A Cenozoic record of the equatorial Pacific carbonate compensation depth

Abstract

Atmospheric carbon dioxide concentrations and climate are regulated on geological timescales by the balance between carbon input from volcanic and metamorphic outgassing and its removal by weathering feedbacks; these feedbacks involve the erosion of silicate rocks and organic-carbon-bearing rocks. The integrated effect of these processes is reflected in the calcium carbonate compensation depth, which is the oceanic depth at which calcium carbonate is dissolved. Here we present a carbonate accumulation record that covers the past 53 million years from a depth transect in the equatorial Pacific Ocean. The carbonate compensation depth tracks long-term ocean cooling, deepening from 3.0-3.5 kilometres during the early Cenozoic (approximately 55 million years ago) to 4.6 kilometres at present, consistent with an overall Cenozoic increase in weathering. We find large superimposed fluctuations in carbonate compensation depth during the middle and late Eocene. Using Earth system models, we identify changes in weathering and the mode of organic-carbon delivery as two key processes to explain these large-scale Eocene fluctuations of the carbonate compensation depth.

Late Cenozoic sea level and the rise of modern rimmed atolls

“…Rapid reef accretion (N50 m) around 5 Ma is also observed in well-dated stratigraphic sections from uplifted atolls in the Pacific (e.g., Kita-Diato-Jima-Ohde and Elderfield, 1992; Niue- Aharon et al, 1993), providing further evidence that a period of sustained low sea level during the late Miocene may have produced the accommodation depth necessary for the observed reef growth during the ensuing early Pliocene transgression. Perhaps release of CO 2 during this rapid buildup of coral reefs (Ca 2+ +2HCO 3 − → CaCO 3 + CO 2 + H 2 O) may have contributed to observed shoaling of the carbonate compensation depth during the late Miocene and early Pliocene (Pälike et al, 2012). Moving into the mid-late Pliocene, the model suggests an escalation of glacial-interglacial sea-level variability.…”

Enhanced primary productivity and magnetotactic bacterial production in response to middle Eocene warming in the Neo-Tethys Ocean

“…2, 3, 8): (2009), the total duration of the MECO event is estimated to be~500 kyr with a warming maxima at the end of the event. During the warming peak, a shoaling of the CCD by up to 500-1500 m has been reported in the Pacific, Atlantic and Indian oceans where a total loss of carbonate is reported at sites with paleodepths below~3000 m (Bohaty et al, 2009;Pälike et al, 2012). Interval 3 of the MCA section is characterized by the lowest CaCO 3 contents in the studied section and the highest bulk carbonate δ 13 C values.…”

Continental erosion and the Cenozoic rise of marine diatoms

“…In the contemporary ocean, diatoms dominate the export flux of photosynthetic organic carbon to the ocean interior (44), and thus their emergence and rise to ecological prominence constitutes a relevant landmark in the history of Earth systems that increased the strength and efficiency of the biological pump over geological time scales. A more efficient biological pump potentially contributed to reduce atmospheric carbon dioxide levels through two different mechanisms, (i) increasing the size of the sedimentary organic carbon reservoir (44,45) and (ii) promoting the acidic dissolution of deep sea sedimentary carbonates, which increases the oceans' storage capacity for atmospheric carbon dioxide (46,47). Moreover, diatoms form the basis of some of the most productive food webs in marine ecosystems, and thus their ecological expansion profoundly influenced the flux of energy through these aquatic ecosystems (40,48).…”