Lipid biomarker-based sea (sub)surface temperature record offshore Tasmania over the last 23 million years

• Main Authors: Hou, Suning, Lamprou, Foteini, Hoem, Frida S., Hadju, Mohammad Rizky Nanda, Sangiorgi, Francesca, Peterse, Francien, Bijl, Peter K.
• Format: Text
• Language: English
• Published: 2022
• Subjects: Antarctic; Pacific; Southern Ocean; The Antarctic; Antarc*; Antarctica
• Online Access: https://doi.org/10.5194/cp-2022-79; https://cp.copernicus.org/preprints/cp-2022-79/

The Neogene (23.04–2.58 Ma) is characterized by progressive buildup of Antarctic and Northern Hemisphere ice volume and climate cooling. Heat/moisture delivery to Antarctica is to a large extent regulated by the strength of meridional temperature gradients. However, the evolution of the Southern Ocean frontal systems remains scarcely studied in the Neogene. Here we present the first long-term continuous sea (sub)surface temperature (SST) record of the subtropical front area in the Southern Ocean at Ocean Drilling Program (ODP) Site 1168 off western Tasmania. This site is at present located near the subtropical front (STF), as it was during the Neogene, despite a 10 degree northward tectonic drift of Tasmania during the Neogene. We analyzed glycerol dialkyl glycerol tetraethers (GDGTs, on 433 samples) and alkenones (on 163 samples) and reconstructed the paleotemperature evolution using TEX 86 and U k’ 37 as two independent quantitative proxies. Both proxies indicate that Site 1168 experienced a temperate ~25 °C during early Miocene (23–17 Ma), reaching ~29 °C during the mid-Miocene Climatic Optimum. The stepwise ~10 °C cooling (20–10 °C) in the mid-to-late Miocene (12.5–5.0 Ma) is larger than observed in records from lower and higher latitudes. From the Pliocene to modern (5.3–0 Ma), STF SST first plateaus at ~15 °C (3 Ma), then decreases to ~6 °C (1.3 Ma), and eventually increases to the modern levels around ~16 °C (0 Ma), with a higher variability of 5 degrees compared to the Miocene. Our results imply that the latitudinal temperature gradient between the Pacific equator and STF during late Miocene cooling increased from 4 °C to 14 °C. Meanwhile, the SST gradient between the STF and the Antarctic margin decreased due to amplified STF cooling compared to the Antarctic Margin. This implies a narrowing SST gradient in the Neogene, with contraction of warm SSTs and northward expansion of subpolar conditions.