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Two talks on Ice-Ocean interaction in East Antarctica

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Anybody wishing to attend from outside BAS please email the seminar organiser beforehand. The talk details are as follows:

Research of Ocean-ice BOundary InTeraction and Change around Antarctica (ROBOTICA): a strategy to explore ice-ocean interactions in East Antarctica

Takeshi Tamura (National Institute of Polar Research)

Antarctica and the surrounding Southern Ocean are changing. Acceleration of ice mass loss and the warming of the coastal ocean in West Antarctica have substantial impacts on the global climate system. In East Antarctica, which has been considered to be stable and attracted relatively less attention, regional characteristics of interactions among climate subsystems have recently been revealed, and evidence of variations on time scales from decadal to millennial, has been accumulating. Totten Glacier Ice Shelf, Wilkes Land, has an ice discharge rate known to be accelerating. A potential pathway for warm water access to the cavity beneath this ice shelf has been discovered

Recent rapid progress in the techniques of remote autonomous observation and satellite communication are improving our ability to observe this system. Under the project called ROBOTICA within the Japanese Antarctic Expedition six-year plan (2016-2023), we plan to utilize state-of-the-art unmanned observations such as under-ice oceanographic, seafloor and cryospheric observations using ROV and geodetic network observations of ice/ocean motion and deformation using GPS /GNSS. In combination with conventional and robust observational techniques this will enable us to acquire detailed temporal and spatial datsets. Implementation of this project can provide a big step forward for realization of the dream of a sustained observation system around Antarctica. As part of preliminary studies, during the 2016-17 and 17-18 seasons we targeted ice ocean interactions in Lutzow-holm Bay in front of Shirase Glacier.

Strong ice-ocean interaction at Shirase Glacier Tongue, East Antarctica

Daisuke Hirano (Institute of Low Temperature Science)

Shirase Glacier Tongue (SGT) is a thick floating slab of ice that forms where the glacier flows down onto the ocean surface at the southern closed-section of L├╝tzow-Holm Bay (LH Bay) off Enderby Land, East Antarctica. Compared with other major ice shelves/tongues around Antarctica, SGT is small in area but, estimated at ~7 m per year, its basal melt rate is relatively high (Rignot et al., 2013), presumably as a result of the presence of warm deep water. LH Bay is usually covered by heavy sea ice, even during the summer, and so hydrographic observations are extremely limited. To explore in detail the SGT -ocean interaction, summer comprehensive hydrographic observations in LH Bay were conducted during JAR E58th in 2017 under the project called ROBOTICA . LH Bay has a deep glacial trough in its center, connecting the shelf break to SGT . Cold, fresh, and oxygen-rich Winter Water (WW: remnant of winter mixed layer) overlies warm, saline, and oxygen-poor modified Circumpolar Deep Water (mCDW) along the trough. This indicates mCDW inflow beneath the SGT , with the inflowing mCDW temperature exceeding the in-situ freezing point by more than 2.7oC. In the surface/sub-surface layers, the water becomes warmer, with lower oxygen content toward the ice front. In d18O-salinity space, this anomalous warm and oxygen poor layer at the ice front is distributed along the line connecting mCDW with glacier end-members, with glacial melt water fraction estimated to be 0.5-1.7%. In addition, the anomalous layer contains relatively high mCDW fraction even at surface/sub-surface layers, indicating the glacial melt water outflow beneath the SGT as a mixture with mCDW. The observational results suggest a 3-dimensional circulation, associated with SGT -ocean interaction (i.e., basal melting of SGT by mCDW), that comprises: (1) warm mCDW flows southward at the deep layer of glacial trough leading into the region beneath SGT , (2) mCDW meets to melt the base of SGT , then a mixture of glacial melt water and mCDW is transported upward as a buoyant melt plume, and (3) the mixture exports northward at surface/sub-surface layers. As is the case with Totten Ice Shelf, the SGT is characterized as a warm ice cavity, atypical in East Antarctica, as a result of the absence of a coastal polynya as well as the presence of a deep trough serving as a pathway for mCDW toward the SGT in LH Bay. In this talk, preliminary results from our recent observations off Totten Ice Shelf in 2018 are also presented.

This talk is part of the British Antarctic Survey - Polar Oceans seminar series series.

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