Southern Ocean frontal structure and sea-ice formation rates revealed by elephant seals

doi:10.1073/pnas.0800790105

Southern Ocean frontal structure and sea-ice formation rates revealed by elephant seals

^aUnité Scientifique du Muséum 402/Laboratoire d'Océanographie et du Climat: Expérimentation et Approches Numériques, Département Milieux et Peuplements Aquatiques, Muséum National d'Histoire Naturelle, 43 rue Cuvier, 75231 Paris Cedex 05, France;
^cAntarctic Wildlife Research Unit, School of Zoology, University of Tasmania, P.O. Box 252-05, Hobart TAS 7001, Australia;
^dWealth from Oceans National Research Flagship and Antarctic Climate and Ecosystems Cooperative Research Centre, Commonwealth Scientific and Industrial Research Organization, Hobart TAS 7001, Australia;
^gNERC Sea Mammal Research Unit, Gatty Marine Laboratory, University of St. Andrews, St. Andrews, Fife KY16 8LB, United Kingdom;
^fCenter for Ocean Health, Institute of Marine Sciences, Long Marine Laboratory, University of California, 100 Shaffer Road, Santa Cruz, CA 95060;
^hCenter for Marine Science, University of Tasmania, Private Bag 78, Hobart, TAS 7001, Australia;
ⁱAlfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany;
^jBritish Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET, United Kingdom;
^kCentre d'Etudes Biologiques de Chizé, Centre National de la Recherche Scientifique, Villiers-en-Bois, F-79360 Beauvoir sur Niort, France;
^lAntarctic Ecosystem Research Division, NOAA/National Marine Fisheries Service, 8604 La Jolla Shores Drive, La Jolla, CA 92037-1508;
^mSchool for Environmental Research, Charles Darwin University, Darwin NT 0909, Australia; and
^eNorwegian Polar Institute, Polar Environmental Centre, NO-9296 Tromsø, Norway

Edited by Hugh Ducklow, Marine Biological Laboratory, Woods Hole, MA, and accepted by the Editorial Board June 3, 2008 (received for review January 25, 2008)

Abstract

Polar regions are particularly sensitive to climate change, with the potential for significant feedbacks between ocean circulation, sea ice, and the ocean carbon cycle. However, the difficulty in obtaining in situ data means that our ability to detect and interpret change is very limited, especially in the Southern Ocean, where the ocean beneath the sea ice remains almost entirely unobserved and the rate of sea-ice formation is poorly known. Here, we show that southern elephant seals (Mirounga leonina) equipped with oceanographic sensors can measure ocean structure and water mass changes in regions and seasons rarely observed with traditional oceanographic platforms. In particular, seals provided a 30-fold increase in hydrographic profiles from the sea-ice zone, allowing the major fronts to be mapped south of 60°S and sea-ice formation rates to be inferred from changes in upper ocean salinity. Sea-ice production rates peaked in early winter (April–May) during the rapid northward expansion of the pack ice and declined by a factor of 2 to 3 between May and August, in agreement with a three-dimensional coupled ocean–sea-ice model. By measuring the high-latitude ocean during winter, elephant seals fill a “blind spot” in our sampling coverage, enabling the establishment of a truly global ocean-observing system.

Footnotes

^bTo whom correspondence should be addressed. E-mail: jbc{at}mnhn.fr
Author contributions: J.-B.C., M.H., S.R.R., F.R., M.B., D.C., L.B., R.C., M.M., Y.-H.P., C.-A.B., M.A.F., and C.G. designed research; J.-B.C., M.H., M.B., F.B., M.G., Y.T., C.R.M., I.C.F., M.A.F., and C.G. performed research; P.L. and M.A.F. developed hardware and analytical tools; J.-B.C., S.R.R., F.R., S.S., L.B., R.C., R.T., and A.M. analyzed data; and J.-B.C., M.H., S.R.R., and R.C. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission. H.D. is a guest editor invited by the Editorial Board.
This article contains supporting information online at www.pnas.org/cgi/content/full/0800790105/DCSupplemental.
Freely available online through the PNAS open access option.