Climate, cryosphere and carbon cycle controls on Southeast Atlantic orbital-scale carbonate deposition since the Oligocene (30–0 Ma)
Authors: Drury Anna Joy , Liebrand Diederik , Westerhold Thomas , Beddow Helen M. , Hodell David A. , Rohlfs Nina , Wilkens Roy H. , Lyle Mitchell , Bell David B. , Kroon Dick , Pälike Heiko , Lourens Lucas J. 
Published: October 2021

Abstract. The evolution of the Cenozoic cryosphere from unipolar to
bipolar over the past 30 million years (Myr) is broadly known. Highly
resolved records of carbonate (CaCO3) content provide insight into the
evolution of regional and global climate, cryosphere, and carbon cycle
dynamics. Here, we generate the first Southeast Atlantic CaCO3 content
record spanning the last 30 Myr, derived from X-ray fluorescence (XRF)
ln(Ca / Fe) data collected at Ocean Drilling Program Site 1264 (Walvis Ridge,
SE Atlantic Ocean). We present a comprehensive and continuous depth and age
model for the entirety of Site 1264 (∼ 316 m; 30 Myr). This
constitutes a key reference framework for future palaeoclimatic and
palaeoceanographic studies at this location. We identify three phases with
distinctly different orbital controls on Southeast Atlantic CaCO3
deposition, corresponding to major developments in climate, the cryosphere
and the carbon cycle: (1) strong ∼ 110 kyr eccentricity pacing
prevails during Oligocene–Miocene global warmth (∼ 30–13 Ma), (2) increased eccentricity-modulated precession pacing appears after the middle Miocene Climate Transition (mMCT) (∼ 14–8 Ma), and (3) pervasive
obliquity pacing appears in the late Miocene (∼ 7.7–3.3 Ma)
following greater importance of high-latitude processes, such as increased
glacial activity and high-latitude cooling. The lowest CaCO3 content
(92 %–94 %) occurs between 18.5 and 14.5 Ma, potentially reflecting dissolution
caused by widespread early Miocene warmth and preceding Antarctic
deglaciation across the Miocene Climatic Optimum (∼ 17–14.5 Ma)
by 1.5 Myr. The emergence of precession pacing of CaCO3 deposition at
Site 1264 after ∼ 14 Ma could signal a reorganisation of
surface and/or deep-water circulation in this region following Antarctic
reglaciation at the mMCT. The increased sensitivity to precession at Site 1264 between 14 and 13 Ma is associated with an increase in mass accumulation
rates (MARs) and reflects increased regional CaCO3 productivity and/or
recurrent influxes of cooler, less corrosive deep waters. The highest
carbonate content (%CaCO3) and MARs indicate that the late Miocene–early Pliocene Biogenic
Bloom (LMBB) occurs between ∼ 7.8 and 3.3 Ma at Site 1264; broadly
contemporaneous with the LMBB in the equatorial Pacific Ocean. At Site 1264,
the onset of the LMBB roughly coincides with appearance of strong obliquity
pacing of %CaCO3, reflecting increased high-latitude forcing. The
global expression of the LMBB may reflect increased nutrient input into the
global ocean resulting from enhanced aeolian dust and/or glacial/chemical
weathering fluxes, due to enhanced glacial activity and increased meridional
temperature gradients. Regional variability in the timing and amplitude of
the LMBB may be driven by regional differences in cooling, continental
aridification and/or changes in ocean circulation in the late Miocene.