scholarly journals Eddy-Driven Exchange between the Open Ocean and a Sub–Ice Shelf Cavity

2013 ◽  
Vol 43 (11) ◽  
pp. 2372-2387 ◽  
Author(s):  
Marius Årthun ◽  
Paul R. Holland ◽  
Keith W. Nicholls ◽  
Daniel L. Feltham
Keyword(s):  
Water Mass ◽  
High Salinity ◽  
Open Ocean ◽  
Weddell Sea ◽  
Buoyancy Flux ◽  
Ice Shelf ◽  
Ice Production ◽  
Surface Buoyancy ◽  
Frontal Instability ◽  
Surface Buoyancy Flux

Abstract The exchange between the open ocean and sub–ice shelf cavities is important to both water mass transformations and ice shelf melting. Here, the authors use a high-resolution (500 m) numerical model to investigate to which degree eddies produced by frontal instability at the edge of a polynya are capable of transporting dense high-salinity shelf water (HSSW) underneath an ice shelf. The applied surface buoyancy flux and ice shelf geometry is based on Ronne Ice Shelf in the southern Weddell Sea, an area of intense wintertime sea ice production where a flow of HSSW into the cavity has been observed. Results show that eddies are able to enter the cavity at the southwestern corner of the polynya where an anticyclonic rim current intersects the ice shelf front. The size and time scale of simulated eddies are in agreement with observations close to the Ronne Ice Front. The properties and strength of the inflow are sensitive to the prescribed total ice production, flushing the ice shelf cavity at a rate of 0.2–0.4 × 106 m3 s−1 depending on polynya size and magnitude of surface buoyancy flux. Eddy-driven HSSW transport into the cavity is reduced by about 50% if the model grid resolution is decreased to 2–5 km and eddies are not properly resolved.

Attenuated carbon sequestration by Weddell Sea dense waters over the 21st century – an assessment with FESOM-REcoM

2021 ◽  
Author(s):  
Cara Nissen ◽  
Ralph Timmermann ◽  
Mario Hoppema ◽  
Judith Hauck
Keyword(s):  
Carbon Sequestration ◽  
Sea Ice ◽  
Continental Shelf ◽  
Bottom Water ◽  
Water Mass ◽  
Weddell Sea ◽  
Ice Shelf ◽  
Deep Waters ◽  
Water Formation ◽  
Water Mass Transformation

<p>Deep and bottom water formation regions have long been recognized to be efficient vectors for carbon transfer to depth, leading to carbon sequestration on time scales of centuries or more. Precursors of Antarctic Bottom Water (AABW) are formed on the Weddell Sea continental shelf as a consequence of buoyancy loss of surface waters at the ice-ocean or atmosphere-ocean interface, which suggests that any change in water mass transformation rates in this area affects global carbon cycling and hence climate. Many of the models previously used to assess AABW formation in present and future climates contained only crude representations of ocean-ice shelf interaction. Numerical simulations often featured spurious deep convection in the open ocean, and changes in carbon sequestration have not yet been assessed at all. Here, we present results from the global model FESOM-REcoM, which was run on a mesh with elevated grid resolution in the Weddell Sea and which includes an explicit representation of sea ice and ice shelves. Forcing this model with ssp585 scenario output from the AWI Climate Model, we assess changes over the 21<sup>st</sup> century in the formation and northward export of dense waters and the associated carbon fluxes within and out of the Weddell Sea. We find that the northward transport of dense deep waters (σ<sub>2</sub>>37.2 kg m<sup>-3</sup> below 2000 m) across the SR4 transect, which connects the tip of the Antarctic Peninsula with the eastern Weddell Sea, declines from 4 Sv to 2.9 Sv by the year 2100. Concurrently, despite the simulated continuous increase in surface ocean CO<sub>2</sub> uptake in the Weddell Sea over the 21<sup>st</sup> century, the carbon transported northward with dense deep waters declines from 3.5 Pg C yr<sup>-1</sup> to 2.5 Pg C yr<sup>-1</sup>, demonstrating the dominant role of dense water formation rates for carbon sequestration. Using the water mass transformation framework, we find that south of SR4, the formation of downwelling dense waters declines from 3.5 Sv in the 1990s to 1.6 Sv in the 2090s, a direct result of the 18% lower sea-ice formation in the area, the increased presence of modified Warm Deep Water on the continental shelf, and 50% higher ice shelf basal melt rates. Given that the reduced formation of downwelling water masses additionally occurs at lighter densities in FESOM-REcoM in the 2090s, this will directly impact the depth at which any additional oceanic carbon uptake is stored, with consequences for long-term carbon sequestration.</p>

