Spatio-temporal variability of surface chlorophyll a in the Yellow Sea and the East China Sea based on reconstructions of satellite data of 2001-2020

Chlorophyll-a(Chl-a)concentration is a primary indicator for marine environmental monitoring.The spatio-temporal variations of sea surface Chl-a concentration in the Yellow Sea(YS)and the East China Sea(ECS)in 2001-2020 were investigated by reconstructing the MODIS Level 3 products with the data interpolation empirical orthogonal function(DINEOF)method.The reconstructed results by interpolating the combined MODIS daily+8-day datasets were found better than those merely by interpolating daily or 8-day data.Chl-a concentration in the YS and the ECS reached its maximum in spring,with blooms occurring,decreased in summer and autumn,and increased in late autumn and early winter.By performing empirical orthogonal function(EOF)decomposition of the reconstructed data fields and correlation analysis with several potential environmental factors,we found that the sea surface temperature(SST)plays a significant role in the seasonal variation of Chl a,especially during spring and summer.The increase of SST in spring and the upper-layer nutrients mixed up during the last winter might favor the occurrence of spring blooms.The high sea surface temperature(SST)throughout the summer would strengthen the vertical stratification and prevent nutrients supply from deep water,resulting in low surface Chl-a concentrations.The sea surface Chl-a concentration in the YS was found decreased significantly from 2012 to 2020,which was possibly related to the Pacific Decadal Oscillation(PDO).

Declined trends of chlorophyll a in the South China Sea over 2005–2019 from remote sensing reconstruction

Chlorophyll a concentration(CHL)is an important proxy of the marine ecological environment and phytoplankton production.Long-term trends in CHL of the South China Sea(SCS)reflect the changes in the ecosystem’s productivity and functionality in the regional carbon cycle.In this study,we applied a previously reconstructed 15-a(2005–2019)CHL product,which has a complete coverage at 4 km and daily resolutions,to analyze the long-term trends of CHL in the SCS.Quantile regression was used to elaborate on the long-term trends of high,median,and low CHL values,as an extended method of conventional linear regression.The results showed downward trends of the SCS CHL for the 75th,50th,and 25th quantile in the past 15 a,which were−0.0040 mg/(m^(3)·a)(−1.62%per year),−0.0023 mg/(m^(3)·a)(−1.10%per year),and−0.0019 mg/(m^(3)·a)(−1.01%per year).The negative trends in winter(November to March)were more prominent than those in summer(May to September).In terms of spatial distribution,the downward trend was more significant in regions with higher CHL.These led to a reduced standard deviation of CHL over time and space.We further explored the influence of various dynamic factors on CHL trends for the entire SCS and two typical systems(winter Luzon Strait(LZ)and summer Vietnam Upwelling System(SV))with single-variate linear regression and multivariate Random Forest analysis.The multivariate analysis suggested the CHL trend pattern can be best explained by the trends of wind speed and mixed-layer depth.The divergent importance of controlling factors for LZ and SV can explain the different CHL trends for the two systems.This study expanded our understanding of the long-term changes of CHL in the SCS and provided a reference for investigating changes in the marine ecosystem.

Distributions of chlorophyll a and carbon fixed strength of phyto-plankton in autumn of the southern Huanghai Sea waters

Chlorophyll a （Chl a） concentration and primary productivity （PP）, namely, carbon fixed strength of phytoplankton along four transects in the southern Huanghai Sea （SHS） were studied for their distribution features and controlling mechanisms based on the investigations from 17 October to 3 November 2005. The Chl a concentration in the study waters dynamically changed spatially. Surface Chl a concentrations ranged from 0.11 to 2.38 mg/m^3 with higher and lower values observed in the nutrient-laden inshore waters and central part of the SHS occupied by oligotrophic current, respectively. The vertical distribution of Chl a concentration showed a predominant pattern of subsurface concentration maximum profile. It followed the previous result of the deep dissolved oxygen concentration maximum profile, which was significantly correlated with phytoplankton and regional water mass. The primary productivity of carbon in autumn of the SHS, ranging from 95 to 1 634 rag/（ m^2· d） mainly varied with nutrient condition, especially phosphate concentration in seawater and hydrological condition. Furthermore, associating the present study results together with previous studies, the annual value of carbon fixed production of phytoplankton in the entire marginal seas of East China （including the Bohai Sea, the Huanghai Sea and the East China Sea） was estimated to be 222 Mt, which accounted for 2% of that in the global margins. Besides, it was as 16.2 times as the annual value of apparent carbon sink strength （ 13.96 Mt） in the marginal seas of East China. This multiple was different in different sea areas （ 3.0 in the Bohai Sea, 6. 7 in the Huanghai Sea and 81.6 in the East China Sea）.

