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Late Paleocene–early Eocene Arctic Ocean sea surface temperatures: reassessing biomarker paleothermometry at Lomonosov Ridge

Abstract. A series of papers published shortly after the Integrated Ocean Drilling Program
Arctic Coring Expedition (ACEX, 2004) on Lomonosov Ridge indicated
remarkably high early Eocene sea surface temperatures (SSTs; ca. 23 to 27 ∘C) and land air temperatures (ca. 17 to 25 ∘C) based
on the distribution of isoprenoid and branched glycerol dialkyl glycerol
tetraether (isoGDGT and brGDGT) lipids, respectively. Here, we revisit these
results using recent analytical developments – which have led to improved
temperature calibrations and the discovery of new temperature-sensitive
glycerol monoalkyl glycerol tetraethers (GMGTs) – and currently available
proxy constraints. The isoGDGT assemblages support temperature as the dominant variable
controlling TEX86 values for most samples. 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
Paleocene–Eocene Thermal Maximum (PETM; ∼ 56 Ma) and the Eocene
Thermal Maximum 2 (ETM2; ∼ 54 Ma). Background early Eocene
SSTs generally exceeded 20 ∘C, with peak warmth during the PETM
(∼ 26 ∘C) and ETM2 (∼ 27 ∘C). We find abundant branched GMGTs, likely dominantly marine in origin, and
their distribution responds to environmental change. Further modern work is
required to test to what extent temperature and other environmental factors
determine their distribution. Published Arctic vegetation reconstructions indicate coldest-month mean
continental air temperatures of 6–13 ∘C, which reinforces the
question of whether TEX86-derived SSTs in the Paleogene Arctic are skewed
towards the summer season. The exact meaning of TEX86 in the Paleogene
Arctic thus remains a fundamental issue, and it is one that limits our assessment
of the performance of fully coupled climate models under greenhouse
conditions.
