Climatology and decadal variability of the Ross Sea shelf waters

The World Ocean Database 2001 data located in the Ross Sea (named WOD01 and containing data in this region since 1928) are merged with recent data collected by the Italian expeditions (CLIMA dataset) in the period November 1994-February 2004 in the same area. From this extended dataset, austral summer climatologies of the main Ross Sea subsurface, intermediate and bottom water masses: High Salinity Shelf Water (HSSW), Low Salinity Shelf Water (LSSW), Ice Shelf Water (ISW) and Modified Circumpolar Deep Water (MCDW) have been drawn. The comparison between the WOD01_1994 climatologies (a subset of the WOD01 dataset until April 1994) and the CLIMA ones for the period 1994/95-2003/04 showed significant changes occurred during the decade. The freshening of the Ross Sea shelf waters which occurred during the period 1960-2000, was confirmed by our analysis in all the main water masses, even though with a spatially varying intensity. Relevant variations were found for the MCDW masses, which appeared to reduce their presence and to deepen; this can be ascribed to the very limited freshening of the MCDW core, which allowed an increased density with respect to the surrounding waters. Variations in the MCDW properties and extension could have relevant consequences, e.g. a decreased Ross Ice Shelf basal melting or a reduced supply of nutrients, and may also be indicative of a reduced thermohaline circulation within the Ross Sea. Shelf Waters (SW) having neutral density γn > 28.7 Kg m-3, which contribute to form the densest Antarctic Bottom Waters (AABW), showed a large volumetric decrease in the 1994/95-2003/04 decade, most likely as a consequence of the SW freshening.

Download Full-text

Water masses’ bacterial community structure and microbial activities in the Ross Sea, Antarctica

Antarctic Science ◽

10.1017/s0954102010000192 ◽

2010 ◽

Vol 22 (4) ◽

pp. 361-370 ◽

Cited By ~ 12

Author(s):

Mauro Celussi ◽

Andrea Bergamasco ◽

Bruno Cataletto ◽

Serena Fonda Umani ◽

Paola Del Negro

Keyword(s):

Community Structure ◽

Bacterial Community ◽

Deep Water ◽

Bacterial Community Structure ◽

Sea Water ◽

Ross Sea ◽

Water Masses ◽

Shelf Water ◽

Microbial Activities ◽

Ice Shelf

AbstractDuring the summer 2005/06, an oceanographic cruise was carried out in the Ross Sea, from Cape Adare, through the Terra Nova Bay polynya to the eastern edge of the Ross Ice Shelf. We analysed microbial activities (prokaryotic carbon production, protease, phosphatase, beta-glucosidase and lipase activity) and bacterial community structure (using Denaturing Gradient Gel Electrophoresis - DGGE) in order to establish if differences in bacterioplankton assemblages and their metabolic requirements occur within the five Ross Sea water masses: Antarctic Surface Waters (AASW), High Salinity Shelf Water (HSSW), Ice Shelf Water (ISW), Antarctic Bottom Water (AABW), Circumpolar Deep Water (CDW). Differences in activities were found between the highly active AASW and all the other water bodies. A Principal Component Analysis highlighted two main gradients: in the Cape Adare area (AASWn, CDW and AABW) higher phosphatase, lipase and glycolytic activities, increasing towards the surface, were identified, whereas in the southern sector of the basin [AASWs and (m)HSSW] higher leucine uptake and polypeptide degradation characterized the second gradient. DGGE fingerprinting showed for the first time that different water masses harboured diverse bacterial communities, highlighting the high specificity of deep water assemblages.Alpha- andGammaproteobacteriarepresented the main phylogenetic groupings in all samples and no substantial difference in the phylogenetic composition of assemblages was found between different water masses.

