(Table 1) Age model of ODP Site 184-1144
Variations in nitrogen isotopic composition (d15N) and total chlorin accumulation rate (AR) are employed asproxies to reconstruct oceanic nitrate inventory, the balance between denitrification and N fixation, and paleoproductivity in a rapidly accumulating sediment drift deposit beneath the Western...
| Main Authors: | , , |
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| Format: | Dataset |
| Language: | English |
| Published: |
PANGAEA
2003
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| Subjects: | |
| Online Access: | https://doi.pangaea.de/10.1594/PANGAEA.734932 https://doi.org/10.1594/PANGAEA.734932 |
| Summary: | Variations in nitrogen isotopic composition (d15N) and total chlorin accumulation rate (AR) are employed asproxies to reconstruct oceanic nitrate inventory, the balance between denitrification and N fixation, and paleoproductivity in a rapidly accumulating sediment drift deposit beneath the Western Pacific Warm Pool for the last 145 Kyr. Subsurface and deep waters of the northern South China Sea (SCS) are sourced from the shallow Kuroshio Current (KC) and Pacific Intermediate Water, respectively. Their relative importance in determining sedimentary d15N and paleoproductivity have been altered by changes in equatorial circulation, summer- and wintermonsoon intensity and relative sea level. The location and basin configuration of the marginal SCS renders it especially sensitive to such changes. Assuming complete annual nitrate utilization, low d15N values during glacial stages are interpreted as a reflection of reduced remote denitrification in the Eastern Tropical North Pacific (ETNP) source waters, while much of marine isotope stage (MIS) 3 and the last interglacial were characterized by high denitrification. However, intervals of anomalously low d15N values are interpreted as reflecting the contribution from regional N fixation in West Pacific surface waters, transmitted to the site by the shallow KC. Unusually, the Holocene is characterized by declining d15N values and an inverse correlation with organic matter content since ca. 8.2 Ka. Millennial-scale variations during MIS 3 indicate higher frequency variations in both ETNP denitrification and local N fixation, which may be coherent with a hemispheric response to Dansgaard-Oeschger events recorded at high latitudes. For much of the last 145 Kyr, paleoproductivity was decoupled from d15N, and instead seems to reflect the extent of the global nitrate inventory stimulated by elevated dust fertilization, and regional mixed-layer deepening associated with the relative intensity of the SE Asian winter monsoon. Despite evaluation of possible conflicting influences ... |
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