North Pacific-wide spreading of isotopically heavy nitrogen during the last deglaciation: Evidence from the western Pacific

Sedimentary delta(15) N records in two IMAGES cores (MD012404 and MD012403) retrieved from the Okinawa Trough (OT) in the western North Pacific reveal deglacial increases with two peaks occurring during the Bolling/Allerod and the Preboreal/early Holocene periods. These peaks are synchronous with previously reported delta(15) N peaks in the Eastern Tropical North Pacific, although the amplitudes (from 3.8 to 5.8%) are much smaller in the OT. Similar delta(15) N values for the last glacial maximum and the late-Holocene observed by us at a site far from the present-day zones of water-column denitrification (WCD) indicate that the mean N-15/N-14 of nitrate in the upper ocean did not differ much between the two climate states. The accumulation rate of organic carbon and total sulfur content are used as indices of the local WCD potential. The results suggest that enhancement of global WCD rather than local denitrification should be responsible for the deglacial maxima of sedimentary delta(15) N in the Okinawa Trough. Our data could provide additional constraints to better understand changes in nitrogen budget during the glacial to interglacial transition.National Science Council of Taiwan [NSC 96-2611-M-001-005]; State Key Laboratory of Marine Environmental Science, ; Xiamen University, Xiame