Millennial Scale Events from Marine Sediment Cores in the SW Pacific During Marine Isotope Stage 3

Marine Isotope Stage 3 (MIS3) is an important period in the Earth's climate history as it contains a series of millennial scale events. These can be reconstructed to help interpret the response of the Earth’s ocean/climate system to rapid climate events and this may have important connotations for the Earth's system response under anthropogenically induced climate change. During MIS3, millennial scale events in the Antarctic ice core record occur out of phase with millennial scale events in the Greenland ice core record. Antarctic millennial scale events are defined peaks in δ¹⁸O and are known as Antarctic Isotope Maxima (AIM) events. These events have been recorded in high-resolution marine sediment records in the Southern Ocean, but there is sparse literature at a high enough resolution to extract the millennial scale signal from marine cores in the SW Pacific during MIS3. This study developed high-resolution marine sediment records in the New Zealand region from cores TAN1106-28, collected in the Solander Trough region south of New Zealand, and MD97-2121, collected off the east coast of Hawkes Bay, to reconstruct millennial scale variability in the SW Pacific during MIS3. Productivity and terrestrial mass accumulation rates (MAR) were combined with stable isotopes and ITRAX XRF analysis to reconstruct ocean/climate variability during MIS3 and identify AIM events. ITRAX XRF produced high-resolution (1 mm scale) elemental proxy data which showed a high correlation coefficient between ITRAX Ca, and CaCO3 % calculated using the vacuum gasometic procedure. This suggested that ITRAX XRF accurately represented elemental variations in these marine sediment cores, and that it may be a valuable tool for high-resolution climate reconstruction. ITRAX XRF was also used to identify the Rotoehu, Tahuna and Kawakawa cryptotephra in MD97-2121. However, this analysis was only moderately successful as ITRAX elemental proxies showed multiple cryptotephra events. Samples which contained these events then had to be classified as a cryptotephra deposit using a binocular microscope, and identified as a specific tephra eruption through electron microprobe analysis.

MIS 3 reconstructions for TAN1106-28 show AIM events in both productivity fluctuations and terrestrial sedimentary input. Productivity at the site of TAN1106-28 increased during AIM events and this is consistent with findings from marine sediment cores throughout the Southern Ocean. In the New Zealand region increased productivity during AIM events was inferred to be a response to the increased availability of light or warmer sea surface temperatures, as iron decreased during AIM events, suggesting productivity was not driven by iron fertilisation. The decrease in iron and other terrigenous proxies likely reflects increased glacial erosion during the stadial phase of Antarctic millennial scale events as recorded in the onshore record during the Antarctic Cold Reversal. Overriding these millennial scale fluctuations was an increase in terrigenous accumulation heading into the MIS 2 glaciation. Like TAN1106-28, sediment accumulation increased at the site of MD97-2121 heading into the MIS 2 glacial. This suggests that eustatic sea level variations have a strong control on terrestrial accumulation in the wider New Zealand region. Unlike TAN1106-28 however, there is little evidence for AIM events in MD97-2121 to the north of the front, strongly suggests the STF acts as a boundary to the AIM signal, restricting northward movement of the signal in the Southern Hemisphere mid latitudes.