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| Titel |
Turbulent heat flux to the ice shelf base: Microstructure measurements in the oceanic boundary layer |
| VerfasserIn |
Emily Venables, Keith Nicholls, Keith Makinson |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250081696
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| Zusammenfassung |
| Basal melting of Antarctic ice shelves plays an important role in ice sheet dynamics, as ice
shelf loss allows the flow of inland glaciers to accelerate. Observed ice shelf thinning leads to
suggestions of an increasing basal melt rate, yet given the inaccessibility of the ice
shelf-ocean interface, the melt rate, vertical heat flux and processes that drive them are rarely
quantified directly.
Microstructure shear and conductivity observations from a tethered profiler were made
beneath Larsen C Ice Shelf in December 2011 and repeated along with microstructure
temperature beneath George VI Ice Shelf in January 2012. Such measurements at the
ice-ocean interface within the cavity of an ice shelf are unprecedented. CTD and 3D current
velocity measurements were also made at both sites, and radar measurements showed that the
ice base was melting.
Mean potential temperature in the upper ocean beneath Larsen C Ice Shelf was 77mË C
above the in situ freezing point. Eddy diffusivities immediately beneath the ice base of up
to 10-4 m2s-1 were calculated from shear derived dissipation rates of turbulent
kinetic energy between 10-9 and 10-7 Wkg-1. Associated mean heat flux of 0.7
Wm-2 leads to an underestimation of the observed melt rate by at least an order of
magnitude.
Sharp interfaces dividing mixed layers of O(4m) thickness were detected in both CTD
and microstructure measurements within a thermohaline staircase beneath George VI Ice
Shelf. Temperature differences of ~0.05Ë C occurred across the steps and temperature at
the ice base was 2Ë C warmer than in situ freezing point. Stability calculations
confirmed that this was a primarily double diffusive environment. Turbulent mixing was
strong in some layers and weak in others, with shear and thermal variance-derived
dissipation rates of turbulent kinetic energy varying between 10-10 (close to the
shear probe noise limit) and 10-7 Wkg-1. Vertical diffusion of heat is thought to
provide the primary contribution to vertical heat flux where turbulent mixing is
weak.
We use the first direct microstructure profiles taken through hot water-drilled access
boreholes in these two different environments to gain insight into the processes involved in
the transport of heat from the upper ocean to the ice shelf base. |
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