Excess helium and neon in the southeast Pacific: Tracers for glacial meltwater

Publication Type  Journal Article
Year of Publication  2002
Authors  Hohmann, R.; Schlosser, P.; Jacobs, S.; Ludin, A.; Weppernig, R.
Journal Title  Journal of Geophysical Research-Oceans
Volume  107
Issue  C11
Pages  -
Journal Date  Nov
ISBN Number  0148-0227
Accession Number  ISI:000180570400019
Key Words  deep-water formation; antarctic ice-sheet; weddell sea; tritium; circulation; gases; ocean
Abstract  

[1] We analyze helium (He) and neon (Ne) isotope data sets from the southeast Pacific sector of the Southern Ocean collected in 1992 and 1994 and describe a new method to estimate glacial meltwater fluxes independent of previous approaches. The waters sampled during these cruises reveal large atmospheric He and Ne excess concentrations in the upper 500 m that are derived predominantly from the dissolution of air contained in glacial ice during melting underneath and at the front of floating ice shelves at elevated hydrostatic pressure. On the stations sampled, the meltwater fractions are largest near the northern and southern ice shelf fronts of George VI Ice Shelf (1.5-2.5%), consistent with prior inferences from delta(18)O. The inventories of He-4 and Ne with local glacial meltwater origin south of 70degreesS between 210degreesE and 295degreesE are (2.5 +/- 0.7) 10(11) cm(3) STP He-4 and (7.9 +/- 2.7) 10(11) cm(3) STP Ne, respectively. The associated meltwater volumes are 430 +/- 120 Gt for He-4 and 400 +/- 140 Gt for Ne. For an estimated seawater residence time of 2 years on the continental shelf, the amounts of glacial meltwater translate into bulk melting rates of 215 +/- 170 Gt yr(-1) for He-4 and 200 +/- 170 Gt yr(-1) for Ne. The values derived from He-4 are expected to be larger than those obtained from Ne because of the terrigenic He component, which accounts for 10-15% of the He excess in this region. Our regional melting rate of 200-215 Gt yr(-1) is comparable to a prior estimate but subject to uncertainties resulting from the station distribution, the air-sea gas exchange, and the estimate of the net transport through the study region.

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URL  <Go to ISI>://000180570400019
DOI  Doi 10.1029/2000jc000378