Maastrichtian–Rupelian paleoclimates in the southwest Pacific – a critical re-evaluation of biomarker paleothermometry and dinoflagellate cyst paleoecology at Ocean Drilling Program Site 1172

Abstract. Sea surface temperature (SST) reconstructions based on isoprenoid glycerol dialkyl tetraether (isoGDGT) distributions from the Eocene southwest (SW) Pacific Ocean are unequivocally warmer than can be reconciled with state-of-the-art fully coupled climate models. However, SST signal preserved in sedimentary archives affected by contributions of additional isoGDGT sources. Methods now exist to identify and possibly correct for overprinting effects distribution marine sediments. Here, we use current proxy insights (re-)assess reliability isoGDGT-based 69 newly analyzed 242 reanalyzed sediments at Drilling Program (ODP) Site 1172 (East Tasman Plateau, Australia) following chromatographic techniques. We compare our results paleoenvironmental paleoclimatologic dinoflagellate cysts. The resulting ? 130 kyr resolution Maastrichtian–Oligocene record TetraEther indeX tetraethers 86 carbon atoms (TEX86) confirms previous conclusions anomalous warmth early SW remarkably cool conditions during mid-Paleocene. Dinocyst diversity assemblages show a strong response local evolution, supporting robustness TEX86 record. Soil-derived branched GDGTs stored same used reconstruct mean annual air (MAAT) nearby land using Methylation index Branched Tetraethers 5-methyl bonds (MBT'5me) proxy. MAAT is consistently lower Eocene, independent calibration chosen. General trends similar, except (1) an enigmatic absence rise Paleocene–Eocene Thermal Maximum Middle Climatic Optimum, (2) subdued middle–late cooling relative SST. Both dinocysts GDGT signals suggest mid-shelf depositional environment river runoff Paleocene–early progressively becoming more thereafter. This trend reflects gradual subsidence pronounced wet/dry seasons northward-drifting Australian hinterland, which may also explain middle that overall correlation between dinocyst assemblages, biodiversity changes suggests exerted influence surface-water ecosystem. Finally, find support potential control compositional monoalkyl (brGMGTs) It encouraging critical evaluation most generated data reliable. this implies high TEX86-based SSTs systematic offset absolute MBT'5me-based estimates remain without definitive explanation.