Basal melting of A-38B: A physical model constrained by satellite observations

摘要

We observed the large tabular iceberg A-38B in the time period from the calving event at the Ronne Ice Shelf in 1998 until its grounding near South Georgia in 2004 by means of various space-borne sensors. The initial ice thickness was determined by radar altimetry, the iceberg shape from radar imaging and optical instruments. The freeboard change at different stages of the drift was derived from ICESat Laser altimeter profiles. The analysis of the satellite data confirms that the decay of A-38B is governed mainly by basal erosion. We then used a numerical model for simulating iceberg melting and fitted the melt rate by varying the turbulent exchange parameters for temperature (γ{sub}T) and salt (γ{sub}S) to match the results obtained by ICESat data. Our results show that the iceberg passed through three melting regimes characterized by iceberg drift velocity: (1) In the Weddell Sea melting conditions are similar to the situation under an ice shelf with strong tidal currents which corresponds to a γ{sub}T of 1.0 × 10{sup}(-4) m s{sup}(-1). (2) In the Scotia Sea, where the iceberg drifts unhindered with the ocean current and is surrounded by its own melt water, γ{sub}T, is 0.4 × 10{sup}(-4)m s{sup}(-1). (3) At the grounding position friction velocity is again high due to tidal currents and γ{sub}T is 1.8×10{sup}(-4) m s{sup}(-1). γ{sub}S is set to 0.00505 γ{sub}T in all cases. The analysis shows that ICESat GLAS data together with satellite imagery can provide better estimates of turbulent exchange parameters, which is a step forward in improving the knowledge of fresh water input from melting icebergs into the Southern Ocean.