Climate, cryosphere and carbon cycle controls on Southeast Atlantic orbital-scale carbonate deposition since the Oligocene (30–0 Ma)

Abstract

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.

Secular and orbital-scale variability of equatorial Indian Ocean summer monsoon winds during the late Miocene

“…Increases in the MAR of biogenic components (CaCO 3 , opal, organic carbon, phosphorus) between ∼ 9 and 4 Ma have been measured in sediments from the Pacific, Indian, and Atlantic Oceans (Farrell et al, 1995;Lyle and Baldauf, 2015;Van Andel et al, 1975;Grant and Dickens, 2002;Delaney and Filippelli, 1994;Hermoyian and Owen, 2001;Dickens and Owen, 1999;Drury et al, 2021). This period of increased biogenic sedimentation, supported by independent paleoproductivity proxies (e.g.…”

“…S4b). A 405 kyr modulation of the ocean carbon cycle, primarily recorded in carbonate content and benthic δ 13 C records (Herbert, 1997;Drury et al, 2021;De Vleeschouwer et al, 2020;Westerhold et al, 2020;Pälike et al, 2012;Paillard, 2017;Holbourn et al, 2007) but also in productivity and monsoon-related dust records (Rickaby et al, 2007;Wang et al, 2010), has been observed throughout the Cenozoic and Mesozoic sedimentary record. In middle Miocene records, poor carbonate preservation noted during eccentricity maxima is interpreted in terms of transient shoaling of the carbonate saturation horizon (Holbourn et al, 2007;Flower and Kennett, 1994).…”

Drivers of Late Miocene Tropical Sea Surface Cooling: A New Perspective From the Equatorial Indian Ocean

“…Obliquity cycles are also identified in the ODP Site 1146 Mg/Ca-SST record from the South China Sea, with a similar increase in power after 7.5 Ma (Figure S8 in Supporting Information S1; Holbourn et al, 2018). The direct effect of obliquity on low-latitude insolation is small, and the appearance of strong obliquity cycles in tropical SSTs is broadly concurrent with their appearance in benthic δ 13 C and δ 18 O from Site U1443 (Bolton et al, 2022) and in a late Miocene benthic δ 18 O global stack (Drury et al, 2021), suggesting an increase in tropical SST sensitivity to obliquity linked to an increase in high-latitude forcing. Cross-wavelet analysis of SST and benthic δ 18 O from Site U1443 show high coherency (>95%) in the obliquity band (Figure 3e), suggesting that SSTs and deep-ocean δ 18 O (linked to continental ice volume and temperature in deepwater formation regions) were coupled on orbital timescales during the late Miocene.…”

Early Miocene Intensification of the North African Hydrological Cycle: Multi‐Proxy Evidence From the Shelf Carbonates of Malta

“…However, the benthic oxygen isotope record also indicates an earlier decreasing δ 18 O trend between ~19.5 Ma and ~17 Ma (Figure 7; De Vleeschouwer et al, 2017;Westerhold et al, 2020 ) which is correlatable with an Early Miocene warming trend from ~20 Ma as indicated by Mg/Ca temperature proxy (Cramer et al, 2011). Widespread decreases in deep ocean CaCO3 mass accumulation rates have also been used to argue for increasing oceanic dissolved inorganic carbon (DIC) concentrations during this interval, suggesting that the gradual warming was caused by changes in the global carbon cycle (Drury et al, 2021). We note a step increase in chert horizons in the global oceanic records, starting around 19 Ma and terminating around 13 Ma (Muttoni & Kent, 2007).…”