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SPRI Review 1999: 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, F. Cottier, I. Jonsdottir, R. Hall, L. Brigham
A. Howell, D. Flocco, N. Egorova

The Sea Ice and Polar Oceanography Group is studying the physical processes occurring in ice-covered seas of the Arctic and Antarctic, with an emphasis on their relevance to climate and climate change. During 1998-99, research was undertaken on projects funded by the Natural Environment Research Council, European Commission, International Arctic Research Centre (Fairbanks, Alaska), and US National Science Foundation. A highlight of the year was a major data release to the group from the United Kingdom Hydrographic Office, Taunton, comprising declassified submarine ice thickness profiles from eight cruises carried out between 1987 and 1994. The analysis of these, in conjunction with the group's existing datasets and satellite imagery, will be vital in determining the rate of change of mean ice thickness in the Arctic during the past decade. For this reason it is the group's intention to reconstitute the Sea Ice Group as an Arctic Marine Science Unit (AMSU), with the mission of understanding the impact of climate change on Arctic sea ice and oceans through field operations and validated remote sensing.

The group was involved in three major projects funded by the Science and Technology Directorate (DGXII) of the European Commission, of which two were completed during 1999.

The first project comprised the second phase (1996-99) of the European Subpolar Ocean Programme (ESOP-2), funded under the MAST-III initiative, in which Dr Peter Wadhams was a principal investigator and member of the Scientific Steering Group. The project was coordinated by Dr Eystein Jansen (University of Bergen) and sought to understand the physical mechanisms underlying the thermohaline circulation in the Greenland Sea and the process of deep-winter convection. Deep convection is associated with brine rejection due to local ice formation in a region of the central Greenland Sea gyre known as the Odden ice tongue, within the area 72-76N, 5E-10W. 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. The loss of ventilation from the surface is affecting the structure of the deep water, and ultimately may reduce the vigour of the North Atlantic thermohaline circulation and thus cause cooling of the northwestern European climate. During the final year of the project, the group completed an analysis and interpretation of data collected within the Odden by a winter research cruise which had run in March 1997 aboard RV Jan Mayen. Data on ice properties, water structure, and ice dynamics (from satellite-tracked ice buoys designed in-house), combined with passive microwave satellite imagery of the ice cover, enabled the construction and testing of a physical model of the convection process. This depends on the density enhancement and overturning of surface water through salt rejection from ice formation within the western part of Odden (a bight known as Nordbukta), with the frazil and pancake ice thus formed being transported eastward by cold westerly winds, and subsequently melting on the outer, eastern fringes of Odden. Dr Wadhams and Jeremy Wilkinson (research associate working on this project) attended the final science workshop for the project in Bologna in October 1998, and meetings for completion of final reports in Bergen and Copenhagen in January-Feberuary 1999.

During the year, results from the first phase of ESOP, which had been coordinated by Dr Wadhams, were assembled into a special issue of Deep-Sea Research Part II: Topical Studies in Oceanography, edited by Dr Wadhams, L. Miller (Institute of Marine Research, Bergen) and J.-C. Gascard (Pierre and Marie Curie University, Paris). The issue (46 (6-7): 1011-1530) contains 19 papers and was published in June 1999. It constitutes the first major work on the physics and biology of the Greenland Sea convection region.

The second project was the ICE STATE programme (1996-99), coordinated by Helsinki University of Technology (Professor Kaj Riska) with Dr Wadhams as a principal investigator, and with Martin Doble and Yevgeny Aksenov as Institute researchers. This investigated 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 was developed, based on parameters that can be observed in remote sensing data, and giving a level of risk expressed as an 'ice state,' the equivalent of 'sea state' for ocean waves. The project concluded in April 1999 with the publication of a final two-volume report. Results from the project formed a special session at the August 1999 conference on Port and Ocean Engineering under Arctic Conditions (POAC '99), with Doble presenting a paper by Doble and Wadhams entitled 'Analysis of concurrent SAR images and submarine ice draft profiles in the Arctic Ocean.' Project meetings were held in Cambridge in October 1998 and Bergen in February 1999, and the final workshop was held in Helsinki in April 1999.

The third project, which is still current, is 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 trans-oceanic travel time for such pulses, either through affecting sound speed or by changing the depth at which upwardly refracting sound is reflected off the bottom of the sea ice. Data used in the project include ice-profile data collected during submarine voyages in the Arctic. 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). Arthur Kaletzky (research associate working on the project) visited NRSC and established a remote link from Cambridge with the University of Bergen supercomputer for travel-time simulations. The group's work on the project during 1998-99 concentrated on small-scale detailed simulations of acoustic reflection phenomena at the ice-ocean interface. A paper by Kaletzky and Wadhams on the results of this work, entitled 'Ice reflection and acoustic monitoring of the ocean climate (AMOC) in the Arctic' was presented in May 1999 at the 1st Workshop on Inverse Problems in Underwater Acoustics, Heraklion. Kaletzky took part in a Greenland Sea cruise by RRS James Clark Ross in July-August 1999, launching sonobuoys and listening by hydrophone to a 19.6 Hz low-frequency source set up off Zemlya Frantsa Iosifa by the collaborating US long-range propagation project. Dr Wadhams and Kaletzky attended project meetings in Hamburg in February 1999 and in St Petersburg (Kaletzky) in September 1999.

