POAC 09 - Bedford Institute of Oceanography

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Jones Sound Devon Is. Ellesmere Is. Glacier Strait Lady Ann Strait Coburg Island Baffin Bay Fig. 9. Trajectory of Iridium GPS beacon deployed on ice island (red line), overlain on contoured bathymetry. The arrow indicates the apparent grounding site. Table 1. Regression and correlation coefficients for a regression model of the form : (Ui,,Vi) = a Uw + b Vw + c + ε, where Ui,,Vi are eastward and northward iceberg drift components respectively, and Uw,Vw are NCEP/NCAR reanalysis surface wind components, a, b, and c are the regression coefficients, and ε is the error term. Dependent variable a b R Ui 0.027 0.008 0.40 Vi -0.010 0.001 0.22 After leaving Jones Sound, the ice island made a small intrusion into Lancaster Sound, reaching the centre of the sound by about 20 Nov 2008. The total travel time from northern Smith Sound (on 22 Aug 2008) to Lancaster Sound was 90 days, with about 50 days spent in Jones Sound (24 September – 13 November 2008), leaving a net travel time of 40 days. From Lancaster Sound in 2008, the Petermann ice island then drifted southward along the coast of Baffin Island, reaching Davis Strait by the end of January. Thus the travel time from Lancaster Sound to Davis Strait was less than 2.5 months.
CONCLUSIONS AND DISCUSSION Understanding of the drift of ice islands and icebergs south from Greenland is important for predicting the timing of their appearance in areas to the south such as the Grand Banks. The passive microwave data show the importance of sea ice in determining when the ice islands escape from the fjords of Greenland into Nares Strait. The GPS data collected with an Iridium ice beacon indicate an apparent grounding event lasting about one day east of Jones Sound. Grounding events are common features of iceberg drift in Baffin Bay, slowing their southward drift (Marko et al., 1982). They are also of interest in assessing risk to pipelines. Comparison of the trajectory into Jones Sound with bathymetry data suggests that the draft of the ice island was less than 60-70 m. Since the iceberg area was about 21 km 2 , assuming a draft of 50 m, a density of 0.9 tonnes/m 3 , and a draft/ freeboard ratio of 7 (Higgins, 1991), the mass of the ice island is approximately 1100x10 6 tonnes. Since the median mass of an iceberg on the Grand Banks is 0.11x10 6 tonnes (Newell, 1993), the mass of the ice island is equivalent to 10,000 typical sized icebergs on the Grand Banks, and the mean number of icebergs drifting south of 48°N is about 480 per year. In northern Smith Sound, the ice island stalled for several days in the same area that ice island fragments from the Ward Hunt Ice Shelf stalled or drifted eastward in August 1963. This drift pattern was attributed to a sluggish cyclonic gyre in Kane Basin (Nutt, 1966). Animation of AMSR-E images from August 2008 also suggests a cyclonic gyre in Kane Basin. The net travel time from the northern Smith Sound to Lancaster Sound (after subtracting the time spent in Jones Sound) was 40 days. This is similar to the travel time of the fastest WH-5 ice island fragments, which drifted from northern Smith Sound to Lancaster Sound in 50 days (Nutt, 1966). Other WH-5 ice island fragments travelled less than half the distance in 50 days. The travel time from Lancaster Sound to Davis Strait (less than 2.5 months) is similar to the 2 month travel time of the WH-5 ice island from the Ward Hunt Ice Shelf (30 Sept to 01 December 1963). In contrast, the icebergs tracked by Marko et al. (1982) that reached Davis Strait took 8-15 months, and it was estimated that the most likely travel time between Lancaster Sound and Davis Strait is 3 years. These longer times are probably due to the larger drafts of the icebergs, so that grounding was more common than for ice islands. They are probably also due to observations during the open water season, when icebergs are more likely to ground because they are not held offshore by sea ice. ACKNOWLEDGEMENTS We would like to thank Dr. Martin Fortier for deploying the two ice beacons, and Adam Drozdowski for plotting of bathymetry. This work was funded in part by the Federal Program of Energy Research and Development (PERD).
Page 1 and 2: POAC 09 Luleå, Sweden Proceedings
Page 3 and 4: across Nares Strait adjacent to the
Page 5 and 6: the ice island. A photograph of the
Page 7: is superimposed on a contour map of

POAC 09 - Bedford Institute of Oceanography

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