Early stage toxicity of excess copper to photosystem II of Chlorella pyrenoidosa–OJIP chlorophyll a fluorescence analysis

Acute toxicity of excess Cu on the photosynthetic performance of Chlorella pyrenoidosa was examined by using chlorophyll a fluorescence transients and JIP-test after exposure to elevated Cu concentrations for a short time period. High Cu concentration resulted in a significant suppression in photosynthesis and respiration. The absorption flux （ABS/RC） per PSII reaction center increased with increasing Cu concentration, but the electron transport flux （ET0/RC） decreased. Excess Cu had an insignificant effect on the trapping flux （TR0/RC）. The decline in the efficiency, with which a trapped exciton can move an electron into the electron transport chain further than QA-（Ψ0）, the maximal quantum yield of primary photochemistry （φP0）, and the quantum yield of electron transport （φE0） were also observed. The amount of active PSII reaction centers per excited cross section （RC/CS） was also in consistency with the change of photosynthesis when cells were exposed to excess Cu concentration. JIP-test parameters had a good linear relationship with photosynthetic O2 evolution. These results suggested that the decrease of photosynthesis in exposure to excess Cu may be a result of the inactivation of PSII reaction centers and the inhibition of electron transport in the acceptor side.

Prediction of chlorophyll a concentration using HJ-1 satellite imagery for Xiangxi Bay in Three Gorges Reservoir

Since the impoundment of the Three Gorges Reservoir in 2003, algal blooms have frequently been observed in it. The chlorophyll a concentration is an important parameter for evaluating algal blooms. In this study, the chlorophyll a concentration in Xiangxi Bay, in the Three Gorges Reservoir, was predicted using HJ-1 satellite imagery. Several models were established based on a correlation analysis between in situ measurements of the chlorophyll a concentration and the values obtained from satellite images of the study area from January 2010 to December 2011. Chlorophyll a concentrations in Xiangxi Bay were predicted based on the established models. The results show that the maximum correlation is between the reflectance of the band combination of B4/（B2＋B3） and in situ measurements of chlorophyll a concentration. The root mean square errors of the predicted values using the linear and quadratic models are 18.49 mg/m3 and 18.52 mg/m3, respectively, and the average relative errors are 37.79% and 36.79%, respectively. The results provide a reference for water bloom prediction in typical tributaries of the Three Gorges Reservoir and contribute to large-scale remote sensing monitoring and water quality management.

Chlorophyll a increase induced by surface winds in the northern South China Sea

The response of chlorophyll a （Chl a） concentration to wind stress is analyzed in the South China Sea （SCS）, using in-situ data of Chl a and remote sensing data （QuikScat-sea surface wind （SSW）, AVHRR-sea surface temperature （SST）, AVISO merged-sea level anomalies （SLA）, SeaWiFS- derived Chl a and MODIS Terra-derived Chl a） in August/September/October 2004, 2006 and 2009. The variability of SSW, SST and SLA 7 d before in-situ Chl a sampling （including the work day of in^situ Chl a sampling） with the same latitude and longitude of the study area are investigated, and the correlation coefficients are calculated between these hydrographic factors and in-situ Chl a concentration. The results show that the Chl a-SSW correlation coefficients at upper layers （such as 0 m and 25 m） are more significant than those at deeper layers （such as 50, 75 and 100 m） 1 3 d before, which indicates that there is a time lag of strong surface winds stimulating phytoplankton bloom. By analyzing the relationship among the daily remote sensing derived （RS- derived） SSW, SST, SLA and 3 d averaged SeaWiFS/MODIS-derived Chl a concentration in the northern SCS in September 2004 and 2009 respectively, it shows that the intensity and speed of surface winds could have great influence on extend of Chl a increase. If surface winds reach 4-5 m/s over, Chl a concentration would increase 1-3 d after the process of strong surface winds in open sea area of the northern SCS mainly during September.