Download Full-text

A modelling study of the hydrographic structure of the Ross Sea

Ocean Science Discussions ◽

10.5194/osd-9-3431-2012 ◽

2012 ◽

Vol 9 (6) ◽

pp. 3431-3449 ◽

Cited By ~ 2

Author(s):

M. Tonelli ◽

I. Wainer ◽

E. Curchitser

Keyword(s):

Thermohaline Circulation ◽

Ross Sea ◽

Ocean Model ◽

Parameter Analysis ◽

Lower Limbs ◽

Shelf Water ◽

Ice Shelf ◽

Current Configuration ◽

Realistic Representation ◽

Dense Water Formation

Abstract. Dense water formation around Antarctica is recognized as one of the most important processes to climate modulation, since that is where the linkage between the upper and lower limbs of Global Thermohaline Circulation takes place. Assessing whether these processes may be affected by rapid climate changes and all the related feedbacks may be crucial to fully understand the ocean heat transport and to provide future projections. Applying the Coordinated Ocean-Ice Reference (CORE) normal year forcing we have run a 100-yr simulation using Regional Ocean Model System (ROMS) with explicit sea-ice/ice-shelf thermodynamics. The normal year consists of single annual cycle of all the data that are representative of climatological conditions over decades and can be applied repeatedly for as many years of model integration as necessary. The experiment employed a circumpolar variable resolution (1/2° to 1/24°) grid reaching less than 5 km over the inner continental shelf. With Optimum Parameter Analysis (OMP) the main Ross Sea (RS) water masses are identified: Antarctic surface water (AASW), circumpolar deep water (CDW), shelf water (SW) and ice shelf water (ISW). Current configuration allows very realistic representation, where results compare extremely well to the observations.

Download Full-text

Modelling the ocean circulation and the basal melting in the Prydz Bay-Amery Ice Shelf system

10.5194/egusphere-egu21-6425 ◽

2021 ◽

Author(s):

Jing Jin ◽

Antony J. Payne ◽

William Seviour ◽

Christopher Bull

Keyword(s):

Heat Transport ◽

Ocean Circulation ◽

Water Masses ◽

Prydz Bay ◽

Effect Of Temperature ◽

Oceanic Circulation ◽

Ice Shelf ◽

Thermodynamic Structure ◽

Amery Ice Shelf ◽

Basal Melting

The basal melting of the Amery Ice Shelf (AIS) in East Antarctica and its connections with the oceanic circulation are investigated by a regional ocean model. The simulated estimations of net melt rate over AIS from 1976 to 2005 vary from 1 to 2 m/yr depending primarily due to inflow of modified Circumpolar Deep Water (mCDW). Prydz Bay Eastern Costal Current (PBECC) and the eastern branch of Prydz Bay Gyre (PBG) are identified as two main mCDW intrusion pathways. The oceanic heat transport from both PBECC and PBG has significant seasonal variability, which is associated with the Antarctic Slope Current. The onshore heat transport has a long-lasting effect on basal melting. The basal melting is primarily driven by the inflowing water masses though a positive feedback mechanism. The intruding warm water masses destabilize the thermodynamic structure in the sub-ice shelf cavity therefore enhancing the overturning circulations, leading to further melting due to increasing heat transport. However, the inflowing saltier water masses due to sea-ice formation could offset the effect of temperature through stratifying the thermodynamic structure, then suppressing the overturning circulation and reducing the basal melting.

Download Full-text

Variability Of Thermohaline Circulation Under An Ice Shelf

Annals of Glaciology ◽

10.1017/s0260305500009009 ◽

1990 ◽

Vol 14 ◽

pp. 338

Author(s):

H.H. Hellmer

Keyword(s):

Sea Ice ◽

Boundary Conditions ◽

Thermohaline Circulation ◽

Circulation Model ◽

Melting Zone ◽

Weddell Sea ◽

Shelf Water ◽

Ice Shelf ◽

Grounding Line ◽

Ice Shelf Water

The production of Antarctic Bottom Water is mainly influenced by Ice Shelf Water, which is formed through the modification of shelf water masses under huge ice shelves. To simulate this modification a two-dimensional thermohaline circulation model has been developed for a section perpendicular to the ice-shelf edge. Hydrographic data from the Filchner Depression enter into the model as boundary conditions. In the outflow region they also serve as a verification of model results. The standard solution reveals two circulation cells. The dominant one transports shelf water near the bottom toward the grounding line, where it begins to ascend along the inclined ice shelf. The contact with the ice shelf causes melting with a maximum rate of 1.5 m a−1 at the grounding line. Freezing and therefore the accumulation of “sea ice” at the bottom of the ice shelf occurs at the end of the melting zone at a rate on the order of 0.1 ma−1. Both rates are comparable with values estimated or predicted by models concerning ice-shelf dynamics. As one example of model sensitivity to changing boundary conditions, a higher sea-ice production in the southern Weddell Sea, as might be expected for a general climatic cooling event, is assumed. The resultant decrease/ increase in temperature/salinity of the inflow (Western Shelf Water) reduces the circulation under the ice shelf and therefore the outflow of Ice Shelf Water by 40%. The maximum melting and freezing rate decreases by 0.1 ma−1 and 0.01 m a−1, respectively. and the freezing zone shifts toward the grounding line by 100 km. In general the intensity of the circulation cells, the characteristics of Ice Shelf Water, the distribution of melting and freezing zones and the melting and freezing rates differ from the standard results with changing boundary conditions. These are the temperature and salinity of the inflow, the surface temperature at the top, and the extension and morphology of the ice shelf.

