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

Abstract

[1] 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 0 -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 0 -CBT records, which provides confidence in absolute temperature estimates. Our record indicates that through this interval, temperatures were typically 5 C warmer than those of today at such latitudes, with more pronounced warming during the Early Eocene Climate Optimum (EECO; 50 Ma) when MAT was 20 C. Moreover, the EECO MATs are similar to those determined for Antarctica, with a weak high-latitude terrestrial temperature gradient ( 5 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 C warmer than MATs. Although the high-calibration error of the MBT 0 -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.

Reply to Reviewer 2

“…This difference in brGDGT distribution suggests that these brGDGTs may not originate exclusively from mineral soils or peat. However, it is worth noting that the LATs derived from MBT'-CBT from some of these sites are in close agreement with LATs derived from pollen assemblages using the nearest living relative methods Pancost et al, 2013). Even when derived from mineral soils, the brGDGT assemblage in marine sediment will reflect varying combinations of settings across an entire terrestrial catchment, including different elevations and microclimates (Bendle et al, 2010).…”

“…However, recent work has shown that glassy foraminifera and some nonglassy planktic and benthic foraminifera appear to yield reliable clumped isotope data for paleoceanographic reconstructions . Solid-state reordering within the calcite mineral will alter the isotope ordering, although only in samples that have experienced burial temperatures well above 100-150 • C for over ∼ 10 Ma (Passey and Henkes, 2012;Henkes et al, 2014;Shenton et al, 2015).…”

“…9-11). The MBT'-CBT proxy has been used to reconstruct early Paleogene terrestrial temperatures from continental margin marine records from the Southern Hemisphere (Bijl et al, 2013;Pancost et al, 2013;Pross et al, 2012) and the PETM in the Northern Hemisphere (Schoon et al, 2015;Weijers et al, 2007). These studies explicitly assumed that the majority of brGDGTs in marine sediment cores are produced within mineral soils at around sea level close to the core site and transported without alteration into marine sediments of similar age.…”

Ecological and biogeochemical change in an early Paleogene peat-forming environment: Linking biomarkers and palynology

“…The early Paleogene (66-34 Ma) is characterised by high atmospheric carbon dioxide (pCO 2 ) concentrations (Pearson and Palmer, 2000;Pagani et al, 2005;Lowenstein and Demicco, 2006;Pearson et al, 2009), high sea surface temperatures (SST) (Pearson et al, 2007;Bijl et al, 2009;Hollis et al, 2012), high land temperatures (Huber and Caballero, 2011;Pancost et al, 2013) and intensification of the hydrological cycle (Pierrehumbert, 2002;Pagani et al, 2006;Krishnan et al, 2014). As a result, early Paleogene wetland environments may have been up to~3 times more abundant than today (Sloan et al, 1992;DeConto et al, 2012).…”

The formation of the oceanic temperate forests of New Zealand

“…Eocene sea surface temperatures in the southwest Pacific peaked at around 34°C falling to 21°C by the beginning of the Oligocene with the initiation of Antarctic cooling (Bijl et al 2009). Early Eocene vegetation reconstructions point to a climate with a mean winter temperature of 11°C and a mean summer temperature of 21°C (Pancost et al 2013).…”