Spatio-temporal variability of chlorophyll a and its responses to sea surface temperature, winds and height anomaly in the western South China Sea

To understand the response of marine ecosystem to environmental factors, the oceanographic （physical and biochemical） data are analyzed to examine the spatio-temporal distributions of chlorophyll a （Chl a） associated with surface temperature, winds and height anomaly for long periods （1997-2008） in the western South China Sea （SCS）. The results indicate that seasonal and spatial distributions of Chl a are primarily in- fluenced by monsoon winds and hydrography. A preliminary Empirical Orthogonal Function （EOF） analysis of remotely sensed data is used to assess basic characteristics of the response process of Chl a to physical changes, which reveals interannual variability of anomalous low Chl a values corresponding to strong E1 Nifio （1997-1998）, high values corresponding to strong La Nifia （1999-2000）, low Chl a corresponding to moderate E1 Nifio （2001-2003）, upward Chl a after warm event in 2005 off the east coast of Vietnam. The variability of Chl a in nearshore and the Mekong River Estuary （MER） waters also suggests its response to these warm or cold processes. Considering the evidence for covariabilities between Chl a and sea surface temperature, winds, height anomaly （upwelling or downwelling）, cold waters input and strong winds mix- ing may play important roles in the spatial and temporal variability of high Chl a. Such research activities could be very important to gain a mechanistic understanding of ecosystem responses to the climate change in the SCS.

Effects of Low Temperature Stress and INA Bacteriaon Chlorophyll a Fluorescence Induction Kineticsin Young Fruit of Two Apricot Cultivars

Effects of low temperature and INA bacteria on the change of chlorophyll a fluorescence in young fruit from two apricot cultivars were investigated. Low temperature decreased the potential activity (Fv/ Fo), conversion efficiency of primary light energy (Fv/Fm)of PS II and photochemical quenching (qP) in young fruit of two apricot cultivars. Low temperature enhanced non-photochemical quenching qN, decreasing the quantum yield of photosynthetic electron transfer. The presence of ice nucleating active (INA) bacteria intensified the effects of low temperature, raised the injury temperature threshold from - 4℃ to - 2 - - 3℃. INA bacteria can be a factor to induce frost susceptibility of apricot fruit. The amount of damaged PS I activity center was related to apricot fruit size and cultivar.

The distribution of chlorophyll a in the tropical eastern Indian Ocean in austral summer

To study the effect of hydrographic factors on the spatial distributions of chlorophyll a （Chl a）, an investigation was carried out in the tropical eastern Indian Ocean （80 –100 E along 7 S, and 7 –18 S along 80 E） in December 2010. The fluorescent method was used to obtain total Chl a and size-fractioned Chl a at the 26 stations. The results show that surface Chl a concentration averaged at （0.168 ± 0.095） mg/m 3 s.d. （range： 0.034–0.475 mg/m 3 ）, concentrations appeared to be higher in the west for longitudinal variations, and higher in the north for latitudinal variations. Furthermore, the surface Chl a concentration was lower （0.034–0.066 mg/m 3 ） in the region to the south of 16 S. There was a strong subsurface Chl a maximum layer at all stations and the depth of the Chl a maximum increased towards to the east and south along with the respective nitracline. The spatial variation of Chl a was significant： correlation and regression analysis suggests that it was primarily affected by PO 3 4 , N（NO 3 –N＋NO 2 –N） and temperature. Size-fractionated Chl a concentration clearly showed that the study area was a typical oligotrophic open ocean, in which picophytoplankton dominated, accounting for approximately 67.8% of total Chl a, followed by nanophytoplankton （24.5%） and microphytoplankton （7.6%）. The two larger fractions were sensitive to the limitation of P, while picophytoplankton was primarily affected by temperature.

Physical structure and vertical distribution of chlorophyll a in winter sea ice from the northwestern Weddell Sea, Antarctica

The investigation on sea-ice biology in combination with physics, chemistry and ecology was carried out in the northwestern Weddell Sea, Antarctica, during the cruise ANT/XX III-7 on board POLARSTERN in the austral winter （August-October） in 2006. The distribution of chlorophyll a was measured and related to sea ice texture. The mean concentrations of chlorophyll a in the sea ice varied considerably with ice texture. The concentration of chlorophyll a per core ranged from 2.10– 84.40 μg/dm ^3 with a mean of 16.56 μg/dm ^3 . And the value of R （chlorophyll a / gross chlorophyll） ranged from 0.79–0.83. These high winter chlorophyll values indicate that primary production is considerable and confirms that there is significant primary production in Antarctic sea ice during winter. Thus this constitutes a major proportion of southern ocean primary production and carbon flux before the sea ice retreats.

