Origin and significance of ice-rafted detritus in the Atlantic sector of the Southern Ocean

Piston core TN057-14 from the eastern Atlantic sector of the Southern Ocean contains several layers rich in volcanic tephra that were deposited during the last glacial period. Comparison with nearby cores (TN057-13PC4/ODP Site 1094) indicates that these tephra layers are correlative with the South Atlantic (SA) ice-rafted detritus (IRD) layers identified by Kanfoush et al. (2000, 2002). We analyzed the tephra for major and trace elements as well as isotopic ratios of strontium, neodymium, and lead. The elemental and isotopic composition of all tephra layers examined indicates the South Sandwich Island volcanic arc (SSI) as their dominant source, with minor input from Bouvet Island. Similar analyses of clear mineral grains (mainly feldspars, quartz, and olivine) also point to the SSI as the main source. We conclude that tephra erupted from the SSI was first deposited as air fall on sea ice and multiyear ice and then secondarily rafted to the studied sites. Deposition of the tephra-rich IRD layers was controlled by changes in sea surface temperature and sea-ice conditions in the Polar Frontal Zone of the South Atlantic, rather than Antarctic ice sheet dynamics.