Late Paleocene – early Eocene Arctic Ocean Sea Surface Temperatures; reassessing biomarker paleothermometry at Lomonosov Ridge

Abstract

Abstract. The Integrated Ocean Drilling Program Arctic Coring Expedition on Lomonosov Ridge, Arctic Ocean (IODP Expedition 302 in 2004) delivered the first Arctic Ocean sea surface temperature (SST) and land air temperature (LAT) records spanning the Paleocene-Eocene Thermal Maximum (PETM; ~56 Ma) to Eocene Thermal Maximum 2 (ETM2; ~54 Ma). The distribution of glycerol dialkyl glycerol tetraether (GDGT) lipids indicated elevated SST (ca. 23 to 27 °C) and LATs (ca. 17 to 25 °C). However, recent analytical developments have led to: (i) improved temperature calibrations and (ii) the discovery of new temperature-sensitive glycerol monoalkyl glycerol tetraethers (GMGTs). Here, we have analyzed GDGT and GMGT distributions in the same sediment samples using new analytical procedures, interpret the results following the currently available proxy constraints and assess the fidelity of new temperature estimates in our study site. The influence of several confounding factors on TEX86 SST estimates, such as variations in export depth and input from exogenous sources, are typically negligible. However, contributions of isoGDGTs from land, which we characterize in detail, complicate TEX86 paleothermometry in the late Paleocene and part of the interval between the PETM and ETM2. The isoGDGT distribution further supports temperature as the likely variable controlling TEX86 values and we conclude that background early Eocene SSTs generally exceeding 20 °C, with peak warmth during the PETM (~26 °C) and ETM2 (~27 °C). We also report high abundances of branched glycerol monoalkyl glycerol tetraethers throughout (branched GMGTs), most likely dominantly marine in origin, and show that their distribution is sensitive to environmental parameters. Further analytical, provenance and environmental work is required to test if and to what extent temperature may be an important factor. Published temperature constraints from branched GDGTs and terrestrial vegetation also support remarkable warmth in the study section and elsewhere in the Arctic basin, with vegetation proxies indicating coldest month mean temperatures of 6–13 °C. If TEX86-derived SSTs truly represent mean annual SSTs, the seasonal range of Arctic SST was in the order of 20 °C, higher than any open marine locality in the modern ocean. If SST estimates are skewed towards the summer season, seasonal ranges were comparable to those simulated in future ice-free Arctic Ocean scenarios. This uncertainty remains a fundamental issue, and one that limits our assessment of the performance of fully-coupled climate models under greenhouse conditions.

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

“…The exact sources of these compounds in sedimentary archives and their temperature relation are as yet not fully understood. For example, brGMGTs in Paleogene Arctic Ocean sediments seem to be produced in a marine system with a strong oxygen minimum zone and substantial input of penecontemporaneous terrestrial matter (Sluijs et al, 2020). Similar to the temperature response of 5-methyl brGDGTs, the degree of methylation of acyclic brGMGTs (HMBT acyclic ) follows the TEX 86 in the Paleogene Arctic record.…”

“…Reconstructions of deep-sea (Westerhold et al, 2020) and sea surface temperature (Bijl et al, 2009(Bijl et al, , 2013aHollis et al, 2012Hollis et al, , 2019Frieling et al, 2014;Inglis et al, 2015;O'Brien et al, 2017;Evans et al, 2018;Cramwinckel et al, 2018;O'Connor et al, 2019;Sluijs et al, 2020) have revealed an overall cool climate in the Maastrichtian and Paleocene, long-term warming towards the early Eocene Climatic Optimum (EECO; 53.4-49.2 Ma) and subsequent cooling during the middle and late . The EECO stands out as particularly warm, with ice-free polar regions (Hollis et al, 2009(Hollis et al, , 2012Pross et al, 2012;Bijl et al, 2013a;Frieling et al, 2014;Hines et al, 2017).…”

“…Lipids from a related biomarker family, the branched glycerol monoalkyl glycerol tetraethers (brGMGTs), were identified in the marine realm in core-top sediments (Liu et al, 2012), oxygen minimum zones (Xie et al, 2014) and Paleogene sediments (Sluijs et al, 2020). In the terrestrial realm, they were described in peats (Naafs et al, 2018a) and East African lake sediments (Baxter et al 2019), the latter identifying seven individual brGMGTs.…”

“…The brGMGTs contain a covalent bond connecting the two alkyl chains, which is thought to enhance membrane stability at higher temperatures (Morii et al, 1998). The abundance of brGMGTs relative to that of brGDGTs, as well as the relative distribution of brGMGT isomers, seems to vary with temperature in both the terrestrial (Naafs et al, 2018a;Baxter et al, 2019;Tang et al, 2021) and marine realms (Sluijs et al, 2020), although this is thus far only based on empirical relationships. The exact sources of these compounds in sedimentary archives and their temperature relation are as yet not fully understood.…”

Clumped isotope evidence for Early Jurassic extreme polar warmth and high climate sensitivity

“…This compilation also reveals lower SSTs near 50°N in the Callovo-Oxfordian. Russian Arctic SST are very close to Campanian-Maastrichtian and Early Eocene TEX86 H -derived SST (Jenkyns et al, 2004;Sluijs et al, 2020) and Early Eocene bioclimatic SST (Suan et al, 2017) from the Arctic (Fig. 5).…”