REE and Neodymium isotope distribution in the northern South China Sea:
particulate dissolution versus water mass mixing
Abstract
Dissolved rare earth elements (REE) and neodymium isotopic compositions
(εNd) were intensively used to evaluate water mass mixing and lithogenic
inputs in oceans. The South China Sea (SCS) is the largest marginal sea
and a key region for reconstructing past hydrological changes in the
West Pacific; however, its REE and εNd distribution are still not well
established. This study investigated dissolved REE concentration and εNd
distribution at four water stations in the northern and central SCS to
better constrain the εNd distribution and REE cycle in the SCS. The
results show relatively high concentrations of REE in surface seawater
due to the terrigenous inputs. Seasonal variability in the middle REE
enrichment is observed, suggesting a controlling role of the lateral
mixing of water masses in the REE fractionation. The decreased REE
concentrations in bottom water are mainly attributed to the re-suspended
particle scavenging. Surface seawater εNd varies from -2.8±0.3 to
-6.7±0.3, implying a significant modification due to riverine inputs.
The intermediate water is characterized by a slightly negative εNd
compared to the North Pacific Intermediate Water (NPIW) suggesting a
vertical mixing between the intermediate and deep water within the SCS.
εNd of deep water shows a narrow range from -3.4±0.3 to -4.2±0.3 (mean
value of ~-3.8), supporting the presence of Pacific Deep
Water (PDW) in the deep SCS basins nowadays. εNd of deep water in the
SCS behaves conservatively along its pathway from the West Pacific to
the SCS even though particle scavenging occurs in bottom water.