δ15Nbulk oscillations linked to monsoon-induced denitrification during the past 1 m.y. in the Eastern Arabian Sea (IODP Exp. 355 Site U1456)

Author(s): Khim, Boo-Keun; Kim, Ji-Eun; Lee, Jongmin; Ikehara, Minoru; Clift, Peter Dominic; Pandey, Dhananjai; Kulhanek, Denise K.
International Ocean Discovery Program, Expedition 355 Scientists
Author Affiliation(s): Primary:
Pusan National University, Busan, South Korea
Other:
University of Kochi, Japan
Louisiana State University, United States
National Centre for Antarctic and Ocean Research, India
Integrated Ocean Drilling Program, United States
Volume Title: AGU 2016 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2016; American Geophysical Union 2016 fall meeting, San Francisco, CA, Dec. 12-16, 2016. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: The Arabian Sea is characterized by a large pool of denitrifying water at intermediate water depths, which plays an important role in the marine nitrogen cycle and resultant response to climate change. A growing body of research emphasizes strong linkage between denitrification strength in the Arabian Sea and climate change at both orbital and millennial timescales. Drilling by International Ocean Discovery Program Expedition 355 was conducted at Site U1456 in the Laxmi Basin, Eastern Arabian Sea, ∼475 km from the Indian coastline and ∼820 km south of the modern Indus River Delta. Four lithologic units are defined onboard at the Site U1456. A total of 282 samples were collected from a composite section of Unit I consisting of Holes U1456A and U1456C. Unit I is composed mostly of nannofossil ooze and/or foraminifer-rich nannofossil ooze with interbedded clay, silt, and sand layers. Oxygen isotope measurements of planktonic foraminifera (G. ruber and G. sacculifer), together with shipboard biostratigraphic and paleomagnetic data, constrain the age of Unit I to younger than about 1.2 Ma. The δ15Nbulk values fluctuate from 4.5 ppm to 9.6 ppm with a mean of 7.3 (±0.95) ppm. Higher δ15Nbulk values coincide with interglacial intervals whereas lower δ15Nbulk values correspond to glacial intervals, representing clear glacial-interglacial cyclicity. These variations demonstrate the distinct climatic linkage with the degree of denitrification at orbital timescales, in association with changes in hydrography and productivity. The relation between denitrification and monsoon intensity, previously reported for the continental margins of the Arabian Sea, is also recorded in the deep water sediments.
Year of Publication: 2016
Research Program: IODP Integrated Ocean Drilling Program
IODP2 International Ocean Discovery Program
Key Words: 24 Surficial Geology, Quaternary Geology; Arabian Sea; Cenozoic; Denitrification; Expedition 355; IODP Site U1456; Indian Ocean; International Ocean Discovery Program; Isotope ratios; Isotopes; N-15/N-14; Nitrogen; Quaternary; Stable isotopes
Coordinates: N163717 N163718 E0685021 E0685020
Record ID: 2017051563
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