Brief communication: Impacts of a developing polynya off Commonwealth Bay,
East Antarctica, triggered by grounding of iceberg B09B

Abstract. The dramatic calving of the Mertz Glacier tongue in 2010, precipitated by the movement of iceberg B09B, reshaped the oceanographic regime across the Mertz Polynya and Commonwealth Bay, regions where high-salinity shelf water (HSSW) – the precursor to Antarctic bottom water (AABW) – is formed. Here we present post-calving observations that suggest that this reconfiguration and subsequent grounding of B09B have driven the development of a new polynya and associated HSSW production off Commonwealth Bay. Supported by satellite observations and modelling, our findings demonstrate how local icescape changes may impact the formation of HSSW, with potential implications for large-scale ocean circulation.

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Brief Communication: Evidence of a developing Polynya off Commonwealth Bay, East Antarctica, triggered by grounding of iceberg

10.5194/tc-2016-19 ◽

2016 ◽

Author(s):

Christopher J. Fogwill ◽

Erik van Sebille ◽

Eva A. Cougnon ◽

Chris S. M. Turney ◽

Steve R. Rintoul ◽

...

Keyword(s):

High Resolution ◽

Ocean Circulation ◽

Large Scale ◽

Bottom Water ◽

High Salinity ◽

Shelf Water ◽

Antarctic Bottom Water ◽

Ocean Modelling ◽

Glacier Tongue ◽

The Impact

Abstract. The dramatic calving of the Mertz Glacier Tongue in 2010, triggered by the impact of iceberg B09B, reshaped the oceanographic regime across the Mertz Polynya and Commonwealth Bay, regions where high salinity shelf water (HSSW) is formed, the precursor to Antarctic bottom water (AABW). Here we compare post-calving observations with high-resolution ocean modelling which suggest that this reconfiguration has led to the development of a new polynya off Commonwealth Bay, where HSSW production continues by the grounding of B09B. Our findings demonstrate how local changes in icescape can impact formation of AABW, with implications for large-scale ocean circulation and climate.

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Rebound of shelf water salinity in the Ross Sea

Nature Communications ◽

10.1038/s41467-019-13083-8 ◽

2019 ◽

Vol 10 (1) ◽

Cited By ~ 11

Author(s):

Pasquale Castagno ◽

Vincenzo Capozzi ◽

Giacomo R. DiTullio ◽

Pierpaolo Falco ◽

Giannetta Fusco ◽

...

Keyword(s):

Large Scale ◽

Bottom Water ◽

High Salinity ◽

Ross Sea ◽

Shelf Water ◽

Antarctic Bottom Water ◽

Sea Bottom ◽

Salinity Increase ◽

Interannual Fluctuations ◽

Observational Record

AbstractAntarctic Bottom Water (AABW) supplies the lower limb of the global overturning circulation and ventilates the abyssal ocean. In recent decades, AABW has warmed, freshened and reduced in volume. Ross Sea Bottom Water (RSBW), the second largest source of AABW, has experienced the largest freshening. Here we use 23 years of summer measurements to document temporal variability in the salinity of the Ross Sea High Salinity Shelf Water (HSSW), a precursor to RSBW. HSSW salinity decreased between 1995 and 2014, consistent with freshening observed between 1958 and 2008. However, HSSW salinity rebounded sharply after 2014, with values in 2018 similar to those observed in the mid-late 1990s. Near-synchronous interannual fluctuations in salinity observed at five locations on the continental shelf suggest that upstream preconditioning and large-scale forcing influence HSSW salinity. The rate, magnitude and duration of the recent salinity increase are unusual in the context of the (sparse) observational record.

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Ventilation of the abyss in the Atlantic sector of the Southern Ocean

Scientific Reports ◽

10.1038/s41598-021-86043-2 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Camille Hayatte Akhoudas ◽

Jean-Baptiste Sallée ◽

F. Alexander Haumann ◽

Michael P. Meredith ◽

Alberto Naveira Garabato ◽

...

Keyword(s):

Southern Ocean ◽

Bottom Water ◽

Climate Models ◽

Deep Ocean ◽

Analytical Framework ◽

Weddell Sea ◽

Global Ocean ◽

Shelf Water ◽

Antarctic Bottom Water ◽

Atlantic Sector

AbstractThe Atlantic sector of the Southern Ocean is the world’s main production site of Antarctic Bottom Water, a water-mass that is ventilated at the ocean surface before sinking and entraining older water-masses—ultimately replenishing the abyssal global ocean. In recent decades, numerous attempts at estimating the rates of ventilation and overturning of Antarctic Bottom Water in this region have led to a strikingly broad range of results, with water transport-based calculations (8.4–9.7 Sv) yielding larger rates than tracer-based estimates (3.7–4.9 Sv). Here, we reconcile these conflicting views by integrating transport- and tracer-based estimates within a common analytical framework, in which bottom water formation processes are explicitly quantified. We show that the layer of Antarctic Bottom Water denser than 28.36 kg m$$^{-3}$$ - 3 $$\gamma _{n}$$ γ n is exported northward at a rate of 8.4 ± 0.7 Sv, composed of 4.5 ± 0.3 Sv of well-ventilated Dense Shelf Water, and 3.9 ± 0.5 Sv of old Circumpolar Deep Water entrained into cascading plumes. The majority, but not all, of the Dense Shelf Water (3.4 ± 0.6 Sv) is generated on the continental shelves of the Weddell Sea. Only 55% of AABW exported from the region is well ventilated and thus draws down heat and carbon into the deep ocean. Our findings unify traditionally contrasting views of Antarctic Bottom Water production in the Atlantic sector, and define a baseline, process-discerning target for its realistic representation in climate models.

