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Discussion papers | Copyright
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 14 Dec 2017

Research article | 14 Dec 2017

Review status
This discussion paper is a preprint. A revision of the manuscript is under review for the journal Climate of the Past (CP).

Oligocene TEX86-derived seawater temperatures from offshore Wilkes Land (East Antarctica)

Julian D. Hartman1, Francesca Sangiorgi1, Ariadna Salabarnada2, Francien Peterse1, Alexander J. P. Houben3, Stefan Schouten1,4, Carlota Escutia2, and Peter K. Bijl1 Julian D. Hartman et al.
  • 1Department of Earth Sciences, Utrecht University, Heidelberglaan 2, 3584CS Utrecht, The Netherlands
  • 2Instituto Andaluz de Ciencias de la Tierra, CSIC/Universidad de Granada, Avenida de las Palmeras 4, 18100 Armilla, Granada, Spain
  • 3Applied Geosciences Team, Netherlands Organisation for applied scientific Research (TNO), Princetonlaan 6, 3584CB Utrecht, The Netherlands
  • 4NIOZ Royal Netherlands Institute for Sea Research, and Utrecht University, Landsdiep 4, 1797SZ ‘t Horntje, Texel, The Netherlands

Abstract. Today, the temperature of the surface waters near the Antarctic coast is a determining factor in the formation of Antarctic Bottom Water (AABW) through sea-ice production, sea-ice extent, and the extent of the ice shelf. For the Oligocene, deep-sea benthic foraminiferal oxygen isotope (δ18O) reconstructions suggest that the volume of the Antarctic continental ice sheet(s) varied substantially both on million-year and on orbital timescales after its inception in the early Oligocene, and even reached larger than modern-day volumes. Replication of such dynamicity through physical modeling remains problematic, suggesting the existence of complex feedbacks between the cryosphere, the ocean and the atmosphere. To assess the relation between cryosphere, ocean and atmosphere, knowledge of sea surface conditions close to the Antarctic margin is essential. We present a TEX86-based surface water paleotemperature record measured on Oligocene sediments from Integrated Ocean Drilling Program (IODP) Site U1356, offshore Wilkes Land, Antarctica. This record allows us to reconstruct the magnitude of seawater temperature variability and trends on both million-year and on glacial-interglacial timescales. TEX86 index values suggest surface temperatures between 10 and 21°C during the Oligocene, which is on the upper end of the few available reconstructions. Sea surface temperature (SST) maxima occur around 30.5 and 25Ma, irrespective of the calibration equation chosen. Based on glacial-interglacial lithological alternations we have established that SST variability between glacial intervals and their successive interglacials ranged between 1.8–3.2°C. As benthic foraminiferal δ18O data incorporate both an ice-volume and a temperature component, our reconstructed Oligocene temperature variability could have implications for current Oligocene ice-volume estimates. If the long-term ad orbital SST variability is representative of that of the nearby region of deep-water formation, we can assess the impact of this temperature record on the volume and dynamics of the Antarctic ice sheet(s) by comparing it with the δ18O trends and variability. From this comparison, we argue that a significant portion of the variability and trends contained in long-term δ18O records can be explained by variability in Southern high-latitude temperature. If indeed a large part of the δ18O variability is due to large glacial-interglacial bottom-water temperature shifts, the Oligocene Antarctic ice volume was less sensitive to climate change than previously assumed.

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Julian D. Hartman et al.
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Short summary
In light of estimates of future atmospheric CO2 concentrations, we reconstructed sea surface temperatures for the Oligocene period (34–22 Ma) based on archaeal lipids from a site close to the Antarctic coast. The temperature of the sea water close to Antarctica is important for the stability of the ice shelves. On average, temperatures during this period were 17 °C. Glacial-interglacial variability was about 3 °C. The long-term trends have implications for Oligocene ice volume reconstructions.
In light of estimates of future atmospheric CO2 concentrations, we reconstructed sea surface...