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Biogeosciences An interactive open-access journal of the European Geosciences Union
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Volume 15, issue 12 | Copyright

Special issue: Progress in quantifying ocean biogeochemistry – in honour...

Biogeosciences, 15, 3779-3794, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 21 Jun 2018

Research article | 21 Jun 2018

What fraction of the Pacific and Indian oceans' deep water is formed in the Southern Ocean?

James W. B. Rae1 and Wally Broecker2 James W. B. Rae and Wally Broecker
  • 1School of Earth & Environmental Sciences, Irvine Building, University of St. Andrews, St. Andrews, KY16 9AL, UK
  • 2Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W/P.O. Box 1000, Palisades, NY 10964, USA

Abstract. In this contribution we explore constraints on the fractions of deep water present in the Indian and Pacific oceans which originated in the northern Atlantic and in the Southern Ocean. Based on PO4* we show that if ventilated Antarctic shelf waters characterize the Southern contribution, then the proportions could be close to 50–50. If instead a Southern Ocean bottom water value is used, the Southern contribution is increased to 75%. While this larger estimate may best characterize the volume of water entering the Indo-Pacific from the Southern Ocean, it contains a significant portion of entrained northern water. We also note that ventilation may be highly tracer dependent: for instance Southern Ocean waters may contribute only 35% of the deep radiocarbon budget, even if their volumetric contribution is 75%. In our estimation, the most promising approaches involve using CFC-11 to constrain the amount of deep water formed in the Southern Ocean. Finally, we highlight the broad utility of PO4* as a tracer of deep water masses, including descending plumes of Antarctic Bottom Water and large-scale patterns of deep ocean mixing, and as a tracer of the efficiency of the biological pump.

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The deep ocean is the major store of heat and carbon in Earth's surface environment and thus has a major impact on climate. Waters that fill the deep ocean come from the North Atlantic and the Southern Ocean, but there is debate on their relative importance. Here we reconcile previous estimates using deep sea phosphate and oxygen data. We show that although a large volume of deep water comes from the south, this does not spend enough time in the southern surface to fully exchange heat and CO2.
The deep ocean is the major store of heat and carbon in Earth's surface environment and thus has...