Intermittent freeze-melt pattern detected at the base of the Ronne Ice Shelf

2020 ◽  
Author(s):  
Irena Vankova ◽  
Keith Nicholls
Keyword(s):  
Water Mass ◽  
High Salinity ◽  
Shelf Water ◽  
Ice Shelf ◽  
Time Period ◽  
Show Evidence ◽  
Phase Sensitive ◽  
Basal Melting

<p>High salinity shelf water (HSSW) is a water mass that drives melting at the Ronne Ice Shelf, entering the sub ice shelf cavity at the western end of the ice front. To monitor the rate of ice shelf basal melting along the path of assumed HSSW inflow, a phase-sensitive radar (ApRES) was deployed and it sampled autonomously for over two years. Although the site is found to melt on average, the data show evidence of freezing occurring intermittently throughout the observed time period. Here we systematically investigate oceanographic processes that could give rise to these observations. Further, we address the question of whether ApRES can be used to quantify the rate of basal freezing.</p>

scholarly journals Water Mass Characteristics and Distribution Adjacent to Larsen C Ice Shelf, Antarctica

2020 ◽  
Author(s):  
Katherine Hutchinson ◽  
Julie Deshayes ◽  
Jean-Baptiste Sallee ◽  
Julian Dowdeswell ◽  
Casimir de Lavergne ◽  
...  
Keyword(s):  
Continental Shelf ◽  
Ocean Circulation ◽  
Deep Water ◽  
Water Mass ◽  
Heat Content ◽  
Weddell Sea ◽  
Global Ocean ◽  
Spatial And Temporal Variability ◽  
Ice Shelf ◽  
Shed Light

<p>The physical oceanographic environment, water mass mixing and transformation in the area adjacent to Larsen C Ice Shelf (LCIS) are investigated using hydrographic data collected during the Weddell Sea Expedition 2019. The results shed light on the ocean conditions adjacent to a thinning LCIS, on a continental shelf that is a source region for the globally important water mass, Weddell Sea Deep Water (WSDW). Modified Weddell Deep Water (MWDW), a comparatively warmer water mass of circumpolar origin, is identified on the continental shelf and is observed to mix with local shelf waters, such as Ice Shelf Water (ISW), which is a precursor of WSDW. Oxygen measurements enable the use of a linear mixing model to quantify contributions from source waters revealing high levels of mixing in the area, with much spatial and temporal variability. Heat content anomalies indicate an introduction of heat, presumed to be associated with MWDW, into the area via Jason Trough. Furthermore, candidate parent sources for ISW are identified in the region, indicating the potential for the circulation of continental shelf waters into the ice shelf cavity. This highlights the possibility that offshore climate signals are conveyed under LCIS. ISW is observed within Jason Trough, likely exiting the sub-ice shelf cavity en route to the Slope Current. This onshore-offshore flux of water masses links the region of the Weddell Sea adjacent to northern LCIS to global ocean circulation and Bottom Water characteristics via its contribution to ISW and hence WSDW properties. </p><p>What remains to be clarified is whether MWDW found in Jason Trough has a direct impact on basal melting and thus thinning of LCIS. More observations are required to investigate this, in particular direct observations of ocean circulation in Jason Trough and underneath LCIS. Modelling experiments could also shed light on this, and so preliminary results based on NEMO global simulations explicitly representing the circulation in under-ice shelf seas, will be presented. </p>

scholarly journals Scaling Laws for the Heterogeneously Heated Free Convective Boundary Layer

