The volume of the Antarctic continental ice sheet(s) varied substantially during the Oligocene and Miocene ( ∼ 34–5Ma)
from smaller to substantially larger than today, both on million-year
and on orbital timescales. However, reproduction through physical
modeling of a dynamic response of the ice sheets to climate forcing
remains problematic, suggesting the existence of complex feedback
mechanisms between the cryosphere, ocean, and atmosphere systems. There
is therefore an urgent need to improve the models for better predictions
of these systems, including resulting potential future sea level
change. To assess the interactions between the cryosphere, ocean, and
atmosphere, knowledge of ancient sea surface conditions close to the
Antarctic margin is essential. Here, we present a new TEX86-based
sea surface water paleotemperature record measured on Oligocene
sediments from Integrated Ocean Drilling Program (IODP) Site U1356,
offshore Wilkes Land, East Antarctica. The new data are presented along
with previously published Miocene temperatures from the same site.
Together the data cover the interval between ∼ 34 and ∼ 11Ma
and encompasses two hiatuses. This record allows us to accurately
reconstruct the magnitude of sea surface temperature (SST) variability
and trends on both million-year and glacial–interglacial timescales. On
average, TEX86 values indicate SSTs ranging between 10 and 21°C
during the Oligocene and Miocene, which is on the upper end of the few
existing reconstructions from other high-latitude Southern Ocean sites.
SST maxima occur around 30.5, 25, and 17Ma.
Our record suggests generally warm to temperate ocean offshore Wilkes
Land. Based on lithological alternations detected in the sedimentary
record, which are assigned to glacial–interglacial deposits, a SST
variability of 1.5–3.1°C at
glacial–interglacial timescales can be established. This variability is
slightly larger than that of deep-sea temperatures recorded in Mg∕Ca
data. Our reconstructed Oligocene temperature variability has
implications for Oligocene ice volume estimates based on benthic δ18O
records. If the long-term and orbital-scale SST variability at Site
U1356 mirrors that of the nearby region of deep-water formation, we
argue that a substantial portion of the variability and trends contained
in long-term δ18O records can be explained by
variability in Southern high-latitude temperature and that the Antarctic
ice volume may have been less dynamic than previously thought.
Importantly, our temperature record suggests that Oligocene–Miocene
Antarctic ice sheets were generally of smaller size compared to today.
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