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SPRI Review 1998: Sea Ice and Polar Oceanography Group

Sea Ice and Polar Oceanography Group

Dr P. Wadhams

Dr N.R. Davis, J. Wilkinson, M. Doble, N. Hughes, A. Kaletzky, Y. Aksenov, Capt. L. Brigham, F. Cottier, R. Hall, M. Huddleston, I. Jonsdottir, Miss A. Howells, Y. Faugere

The Sea Ice and Polar Oceanography Group continued to seek to understand the physical processes occurring in ice-covered seas of the Arctic and Antarctic, with special relevance to their influence on climate and climate change. During 1997-1998, research was undertaken on a wide variety of projects, with funding from the European Commission, Natural Environment Research Council, and US National Science Foundation.

The group was involved in four major projects funded by the European Commission during the year. Three of these were with the Science and Technology Directorate (DGXII) and one with the Transport Directorate (DGVII).

With DGXII, the first project comprised the second phase (1996-1999) of the European Subpolar Ocean Programme (ESOP-2), funded by the EU under the MAST-III initiative, in which Dr Wadhams is a principal investigator. The project is coordinated by Dr Eystein Jansen (University of Bergen), and seeks to understand the nature of the thermohaline circulaton in the Greenland Sea and the mechanism for deep-winter convection. Deep convection is a process whereby surface water becomes more dense through cooling and local ice formation (which involves rejection of salt back into the water column), and, losing stability, overturns in the form of convective plumes that sink into the deep ocean. The convection ventilates the deep waters of the Greenland Sea, helps to sequester carbon dioxide, and helps to drive the global thermohaline circulation, or Global Conveyor Belt. It has been found from tracer studies that convection has slowed in recent years and is now no longer reaching the deep ocean; at the same time, local ice formation has diminished within the central region. The critical area is known as the Odden ice tongue, a protuberance from the main East Greenland ice edge. ESOP-2 sets out to understand the critical air-sea-ice thermodynamic and dynamic processes responsible for the changes, which may have a worldwide climatic impact; for instance, models predict that that a cessation of convection will lead to a large-scale cooling of northwest Europe after 2100, as the Gulf Stream weakens. During the year, the group worked on data collected within the Odden by an in situ cruise that was run in March 1997 aboard the RV Jan Mayen. Results of the analyses of ice samples were used to construct a salt flux model (Wilkinson), whereby ice-physics data and satellite imagery are combined to estimate the rate of deposition of salt in the upper ocean over the Odden region through the winter season, and hence the rate at which the water becomes more dense and approache the condition for convection to begin.

During the year, results from the first phase of ESOP were assembled into a special issue of Deep-sea research part II: topical studies in oceanography, edited by P. Wadhams, L. Miller (Institute of Marine Research, Bergen) and J.-C. Gascard (Pierre and Marie Curie University, Paris). The issue contains 19 papers and is scheduled for publication in spring 1999. Collaboration among the partners in ESOP-2 involved a mid-term workshop at Villefranche in October 1997, attended by Dr Wadhams and Jeremy Wilkinson (Research Associate), and a data workshop at Bergen in May 1998, attended by Dr Wadhams. The final science workshop was held in Bologna in October 1998, also attended by Dr Wadhams and Wilkinson.

The second project was the 'Ice State' programme (1996-1999), coordinated by Helsinki University of Technology (Professor Kaj Riska) with Dr Wadhams as a principal investigator. This seeks to understand the relationship between sea ice mechanical processes and the resistance offered by an ice sheet to ship passage. A classification scheme for ice resistance forces is sought, based on parameters that can be observed in remote-sensing data, and giving the level of risk experienced by an ice-strengthened ship in given ice conditions, an 'ice state' equivalent of 'sea state' for ocean waves. Again, much of the year was spent analysing data collected during a 1997 field experiment in the Gulf of Bothnia called ZIP-97 (Zooming in Ice Physics), which dealt with the scaling problem in calculating ice forces. Again a mid-term science workshop was held on 9-10 October 1997, hosted by Dr Wadhams at the Møller Centre, Churchill College. Martin Doble (Research Associate) worked on the evaluation and testing of algorithms to compare statistical features of SAR (synthetic aperture radar) satellite images with those of ice draft profiles from submarine upward looking sonars, and on the investigation of similarities in fractal dimensions between datasets, and attended a further projct meeting in Bergen in February 1998. In June 1998, he attended a longer workshop in Helsinki, dealing with relationships between satellite and submarine data. Yevgeny Aksenov (Research Student) worked on the analysis of thermally and dynamically induced local ice deformations.

The third project, which began during the year, was AMOC, the acoustic monitoring of ocean circulation in the Arctic. The aim is to model the propagation of under-ice acoustic energy across the Arctic Ocean as a way of monitoring the evolving temperature-salinity structure (due to global change) and the changing ice thickness. Both types of change affect the transoceanic travel time for such pulses, either through affecting sound speed or by changing the depth at which upwardly refracting sound is reflected off the sea ice bottom. Data used in the project include ice profile data collected during submarine voyages in the Arctic. Project development nvolved research workshops in Bergen on 19-20 March and 25-27 June 1998, attended by Dr Wadhams and Arthur Kaletzky (Research Associate, who joined the Group during the year to work on this project). The partners in the project are the Nansen Environmental and Remote Sensing Centre (Bergen), the St Petersburg branch of the same centre, and the Max-Planck-Institut für Meteorologie (Hamburg).

