Structure, Transport, and Seasonality of the Atlantic Water Boundary Current North of Svalbard: Results From a Yearlong Mooring Array

Pérez‐Hernández, M. Dolores; Pickart, Robert S.; Torres, Daniel J.; Bahr, Frank; Sundfjord, Arild; Ingvaldsen, Randi; Renner, Angelika; Beszczynska-Möller, Agnieszka; Appen, Wilken-Jon von; Pavlov, Vladimir

doi:10.1029/2018jc014759

Cited by 38 publications

(83 citation statements)

References 45 publications

(94 reference statements)

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“…(2017) observed an AW volume transport of 2.3 ± 0.3 Sv farther east, between 21°E and 33°E. The transport estimated from a mooring array at 30°E during 2013, averaged over the open water season to be comparable to our measurements, was 2.4 ± 0.1 Sv (Pérez‐Hernández et al., 2019). We note that the definition of AW used by Pérez‐Hernández et al.…”

Section: Discussionsupporting

confidence: 81%

Structure and Transport of Atlantic Water North of Svalbard From Observations in Summer and Fall 2018

et al. 2020

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The transport of warm Atlantic Waters north of Svalbard is one of the major heat and salt sources to the Arctic Ocean. The circulation pathways and the associated heat transport influence the variability in the Arctic sea ice extent, the onset of freezing, and marine ecosystems. We present observations obtained from research cruises and an autonomous underwater glider mission in summer and fall 2018, to describe the hydrographic structure, volume transport, and circulation patterns of the warm Atlantic Water Boundary Current between 12°E and 24°E north of Svalbard. The Atlantic Water volume transport reaches a maximum of 3.0 ± 0.2 Sv in October, with an intraseasonal variability of 1 Sv (1 Sv = 106 m3 s−1). During summer and late fall, we observed an Atlantic Water recirculation flowing westward (0.1–0.2 Sv) in the outer part of the section away from the shelf break. This counter current appears to be a part of an anticyclonic circulation in the Sofia Deep. The strength of the Atlantic Water recirculation and the Atlantic Water boundary current is very sensitive to the wind stress curl: The boundary current volume transport doubled in less than a week, corresponding to a transition from strongly negative (−10−6 N m−3) to strongly positive (10−6 N m−3) wind stress curl over the Sofia Deep. A previously unknown, deep bottom‐intensified current is observed to flow parallel to the boundary current, between the 1,500 and 2,000 m isobaths. Historical data in the region support the presence of the bottom‐intensified current.

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Section: Discussionsupporting

confidence: 81%

Structure and Transport of Atlantic Water North of Svalbard From Observations in Summer and Fall 2018

et al. 2020

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“…We analyzed the conditions that led to the disruption of the AW layer observed on 15 April 2013 ( Figures 7, 12f) that stood out in the A-TWAIN time series (Pérez-Hernández et al, 2019;Renner et al, 2018). Two simultaneous features from Kvitøya trough were concurrently involved: a cyclone in the upper 300 m and below, a low-N 2 plume with density in the range of intermediate water.…”

Section: Disruption Of the Aw Layer On The 15 April 2013mentioning

confidence: 99%

Atlantic Water Modification North of Svalbard in the Mercator Physical System From 2007 to 2020

