Topographical Control of the Source‐Sink and Wind Stress‐Driven Planetary Geostrophic Circulation in a Polar Basin

Pascual-Ahuir, Estanislao Gavilan; Willmott, Andrew J.; Maqueda, Miguel Morales; Luneva, Maria

doi:10.1029/2019jc015571

Cited by 1 publication

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“…Bottom shear stresses act in the opposite direction to the current, and steady‐state Ekman flux is perpendicular to the shear stresses. In the Eurasian Arctic, where the near‐bottom circulation is cyclonic (follows f / H contours; Aksenov et al, 2011; Gavilan Pascual‐Ahuir et al, 2020), the bottom Ekman flux (BEF) is positive and offshore. If the wind circulation is anticyclonic, shear stresses applied to the ocean are negative, and the SEF is positive and offshore.…”

Section: Cascading and Cross‐shelf Fluxes Evaluationmentioning

confidence: 99%

Hotspots of Dense Water Cascading in the Arctic Ocean: Implications for the Pacific Water Pathways

et al. 2020

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We explore dense water cascading (DWC), a type of bottom-trapped gravity current, on multidecadal time scales using a pan-Arctic regional ocean-ice model. DWC is particularly important in the Arctic Ocean as the main mechanism of ventilation of interior waters when open ocean convection is blocked by strong density stratification. We identify the locations where the most intense DWC events occur and evaluate the associated cross-shelf mass, heat, and salt fluxes. We find that the modeled locations of cascading agree well with the sparse historical observations and that cascading is the dominant process responsible for cross-shelf exchange in the boundary layers. Simulated DWC fluxes of 1.3 Sv (1 Sv = 10 6 m 3 /s) in the Central Arctic are comparable to Bering Strait inflow, with associated surface and benthic Ekman fluxes of 0.85 and 0.58 Sv. With ice decline, both surface Ekman flux and DWC fluxes are increasing at a rate of 0.023 and 0.0175 Sv/year, respectively. A detailed analysis of specific cascading sites around the Beaufort Gyre and adjacent regions shows that autumn upwelling of warm and saltier Atlantic waters on the shelf and subsequent cooling and mixing of uplifted waters trigger the cascading on the West Chukchi Sea shelf break. Lagrangian particle tracking of low salinity Pacific waters originating at the surface in the Bering Strait shows that these waters are modified by brine rejection and cooling, and through subsequent mixing become dense enough to reach depths of 160-200 m. Plain Language Summary In this study we explore dense water cascading, а specific type of bottom-trapped gravity current. This current of very dense waters originates on the shelves, due to winter cooling and sea ice freezing, and slowly propagates downslope to deep waters. It is specifically important in the Arctic Ocean as the main mechanism of deep water mass formation and carbon storage. We use numerical model of the Arctic Ocean to predict preferable locations of the cascading, its intensity mass, and heat fluxes. Our results are in agreement with available very sparse observations. Our model predicts that with sea ice melting, cascading formation will accelerate. One of the crucial processes contributing to the upper ocean to abyssal exchange in the Arctic Ocean is shelf convection, also known as dense water cascading (DWC), a specific type of bottom-trapped gravity current (Shapiro et al., 2003). At high latitudes, the dense waters feeding DWC are formed on shallow shelves in the cold season due to heat loss to the atmosphere, resulting in freezing and subsequent brine injection into the water column. Preconditioning of DWC happens if the convection reaches the bottom, forming a well-mixed water mass denser than the waters downslope. In this case, dense water propagates mainly along-slope (due to Coriolis forcing) and downslope (due to bottom friction) as a bottom boundary current, mixing with the ambient waters en route. Descending DWC waters interact with bottom topographic features such as sills and canyons (Chap...

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Section: Cascading and Cross‐shelf Fluxes Evaluationmentioning

confidence: 99%