Arctic Ice‐Ocean Coupling and Gyre Equilibration Observed With Remote Sensing

Dewey, Sarah R.; Morison, James H.; Kwok, R.; Dickinson, S.M.; Morison, D. H.; Andersen, R.

doi:10.1002/2017gl076229

Cited by 58 publications

(88 citation statements)

References 53 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This corresponds to a uniform Ekman pumping velocity of about 10 m/year. This is potentially an overestimate of Ekman pumping rates in light of new observational studies that incorporate satellite‐derived surface geostrophic flow (Armitage et al, ) in calculations of the ocean surface stress (Dewey et al, ; Meneghello et al, ; Zhong et al, ). However, our results do not qualitatively depend on the magnitude of the Ekman pumping, a sensitivity to which has been explored in detail in Manucharyan and Spall () and Manucharyan et al (); here we focus on highlighting the critical impacts brought by the inclusion of continental slopes.…”

Section: Idealized Bg Model With Continental Slopesmentioning

confidence: 99%

“…Hypotheses about the BG equilibration processes, among others, include (i) halocline flattening due to mesoscale eddies formed via baroclinic instability in order to release the available gravitational potential energy (APE) stored in a bowl‐shape halocline (Manucharyan & Spall, ), (ii) frictional dissipation of its geostrophic currents by rubbing against the sea ice (Dewey et al, ; Meneghello et al, ; Zhong et al, ), and (iii) a balance between vertical diffusion in the interior of the gyre and eddy fluxes from its boundaries (Spall, ). The vertical mixing hypothesis does not rely on the intensity of Ekman pumping and hence can only provide a partial explanation of the dynamics.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Critical Role of Continental Slopes in Halocline and Eddy Dynamics of the Ekman‐Driven Beaufort Gyre

Manucharyan

Isachsen

2019

JGR Oceans

View full text Add to dashboard Cite

The Beaufort Gyre (BG) is a large‐scale bathymetrically constrained circulation driven by a surface Ekman convergence that creates a bowl‐shaped halocline and stores a significant portion of the Arctic Ocean's freshwater. Theoretical studies suggest that in the gyre interior, the halocline is equilibrated by a balance between Ekman pumping and counteracting mesoscale eddy transport energized by baroclinic instability. However, the strongest anticyclonic flows occur over steep continental slopes, and, despite bathymetric slopes being known to influence baroclinic instability, their large‐scale impacts on BG halocline remain unexplored. Here we use an idealized eddy‐resolving BG model to demonstrate that the existence of continental slopes dramatically affects key gyre characteristics leading to deeper halocline, stronger anticyclonic circulation, and prolonged equilibration. Over continental slopes, the magnitude of the Eulerian mean circulation is dramatically reduced due to the Ekman overturning being compensated by the eddy momentum‐driven overturning. The eddy thickness flux overturning associated with lateral salt transport is also weakened over the slopes, indicating a reduction of eddy thickness diffusivity despite the isopycnal slopes being largest there. Using a theoretical halocline model, we demonstrate that it is the localized reduction in eddy diffusivity over continental slopes that is critical in explaining the halocline deepening and prolonged equilibration time. Our results emphasize the need for observational studies of eddy overturning dynamics over continental slopes and the development of slope‐aware mesoscale eddy parameterizations for low‐resolution climate models.

show abstract

Section: Idealized Bg Model With Continental Slopesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Critical Role of Continental Slopes in Halocline and Eddy Dynamics of the Ekman‐Driven Beaufort Gyre

Manucharyan

Isachsen

2019

JGR Oceans

View full text Add to dashboard Cite

show abstract

“…Theoretical and numerical modeling based on idealized process models have suggested that the main dynamical balance of the BG is between Ekman pumping and eddy salt fluxes arising from baroclinic instability that tend to arrest the steepening of the isohalines through lateral salt fluxes (Davis et al, ; Manucharyan et al, ). Other recent studies have shown that, when the ocean speed approaches that of the ice, the Ekman convergence can be modulated or canceled due to the resulting reduction in the ice‐ocean stress (e.g., Dewey et al, ; Meneghello, Marshall, Campin, et al, ; Meneghello, Marshall, Timmermans, & Scott, ; Zhong et al, ) in an apparent negative feedback mechanism (e.g., Meneghello, Marshall, Campin, et al, ). The balance between these three processes is established over a decadal timescale, suggesting that the variations of the BG freshwater content carry the imprint of a decade or more of the atmospheric forcing (Johnson et al, ).…”

Section: Introductionmentioning

confidence: 99%

The Beaufort Gyre Extent, Shape, and Location Between 2003 and 2014 From Satellite Observations

