Observations of a Submesoscale Cyclonic Filament in the Marginal Ice Zone

Appen, Wilken-Jon von; Wekerle, Claudia; Hehemann, Laura; Schourup-Kristensen, Vibe; Konrad, Christian; Iversen, Morten Hvitfeldt

doi:10.1029/2018gl077897

Cited by 50 publications

(110 citation statements)

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“…In the marginal ice zones, cyclonic eddies and filaments tend to accumulate the sea ice and anticyclonic flows repel the sea ice (Manucharyan & Thompson, ), explaining the formation of eddy‐like structures in sea ice concentration patterns seen in SAR images. The accumulation of sea ice in a cyclonic filament was also observed during an observational campaign in Fram Strait (Von Appen et al, ). Thus, SAR snapshots often contain strong signatures of ocean eddies and can be used for their detection.…”

Section: Introductionmentioning

confidence: 61%

Eddies in the Western Arctic Ocean From Spaceborne SAR Observations Over Open Ocean and Marginal Ice Zones

et al. 2019

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The Western Arctic Ocean is a host to major ocean circulation systems, many of which generate eddies that can transport water masses and corresponding tracers over long distances from their formation sites. However, comprehensive observations of critical eddy characteristics are currently not available and are limited to spatially and temporally sparse in situ observations. Here we use high-resolution spaceborne synthetic aperture radar measurements to detect eddies from their surface imprints in ice-free sea surface roughness, and in sea ice patterns throughout marginal ice zones. We provide the first estimate of eddy characteristics extending over the seasonally ice-free and marginal ice zone regions of the Western Arctic Ocean, including their locations, diameters, and monthly distribution. Using available synthetic aperture radar data, we identified over 4,000 open ocean eddies, as well as over 3,500 eddies in marginal ice zones from June to October in 2007, 2011, and 2016. Eddies range in size between 0.5 and 100 km and are frequently found over the shelf and near continental slopes but also present in the deep Canada Basin and over the Chukchi Plateau. We find that cyclonic eddies are twice more frequent compared to anticyclonic eddies at the surface, distinct from the dominating anticyclonic eddies observed at depth by in situ moorings and ice-tethered profilers. Our study supports the notion that eddies are ubiquitous in the Western Arctic Ocean even in the presence of sea ice and emphasizes the need for improved ocean observations and modeling at eddy scales. Plain Language SummaryOcean eddies play an important role in the transport of heat, salt, and pollutants over long distances from their formation sites. However, their observations in the Arctic Ocean are complex due to severe weather and sea ice cover. Here we present results of high-resolution satellite observations over the ice-free ocean and in the marginal ice zones. Detailed eddy characteristics are for the first time presented for the Western Arctic Ocean. These results provide observational evidence that eddies are ubiquitous in this Arctic region even in the presence of sea ice and emphasize the need for improved ocean observations and modeling at eddy scales. Key Points: • First account of eddies in the Western Arctic Ocean is presented based on satellite observations over open ocean and marginal ice zones • Eddies range in size between 0.5 and 100 km and are ubiquitous over deep and shelf regions of the Western Arctic Ocean • Cyclonic eddies are twice more frequent compared to anticyclones

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Section: Introductionmentioning

confidence: 61%

Eddies in the Western Arctic Ocean From Spaceborne SAR Observations Over Open Ocean and Marginal Ice Zones

et al. 2019

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“…Frontal processes are not well documented in the Arctic, but the existing studies suggest energetic turbulence and mixing at frontal systems. Von Appen et al () observed a submesoscale filament in the marginal ice zone in Fram Strait. This filament was characterized by a strong ageostrophic circulation that accumulated sea ice and had local subduction of more than 50 m day −1 , much larger than what is observed at our front (around 5 m day −1 ), impacting mixing, sea ice, and biological productivity.…”

Section: Discussionmentioning

confidence: 99%

Observations of Turbulence at a Near‐Surface Temperature Front in the Arctic Ocean

