Simultaneous increase in planktonic-benthic carbon isotope gradients and reactive phosphorus deposition in sediments from the Caribbean (ODP Site 999) provide evidence for increased export productivity and organic carbon burial during a late Miocene volcanic ash event

Author(s): Dirksen, Emily R.; Faul, Kristina L.; Lear, Caroline
Author Affiliation(s): Primary:
Mills College, Oakland, CA, United States
Cardiff University, United Kingdom
Volume Title: Geological Society of America, Rocky Mountain Section, 66th annual meeting; Geological Society of America, Cordilleran Section, 110th annual meeting
Source: Abstracts with Programs - Geological Society of America, 46(5), p.13; Geological Society of America, Rocky Mountain Section, 66th annual meeting; Geological Society of America, Cordilleran Section, 110th annual meeting, Bozeman, MT, May 19-21, 2014. Publisher: Geological Society of America (GSA), Boulder, CO, United States. ISSN: 0016-7592 CODEN: GAAPBC
Note: In English
Summary: The late Miocene experienced a cooling trend and simultaneous positive carbon (C) isotope excursion. A possible mechanism for the cooling is increased global volcanism leading to increased nutrient supply, increased export productivity, increased organic C burial, and atmospheric carbon dioxide drawdown. We test the hypothesis that intense volcanism in the Caribbean during the late Miocene could have served as an external source for an increase of nutrients, thereby locally increasing export productivity and organic C deposition. We measured biologically reactive phosphorous (P, the sum of oxide bound, authigenic, and organic P) as a tracer for organic C burial in volcanic ash layers deposited in the Caribbean basin (ODP Site 999, Core 28X) of approximate age 9.6 million years. The highest concentrations of reactive P were 17.08 µmol g-1 and 19.68 µmol g-1 at 254.75 and 254.55 meters below sea floor (mbsf), respectively, and were located in and just above the ash layer (∼254.75-254.65 mbsf). The first peak in reactive P (∼254.75 mbsf) occurs coincident with a peak in the planktonic to benthic C isotope gradient, whereas the second reactive P peak occurs subsequently. We interpret the overlapping sequence of events of the occurrence of the ash layer, an increase in the planktonic to benthic C isotope gradient, and an increase in reactive P burial to indicate that Caribbean volcanism provided increased nutrients causing increased export productivity and increased organic C burial at this time. Furthermore, the effect of a volcanism event would have had a global effect on climate of the Miocene; the Panamanian isthmus was not yet closed, so phosphorous would have flowed to the Pacific Ocean as well. This is the first evidence that we know of to support a late Miocene volcanic event causing productivity increases. Moreover, this increased productivity, both locally in the Caribbean and wider spread to the Pacific, is a plausible mechanism for carbon drawdown and a general cooling trend.
Year of Publication: 2014
Research Program: ODP Ocean Drilling Program
Key Words: 02 Geochemistry; 12 Stratigraphy, Historical Geology and Paleoecology; Atlantic Ocean; C-13/C-12; Carbon; Caribbean Sea; Cenozoic; Colombian Basin; Isotope ratios; Isotopes; Leg 165; Marine environment; Miocene; Neogene; North Atlantic; ODP Site 999; Ocean Drilling Program; Organic carbon; Paleoclimatology; Paleoecology; Paleoenvironment; Phosphorus; Productivity; Stable isotopes; Tertiary; Upper Miocene; Volcanism
Coordinates: N124437 N124437 W0784422 W0784422
Record ID: 2015017195
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