sea ice near an ice shelf
DESCRIPTION
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) - PowerPoint PPT PresentationTRANSCRIPT
Sea ice near an ice shelf
Pat Langhorne
Department of Physics
University of Otago
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)
Alex Gough (PhD student)
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)
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?
Overarching research question
EC-PORS, Wellington, 27 Feb 2014
West Antarctica
East Antarctica
WeddellSea
RossSea
Amundsen Sea
Bellinghausen Sea
Indian Ocean
Pacific Ocean
Filchner
Fimbulisen
Ronne
Amery
Larsen
Ross
Antarctica: more than half of coastline is ice shelf (Bindschadler et al, 2011)
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Figure from Hughes (MSc, unpublished)
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.
West Antarctica
East Antarctica
WeddellSea
RossSea
Amundsen Sea
Bellinghausen Sea
Indian Ocean
Pacific Ocean
Filchner
Fimbulisen
Ronne
Amery
Larsen
Ross
McMurdoSound
McMurdo Sound extensively researched, beginning about 100 years ago
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
Members of 2009 winter team setting up an oceanographic mooring through the sea ice cover
In the ocean (2008/09)
temperature
Rapid warming in summer, more gradual cooling through autumn
salinity
Rapid freshening as sea ice melts, gradually more saline as sea ice freezes.
spring summer autumn winter spring
From Mahoney et al (2011)
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
Observation 2:
Effect of supercooled water on ice growth in the ocean and at the ice-water interface.
Observations from winters 2003 and 2009
Ice crystals in the water column:Underwater snow storms do happen
Paul Cziko, University of Oregon, McMurdo Sound, Oct 2012
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
…. and they cling to everything, providing buoyancy.
31 August 2009
The crystals accumlate and grow beneath the sea ice, forming a porous layer:
the sub-ice platelet layer
Photo: 2009 winter team
5 cm
Observation 3:
Effect of supercooled water on the structure and thickness of the sea ice cover.
Observations from winters 2003 and 2009
Timeline of sea ice-ocean interaction
From Mahoney et al (2011) J. Geophys. Res.
“regular” ice
sub-ice platelet layer
platelet ice
no sensible thermal energy remaining
in near-surface ocean
Timeline of sea ice-ocean interaction
From Mahoney et al (2011) J. Geophys. Res.
“regular” ice
sub-ice platelet layer
platelet ice
persistent presence of ice shelf water
Difference of ocean temperature at 50 m depth from the freezing point temperature at the surface.
How much sea ice is formed due to heat flux to the ocean?
Time period Ice growth /
m
% ice growth due to heat
flux to ocean
Mar-Sep 2003
1.81 14%
Feb-Oct 2009
2.10 12%
Taken from Purdie et al (2006) & Gough et al (2012)
Sites within 10 km of the ice shelf edge
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)
Observations of frazil and platelet ice around Antarctica
Figure compiled by Ken Hughes & Alex Gough
McMurdo Sound
McMurdo Ice Shelf
Ross Island
Sub-ice platelet layer in McMurdo Sound
Related to mean late-winter heat flux to the ocean.
Data principally from 1986, 2009 & 2011, 2013.
Figure from Gough (PhD thesis), Price et al (submitted) and modified and extended by Ken Hughes.
McMurdo Sound
McMurdo Ice Shelf
Ross Island
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.
Interrogating sea ice
Timeline of platelet ice observationsMcMurdo Sound: 1902-present
Figure compiled by Ken Hughes
• 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.
Where to from here?
Antarctic sea ice is a complex beast: a big challenge to measure sea ice thickness on regional scale.
AcknowledmentsAntarctica 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
Satellite proxy measurements
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.
Freeboard maximum is aligned with platelet ice maximum
167oE
1m ice 1m platelets
164oE 30' 165oE 30' 166oE 30' 78oS
54'
48'
42'
36'
30'
Ross Island
McMurdo Ice Shelf
1m ice1m platelets