Antarctic ice sheet and oceanographic response to eccentricity forcing during the early Miocene

Abstract

Stable isotope records of benthic foraminifera from ODP Site 1264 in the southeastern Atlantic Ocean are presented which resolve the latest Oligocene to early Miocene (~24–19 Ma) climate changes at high temporal resolution (<3 kyr). Using an inverse modelling technique, we decomposed the oxygen isotope record into temperature and ice volume and found that the Antarctic ice sheet expanded episodically during the declining phase of the long-term (~400 kyr) eccentricity cycle and subsequent low short-term (~100 kyr) eccentricity cycle. The largest glaciations are separated by multiple long-term eccentricity cycles, indicating the involvement of a non-linear response mechanism. Our modelling results suggest that during the largest (Mi-1) event, Antarctic ice sheet volume expanded up to its present-day configuration. In addition, we found that distinct ~100 kyr variability occurs during the termination phases of the major Antarctic glaciations, suggesting that climate and ice-sheet response was more susceptible to short-term eccentricity forcing at these times. During two of these termination-phases, δ<sup>18</sup>O bottom water gradients in the Atlantic ceased to exist, indicating a direct link between global climate, enhanced ice-sheet instability and major oceanographic reorganisations

Evolution of the early Antarctic ice ages

“…Published proxy records of atmospheric CO 2 concentration show a decline from the Oligocene to the Miocene (6, 7) that is broadly contemporaneous with a strong minimum in the ∼2.4-My eccentricity cycle ∼24 My ago (8), which would promote continental ice sheet expansion if radiative forcing was the dominant control on ice volume. Previous studies using drill core records from the deep ocean demonstrate a climatic response to astronomical forcing for the Oligocene (9,10) and parts of the Miocene (11)(12)(13). However, to improve understanding of the behavior of the climate/cryosphere system, we need longer high-resolution records from strategic locations that capture the changing response of the high latitudes to the combined effects of CO 2 , astronomical forcing, and tectonic boundary conditions.…”

Late Oligocene obliquity-paced contourite sedimentation in the Wilkes Land margin of East Antarctica: implications for paleoceanographic and ice sheet configurations

“…This is also reinforced by several interpretations that document a late Oligocene increase in the influence of North Component Water (e.g. NADW-like) in the Southern Ocean (Billups et al, 2002;Pekar et al, 2006;Villa and Persico, 2006;Scher and Martin, 2008;Liebrand et al, 2011). These data are also in 675 agreement with the δ 13 C global isotopes oscillations between 26 and 25 Ma (Cramer et al, 2009), that suggest low values for an AABW and high δ 13 C values for a NADW, that may represent the different oceanic primary production and ventilation rates, as proposed in this work.…”

“…In addition, δ 13 C records on the Atlantic show systematic offsets to lower values toward a North Atlantic signal for most of the late Oligocene to early Miocene. These data suggest the influence of two distinct deep-water sources: cooler 680 southern component water and warmer northern component water (Billups et al, 2002;Pekar et al, 2006;Liebrand et al, 2011). The observed carbonate-rich facies suggest an increased influence of warmer northern component waters over the site at least in 13 occasions between 26 and 25 Ma.…”

“…Geological records of heavy isotope values ~2.5 ‰ and far field sea level records from passive margins during the Oligocene suggest that, following the continental-wide expansion of ice during the EoceneOligocene transition that culminated at the Oi-1 event (33.6 Ma), the Antarctic ice cover was at least 100 ~50 % of the current volume (e.g., Kominz and Pekar, 2001;Coxall et al, 2005;Pekar et al, 2006;Liebrand et al, 2011Liebrand et al, , 2017Mudelsee et al, 2014). The early part of the Oligocene records a significant δ 18 O decreasing slope with high-latitude sites exhibiting a strong deglaciation/warming that persisted until ~32 Ma (Mudelsee et al, 2014).…”

“…Nevertheless, there are marked differences between the late Oligocene low δ 18 O values recorded in 110 Pacific, Indian and Atlantic Ocean sites (e.g., Pälike et al, 2006;Cramer et al, 2009;Liebrand et al, 2011;Mudelsee et al, 2014;Hauptvogel et al, 2017), and the sustained high δ 18 O values recorded in Southern Ocean sites (Pekar et al, 2006;Mudelsee et al, 2014). High δ 18 O values in the Southern Ocean sediments are in agreement with the ice proximal record recovered by the Cape Roberts Project (CRP) in the Ross Sea, which show the existence of glaciers/ice sheets at sea level (Barrett et al, 2007; 115 Hauptvogel et al, 2017).…”