Transient Shoaling, Over‐Deepening and Settling of the Calcite Compensation Depth at the Eocene‐Oligocene Transition

• Published in: Paleoceanography and paleoclimatology Vol. 38; no. 6
• Main Authors: Taylor, V. E., Westerhold, T., Bohaty, S. M., Backman, J., Dunkley Jones, T., Edgar, K. M., Egan, K. E., Lyle, M., Pälike, H., Röhl, U., Zachos, J., Wilson, P. A.
• Format: Journal Article
• Language: English
• Published: Hoboken Blackwell Publishing Ltd 01-06-2023
• Subjects: Antarctic glaciation; Benthos; Calcite; Calcium; Calcium carbonate; Calcium carbonates; Carbon cycle; Carbon isotopes; Carbonate compensation depth; Carbonates; Cenozoic; Compensation; Compensation depth; Eocene; Foraminifera; Glaciation; Glaciers; Glaciology; Isostasy; New records; Oceans; Oligocene; Seawater; Seawater chemistry; Settling; Shoaling; Stable isotopes
• ISSN: 2572-4517; 2572-4525; 2572-4525
• DOI: 10.1029/2022PA004493

The major Cenozoic shift from a shallow (∼3–4 km) to deep (∼4.5 km) calcite compensation depth (CCD) occurred at the Eocene‐Oligocene Transition (∼34 Ma), suggesting a strong relationship between calcium carbonate (CaCO3) cycling and Antarctic glaciation. However, the linkages between these two events are debated. Here we present new records of bulk sediment stable isotope and carbonate composition from a depth transect of sites in the low‐latitude Pacific Ocean and one site from the South Atlantic Ocean, together with a new benthic foraminiferal stable isotope record (δ13Cb and δ18Ob) from the Pacific where the sedimentary sequence is most expanded. Our records reveal a short‐lived (∼3,000 Kyr) CCD shoaling event closely associated with a negative carbon isotope excursion in the latest Eocene. This event is immediately followed by CCD deepening which occurs in two rapid (∼40 Kyr‐long) steps. Our data show that the first of these deepening steps represents recovery from the latest Eocene shoaling event while the second was closely associated with a rapid increase in δ18Ob and shows a distinctive over‐deepening and settling pattern to >5 and 4.4 km, respectively. These results, together with good agreement between Pacific and South Atlantic records, strongly suggest that the carbon cycle was perturbed globally shortly before the inception of Antarctic glaciation. Once large‐scale Antarctic glaciation was initiated, rapid further change in global seawater chemistry triggered transitory deep ocean carbonate burial fluxes far exceeding their early Oligocene steady state values.
Key Points
A short‐lived calcite compensation depth (CCD) shoaling event occurred in the latest Eocene associated with a negative excursion in oceanic δ13C
The two‐step Eocene‐Oligocene Transition CCD deepening occurred in both the Pacific and Atlantic Oceans
First CCD deepening step is coupled to recovery from latest Eocene shoaling event and the second CCD step is coupled to Antarctic glaciation