Distribution characteristics of size-fractionated chlorophyll a, primary production and new production in the Laizhou Bay, July 1997

The distributions of chlorophyll a concentration, primary production and new productionwere observed in the Laizhou Bay of the Bohai Sea in both spring and neap tides during July 1997. The results showed that there were marked features of spatial zonation in the surveyed area, due to the differences between the geographic environment and the hydrological conditions. Chlorophyll a, primary production and new production were all higher in spring tides than that in neap tides in the Laizhou Bay. The highest values of these parameters were encountered in the central regions of the bay. At most stations, chlorophyll a concentrations at the bottom were higher than that at the surface. The results of size-fractionated chlorophyll a and primary production showed that contributions of nanocombining pi-coplankton ( <20 μm) to total chlorophyll a and primary production were dominant in phytoplankton community biomass and production of the Laizhou Bay. The environmental factors, primary production and new production in the Laizhou Bay are compared with other sea areas.

Comparison of summer chlorophyll a concentration in the South China Sea and the Arabian Sea using remote sensing data

The South China Sea（SCS） and the Arabian Sea（AS） are both located roughly in the north tropical zone with a range of similar latitude（0°–24°N）. Monsoon winds play similar roles in the upper oceanic circulations of the both seas. But the distinct patterns of chlorophyll a（Chl a） concentration are observed between the SCS and the AS.The Chl a concentration in the SCS is generally lower than that in the AS in summer（June–August）; the summer Chl a concentration in the AS shows stronger interannual variation, compared with that in the SCS; Moderate resolution imaging spectroradiometer（MODIS）-derived data present higher atmospheric aerosol deposition and stronger wind speed in the AS. And it has also been found that good correlations exist between the index of the dust precipitation indicated by aerosol optical thickness（AOT） and the Chl a concentration, or between wind and Chl a concentration. These imply that the wind and the dust precipitation bring more nutrients into the AS from the sky, the sub-layer or coast regions, inducing higher Chl a concentration. The results indicate that the wind velocity and the dust precipitation can play important roles in the Chl a concentration for the AS and the SCS in summer. However aerosol impact is weak on the biological productivity in the west SCS and wind-induced upwelling is the main source.

The size-fractionated chlorophyll a and primary productivity in the Bering Sea during the summer of 2003

Investigations of chlorophyll a and primary productivity were carried out inthe Bering Sea along the BR line and the BS line during the Second Chinese National Arctic ResearchExpedition in the summer of 2003. The results showed that the surface chlorophyll a concentrationswere 0.199～1.170 μg/dm^3, and the average value was 0.723 μg/dm^3 on the BR line. For the BSline, the surface chlorophyll a concentrations were 0.519～4.644 μg/dm^3 (average 1.605 μg/dm^3)and 0.568～14.968 μg/dm^3 (average 5.311 μg/dm^3) during the early and late summer, respectively.The average value in the late summer was much higher than that in the early summer. The high values(more than 4.0 μg/dm^3) occurred at stations of the BS line in the southern Bering Strait. Thechlorophyll a concentrations in the subsurface layer were higher than those in the surface layer.The results of the size-fractionated chlorophyll a showed that the contribution of the picoplanktonto total chlorophyll a was the predominance at the early summer and the contribution of thenetplankton was the predominance at the late summer. The carbon potential primary productivitiesvaried between 0.471 and 1.147 mg/(m^3·h) on the BR line, with average rates of 0.728 mg/(m^3·h).The primary productivities on the BS line were much higher than those of the BR line, ranging from1.227 mg/(m^3·h) at the early summer to 19.046 mg/(m^3·h) at the late summer. The results of thesize-fractionated primary productivity showed that the contribution of the nanoplankton to totalproductivity was the predominance at the early summer and the contribution of the netplankton waspredominance at the late summer. The assimilation number of photosynthesis was 0.45～2.80 mg/(mg·h)in the surveyed stations.