NERC supported four projects during the year, of which two were new. The first new project, starting in May 1999, is called STIMPI (Short Timescale Motion of Pancake Ice) and is a three-year joint project between the Institute and the Dunstaffnage Marine Laboratory, Oban (David Meldrum). The objective is to improve understanding of the mechanisms of Antarctic sea ice formation and deformation in winter, using a novel design of drifting buoy. An array of six buoys, designed for deployment in the highly mobile ice formation zone, will be used to clarify the processes involved in deformation, seasonal variability, and dynamics of sea ice in the advancing winter marginal ice zone. Global Positioning System (GPS) and Low Earth Orbit (LEO) satellite technology will allow location and environmental data to be provided at a frequency high enough to resolve many of these processes for the first time. The array will map the dynamics of first-year ice from its formation in early winter to its decay the following summer. The buoys will be launched from FS Polarstern during her ANT-XVII/3 cruise to the Weddell Sea in April-June 2000. The buoys will measure sea surface temperature over wide and narrow ranges, wind speed and directi on, vertical acceleration (hence wave height) with spectral moments transmitted, and differential GPS position. Differential GPS bases will be set up at Neumayer and Halley Bay stations. The buoy design, which mimics the shape, draft, and freeboard of the pancake floes among which the buoys will be deployed, is developed from design studies of Yannice Faugere, a 1997-98 exchange student from Ecole Supérieure d'Ingenieurs de Marseille. Doble is the Institute researcher.

The second new project is part of the NERC ARCICE thematic programme (Arctic Ice and Climate Change) and is joint with the James Rennell Division of Southampton Oceanography Centre (Sheldon Bacon), with Jeremy working as the Institute researcher. ARCICE, a programme for which Dr Wadhams was a co-author of the original bid to NERC, aims to enhance understanding of, and capacity to predict, the fluctuations of Arctic sea-ice and glaciers and their influence on climate. Our own project, entitled 'Sea ice and oceanic vertical circulation,' studies the effects of sea ice on convection in the Greenland Sea, and represents a continuation of work carried out under ESOP-2. A summer (July-August 1999) and a winter (February-March 2000) expedition to the nordic seas are associated with this project. The summer cruise, by RRS James Clark Ross, was an oceanographic survey of the Greenland Sea system to map the results of the previous winter's convection on the intermediate and deep waters, and the effects of the summer's ice melt on the surface waters. The cruise reached the marginal ice zone (MIZ) in Fram Strait, and the Institute participants, Nick Hughes and Kaletzky, carried out acoustic studies, tested a video ice-monitoring system and assisted with the oceanographic programme. The winter cruise, using the ice-strengthened RV Jan Mayen, chartered from the University of Tromsø, will involve 27 scientists from Hamburg University (Dr Jan Backhaus) and the University of Tromsø (Dr Else Hedgpeth) as well as the Institute, and will spend one month in the Odden ice tongue region, mapping ocean circulation, deep and shallow convective intensity, winter ice formation and melt, salt flux associated with ice formation, physical properties of ice, and ice dynamics. Ice motion will be tracked by deployment of drifting pancake buoys similar to those being developed for STIMPI, together with simpler ice drifters constructed at Southampton Oceanography Centre. Results from these cruises combined with satellite images will allow us to gauge the influence of sea ice on the thermohaline circulation.

A continuing NERC project 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 is 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 significant reduction in the ice thickness in the Eurasian Basin of the Arctic Ocean and the Greenland Sea, relative to earlier UK datasets, a result that agrees with US results recently published by Rothrock and others for the Canada Basin region. The results are being archived to begin a NERC ice thickness data archive. A database has been set up at the Institute for archiving on to CD-ROM and all standardised data from this database will be placed on the Institute FTP site.

The fourth NERC 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 one-km grid out to a range of 50 km using doppler shift. The plan is 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 co-operation with the Italian CLIMA oceanographic programme, in order to determine the physics of heat l oss and ice production in the polynya. During the year the radar system was transferred from NERC ownership to that of Saturn Solutions Ltd, Southampton, and a new arrangement was made with the company for deployment of the system in December 1999.

The US National Science Foundation supported a project to compare the submarine data from the British cruise in 1996 and other years with complementary data collected by a US submarine during the same period in the SCICEX Programme, 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. Hughes is supported as a research associate for this project.

