Principal Investigators: Sheldon Bacon (JRD - Lead division), Robin Pascal (OTD),
John Smithers (OTD), Ian Waddington (GDD).

1. Scientific Context and Rationale

The NERC ARCICE Thematic Programme began late last year; one of its aims is to enhance our understanding of the variations in Arctic ice cover relevant to climate in NW Europe. SB in collaboration with Peter Wadhams (SPRI) were awarded £300K by ARCICE to conduct two polar cruises, one in summer 1999 on the James Clark Ross (PSO SB, cruise JR44), one in March 2000 on the Jan Mayen (PSO PW). The winter cruise is aimed at understanding the ice dynamics in the Odden ice tongue of the Iceland / Greenland Seas. Cold, fresh surface waters flow out of the Arctic through Fram strait as the East Greenland Current, an eastgoing branch of which forms the Jan Mayen Current. This current is also the south side of the Greenland Sea gyre. Nearly every winter since records began (back to the 19th century sealers and whalers), an open-ocean pancake ice field has formed here, of average extent 100,000 km², to the north of which is the open water embayment called Nordbukta. This is the centre of the Greenland Sea gyre where deep convection is known to occur. One scientific question which we wish to address via the ARCICE programme is: is the Odden a salt pump? If freezing and melting occur in the same place, then on average over a year no change results. If however the freezing and melting are not co-located - meaning simply that the ice is blown elsewhere after it is formed - then there is the possibility that differential salt input may have great effects on local water column stability, at least influencing Arctic Intermediate Water properties and formation rates (Bacon, 1998, Nature), and maybe influencing deep convection also. One way to achieve this aim is to track ice motion using surface-following floats.

The proposed float, either in in-ice or open-ocean forms, will enhance both SOC's and the UK's capacity to monitor surface and near-surface ocean, ice and atmospheric properties cheaply. It would contribute to UK programmes like ARCICE and international programmes like CLIVAR. Plus, through ARCICE, it helps increase SOC's expertise in the under-represented field of sea-ice interaction.

SB's component of the ARCICE work is explicitly directed at examining the controls on the oceanic thermohaline circulation (SOC research theme A3) and European climate (F5). This proposal also relates directly to fluxes (A1) and communications (G2).

In this proposal, we seek to design, test and build a new type of float, called PIMMs - for Pancake Ice Motion Monitors - to help address the question of ice motion in the Odden. No such float exists at present, commercially or otherwise.

We aim to make expendable floats for use in thin ice (not pack ice), so they must be robust and cheap. For this application, they would contain a minimal sensor package - GPS position plus air and sea temperatures. An important aim for SOC would be the gaining of experience with Orbcomm communications, the new low-earth-orbit, 2-way system, which we would use for data transmission. Build costs would be kept low by using existing forms and materials for the hulls: we propose a spherical hull plan with lower section a steel hemisphere and upper section a boiler plate end. With an eye to the future, having evaluated this float in extreme conditions and gained knowledge of construction techniques and performance, we could then consider other applications: ocean drifters, drifting met. buoys, drogued, carrying TS chains . . . We show below an initial design sketch by IW.

The design constraints are that the hull should be strong (steel) to withstand surface ice conditions; it should be nearly surface following, so of a similar profile to ice pancakes; it should be stable the right way up; and if squeezed by ice it should rise and not sink (same idea as for Nansen's Fram, on a smaller scale); and to be of a similar size to ice pancakes, it would be about one metre diameter.

3. Exploitation

There is a potential market for an expendable thin-ice drifter. No equivalent vehicle exists commercially at present. We are keeping Paul Ridout informed of progress with a view to Ocean Scientific handling commercial exploitation of PIMMs.

Overall aims:

Production of a hull design which approximates to a pancake ice form; it is to be low cost and rugged and to be capable of carrying telemetry and sensors. It must withstand extremes of temperature whilst providing insulation from the air. Two test floats will be built first, followed by a trial batch of six which will be deployed in the Odden in March 2000. The design is to be marketable and versatile. The scientific results will be a contribution to the ARCICE programme.

Specifics:

4.1.1 Evaluation of hull forms from simple industrial products (boiler components in stainless or mild steels).

4.1.2 Purchase of 2 hulls: one as the development prototype buoy, one as an engineering test buoy.

4.1.3 Design of a 'deck' in GRP for antenna / sensor mounting to the top sides. Much of this will be experimental with the Orbcomm and GPS antennae. Trials for effects on hull and deck materials / bonding and fixtures due to very low air temperatures.

4.1.4 Optimisation of buoy stability. Dock trials and open sea trials in the vicinity of SOC.

4.1.5 Future developments to be taken into account during design process: expansion of sensor suite; attachment of drogue systems.

4.2.1 Evaluation of antennae and housings.

4.2.2 Development of interfacing for sensors.

4.2.3 Battery packs and power supply design.

4.2.4 Dock and offshore testing of antennae, washover, inclination, performance in open sea conditions. Testing at sea in polar conditions, JR44.

4.3.1 Production of trial batch of 6 floats for scientific and technical evaluation in winter ice conditions, for deployment on Jan Mayen cruise, March 2000.

4.3.2 Analysis of results from trial batch.

4.3.3 All results to be presented in report form and/or in journals, as appropriate. Any results relevant to ARCICE to be published on ARCICE web page.

4.4.1 Initial design can start immediately. Preliminary stability trials on a half-size model have already been carried out in Southampton Water.

4.4.2 Dock & local sea trials and relevant preparatory work would take place before July 1999.

4.4.3 One or two test floats would be made operational for trials in ice during JR44.

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Page last updated by SB 17 May 1999.