Early Paleogene evolution of terrestrial climate in the SW Pacific, Southern New Zealand

We present a long-term record of terrestrial climate change for the Early Paleogene of the Southern Hemisphere that complements previously reported marine temperature records. Using the MBT-CBT proxy, based on the distribution of soil bacterial glycerol dialkyl glycerol tetraether lipids, we reconstructed mean annual air temperature (MAT) from the Middle Paleocene to Middle Eocene (62-42 Ma) for southern New Zealand. This record is consistent with temperature estimates derived from leaf fossils and palynology, as well as previously published MBT-CBT records, which provides confidence in absolute temperature estimates. Our record indicates that through this interval, temperatures were typically 5 degrees C warmer than those of today at such latitudes, with more pronounced warming during the Early Eocene Climate Optimum (EECO; approximate to 50 Ma) when MAT was approximate to 20 degrees C. Moreover, the EECO MATs are similar to those determined for Antarctica, with a weak high-latitude terrestrial temperature gradient (approximate to 5 degrees C) developing by the Middle Eocene. We also document a short-lived cooling episode in the early Late Paleocene when MAT was comparable to present. This record corroborates the trends documented by sea surface temperature (SST) proxies, although absolute SSTs are up to 6 degrees C warmer than MATs. Although the high-calibration error of the MBT-CBT proxy dictates caution, the good match between our MAT results and modeled temperatures supports the suggestion that SST records suffer from a warm (summer?) bias, particularly during times of peak warming.