EOCENE FLUCTUATIONS IN THE CCD & CLIMATE: EVIDENCE FROM CARBONATE & OXYGEN ISOTOPES (ODP SITE 1090)

The transition from warm global climates in the early Paleogene to cool global climates by the early Oligocene was accompanied by a large-scale reorganization of deep-sea circulation patterns (Cramer et al. 2009), small transient Antarctic glaciations (e.g., Browning et al. 1996) and large fluctuations in the Calcite Compensation Depth (CCD) (e.g., Coxall et al. 2005; Lyle et al. 2005). Using CaCO₃ and stable isotopic data from a central Pacific location, Lyle et al. (2005) proposed that the CCD changes reflected by changes in accumulation of calcium carbonate were linked to global cooling events, and possibly small glaciations in Antarctica.

We build on the Pacific study by analyzing the mid- to late Eocene (~36 to 40 Ma) section from Ocean Drilling Program (ODP) Site 1090, located in the Atlantic sector of the Southern Ocean. At a paleodepth of ~2500-3000m, this site is well located to monitor changes in the CCD. We analyzed bulk sediments from Site 1090 for (1) %CaCO₃ to document changes in the CCD in this region and (2) bulk sediment oxygen isotopes (d¹⁸O) as an indicator of cooling events and possible Antarctic glaciation from ~36-40 Ma. Our CaCO₃ data at Site 1090 record substantial variability in carbonate content, indicating fluctuations in the CCD. There is good agreement between high %CaCO₃ and high d¹⁸O, linking a deeper CCD to cooling and possible Antarctic ice sheet growth. Our results support the hypothesis proposed by Lyle et al. (2005).