Abstract
We explore the imprint of orbital variability on Arctic temperature and
hydrology using sediments recovered during the Arctic Coring Expedition
in 2004. High resolution records of lipid biomarkers (GDGTs; 2-kyr) and
palynological assemblages (5-kyr) in the ~4 m interval
below Eocene Thermal Maximum 2 (~54 Ma) show highly
cyclic signals related to ~20-kyr precession,
~40-kyr obliquity and ~100-kyr
eccentricity. The GDGTs indicate obliquity and precession variability
representative of sea surface temperature (SST) variations up to
~1.4 and ~0.5 ºC, respectively. Peak
SSTs coincide with an elevated supply of pollen and spores and increased
marine productivity. Together, this implies an orbital control on
precipitation and terrestrial nutrient supply to the Arctic Basin.
Assuming that SST maxima correspond to Arctic insolation maxima
(precession minima/obliquity maxima), precipitation maxima also
correspond to insolation maxima, implying regional hydrological
processes as a forcing rather than variations in meridional water
transport, starkly contrasting Pleistocene Arctic hydrology. The
relative amplitudes of precession and obliquity in the SST record match
that of local insolation between spring and fall, corroborating previous
suggestions of a seasonal GDGT bias. The reconstructed complete orbital
imprint refutes that ACEX temperature reconstructions are biased to one
end of the orbital variability. Eccentricity-related SST variability was
~0.8 ºC, ~2–3 times higher than
synchronous variability in the deep ocean, and 3–4 times higher than
similar variations in the tropics. This confirms eccentricity-forced
global temperature variability during the Eocene, and that this had
pronounced polar amplification, despite the absence of ice and snow
albedo feedbacks.