Greenland arctic shelf ice and climate experiment

Sediment coring were undertaken in a hitherto unexplored part of the Arctic Ocean, the margin of the Lomonosov Ridge facing the Lincoln Sea. The aim of the GreenICE project was to study the structure and dynamics of the sea ice cover and attempt to relate these to longer-term records of climate variability retrieved from sediment cores. The main field work was carried out in May 2004 from an ice camp established by a Twin Otter aircraft on drifting sea ice c.170 km north of Alert, Arctic Canada. The recovered sediment cores contain very well-preserved calcareous microfossils allowing the establishment of reliable age models and fix points for correlation with other interior Arctic Ocean late Quaternary records. The sediment records reveal new data on variable Arctic Ocean paleoceanographic conditions during the last two glacial-interglacial cycles (last 200.000 years BP). The planktic foraminifera assemblage record reveals high abundances of small subpolar T. quinqueloba in the early and late interval of marine isotope stage 5. The abundance peaks are assigned to substage 5e (last interglacial) and 5a (warm interstadial). These data indicate that the area, which totay is heavily ice-covered, has undergone extended periods of a reduced summer sea ice cover during earlier warm periods. With respect to glacial conditions, increased ice rafted debris deposition in the area appear to be associated with glacial isotope stages 6, 4 and late 3. The results are of particular interest for testing of climate model results of Arctic Ocean conditions under global warming influence. Results of the sediment core study are published in peer-reviewed international journals.

Airborne EM ice thickness surveys have been performed during all three GreenICE field campaigns, in Fram Strait (2003) and in the Arctic Ocean/Lincoln Sea north off Alert/Ellesmere Island (2004 and 2005). All surveys have been carried out in April/May. Modal ice thickness was 2.8 m in Fram Strait, relatively thick compared to measurements in other years. In 2004, modal thicknesses were between 3.6 and 4 m north of Alert and around the GreenICE ice camp. In 2005, ice thicknesses ranged around 4.6 m in the same region, showing a 0.8 m increase. In addition, the amount of deformed ice was considerably larger. In all three cases, the thick ice is a result of variable ice dynamics, as can be shown with ice drift data obtained by other GreenICE project partners. In 2003, thick ice has moved into Fram Strait from the west, due to a basin wide, anomaluos cyclonic drift pattern during the preceding months. Buoy deployed in 2004 showed a southward drift of 60 miles between 2004 and 2005, resulting in compression of the ice against the coast and consequently much thicker ice in the same area in 2005.

Simulations, using the new radar altimeter sea ice model, show that the Ku-band effective scattering surface depth is sensitive to snow density, thickness and the snow and ice surface roughness. In order to reduce errors in sea ice freeboard estimation and the derived ice thickness to acceptable levels it will be necessary to have access to these snow and ice parameters. The result is significant for the systematic mapping of sea ice thickness and the upcoming European ESA CRYOSAT mission, where part of the objective is to measure sea ice freeboard and thickness.

The utility of long period wave measurements in the ice covered Arctic Ocean was examined, with the aim of using the measurements to diagnose the path-integrated ice thickness between the source of the waves (the open ocean beyond Fram Strait) and the measurement point, in this case to the north of Greenland. Autonomous wave measuring buoys were developed and successfully deployed for over two years. Considerable practical and theoretical problems were encountered with the resonant wave theory, however, leading to the evaluation of alternative formulations to extract ice thickness. Viscoelastic parameterisations seemed most promising, and the evaluation of this method is currently underway as part of a follow-up project. The buoys also allowed the drift and dynamics of the ice to be determined. Drift was dominantly southwards, with the ice exiting the region through Nares Strait, between Greenland and Ellesmere Island.

Airborne laser freeboard surveys were performed north of Greenland for the first time, in a data sparse area of the Arctic Ocean, which should be the most sensitive region to changing ice thickness. The freeboard measurements can be correlated with thickness measurements from electromagnetic induction and submarine draft profiles to give new insight into the freeboard/draft relation and the extent of pressure ridging in this most deformed area (zone of convergence).

The success of the GreenICE camp shows that European laboratories, working together, are capable of deploying modestly budgeted ice camps in the Arctic Ocean and accomplishing serious scientific work. This is an inspiration to future research efforts of the same kind, in that in the past an Arctic ice camp was always regarded as a high-budget logistical item, deployed by a national government (Russian, US) to perform a multiplicity of tasks in an inflexible way.

3-day ice drift data for the centran Arctic Ocean is being derived in near real time from ENVISAT GMM ASAR data. Accuracy is in the order of 3 kilometers or 1km/day. Data has been derived for the period July 2004, and December 2004-June 2005. Data are stored in ASCII files with time and location of the ice features. Every possible matching pairs of images between day 1 and day day 4 (3-day interval) has been tried.

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