Petrography and carbonate isotope stratigraphy from MIS AND-1B core, Antarctica: Evidence of the early Pliocene warming event

A large portion of ANDRILL (ANtarctic geological DRILLing) core AND-1B recovered in the Western Ross Sea and spanning the early Pliocene has been investigated in order to obtain a detailed carbonate isotope record from Antarctic margin sediments through the early Pliocene warming event. Petrographic observations and mineralogical analyses reveal the authigenic nature of the carbonate and small proportions of Fe and Mg incorporated within the calcite lattice. High productivity conditions testified by ~80 m-thick diatomite interval (383 to 460 mbsf) well fit with the composite nature of the authigenic carbonate generally characterizing organic matter-rich sediments. As is known, sediments from the Polar Region are generally poor in carbonate. Although in the investigated portion of AND-1B core the carbonate seldom exceeds 5% in content, an automated Carbonate Preparation Device was used to obtain a high-resolution stable isotope dataset. Paleoenvironmental conditions characterized by high organic matter flux are supported by negative δ13C values suggesting a contribution of isotopically light biogenic CO2 during the carbonate precipitation. As to δ18O, even if melting glaciers are thought to be responsible for depletion in 18O composition, the isotope record exhibits long- and short-term trends. Analysis of the long-term trend constrains the Pliocene warming climax in an interval between 400–450 mbsf highlighting that most of the event is not documented because of a 800 kyr hiatus. The short-term trend documents the influence of obliquity controlling the annual insolation, but also that of precession-linked cyclicity seldom documented at high latitude.