Ocean Science www.ocean-sci.net 1812-0784 1812-0792 4 1 2008 10.5194/os-4-89-2008 http://www.ocean-sci.net/4/89/2008/ http://www.ocean-sci.net/4/89/2008/os-4-89-2008.html http://www.ocean-sci.net/4/89/2008/os-4-89-2008.pdf 89 98 2008-03-05 Ice-shelf – ocean interactions at Fimbul Ice Shelf, Antarctica from oxygen isotope ratio measurements M. R. Price K. J. Heywood k.heywood@uea.ac.uk K. W. Nicholls School of Environmental Sciences, University of East Anglia, Norwich, NR4 7TJ, UK British Antarctic Survey, High Cross, Madingley Road, Cambridge, CB3 0ET, UK Melt water from the floating ice shelves at the margins of the southeastern Weddell Sea makes a significant contribution to the fresh water budget of the region. In February 2005 a multi-institution team conducted an oceanographic campaign at Fimbul Ice Shelf on the Greenwich Meridian as part of the Autosub Under Ice programme. This included a mission of the autonomous submarine Autosub 25 km into the cavity beneath Fimbul Ice Shelf, and a number of ship-based hydrographic sections on the continental shelf and adjacent to the ice shelf front. The measurements reveal two significant sources of glacial melt water at Fimbul Ice Shelf: the main cavity under the ice shelf and an ice tongue, Trolltunga, that protrudes from the main ice front and out over the continental slope into deep water. Glacial melt water is concentrated in a 200 m thick Ice Shelf Water (ISW) layer below the base of the ice shelf at 150–200 m, with a maximum glacial melt concentration of up to 1.16%. Some glacial melt is found throughout the water column, and much of this is from sources other than Fimbul Ice Shelf. However, at least 0.2% of the water in the ISW layer cannot be accounted for by other processes and must have been contributed by the ice shelf. Just downstream of Fimbul Ice Shelf we observe locally created ISW mixing out across the continental slope. The ISW formed here is much less dense than that formed in the southwest Weddell Sea, and will ultimately contribute a freshening (and reduction in δ¹⁸O) to the upper 100–150 m of the water column in the southeast Weddell Sea. Beckmann A., Hellmer, H. H., and Timmermann, R.: A numerical model of the Weddell Sea: Large-scale circulation and water mass distribution, J. Geophys. Res., 104(C10), 23 375–23 391, 1999. Beckmann, A. and Goose, H.: A parameterization of ice shelf-ocean interaction for climate models, Ocean Mod., 5, 157–170, 2004. Bromwich, D. H., Guo, Z., Bai, L., and Chen, W.: Modeled Antarctic precipitation. Part 1: Spatial and temporal variability, J. Climate, 17, 427–447, 2004. Darelius, E. and Wåhlin, A. K.: Downward flow of dense water leaning on a submarine ridge, Deep Sea Res., 54, 1173–1188, 2007. Eicken, H.: Salinity Profiles of Antarctic Sea Ice: Field Data and Model Results, J. Geophys. Res., 97(C10), 15 545–15 557, 1992. Eicken, H.: Deriving Modes and Rates of Ice Growth in the Weddell Sea From Microstructural, Salinity and Stable-Isotope Data, in: Antarctic Sea Ice: Physical Processes, Interactions and Variability, edited by: Jeffries, M. O., AGU, Antarctic Research Series, 89–122, 1998. EPICA Community Members: One-to-one coupling of glacial climate variability in Greenland and Antarctica, Nature, 444, 195–198, 2006. Epstein, S. and Mayeda, T.: Variations of O18 content of waters from natural sources, Geochim. Cosmochim. Acta, 4, 213–224, 1953. Fahrbach, E., Peterson, R. G., Rohardt, G., Schlosser, P., and Bayer, R.: Suppression of bottom water formation in the southeastern Weddell Sea, Deep-Sea Res. I, 41(2), 389–411, 1994. Foldvik, A., Gammelsrod, T., Osterhus, S., Fahrbach, E., Rohardt, G., Schroder, M., Nicholls, K. W., Padman, L., and Woodgate, R. A.: Ice shelf water overflow and bottom water formation in the southern Weddell Sea, J. Geophys. Res., 109, C02015, doi:10.1029/2003JC002008, 2004. Gammelsrod T., Foldvik, A., Nost, O. A., Skagseth, O., Anderson, L. G., Fogelqvist, E., Olsson, K., Tanhua, T., Jones, E. P., and Osterhus, S.: Distribution of Water Masses on the Continental Shelf in