2014 ◽  
Vol 71 (11) ◽  
pp. 3975-4000 ◽  
Author(s):  
Chiel C. van Heerwaarden ◽  
Juan Pedro Mellado ◽  
Alberto De Lozar
Keyword(s):  
Boundary Layer ◽  
Kinetic Energy ◽  
Convective Boundary Layer ◽  
Scaling Laws ◽  
Fixed Ratio ◽  
Buoyancy Flux ◽  
Convective Boundary ◽  
Optimal State ◽  
Surface Buoyancy ◽  
Surface Buoyancy Flux

Abstract The heterogeneously heated free convective boundary layer (CBL) is investigated by means of dimensional analysis and results from large-eddy simulations (LES) and direct numerical simulations (DNS). The investigated physical model is a CBL that forms in a linearly stratified atmosphere heated from the surface by square patches with a high surface buoyancy flux. Each simulation has been run long enough to show the formation of a peak in kinetic energy, corresponding to the “optimal” heterogeneity size with strong secondary circulations, and the subsequent transition into a horizontally homogeneous CBL. Scaling laws for the time of the optimal state and transition and for the vertically integrated kinetic energy (KE) have been developed. The laws show that the optimal state and transition do not occur at a fixed ratio of the heterogeneity size to the CBL height. Instead, these occur at a higher ratio for simulations with increasing heterogeneity sizes because of the development of structures in the downward-moving air that grow faster than the CBL thickness. The moment of occurrence of the optimal state and transition are strongly related to the heterogeneity amplitude: stronger amplitudes result in an earlier optimal state and a later transition. Furthermore, a decrease in patch size combined with a compensating increase in patch surface buoyancy flux to maintain the energy input results in decreasing KE and a later transition. The simulations suggest that a CBL with a heterogeneity size smaller than the initial CBL height has less entrainment than a horizontally homogeneous CBL, whereas one with a larger heterogeneity size has more.

A recent update on the circulation and water masses around the Filchner and Ronne ice shelves in the southern Weddell Sea

2020 ◽  
Author(s):  
Markus Janout ◽  
Hartmut Hellmer ◽  
Tore Hattermann ◽  
Svein Osterhus ◽  
Lucrecia Stulic ◽  
...  
Keyword(s):  
Sea Ice ◽  
Ocean Circulation ◽  
Large Scale ◽  
Austral Summer ◽  
Weddell Sea ◽  
Shelf Water ◽  
Ice Shelf ◽  
Present Context ◽  
The Stability ◽  
Ice Production

<p>The Filchner and Ronne ice sheets (FRIS) compose the second largest contiguous ice sheet on the Antarctic continent. Unlike at several other Antarctic glaciers, basal melt rates at FRIS are comparatively low, as cold and dense waters presently dominate the wide southern Weddell Sea (WS) continental shelf and effectively block out any significant inflow of warmer ocean waters. We revisited the southern WS shelf in austral summer 2018 during Polarstern expedition PS111 with detailed hydrographic and tracer measurements along both the Ronne and Filchner ice fronts. The hydrography along FRIS was characterized by near-freezing high salinity shelf water (HSSW) in front of Ronne, and a striking dominance of ice shelf water (ISW) in Filchner Trough. The cold (-2.2°C) and fresher (34.6) ISW was formed by the interaction of Ronne-sourced HSSW with the ice shelf base. The strong dominance of ISW in Filchner Trough indicates a recently enhanced circulation below FRIS, likely fueled by enhanced sea ice production in the southwestern WS. We view these recent observations in a multidecadal (1973-present) context, contrast the two dominant circulation modes below FRIS, and discuss the importance of sea ice formation and large-scale sea level pressure patterns for the stability of the ocean circulation and basal melt rates underneath FRIS.</p>

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