Download Full-text

Modelling the ocean circulation beneath the Ross Ice Shelf

Antarctic Science ◽

10.1017/s0954102003001019 ◽

2003 ◽

Vol 15 (1) ◽

pp. 13-23 ◽

Cited By ~ 58

Author(s):

DAVID M. HOLLAND ◽

STANLEY S. JACOBS ◽

ADRIAN JENKINS

Keyword(s):

Ocean Circulation ◽

General Circulation ◽

Ross Sea ◽

Circulation Model ◽

Ocean General Circulation Model ◽

Shelf Water ◽

Ice Shelf ◽

Ross Ice Shelf ◽

The North ◽

Ice Shelf Water

We applied a modified version of the Miami isopycnic coordinate ocean general circulation model (MICOM) to the ocean cavity beneath the Ross Ice Shelf to investigate the circulation of ocean waters in the sub-ice shelf cavity, along with the melting and freezing regimes at the base of the ice shelf. Model passive tracers are utilized to highlight the pathways of waters entering and exiting the cavity, and output is compared with data taken in the cavity and along the ice shelf front. High Salinity Shelf Water on the western Ross Sea continental shelf flows into the cavity along the sea floor and is transformed into Ice Shelf Water upon contact with the ice shelf base. Ice Shelf Water flows out of the cavity mainly around 180°, but also further east and on the western side of McMurdo Sound, as observed. Active ventilation of the region near the ice shelf front is forced by seasonal variations in the density structure of the water column to the north, driving rapid melting. Circulation in the more isolated interior is weaker, leading to melting at deeper ice and refreezing beneath shallower ice. Net melting over the whole ice shelf base is lower than other estimates, but is likely to increase as additional forcings are added to the model.

Download Full-text

Ice Production in Ross Ice Shelf Polynyas during 2017–2018 from Sentinel–1 SAR Images

Remote Sensing ◽

10.3390/rs12091484 ◽

2020 ◽

Vol 12 (9) ◽

pp. 1484 ◽

Cited By ~ 2

Author(s):

Liyun Dai ◽

Hongjie Xie ◽

Stephen F. Ackley ◽

Alberto M. Mestas-Nuñez

Keyword(s):

Thermohaline Circulation ◽

Ross Sea ◽

Passive Microwave ◽

Ice Shelf ◽

High Salinity Water ◽

Ross Ice Shelf ◽

Coarse Spatial Resolution ◽

Salinity Water ◽

Ice Production ◽

Microwave Data

High sea ice production (SIP) generates high-salinity water, thus, influencing the global thermohaline circulation. Estimation from passive microwave data and heat flux models have indicated that the Ross Ice Shelf polynya (RISP) may be the highest SIP region in the Southern Oceans. However, the coarse spatial resolution of passive microwave data limited the accuracy of these estimates. The Sentinel-1 Synthetic Aperture Radar dataset with high spatial and temporal resolution provides an unprecedented opportunity to more accurately distinguish both polynya area/extent and occurrence. In this study, the SIPs of RISP and McMurdo Sound polynya (MSP) from 1 March–30 November 2017 and 2018 are calculated based on Sentinel-1 SAR data (for area/extent) and AMSR2 data (for ice thickness). The results show that the wind-driven polynyas in these two years occurred from the middle of March to the middle of November, and the occurrence frequency in 2017 was 90, less than 114 in 2018. However, the annual mean cumulative SIP area and volume in 2017 were similar to (or slightly larger than) those in 2018. The average annual cumulative polynya area and ice volume of these two years were 1,040,213 km2 and 184 km3 for the RSIP, and 90,505 km2 and 16 km3 for the MSP, respectively. This annual cumulative SIP (volume) is only 1/3–2/3 of those obtained using the previous methods, implying that ice production in the Ross Sea might have been significantly overestimated in the past and deserves further investigations.