the Southern Weddell Sea, in: The Polar Oceans and Their Role in Shaping the Global Environment, edited by: Johannessen, O. M., Monogr. Ser., 85, 159–176, 1994. Grosfeld, K., Gerdes, R., and Determann, J.: Thermohaline circulation and interaction between ice shelf cavities and the adjacent open ocean, J. Geophys. Res., 102(C7), 15 595–15 610, 1997. Helsen, M. M., Van De Wal, R. S. W., Van Den Broeke, M. R., Van As, D., Meijer, H. A. J., and Reijmer, C. H.: Oxygen isotope variability in snow from western Dronning Maud Land, Antarctica and its relation to temperature, Tellus, 57B, 423–435, 2005. Heywood, K. J., Locarnini, R. A., Frew, R. D., Dennis, P. F., and King, B. A.: Transport and Water Masses of the Antarctic Slope Front System in the Eastern Weddell Sea, Ocean, Ice and Atmosphere: Interactions at the Antarctic Continental Margin, Antarctic Research Series, 75, 203–214, 1998. Jacobs, S. S., Fairbanks, R. G., and Horibe, Y.: Origin and evolution of water masses near the Antarctic continental margin: Evidence from H218O/H216O ratios in seawater, in: Oceanology of the Antarctic continental shelf, edited by: Jacobs, S. S., AGU, Washington D.C., Antarctic Research Series, 43, 59–85, 1985. Klatt, O., Fahrbach, E., Hoppema, M., and Rohardt, G.: The transport of the Weddell Gyre across the Prime Meridian, Deep-Sea Res. II, 52, 513–528, 2005. Melling, H. and Moore, R. M.: Modification of halocline source waters during freezing on the Beaufort Sea shelf: evidence from oxygen isotopes and dissolved nutrients, Cont. Shelf Res., 15, 89–113, 1995. Meredith, M. P., Heywood, K. J., Frew, R. D., and Dennis, P. F.: Formation and circulation of the water masses between the southern Indian Ocean and Antarctica: Results from $\delta ^18$O, J. Mar. Res., 57, 449–470, 1999. Nicholls, K. W., Abrahamsen, E. P., Buck, J. J. H., Dodd, P. A., Goldblatt, C. , Griffiths, G., Heywood, K. J., Hughes, N. E., Kaletzky, A., Lane-Serff, G. F., McPhail, S. D. Millard, N. W., Oliver, K. I. C., Perrett, J., Price, M. R., Pudsey, C. J., Saw, K., Stansfield, K., Stott, M. J., Wadhams, P., Webb, A. T., and Wilkinson, J. P.: Measurements beneath an Antarctic ice shelf using an autonomous underwater vehicle, Geophys. Res. Lett., 33, L08612, doi:10.1029/2006GL025998, 2006. Nost, O. A.: Measurements of ice thickness and seabed topography under the Fimbul Ice Shelf, Dronning Maud Land, Antarctica, J. Geophys. Res., 109, C10010, doi:10.1029/2004JC002277, 2004. Rignot, E. and Jacobs, S. S.: Rapid Bottom Melting Widespread near Antarctic Ice Sheet Grounding Lines, Science, 296, 2020–2022, 2002. Schlosser, P., Bayer, R., Foldvik, A., Gammelsrod, T., Rohardt, G., and Munnich, K. O.: Oxygen 18 and Helium as Tracers of Ice Shelf Water and Water/Ice Interactions in the Weddell Sea, J. Geophys. Res., 95(C3), 3253–3263, 1990. Smedsrud, L. H., Jenkins, A., Holland, D. M., and Nost, O. A.: Modeling Ocean Processes Beneath Fimbulisen, Antarctica, J. Geophys. Res., 111, C01007, doi:10.1029/2005JC002915, 2006. Stenberg, M., Isaksson, E., Hansson, M., Karlen, W., Mayewski, P. A., Twickler, M. S., Whitlow, S. I., and Gundestrup, N.: Spatial variability of snow chemistry in western Dronning Maud Land, Antarctica, Ann. Glaciol., 27, 378–384, 1998. Toggweiler, J. R. and Samuels, B.: Effect of Sea Ice on the Salinity of Antarctic Bottom Waters, J. Phys. Oceanogr., 25, 1980–1997, 1995. Vaughan, D. G., Bamber, J. L., Giovinetto, M., Russell, J., and Cooper, A. P. R.: Reassessment of net surface mass balance in Antarctica, J. Climate, 12, 933–946, 1999 Weiss, R. F., Ostlund, H. G., and Craig, H.: Geochemical studies of the Weddell Sea, Deep-Sea Res., 26A, 1093–1120, 1979. Weppernig, R., Schlosser, P., Khatiwala, S., and Fairbanks, R. G.: Isotope data from Ice Station Weddell: Implications for deep water formation in the Weddell Sea, J. Geophys. Res., 101(C10), 25 723–25 739, 1996. Zwally, H. J., Comiso, J. C., Parkinson, C. L., Cavalieri, D. J., and Gloersen, P.: Variability of Antarctic sea ice 1979–1998, J Geophys. Res., 107(C5), doi:10.1029/2000JC000733, 2002.