Late Quaternary ice-rafting events in the SW Pacific Ocean, off eastern New Zealand

• Published in: Marine geology 2002-11, Vol.191 (1), p.19-35
• Main Authors: Carter, Lionel, Neil, Helen L, Northcote, Lisa
• Format: Article
• Language: English
• Subjects: Antarctic Circumpolar Current; Antarctica; Campbell Plateau; ice-rafted debris; palaeoclimate
• ISSN: 0025-3227; 1872-6151
• DOI: 10.1016/S0025-3227(02)00509-1

New records of ice-rafted debris (IRD) in eight cores from Campbell Plateau reveal periodic incursions of icebergs over the last 200 kyr. Observations of modern iceberg trajectories and provenance studies show the icebergs originated mainly in Antarctica and traveled east and north to the plateau margins via the Antarctic Circumpolar Current. There, local currents and winds dispersed icebergs across the plateau and adjacent regions as far north as Chatham Rise at 43°S. The shallow rise crest, along-rise circulation and strong thermal gradient associated with the nearby Subtropical Front inhibited further northward transport. Although IRD concentrations are very low (≤26 grains/g), downcore profiles and a δ 18O chronology reveal distinct peaks during (i) the transition from marine isotope stages (MIS) 7 to 6, (ii) late interglacial MIS 5 and (iii) glacial MIS 2. In addition, smaller peaks occur in MIS 4 and 3. This generalised pattern is also evident off Antarctica, indicating that periodic destabilisation of ice shelves was the main driving force behind the Campbell Plateau IRD events. However, there are significant differences between Antarctic and New Zealand IRD records that probably reflect palaeoceanographic influences on iceberg dispersal. The MIS 5 IRD event is better represented off Antarctica, confirming that last interglacial changes in sea level and temperatures encouraged iceberg discharge and proximal melting. Conversely, the MIS 2 event is relatively better shown on Campbell Plateau, implying that last glacial temperatures inhibited proximal iceberg melting and, together with a more vigorous oceanic circulation, allowed more icebergs to reach the distant plateau. A tentative correlation with records from the Southeast Atlantic and Southwest Indian oceans suggests that the IRD events were felt over much of the Southern Ocean for at least the last 70 kyr.