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Spatial distribution of the summer subsurface chlorophyll maximum in the North South China Sea.

ABSTRACT: Based on the biological, nutrients and hydrological data in August 2018, the vertical chlorophyll a (Chl-a) concentration profiles and the relationship among surface Chl-a (Chl-a(0)) concentration, maximum Chl-a (Chl-a(m)) concentration and depth-integrated Chl-a (Chl-a(int)) concentration were studied in the Northern South China Sea (NSCS). The results indicate that there are 4 different patterns in the vertical Chl-a profiles in the NSCS: (i) Chl-a increases with depth from the surface (e.g. station 1); (ii) there exists subsurface chlorophyll maximum (SCM), with low Chl-a on the surface and at the bottom layers respectively (e.g. station 5); (iii) there is no SCM, only with high Chl-a on the surface and in the bottom (e.g. station 14); (iv) the 4th pattern is similar to (ii), with the higher Chl-a(0) (e.g. station 28). The SCM is observed at 95% stations in the NSCS and is not detected only at a few stations near the Pearl River (PR) estuary. These patterns are mainly regulated by alternative limitation of nutrients and light from the surface to the bottom of euphotic layer. For the pattern 1 (e.g. station 1), light is not a limited factor, and Chl-a and nutrients increase with depth. The pattern 2 (e.g. station 5) exists with the limitation of surface nutrients in offshore region. The nutrients increases with depth and the nutrients limitation turns to light limitation gradually from surface to bottom. And the SCM appears in the layer which need of the light and nutrients is roughly equivalent. Compared with that the offshore SCM, the nutrients for the pattern 3 (e.g. station 14) are rich on the surface with nutrients concentration and light irradiance. Therefore, it is seawater intrusion from the bottom that brings the higher nutrients concentration. The reason for the high Chl-a(0) on the pattern 4 (e.g. station 28) is terrestrial matter from the nearshore. High correlation (R2 = 0.5206, p<0.01) between the depth of SCM (Depth(m)) and Chl-a(0) indicates that the SCM depth is regulated by light masking effect of surface phytoplankton, generally with shallow nutriclines and fast light attenuation for high Chl-a(0) and vice versa low Chl-a(0) brings deeper nutriclines and light attenuate slowly with less shading effect. Further research results shows that Chl-a(int) and Chl-a(m) have a good correlation(R2 = 0.6397, p<0.01). However, the correlation between Chl-a(int) and Chl-a(0) is relative weak (R2 = 0.3202, p<0.01). That could be attributed to the availability of nutrients playing an important role in growth of phytoplankton, with high nutrients at upper euphotic layers for the stations with high Chl-a(0).

SUBMITTER: Chen Y

PROVIDER: S-EPMC8026054 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Marine viral concentrates (VCs) contains a substantial amount of non-cellular biological particles, e.g. viruses, gene transfer agents (GTAs) and membrane vesicles that are ecological significant. Metagenomic sequencing of VCs has been extensively applied to study the diversity and function potential of natural virions whereas information of nonn-viral components are often excluded for investigation. Here we apply a shotgun proteomic approach to characterize the origin and function of proteins in the VCs collected from the deep chlorophyll maximum (DCM) of the South China Sea. Using a custom database, we identified 636 non-redundant proteins represented by a total of 7220 spectra from the two VC samples. Cyanophages, pelagiphages, Phycodnaviridae and a group of uncultured viruses (previouly collected from DCM of Mediterranean Sea) contributed the most in the viral proteome. Seldom proteins related to RNA viruses and known GTAs were found despites of the presence of their sequences in the protein-searching database, suggested that these particles might be low abundant in the samples. Over 60% of identified spectra could not be assigned to viruses. The non-viral spectra were dominated by microbial groups of SAR324, SAR11, Actinobacteria and picoeukaryotic algae such as prasinophytes.Interestingly, we found that periplasmic proteins such as diverse ABC and TRAP transporters, and 56 kDa selenium-binding proteins, were enriched in this fraction.Together with other detected non-viral proteins,we could identify significant microbial functions, such as the utilization of glycine betaine, 3-dimethylsulphoniopropionate,and taurine by SAR11,and urea by prochlorococcus, nitrous oxide production by ammonia-oxidizing archaea and peroxide detoxification by unkonwn gammaproteobacteria. Our study of marine VCs demonstrates the potential application of metaproteomics to link the nano-size materials to the diversity of virions and interesting microbial functions in the ocean.

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Spatial distribution of the summer subsurface chlorophyll maximum in the North South China Sea.

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