Orbital pacing of Southeast Atlantic carbonate deposition since the Oligocene (30-0 Ma): tracing entwined climate and carbon cycle interactions

The last 30 million years (Myr) of Cenozoic climate change broadly charted the transformation from a world with solitary Antarctic ice sheets through to a bipolar glaciated Earth. Highly resolved records of carbonate content (�CO3) provide insight into regional impacts of ever shifting climate, cryosphere and carbon cycle interactions. Here, we use X-ray fluorescence (XRF) ln(Ca/Fe) data collected at Ocean Drilling Program Site 1264 (Angola Basin side of Walvis Ridge, SE Atlantic Ocean) to generate the first SE Atlantic �CO3 record spanning 30-0 Myr ago (Ma). Minimal changes in terrigenous-derived XRF data supports that the �CO3 reflects the balance between productivity and dissolution in this region. This XRF data also helped to formulate a comprehensive and continuous depth and age model for the entirety of Site 1264 (~316 m; 30-0 Ma). These verified depth and age models constitute a key framework for future palaeoceanographic studies at this location.

We identify three phases with distinctly different orbital imprints of CaCO3 deposition in the SE Atlantic. The shifts between these phases broadly occur across major developments in climate, the cryosphere and/or the carbon cycle: 1) strong ~110 kyr eccentricity pacing prevails during Oligo-Miocene global warmth (~30-13 Ma); 2) eccentricity-modulated precession imprints more strongly after the mid Miocene Climate Transition (mMCT) (~14-8 Ma); 3) strong obliquity pacing prevails in the late Miocene (~7.7-3.3 Ma) following widespread cooling and the increasing influence of high-latitude processes.

The lowest �CO3 (92-94%) occur between 18.5-14.5 Ma, potentially reflecting increased dissolution or decreased productivity driven by widespread early Miocene warmth. Deposition recovered after the mMCT (~14 Ma), likely associated with changes in regional surface and/or deep-water circulation following Antarctic reglaciation. The highest Site 1264 �CO3 and MARs indicate the late Miocene Biogenic Bloom (LMBB) occurs between ~7.8-3.3 Ma. The LMBB’s onset (~7.8 Ma) and peak productivity (~7 Ma) at 1264 are contemporaneous with the LMBB in the equatorial Pacific Ocean; however the termination is ~1 Myr later in the Atlantic compared to the Pacific. Globally synchronous patterns in the LMBB, including the onset and peak, may be driven by an increased nutrient input into the global ocean, for instance from enhanced aeolian dust and/or weathering fluxes. Regional diachrony and variability in the LMBB’s expression may be driven by regional differences in cooling, continental aridification and/or changes in ocean circulation during the latest Miocene.