Phytoplankton Primary Production Research Articles

Impact of climate change and oligotrophication on quality and quantity of lake primary production: A case study in Lake Biwa

Global climate change and anthropogenic oligotrophication are expected to reshape the dynamics of primary production (PP) in aquatic ecosystems; however, few studies have explored their long-term effects. In theory, the PP of phytoplankton in Lake Biwa may decline over decades due to warming, heightened stratification, and anthropogenic oligotrophication. Furthermore, the PP of large phytoplankton, which are inedible to zooplankton, along with biomass-specific productivity (PBc), could decrease. In this study, data from 1976 to 2021 and active fluorometry measurements taken in 2020 and 2021 were evaluated. Quantitatively, the temporal dynamics of mean seasonal PP during 1971–2021 were assessed according to the carbon fixation rate to investigate relationships among environmental factors. Qualitatively, phytoplankton biomass, PP, and PBc were measured in two size fractions [edible (S) or inedible (L) for zooplankton] in 2020 and 2021, and the L:S balance for these three measures was compared between 1992 (low-temperature/high-nutrient conditions) and 2020–2021 (high-temperature/low-nutrient conditions) to assess seasonal dynamics. The results indicated that climate change and anthropogenic oligotrophication over the past 30 years have diminished Lake Biwa's PP since the 1990s, impacting the phenology of PP dynamics. However, the L:S balance in PP and PBc has exhibited minimal change between the data from 1992 and the 2020–2021 period. These findings suggest that, although climate change and oligotrophication may reduce overall PP, they may not markedly alter the inedible/edible phytoplankton balance in terms of PP and PBc. Instead, as total PP declines, the production of small edible phytoplankton may decrease proportionally, potentially affecting trophic transfer efficiency and material cycling in Lake Biwa.

Water mass exchange in triangle seas of the Java-Makassar-Flores (JMF): A modeling study

The ocean dynamics of the marginal seas in the Java-Makassar-Flores (JMF) Triangle seas facilitates the seasonal exchange of water masses between Java, Makassar, and Flores, which influences the occurrence of small pelagic fish. This research investigates seasonal fluctuations in sea currents, seawater temperature, salinity, and phytoplankton primary production (PPN and PPD) based on validated model output datasets from NEMO and PISCES from the INDESO simulation (2008–2015). The model demonstrated seasonal exchanges of the top 50 m of water masses in the area, where the eastward monsoon current transported freshwater (salinity<31 psμ) from the Java Sea to southern Makassar and Flores. This northwest monsoon produced a much fresher water in the southern region of Makassar and western region of Flores. During the southeast monsoon, the surface component of the Makassar throughflow, which transports saline water (salinity >34 PSU) into the Java Sea, pushes fresh Java waters westward. Seasonal salinity changes and PPN/PPD in the shelf region of southern Kalimantan correlated with substantial small pelagic fishing.

Seasonal variations in chlorophyll–a and sea surface temperature in the exclusive economic zone of Sri Lanka

Oceanic phytoplankton plays a crucial role in regulating the biogeochemical cycle in marine ecosystems. Light harvesting pigments such as chlorophyll–a (chl–a) can be used to understand marine primary productivity, especially phytoplankton abundance. Sea surface temperature is closely linked with phytoplankton abundance and climatic changes. The objective of the current study is to determine spatial and temporal variations of chl–a and sea surface temperature and their co-variation, over 12 years using statistical methodologies and Remote Sensing, Geographic Information System (GIS) and Cloud Computing Approach. In this study, the available sea surface temperature and chl–a data acquired from a Moderate Resolution Imaging Spectroradiometer (MODIS) satellite sensor were proceeded through Google Earth Engine and Earth Science Data System. Data visualization was carried out using ArcMap™ software. Results show a weak negative linear relationship (–0.40, P < 0.05) between sea surface temperature and chl–a. Therefore, additional favorable environmental factors such as coastal upwelling, and nutrient discharge through river run-off can control the primary productivity of phytoplankton. We also illustrated spatial and temporal maps for chl–a and sea surface temperature distribution in the exclusive economic zone of Sri Lanka. Chlorophyll–a concentration is enhanced during the southwest monsoon, and the lowest concentration is observed during the first inter-monsoon period. Next, the highest sea surface temperature is recorded during the first inter-monsoon period, and the lowest sea surface temperature is observed during the northeast monsoon. Seasonal behavior of chl–a concentration and sea surface temperature are changed as chl–a (SWM) > chl–a (NEM) > chl–a (SIM) > chl–a (FIM) and SST (FIM) > SST (SIM) > SST (SWM) > SST (NEM), respectively. In addition, both trend lines for each variable show a positive gradient, which may be attributed to global warming. Finally, we observed the alteration of chl–a and sea surface temperature that linked to changes in ocean chemistry during the global COVID–19 pandemic.

