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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 ClimateTransition (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 PlioceneBiogenic Bloom (LMBB) occurs between ~7.8 and 3.3Ma 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. 

Abstract. Coherent variation in CaCO₃ burial is a feature ofthe Cenozoic eastern equatorial Pacific. Nevertheless, there has been along-standing ambiguity in whether changes in CaCO₃ dissolution or changesin equatorial primary production might cause the variability. Sinceproductivity and dissolution leave distinctive regional signals, a regionalsynthesis of data using updated age models and high-resolution stratigraphiccorrelation is an important constraint to distinguish between dissolutionand production as factors that cause low CaCO₃. Furthermore, the newchronostratigraphy is an important foundation for future paleoceanographicstudies. The ability to distinguish between primary production anddissolution is also important to establish a regional carbonate compensationdepth (CCD). We report late Miocene to Holocene time series of XRF-derived (X-rayfluorescence) bulk sediment composition and mass accumulation rates (MARs) from easternequatorial Pacific Integrated Ocean Drilling Program (IODP) sites U1335,U1337, and U1338 and Ocean Drilling Program (ODP) site 849, and we also report bulk-density-derived CaCO₃ MARs at ODP sites 848, 850, and 851. We usephysical properties, XRF bulk chemical scans, and images along withavailable chronostratigraphy to intercorrelate records in depth space. Wethen apply a new equatorial Pacific age model to create correlated agerecords for the last 8 Myr with resolutions of 1–2 kyr. Large magnitudechanges in CaCO₃ and bio-SiO₂ (biogenic opal) MARs occurred withinthat time period but clay deposition has remained relatively constant,indicating that changes in Fe deposition from dust is only a secondaryfeedback to equatorial productivity. Because clay deposition is relativelyconstant, ratios of CaCO₃ % or biogenic SiO₂ % to clayemulate changes in biogenic MAR. We define five major Pliocene–Pleistocene low CaCO₃ % (PPLC) intervalssince 5.3 Ma. Two were caused primarily by high bio-SiO₂ burial thatdiluted CaCO₃ (PPLC-2, 1685–2135 ka, and PPLC-5, 4465–4737 ka),while three were caused by enhanced dissolution of CaCO₃ (PPLC-1, 51–402 ka, PPLC-3, 2248–2684 ka, and PPLC-4, 2915–4093 ka). Regional patterns ofCaCO₃ % minima can distinguish between low CaCO₃ caused by highdiatom bio-SiO₂ dilution versus lows caused by high CaCO₃dissolution. CaCO₃ dissolution can be confirmed through scanning XRFmeasurements of Ba. High diatom production causes lowest CaCO₃ %within the equatorial high productivity zone, while higher dissolutioncauses lowest CaCO₃ percent at higher latitudes where CaCO₃ production islower. The two diatom production intervals, PPLC-2 and PPLC-5, havedifferent geographic footprints from each other because of regional changesin eastern Pacific nutrient storage after the closure of the Central American Seaway.Because of the regional variability in carbonate production andsedimentation, the carbonate compensation depth (CCD) approach is onlyuseful to examine large changes in CaCO₃ dissolution. 

The Line Islands Ridge (LIR), located south of the Hawaiian Islands between 7°N and 1°S, is one of the few large central Pacific regions shallower than the regional carbonate compensation depth. Thick sequences of carbonate sediments have accumulated around the LIR despite it being located in the sediment-starved central tropical Pacific. The LIR is an important source of carbonates to the surrounding region and deposition around the LIR has expanded the equatorial Pacific carbonate sediment tongue by about 5% of its total area. Furthermore, sediments on the ridge are potentially important paleoceanographic archives. A recent survey at the crest of the LIR finds evidence for high current activity, significant erosion, but overall net sediment deposition. Currents are strong enough to form sediment waves and lee drifts in the Palmyra Basin, at the northern terminus of the LIR. Sediments along the LIR are pelagic foraminiferal sands that are easily eroded and flow out into the surrounding abyssal plain in active submarine channel systems. As channels migrate, pelagic sediments fill in the abandoned channel arms. Despite significant sediment losses from the top of the ridge, 1.3 km of sediment has accumulated in the upper Palmyra Basin over basement formed 68 to 85 million years ago (Ma). Late Neogene erosion may be more extensive than earlier erosion cycles, in response to reduced sediment production as the Palmyra Basin exited the high productivity equatorial latitudes. Sediments with good stratigraphic order needed for paleoceanographic study are limited in this dynamic sedimentary environment, but can be found with proper survey. 

Abstract Much uncertainty exists about the state of the oceanic and atmospheric circulation in the tropical Pacific over the last glacial cycle. Studies have been hampered by the fact that sediment cores suitable for study were concentrated in the western and eastern parts of the tropical Pacific, with little information from the central tropical Pacific. Here we present information from a suite of sediment cores collected from the Line Islands Ridge in the central tropical Pacific, which show sedimentation rates and stratigraphies suitable for paleoceanographic investigations. Based on the radiocarbon and oxygen isotope measurements on the planktonic foraminiferaGlobigerinoides ruber, we construct preliminary age models for selected cores and show that the gradient in the oxygen isotope ratio ofG. ruberbetween the equator and 8°N is enhanced during glacial stages relative to interglacial stages. This stronger gradient could reflect enhanced equatorial cooling (perhaps reflecting a stronger Walker circulation) or an enhanced salinity gradient (perhaps reflecting increased rainfall in the central tropical Pacific). 

Much of our understanding of Earth’s past climate comes from the measurement of oxygen and carbon isotope variations in deep-sea benthic foraminifera. Yet, long intervals in existing records lack the temporal resolution and age control needed to thoroughly categorize climate states of the Cenozoic era and to study their dynamics. Here, we present a new, highly resolved, astronomically dated, continuous composite of benthic foraminifer isotope records developed in our laboratories. Four climate states—Hothouse, Warmhouse, Coolhouse, Icehouse—are identified on the basis of their distinctive response to astronomical forcing depending on greenhouse gas concentrations and polar ice sheet volume. Statistical analysis of the nonlinear behavior encoded in our record reveals the key role that polar ice volume plays in the predictability of Cenozoic climate dynamics.