983 / 2024-09-19 23:35:08
Spatiotemporal variability of dissolved rare earth elements in the North Pacific Subtropical Gyre: influences of biogeochemical cycling and application in tracing deep water
Rare earth elements,North Pacific Subtropical Gyre,Seasonal variations,Biogeochemical cycling,Ocean interfaces,Water mass tracing
Session 10 - The biogeochemistry of trace metals in a changing ocean
Abstract Accepted
Axiang Cao / Ocean University of China
Qian Liu / Ocean University of China
Jing Zhang / Ocean University of China;University of Toyama
Jingling Ren / Ocean University of China
The North Pacific Subtropical Gyre (NPSG), the largest marine ecosystem, plays a crucial role in trace element cycling through biological and seawater interface processes. However, the seasonal impact on these processes remains underexplored. Rare earth elements (REEs) serve as effective tracers for studying ocean dynamics. This study, based on two GEOTRACES-CHINA process study cruises (GPpr15) in summer and winter, along with spring data from a GEOTRACES-CHINA cruise (GP09), reveals significant seasonal variations in REE concentrations above the depth of chlorophyll maxima (DCM) (<150 m) (p < 0.05). No significant changes were observed in subsurface (200–1000 m) or deep waters (1000 m to the bottom) (p > 0.05). Winter showed the lowest REE levels above the DCM due to enhanced scavenging by particulate matter, driven by increased chlorophyll. In subsurface to intermediate waters (150–1000 m), REE release efficiency through remineralization remained consistent (~0.04 pmol Nd/μmol apparent oxygen utilization) across seasons, and similar between the NPSG and North Atlantic Gyre.

In winter, higher Ce anomalies in intermediate waters (500–1000 m) near the Philippine Islands suggest seasonal sediment contributions driven by lateral transport, with slope sediments contributing 15-43% of Nd in winter, 1-29% in summer, and 5-18% in spring. At deep-water stations K13/13a, elevated REE concentrations and low transmission indicate additional sources from seafloor and lateral transport from the Philippines, beyond settled particles. Water masses contributed 71 ± 3% of elevated Nd, with remineralization/dissolution processes contributing 18 ± 8%, and other sources 11 ± 5%. Furthermore, Yb effectively traces the distribution of lower circumpolar deep water in the Philippine Basin. In summary, this study highlights the significant influence of biogeochemical processes on seasonal variations of REEs above the DCM and underscores the potential of REEs in tracking deep water transport. Given the impacts of global warming and temperature changes in deep water, relying solely on temperature and salinity to resolve water masses may introduce bias, making REE a valuable complementary tool.