et al. 2020

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The Atlantic Water (AW) inflow through Fram Strait, largest oceanic heat source to the Arctic Ocean, undergoes substantial modifications in the Western Nansen Basin (WNB). Evaluation of the Mercator system in the WNB, using 1,500 independent temperature-salinity profiles and five years of mooring data, highlighted its performance in representing realistic AW inflow and hydrographic properties. In particular, favorable comparisons with mooring time-series documenting deep winter mixed layers and changes in AW properties led us to examine winter conditions in the WNB over the 2007-2020 period. The model helped describe the interannual variations of winter mixed layers and documented several processes at stake in modifying AW beyond winter convection: trough outflows and lateral exchange through vigorous eddies. Recently modified AW, either via local convection or trough outflows, were identified as homogeneous layers of low buoyancy frequency. Over the 2007-2020 period, two winters stood out with extreme deep mixed layers in areas that used to be ice-covered: 2017/18 over the northern Yermak Plateau-Sofia Deep; 2012/13 on the continental slope northeast of Svalbard with the coldest and freshest modified AW of the 12-year time series. The northern Yermak Plateau-Sofia Deep and continental slope areas became "Marginal Convection Zones" in 2011 with, from then on, occasionally ice-free conditions, 50-m-ocean temperatures always above 0°C and highly variable mixed layer depths and ocean-to-atmosphere heat fluxes. In the WNB where observations require considerable efforts and resources, the Mercator system proved to be a good tool to assess Atlantic Water modifications in winter. Plain Language Summary The Atlantic Water inflow through Fram Strait, largest oceanic heat source to the Arctic Ocean, undergoes severe modifications in the Western Nansen Basin in winter. We used 14 years of high-resolution ocean model simulations to identify winters with intense Atlantic Water modifications (cooling and freshening) in this region. Over the 2007-2020 period, two winters stood out with extreme deep convection events in areas that used to be ice-covered: 2017/18 over the northern Yermak Plateau; and 2012/13 on the continental slope northeast of Svalbard, with the coldest, freshest modified Atlantic Water over 2007-2020. The northern Yermak Plateau and continental slope became "Marginal Convection Zones" in 2011 as they started to occasionally exhibit open-ocean conditions in winter. In this region where observations require considerable efforts and resources, the model simulations proved to be a good tool to assess Atlantic Water modifications in winter. As the transition towards a seasonally ice-free Arctic Ocean continues, more years of extreme Atlantic Water modification can be expected.

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“…Winter mixed layers in parts of Nansen Basin now regularly reach 150 m depth (Figures 8a and 8b) and homogenize the water column down to a density of 27.85 kg•m −3 and a salinity of 34.9 g•kg −1 . Winter mixed layers of 150 m depth or more have been observed along the continental slope at different longitudes (e.g., Pérez-Hernández et al, 2019;Polyakov et al, 2017). Atlantification resulted in a salinification of the mixed layer in Nansen Basin.…”

Section: Definition Of the Base Of The Halocline Of Lhw In A Period Omentioning

confidence: 99%

The Western Eurasian Basin Halocline in 2017: Insights From Autonomous NO Measurements and the Mercator Physical System

et al. 2020

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We present the first sensor‐based profiles of the quasi‐conservative NO parameter obtained with an autonomous ice‐tethered buoy in the Arctic Ocean. Data documented the halocline in the Transpolar Drift and Nansen Basin in 2017. A NO minimum was found in the Nansen Basin on a σ‐horizon of 27.8 kg·m−3 corresponding to the lower halocline, while a lower NO minimum of 380 μM straddled the 27.4 σ‐horizon and marked the cold halocline in the Transpolar Drift. Back trajectories of water parcels encountered along the buoy drift were computed using the Mercator physical system. They suggested that waters within the NO minimum at 27.4 kg·m−3 could be traced back to the East Siberian Sea continental. These trajectories conformed with the prevailing positive phase of the Arctic Oscillation. The base of the lower halocline, at the 27.85 σ‐horizon, corresponded to the density attained in the deepest winter mixed layer north of Svalbard and cyclonically slowly advected from the slope into the central Nansen Basin. The 27.85 σ‐horizon is associated with an absolute salinity of 34.9 g·kg−1, a significantly more saline level than the 34.3 psu isohaline commonly used to identify the base of the lower halocline. This denser and more saline level is in accordance with the deeper winter mixed layers observed on the slopes of Nansen Basin in the last 10 years. A combination of simulations and NO parameter estimates provided valuable insights into the structure, source, and strength of the Arctic halocline.

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Structure, Transport, and Seasonality of the Atlantic Water Boundary Current North of Svalbard: Results From a Yearlong Mooring Array

Cited by 38 publications

References 45 publications

Structure and Transport of Atlantic Water North of Svalbard From Observations in Summer and Fall 2018

Structure and Transport of Atlantic Water North of Svalbard From Observations in Summer and Fall 2018

Atlantic Water Modification North of Svalbard in the Mercator Physical System From 2007 to 2020

The Western Eurasian Basin Halocline in 2017: Insights From Autonomous NO Measurements and the Mercator Physical System

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