Chlorophyll a and primary production in the northeastern Pacific Ocean

The primary production and chlorophyll a concentration of picoplankton （0.2 - 2 μm） , nanoplankton （2 - 20μm） and micro- plankton （20 -200 μm） are described in the northeastern Pacific Ocean near the Hawaii Islands during the six survey cruises from 1996 to 2003：DY85-4, DY95-7, DY95-8, DY95-10, DY105-11 and DY105-12.14. The primary production of carbon was in range from 76.8 to 191.9 mg/（m^2 · d） with an average of 116.1 mg/（ m^2 · d） in the east region, and from 73.1 to 222.5 mg/（ m^2 · d） with an average of 127.1 mg/（ m^2 · d） in the west region, similar to the other oligotrophic regions of the Pacific Ocean investigated. The chlorophyll a concentration was about 0.1 mg/m^3 from the surface to the 50 m depth, about 0.2 -0.4 mg/m^3from 50 to 100 m, and gradually decreased below the 100 m depth. The picoplankton accounted for more than 70% of the total chlorophyll a in the upper layer （ surface to 125 m）, but it decreased to less than 50% in depth below 125 m. The nanoplankton and microplankton combined only accounted for less than 30% of the total chlorophyll a in the upper layer, but showed a more even vertical distribution.

Spatial and temporal variability and size fractionation of chlorophyll a in the tropical and subtropical Pacific Ocean

The spatial and temporal variability and size fractionation of chlorophyll a (Chl a) were investigated in the tropical and subtropical Pacific Ocean during four survey cruises from 2005 to 2009.The surface Chl a (S-Chl a) concentration ranged from 0.002 to 0.497 mg/m3 and was obviously higher in the eastern Pacific than in the western and central Pacific.The vertical distribution of Chl a displayed a single peak pattern,and the maximum Chl a layer (MCL) was observed at a shallower depth in the eastern Pacific than in the western Pacific.All three size fractions of Chl a measurements in the surface water showed a similar distribution to total Chl a and were found in higher concentrations in the eastern Pacific than in the western and central Pacific.Picoplankton dominated the phytoplankton in the surveyed tropical and subtropical Pacific Ocean.Furthermore,pico-Chl a (0.2-2 μm) accounted for a larger percentage of the total Chl a in the central Pacific than it did in the western Pacific and eastern Pacific.In the western Pacific,there seemed to be a latitudinal variability in the phytoplankton community composition where small-sized phytoplankton (＜2 μm) were more dominant in the tropical than in the subtropical western Pacific.The spatial and temporal variability and size fractionation of Chl a were controlled by hydrological and chemical characteristics and climate events,such as El Ni(n)o and La Ni(n)a.

Determination of the Content of Chlorophyll a in Surface Water

Advantages and disadvantages of three extraction methods （acetone grinding, heating and freezing extraction methods） in determination of chlorophyll a in surface water were compared, and the distribution of chlorophyll a in the Fenhe River in Taiyuan region was discussed. The results showed that more chlorophyll a was extracted using acetone heating and freezing extraction methods compared with acetone grinding method, and standard deviation （SD） was smaller. Interference of pheophytin a was eliminated, so accuracy of chlorophyll a content was improved. Chlorophyll a content at points 1 # and 2# in the upper reaches of the Fenhe River was lower than that at other points close to residential areas.

Discussion on Extraction of the Chlorophyll a from Phytoplankton by Hotethanol Method

[Objective] The research aimed to discuss extraction of the chlorophyll a from phytoplankton by hot-ethanol method. [Method] The measurement method of chlorophyll a was improved. By contrast test, the best extraction temperature and time of chlorophyll a by hot-ethanol meth- od were studied. Meanwhile, we contrasted hot-ethanol method with specification. I Result] It was simple to use hot-ethanol method to extract chlo- rophyll a from phytoplankton, and it was safe and reliable. When extraction temperature was 75℃ , extraction efficiency of the chlorophyll a was the highest using hot ethanol to hot for 3 min. Chlorophyll a extracted by specification presented significant positive correlation with that by hot-ethanol method. Extraction efficiency of the hot-ethanol method was higher than that of the specification. [ Condusion] The research could provide theoretical reference for extraction of the chlorophyll a from phytoplankton in surface water.

