result of the spatial heterogeneity of chl a noted above. As for the eastern regions, the cyclical patterns of annual, summer median chl a deserve more attention with respect to other physical structures such as eddies, which are seasonally modulated, interannually variable, and have been associated with high chlorophyll concentrations (Okkonen et al 2003, Ladd et al 2005b.…”

Section: Chlorophyll a Heterogeneitymentioning

confidence: 99%

Regional differences in the spatial and temporal heterogeneity of oceanographic habitat used by Steller sea lions

Lander

Loughlin

Logsdon

et al. 2009

Ecological Applications

View full text Add to dashboard Cite

Abstract. Over the past three decades, the decline and altered spatial distribution of the western stock of Steller sea lions (Eumetopias jubatus) in Alaska have been attributed to changes in the distribution or abundance of their prey due to the cumulative effects of fisheries and environmental perturbations. During this period, dietary prey occurrence and diet diversity were related to population decline within metapopulation regions of the western stock of Steller sea lions, suggesting that environmental conditions may be variable among regions. The objective of this study, therefore, was to examine regional differences in the spatial and temporal heterogeneity of oceanographic habitat used by Steller sea lions within the context of recent measures of diet diversity and population trajectories. Habitat use was assessed by deploying satellite-depth recorders and satellite relay data loggers on juvenile Steller sea lions (n ¼ 45) over a five-year period (2000)(2001)(2002)(2003)(2004) within four regions of the western stock, including the western, central, and eastern Aleutian Islands, and central Gulf of Alaska. Areas used by sea lions during summer months (June, July, and August) were demarcated using satellite telemetry data and characterized by environmental variables (sea surface temperature [SST] and chlorophyll a [chl a]), which possibly serve as proxies for environmental processes or prey. Spatial patterns of SST diversity and Steller sea lion population trends among regions were fairly consistent with trends reported for diet studies, possibly indicating a link between environmental diversity, prey diversity, and distribution or abundance of Steller sea lions. Overall, maximum spatial heterogeneity coupled with minimal temporal variability of SST appeared to be beneficial for Steller sea lions. In contrast, these patterns were not consistent for chl a, and there appeared to be an ecological threshold. Understanding how Steller sea lions respond to measures of environmental heterogeneity will ultimately be useful for implementing ecosystem management approaches and developing additional conservation strategies.

show abstract

“…These offshore currents in the bottom boundary layer are thought to help stabilize the mean frontal position over hundreds of km of the shelf [Chapman and Lentz, 1994;Chapman, 2000]. Studies that have explored the mechanisms for export of shelf water to the open ocean have focused on the surface ocean, specifically Gulf Stream rings and frontal instabilities [Mitzoba et al, 2006;Okkonen et al, 2003;Ryan et al, 1999].…”

Section: General Circulation Of the Mid-atlantic Bightmentioning

confidence: 99%

Nutrient exchange and ventilation of benthic gases across the continental shelf break

2011

View full text Add to dashboard Cite

[1] On western margins of ocean basins, such as the eastern continental shelf of the United States, rates of biological productivity are higher than in the open ocean, in spite of the mean downwelling circulation. We use a nonhydrostatic, three-dimensional, process study ocean model with idealized shelf-slope geometry, wind forcing, and tracers to explore the interplay between the circulation and the biogeochemistry of the shelf and slope; the pathways that can transport nutrients from the deep ocean and from the sediments to the surface ocean euphotic zone. Cross-shelf exchange between the open and coastal ocean is regulated by a shelf break front that separates light waters on the shelf from denser waters on the slope. The wind direction and strength influence both the position and slope of the isopycnals at the front, which become more vertical in response to northerly winds and flatten in response to southerly winds. When the wind direction oscillates between northerly and southerly, it pumps nutrient and gas-rich bottom boundary layer water up to the sea surface. Nutrients tend to accumulate in the benthic boundary layer during southerly winds and are pumped to the surface during periods of northerly winds. Stratification of the water column in summertime reduces the shelf break pump by dampening the effect of the winds on the movement of the front. When extrapolated over the northeast coast of the United States, the nutrients supplied by the shelf break pump from the open ocean to the coastal ocean are three times the estimated nitrogen delivered to the shelf from estuaries.

show abstract

Satellite and hydrographic observations of eddy‐induced shelf‐slope exchange in the northwestern Gulf of Alaska

Cited by 105 publications

References 22 publications

Offshore Transport of Shelf Water by Deep-Ocean Eddies

Offshore Transport of Shelf Water by Deep-Ocean Eddies

Regional differences in the spatial and temporal heterogeneity of oceanographic habitat used by Steller sea lions

Nutrient exchange and ventilation of benthic gases across the continental shelf break

Contact Info

Product

Resources

About