How greenhouse forcing affects ice sheets and sea level during peak interglacial times is an unresolved question of great societal importance. Here we examine the development of glacial-interglacial sequence motifs in drill cores from the Pacific margin of Antarctica and
explore how the West Antarctic Ice Sheet impacted sedimentary systems under different climate states, including during the Pliocene Climatic Optimum (PCO) ~4.5-4.0 Ma. Hundreds of meters of Pliocene sediments were recovered during IODP Expedition 379 in two drill sites within the Resolution Drift. Site U1533 was positioned near a submarine channel originating from the Amundsen Sea continental slope, and Site U1532 was located on the western upper flank of the hemipelagic drift. Abundance and type of sediment transport structures in the cores change gradually in lower Pliocene strata in both drill sites in concert with changes in sedimentation rate. Pliocene strata are characterized with a repetitive facies stacking pattern composed of greenish gray clast-bearing mud with a biosiliceous component, interbedded with dark brownish gray laminated silty clay. The greenish gray clast-bearing muds are tentatively interpreted as “interglacials”, however, many greenish grey units have sharp upward transitions into “glacial” laminated mud and the units are irregularly spaced with depth. Analysis of the red-green channel (a*) in shipboard reflectance spectroscopy and colorimetry (RSC) data for Site U1532 on the shipboard age model demonstrates the variable orbital cyclicity of the facies assemblage. Sequence motifs, which are further explored in half-core magnetic susceptibility and XRF core-scanner data, highlight how ice growth and decay, downslope sediment transport, and the position and intensity of ocean currents affected the depositional systems. The ultimate goal of this work is to combine facies interpretations with the detrital sedimentology and other data sets to assess the behavior of the West Antarctic Ice Sheet in a warmer than present climate scenario.
Recognizing and deciphering transient global warming events triggered by massive release of carbon into Earth's ocean-atmosphere climate system in the past are important for understanding climate under elevated pCO 2 conditions. Here we present new high-resolution geochemical records including benthic foraminiferal stable isotope data with clear evidence of a short-lived (30 kyr) warming event at 41.52 Ma. The event occurs in the late Lutetian within magnetochron C19r and is characterized by a ∼2°C warming of the deep ocean in the southern South Atlantic. The magnitudes of the carbon and oxygen isotope excursions of the Late Lutetian Thermal Maximum are comparable to the H2 event (53.6 Ma) suggesting a similar response of the climate system to carbon cycle perturbations even in an already relatively cooler climate several million years after the Early Eocene Climate Optimum. Coincidence of the event with exceptionally high insolation values in the Northern Hemisphere at 41.52 Ma might indicate that Earth's climate system has a thermal threshold. When this tipping point is crossed, rapid positive feedback mechanisms potentially trigger transient global warming. The orbital configuration in this case could have caused prolonged warm and dry season leading to a massive release of terrestrial carbon into the ocean-atmosphere system initiating environmental change.
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