0.9 Ma oxygen isotope stratigraphy for a shallow-water sedimentary transect across three IODP 317 sites in the Canterbury Bight of the southwest Pacific Ocean

Abstract

Sedimentary records in shallow-water environments provide a unique opportunity to further our understanding of regional relative sea level changes in relation to global climate change. Here we present a 0.9Ma oxygen isotope stratigraphy for a shallow-water sedimentary transect across three IODP 317 sites in the Canterbury Bight of the southwest Pacific Ocean. The sites, located on the eastern margin of the South Island of New Zealand, include a continental slope site (U1352) and two continental shelf sites (U1354 and U1351). We first generated benthic foraminifers (Nonionella flemingi) δ18O records for the three sites and a planktonic (Globigerina bulloides) record for U1352B. An initial chronological framework for the benthic δ18O record of U1352B was constructed using two accelerator mass spectrometry radiocarbon dates and four biostratigraphic events. Then a refined age model was established by correlating the U1352B benthic δ18O record with the EDC (EPICA Dome C) δD record on the AICC2012 time-scale and LR04 benthic δ18O stack. Although U1354B and U1351B have lower sedimentation rates, their benthic δ18O records correlate well with that of U1352B. To ensure the accuracy of the chronostratigraphic framework established, we also analyzed characteristics of sedimentary grain size and planktonic and benthic δ18O values. In accord with the adjacent sites, the results show that melting of the Southern Alps glaciers resulting from the warming climate during the Marine Isotope Stage (MIS) 11 and MIS 5.5 led to increased fresh water delivery, with massive terrigenous deposits. The warm sea surface temperature during MIS 7 is related to Subtropical Front migration, which led to strong current activity and coarsened grain size. Meanwhile, records of the benthic δ18O, sedimentation rate, and >63μm coarse fraction contents of Site U1352 all indicate that MIS 20 was indeed a colder interval compared to subsequent glacial times.