The impacts of ambiguity in preparation of 80% sulfuric acid solution and shaking time control of calibration solution on the determination of transparent exopolymer particles

The quantification of transparent exopolymer particles(TEP) by colorimetric method is of large error and low repeatability,one major reason of which is related to the absence of clear definition and evaluation for part steps of the original method.It is obscure that the 80% sulfuric acid solution,acted as the extraction solution in the determination of TEP,is prepared based on a volume ratio or mass ratio.Furthermore,the change of solubility of recently available Gum Xanthan(GX) from the market means that the original protocol is no longer applicable,and the grinding of GX stock solution with a tissue grinder is replaced by shaking with a rotating shaker in the study to prevent the excessive dissolution of GX.We found that different preparation techniques could result in the varied concentrations of 80% H_(2)SO_(4).The duration of shaking during the preparation of standard solution significantly affected the slope of the calibration curve,which caused different correction results of TEP.The impacts of different extraction solution concentrations and shaking time of GX solution on the quantification of TEP were investigated based on the field sampling and laboratory analysis.The extraction capacities of H_(2)SO_(4) with different concentrations for Alcian Blue were distinct,but had limited effect on the final measuring result of TEP.The change of the standard curve slope came along with the variation of shaking time,which markedly altered the detection limit and calibration result,and the extended shaking time was in favor of the determination of low-concentration TEP.It was suggested that the extraction solution concentration,shaking time and filtration volume of standard solution are required to be well controlled and selected to obtain more accurate results for TEP with different concentrations.

Spatial-temporal dynamics of biogenic silica in the southern Yellow Sea

Concentrations of biogenic silica(BSi) in the southern Yellow Sea were determined during four cruises(spring:April–May 2014;autumn: November 2014;summer: August–September 2015;winter: January 2016). Samples of BSi were measured using the double extraction method. Seasonal and spatial variations of BSi and the potential correlation between chlorophyll a(Chl a) content and BSi in four seasons were measured in this study. Significant spatial variability was observed in seawater BSi concentrations. The average concentration of BSi was highest in winter and lowest in spring. Furthermore, the relationships between concentrations of BSi and hydrological parameters were also discussed. There was a significant positive correlation between Chl a and BSi. The concentrations of BSi showed significant relationships with temperature and the concentrations of silicates, total inorganic nitrogen and total inorganic phosphorus, indicating that distribution of BSi was affected by temperature and nutrient level.

Living coccolithophores in the western Pacific Ocean with mesoscale eddies

Living coccolithophores(LCs)are regarded as a group of calcifiers and play important roles in global carbon cycle.This study used microscopic observations of LCs in the western Pacific Ocean to investigate their community structure and biodiversity,especially to test whether local physical traits(mesoscale eddies)could explain their biogeographic distributions during autumn of 2017.The coccolithophore calcite inventory based on carbon-volume transformation was estimated in this study.A total of 28 taxa of coccospheres and 19 types of coccoliths were identified from 161 samples.Gephyrocapsa oceanica was the most predominant species in all the coccolithophore community,followed by Florisphaera profunda,Emiliania huxleyi,Umbilicosphaera sibogae,Gladiolithusflabellatus and Umbellosphaera tenuis.The abundance of coccospheres and coccoliths ranged from 0 to 26.8×10^(3)cells/L and from 0 to 138.5×10^(3)coccoliths/L,averaged at 4.2×10^(3)cells/L and 10.9×10^(3)coccoliths/L,respectively.This study indicated that coccolithophore community in the survey area can be clustered into four groups.Three ecological niches of coccolithophores were characterized by their vertical profiles and multivariate statistical analysis.Coccolithophore abundance and species composition were remarkably different among warm-eddy region,G.oceanica dominated warm-eddy region,while F.profunda dominated warm-eddy and none-eddy region.The average values of estimated particulate inorganic carbon,particulate organic carbon were0.197μg/L and 0.140μg/L,respectively.The current field study widened the dataset of coccolithophores in western Pacific Ocean.

The ecological response of natural phytoplankton population and related metabolic rates to future ocean acidification

Ocean acidifi cation(OA)and global warming-induced water column stratification can signifi cantly alter phytoplankton-related biological activity in the marine ecosystem.Yet how these changes may play out in the tropical Indian Ocean remains unclear.This study investigated the ecological and metabolic responses of the different phytoplankton functional groups to elevated CO_(2) partial pressure and nitrate deficiency in two different environments of the eastern Indian Ocean(EIO).It is revealed that phytoplankton growth and metabolic rates are more sensitive to inorganic nutrients rather than CO_(2).The combined interactive effects of OA and N-limitation on phytoplankton populations are functional groupspecific.In particular,the abundance and calcification rate of calcifying coccolithophores are expected to be enhanced in the future EIO.The underlying mechanisms for this enhancement may be ascribed to coccolithophore’s lower carbon concentrating mechanisms(CCMs)efficiency and OA-induced[HCO^(-)_(3)]increase.In comparison,the abundance of non-calcifying microphytoplankton(e.g.,diatoms and dinoflagellates)and primary productivity would be inhibited under those conditions.Diff erent from previous laboratory experiments,interspecifi c competition for resources would be an important consideration in the natural phytoplankton populations.These combined factors would roughly determine calcifying coccolithophores as“winners”and non-calcifying microphytoplankton as“losers”in the future ocean scenario.Due to the large species-specific differences in phytoplankton sensitivity to OA,comprehensive investigations on oceanic phytoplankton communities are essential to precisely predict phytoplankton ecophysiological response to ocean acidification.

Environmental influence on transparent exopolymer particles and the associated carbon distribution across northern South China Sea

Microgels are plankton-derived transparent exopolymer particles(TEP)and have a significant impact on global marine carbon cycle.We investigated the influence of biogeochemical variables on the pattern of TEP abundance and its associated carbon(TEP C)distribution through a vertical transect of the northern South China Sea(nSCS)during summer,2014.The average TEP concentration was 58.32±30.56μg Xeq./L.Vertically,it was higher in the subsurface water column and lower at 200-m water depths.As chlorophyll a(chl a),TEP,and TEP C were highly concentrated at the bottom of the study transect,mainly on the continental shelf bottom and slope regions.Among biotic factors,cyanobacteria,especially Trichodesmium thiebautii showed significant positive correspondences with TEP through studied water columns in nSCS.In addition,TEP showed a positive correlation with chl-a distribution and clustered closely with diatom as well.It indicates a combined contribution of them on TEP sourcing accordingly.Nutrient concentrations were also high due to estuarine diluted water from Zhujiang(Pearl)River in the season that may intrigue those scenarios.Significant positive correlation(P<0.05)among biotic and abiotic parameters also supported the statement.Furthermore,mentionable contribution of TEP-derived TEP C was found after comparing the particulate organic carbon data,which may signify the importance of TEP in local carbon cycle in the nSCS.