Primary production of phytoplankton of the river Ob and the estuaries of its large tributaries in the site from the lower point of the Novosibirsk hydraulic system to the Novosondrovo (2022, 2023)

An assessment of the state of the river ecosystem was carried out. Ob based on the characteristics of the gross primary production of phytoplankton and BOD5 in the area from the lower pool of the Novosibirsk hydroelectric complex to the village. Novosondrovo (below the mouth of the Chulym River). The study was conducted in July 2022 and 2023. on the targets. The determination of gross primary production of phytoplankton was carried out using the flask method in oxygen modification in situ. At the same time, we determined the mineralization, transparency and temperature of water, pH, the content of oxygen dissolved in water, and the concentration of easily oxidized organic substances (BOD5) in the river. Ob and the mouth areas of Tom and Chulym. It was shown that the obtained values of the average gross primary production of Ob phytoplankton were significantly higher than in the summer low-water period in the Ob Bay and the upper reaches of the river. Yenisei. Particularly high rates were noted in areas subject to anthropogenic load and off the coast with a well-developed floodplain. The influence of tributaries on the functioning of Ob phytoplankton is shown. The key abiotic factors for the functioning of phytoplankton have been identified. It was revealed that, in terms of gross primary production and BOD5, the trophic status of the Ob and its tributaries during the studied period ranged from mesotrophic to polytrophic waters. The highest level of trophicity in 2022 was noted in local areas in the area of large settlements, in 2023 — in a more significant section of the Ob from the village. Dubrovino to the village. Krivosheino and at the mouth of the Tom, decreasing downstream the Ob to a mesotrophic level. It was noted that the trophic status of the Ob has increased significantly over the past 20 years, which may be a consequence of the increased anthropogenic load on the watercourse.

Two-decade satellite observations reveal variability in size-fractionated phytoplankton primary production in the South China Sea

Understanding variations in marine phytoplankton primary production (PP) is crucial for assessing the response of the marine environment to climate change and for quantifying the ocean carbon cycle. However, the spatiotemporal variability of size-fractionated PP in the South China Sea (SCS) remains ambiguous. Our study investigated the monthly, seasonal, and inter-annual variability of size-fractionated PP in the SCS using satellite observations from 2002 to 2022. There were noticeable seasonal and monthly variations in size-fractionated PP, with notably high PP values appearing during the cold season. The disparities in distribution and the distinct fluctuation patterns between size-fractionated PP suggest that total PP alone is not a comprehensive indicator of marine ecosystem health. Over the past two decades in the SCS, there were more pronounced decreases in total, pico-, and nano-PP, whereas micro-PP displayed no significant trend. The most pronounced decline occurred in the northern SCS, contrasted by increases in coastal areas. These size-fractionated PP anomalies showed strong correlations with climate change indices, highlighting the impact of environmental factors on these anomalies, such as sea surface temperature, mixed layer depth, and wind speed. Our findings emphasize the importance considering size-fractionated PP to gain a more nuanced understanding of the ocean carbon cycle and the marine ecosystem's response to climate changes.

Herbicide leakage into seawater impacts primary productivity and zooplankton globally.