The fourth EU project was 'Ice Routes,' under the Transport Programme, coordinated by Earth Observation Sciences Ltd (Farnham). The purpose was to devise improved techniques for real-time classification of ice types from SAR images, for use in a future ice management and forecasting system. The Institute was a partner in the programme, with Dr Wadhams as principal investigator and Richard Hall and Lawson Brigham also involved. Meetings were held at Farnham in November 1997 and Bergen in March 1998, with a final meeting in Tromsø and Trondheim on 3-9 July 1998, attended by Capt Brigham. The project was completed during the summer of 1998.

NERC funded two projects during the year. The larger was the analysis and interpretation of ice thickness and along-track oceanographic data collected by Dr Wadhams aboard HMS Trafalgar in the Arctic during August-September 1996. Dr Norman Davis was the Senior Research Associate in this project. The datasets comprise upward-looking sonar profiles of ice thickness, sidescan sonar imagery of the ice underside, and along-track temperature and salinity data. The interpretation of the data shows that during the summer of 1996 there was a considerable reduction in the ice thickness in the Eurasian Basin of the Arctic Ocean and the Greenland Sea, relative to any previous data set. The results are being archived to begin a NERC ice thickness data archive. During the year, the group received further data from the Hydrographic Office, Taunton, comprising submarine ice thickness profiles from cruises in 1991 and 1994. The analysis of these will assist in determining the rate of change of mean ice thickness in the Arctic during the past decade.

The second project was for the deployment and use in Antarctica of the OSCR-II (Ocean Surface Current Radar) system, a shore-based HF radar system that maps surface currents over a 1 km grid out to a range of 50 km using Doppler shift. The intention was to mount the system near the Italian base at Terra Nova Bay, Ross Sea, and use it to map currents in the coastal polynya there, in cooperation with an Italian oceanographic programme, in order to determine the physics of heat loss and ice production in the polynya. In the event, the radar system, owned by NERC and maintained by Southampton Oceanography Centre, was not made available in the intended season, and the field programme was rescheduled for November 1999.

The US National Science Foundation supported a project whereby the submarine data from the British cruise in 1996 are compared with complementary data collected by a US submarine during the same period in the SCICEX Program, a five-year US programme whereby one civilian research cruise is carried out per year into the Arctic by a US submarine. The US boat in 1996 covered the western Arctic and the North Pole, and thus slightly overlapped the British boat, which covered the Greenland Sea and Eurasian Basin up to the Pole. Our statistics are being compared with similar statistics generated for the US cruise by Dr Terry Tucker of the US Army Cold Regions Research and Engineering Laboratory (CRREL), Hanover, New Hampshire. The aim is a mutually validated joint dataset covering the entire Arctic for the summer of 1996. Nick Hughes joined the group as a Research Associate to work on this project.

During both 1997 and 1998, the group was partners in the two phases of INTERICE, a project to carry out sea ice physics research on a laboratory scale using the 20 m-long ice testing tank of HSVA (Hamburgische Schiffbau-Versuchsanstalt GmbH), Hamburg. The European Commission has designated this a European Large Facility, and invited bids for coordinated experimental projects, for which all travel and maintenance costs are covered for the participants. The INTERICE group, a group of mainly university laboratories from several European countries, made a successful bid. The first phase, during 1997, was coordinated by Dr Hajo Eicken, Alfred-Wegener-Institut für Polar- und Meeresforschung, Bremerhaven. Finlo Cottier (Research Student) carried out measurements of brine drainage channel development and properties in young sea ice sheets, and Richard Hall (Research Student) carried out measurements of wave velocities in frazil and pancake ice. Dr Wadhams was appointed coordinator of INTERICE-II, on the departure of Dr Eicken to the University of Alaska. A new experimental programme was carried out during the autumn of 1998, again involving brine channel measurements by Finlo Cottier, and wave-ice measurements by Dr Wadhams.

Dr Wadhams, the Reader in Polar Studies and leader of the group, gave invited lectures at the following meetings during the year: 'Cryospheric processes and climate,' at the 'Physics of climate conference,' Royal Meteorological Society, held at the Royal Society, 29-30 October 1997; 'Ice thickness changes in the Arctic Ocean,' the keynote address at the 13th International symposium on Okhotsk Sea and Sea Ice, Mombetsu, Japan, 2-6 February 1998; and 'Ice-ocean interaction and convection in the Greenland Sea,' the guest address for the National Research Council of Iceland, at the 'International workshop on environmental and climate variations and their impact on the North Atlantic region,' Reykjavik, 23-27 September 1998.

