Simulations of Annual Cycle of Phytoplankton Production and the Utilization of Nitrogen in the Yellow Sea (original) (raw)
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Continental Shelf Research, 2009
Nutrients, chlorophyll-a (Chl-a), and environmental conditions were extensively investigated in the northern East China Sea (ECS) near Cheju Island during five research cruises from 2003 to 2007. In the eastern part of the study area, surface waters were characterized only by the Tsushima Current Water (TCW) during all five cruises. However, the western surface waters changed with season and were characterized by the Yellow Sea Cold Water (YSCW) in spring, the Changjiang Diluted Water (CDW) in summer, and the Yellow Sea Mixed Water (YSMW) in autumn. In spring and autumn, relatively high concentrations of nitrate and phosphate were observed in the surface waters in the western part of the study area, where vertical mixing brought large supplies of nutrients from deep waters. Changes in wind direction occasionally varied the inflow of the Changjiang plume in summer, clearly causing the annual variation in surface nitrate and phosphate concentrations in summer. In summer, the surface distribution of nitrate and phosphate did not coincide with that of silicate in the study area, which probably resulted from the significant drop in the Si:N ratio in the Changjiang plume since construction of the Three Gorges Dam (TGD). Despite large temporal and spatial variations in surface Chl-a concentrations, depth-integrated Chl-a concentrations exhibited little variation temporally and spatially. In the study area, surface Chl-a concentration did not well reflect the standing stocks of phytoplankton. The vertical distribution of Chl-a showed large temporal and spatial variations, and the main factor controlling the vertical distribution of Chl-a in summer was the availability of nitrate. The thermohaline front may play an important role for accumulation of phytoplankton biomass in spring and autumn.
High-resolution phytoplankton diel variations in the summer stratified central Yellow Sea
Vertical distributions of phytoplankton biomass and community structure were studied in the summer stratified central Yellow Sea (YS) using a submersible spectrofluorometer (Fluoroprobe, bbe Moldaenke, Germany), along with photosynthetic pigments analysis (HPLC-CHEM-TAX), and microscope observation. Above all, the results of the dominating group obtained from these methods generally coincided with each other on the transect 35°N. The concentrations of brown algae, green algae and total chlorophyll a (Chl a) biomass were highly correlated between the results of Fluoroprobe observations and pigments analysis (r = 0.79, 0.91 and 0.82, respectively, n = 54, p \ 0.01). In the summer stratified central YS, significant differences in phytoplankton compositions on the vertical distribution was observed. On the basis of HPLC-CHEMTAX results, the dominating group of phytoplankton composition generally changed from cyanobacteria to chrysophytes and then to diatoms, from surface to bottom. Interestingly, on the basis of high-resolution observations using Fluoroprobe, a periodic fluctuation of the pycnocline presumably due to the semidiurnal internal tides was observed at an anchor station (35°N, 123°E). In addition, both nutrients and Chl a concentrations at the depth of the subsurface chlorophyll maximum (SCM) seemed to coincide with the rhythm of the pycnocline fluctuation, indicating the latter might have a potential impact on the dynamics of SCM phenomena in the summer stratified central YS.
