Paleo-oceanographic and -climatic reconstruction in the Southwest Pacific [ODP Site 1123] during MIS 11

• Main Author: Christiansen, Kylie Jane
• Other Authors: Carter, Lionel
• Format: Master Thesis
• Language: English
• Published: Victoria University of Wellington 2012
• Subjects: MIS 11; Marine Isotope Stage 11; Ocean Drilling Program Site 1123; ODP Site 1123; Foraminifera; New Zealand; Pacific; Planktonic foraminifera
• Online Access: http://researcharchive.vuw.ac.nz/handle/10063/4203

Marine Isotope Stage 11 [424 to 374 ka] is unique compared to most other recent Quaternary interglacial periods due to its duration and orbital geometry, both of which have previously been cited as evidence that MIS 11 may be a suitable analogue to project future climate. This study aims to evaluate this prolonged warm period at a key site in the sparsely studied Southwest Pacific Ocean at Ocean Drilling Program [ODP] 1123. This cored site, situated at 3290 m water depth on the northern flank of the Chatham Rise, straddles the northern limit of the modern Subtropical Front, 1100 km east of New Zealand, where sediments record strong subtropical and subpolar signals over interglacial to glacial cycles. Two species of planktonic foraminifera were analysed, Globigerinoides ruber and Globigerina bulloides [Gs. ruber and Gg. bulloides], for trace elements and size-normalised test weights [SNW; Gg. bulloides only] in order to reconstruct ocean temperature, chemistry, structure and circulation during MIS 11. Gg. bulloides was found to have anomalously low SNW [~50% compared to modern specimens] implying either [i] poor calcification environment due to low CO₃⁻² concentrations, or [ii] post-mortem alteration either in the deep water column or ocean floor environment. Traditional dissolution proxies for ODP 1123 do not indicate significant dissolution during MIS 11. Nevertheless, the inception of modern carbonate platforms and reefs at this time leads to the hypothesis that CO₃⁻² concentrations in the surface ocean were low due to a shifting in the locus of carbonate production, and this is a potential cause, amongst other possibilities, of the low SNW in Gg. bulloides. However, calcification in a low CO₃⁻² concentration ocean does not appear to have significantly affected the geochemical proxies utilised in this study [Mg/Ca-derived paleo-ocean temperatures, δ¹⁸O and micro-nutrients Mn/Ca and Zn/Ca ratios as water-mass tracers] based on comparison with a similar study on younger sediments in the same core. The ...