Vertical transport in the ocean due to sub-mesoscale structures: Impacts in the Kerguelen region

Rosso, Isabella; Hogg, Andrew McC.; Strutton, Peter G.; Kiss, Andrew E.; Matear, Richard J.; Klocker, Andreas; Sebille, Erik van

doi:10.1016/j.ocemod.2014.05.001

Cited by 71 publications

(107 citation statements)

References 39 publications

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“…Insight into submesoscale processes has, to date, largely been achieved through careful numerical simulations (Haine and Marshall 1998;Boccaletti et al 2007; Thomas et al 2008;Capet et al 2008;Ferrari 2009, 2010;Mahadevan et al 2010;Rosso et al 2014) that directly resolve the evolution of submesoscale fronts and eddies. Most, but not all of these studies, examine idealized ocean configurations, such as periodic fronts with unidirectional wind stress forcing or constant buoyancy forcing.…”

Section: Introductionmentioning

confidence: 99%

Open-Ocean Submesoscale Motions: A Full Seasonal Cycle of Mixed Layer Instabilities from Gliders

Thompson

Lazar

Buckingham

et al. 2016

Journal of Physical Oceanography

174

227

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The importance of submesoscale instabilities, particularly mixed layer baroclinic instability and symmetric instability, on upper-ocean mixing and energetics is well documented in regions of strong, persistent fronts such as the Kuroshio and the Gulf Stream. Less attention has been devoted to studying submesoscale flows in the open ocean, far from long-term, mean geostrophic fronts, characteristic of a large proportion of the global ocean. This study presents a year-long, submesoscale-resolving time series of near-surface buoyancy gradients, potential vorticity, and instability characteristics, collected by ocean gliders, that provides insight into open-ocean submesoscale dynamics over a full annual cycle. The gliders continuously sampled a 225 km 2 region in the subtropical northeast Atlantic, measuring temperature, salinity, and pressure along 292 short (;20 km) hydrographic sections. Glider observations show a seasonal cycle in near-surface stratification. Throughout the fall (September-November), the mixed layer deepens, predominantly through gravitational instability, indicating that surface cooling dominates submesoscale restratification processes. During winter (December-March), mixed layer depths are more variable, and estimates of the balanced Richardson number, which measures the relative importance of lateral and vertical buoyancy gradients, depict conditions favorable to symmetric instability. The importance of mixed layer instabilities on the restratification of the mixed layer, as compared with surface heating and cooling, shows that submesoscale processes can reverse the sign of an equivalent heat flux up to 25% of the time during winter. These results demonstrate that the openocean mixed layer hosts various forced and unforced instabilities, which become more prevalent during winter, and emphasize that accurate parameterizations of submesoscale processes are needed throughout the ocean.

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Section: Introductionmentioning

confidence: 99%

Open-Ocean Submesoscale Motions: A Full Seasonal Cycle of Mixed Layer Instabilities from Gliders

Thompson

Lazar

Buckingham

et al. 2016

Journal of Physical Oceanography

174

227

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“…It is becoming increasingly apparent that fronts, or ocean currents, can transport iron thousands of kilometres into the open ocean from iron sources upon continental shelves (De Baar et al, 1995;Planquette et al, 2007;Boyd and Ellwood, 2010;Boyd et al, 2012a;De Jong et al, 2012;Whitehouse et al, 2012;Measures et al, 2013;Klunder et al, 2014). However, high productivity at fronts in the open ocean is commonly attributed to the upwelling of nutrient enriched deep waters, rather than the horizontal advection of iron (Read et al, 2000;Measures and Vink, 2001;Moore and Abbott, 2002;Romero et al, 2006;Sokolov and Rintoul, 2007b;Boyd and Ellwood, 2010;Boyd et al, 2012a;Rosso et al, 2014). The strong currents associated with ocean fronts generate intense upwelling where these fronts cross over rough bottom topography and mid ocean ridges (Sokolov and Rintoul, 2007b;Rosso et al, 2014).…”

Section: Introductionmentioning

confidence: 99%

“…However, high productivity at fronts in the open ocean is commonly attributed to the upwelling of nutrient enriched deep waters, rather than the horizontal advection of iron (Read et al, 2000;Measures and Vink, 2001;Moore and Abbott, 2002;Romero et al, 2006;Sokolov and Rintoul, 2007b;Boyd and Ellwood, 2010;Boyd et al, 2012a;Rosso et al, 2014). The strong currents associated with ocean fronts generate intense upwelling where these fronts cross over rough bottom topography and mid ocean ridges (Sokolov and Rintoul, 2007b;Rosso et al, 2014). This upwelling is believed to be strong enough to deliver large quantities of dissolved iron to the ocean surface, from deep sources such as hydrothermal vents (Sokolov and Rintoul, 2007b;Klunder et al, 2011;Rosso et al, 2014).…”

Section: Introductionmentioning

confidence: 99%

Inferring source regions and supply mechanisms of iron in the Southern Ocean from satellite chlorophyll data

