Journal of Oceanography最新文献

Aluminium (Al), manganese (Mn), iron (Fe), cobalt (Co), and lead (Pb) are trace metals that exhibit significant scavenging tendencies in the oceans. This study presents the full-depth distributions of the dissolved (d) and labile particulate (lp) fractions of these five elements in the subarctic Pacific Ocean, obtained during the GEOTRACES Japan KH-17-3 cruise. Along the 145° W meridional transect, the d and lp species of Al, Mn, Fe, and Co reflected fluvial supply from Alaska and benthic input from the continental shelf. We estimated that the boundary-scavenging zone has a width of approximately 250 km off Alaska. Along the 47° N zonal transect (GEOTRACES GP02 Line), we found input of trace metals from the Okhotsk and Bering Seas in the west, contrasting to the limited input of trace metals due to boundary scavenging in the east. The hydrothermal activity of the Juan de Fuca Ridge influenced the distribution of deep-water trace metals at the easternmost station, CL-21. Temporal change in the vertical profiles of dPb in the middle of the subarctic gyre highlighted a decline in anthropogenic Pb emissions from 2005 to 2017. Temporal change of the vertical profiles of Al, Mn, and Fe at 47° N, 160° E from 2011 to 2017 indicates the influence of the Great East Japan Earthquake. In particular, lp trace metals were brought by tsunami and ocean circulation in 2011, and decreased over time through scavenging.

Abstract

Vortex pairs formed at a strait outlet by tidal flow effectively induce water exchange and material transport in coastal areas. However, the effects of complex bottom topography and density stratification remain unclear. Here, we investigated the development and propagation of vortex pairs in the Naruto Strait, which has complex topography. Satellite observations indicated that the vortex pairs formed on the northern side of the strait continue to move away from the strait after the reversal of tidal flow, shifting their propagation from northward to westward. Numerical experiments revealed that: (1) changes in depth affect the propagation speed and overall size of vortex pairs; (2) density stratification reduces the effects of depth changes; (3) coastline geometry affects the propagation direction of vortex pairs. Furthermore, experiments with idealized topography showed that in a region where depth increases with vortex-pair propagation, the jet decelerates, and the vortex pair shrinks in size. Conversely, in a region where depth decreases, the jet widens, and the vortex pair expands. The changes in jet flow speed can be attributed to flow continuity and depth change, as the latter alters the cross-sectional area. Meanwhile, the changes in vortex pair size and jet width can be explained by vortex propagation on a slope due to potential vorticity conservation. These effects of topography and density stratification may also be significant in other coastal areas and potentially influence the Strouhal number threshold below which vortex pairs leave an outlet.

Estuarine processes regulate the transport of dissolved black carbon (DBC) and associated contaminants to the ocean. However, there is limited understanding of the geochemical behavior of DBC in estuaries. In this study, DBC in the Pearl River Estuary (PRE) and the northern shelf of the South China Sea were examined using the benzene polycarboxylic acid (BPCA) method. DBC, bulk dissolved organic carbon (DOC), and chromophoric dissolved organic matter (CDOM) exhibited distinct behaviors during their transport from the PRE to the sea. DOC and CDOM decreased during the initial mixing of river water and seawater but increased at the lower PRE. In contrast, high aromaticity DBC inputs were observed throughout the PRE, likely originating from local terrestrial sources, such as runoff from nearby islands, as indicated by the high R_H/L values (i.e., the ratio of BPCA containing 5 and 6 carboxyl groups to that containing 3 and 4 carboxyl groups; 2.03–2.30). In the Pearl River-plume zone (salinity < 33.0), DOC, CDOM, and DBC showed quasi-conservative behaviors against salinity, indicating that their geochemical behaviors were primarily governed by physical mixing between plume water and seawater. Using a flux model, it was estimated that the discharge of riverine DBC from the Pearl River Delta ranged from 11.2 to 16.3 Gg year⁻¹, representing an important source of bio-resistant DOC to the northern South China Sea.