Deep-sea Research Part Ii-topical Studies in Oceanography, 2003
Chlorophyll a concentration, primary production, and environmental conditions over the entire shelf of the subtropical East China Sea (ECS) were studied extensively during four seasonal cruises between December 1997 and October 1998. Nutrient concentrations in the northwestern half of the shelf were enriched all year-round, but primary production showed high seasonal variations. Intensive primary production was mostly observed in summer at about 939 mg C m À2 d À1 . On average, the value in summer was about 3 times higher than that in other seasons. Annual primary production was 155 g C m À2 y À1 . In the southeastern half of the shelf, on the other hand, nutrient concentrations were seasonally variable, but primary production showed only slight seasonal variations with a mean value of 395 mg C m À2 d À1 . Annual primary production was 144 g C m À2 y À1 . The annual variations in shelf-averaged primary production can be well described with a normal distribution curve. For the entire shelf of the ECS, annual primary production was 145 g C m À2 y À1 . The rate of primary production was regulated by seawater temperature from winter to early spring. The rate of primary production was, in turn, regulated by the availability of nutrients, especially phosphate, from summer to autumn. In addition, turbidity might also play a role in the regulation of primary production in the waters of the inner shelf. r
Regional and Seasonal Variations in Phytoplankton
2018
Vertical variation in production is also observed in oceans. The deep layers of ocean are light limited and hence photosynthesis, a process associated with sunlight cannot proceed leading low phytoplankton production. Another requirement for photosynthesis are sufficient concentration of nutrients (nitrates, phosphates, silicates, iron, etc.). In stratified waters, growth of phytoplankton is “nutrient limited”. The nutrients in the upper mixed layer are consumed by phytoplankton. The growth of phytoplankton occurs in the layer where both light and nutrient concentration are sufficient. The depth at which maximum phytoplankton growth occurs is known as deep chlorophyll maxima (Figure 2). 08 C H A P T E R REGIONAL AND SEASONAL VARIATIONS IN PHYTO LANKTON
Continental Shelf Research, 2000
Chemical hydrography, chlorophyll a distribution and primary productivity in the southern East China Sea from the inner shelf to the o!shore region were examined for their temporal and spatial variability based on observations along a cross-shelf transect during 1991}1995. In summer, all surface waters were depleted in nutrients and low in chlorophyll, resulting in widespread subsurface chlorophyll a maxima. In other seasons, shelf waters were usually nutrient-laden, but phytoplankton biomass was limited by light availability in the turbid inner shelf water and the short exposure time of the upwelled water in the outer shelf. The main nitrogen source in the inner shelf was from river runo!. Nitrate de"cit, de"ned as the negative deviation from the conservative mixing line, was well correlated with phytoplankton biomass. In spite of the seasonal and spatial variability of chlorophyll a distribution, the euphotic zone integrated value of chlorophyll a was correlated well with that of primary production in shelf waters. This relationship was used to convert chlorophyll a data from 28 cruises to primary production. The results showed that the lowest productivity on the shelf was in summer with little spatial variation. The elevated primary productivity in the inner shelves in spring was due to a mild spring bloom. On the other hand, the elevated primary productivity in the middle and outer shelves in autumn was due to the intensi"cation of upwelling during the transition of the monsoon. The annual mean values of the euphotic zone integrated primary production in the shelf waters were quite uniform (513}576 mgC m\ d\) with an overall mean of 549$84 mgC m\ d\. The o!shore Kuroshio Water showed a weak seasonal variation 0278-4343/00/$ -see front matter 2000 Elsevier Science Ltd. All rights reserved. PII: S 0 2 7 8 -4 3 4 3 ( 9 9 ) 0 0 0 7 9 -5 Fig. 1. Station locations for the KEEP-Box (ᮀ), KEEP-Key (᭡) cruises and Cruise 414 (;).
I. Monitoring Spring Phytoplankton Bloom Progression in
2013
There is evidence that primary productivity is inhibited in Suisun Bay, and that NH4 may be causing that inhibition. The main purpose of this study is to measure nutrients, primary production, nutrient uptake by phytoplankton and, phytoplankton biomass and species composition in Suisun Bay in the spring to determine if there is inhibition, and if so, to determine what is causing the inhibition. Suisun Bay is an area identified as critical habitat for the threatened Delta Smelt (Hobbs et al., 2006). Several important changes in the pelagic food web of this area have been documented over the last two decades indicating that food for Delta Smelt and other threatened fishes is in short supply (Müeller-Solger et al. 2002; Sommer et al. 2007). One of the most striking changes in Suisun Bay is the decline in phytoplankton between 1975- 1995 (Jassby et al. 2002) and the shift from large accumulations of phytoplankton biomass (>40 μg L-1 chlorophyll) during the summer (Cloern 1979) to muc...