Graham

Boer

Sebille

et al. 2015

Deep Sea Research Part I: Oceanographic Research Papers

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Keywords: chlorophyll shelf sediments upwelling ocean fronts sea surface height dust glacial-interglacial cycles a b s t r a c t Primary productivity is limited by the availability of iron over large areas of the global ocean. Changes in the supply of iron to these regions could have major impacts on primary productivity and the carbon cycle. However, source regions and supply mechanisms of iron to the global oceans remain poorly constrained. Shelf sediments are considered one of the largest sources of dissolved iron to the global ocean, and a large shelf sediment iron flux is prescribed in many biogeochemical models over all areas of bathymetry shallower than 1000 m. Here, we infer the likely location of shelf sediment iron sources in the Southern Ocean, by identifying where satellite chlorophyll concentrations are enhanced over shallow bathymetry ( o1000 m). We further compare chlorophyll concentrations with the position of ocean fronts, to assess the relative role of horizontal advection and upwelling for supplying iron to the ocean surface. We show that mean annual chlorophyll concentrations are not visibly enhanced over areas of shallow bathymetry that are located more than 500 km from a coastline. Mean annual chlorophyll concentrations 4 2 mg m À 3 are only found within 50 km of a continental or island coastline. These results suggest that sedimentary iron sources only exist on continental and island shelves. Large sedimentary iron fluxes do not seem present on seamounts and submerged plateaus. Large chlorophyll blooms develop where the western boundary currents detach from the continental shelves, and turn eastward into the Sub-Antarctic Zone. Chlorophyll concentrations are enhanced along contours of sea surface height extending off the continental shelves, as shown by the trajectories of virtual water parcels in satellite altimetry data. These analyses support the hypothesis that bioavailable iron from continental shelves is entrained into western boundary currents, and advected into the Sub-Antarctic Zone along the Dynamical Subtropical Front. Our results indicate that upwelling at fronts in the open ocean is unlikely to deliver iron to the ocean surface from deep sources. Finally, we hypothesise how a reduction in sea level may have altered the distribution of shelf sediment iron sources in the Southern Ocean and increased export production over the Sub-Antarctic Zone during glacial intervals.

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“…Previous studies indicate that the existence of the Kerguelen Plateau leads to a complex regional ACC structure (e.g., Sparrow et al 1996;Park et al 2009;Rosso et al 2015), but its impacts on the basin-and global-scale ocean circulation remain unclear.…”

Section: A Steering Effect On the Accmentioning

confidence: 99%

“…The KP deflects the northern ACC front, that is, the Subantarctic Front (SAF), equatorward toward the energetic, warm, and saline Agulhas Return Current and adjacent subtropical front. The confluence of these currents leads to instabilities and the presence of high mesoscale eddy energy downstream of the plateau, which subsequently results in intense mixing and biological productivity (Gille 1997;Jayne and Marotzke 2002;Fu 2009;Lu and Speer 2010;Sallée et al 2011;Waterman et al 2013;Gille et al 2014;Rosso et al 2014). Even with these circulation patterns, it is unclear, however, whether there exists a Kerguelen Plateau effect as important as the Drake Passage effect with respect to the global ocean properties.…”

Section: Introductionmentioning

confidence: 99%

The Effect of the Kerguelen Plateau on the Ocean Circulation

Wang

Mazloff

Gille

2016

Journal of Physical Oceanography

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The Kerguelen Plateau is a major topographic feature in the Southern Ocean. Located in the Indian sector and spanning nearly 2000 km in the meridional direction from the polar to the subantarctic region, it deflects the eastward-flowing Antarctic Circumpolar Current and influences the physical circulation and biogeochemistry of the Southern Ocean. The Kerguelen Plateau is known to govern the local dynamics, but its impact on the large-scale ocean circulation has not been explored. By comparing global ocean numerical simulations with and without the Kerguelen Plateau, this study identifies two major Kerguelen Plateau effects: 1) The plateau supports a local pressure field that pushes the Antarctic Circumpolar Current northward. This process reduces the warm-water transport from the Indian to the Atlantic Ocean.2) The plateau-generated pressure field shields the Weddell Gyre from the influence of the warmer subantarctic and subtropical waters. The first effect influences the strength of the Antarctic Circumpolar Current and the Agulhas leakage, both of which are important elements in the global thermohaline circulation. The second effect results in a zonally asymmetric response of the subpolar gyres to Southern Hemisphere wind forcing.

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Vertical transport in the ocean due to sub-mesoscale structures: Impacts in the Kerguelen region

Cited by 71 publications

References 39 publications

Open-Ocean Submesoscale Motions: A Full Seasonal Cycle of Mixed Layer Instabilities from Gliders

Open-Ocean Submesoscale Motions: A Full Seasonal Cycle of Mixed Layer Instabilities from Gliders

Inferring source regions and supply mechanisms of iron in the Southern Ocean from satellite chlorophyll data

The Effect of the Kerguelen Plateau on the Ocean Circulation

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