Oligocene to Miocene carbon isotope cycles and abyssal circulation changes

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doi: 10.1029/GM032p0469
Author(s): Miller, Kenneth G.; Fairbanks, Richard G.
Author Affiliation(s): Primary:
Lamont-Doherty Geol. Obs., Palisades, NY, United States
Other:
Lamont-Doherty Geol. Obs., United States
Volume Title: Carbon cycle and atmospheric CO<sub>2</sub>; natural variations Archean to present
Volume Author(s): Sundquist, Eric T., editor; Broecker, Wallace S.
Source: Geophysical Monograph, Vol.32, p.469-486; Chapman Conference on natural variations in carbon dioxide and the carbon cycle, Tarpon Springs, FL, Jan. 9-13, 1984, edited by Eric T. Sundquist and Wallace S. Broecker. Publisher: American Geophysical Union, Washington, DC, United States. ISSN: 0065-8448. ISBN: 978-1-118-66432-2 CODEN: GPMGAD
Note: In English. 70 refs.; illus. incl. 2 tables
Summary: Three cycles of δ13C occurred in Oligocene to Miocene benthic and planktonic foraminifera at western North Atlantic Sites 558 and 563. Intervals of high δ13C occurred at about 35-33 Ma (early Oligocene), 25-22 Ma (across the Oligocene/Miocene boundary), and 18-14 Ma (across the early/middle Miocene boundary). Similar carbon isotopic fluctuations have been measured in benthic and planktonic foraminifera from the Atlantic, Pacific, and Indian oceans, suggesting that these cycles represent global changes in the δ13C of mean ocean water. The average duration of the carbon cycles is 50 times greater than the residence time of carbon in the oceans.Therefore, the mechanism controlling these cycles must be tied to changes in the input ratio of organic carbon to carbonate from weathering rocks or to changes in the output ratio of organic carbon to carbonate in marine sediments. Following a strategy used to study modern and Pleistocene oceans, benthic foraminiferal δ13C differences between the Atlantic and Pacific are used to infer Oligocene through Miocene abyssal circulation changes. The Atlantic was most enriched in l3C relative to the Pacific from about 36-33 Ma (early Oligocene) and 26-10 Ma (late Oligocene to late Miocene). We interpret this as indicating supply of nutrient-depleted bottom water in the North Atlantic, perhaps analogous to modern North Atlantic Deep Water. High benthic foraminiferal δ13O values at about 36-35 Ma, 31-28 Ma, 25-24 Ma, and younger than 15 Ma indicate the presence of ice sheets at these times. Covariance between benthic and planktonic foraminiferal δ18O records of 0.3-0.5°/ ppm ppm at 36 Ma, 31 Ma, and 25 Ma suggests that three periods of continental glaciation caused eustatic (global sea-level) lowerings of 30-50 m during the Oligocene epoch. The δ13C cycles do not correlate with sea-level changes deduced from oxygen isotopic data, nor do they correlate with other proxy indicators for sea level.
Year of Publication: 1985
Research Program: DSDP Deep Sea Drilling Project
IPOD International Phase of Ocean Drilling
Key Words: 02 Geochemistry; 12 Stratigraphy, Historical Geology and Paleoecology; Atlantic Ocean; Atmosphere; Benthic taxa; C-13/C-12; Carbon; Carbon dioxide; Cenozoic; Composition; DSDP Site 558; DSDP Site 563; Deep Sea Drilling Project; Deep-sea environment; Foraminifera; Geochemical cycle; Geochemistry; IPOD; Invertebrata; Isotopes; Leg 82; Marine environment; Microfossils; Miocene; Neogene; North Atlantic; O-18/O-16; Oligocene; Oxygen; Paleogene; Planktonic taxa; Protista; Ratios; Sea water; Stable isotopes; Stratigraphy; Tertiary
Coordinates: N374614 N374615 W0372036 W0372037
N333831 N333832 W0434602 W0434603
Record ID: 1986014769
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