et al. 2020

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High-resolution ocean temperature, salinity, current, and turbulence data were collected at an Arctic thermohaline front in the Nansen Basin. The front was close to the sea ice edge and separated the cold and fresh surface melt water from the warm and saline mixed layer. Measurements were made on 18 September 2018, in the upper 100 m, from a research vessel and an autonomous underwater vehicle. Destabilizing surface buoyancy fluxes from a combination of heat loss to the atmosphere and cross-front Ekman transport by down-front winds reduced the potential vorticity in the upper ocean. Turbulence structure in the mixed layer was generally consistent with turbulence production through convection by heat loss to atmosphere and mechanical forcing by moderate winds. Conditions at the front were favorable for forced symmetric instability, a mechanism drawing energy from the frontal geostrophic current. A clear signature of increased dissipation from symmetric instability could not be identified; however, this instability could potentially account for the increased dissipation rates at the front location down to 40 m depth that could not be explained by the atmospheric forcing. This turbulence was associated with turbulent heat fluxes of up to 10 W m −2 , eroding the warm and cold intrusions observed between 30 and 60 m depth. A Seaglider sampled across a similar frontal structure in the same region 10 days after our survey. The submesoscale-to-turbulence-scale transitions and resulting mixing can be widespread and important in the Atlantic sector of the Arctic Ocean. Plain Language SummaryOn 18 September 2018, high-resolution temperature, salinity, current, and turbulence data were collected near a surface temperature and salinity front in the Nansen Basin north of Svalbard, within the framework of the Nansen Legacy Project. Measurements were performed from the research icebreaker Kronprins Haakon and using an autonomous underwater vehicle. The front separates warm and salty Atlantic-origin waters from cold and fresh Arctic-origin waters. Energetic turbulence in the upper 30 m was consistent with convection by heat loss to the atmosphere and mechanical forcing by moderate winds at the surface of the ocean. At the front, the conditions were favorable for forced symmetric instability, a mechanism drawing energy from the large-scale current. The contribution to turbulence from this instability could not be clearly identified but can be potentially important. Such observations linking 1-3 km scales to turbulence in the Arctic Ocean are rare. Turbulence at a front in the Arctic has consequences on the heat and nutrient transport from the slope to the deep Arctic Basin. A Seaglider sampled across a similar frontal structure in the same region end of September 2018. Observed frontal structure and mixing processes can be common in the Atlantic sector of the Arctic Ocean.

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“…In situ and satellite observations in the northwestern and the southeastern Nordic Seas suggest typical eddy radii of 10-40 km (on average 15 km) and eddy azimuthal velocities of 10 to 40 cm s −1 (Bondevik, 2011;Johannessen et al, 1983Johannessen et al, , 1987Richards & Straneo, 2015;Sandven et al, 1991;von Appen et al, 2018;Yu et al, 2017). A study of eddies in the MIZ using spaceborne synthetic aperture radar (SAR) images suggests the mean eddy radius of 30 km, which is in the range of that derived from in situ data (Bondevik, 2011).…”

Section: Introductionmentioning

confidence: 99%

Eddies in the North Greenland Sea and Fram Strait From Satellite Altimetry, SAR and High‐Resolution Model Data

et al. 2020

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In this study, we investigate eddy dynamics in the northern Greenland Sea and the Fram Strait using AVISO altimetry, spaceborne synthetic aperture radar (SAR), and Finite Element Sea ice‐Ocean Model (FESOM) high‐resolution numerical model data. In the region, eddies are thought to play an important role in the redistribution of the warmer and saltier Atlantic Water between the Arctic Ocean and the areas of deep convection in the central Greenland Sea. We found that eddies detected in AVISO and in SAR form two complementary data sets of large mesoscale eddies (with typical radii of 30–50 km) and of small mesoscale/submesoscale eddies (with typical radii of 1–5 km and not exceeding 30 km), respectively. For large mesoscale eddies, the number of cyclones and anticyclones is approximately the same, while for submesoscale eddies, cyclones are strongly dominating. The limitations and possible biases in each of the data sets are discussed and cross‐validated against FESOM results. It is noted that the most energetic eddies are concentrated along the major currents and in the northern part of the region. Eddy translations follow the mean currents in their overall cyclonic circulation around the northern Greenland Sea. A convergence of the eddies toward the Nordbukta area is detected. On seasonal time scale, a higher number of more intense mesoscale eddies is observed during winter, associated with a quasi‐simultaneous intensification of the mean currents. Model results also show an increase in the number of small eddies in spring‐early summer attributed to the decay of large eddies, while in late autumn, the opposite tendency suggests eddy merger.

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Observations of a Submesoscale Cyclonic Filament in the Marginal Ice Zone

Cited by 50 publications

References 30 publications

Eddies in the Western Arctic Ocean From Spaceborne SAR Observations Over Open Ocean and Marginal Ice Zones

Eddies in the Western Arctic Ocean From Spaceborne SAR Observations Over Open Ocean and Marginal Ice Zones

Observations of Turbulence at a Near‐Surface Temperature Front in the Arctic Ocean

Eddies in the North Greenland Sea and Fram Strait From Satellite Altimetry, SAR and High‐Resolution Model Data

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