To assess zonal temperature and biogeographical patterns in the Paleogene of the Southern Ocean, we present new multi-proxy air and sea surface temperature data for the latest Paleocene (~57–56 Ma) and the Paleocene-Eocene Thermal Maximum (PETM; ~56 Ma) from the northern margin of the Australo-Antarctic Gulf (AAG). The various proxies document the well-known late Paleocene gradual warming and, superimposed, two late Paleocene pre-cursor warming events, hundreds of kyrs prior to the PETM. Remarkably, however, air and sea surface temperature reconstructions for the AAG and SW Pacific during the latest Paleocene, PETM and Early Eocene Climatic Optimum (~53–49 Ma) show similar trends and, within proxies, similar absolute temperatures. The record implies that the exceptional warmth previously recorded in the SW Pacific extended westward into the AAG. This contrasts with the modeled circulation and temperature patterns. We suggest that simulations of ocean circulation underestimate heat transport in the SW Pacific due insufficient resolution, not allowing for mesoscale eddy-related heat transport. We argue for a systematic approach to tackle model and proxy biases in marginal marine settings, including assessment of underexplored factors as high-latitude proxy mechanisms to confidently assess temperature in these non-analogue climates.

Earth’s hydrological cycle is expected to intensify in response to global warming, with a ‘wet-gets-wetter, dry-gets-drier’ response anticipated. The subtropics (~15-30°N/S) are predicted to become drier, yet proxy evidence from past warm climates suggests these regions may be characterised by wetter conditions. Here we use an integrated data-modelling approach to reconstruct global- and regional-scale rainfall patterns during the early Eocene (~48-56 million years ago), with an emphasis on the subtropics. Model-derived precipitation–evaporation (P–E) estimates in the tropics (0-15° N/S) and high latitudes (>60° N/S) are positive and increase in response to higher temperatures, whereas model-derived P–E estimates in the subtropics (15-30° N/S) are negative and decrease in response to higher temperatures. This is consistent with a ‘wet-gets-wetter, dry-gets-drier’ response. However, some DeepMIP model simulations predict increasing – rather than decreasing – subtropical precipitation at higher temperatures (e.g., CESM, GFDL). Using moisture budget diagnostics we find that the models with higher subtropical precipitation are characterised by a reduction in the strength of subtropical moisture circulation due to weaker meridional temperature gradients. These model simulations (e.g., CESM, GFDL) agree more closely with various proxy-derived climate metrics and imply a reduction in the strength of subtropical moisture circulation during the early Eocene. Although this was insufficient to induce subtropical wetting, if the meridional temperature was weaker than suggested by the DeepMIP models, this may have led to wetter subtropics. This highlights the important role of the meridional temperature gradient when predicting past (and future) rainfall patterns.