Eocene "jump-starting" of thermohaline upwelling in the Southern Ocean

Author(s): Bohaty, Steven M.; Harwood, David M.; Zachos, James C.
Author Affiliation(s): Primary:
University of California at Santa Cruz, Earth Sciences Department, Santa Cruz, CA, United States
University of Nebraska, United States
Volume Title: Geological Society of America, 2000 annual meeting
Source: Abstracts with Programs - Geological Society of America, 32(7), p.146; Geological Society of America, 2000 annual meeting, Reno, NV, Nov. 9-18, 2000. Publisher: Geological Society of America (GSA), Boulder, CO, United States. ISSN: 0016-7592 CODEN: GAAPBC
Note: In English
Summary: The late middle Eocene through early Oligocene (42 to 29 Ma) represents an important transition period in Antarctic climates and Southern Ocean circulation. Recent Mg/Ca studies suggest that the positive excursion in benthic foraminiferal oxygen isotope values in the earliest Oligocene (the Oi-1 event) results largely from increased Antarctic ice volume. Southern Ocean surface waters, however, are also interpreted to have cooled at this time, based on increased "cool-water" nannofossil abundance and increased oxygen isotope values in planktic foraminifers. A significant early Oligocene increase in biosiliceous sedimentation also coincides with the Oi-1 event and is interpreted to indicate increased Southern Ocean upwelling and enhanced regional export productivity. Many studies have focused on Eocene-Oligocene boundary records in the Southern Ocean, with less attention directed towards long-term trends during the middle to late Eocene. The upper middle Eocene to lower Oligocene section of ODP Hole 748B, located on the southern Kerguelen Plateau, was examined in the present study. Two pulses in biosiliceous sedimentation are documented in Eocene cores from this hole (centered at approximately 42 and 35 Ma). Although minor in comparison, these events precede the major lower Oligocene increase in biosiliceous sedimentation associated with the Oi-1 isotope event. Additionally, these Eocene events are concomitant with increases in "cool-water" nannofossils, providing direct evidence that increased biosiliceous sedimentation is linked with local surface-water cooling at the site. The Eocene biosiliceous events at Site 748 include a component of radiolarians, sponge spicules, and siliceous plankton (diatoms, silicoflagellates, and ebridians). Increased biosilicification by this range of organisms indicates increased silica availability to all levels of the water column. Furthermore, these events are interpreted to represent the initial stages of deep-water production on the Antarctic shelves and associated upwelling driven by thermohaline circulation. This interpretation is supported by a long-term, middle to upper Eocene increase in benthic foraminiferal oxygen isotope values at Site 748.
Year of Publication: 2000
Research Program: ODP Ocean Drilling Program
Key Words: 12 Stratigraphy, Historical Geology and Paleoecology; Algae; Alkaline earth metals; Antarctic Ocean; Antarctica; Benthic taxa; Calcium; Cenozoic; Cooling; Cores; Deep-water environment; Diatoms; Eocene; Foraminifera; Invertebrata; Isotope ratios; Isotopes; Kerguelen Plateau; Leg 120; Magnesium; Metals; Microfossils; Nannofossils; O-18/O-16; ODP Site 748; Ocean Drilling Program; Oxygen; Paleo-oceanography; Paleoclimatology; Paleogene; Plankton; Planktonic taxa; Plantae; Porifera; Productivity; Protista; Radiolaria; Sedimentation; Stable isotopes; Tertiary; Thermohaline circulation; Upwelling
Coordinates: S582627 S582627 E0785854 E0785853
Record ID: 2002068168
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States