Predicting the magnitude of herbicide impacts on marine primary productivity remains challenging because the extent of worldwide herbicide pollution in coastal waters and the concentration-response relationships of phytoplankton communities to multiple herbicides are unclear. By analyzing the spatiotemporal distribution of herbicides at 661 bay and gulf stations worldwide from 1990 to 2022, we determined median, third quartile and maximum concentrations of 12 triazine herbicides of 0.18 nmol L-1, 1.27 nmol L-1 and 29.50 nmol L-1 (95%Confidence Interval: CI 1.06, 1.47), respectively. Under current herbicide stress, phytoplankton primary productivity was inhibited by more than 5% at 25% of the sites and by more than 10% at 10% of the sites (95%CI 3.67, 4.34), due to the inhibition of highly abundant sensitive species, community structure/particle size succession (from Bacillariophyta to Dinophyceae and from nano-phytoplankton to micro-phytoplankton), and resulting growth rate reduction. Concurrently, due to food chain cascade effects, the dominant micro-zooplankton population shifted from larger copepod larvae to smaller unicellular ciliates, which might prolong the transmission process in marine food chain and reduce the primary productivity transmission efficiency. As herbicide application rates on farmlands worldwide are correlated with residues in their adjacent seas, a continued future increase in herbicide input may seriously affect the stability of coastal waters.

Iodide, iodate &amp; dissolved organic iodine in the temperate coastal ocean

The surface ocean is the main source of iodine to the atmosphere, where it plays a crucial role including in the catalytic removal of tropospheric ozone. The availability of surface oceanic iodine is governed by its biogeochemical cycling, the controls of which are poorly constrained. Here we show a near two-year time series of the primary iodine species, iodide, iodate and dissolved organic iodine (DOI) in inner shelf marine surface waters of the Western English Channel (UK). The median ± standard deviation concentrations between November 2019 and September 2021 (n=76) were: iodide 88 ± 17 nM (range 61-149 nM), iodate 293 ± 28 nM (198-382 nM), DOI 16 ± 16 nM (&amp;lt;0.12-75 nM) and total dissolved iodine (dIT) 399 ± 30 nM (314-477 nM). Though lower than inorganic iodine ion concentrations, DOI was a persistent and non-negligible component of dIT, which is consistent with previous studies in coastal waters. Over the time series, dIT was not conserved and the missing pool of iodine accounted for ~6% of the observed concentration suggesting complex mechanisms governing dIT removal and renewal. The contribution of excess iodine (I*) sourced from the coastal margin towards dIT was generally low (3 ± 29 nM) but exceptional events influenced dIT concentrations by up to ±100 nM. The seasonal variability in iodine speciation was asynchronous with the observed phytoplankton primary productivity. Nevertheless, iodate reduction began as light levels and then biomass increased in spring and iodide attained its peak concentration in mid to late autumn during post-bloom conditions. Dissolved organic iodine was present, but variable, throughout the year. During winter, iodate concentrations increased due to the advection of North Atlantic surface waters. The timing of changes in iodine speciation and the magnitude of I* subsumed by seawater processes supports the paradigm that transformations between iodine species are biologically mediated, though not directly linked.

Primary production and microbial heterotrophy in the Siberian arctic seas, Bering Strait, and Gulf of Anadyr, Bering Sea

