Sea ice Processes and Mass Balance in the Bellingshausen Sea

Lead Research Organisation: NERC British Antarctic Survey
Department Name: Science Programmes


Antarctic sea ice thickness is arguably the largest gap in our knowledge of the climate system. While rapid changes in ice extent are evident in satellite imagery collected over the last three decades, we have little information with which to assess the thickness of the ice. Knowledge of the thickness distribution of sea ice and its snow cover is critical in understanding a wide range of air-sea-ice interactions. It's evolution over time provides a sensitive measure of the response of the polar regions to climate change and variability, and it controls the fluxes of heat, salt, and freshwater that govern air-sea interactions and water mass transformation. Whilst we are moving closer to the 'holy grail' of measuring Arctic sea ice thickness from space, such methods are severely limited in the Antarctic due to the deep snow cover. Moreover, our understanding of the processes that control Antarctic snow and ice thickness is inadequate. This proposal has two complementary lines of investigation: (1) To determine robust statistical relationships between snow depth, ice thickness, and freeboard distribution for a range of ice classes. Understanding these relationships is critical if we are to be able to determine either snow depth or ice thickness from space - the only viable means of determining large-scale snow and sea ice thickness, trends, and variability. (2) To quantify the role that key Antarctic sea ice processes play in controlling the ice thickness evolution and its response to climate forcing. This can only be achieved through detailed simultaneous measurements of both the surface topography and ice underside. We will obtain, for the first time anywhere, coincident 3D topography maps of both the surface (from airborne Lidar) and underside (from AUV mounted multibeam sonar) for a variety of ice types and conditions. With over 1 million individual measurements per sampling station, the richness of the data set will be several orders of magnitude more than is possible with traditional methods. This will allow us to determine, for the first time, robust statistical relationships between snow depth and ice thickness spatial variability. These data will allow a definitive assessment of the feasibility and accuracy of satellite methods for estimating Antarctic sea ice thickness and snow depth for a range of ice conditions. In addition we will deploy an unprecedented number (20) of novel ice mass balance buoys (IMBs) to monitor the evolution of the snow and sea ice throughout the annual sea ice cycle. The large number of IMB deployments will allow the first regional assessment of snow accumulation rates and ice mass balance of Antarctic sea ice. To achieve these goals we have secured a 30-day dedicated cruise aboard the James Clark Ross, scheduled for November 2010, as well as use of a BAS Twin Otter for airborne Lidar missions over ice stations and the surrounding region. These platforms, provided as part of the BAS core programme, along with support and instrumentation provided by project partners at no cost, represent a unique opportunity, and a significant leverage of over £1,000,000 of in-kind contribution. This is an unprecedented opportunity for the UK to lead a coordinated campaign to produce a definitive picture of snow and sea ice thickness distribution, and to continuously monitor the processes that control these distributions throughout the annual cycle. Our programme will deliver a major step forward in our knowledge of the snow and ice thickness distribution. It will advance our understanding of Antarctic sea ice processes and improve our ability to monitor the evolution of the ice cover and air-ice-ocean interactions on a large scale. This will allow improved representation of sea ice in large-scale and global climate models, and ultimately improve our understanding of the response of the Antarctic ice cover to current and future climate change and variability.


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Description Key findings within this successful programme include:
? Observations suggesting that Antarctic sea ice is likely to be, on average, thicker than is suggested from prior in situ surveys. Areas of thick, heavily deformed ice have likely been underrepresented in prior surveys due to a combination of heavy pack ice preventing access to ships, difficulties in making drill hole measurements in heavily deformed ice, and potential biases towards thinner ice in shipboard surveys. The AUV surveys were able to capture the full distribution of thickness of sea ice floes and show that very thick, heavily deformed first year sea ice in Antarctic Spring

? The combination of the full 3-D topography of the underside (multi-beam sonar from the AUV) and surface (Lidar from fixed wing aircraft) of the sea ice provides a new richness of information about the structure of sea ice, it's snow cover, and the processes that created it. Ongoing analysis of these data will provide improved algorithms for determination of ice thickness from satellites and improved understanding of the processes that drive snow distribution and ice mass balance in the Antarctic.

? The AUV data showed that deformation was particularly heavy in the surveyed area in Spring, with ice floes often composed of rubble produced during repeated floe collisions rather than classical linear ridge features. The degree of deformation was far greater than has been reported in most prior surveys of first year Antarctic sea ice, with many ridge keels exceeding 10 m in draft.

? Results from this project have contributed to several papers in the peer-reviewed literature, including for Nature Geoscience, Journal of Geophysical Research, and Annals of Glaciology. Several more papers are currently in preparation on snow and sea ice properties and processes, and the relationship between snow distribution, ice morphology, and ice thickness.
Exploitation Route Two papers of interest (1) Williams, G., Maksym, T., Wilkinson, J., Kunz, C., Murphy, C., Kimball, P., Singh, H.: Thick and deformed Antarctic sea ice mapped with autonomous underwater vehicles. Nat. Geosci. 8(1), 61-67 (2015) also (2) Singh, H and Maksym, T and Wilkinson, J and Williams, G, Inexpensive, small AUVs for studying ice-covered polar environments, Science Robotics, 2, (7) Article eaan4809. ISSN 2470-9476 (2017)
Sectors Aerospace, Defence and Marine,Digital/Communication/Information Technologies (including Software),Education,Electronics,Environment,Other

Description Background: Direct measurements of sea ice thickness in the Antarctic are sparse. Without this information, we cannot assess synoptic variability and air-ice-ocean interactions or adequately assess the role sea ice plays in modulating its response to climate change and variability. We can neither routinely monitor the large-scale evolution of ice thickness, nor evaluate the role that the key thermodynamic mass balance processes play in maintaining the ice cover. The situation has been stressed in the WCRP-SCAR summary report on the International Workshop on Antarctic Sea Ice Thickness: "Sea ice thickness remains arguably the largest single gap in our knowledge of the climate system". The primary aim of this programme was to address this gap through detailed measurement of the snow and sea ice thickness distribution in the Bellingshausen (and Weddell) Sea. This was achieved through a comprehensive in situ ice and snow physics programme coupled with a simultaneous airborne and under-ice measurement campaign using the British Antarctic Survey (BAS) Twin Otter Aircraft, and an autonomous underwater vehicle (AUV) from the Woods Hole Oceanographic Institution (WHOI). These data were combined with an in situ snow and sea ice sampling effort that was concurrently performed from the UK research vessel James Clark Ross. To extend our understanding of sea ice processes beyond the field campaign a series of Ice Mass Balance buoys (IMBs) were deployed during the cruise of the James Clark Ross. This successful programme brought together sea ice scientists from UK, USA, Canada, and Australia with underwater robotics specialists from WHOI. Narrative Impact These results are especially important given the 'Antarctic paradox' of recent increases in sea ice extent contrasting with climate model predictions of diminishing extent. Some models suggest that ice extent increases have been accompanied by increases in ice thickness and deformation. These data provide the first successful mapping of the thickness distribution of Antarctic sea ice floes from an AUV, and the first to combine these measurements with coincident airborne measurements. This provides the most comprehensive dataset to date for the development of more robust algorithms for the improvement of both airborne and spaceborne estimates of Antarctic sea ice thickness. Moreover, this campaign provides a successful demonstration of the feasibility of AUV operations under Antarctic sea ice, leading the way for larger scale campaigns for in situ validation of remote sensing campaigns to monitor ice thickness, such as CryoSat-II, IceSat-II, and NASA's Operation IceBridge.
First Year Of Impact 2013
Sector Digital/Communication/Information Technologies (including Software),Education,Environment,Other