Publication Date:
2024-03-09
Description:
The sensitivities of benthic foraminiferal Mg/Ca and Li/Ca to bottom water temperature and carbonate saturation state have recently been assessed. Here we present a new approach that uses paired Mg/Ca and Li/Ca records to calculate simultaneous changes in temperature and saturation state. Using previously published records, we first use this approach to document a cooling of deep ocean waters associated with the establishment of the Antarctic ice sheet at the Eocene-Oligocene climate transition. We then apply this approach to new records of the Middle Miocene Climate Transition from ODP Site 761 to estimate variations in bottom water temperature and the oxygen isotopic composition of seawater. We estimate that the oxygen isotopic composition of seawater varied by ~1 per mil between the deglacial extreme of the Miocene Climatic Optimum and the glacial maximum following the Middle Miocene Climate Transition, indicating large amplitude variations in ice volume. However, the longer-term change between 15.3 and 12.5 Ma is marked by a ~1°C cooling of deep waters, and an increase in the oxygen isotopic composition of seawater of ~0.6 per mil. We find that bottom water saturation state increased in the lead up to the Middle Miocene Climate Transition and decreased shortly after. This supports decreasing pCO2 as a driver for global cooling and ice sheet expansion, in agreement with existing boron isotope and leaf stomatal index CO2 records but in contrast to the published alkenone CO2 records.
Keywords:
122-761; AGE; Bottom water temperature; Calculated; Calculated moving averages; Cibicidoides mundulus, δ13C; Cibicidoides mundulus, δ18O; COMPCORE; Composite Core; Grain size, sieving; Inductively coupled plasma - mass spectrometry (ICP-MS); Joides Resolution; Leg122; Mass spectrometer Finnigan MAT 252; Ocean Drilling Program; ODP; Oridorsalis umbonatus, Lithium/Calcium ratio; Oridorsalis umbonatus, Magnesium/Calcium ratio; Size fraction 〉 0.063 mm, sand; South Indian Ridge, South Indian Ocean; Δ carbonate ion content; δ18O
Type:
Dataset
Format:
text/tab-separated-values, 2998 data points
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