Journal of Geophysical Research, 2004
1] Two cruises were carried out in the summer and winter of 1998 to study coupled physical-chemical-biological processes in the South China Sea and their effects on phytoplankton stock and production. The results clearly show that the seasonal distributions of phytoplankton were closely related to the coupled processes driven by the East Asian Monsoon. Summer southwesterly monsoon induced upwelling along the China and Vietnam coasts. Several mesoscale cyclonic cold eddies and anticyclonic warm pools were identified in both seasons. In the summer, the upwelling and cold eddies, both associated with rich nutrients, low dissolved oxygen (DO), high chlorophyll a (Chl a) and primary production (PP), were found in the areas off the coast of central Vietnam, southeast of Hainan Island and north of the Sunda shelf, whereas in the winter they form a cold trough over the deep basin aligning from southwest to northeast. The warm pools with poor nutrients, high DO, low Chl a, and PP were found in the areas southeast of Vietnam, east of Hainan, and west of Luzon during the summer, and a northwestward warm jet from the Sulu Sea with properties similar to the warm pools was encountered during the winter. The phytoplankton stock and primary production were lower in summer due to nutrient depletion near the surface, particularly PO 4 . This phosphorus depletion resulted in phytoplankton species succession from diatoms to dinoflagellates and cyanophytes. A strong subsurface Chl a maximum, dominated by photosynthetic picoplankton, was found to contribute significantly to phytoplankton stocks and production.
Nutrients and mixing, chlorophyll and phytoplankton growth
Deep Sea Research Part A. Oceanographic Research Papers, 1990
, we observed an event of windinduced mixing during a 4-day sequence of observations while operating in a Lagrangian sampling mode. The sharp increase in wind stress was followed by a sharp increase in nitrate concentration in the euphoric zone. The nitrate declined rapidly, and over the next 2 days the quantity of chlorophyll a in the ¢uphotic zone increased by a factor of three. The phytoplankton community was dominated by diatoms; this and other evidence indicates that the events observed were part of the spring bloom in the north Sargasso Sea. These observations are interpreted in terms of laboratory models for nutrient-dependent phytoplankton growth. The cell-quota model of Caperon and Droop provides an internally consistent explanation of the observed data. The data also suggest the notion of "nutrient switching" (rather than a multiplicative form of nutrient interaction) in the interaction of nitrate and silicate, although this could not be verified.
Limnology and Oceanography, 2003
Simulation modeling provides a means for testing the limits of our quantitative understanding of the factors that control phytoplankton biomass, growth rate, and primary productivity in the sea. We simulated the annual cycles of chlorophyll a (Chl a) concentration, primary productivity, nitrogen export, phytoplankton carbon to nitrogen (C : N) and carbon to Chl a ratios (C : Chl a) using a physiological model of phytoplankton carbon, nitrogen, and Chl a dynamics. The model was embedded within a one-dimensional physical model of vertical exchanges that included simple mortality and recycling terms. A sensitivity analysis allowed evaluation of the relative effects of changes in phytoplankton physiology, physical forcing, mortality, and nutrient cycling on Chl a distributions and phytoplankton C : N. Critical to the success of the model was the treatment of mortality, which included seasonal (temperature) and depth-related components, and the treatment of recycling efficiency, which was considered to be a function of the inorganic nitrogen concentration. The subtropical simulation compared favorably with data obtained at the Bermuda Atlantic Time-series Study (BATS) station. Our results illustrate the utility of physiological data in validation of biogeochemical models. In particular, model predictions of phytoplankton C : Chl a, which ranged from 30 to 170 g C (g Chl a) Ϫ1 , compared well with direct estimates based on 14 C labeling of Chl a. However, predictions of phytoplankton C : N, which ranged from ϳ5-9 g C (g N) Ϫ1 , could not be verified because of lack of data. This range of C : N suggests a slight limitation of phytoplankton growth rates by nutrients in surface waters.