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Lu W.,Delaware State University | Yan X.-H.,Delaware State University | Jiang Y.,State Key Laboratory of Marine Environmental ScienceXiamen UniversityXiamen China
Journal of Geophysical Research C: Oceans | Year: 2015

For this paper, a coupled physical-biological model was developed in order to study the mechanisms of the winter bloom in the Luzon Strait (referred as LZB). Based on a simulation for January 2010, the results showed that the model was capable of reproducing the key features of the LZB, such as the location, inverted-V shape, twin-core structure and bloom intensity. The simulation showed that the LZB occurred during the relaxation period of intensified northeasterly winds, when the deepened mixed layer started to shoal. Nutrient diagnostics showed that vertical mixing was responsible for the nutrient supply to the upper ∼40 m layer, while subsurface upwelling supplied nutrients to the region below the mixed layer. Hydrodynamic diagnostics showed that the advection of relative vorticity (RV) primarily contributed to the subsurface upwelling. The RV advection was resulted from an offshore jet, which was associated with a northeasterly wind, flowed across the ambient RV field. © 2014. American Geophysical Union. Source

Xie Y.,State Key Laboratory of Marine Environmental ScienceXiamen UniversityXiamen China | Huang B.,State Key Laboratory of Marine Environmental ScienceXiamen UniversityXiamen China | Lin L.,State Key Laboratory of Marine Environmental ScienceXiamen UniversityXiamen China | Laws E.A.,Louisiana State University | And 4 more authors.
Journal of Geophysical Research C: Oceans | Year: 2015

Many recent models for retrieval of primary production in the sea from ocean-color data are temperature based. But previous studies in low latitudes have shown that models that include phytoplankton community structure can have improved predictive capability. In this study, we measured photosynthetic parameters from photosynthesis-irradiance (P-E) experiments, phytoplankton absorption coefficients, and phytoplankton community structure derived from algal pigments during four cruises in the northern South China Sea (NSCS). The maximum quantum yield of CO2 ( ΦmC) and the chlorophyll a-normalized P-E curve light-limited slope (αB) varied significantly with the blue-to-red ratio of phytoplankton absorption peaks (aph(435)/aph(676)) (p<0.001, r=-0.459 and -0.332, respectively). The unexplained variability could be due in part to the absorption associated with nonphotosynthetic pigments. The chlorophyll a-normalized light-saturated photosynthetic rate ( PmB) at the surface showed a unimodal distribution over the chlorophyll a range during the spring and summer, and significantly increased when Prochlorococcus was outcompeted by other picophytoplankton (p<0.01). Almost 60% of the variance of PmB could be explained by a piecewise regression with phytoplankton absorption coefficients and pigment markers. Unlike previous studies, our data showed that changes of PmB were unrelated to the size structure of phytoplankton. Although a temperature-based approach could not effectively predict αB and PmB in the NSCS, a trophic-based approach can be used for assignment of these parameters in a regional primary production model using ocean-color data. © 2015. American Geophysical Union. Source

Fu B.,Ocean University of China | Liu J.,Ocean University of China | Yang H.,Ocean University of China | Hsu T.C.,State Key Laboratory of Marine Environmental ScienceXiamen UniversityXiamen China | And 4 more authors.
Journal of Geophysical Research C: Oceans | Year: 2015

Anaerobic ammonium oxidation (anammox) plays an important role in the marine nitrogen cycle. The Pearl Estuary, a typical subtropical estuary characterized by hypoxia upstream and high loads of organic matter and inorganic nutrients caused by anthropogenic activities, has received extensive attention. In this study, anammox bacterial community structures in surface sediments along the Pearl Estuary were investigated using 16S rRNA and hydrazine oxidoreductase (HZO) genes. In addition, abundance of anammox bacteria in both water and surface sediments was investigated by quantitative PCR. Obvious anammox bacterial community structure shift was observed in surface sediments, in which the dominant genus changed from "Candidatus Brocadia" or "Candidatus Anammoxoglobus" to "Candidatus Scalindua" along the salinity gradient from freshwater to the open ocean based on 16S rRNA gene and HZO amino acid phylotypes. This distribution pattern was associated with salinity, temperature, pH of overlying water, and particularly C/N ratio. Phylogenetic analysis unraveled a rich diversity of anammox bacteria including four novel clusters provisionally named "Candidatus Jugangensis," "Candidatus Oceanicum," "Candidatus Anammoxidans," and "Candidatus Aestuarianus." The abundance of anammox bacteria in surface sediments, bottom and surface waters ranged from 4.22 × 105 to 2.55 × 106 copies g-1, 1.24 × 104 to 1.01×105 copies L-1, and 8.07×103 to 8.86×105 copies L-1, respectively. The abundance of anammox bacteria in the water column was positively correlated with NO2- and NO3-, and negatively correlated with dissolved oxygen, although an autochthonous source might contribute to the observed abundance of anammox bacteria. © 2015. American Geophysical Union. All Rights Reserved. Source

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