Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - OceanIS (Ocean Interaction with Antarctic Ice Shelves)

Teaser

The primary goal OceanIS is to constrain the contribution of changes in Southern Ocean circulation to the recent acceleration in Antarctic Ice Sheet mass loss. Improving our knowledge of ice shelf–ocean interactions is a critical step toward reducing uncertainty in future...

Summary

The primary goal OceanIS is to constrain the contribution of changes in Southern Ocean circulation to the recent acceleration in Antarctic Ice Sheet mass loss. Improving our knowledge of ice shelf–ocean interactions is a critical step toward reducing uncertainty in future sea level rise projections. Ice shelves are coastal areas of floating ice that extend from an ice sheet out over the ocean, and their destabilization can trigger rapid ice discharge. It is now evident that ocean–driven basal melt is the major cause of ice loss from Antarctica’s fringing ice shelves. However much of the fundamental dynamics of how the ocean delivers heat to the ice shelves remains unresolved. Progress in this area requires bringing together the fields of ice shelf–ocean interactions and large–scale Southern Ocean oceanography. The Southern Ocean overturning entails the upwelling of Circumpolar Deep Water (CDW) offshore Antarctica. The Antarctic Circumpolar Current has shifted poleward, the impact of which, e.g. over the upwelling of CDW, remains unknown. Since CDW is linked to the highest ice shelf thinning rates yet observed, the variability of the CDW properties and its interaction with the ice shelves is the focus of this proposal. To do this, OceanIS integrates, for the first time, several unique data sets, which extend from the deep ocean to the sub–ice shelf environment. Observations show that changes in the thermohaline properties of the Southern Ocean water masses over the last 20 years are consistent with a southward shift of warm CDW towards the Antarctic continent. Our results also show that the areas with the largest thermohaline changes coincide with the regions where Antarctic ice shelves are melting the fastest, especially in East Antarctica. East Antarctica has long been thought to be a stable part of Antarctica. However, OceanIS results suggest East Antarctica is more vulnerable to ocean forcing changes than previously thought. OceanIS provides critical information to guide current ocean/ice sheet models addressing Antarctic Ice Sheet mass loss and rates of sea level change projections.

Work performed

The project listed four goals.

Goal 1: Produce a new data synthesis using historical and contemporary observations.
Completed.
This goal was reached within the first few months of the project. It keeps been updated as more data become available. There is an interest for the data set to be made public through the Southern Ocean Observing System (SOOS) platform or through the WOCE Southern Ocean data set in collaboration with University of Texas (USA).
This data set has also been used to identify regions near Antarctic ice shelves and document any relationship between southward shift of warm water and increased ice shelf thinning.

Goal 2: Document circum–Antarctic and inter–decadal variability of CDW in the context of ice shelf basal melting. 90% completed.
I have completed time series of the CDW properties and Southern boundary Front position from each region,and compared ocean-based observations with satellite-based observations. I am currently assessing the coherence of (i) with atmospheric forcing, (ii) sea ice extent and (iii) the regional pattern of basal melting.

Goal 3: Document how the southward shift of the ACC impacts the CDW transport across the continental shelf break, offshore Prydz Bay, from 1997 to 2012.
This part is an extention of Goal 2, but applied to a heavily sampled area near Antarctica and involves a complete time series of the Southern Boundary Front from hydrography and satellite altimetry, of wind stress, and of atmospheric modes of variability. This work documents the impact of Southern Ocean dynamics on the basal melting beneath the Amery ice shelf.

Exploitation and Dissemination
Two publications are currently planned as a direct product of the project:
- Paper 1 (Impact of recent Circumpolar Deep Water variability in Antarctic Ice Shelf – Ocean Interactions) is on draft and expected to be ready for submission by the end of the year (I am currently on maternity leave).
- Paper 2 (On the interaction of Circumpolar Deep Water with the Amery Ice Shelf from 1997 to 2012). This paper is on very early stages.

Attendance to several meetings have provided a very productive platform to showcase the results from this project. I attended European Geophysical Union annual meeting in 2018. I also had planned to attend the American Geophysical Union Ocean Sciences Meeting in Portland in February 2018 as an invited speaker. Unfortunately, I could not attend due to health issues. However, I will be presenting results from this project in the next Ocean Sciences meeting in February 2020. I have also been invited to visit several institution within Europe. For example, the British Antarctic Survey (twice), the University of East Anglia, the University of Copenhagen and the Alfred Wegener Institut (AWI) in Germany.

I am in contact with Emily Kastner, an author-illustrator of children’s books, to collaborate in her next book, “oceans” (https://www.emmykmakes.com). I hope we can extend this collaboration to include the role of the ocean in shaping up the coast lines through the poles.

Final results

I have identified regions where there is a link between the Southern ocean Antarctic Circumpolar Current (ACC) dynamics and Antarctic ice shelves thinning. The ACC moves north and south as part of its natural dynamics. However, I have identified a trend in changing in water masses driven by the southward shift of the region where warm waters reach shallow depths around Antarctica. This is a new exciting results, with potential for studying the delivery of heat to the Antarctic coast using all year-round satellite observations and targeted areas of the ocean where to deploy long term observations platforms. This is an important advance as it provides a platform to target a critical player in setting future sea level rise by understanding how ocean heat is delivered to Antarctica and what drives it variability. Assessing how models currently reproduce the link and trends documented by this project will be an important step forward in improving estimates of sea level rise rates by considerably reducing model uncertainties of the estimates of future rates of sea level rise.