Hydrogen and oxygen isotope studies on the McMurdo Ice Shelf, Antarctica

Stewart, M. K.

doi:10.1080/00288306.1975.10426346

Cited by 15 publications

(7 citation statements)

References 24 publications

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“…Preferential removal of H 2 16 O during evaporative concentration of seawater results in 18 O enrichment of the brine (Craig and Gordon, 1965). Although there is little fractionation associated with sea ice formation, mirabilite precipitation is known to cause 18 O depletion in the residual brine (Stewart, 1974).…”

Section: Discussionmentioning

confidence: 99%

Cryogenic origin for brine in the subsurface of southern McMurdo Sound, Antarctica

Frank

Gui

2010

Geology

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Sampling of interstitial fl uids during deep coring in southern McMurdo Sound, Antarctica,\ud revealed the presence of seawater-sourced, hypersaline brine at depths >200 m below the seafl\ud oor. Na-Cl-Br and SO4-Cl-Br relationships are consistent with a concentration mechanism\ud that involves the removal of pure H2O as ice and precipitation of mirabilite (Na2SO4·10H2O)\ud during progressive freezing of seawater. The brine is in Neogene subglacial, glacimarine, and\ud marine facies that record advance and retreat of glaciers through the Ross Sea embayment.\ud In this environment, sea ice formation in semi-isolated marine basins that occupied fl exural\ud troughs along ice sheet margins produced dense brines that sank and infi ltrated the permeable\ud subglacial sediment. Repeated cycles of glacial advance and retreat provided multiple\ud opportunities for batches of seawater to be transformed into brine that now is in the subsurface\ud of southern McMurdo Sound. Results demonstrate the feasibility of brine formation via\ud seawater freezing and attest to the potential of a cryogenic origin for subsurface brines in\ud high-latitude regions of the Northern Hemisphere, as proposed by some workers

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Section: Discussionmentioning

confidence: 99%

Cryogenic origin for brine in the subsurface of southern McMurdo Sound, Antarctica

Frank

Gui

2010

Geology

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“…The salinity of sea ice was determined as 5.0 ± 1.1 [e.g., Eicken , ], and the δ 18 O as 2.05 ± 0.20‰ [e.g., Melling and Moore , ], the latter from simple extrapolation to the sea ice salinity along the melt‐freeze line from the winter water values; notwithstanding that there are large uncertainties in sea ice composition and interannual variability. The “meteoric” component was set to −30‰, based on the likely value for the deep portion of continental ice in the surrounding area [e.g., Stewart , ; Dansgaard et al ., ]. The effect of local precipitation on the “meteoric” component was not considered, assuming that the amount is relatively small and that snow on sea ice tends to drift away from the shelf region.…”

Section: Discussionmentioning

confidence: 99%

Changes in water properties and flow regime on the continental shelf off the Adélie/George VLand coast, East Antarctica, after glacier tongue calving

et al. 2017

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Oceanic changes before and after the relocation of iceberg B9B and calving of the Mertz Glacier Tongue (MGT) in February 2010 are examined on the continental shelf off the Adélie Land/George V Land coast, East Antarctica. Summer hydrographic observations, including stable oxygen isotope ratio (δ18O), in 2001/2008 and 2011/2015 and results of a numerical model are used. Along the western flank of the MGT, temperature decreased between 2001 and 2015 for most of the water column in the Adélie Depression. δ18O generally decreased, especially at the MGT draft depths on the northern side. West of the MGT, temperature, salinity, and δ18O decreased in the intermediate layer. East of the MGT, in contrast, temperature increased between 2001 and 2011 at intermediate depths, salinity increased in the intermediate and deep layers, and δ18O slightly decreased in the deep layer but did not change much around 300 dbar. The numerical experiment exhibits a change in ocean circulation, revealing an increase in modified Circumpolar Deep Water (mCDW) inflow in the east and a decrease in the west. The contrasting changes in mCDW intrusion are consistent between the observations and numerical model, and are indicative of the effect of removal of the ice barriers. The contrast is overlain by overall decreases in salinity and δ18O, which suggests an increase in the continental meltwater fraction of 5–20% and might reveal a wide‐ranging influence from West Antarctica. The oxygen isotope ratio is, hence, effective in monitoring the increase in continental melt over the Antarctic shelf.

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“…Fractionation occurs with the loss of SO: and someNa+ through the deposition of mirabilite with other elements retaining their sea water ratios to C1-(Cragin et al 1986). The brines originate through lateral infiltration of sea water into firn ice at the shelf front or along tide cracks, and therefore may be responsible for mirabilite near White Island (Stewart 1975). Brady & Batts (1981) suggested that mirabilite beds near Black Island were precipitated at the surface from sub-ice shelf sea water brines which had moved to the surface through tide cracks in response to ice shelf grounding.…”

Section: Terrain Considerationsmentioning

confidence: 99%

The chemical composition of glacial melt water ponds and streams on the McMurdo Ice Shelf, Antarctica

1994

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Melt waters cover c. 20% of the McMurdo Ice Shelf during the austral summer. The streams, ponds, and lakes up to 104 m2 in area occur in two types of terrain systems with differing morphological, chemical, and biological characteristics: pinnacled ice (PI) areas with sparse sediment cover, low relief, and little biomass; and ice-cored moraine (ICM) areas with 10–20 cm sediment cover, hummocky topography with up to 20 m relief, occasional mirabilite deposits, and dense benthic cyanobacterial mats. Pond water composition in the two areas is markedly different. PI area melt waters have low salinities, <2270 mg 1−1 total dissolved salts (TDS), and near neutral pH, mean = 7.8. The chemical composition of PI waters closely follows that of diluted sea water, suggesting that the release of ions from the sea ice matrix of the ice shelf is the major solute source. In contrast, ICM area melt waters have a wide range of salinities, up to 60 400 mg 1−1 TDS and alkaline pH, mean = 9.3. The chemical composition in c. 40% of the ICM ponds investigated did not resemble that of sea water, but had higher relative abundances of SO2−4, Na+, K+ and Ca2+. Leaching of local salt deposits, particularly mirabilite, weathering of surficial sediments, and morphological features promoting closed-basin brine evolution are possible contributing factors to the enrichments.

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Hydrogen and oxygen isotope studies on the McMurdo Ice Shelf, Antarctica

Cited by 15 publications

References 24 publications

Cryogenic origin for brine in the subsurface of southern McMurdo Sound, Antarctica

Cryogenic origin for brine in the subsurface of southern McMurdo Sound, Antarctica

Changes in water properties and flow regime on the continental shelf off the Adélie/George VLand coast, East Antarctica, after glacier tongue calving

The chemical composition of glacial melt water ponds and streams on the McMurdo Ice Shelf, Antarctica

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