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. Sea surface temperature (SST) reconstructions based onisoprenoid glycerol dialkyl glycerol tetraether (isoGDGT) distributions fromthe Eocene southwest (SW) Pacific Ocean are unequivocally warmer than can bereconciled with state-of-the-art fully coupled climate models. However, theSST signal preserved in sedimentary archives can be affected bycontributions of additional isoGDGT sources. Methods now exist to identifyand possibly correct for overprinting effects on the isoGDGT distribution inmarine sediments. Here, we use the current proxy insights to (re-)assess thereliability of the isoGDGT-based SST signal in 69 newly analyzed and 242reanalyzed sediments at Ocean Drilling Program (ODP) Site 1172 (East Tasman Plateau, Australia)following state-of-the-art chromatographic techniques. We compare ourresults with paleoenvironmental and paleoclimatologic reconstructions basedon dinoflagellate cysts. The resulting ∼ 130 kyr resolutionMaastrichtian–Oligocene SST record based on the TetraEther indeX oftetraethers with 86 carbon atoms (TEX86) confirms previous conclusions of anomalous warmth in the early Eocene SW Pacific andremarkably cool conditions during the mid-Paleocene. Dinocyst diversity andassemblages show a strong response to the local SST evolution, supportingthe robustness of the TEX86 record. Soil-derived branched GDGTs storedin the same sediments are used to reconstruct mean annual air temperature(MAAT) of the nearby land using the Methylation index of Branched Tetraethers with 5-methyl bonds (MBT'5me) proxy. MAAT is consistentlylower than SST during the early Eocene, independent of the calibrationchosen. General trends in SST and MAAT are similar, except for (1) anenigmatic absence of MAAT rise during the Paleocene–Eocene Thermal Maximumand Middle Eocene Climatic Optimum, and (2) a subdued middle–late EoceneMAAT cooling relative to SST. Both dinocysts and GDGT signals suggest amid-shelf depositional environment with strong river runoff during thePaleocene–early Eocene progressively becoming more marine thereafter. Thistrend reflects gradual subsidence and more pronounced wet/dry seasons in thenorthward-drifting Australian hinterland, which may also explain the subduedmiddle Eocene MAAT cooling relative to that of SST. The overall correlationbetween dinocyst assemblages, marine biodiversity and SST changes suggeststhat temperature exerted a strong influence on the surface-water ecosystem.Finally, we find support for a potential temperature control oncompositional changes of branched glycerol monoalkyl glycerol tetraethers(brGMGTs) in marine sediments. It is encouraging that a critical evaluationof the GDGT signals confirms that most of the generated data are reliable.However, this also implies that the high TEX86-based SSTs for theEocene SW Pacific and the systematic offset between absoluteTEX86-based SST and MBT'5me-based MAAT estimates remain without definitive explanation.

climate of the past

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