The data obtained during the recent decades indicate large-scale climatic changes in the Arctic Ocean, especially in the Siberian shelf seas. The impact of shrinking of the Arctic ice cover on marine net primary production (PP) was mostly studied using satellite-derived estimates of chlorophyll-a (Chl a), sea surface temperature, and sea ice concentrations, as well as various modeling approaches. However, no data are available on the quantitative relations between phytoplankton production and heterotrophic bacterioplankton activity in the broadest and shallowest shelf of the World Ocean - the East Siberian Arctic seas (ESAS). In this paper we present a full set of in situ measurements of main PP and microbial heterotrophy characteristics required for better understanding and further validation of the satellite and modeling approaches. In September–October 2011, during the 57th cruise of RV Akademik M.A. Lavrent'ev, PP, bacterioplankton abundance (BA) and bacterioplankton production (BP), as well the rates of dark CO2 assimilation (DCA) were determined in the Chukchi, East Siberian, and Laptev seas and in the Gulf of Anadyr of the Bering Sea (a total of 26 stations) by in situ measurements using radiolabeled bicarbonate. All three important production indicators exhibited significant variance within the studied water areas of the Arctic (РР from 0.98 to 54.7 μg C L−1 day−1), (ВР from 1.1 to 17.1 μg C L−1 day−1), and (DCA from 0.23 to 8.7 μg C L−1 day−1). The state of phyto- and bacterioplankton was determined by analysis of the BP/PP and DCA/PP ratios. Active photosynthesis with efficient incorporation of inorganic carbon into the biomass was observed in the Chukchi Sea coastal eastern waters and in the Gulf of Anadyr. On the contrary, the phytoplankton primary production was extremely low in oligotrophic basins of the East Siberian and Laptev seas, while the activity of heterotrophic bacterioplankton consuming organic matter of phytoplankton origin was relatively high. The data of direct measurements can be used for further adjustment of the indirect assessments of production obtained by satellite observations. Glossary East Siberian Arctic seas (ESAS), net primary production (PP), bacterioplankton abundance (BA), bacterial biomass (BB), bacterial production (BP), Arctic Ocean PP (AO-PP), organic matter (OM), dissolved organic matter (DOM), colored dissolved organic matter (CDOM), light CO2 assimilation (LCA), dark (heterotrophic + chemotrophic) CO2 assimilation (DCA), production indicators of the surface water layer (PPsurf, DCAsurf, BPsurf), estimated production indicators for the entire depth of the sea (PPint, DCAint, BPint; mg C m−2 day−1).

Long-Term Changes in the Primary Production of Phytoplankton in the Ecosystem of the Vistula Lagoon of the Baltic Sea

Long-Term Changes in the Primary Production of Phytoplankton in the Ecosystem of the Vistula Lagoon of the Baltic Sea

Primary Productivity of Phytoplankton in Mandalika Coastal Area, Central Lombok Regency

The research entitled "Primary Productivity of Phytoplankton in Mandalika Coastal Area, Central Lombok Regency" was conducted from March to August 2023. This study aims to analyze the primary productivity of phytoplankton and physical and chemical parameters in Mandalika Coastal waters at three different stations (Kuta Beach, Tanjung Aan, and Gerupuk Bay) using dark and light bottles. Based on the results of the study, it is known that Mandalika Coastal waters have phytoplankton primary productivity values ranging from 122.619 - 329.166 mgC/m2/day. The lowest productivity value (122.619 mgC/m2/day) occurs at station III classified as mesotrophic. Station III also has relatively lower physical and chemical parameter values such as an average pH of 7.7 mg/L and an average temperature of 29ºC compared to other stations. The highest productivity value (329.166 mgC/m2/day) occurred at Station II classified as eutrophic and Station I (189.285 mgC/m2/day) also classified as eutrophic. This is supported by pH worth 7.8 mg/L and temperatures ranging from 29.3 - 29.7 ºC, where the value is relatively higher than station III.

Assessing Phytoplankton Primary Productivity Variability in the Changjiang Estuary, East China Sea From Coupled Fast Repetition Rate (FRR) Fluorometry and Chlorophyll‐a Measurements

AbstractPhytoplankton primary productivity (PP) varies significantly over environmental gradients, particularly in physically‐dynamic systems such as estuaries and coastal seas. During summer, runoff peaks in the Changjiang River driving large environmental gradients in both the Changjiang estuary and adjacent East China Sea (ECS), likely driving significant variability in PP. As satellite models of PP often underperform in coastal waters, we aimed to develop a novel approach for assessing net PP variability in such a dynamic environment. Parallel in situ measurements of Fast Repetition Rate (FRR) fluorometry and carbon (C) uptake rates were conducted for the first time in this region during two summer cruises in 2019 and 2021. A series of 13C‐incubations (n = 31) were performed, with measured PP ranging from ∼6 to 1,700 mgC m−3 d−1. Net PP values were significantly correlated with salinity (r = 0.45), phytoplankton chlorophyll a (Chl‐a, r = 0.88), Photosystem II (PSII) functional absorption cross‐section (σPSII, r = −0.76) and maximum PSII quantum yield (Fv/Fm, r = 0.59). Stepwise regression analysis showed that Chl‐a and σPSII were the strongest predictors of net PP. A generalized additive model (GAM) was also used to estimate net PP considering nonlinear effects of Chl‐a and σPSII. We demonstrate that GAM outperforms linear modeling approaches in estimating net PP in this study, as evidenced by a lower root mean square error (∼140 vs. 250 mgC m−3 d−1). Our novel approach provides a valuable tool to examine carbon cycling dynamics in this important region.