During 1998-99 work was completed on the 1996 joint datasets and began on datasets from 1987 and 1991. The analysed data are being included in an international data management system on Arctic Basin ice thickness set up at NSIDC (National Snow and Ice Data Center), Boulder. Common formats for statistical analysis techniques and data layouts have been agreed with our CRREL collaborators, and a suite of programs has been written and tested for the correction, interpolation, and statistical analysis of the processed sonar data; a comparison of sonar data from two different systems has been conducted as a check on the quality of the data. In addition, agreements have been negotiated with British MOD/Naval security for the handling and presentation of restricted data from the recent UKHO release, and specifically designed hardware for digitising sonar data in the form of paper charts has been built and tested for the extensive data processing task that awaits.

An in-house project carried out by Hughes was the development of ICE CAM, an integrated visual monitoring and environmental data logging package for use on ships of opportunity. ICE CAM was taken to sea by Hughes in June 1999 on an Arctic cruise of the USCG icebreaker Polar Star, which was aborted because of engine trouble. Subsequently Hughes tested the system successfully on the July-August 1999 Arctic cruise of RRS James Clark Ross to the Greenland Sea, and it will be deployed again in February 2000. The design has been taken up for promotion commercially by the Wolfson Cambridge Industrial Unit of Cambridge University, and an internet page providing details of the project can be found at http://www.spri.cam.ac.uk/people/neh25/IceCam.html.

In October-December 1998 Dr Wadhams was coordinator for the second phase of INTERICE, a project to carry out sea-ice physics research on a laboratory scale using the 40 m-long ice testing tank of HSVA (Hamburgische Schiffbau-Versuchsanstalt GmbH), Hamburg. The European Commission designated this a European Large Facility, and the INTERICE group, a group of mainly university laboratories from several European countries, made a successful bid for a series of physical and biological experiments. The first phase took place in 1997, and included experiments by Finlo Cottier and Richard Hall (research students). The second phase took place in autumn 1998, involving measurements on the development of brine drainage channels in young ice by Cottier, and measurements of the phase velocity of water waves through frazil and pancake icefields by Dr Wadhams in December 1998. The latter experiments were also filmed by the BBC Natural History Unit for use in a series on Arctic sea ice.

The International Arctic Research Centre (IARC), Fairbanks, Alaska, a newly established research centre on the campus of the University of Alaska funded by the Japanese government's Frontier Research Consortium, awarded a grant to Dr Wadhams for a modelling study, based on ICE STATE results, of the role of sea ice mechanical processes on different scales in ice-ocean models. The study, joint with Dr W.D. Hibler III (IARC), involved a four-month visit by Aksenov in 1999 and will be completed by a visit by Dr Wadhams. The aim is to incorporate small-scale results on ice deformation mechanisms into the larger-scale ice-ocean Hibler model.

Cottier completed his PhD thesis, entitled 'Brine distribution in young sea ice,' which was submitted in March 1999 and approved in June. During November-December 1998 he carried out a final set of experiments on brine drainage at the Hamburg Ice Tank, and also co-authored two papers on the topic, for EOS and the Journal of Geophysical Research.

Hall, a research student on a NERC CASE studentship sponsored by Earth Observation Sciences Ltd, Farnham, 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.

Aksenov continued PhD research with support from the EU Ice State programme on sea ice mechanics. He spent four months at the International Arctyc Research Centre, Fairbanks, Alaska, during 1999, working on the improved representation of sea ice mechanics in ice-ocean models in collaboration with Dr W.D. Hibler, as part of the IARC-funded project. He then moved to a research associate position at Southampton Oceanography Centre on an ARCICE project whilst completing his thesis.

Ingibjorg Jonsdottir continued PhD research on the historical statistics of sea ice distribution around Iceland. She gave two lectures at a one-day course on the remote sensing of sea ice in Icelandic waters, on the interpretation of SAR images for sea-ice monitoring and the distribution of sea-ice information in Icelandic waters. The course was organized by the Icelandic Meteorological Office and held on 4 March 1999 at the University of Iceland. Jonsdottir was co-author with Dr Astrid Ogilvie of a poster and presentation on 'Seascapes of Iceland: climate change and fisheries history' at the Arctic Forum in Arlington, Virginia, in March 1999. She presented a paper on 'Historical sources of sea ice, climate and fisheries in Iceland' jointly with A. Ogilvie at a conference on 'Historical dimensions of human adaptability and environmental change in North Atlantic regions' at Akureyri, Iceland, 16-21 July 1999.