Download Full-text

Variability in high-salinity shelf water production in the Terra Nova Bay polynya, Antarctica

Ocean Science ◽

10.5194/os-16-373-2020 ◽

2020 ◽

Vol 16 (2) ◽

pp. 373-388 ◽

Cited By ~ 1

Author(s):

Seung-Tae Yoon ◽

Won Sang Lee ◽

Craig Stevens ◽

Stefan Jendersie ◽

SungHyun Nam ◽

...

Keyword(s):

High Salinity ◽

Ross Sea ◽

Coastal Region ◽

Shelf Water ◽

Antarctic Bottom Water ◽

Ice Shelf ◽

Terra Nova Bay ◽

Salinity Variability ◽

Salinity Increase ◽

Terra Nova

Abstract. Terra Nova Bay in Antarctica is a formation region for high-salinity shelf water (HSSW), which is a major source of Antarctic Bottom Water. Here, we analyze spatiotemporal salinity variability in Terra Nova Bay with implications for the local HSSW production. The salinity variations in the Drygalski Basin and eastern Terra Nova Bay near Crary Bank in the Ross Sea were investigated by analyzing hydrographic data from instrumented moorings, vessel-based profiles, and available wind and sea-ice products. Near-bed salinity in the eastern Terra Nova Bay (∼660 m) and Drygalski Basin (∼1200 m) increases each year beginning in September. Significant salinity increases (>0.04) were observed in 2016 and 2017, which is likely related to active HSSW formation. According to velocity data at identical depths, the salinity increase from September was primarily due to advection of the HSSW originating from the coastal region of the Nansen Ice Shelf. In addition, we show that HSSW can also be formed locally in the upper water column (<300 m) of the eastern Terra Nova Bay through convection supplied by brine from the surface, which is related to polynya development via winds and ice freezing. While the general consensus is that the salinity of the HSSW was decreasing from 1995 to the late 2000s in the region, the salinity has been increasing since 2016. In 2018, it returned to values comparable to those in the early 2000s.

Download Full-text

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

10.5194/egusphere-egu2020-6108 ◽

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

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.

Download Full-text

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

10.5194/egusphere-egu2020-10194 ◽

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

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&#176;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.

Download Full-text

A model for the spreading and sinking of the Deep Ice Shelf Water in the Ross Sea

Antarctic Science ◽

10.1017/s0954102003001020 ◽

2003 ◽

Vol 15 (1) ◽

pp. 25-30 ◽

Cited By ~ 14

Author(s):

ANGELO RUBINO ◽

GIORGIO BUDILLON ◽

STEFANO PIERINI ◽

GIANCARLO SPEZIE

Keyword(s):

Ross Sea ◽

Deep Ocean ◽

Ocean Dynamics ◽

Shelf Water ◽

Density Structure ◽

Ice Shelf ◽

Ice Shelf Water ◽

Realistic Topography ◽

Good Agreement

Spreading and sinking of the Deep Ice Shelf Water (DISW) in the Ross Sea are analysed using in situ observations and the results of a nonlinear, reduced gravity, layered numerical model, which is able to simulate the motion of a bottom trapped current over realistic topography. The model is forced by prescribing thickness and density of the DISW layer at the southern model boundary as well as ambient density stratification above the DISW layer. This density structure is imposed using hydrographic data acquired by the Italian PNRA-CLIMA project. In the model water of the quiescent ambient ocean is allowed to entrain in the active deep layer due to a simple entrainment parameterization. The importance of forcing the model with a realistic ambient density is demonstrated by carrying out a numerical simulation using an idealized ambient density. In a more realistic simulation the path and the density structure of the DISW vein flowing over the Challenger Basin are obtained and are found to be in good agreement with data. It is found that entrainment, which is particularly active in regions of strong topographic variation, significantly influences the pattern followed by the DISW layer. The evolution of the DISW layer beyond the continental shelf, i.e., in a region where the paucity of experimental data does not allow for a detailed description of the deep ocean dynamics, is also investigated.

Download Full-text