A coordinated increase in export production and denitrification on the Costa Rica margin during the early Pleistocene

Author(s): Yuan, V.; Bascom, C., Jr.; Robinson, R. S.
Author Affiliation(s): Primary:
University of Rhode Island, Graduate School of Oceanography, Narragansett, RI, United States
Volume Title: AGU 2013 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2013; American Geophysical Union 2013 fall meeting, San Francisco, CA, Dec. 9-13, 2013. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: The oceanic carbon, nitrogen, and oxygen cycles are linked through export production, oxygen consumption, and denitrification. Denitrification, the bacterial reduction of nitrate, is an anoxic process that serves as the primary sink for fixed nitrogen in the ocean. The Eastern Tropical Pacific (ETP) houses an oxygen minimum zone (OMZ) where pelagic denitrification proceeds as a result of both large scale circulation and regionally high export of organic matter that fuels oxygen consumption in the subsurface. Here we present a 2.4 million year long record of denitrification and productivity in the ETP using ODP Site 1242. Site 1242 is located ≈70 km off the west coast of Costa Rica, beneath the OMZ. Downcore records of bulk sedimentary nitrogen isotope values (δ15N) and opal and organic matter accumulation rates show near synchronous increases in δ15N values and biogenic sediment accumulation at approximately 1.6 My. The concurrent increase in the denitrification and productivity proxies suggests that regional oxygen demand could be driving the increase in denitrification observed at Site 1242. This is in contrast to what is observed elsewhere, where export productivity and denitrification changes do not appear to be coupled locally. Moreover, the timing of this increase is distinct from a previously observed increase in δ15N at California Margin Site 1012 which occurred at ≈2.1 Ma (Liu et al., G-cubed, 2008) and is also attributed to enhanced denitrification in the OMZ. These differences suggest that the Site 1242 record reflects a purely local or regional process. Interestingly, the later increase in denitrification at 1.6 Ma observed at Site 1242 does not appear to be restricted to the ETP, but rather shows similar timing to a δ15N shift in a site from the Arabian Sea OMZ (Muzuka et al., Proceedings of the ODP, 1991). The new data presented here will help in the development of a mechanistic understanding of relative roles of local and regional processes over global controls on intermediate water OMZ intensity.
Year of Publication: 2013
Research Program: ODP Ocean Drilling Program
Key Words: 24 Surficial Geology, Quaternary Geology; Central America; Continental margin; Costa Rica; Denitrification; East Pacific; Equatorial Pacific; Leg 167; Leg 202; North Pacific; Northeast Pacific; ODP Site 1012; ODP Site 1242; Ocean Drilling Program; Pacific Ocean
Coordinates: N321658 N321658 W1182302 W1182302
N075100 N075100 W0833600 W0833600
Record ID: 2015080564
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