Presentation Information
[U11-P13]Precessional and Millennial Intensification of the Kuroshio Current in the Okinawa Trough Revealed by Foraminifera-Bound Nitrogen Isotopes
*Haojia Abby Ren1,2, Wen-Hui Chen1,2, Er-Wen Yang1, Yuan-Pin Chang3, Min-Te Chen4, Yu-Chen Liu1, Ya-Hsien Lan2, Yi-Jun Lin1 (1.National Taiwan University, 2.Academia Sinica, 3.National Sun Yat-Sen University, 4.National Taiwan Ocean University)
Keywords:
Kuroshio Current,Okinawa Trough,Foraminifera-bound nitrogen isotopes,Precessional forcing,Northern Hemisphere cold events,East Asian Summer Monsoon
The Kuroshio Current is the principal western boundary current of the North Pacific and a major conduit of heat and salt to the Northern Hemisphere, exerting strong influence on regional hydroclimate and the Okinawa Trough. Variations in its strength affect East Asian monsoon dynamics, marginal-sea stratification, and nutrient supply to the continental shelf. Yet reconstructing past Kuroshio transport remains challenging because conventional proxies—such as faunal assemblages, SST, or grain size—cannot uniquely distinguish transport intensity from pathway shifts or local hydrographic changes.
Here we apply foraminifera-bound nitrogen isotopes (FB-δ15N) as a circulation-sensitive tracer. Nitrogen isotopes provide a distinctive fingerprint for Kuroshio waters because Kuroshio Tropical Water carries characteristically low δ15N nitrate values, reflecting basin-wide N2 fixation in the western subtropical Pacific. We generate two FB-δ15N records spanning the past 100 kyr: one from the upstream Kuroshio in the open western North Pacific and one from the Okinawa Trough. The upstream record exhibits persistently low δ15N values, indicating a stable tropical N2-fixation imprint in source waters. In contrast, the Okinawa Trough record shows pronounced oscillations paced by precession and amplified during Northern Hemisphere cold events.
Lower δ15N values in the Okinawa Trough—indicating enhanced penetration of low-δ15N Kuroshio Tropical Water—occur when Northern Hemisphere summer insolation is reduced at precessional maxima. This pacing is punctuated by additional low-δ15N excursions that coincide with millennial-scale Northern Hemisphere cooling events, suggesting transient intensification of Kuroshio transport during stadials. The Okinawa Trough δ15N variability closely parallels Chinese speleothem δ18O records of the East Asian Summer Monsoon, highlighting a coherent link between boundary current dynamics and large-scale atmospheric circulation.
Together, these results demonstrate that Kuroshio intensification in the Okinawa Trough during precession maxima and Northern Hemisphere cold events was driven primarily by large-scale wind reorganization. By exploiting the low-δ15N signature imparted by subtropical N2 fixation, foraminifera-bound nitrogen isotopes provide a robust circulation-specific proxy that reveals wind-forced modulation of western boundary current strength on orbital and millennial timescales.
Here we apply foraminifera-bound nitrogen isotopes (FB-δ15N) as a circulation-sensitive tracer. Nitrogen isotopes provide a distinctive fingerprint for Kuroshio waters because Kuroshio Tropical Water carries characteristically low δ15N nitrate values, reflecting basin-wide N2 fixation in the western subtropical Pacific. We generate two FB-δ15N records spanning the past 100 kyr: one from the upstream Kuroshio in the open western North Pacific and one from the Okinawa Trough. The upstream record exhibits persistently low δ15N values, indicating a stable tropical N2-fixation imprint in source waters. In contrast, the Okinawa Trough record shows pronounced oscillations paced by precession and amplified during Northern Hemisphere cold events.
Lower δ15N values in the Okinawa Trough—indicating enhanced penetration of low-δ15N Kuroshio Tropical Water—occur when Northern Hemisphere summer insolation is reduced at precessional maxima. This pacing is punctuated by additional low-δ15N excursions that coincide with millennial-scale Northern Hemisphere cooling events, suggesting transient intensification of Kuroshio transport during stadials. The Okinawa Trough δ15N variability closely parallels Chinese speleothem δ18O records of the East Asian Summer Monsoon, highlighting a coherent link between boundary current dynamics and large-scale atmospheric circulation.
Together, these results demonstrate that Kuroshio intensification in the Okinawa Trough during precession maxima and Northern Hemisphere cold events was driven primarily by large-scale wind reorganization. By exploiting the low-δ15N signature imparted by subtropical N2 fixation, foraminifera-bound nitrogen isotopes provide a robust circulation-specific proxy that reveals wind-forced modulation of western boundary current strength on orbital and millennial timescales.