State Key Laboratory of Marine Environmental ScienceXiamen UniversityXiamen China

Laboratory of, China

State Key Laboratory of Marine Environmental ScienceXiamen UniversityXiamen China

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Zhang W.-Z.,Communication University of China | Wang H.,State Key Laboratory of Marine Environmental ScienceXiamen UniversityXiamen China | Qiu G.,State Key Laboratory of Marine Environmental ScienceXiamen UniversityXiamen China
Journal of Geophysical Research: Oceans | Year: 2016

The variability of chlorophyll a concentration (Chl a) in the open South China Sea (SCS) was examined using observations from two Bio-Argo floats. During the period of September 2014 to August 2015, there was a permanent subsurface Chl a maximum (SCM) in the depth range of 48 to 96 m in the central basin of the SCS. In the northern basin, the SCM disappeared in winter, replaced by enhanced surface layer phytoplankton with high Chl a. The values of the SCM were influenced by the vertical displacement of isotherms. Strong wind forcing and surface cooling were the main physical drivers of high surface Chl a in winter. In the north, stronger wind than in the center, lower sea surface temperature (SST) than in the center, and Kuroshio water intrusion were more favorable for the upward transport of nutrient-rich deep water. A large amount of nitrate could be advected from the Taiwan Strait and shallow continental shelf to the northern basin in winter. A combination of strong wind mixing, surface cooling, Kuroshio water intrusion, and horizontal advection caused the winter surface phytoplankton bloom in the north. © 2016. American Geophysical Union. All Rights Reserved.


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.


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.


Tong S.,State Key Laboratory of Marine Environmental ScienceXiamen UniversityXiamen China | Hutchins D.A.,University of Southern California | Fu F.,University of Southern California | Gao K.,State Key Laboratory of Marine Environmental ScienceXiamen UniversityXiamen China
Limnology and Oceanography | Year: 2016

Gephyrocapsa oceanica is a widespread species of coccolithophore that has a significant impact on the global carbon cycle through photosynthesis and calcium carbonate precipitation. We investigated combined effects of light (50 μmol m-2 s-1, 190 μmol m-2 s-1, and 400 μmol m-2 s-1) and the nitrogen sources NO3- and NH4+ on its physiological performance under nitrogen-limited conditions. The specific growth rate was highest at the mid-range light level of 190 μmol m-2 s-1, where it was further accelerated by NH4+ relative to NO3-. There were no significant growth rate differences between NO3-- and NH4+-grown cells at the two light levels either above or below this optimum irradiance. Cellular particulate organic carbon (POC) and nitrogen (PON) content were not significantly affected by different light intensities and nitrogen sources. However, both the cellular particulate inorganic carbon (PIC) content and the PIC to POC ratio were greatly decreased by increased light levels, and were further decreased by NH4+ only at the highest light level. Non-photochemical quenching (NPQ) increased with increasing light intensity, and was higher in NO3- rather than in NH4+-grown cells at medium and high light intensities. Our results demonstrate that under low, relatively realistic oceanic nitrogen concentrations, increasing light intensity and the replacement of NO3- by NH4+ would have a significant negative effect on the calcification of the coccolithophore G. oceanica. If these findings are also applicable to other coccolithophore species, the future ocean carbon cycle may be greatly affected. © 2016 Association for the Sciences of Limnology and Oceanography.


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.

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