Factors affecting abundance and primary productivity of phytoplankton in a wetland ecosystem of Bangladesh

Wetlands are the most productive, economically important and hydrologically variable ecosystems. In this study, the abundance of phytoplankton and its primary productivity were evaluated in Dingapota Haor of Bangladesh. A total of 41 phytoplankton genera belong to Chlorophyceae (15), Bacillariaophyceae (14), Cyanophyceae (8) and Euglenophyceae (4) were recorded whereas Bacillariaophyceae (37.02%) was the most dominant. The highest cell density (22.71×104 cell L–1) was recorded in pre-monsoon. Diversity indices were also significantly higher in pre-monsoon. The species diversity, evenness and richness varied from 2.51–3.79, 0.57–0.90 and 4.65–7.50 respectively. Difference in phytoplankton assemblage with an overall average dissimilarity value of 52.56 % was recorded. Cyclotella (3.60%), Bacillaria (3.13%), Volvox (2.95%), Spirulina (2.92%) and Euglena (2.88%) were the five most contributory species to the seasonal variation. Gross Primary Production, Net Primary Production and Community Respiration values ranged from 0.90–2.49, 0.68–1.60 and 0.35–0.89 mgCm–3day–1 respectively. Alkalinity and Chl-a showed significant positive correlation with GPP, NPP and CR. Pre-monsoon was the most productive phase whereas the monsoon season was the least productive. The current study produced valuable baseline data that will aid in the formulation of wetland conservation and management strategies.

Influence of circulation processes on cyanobacteria bloom and phytoplankton succession in the Baltic Sea coastal area

Many studies related to the influence of eddies on the primary production chain of marine ecosystems have been conducted; however, this effect tends to be regionally specific, especially in coastal dynamic waters. In the Baltic Sea, mesoscale and submesoscale eddies are a ubiquitous feature of water circulation during summer, when diazotrophic cyanobacteria blooms occur in surface waters due to the excess of phosphorus in seawater. Climatic change may increase the frequency and duration of these negative events in the marine ecosystem. We examined the taxonomic composition, abundance, and primary production of phytoplankton in the southeastern Baltic Sea during the occurrence of the packed eddy system at the end of the abnormally warm summer of 2018. Massive cyanobacteria growth was observed in the plume of the eutrophic Vistula Lagoon in the Gulf of Gdansk. The only species diazotrophic Dolichospermum flos-aquae ((Bornet &amp; Flahault) P. Wacklin, L. Hoffmann &amp; Komárek, 2009) vegetated along the western coast of the Sambia Peninsula. Its colonies reached the highest biomass nearby the dumping site of the Amber Mining Plant in Yantarny, Kaliningrad Region, Russia. The cyanobacteria colonies dispersed in the outgoing jet of a relatively warm eddy dipole. Chrysochromulina spp. (Lackey, 1939) was dominant in these nitrogen-rich waters. In contrast, cryptophyte species dominated in the relatively cold waters of the dipole anticyclone that resulted in a fourfold decline in primary production. The decrease in the number of mobile phytoplankton species was revealed within the “old” eddies near the northern coast of the Sambia Peninsula and the Curonian Spit. Meanwhile, species of the spring–autumn complex Coscinodiscus granii (Gough, 1905), Peridiniella catenate ((Levander) Balech, 1977) and other developed in the community. This implies that the appearance of eddies can cause phytoplankton succession in the coastal area. The mechanism of their influence was similar to the action of other physical factors perturbing a relatively stationary environment. Capture of cyanobacterial colonies by eddies led to an improvement of the ecological situation in the area, as cyanobacteria transported their biomass outside the coastal area. However, the opposite direction processes obviously were the deterioration of light conditions, increased water turbidity, and organic matter concentration.

