Relict sea-floor ploughmarks record deep-keeled Antarctic icebergs to 45°S on the Argentine margin

This paper reports ploughmarks on the Argentine continental margin up to 44° 50′S, the most northerly morphological evidence of giant icebergs in the southern Atlantic. More than 2500 ploughmarks up to 32 km long, 685 m wide and more than 20 m deep have been observed at modern water depths up to 646 m. Taking into account these iceberg sizes, and ocean current directions which appear to have remained similar from the last full-glacial to the present interglacial, the icebergs that produced the ploughmarks are interpreted to be calved from fast-flowing ice streams draining huge basins of the West Antarctic Ice Sheet and the western Antarctic Peninsula during the Last Glacial Maximum (LGM) about 20,000 years ago. Ploughmarks at the deepest water depths correspond to icebergs more than 500 m thick and at least 2 km wide, given a sea-level rise of 120 m since the LGM. The icebergs, after having drifted northeast in the Antarctic Circumpolar Current, were transported northward by the Falklands/Malvinas Current; a total distance of 2000 to 4000 km. The waters north of the Falkland Islands in particular were probably several degrees colder than today to prevent rapid iceberg melting and deterioration.