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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.

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 30gMyr, derived from X-ray fluorescence (XRF) ln(Cag/gFe) 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 (g1/4g316gm; 30gMyr). 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 g1/4g110gkyr eccentricity pacing prevails during Oligocene-Miocene global warmth (g1/4g30-13gMa), (2) increased eccentricity-modulated precession pacing appears after the middle Miocene Climate Transition (mMCT) (g1/4g14-8gMa), and (3) pervasive obliquity pacing appears in the late Miocene (g1/4g7.7-3.3gMa) following greater importance of high-latitude processes, such as increased glacial activity and high-latitude cooling. The lowest CaCO3 content (92g%-94g%) occurs between 18.5 and 14.5gMa, potentially reflecting dissolution caused by widespread early Miocene warmth and preceding Antarctic deglaciation across the Miocene Climatic Optimum (g1/4g17-14.5gMa) by 1.5gMyr. The emergence of precession pacing of CaCO3 deposition at Site 1264 after g1/4g14gMa 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 13gMa 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 g1/4g7.8 and 3.3gMa 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.

These are the supplementary datasets for the manuscript: Drury, A.J., Liebrand, D., Westerhold, T., Beddow, H., Hodell, D., Rohlfs, N., Wilkens, R.H., Lourens, L., 'History of South Atlantic carbonate deposition since the Oligocene (30-0 Ma)', in final preparation for submission Climate of the Past

Contains fulltext : 190522.pdf (Publisher’s version ) (Open Access) 45 p.

Astronomical tuning of sediment sequences requires both unambiguous cycle pattern recognition in climate proxy records and astronomical solutions, as well as independent information about the phase relationship between these two. Here we present two different astronomically tuned age models for the Oligocene–Miocene transition (OMT) from Integrated Ocean Drilling Program Site U1334 (equatorial Pacific Ocean) to assess the effect tuning has on astronomically calibrated ages and the geologic timescale. These alternative age models (roughly from ∼ 22 to ∼ 24 Ma) are based on different tunings between proxy records and eccentricity: the first age model is based on an aligning CaCO3 weight (wt%) to Earth's orbital eccentricity, and the second age model is based on a direct age calibration of benthic foraminiferal stable carbon isotope ratios (δ13C) to eccentricity. To independently test which tuned age model and associated tuning assumptions are in best agreement with independent ages based on tectonic plate-pair spreading rates, we assign the tuned ages to magnetostratigraphic reversals identified in deep-marine magnetic anomaly profiles. Subsequently, we compute tectonic plate-pair spreading rates based on the tuned ages. The resultant alternative spreading-rate histories indicate that the CaCO3 tuned age model is most consistent with a conservative assumption of constant, or linearly changing, spreading rates. The CaCO3 tuned age model thus provides robust ages and durations for polarity chrons C6Bn.1n–C7n.1r, which are not based on astronomical tuning in the latest iteration of the geologic timescale. Furthermore, it provides independent evidence that the relatively large (several 10 000 years) time lags documented in the benthic foraminiferal isotope records relative to orbital eccentricity constitute a real feature of the Oligocene–Miocene climate system and carbon cycle. The age constraints from Site U1334 thus indicate that the delayed responses of the Oligocene–Miocene climate–cryosphere system and (marine) carbon cycle resulted from highly non-linear feedbacks to astronomical forcing.

Astronomical tuning of sediment sequences requires both unambiguous cycle-pattern recognition in climate proxy records and astronomical solutions, and independent information about the phase relationship between these two. Here we present two different astronomically tuned age models for the Oligocene-Miocene Transition (OMT) from Integrated Ocean Drilling Program Site U1334 (equatorial Pacific Ocean) to assess the effect tuning has on astronomically calibrated ages and the geologic time scale. These alternative age models (from ~22 to ~24 Ma) are based on different tunings between proxy records and eccentricity: the first age model is based on an aligning CaCO3 weight (wt%) to Earth's orbital eccentricity, the second age model is based on a direct age calibration of benthic foraminiferal stable carbon isotope ratios (d13C) to eccentricity. To independently test which tuned age model and associated tuning assumptions is in best agreement with independent ages based on tectonic plate-pair spreading rates, we assign our tuned ages to the magnetostratigraphic reversals identified in deep-marine magnetic anomaly profiles. Subsequently, we compute tectonic plate-pair spreading rates based on the tuned ages. The resultant, alternative spreading rate histories indicate that the CaCO3 tuned age model is most consistent with a conservative assumption of constant, or linearly changing, spreading rates. The CaCO3 tuned age model thus provides robust ages and durations for polarity chrons C6Bn.1n-C6Cn.1r, which are not based on astronomical tuning in the latest iteration of the Geologic Time Scale. Furthermore, it provides independent evidence that the relatively large (several 10,000 years) time lags documented in the benthic foraminiferal isotope records relative to orbital eccentricity, constitute a real feature of the Oligocene-Miocene climate system and carbon cycle. The age constraints from Site U1334 thus provide independent evidence that the delayed responses of the Oligocene-Miocene climate-cryosphere system and carbon cycle resulted from highly nonlinear feedbacks to astronomical forcing. Supplement to: Beddow, Helen M; Liebrand, Diederik; Wilson, Douglas S; Hilgen, Frederik J; Sluijs, Appy; Wade, Bridget S; Lourens, Lucas Joost (2018): Astronomical tunings of the Oligocene-Miocene transition from Pacific Ocean Site U1334 and implications for the carbon cycle. Climate of the Past, 14(3), 255-270

Pelagic sediments from the subtropical South Atlantic Ocean contain geographically extensive Oligocene ooze and chalk layers that consist almost entirely of the calcareous nannofossil Braarudosphaera. Poor recovery and the lack of precise dating of these horizons in previous studies has limited our understanding of the exact number of acmes, their timing and durations, and the causes of their recurrence. Here we present a high-resolution, astronomically tuned stratigraphy of Braarudosphaera oozes (29.5-27.9 Ma) from Ocean Drilling Program Site 1264 in the subtropical southeastern Atlantic Ocean. We identify seven acme events in the Braarudosphaera abundance record. The longest lasting acme event corresponds to a strong minimum in the ~2.4-My eccentricity cycle, and four acme events coincide with ~110-ky and 405-ky eccentricity maxima. We propose that eccentricity-modulated precession forcing of the freshwater budget of the South Atlantic Ocean resulted in the episodic formation of a shallow pycnocline and hyperstratification of the upper water column. We speculate that stratified surface water conditions may have served as a virtual sea floor, which facilitated the widespread Braarudosphaera acmes. This explanation reconciles the contrasting distribution patterns of Braarudosphaera in the modern ocean, limited largely to shallow water coastal settings, compared to their relatively brief and expanded oceanic distribution in the past. Supplement to: Liebrand, Diederik; Raffi, Isabella; Fraguas, Ángela; Laxenaire, Rémi; Bosmans, Joyce H C; Hilgen, Frederik J; Wilson, Paul A; Batenburg, Sietske J; Beddow, Helen M; Bohaty, Steven M; Bown, Paul R; Crocker, Anya J; Huck, Claire E; Lourens, Lucas Joost; Sabia, Luciana (2018): Orbitally Forced Hyperstratification of the Oligocene South Atlantic Ocean. Paleoceanography and Paleoclimatology, 33(5), 511-529