A 450-kyr planktonic foraminiferal assemblage record of IODP site U1352 and its implications for the migration of the subtropical front in the south-west Pacific

Abstract

Abstract The Subtropical Front (STF) is one of the major ocean fronts in the south-west Pacific. The STF migration has a distinct but varying impact on the temperature change throughout the region. To improve our understanding on the history of the STF migration and the relationship between STF migration and global climate change, we have generated a 450-kyr record of sea surface temperature (SST) change at IODP Site U1352 located in the Canterbury Basin off New Zealand. Planktonic foraminiferal assemblages from the site were used to derive SST estimates. Comparisons of the planktonic foraminiferal assemblage and SST record of IODP Site U1352 with those of ODP Site 1119, DSDP Site 594 and core MD06-2986 allow us to reconstruct the spatial change of the STF over the last 450 kyr by locating the positions of its Southland Front (SF) section, which runs nearly parallel to the South Island's shoreline. The percentage of Neogloboquadrina pachyderma in the sum of Nq. pachyderma and Nq. incompta was below 40% at Sites IODP U1352, ODP 1119 and DSDP 594 during Marine Isotope Stage (MIS) 11c, MIS 7a–c and MIS 5e. Moreover, the SSTs of the three sites during these periods were similar and close to that of the present-day. This indicates that the three sites were covered by a Subtropical Water–Subantarctic Water (STW–SAW) mixture during these interglacials. IODP Site U1352 recorded a similar scenario during MIS 7e. In comparison with previous studies, the higher resolution record of IODP Site U1352 showed the influence of an STW–SAW mixture was limited to MIS 11c, MIS 7e, MIS 7a–c and MIS 5e at this site. The SSTs of Sites IODP U1352, ODP 1119 and DSDP 594 were similar during MIS 11a–b and MIS 9a–d. At the same time, the temperature differences among the three sites and core MD06-2986 (west of New Zealand) during MIS 11a–b and MIS 9a–d were larger than during interglacials MIS 11c, MIS 7a–c, and MIS 5e. These indicate that the Subantarctic Water (SAW) influenced Sites IODP U1352, ODP 1119 and DSDP 594 during MIS 11a–b and MIS 9a–d. The ~3–4 °C warmer SSTs at Sites IODP U1352 and ODP 1119 than at DSDP Site 594 suggest that the SF is situated between DSDP Site 594 and Sites IODP U1352, ODP 1119 during MIS 7d and glacial periods of MIS 10, MIS 8, and MIS 6. Hence, unlike previous studies in the region, MIS 7d is identified as a glacial period.