Lawson Brigham continued has PhD research on the Northern Sea Route. He participated as a lead author in the integration phase of the International Northern Sea Route Programme (INSROP) and, with colleagues from the Arctic and Antarctic Research Institute in Russia and NKK Engineering in Japan, authored the INSROP integration chapter 'The natural environment, ice navigation and ship technology' in the volume The natural and societal challenges of the Northern Sea Route. Brigham gave invited lectures at the following institutions during the year: 'Sea ice variability and environmental change in the Russian Arctic' at the Department of Atmospheric Sciences, University of Illinois-Urbana, 7 October l998; 'Science across the Arctic Ocean: the US/Canada Arctic Ocean Section 1994 Expedition' at the Byrd Polar Research Center, Ohio State University, on 8 October 1998; 'Russia's Northern Sea Route - Soviet legacy and future as a trade route' at the Conflict Studies Research Centre, Royal Military Academy, Sandhurst, on 26 November 1998; 'Russia's Northern Sea Route - Soviet legacy and future under climate change' at the British Antarctic Survey, Cambridge, on 21 April 1999; and 'The 1994 US/Canada Arctic Ocean Section Expedition' at the Arctic Institute of North America, University of Calgary, Alberta, Canada on 21 July 1999. Brigham also presented the paper 'Environmental change and the Russian Arctic coastal seas' at the international symposium 'Arctic seas: currents of change' hosted by the Sea Research Foundation and Mystic Aquarium, Mystic, Connecticut, 21-24 October 1998. He presented a paper 'Scientific expedition across the Arctic Ocean' at the American Polar Society symposium on polar exploration held at the Byrd Polar Research Center, Ohio State University, on 9-11 October 1998. He also participated in the 'Workshop on the impacts of global change' sponsored by the International Arctic Science Committee in Tromso, Norway, on 25-26 April 1999.

All the above students were supervised by Dr Wadhams.

Daniela Flocco spent most of 1999 with the group, on a Leonardo da Vinci studentship from the Oceanography Department of the Istituto Universitario Navale, Napoli. During this time she worked on a theoretical model of coastal polynya dynamics for her Naples thesis.

Dr Wadhams, the Reader in Polar Studies and leader of the group, was an invited lecturer at the Gordon Research Conference on Polar Marine Science, held in Ventura, California, on 7-12 March 1999, and organised by Professor L. Legendre on the topic of 'Controls and significance of carbon fluxes in polar seas.' Dr Wadhams attended the Workshop on Arctic Climate Change at the Norsk Polarinstitutt, Tromsø, on 25-26 April 1999, and at the subsequent one-day workshop on 'Marine climate of the Arctic' gave an invited paper on sea ice changes during recent centuries. In May 1999 he was invited by the Academy of Finland to be a member of a four-man visiting group to carry out a research assessment exercise on the geoscience departments of the University of Helsinki.

During June 28-July 2 1999 Dr Wadhams was an invited participant in the meetings of the WCRP ACSYS (Arctic Climate System Study) Observational Products Panel and Numerical Experimentation Group in Koblenz. On 26-27 July he was convenor of session P13 on 'Sea ice-ocean dynamics' at the 1999 Congress of the International Union of Geodesy and Geophysics (IUGG) in Birmingham. At the same meeting he was appointed chairman of the Sea Ice Working Group of IAPSO (International Association of Physical Sciences of the Ocean).

Dr Wadhams had been an invited rapporteur at the NATO Advanced Research Workshop on the Fresh Water Budget of the Arctic Ocean, Tallinn, Estonia, 26 April 26-1 May 1998. He became co-editor of the book that is being produced from the conference and hosted a further meeting of rapporteurs at SPRI on 12-15 October 1998. As the 1990 winner of the Italgas Prize for Environmental Sciences, he was invited by Italgas to help form the Club Premio Italgas, which is organising a series of conferences on sustainable development. Planning meetings were held in Turin in October 1998 and June 1999.

Dr Wadhams was an invited lecturer at the Orkney Science Festival on 3-8 October 1999, giving two lectures on 'The finnman cometh' (recorded landings of Inuit in Scotland and past changes in Atlantic ice limits) and 'Back to the ice time?' (possible North Atlantic cooling). He was also appointed UK delegate to the European Union COST Action 714 programme on Directional Spectra of Ocean Waves, and attended their meeting in Bergen on 24-25 September 1999.

A new intergovernmental initiative involving collaborative research between the UK and Norway on rapid climatic cooling in the European Arctic seas began during 1999 with a meeting at Bergen University on 9-10 September. Dr Wadhams was invited by NERC to be on the steering committee of this programme, and, together with Keith Nicholls (BAS), compiled the bilateral science plan that emerged from the meeting.

Other meetings that Dr Wadhams attended during the year included the Antarctic Large Scale Change Workshop at BAS in August 1999, where he spoke on Antarctic sea-ice limits, and the American Geophysical Union meeting in San Francisco in December 1998, which coincided with a meeting on UK-US joint submarine data analysis. Dr Wadhams continued as coordinator of the WCRP International Programme for Antarctic Buoys, and began to implement a strategy for data transfer from Hobart and storage in Cambridge.