Early Paleogene temperature history of the Southwest Pacific Ocean: Reconciling proxies and models

Abstract

We present a new multiproxy (TEX86, δ18O and Mg/Ca), marine temperature history for Canterbury Basin, eastern New Zealand, that extends from middle Paleocene to middle Eocene, including the Paleocene–Eocene thermal maximum (PETM) and early Eocene climatic optimum (EECO). In light of concerns that proxy-based sea surface temperature (SST) estimates are untenably warm for the southwest Pacific during the Eocene, we review the assumptions that underlie the proxies and develop a preliminary paleo-calibration for TEX86 that is based on four multiproxy Eocene records that represent an SST range of 15–34°C. For the southwest Pacific Paleogene, we show that TEX86L exhibits the best fit with the Eocene paleo-calibration. SSTs derived from related proxies (TEX86H, 1/TEX86) exhibit a systematic warm bias that increases as TEX86 values decrease (a warm bias of 4–7°C where TEX86<0.7). The TEX86L proxy indicates that southwest Pacific SST increased by ∼10°C from middle Paleocene to early Eocene, with SST maxima of 26–28°C (tropical) during the PETM and EECO and an SST minimum of 13–16°C (cool–warm temperate) at the middle/late Paleocene transition (58.7Ma). The base of the EECO is poorly defined in these records but the top is well-defined in Canterbury Basin by a 2–5°C decrease in SST and bottom water temperature (BWT) in the latest early Eocene (49.3Ma); BWT falls from a maximum of 18–20°C in the EECO to 12–14°C in the middle Eocene. Overall, cooler temperatures are recorded in the mid-Waipara section, which may reflect a deeper (∼500m water depth) and less neritic depositional setting compared with Hampden and ODP 1172 (∼200m water depth). The high SSTs and BWTs inferred for the PETM and EECO can be reconciled with Eocene coupled climate model results if the proxies are biased towards seasonal maxima and the likely effect of a proto-East Australian Current is taken into account.