Phytoplankton primary production in Chascomus pond (Provincia de Buenos Aires, Argentina)

In situ phytoplankton primary production in Chascomús pond (eutrophic Pampasic “laguna”) was studied by the oxygen method (light and dark bottle) between.January 1984-January 1985. Valúes obtained ranged from37,9 to 981,6 mg C • m-1 • d-1. Factors influencing it, as suspended particulate matter and hydrological changes, are discussed. Parallel determinations of the artificial light photosynthesis response proved to be useful,almostqualitatively under the experimental conditions applied, to follow the behaviour obtained by incubations in natural environment.

INFLUENCE OF RIPARIAN FOREST AND TEMPERATURE ON PRIMARY PRODUCTION OF TROPICAL STREAMS

Primary production is a key feature for the functioning of aquatic ecosystems. The trophic state of the streams reflects this primary production and is influenced by local limnological variables and level of integrity of the watershed. Thus, in this study, habitat integrity index (HII) and physical, chemical, and biological parameters of tropical streams were sampled in two sub-basins to understand the functioning of these ecosystems. We hypothesized that the variables association to the environmental integrity should determine the primary production in the streams. Because of the similar land use in the sub-basins (ex.: agriculture and livestock) they will show similar limnological variables. To identify how the streams differed in relation to their limnological characterization and the HII, we performed a Principal Component Analysis (PCA). The association between variables was assessed by Pearson's correlation analysis. To identify the difference between the two basins, a Student's Test was performed. The best predictors of primary production were determined using a multiple regression analysis with the Akaike selection criteria. The concentration of chlorophyll-a in the surface water indicated that the tropical streams sampled have, in general, low concentrations of nutrients, except for some more urban points. The variables that most differed among streams were blue-green cells/ml, pH, conductivity, and width of the riparian forest. Only redox potential and pH differed between the two watersheds. Temperature, blue-green cells/ml and width of the riparian forest were the variables that best predicted the phytoplankton primary production of watercourses in both watersheds. In this study we reinforce the importance of temperature in aquatic productivity, even more present in the face of climate change, which, added to deforestation, increases the surface area of sunlight in water courses, increases primary productivity and the eutrophication process.Keywords: blue-green algae; chemical variables; chlorophyll-a; HII; phytoplankton.

Anomalous trend of chlorophyll-a as a response to mesoscale phenomena in a Brazilian oligotrophic ria

Saco do Mamanguá is a tropical Brazilian ria characterized by low nutrient availability and subject to seasonal thermocline, which is mainly influenced by the intrusion of South Atlantic Central Water (SACW) on the continental shelf. Sampling was performed in summer (2014, 2015) and spring (2017). The dissolved inorganic and organic nutrients (nitrogen [N] and phosphorus [P]), along with chlorophyll-a (Chl-a), were evaluated to characterize this area. As a result, the general trophic condition of Saco do Mamanguá is a meso-oligotrophic ria with low Chl-a concentrations. Due to the presence of an atmospheric phenomena that causes an extremely dry period during the summer of 2014, a strong thermocline was observed in the water column which was associated with high Chl-a concentrations (median of 6.14 mg m−3). These values were much higher than those observed during the summer of 2015 and in the spring of 2017 (median of 1.03 mg m−3). The dissolved inorganic nutrients presented low values in all studied periods with concentrations of nitrate (0.00–0.20 μmol L−1) and phosphate (0.00–0.20 μmol L−1). A wide range of dissolved organic compounds were also observed, as shown by the presence of dissolved organic carbon (DOC), which varied from 63 to 212 μmol L−1; dissolved organic nitrogen (DON), which varied from 2.97 to 12.92 μmol L−1; and dissolved organic phosphorus (DOP), which reached a maximum value of 0.63 μmol L−1. DON and DOP represented at least 50% total dissolved N and P. In this region, the biogeochemical cycles of N and P could ensure the availability of regenerated nutrients from organic sources to support primary production of phytoplankton.

Parameterization of Water Transparency in Natural Water Bodies

A new parameterization is presented to describe the space and time variations of Secchi depth depending on the integral phytoplankton biomass and surface water temperature. The parameterization was verified against field data in lakes with different types of physiographic and chemical–biological characteristics—from deep oligotrophic northern regions of Lake Ladoga to shallow hypereutrophic Pskovskoe Lake. The results of verification show that the new parameterization can be used for solving a wide range of either hydrothermodynamic or hydrobiological problems. In particular, in the simulation of the thermal regime of water bodies, the proposed parameterization can be used to evaluate the coefficient of extinction of solar radiation. In the development of models to describe aquatic ecosystem functioning, the new parameterization can be used to evaluate the thickness of the trophogenic layer and phytoplankton primary production.

