Southwest Pacific sea surface conditions during marine isotope stage 11 – results from dinoflagellate cysts

Dinoflagellate cyst (dinocyst) assemblages are examined from three SW Pacific marine sediment cores covering Marine Isotope Stage 11 (MIS11, 423ka–380ka). MD06-2988 and MD06-2989 are in the east Tasman Sea, north of the Subtropical Front (STF), whilst DSDP594 is in Subantarctic surface waters (SAW) off eastern New Zealand. Sea surface temperature (SST) estimates from dinocyst assemblages indicate that the east Tasman Sea was ~2.5°C warmer than present during the peak warmth of MIS11. In the east Tasman Sea, north of the STF, there is a two-step warming into MIS11 in cores MD06-2988 and MD06-2989. East of New Zealand and south of the STF, at core site DSDP594, dinocyst SST estimates suggest that MIS11 was an extended warm period similar to, or slightly warmer than, present conditions, although data from the early phase (prior to 417ka) may be compromised due to insufficient modern analogues. At all sites, glacial/interglacial climatic fluctuations were accompanied by large assemblage changes. Glacial intervals were characterised by higher abundances of assemblages typical of SAW (Nematosphaeropsis labyrinthus, Selenopemphix antarctica±Brigantedinium spp). Subtropical surface water (STW) assemblages dominated during the interglacial in the east Tasman Sea (including Impagidinium aculeatum, I. patulum, and Spiniferites mirabilis), whilst assemblages consistent with continued SAW influence remained during the interglacial at core site DSDP594, albeit with reduced cold water indicators such as S. antarctica. The changes are particularly pronounced in the east Tasman Sea, where the STF is inferred to have been located further north during glacials MIS12 and MIS10. The influence of STW at DSDP594 during MIS11 and the Holocene is inferred to have been less than during MIS5e. A qualitative dinocyst-based index likely reflecting primary productivity (also influenced by oxygen concentration on the sea floor) is broadly anti-phased with SST on glacial–interglacial timescales at all sites.