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Sea ice near an ice shelf

Sea ice near an ice shelf. Pat Langhorne Department of Physics University of O tago. EC-PORS, Wellington, 27 Feb 2014. 2003 Jono Leitch (field assistant) Greg Leonard (post-doc) Craig Purdie (PhD student). 2009 Brian Staite (field assistant) Andy Mahoney (post-doc)

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Sea ice near an ice shelf

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  1. Sea ice near an ice shelf Pat Langhorne Department of Physics University of Otago EC-PORS, Wellington, 27 Feb 2014

  2. 2003 Jono Leitch (field assistant) Greg Leonard (post-doc) Craig Purdie (PhD student) 2009 Brian Staite (field assistant) Andy Mahoney (post-doc) Alex Gough (PhD student)

  3. Erebus Bay: 15 July 2009 • Callaghan Innovation • Tim Haskell • University of Otago • Inga Smith, Ken Hughes, Alex Gough, David Dempsey, Pat Wongpan, Andy Mahoney, Craig Purdie, Greg Leonard • NIWA • Mike Williams, Craig Stevens, Natalie Robinson, Stefan Jendersie • University of Canterbury • Wolfgang Rack, Daniel Price • Victoria University of Wellington • Joe Trodahl, Malcolm Ingham, Mark McGuinness • Rest of the World • Christian Haas (Canada)

  4. Overarching research question What is the contribution of the ocean, conditioned by processes at the base of an Antarctic ice shelf, to the winter growth and thickness of the coastal sea ice? EC-PORS, Wellington, 27 Feb 2014

  5. Indian Ocean Weddell Sea Fimbulisen Larsen Filchner Amery Bellinghausen Sea Ronne East Antarctica West Antarctica Amundsen Sea Ross Ross Sea Pacific Ocean Antarctica: more than half of coastline is ice shelf (Bindschadler et al, 2011)

  6. Ice shelves and sea ice Interaction between an ice shelf and the ocean causes cooling of the water below its surface freezing point. Ice crystals form and float up under the ice shelf and under sea ice. Figure from Hughes (MSc, unpublished)

  7. What we will show… • Key features of sea ice-ocean interaction near an ice shelf as illustrated by 2003 and 2009 winter campaigns. (Leonard et al, 2006; 2011: Purdie et al, 2006: Mahoney et al, 2011: Gough et al, 2012a,b: Gough et al, 2013) • Ask how pervasive is the influence of ice shelves on sea ice thickness around Antarctica. • Examine whether these conditions have changed in the past century.

  8. Indian Ocean Weddell Sea Fimbulisen Larsen Filchner Amery Bellinghausen Sea Ronne East Antarctica West Antarctica Amundsen Sea Ross Ross Sea Pacific Ocean McMurdoSound McMurdo Sound extensively researched, beginning about 100 years ago

  9. Observations from winters 2003 and 2009 Observation 1: Seasonal evolution of much of the water column to temperatures below the surface freezing point. Signature of interaction with ice shelf

  10. Members of 2009 winter team setting up an oceanographic mooring through the sea ice cover

  11. In the ocean (2008/09) spring summer autumn winter spring temperature Rapid warming in summer, more gradual cooling through autumn salinity Rapid freshening as sea ice melts, gradually more saline as sea ice freezes. From Mahoney et al (2011)

  12. How have ocean conditions changed in McMurdo Sound? Ocean surface temperature seems unchanged since 1900s. Salinity has probably decreased. Ocean surface temperatures held just below freezing point in winter - regulating influence of basal melting deep in the ice shelf cavity? Figure compiled by Ken Hughes, Andy Mahoney & Mike Williams

  13. Observations from winters 2003 and 2009 Observation 2: Effect of supercooled water on ice growth in the ocean and at the ice-water interface.

  14. Ice crystals in the water column:Underwater snow storms do happen Paul Cziko, University of Oregon, McMurdo Sound, Oct 2012

  15. Ice crystals form at depth in the ocean, rise and become large close to the ice-water interface where the water is supercooled in situ. Photo: Brett Grant, NIWA

  16. …. and they cling to everything, providing buoyancy. 31 August 2009

  17. Photo: 2009 winter team 5 cm The crystals accumlate and grow beneath the sea ice, forming a porous layer: the sub-ice platelet layer

  18. Observations from winters 2003 and 2009 Observation 3: Effect of supercooled water on the structure and thickness of the sea ice cover.

  19. Timeline of sea ice-ocean interaction “regular” ice platelet ice sub-ice platelet layer no sensible thermal energy remaining in near-surface ocean From Mahoney et al (2011) J. Geophys. Res.

  20. Timeline of sea ice-ocean interaction “regular” ice platelet ice sub-ice platelet layer persistent presence of ice shelf water Difference of ocean temperature at 50 m depth from the freezing point temperature at the surface. From Mahoney et al (2011) J. Geophys. Res.

  21. How much sea ice is formed due to heat flux to the ocean? Sites within 10 km of the ice shelf edge Taken from Purdie et al (2006) & Gough et al (2012)

  22. How pervasive is the effect of ice shelves? We have observed that ice shelves contribute to sea ice thickness, but ….. - is this effect important to the climate system? - is this sea ice a measure of the “health” of an ice shelf? Figure from Hughes et al (submitted, JGR)

  23. Observations of frazil and platelet ice around Antarctica McMurdo Sound Victoria Land Ross Island McMurdo Ice Shelf Figure compiled by Ken Hughes & Alex Gough

  24. Sub-ice platelet layer in McMurdo Sound McMurdo Sound Related to mean late-winter heat flux to the ocean. Data principally from 1986, 2009 & 2011, 2013. Victoria Land Ross Island Figure from Gough (PhD thesis), Price et al (submitted) and modified and extended by Ken Hughes. McMurdo Ice Shelf

  25. Shown that it is possible to detect sub-ice platelet layer using helicopter-borne electromagnetic induction, but extending to satellite altimeter will be very difficult.

  26. Interrogating sea ice

  27. Timeline of platelet ice observationsMcMurdo Sound: 1902-present Figure compiled by Ken Hughes

  28. Observations and implications • Sea ice close to an ice shelf is 15% thicker than the case where only atmospheric heat flux. Effect may extend for 100s km • Platelet ice can be used as a proxy for integrated oceanic heat flux. • Thus we can use 100 year record of sea ice and ocean observations in McMurdo Sound to estimate time variability of this heat flux. • Presence of subice platelet layer will influence the sea ice freeboard and therefore satellite measurements of sea ice thickness.

  29. Where to from here? Antarctic sea ice is a complex beast: a big challenge to measure sea ice thickness on regional scale.

  30. Acknowledments Antarctica New Zealand, 2003 & 2009 Scott Base winter teams, University of Otago, Canterbury, VUW & Antarctica New Zealand scholarships, Foundation for Research Science and Technology, Marsden Fund. EC-PORS, Wellington, 27 Feb 2014

  31. Satellite proxy measurements Freeboard maximum is aligned with platelet ice maximum Sea ice freeboard derived from ICESat (2003-2009). Black = first year ice; coloured = multi-year sea ice in McMurdo Sound From Price et al (2013) JGR.

  32. 1m ice 1m platelets Ross Island McMurdo Ice Shelf

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