Spatiotemporal patterns and drivers of phytoplankton primary productivity in China's lakes and reservoirs at a national scale

Spatiotemporal patterns and drivers of phytoplankton primary productivity in China's lakes and reservoirs at a national scale

Assessment of satellite-based Net Primary Productivity models in different biogeochemical provinces over the northern Indian Ocean

ABSTRACT The biological productivity in the oceanic ecosystem plays a vital role in the global carbon cycle and energy flow in the oceanic food chain. Therefore, proper monitoring of phytoplankton primary production in the ocean is essential to understand the role and responses of aquatic ecosystems to global climate change. Its quantification is also important for higher trophic-level studies and sustainable ecosystem management. The advent of satellite technology has provided an opportunity to retrieve Net Primary Productivity (NPP) at high spatial and temporal resolution. However, for efficient utilization of satellite NPP it is imperative to assess the models for their accuracy and variability. The present study described NPP estimated from MODIS-Aqua satellite data (2003–2021) using five models (VGPM, Eppley-VGPM, CbPM, CAFE, and SABPM) and their variability in the four biogeochemical provinces (ARAB, MONS, INDW and INDE) in the northern Indian Ocean. The temporal variability indicated all models exhibit seasonal variability in ARAB and INDW with two prominent peaks during peak southwest monsoon (June-August) and winter monsoon (December-January). However, there was significant difference in the magnitude. The seasonal peak was primarily due to increase in NPP due to summer upwelling and winter mixing. The spatially averaged diversity index indicated maximum variability in INDW (74.6–77.1%), followed by INDE (77.2–78.0%), ARAB (77.2–78.4%), and MONS (78.6–78.9%). The satellite retrieved NPP by various models showed maximum diversity in the region above 15°N and west of 60°E in AS and 20°N and east 90°E in the BoB indicating a significant influence of discharge from perennial rivers resulting in poor performance of the models in these regions. The variability of other models was then assessed with respect CbPM as the model was known to perform better. The Eppley-VGPM showed a maximum (55%) and SABPM showed a minimum (11%) Mean Absolute Percentage Difference with respect to CbPM. The long-term spatio-temporal and quantifiable variability between the NPP models, and biogeochemical provinces, indicated that the study provided useful information on the selection and utilization of an appropriate model for future sustainability and climate change studies.

Primary Production in the Kara, Laptev, and East Siberian Seas.

Understanding of the primary production of phytoplankton in the Kara Sea (KS), the Laptev Sea (LS), and the East Siberian Sea (ESS) remains limited, despite the recognized importance of phytoplankton in the Arctic Ocean. To address this knowledge gap, we conducted three NABOS (Nansen and Amundsen Basins Observational System) expeditions in 2013, 2015, and 2018 to measure in situ primary production rates using a 13C-15N dual-tracer method and examine their major controlling factors. The main goals in this study were to investigate regional heterogeneity in primary production and derive its contemporary ranges in the KS, LS, and ESS. The daily primary production rates in this study (99 ± 62, 100 ± 77, and 56 ± 35 mg C m-2 d-1 in the KS, LS, and ESS, respectively) are rather different from the values previously reported in each sea mainly because of spatial and regional differences. Among the three seas, a significantly lower primary production rate was observed in the ESS in comparison to those in the KS and LS. This is likely mainly because of regional differences in freshwater content based on the noticeable relationship (Spearman, rs = -0.714, p < 0.05) between the freshwater content and the primary production rates observed in this study. The contemporary ranges of the annual primary production based on this and previous studies are 0.96-2.64, 0.72-50.52, and 1.68-16.68 g C m-2 in the KS, LS, and ESS, respectively. Further intensive field measurements are warranted to enhance our understanding of marine microorganisms and their community-level responses to the currently changing environmental conditions in these poorly studied regions of the Arctic Ocean.