Dr Wadhams was an invited participant at the planning meeting for the new Japanese-US International Arctic Research Centre, Fairbanks, Alaska, 8-12 March 1998. He was an invited rapporteur at the NATO 'Advanced research workshop on the fresh water budget of the Arctic Ocean,' Tallinn, Estonia, 26 April-1 May 1998. He became co-editor of the conference proceedings and hosted a further meeting of rapporteurs at the Institute in October 1998. He attended a meeting of the WCRP International Programme for Antarctic Buoys, Naples, 10-13 May 1998, and was made coordinator of the programme from January 1999 onwards, when all data will be stored at the Institute. Dr Wadhams was also appointed to the Council of the Italgas Prize Committee, Turin, to develop a European conference on sustainable development.

Dr Wadhams gave a poster at the ACSYS conference on 'Polar processes and global change,' Orcas Island, Washington, 3-6 November 1997; attended an IANZONE/ASPECT meeting at Biosphere 2, Tucson, on 1-5 December 1997, on implementation of the SCAR ASPECT programme ('Antarctic sea ice processes and climatic change'); and gave two papers at the European Geophysical Society meeting, Nice, 20-24 April 1998.

In November 1997 Dr Wadhams hosted a workshop on strainmeter design, held at the British Antarctic Survey, aiming at a development programme for a new generation of glaciological sensors.

Dr Wadhams was a lecturer on a voyage of the Russian nuclear icebreaker Sovetsky Soyuz from Murmansk to the North Pole, July 1998, and collected along-track video data for comparison with SAR imagery for ice type analysis.

Huddleston completed a PhD thesis on 'Modelling the sea ice thickness in the Greenland Sea.' The thesis was submitted in July 1998 and was approved for the award of a PhD. Huddleston proceeded to a research position in climate modelling at the Hadley Centre, Meteorological Office.

Hall (Research Student on a NERC CASE studentship sponsored by Earth Observation Sciences, Farnham (Dr Neil McIntyre)) continued his research on remote sensing and classification of ice types in the Greenland Sea and Kara Sea, concentrating on the signatures of the developing forms of young ice. Part of his work formed a component of our contribution to the EU 'Ice Routes' project.

Cottier continued PhD research on the physics of brine drainage channels in sea ice and their influence on thermal properties and salinity distribution, with support from the Isle of Man Department of Education and from private sources. Together with Hall, he visited the National Institute of Polar Research, Tokyo, April 1998, with support from the British Council, to renew contacts made during a previous visit in 1997.

Aksenov continued PhD research with support from the EU 'Ice State' programme on sea ice mechanics. As well as working on results from ZIP-97, he visited Helsinki University of Technology for discussions on results and laboratory experiments.

Ingibjorg Jonsdottir continued PhD research on the historical statistics of sea-ice distribution around Iceland. She spent October 1997 to June 1998 based at the Icelandic Meteorological Office, Reykjavik, working on the collection and evaluation of historical sources on the sea-ice history of Iceland, and on sea-ice monitoring techniques currently in use around Iceland, especially involving remote sensing. This research included several ice reconnaissance flights with the Icelandic Coast Guard. She gave papers on the sea-ice history of Iceland at the ACROSS Conference in Reykjavik, 26-28 March 1998, and at the ACSYS Conference in Seattle, 3-7 August 1998. She gave a paper on sources for sea ice information at the 'Climate and history' conference in Norwich, and presented a poster at the 'North Atlantic climate impacts' workshop, Reykjavik, 23-26 September 1998.

Capt Lawson Brigham continued his PhD research on the ice cover of the Kara, Laptev, and East Siberian seas. His work contributed towards the EU 'Ice Routes' project and the International Northern Sea Route Programme (INSROP). He presented a paper on 'Recent environmental change in the Russian maritime Arctic' at the NSF 'Arctic change' workshop in Seattle, 10-12 November 1997. He attended the first IASC-SCAR joint symposium in Tromsø on 'Polar aspects of global change,' 24-28 August 1998, and presented a paper with Dr Wadhams entitled 'Sea ice variability and implications for the Northern Sea Route.' Brigham also attended the following: 'Harmonization of polar ship rules' meeting, Hamburg, 27-31 October 1997; ACSYS conference on 'Polar processes and global climate,' Orcas Island, Washington, 3-6 November 1997 (with Dr Wadhams); workshop on 'Operational sea ice monitoring by satellites in Europe,' Helsinki, 5-6 February 1998; US Arctic Research Commission meetings (as advisor), Washington, 23-25 February 1998; INSROP working group meetings, 16-17 March 1998 in Oslo; NATO 'Workshop on the freshwater budget of the Arctic Ocean,' Tallinn, 25 April-2 May 1998; and ACSYS workshop on 'Operational sea ice charts in the Arctic,' Seattle, 5-7 August 1998.

Yanice Faugere (CNRS, Marseille) visited the Institute during 1997-1998 on an EU exchange scheme to carry out a design study for a new type of rugged long-lasting satellite-tracked drifter for data gathering on polar pack ice, continuing a project begun in the previous year by Karine Thoral.