Abstract
AbstractA 1-yr experiment using a pressure-sensor-equipped inverted echo sounder (PIES) was conducted in Sermilik Fjord in southeastern Greenland (66°N, 38°E) from August 2011 to September 2012. Based on these high-latitude data, the interpretation of PIESs’ acoustic travel-time records from regions that are periodically ice covered were refined. In addition, new methods using PIESs for detecting icebergs and sea ice and for estimating iceberg drafts and drift speeds were developed and tested. During winter months, the PIES in Sermilik Fjord logged about 300 iceberg detections and recorded a 2-week period in early March of land-fast ice cover over the instrument site, consistent with satellite synthetic aperture radar (SAR) imagery. The deepest icebergs in the fjord were found to have keel depths greater than approximately 350 m. Average and maximum iceberg speeds were approximately 0.2 and 0.5 m s−1, respectively. The maximum tidal range at the site was ±1.8 m and during neap tides the range was ±0.3 m, as shown by the PIES’s pressure record.
Highlights
The Greenland Ice Sheet sequesters about 2.9 million km3 of water (Bamber et al 2001) and serves as a significant freshwater source to the ocean
Because of concern about strong sedimentation in Sermilik Fjord, the pressure-sensor-equipped inverted echo sounder (PIES) discussed in section 4 was deployed with a 1.5-m mooring line attached to an anchor weight, rather than with a rigid stand
Study site In August 2011 a PIES was deployed on the seafloor at ;860-m depth in Sermilik Fjord at 658540N, 378540E, roughly in the center of the fjord, which is approximately 6–8 km wide and 65 km long (Fig. 1)
Summary
The Greenland Ice Sheet sequesters about 2.9 million km of water (Bamber et al 2001) and serves as a significant freshwater source to the ocean. Freshwater enters the oceans from the ice sheet via surface meltwater runoff forced by atmospheric heating and via basal melting driven at the ice sheet’s marine-terminating glaciers (Straneo et al 2013 and references therein) In addition to this meltwater contribution, a significant fraction of the freshwater flux from Greenland. To put the recent acceleration into context, deposits of ice-rafted debris, which has accumulated on the fjord bed (Boldt et al 2013 and references therein), have been used to infer the history of calving and iceberg discharge rate (e.g., Andresen et al 2012) In these studies, it is often assumed that changes in sediment deposition rate primarily reflect changes in iceberg discharge rate rather than variations in iceberg melt rate or changes in the icebergs’ residence times in the fjord. In addition to icebergs’ effects on ocean and fjord circulation and their impact on sedimentation rates in fjords, icebergs present tremendous risk for oceanographic and commercial equipment.
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