2019

View full text Add to dashboard Cite

The Beaufort Gyre is a significant reservoir of freshwater in the Arctic. It is thought to play a key role in regulating Arctic freshwater discharge to the North Atlantic, and in recent decades its freshwater content has increased in a time of rapid Arctic change. Despite this, its exact dynamical behavior is not fully understood. Here, we make use of an Arctic‐wide dataset of dynamic ocean topography, including data under sea ice, to characterize the time‐varying extent, shape, and location of the Beaufort Gyre. We show that the gyre expanded toward the northwest between 2003 and 2014, resulting in increased proximity to the Chukchi Plateau and Mendeleev Ridge by 2014. We find that the gyre strength and maximum dynamic ocean topography both respond readily to changes in intensity of the surface forcing, but the gyre area is additionally affected by the location of the Beaufort Sea High. This results in expansion over the Chukchi Plateau and increased asymmetry of the gyre as it becomes constrained by the shallow bathymetry. The gyre strength is correlated with the integrated surface stress on the ocean over the previous 3 months. We discuss the implications of the expansion over shallow bathymetry on gyre dynamical behavior and the potential impacts on the physical properties in the Canada Basin.

show abstract

“…While the second regime, in which u i < u g , is likely important over the seasonal cycle and during the transient response to changing surface forcings, it is an implausible equilibrium state since the large fraction of open water required for the wind stress to directly accelerate the gyre means that the sea ice is likely to be in free drift (Martin et al, ), and the Ice‐Ocean Governor will therefore be ineffective. Dewey et al () present a discussion of these regimes in the BG. Here we extend the concept to include a rigorous dynamical framework and explore the implications of this framework for the BG.…”

Section: Governoring Equationmentioning

confidence: 99%

“…This mechanism is dubbed the Ice‐Ocean Governor by analogy with mechanical governors that regulate the speed of engines and other devices through dynamical feedbacks (see, e.g., Maxwell, ). The ocean velocity has long been included when calculating the ice‐ocean stress in numerical models (see, e.g., Hibler, ), but appreciation of the importance of this effect has been very recent (Dewey et al, ; Kwok & Morison, ; Meneghello et al, ; Meneghello, Marshall, Timmermans, et al, ; Meneghello, Marshall, Campin, et al, ; Zhong et al, ) following the publication of a data set that estimates sea surface height and surface geostrophic velocity in sea ice‐covered areas (Armitage et al, ).…”

Section: Introductionmentioning

confidence: 99%

A Three‐Way Balance in the Beaufort Gyre: The Ice‐Ocean Governor, Wind Stress, and Eddy Diffusivity

et al. 2019

View full text Add to dashboard Cite

The Beaufort Gyre (BG) is a large anticyclonic circulation in the Arctic Ocean. Its strength is directly related to the halocline depth, and therefore also to the storage of freshwater. It has recently been proposed that the equilibrium state of the BG is set by the Ice‐Ocean Governor, a negative feedback between surface currents and ice‐ocean stress, rather than a balance between lateral mesoscale eddy fluxes and surface Ekman pumping. However, mesoscale eddies are present in the Arctic Ocean; it is therefore important to extend the Ice‐Ocean Governor theory to include lateral fluxes due to mesoscale eddies. Here, a nonlinear ordinary differential equation is derived that represents the effects of wind stress, the Ice‐Ocean Governor, and eddy fluxes. Equilibrium and time‐varying solutions to this three‐way balance equation are obtained and shown to closely match the output from a hierarchy of numerical simulations, indicating that the analytical model represents the processes controlling BG equilibration. The equilibration timescale derived from this three‐way balance is faster than the eddy equilibration timescale and slower than the Ice‐Ocean Governor equilibration timescales for most values of eddy diffusivity. The sensitivity of the BG equilibrium depth to changes in eddy diffusivity and the presence of the Ice‐Ocean Governor is also explored. These results show that predicting the response of the BG to changing surface forcing and sea ice conditions requires faithfully capturing the three‐way balance between the Ice‐Ocean Governor, wind stress, and eddy fluxes.

show abstract

Arctic Ice‐Ocean Coupling and Gyre Equilibration Observed With Remote Sensing

Cited by 58 publications

References 53 publications

Critical Role of Continental Slopes in Halocline and Eddy Dynamics of the Ekman‐Driven Beaufort Gyre

Critical Role of Continental Slopes in Halocline and Eddy Dynamics of the Ekman‐Driven Beaufort Gyre

The Beaufort Gyre Extent, Shape, and Location Between 2003 and 2014 From Satellite Observations

A Three‐Way Balance in the Beaufort Gyre: The Ice‐Ocean Governor, Wind Stress, and Eddy Diffusivity

Contact Info

Product

Resources

About