ALBERT

Description: The dataset compiles reconstructed changes in bottom water temperature and global ice volume from 0 to 17 Ma using δ18O in conjunction with Mg/Ca records of the infaunal benthic foraminifer, O. umbonatus from Ocean Drilling Program (ODP) Site 130-806 (equatorial Pacific; ~2500 m). This dataset covers the middle Miocene to present (17-0 Ma) and has an average temporal resolution of ~0.2 Ma. Application of the new equations to the Site 130-806 record leads to the suggestion that global ice volume was greater than today after the Middle Miocene Climate Transition (~14 Ma). ODP Site 130-806 bottom waters cooled and freshened as the Pacific zonal sea surface temperature gradient increased, and climate cooled through the Pliocene, prior to the Plio‐Pleistocene glaciation of the Northern Hemisphere.

Description: Earth's climate cooled markedly during the Late Miocene from 12 to 5 million years ago, with far-reaching consequences for global ecosystems. However, the driving forces of these changes remain controversial. A major obstacle to progress is the uncertainty over the role played by greenhouse gas radiative forcing. Here we present boron isotope compositions for planktonic foraminifera, which record carbon dioxide change for the interval of most rapid cooling, the Late Miocene Cooling event between 7 and 5 Ma. Our record suggests that CO₂ declined by some 100 ppm over this two-million year-long interval to a minimum at approximately 5.9 Ma. Having accounted non-CO₂ greenhouse gasses and slow climate feedbacks, we estimate global mean surface temperature change for a doubling of CO₂ - Equilibrium Climate Sensitivity - to be 3.9˚C (1.8–6.7 ˚C at 95% confidence) based on comparison of our record of radiative forcing from CO₂ with a record of global mean surface temperature change. We conclude that changes in CO₂ and climate were closely coupled during the latest Miocene and that Equilibrium Climate Sensitivity was within range of estimates for the late Pleistocene, other intervals of the Cenozoic, and the 21st century as presented by the Intergovernmental Panel on Climate Change.

Description: A Cenozoic multi-species record of benthic foraminiferal calcite Sr/Ca has been produced and is corrected for interspecific offsets (typically less than 0.3 mmol/mol) and for the linear relationship between decreasing benthic foraminiferal Sr/Ca and increasing water depth. The water depth correction, determined from Holocene, Late Glacial Maximum and Eocene paleowater-depth transects, is ~0.1 mmol/mol/km. The corrected Cenozoic benthic foraminiferal Sr/Ca record ranges from 1.2 to 2.0 mmol/mol, and has been interpreted in terms of long-term changes in seawater Sr/Ca, enabling issues related to higher-resolution variability in Sr/Ca to be ignored. We estimate that seawater Sr/Ca was ~1.5 times modern values in the late Cretaceous, but declined rapidly into the Paleogene. Following a minimum in the Eocene, seawater Sr/Ca increased gradually through to the present day with a minimum superimposed on this trend centered in the late Miocene. By assuming scenarios for changing seawater calcium concentration, and using published carbonate accumulation rate data combined with suitable values for Sr partition coefficients into carbonates, the seawater Sr/Ca record is used to estimate global average river Sr fluxes. These fluxes are used in conjunction with the seawater strontium isotope curve and estimates of hydrothermal activity/tectonic outgassing to calculate changes in global average river 87Sr/86Sr through the Cenozoic. The absolute magnitude of Sr fluxes and isotopic compositions calculated in this way are subject to relatively large uncertainties. Nevertheless, our results suggest that river Sr flux increased from 35 Ma to the present day (roughly two-fold) accompanied by an overall increase in 87Sr/86Sr (by ~0 to 0.001). Between 75 and 35 Ma, river 87Sr/86Sr also increased (by ~0.001 to 0.002) but was accompanied by a decrease (two- to three-fold) in river Sr flux.

Description: A deep-sea temperature record for the past 50 million years has been produced from the magnesium/calcium ratio (Mg/Ca) in benthic foraminiferal calcite. The record is strikingly similar in form to the corresponding benthic oxygen isotope (δ18O) record and defines an overall cooling of about 12°C in the deep oceans with four main cooling periods. Used in conjunction with the benthic δ18O record, the magnesium temperature record indicates that the first major accumulation of Antarctic ice occurred rapidly in the earliest Oligocene (34 million years ago) and was not accompanied by a decrease in deep-sea temperatures.

Description: Paired benthic foraminiferal trace metal and stable isotope records have been constructed from equatorial Pacific Ocean Drilling Program Site 1218. The records include the two largest abrupt (〈1 Myr) increases in the Cenozoic benthic oxygen isotope record: Oi‐1 in the earliest Oligocene (∼34 Ma) and Mi‐1 in the earliest Miocene (∼23 Ma). The paired Mg/Ca and oxygen isotope records are used to calculate seawater δ18O (δw). Calculated δw suggests that a large Antarctic ice sheet formed during Oi‐1 and subsequently fluctuated throughout the Oligocene on both short (〈0.5 Myr) and long (2–3 Myr) timescales, between about 50 and 100% of its maximum earliest Oligocene size. The magnitudes of these fluctuations are consistent with estimates of sea level derived from sequence stratigraphy. The transient expansion of the Antarctic ice sheet at Mi‐1 is marked in the benthic δ18O record by two positive excursions between 23.7 and 22.9 Ma, each with a duration of 200–300 kyr. Bottom water temperatures decreased by ∼2°C over the 150 kyr immediately prior to both rapid δ18O excursions. However, the onset of each of these phases of ice growth is synchronous, within the resolution of the records, with the onset of a 2°C warming over ∼150 kyr. We suggest that the warming during these glacial expansions reflect increased greenhouse forcing prompted by a sudden decrease in global chemical weathering rates as Antarctic basement silicate rocks became blanketed by an ice sheet. This represents a negative feedback process that might have operated during major abrupt growth phases of the Antarctic ice sheet.

Description: We present a sedimentary record from a marine core, KL11, taken from the central Red Sea, spanning the last ca. 210 kyr. The core was recovered at 18°44.5' N and 39°20.6' E from a water depth of 825 m during RV Meteor expedition M5/2 in 1987. We combine high-resolution grain size, clay mineral and geochemical data, together with Nd and Sr isotope data to identify provenance and reconstruct changes in aridity/humidity through time.

Description: Strontium, neodymium and lead isotopic signatures were measured on fluvially-derived and hemipelagic sedimentary horizons in Late Quaternary age marine sediments from Ocean Drilling Project sites 893 and 1015 in the California Borderland Basins. All samples had carbonates, organic material, biogenic silica and Fe-Mn oxides removed before full chemical digestion prior to analysis. Age estimates of samples based upon Rack and Merrill (1995), Roark et al. (2003), Romans et al. (2009), Balestra et al. (2018) and Du et al. (2018).