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 Icehouse over the past 30 million years (Myr) from a unipolar to a bipolar world is broadly known; however, the exact development of orbital-scale climate variability is less well understood. 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 (Angola Basin side of the 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), which constitutes a key reference framework for future palaeoclimatic and palaeoceanographic studies at this site. We identify three phases with distinctly different orbital controls on Southeast Atlantic CaCO3 deposition, corresponding to 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) increased eccentricity-modulated precession pacing appears after the mid Miocene Climate Transition (mMCT) (~14–8 Ma); 3) strong obliquity pacing appears in the late Miocene (~7.7–3.3 Ma) following the increasing influence of high-latitude processes. The lowest CaCO3 content (92–94 %) occur between 18.5–14.5 Ma, potentially reflecting dissolution caused by widespread early Miocene warmth and preceding Antarctic deglaciation across the Miocene Climate 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 is associated with an increase in mass accumulation rates (MARs) and reflects increased regional CaCO3 productivity and/or an influx of cooler, less corrosive deep-waters. The highest %CaCO3 and MARs indicate the late Miocene Biogenic Bloom (LMBB) occurs between ~7.8–3.3 Ma at Site 1264, which is broadly, but not exactly, contemporaneous with the LMBB in the equatorial Pacific Ocean. The global expression of the LMBB may reflect an increased nutrient input into the global ocean resulting from enhanced aeolian dust and/or glacial/chemical weathering fluxes. 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.

Abrupt conclusion of the late Miocene-early Pliocene biogenic bloom at 4.6-4.4 Ma

“…To further demonstrate the complexity of PP patterns, differential biogenic sedimentation has in some cases been reported even within small distances in the same basin. For example, ODP Site 1085 shows a rebound in CMAR after 3 Ma while the biogenic bloom seems to have persisted at Site 1264 until 3 Ma 27 .…”

Late Miocene Onset of Tasman Leakage and Southern Hemisphere Supergyre Ushers in Near‐Modern Circulation

“…The late Miocene onset of the SHS is coeval with many important climatic and oceanographic events, including the LMCIS, establishment of "modern" intermediate waters (Hodell & Venz-Curtis, 2006) and simultaneous peaks in carbonate production between the eastern Pacific and the South Atlantic (Drury et al, 2021). Our study demonstrates that TL turned on at 7 Ma, and therewith provides a new piece of the cause-and-effect chain shaping the major transformation of oceans and climate at that time.…”

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

“…Increases in the MAR of biogenic components (CaCO3, 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 525 Filippelli, 1994;Hermoyian and Owen, 2001;Dickens and Owen, 1999;Drury et al, 2020). This period of increased biogenic sedimentation, supported by independent paleoproductivity proxies (e.g., Diester Haass et al, 2005), is thought to reflect higher biological productivity and was dubbed the "biogenic bloom" by Farrell et al (1995).…”

“…S3b). 405-kyr modulation of the ocean carbon cycle, primarily recorded in carbonate content and benthic δ 13 C records (Herbert, 1997;Drury et al, 2020;De Vleeschouwer et al, 2020;Westerhold et al, 2020;Pälike et al, 2012;640 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 as indicating transient shoaling of the carbonate compensation depth (Holbourn et al, 2007;Flower and Kennett, 1994).…”