Global climate and cryosphere controls on South Atlantic carbonate deposition since the Oligocene (30-0 Ma)

Abstract:

The evolution of the Cenozoic Icehouse from a unipolar to a bipolar world is broadly known; however, the exact development of orbital-scale climate variability is less well understood. High-resolution carbonate (CaCO₃) records can provide insight into climate and carbon cycle dynamics, however few suitable Atlantic CaCO₃ records exist. Here, we present the first astronomically-tuned South Atlantic CaCO₃ record spanning the last 30 Myr, derived from X-ray fluorescence (XRF) ln(Ca/Fe) data collected at Ocean Drilling Program Site 1264. This new CaCO₃ record allows us to investigate how changes in global climate and the cryosphere influenced orbital-scale dynamics during the Cenozoic Icehouse. We recognise three phases with distinctly different orbital controls on South Atlantic CaCO₃ deposition, driven by major shifts in global climate: 1) strong ~110 kyr eccentricity pacing prevails during Oligo-Miocene global warmth (~30-13 Ma); 2) increased precession pacing appears after the mid Miocene Climate Transition (MMCT) (~14-8 Ma); 3) obliquity pacing appears in the late Miocene (~8 to ~3.3 Ma) following the increasing influence of high-latitude processes. Extensive CaCO₃ dissolution occurs between 18.5-14.5 Ma, in response to the widespread early Miocene warmth and preceding Antarctic deglaciation across the Miocene Climate Optimum (~17-14.5 Ma) by 1.5 Myr. The precession-pacing of CaCO₃ deposition after ~14 Ma signals a reorganisation of South Atlantic surface and/or deep-water circulation following Antarctic reglaciation at the MMCT. The increased sensitivity to precession at Site 1264 likely reflects increased regional CaCO₃ productivity and/or an influx of cooler, less corrosive deep-waters. The highest %CaCO₃ and mass accumulation rates indicate the late Miocene Biogenic Bloom (LMBB) occurs between ~7.8-3.3 Ma at Site 1264. The global onset of the LMBB may reflect an increased nutrient flux into the oceans due to enhanced glacial/chemical weathering and/or increased dust input. Regional variability in the timing and amplitude of the LMBB could reflect geographical differences in the degree of cooling, continental aridification and/or changes in oceanic circulation during the latest Miocene.