Upper limits for chlorophyll a changes with brine volume in sea ice during the austral spring in the Weddell Sea,Antarctica

During the winter and spring of 2006, we investigated the sea ice physics and marine biology in the northwest Weddell Sea, Antarctica aboard R/V Polarstern. We determined the texture of each ice core and 71 ice crystal thin sections from 27 ice cores. We analyzed 393 ice cores, their temperatures, 348 block density and salinity samples,and 311 chlorophyll a（Chl a） and phaeophytin samples along the cruise route during the investigation. Based on the vertical distributions of 302 groups of data for the ice porosity and Chl a content in the ice at the same position, we obtained new evidence that ice physical parameters influence the Chl a content in ice. We collected snow and ice thickness data, and established the effects of the snow and ice thickness on the Chl a blooms under the ice, as well as the relationships between the activity of ice algae cells and the brine volume in ice according to the principle of environmental control of the ecological balance. We determined the upper limits for Chl a in the brine volume of granular and columnar ice in the Antarctica, thereby demonstrating the effects of ice crystals on brine drainage, and the contributions of the physical properties of sea ice to Chl a blooms near the ice bottom and on the ice-water interface in the austral spring. Moreover, we found that the physical properties of sea ice affect ice algae and they are key control elements that modulate marine phytoplankton blooms in the ice-covered waters around Antarctica.

Interannual variability of remotely sensed chlorophyll a during an autumn monsoon transitional period in the Taiwan Strait

The time series of multiple sources of satellite data are used to examine the interannual variability of chlorophyll a concentration （Chl a） and its relation to the physical environment during the autumn monsoon transitional period in the Taiwan Strait （TWS）. The satellite data included the Chl a concentration and sea surface temperature （SST） derived from the Moderate Resolution Imaging Spectroradiometer （MODIS）/ Aqua as well as the multi-sensors merged wind products from 2002 to 2012. The results show that the average Chl a concentration of the whole TWS is mainly contributed by the northern TWS. The average Chl a in the northern TWS is 3.6 times that in the southern TWS. The maximum variability of Chl a is located in the frontal regions between the cold Zhe-Min Coastal Water and the strait warm water. The temporal change of Chl a concentration is different in the northern and southern TWS. The changes in the relative strength of the cold and warm water masses is suggested to be the dominant processes in controlling the phytoplankton growth in the northern TWS, while there is wind-induced mixing in the southern TWS. Additionally, La Nina events exhibited complex effects on the interannual variability of Chl a concentration in autumn. The longterm time series of physical and biological observations are especially needed to better understand how the TWS complex ecosystem responds to climate variations.

The distribution of chlorophyll a and its influencing factors in different regions of the Bering Sea

The distribution of chlorophyll a （Chl a） and its relationships with physical and chemical parameters in different regions of the Bering Sea were discussed in July 2010. The results showed the seawater column Chl a concentrations were 13.41-553.89 mg/m2 and the average value was 118.15 mg/m2 in the study areas. The horizontal distribution of Chl a varied remarkably from basin to shelf in the Bering Sea. The regional order of Chl a concentrations from low to high was basin, slope, outer shelf, inner shelf, and middle shelf. The verti- cal distribution of Chl a was grouped mainly from single-peak type in basin, slope, outer shelf, and middle shelf, where the deep Chl a maxima （DCM） layer was observed at 25-50 m, 30-35 m, 36-44 m, and 37-47 m, respectively. The vertical distribution of Chl a mainly had three basic patterns： standard single-peak type, surface maximum type, and bottom maximum type in the inner shelf. The analysis also showed that the transportation of ocean currents may control the distribution of Chl a, and the effects were not simple in the basin of the Bering Sea. There was a positive correlation between Chl a and temperature, but no significant correlation between Chl a and nutrients. The Bering Sea slope was an area deeply influenced by slope current. Silicate was the factor that controlled the distribution of Chl a within parts of the water in the slope. Light intensity was an important environmental factor in controlling seawater column Chl a in the shelf, where Chl a was limited by nitrate rather than phosphate within the upper water. Meanwhile, there was a positive relationship between Chl a and salinity. Algal blooms broke out at Sta. B6 of the southwestern St. Lawrence Island and Stas F6 and F11 in the middle of the Bering Strait.