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A Numerical Investigation of Formation and Variability of Antarctic Bottom Water off Cape Darnley, East Antarctica

Journal of Physical Oceanography ◽

10.1175/jpo-d-14-0069.1 ◽

2014 ◽

Vol 44 (11) ◽

pp. 2921-2937 ◽

Cited By ~ 14

Author(s):

Yoshihiro Nakayama ◽

Kay I. Ohshima ◽

Yoshimasa Matsumura ◽

Yasushi Fukamachi ◽

Hiroyasu Hasumi

Keyword(s):

Sea Ice ◽

Continental Slope ◽

Bottom Water ◽

Heat Budget ◽

East Antarctica ◽

Salt Flux ◽

Ice Formation ◽

Minor Importance ◽

Antarctic Bottom Water ◽

Dense Water

Abstract At several locations around Antarctica, dense water is formed as a result of intense sea ice formation. When this dense water becomes sufficiently denser than the surrounding water, it descends the continental slope and forms Antarctic Bottom Water (AABW). This study presents the AABW formation off the coast of Cape Darnley [Cape Darnley Bottom Water (CDBW)] in East Antarctica, using a nonhydrostatic model. The model is forced for 8 months by a temporally uniform surface salt flux (because of sea ice formation) estimated from Advanced Microwave Scanning Radiometer for Earth Observing System (EOS; AMSR-E) data and a heat budget calculation. The authors reproduce AABW formation and associated periodic downslope flows of dense water. Descending pathways of dense water are largely determined by the topography; most dense water flows into depressions on the continental shelf, advects onto the continental slope, and is steered downslope to greater depths by the canyons. Intense sea ice formation is the most important factor in the formation of AABW off Cape Darnley, and the existence of depressions is of only minor importance for the flux of CDBW. The mechanism responsible for the periodic downslope flow of dense water is further analyzed using an idealized model setup. The period of dense water outflow is regulated primarily by the topographic beta effect.

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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.

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Freshening of Antarctic Bottom Water Off Cape Darnley, East Antarctica

Journal of Geophysical Research Oceans ◽

10.1029/2020jc016374 ◽

2020 ◽

Vol 125 (8) ◽

Author(s):

S. Aoki ◽

K. Katsumata ◽

M. Hamaguchi ◽

A. Noda ◽

Y. Kitade ◽

...

Keyword(s):

Bottom Water ◽

East Antarctica ◽

Antarctic Bottom Water

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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

<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&#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.</p>

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North Atlantic Deep Water and Antarctic Bottom Water: Their interaction and influence on the variability of the global ocean circulation

Journal of Geophysical Research Atmospheres ◽

10.1029/2002jc001335 ◽

2003 ◽

Vol 108 (C2) ◽

pp. n/a-n/a ◽

Cited By ~ 23

Author(s):

H. Brix ◽

R. Gerdes

Keyword(s):

Ocean Circulation ◽

North Atlantic ◽

Deep Water ◽

Bottom Water ◽

North Atlantic Deep Water ◽

Global Ocean ◽

Antarctic Bottom Water ◽

Global Ocean Circulation

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Assessment of the representation of Antarctic Bottom Water properties in the ECCO2 reanalysis

Ocean Science ◽

10.5194/os-10-923-2014 ◽

2014 ◽

Vol 10 (6) ◽

pp. 923-946 ◽

Cited By ~ 9

Author(s):

M. Azaneu ◽

R. Kerr ◽

M. M. Mata

Keyword(s):

Southern Ocean ◽

Ocean Circulation ◽

Bottom Water ◽

Potential Temperature ◽

World Ocean ◽

Volume Transport ◽

Weddell Sea ◽

Antarctic Bottom Water ◽

Water Properties ◽

The Absolute

Abstract. We analyzed the ability of the Estimating the Circulation and Climate of the Ocean – Phase II (ECCO2) reanalysis to represent the hydrographic properties and variability of Antarctic Bottom Water (AABW) in the Southern Ocean. We used a 20-year (1992–2011) observational database to perform comparisons of hydrographic properties and reanalysis output for the same time period. Four case studies based on current meter data and the AABW volume transport estimates previously reported in the literature were also evaluated. The opening and maintenance of an oceanic polynya in the Weddell Sea sector is observed after 2004 in the reanalysis product. Moreover, intense deep water production due to deep convection occurs, which leads to a scenario in which the Weddell Sea is flooded with AABW. For this reason, our analyses focused on the period that was identified as more reliable (1992–2004). The main Southern Ocean oceanographic features, as well as the characteristic shape of the regional potential temperature–salinity (θ–S) diagrams, are coincident with observations. However, the reanalysis output produces surface waters that are generally denser than observations due to the reproduction of waters that are generally saltier than expected, which probably resulted from the strong seasonality of sea ice concentrations. Bottom waters are warmer and less dense, while intermediate waters are statistically closest to the observations. The differences in bottom water properties are partially due to the inability of the reanalysis to properly reproduce the formation and export of dense waters from the shelf and the consequent absence of the densest AABW variety for most of the analyzed period. Despite differences in the absolute values, the upper AABW limit (γn ≥ 28.27 kg m−3) and AABW occupied area estimates are coincident with the observations in the World Ocean Circulation Experiment (WOCE) repeat sections SR2 and SR4. Moreover, the AABW volume export and current velocity variability are correlated with the observed time series in the most important region of dense water export (i.e., the Weddell Sea). Despite the consistency in terms of variability, the absolute volume transport and velocity estimates are underrepresented in all cases.

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