Phytoplankton Biomass Dynamics Research Articles

Importance of light status on phytoplankton biomass in the turbid Bisan Strait, Japan: results from a high-frequency sampling study

AbstractThe dynamics of phytoplankton biomass in the vertically mixed south-eastern part of the Bisan Strait, in the Seto Inland Sea of Japan, may be considered to be strongly dependent not only on nutrients but also on light status. This was investigated by examining variations in chlorophyll-a (Chl-a), nutrients, and Secchi-disc depth through high-frequency sampling (a mean of once every 1.7 days) at the same station from April to October 2019. Precipitation during the Japanese rainy season (East Asian monsoon rains) was associated with a decrease in salinity from 32 to 31 in late July. The highest concentration of dissolved inorganic nitrogen (DIN), the most deficient nutrient, also was recorded in late July in association with seasonal precipitation. However, the measured Chl-a peak (max. 4 μg l−1) in early August was not as high as expected, possibly due to low water clarity. A relatively small but substantial peak of DIN (max. 4 μM) was recorded in mid-August, which coincided with the passing of a typhoon. The small peak of DIN coupled with higher water clarity thereafter was followed by a phytoplankton bloom from mid-August to early September, at which the highest Chl-a (7 μg l−1) occurred. It is suggested that increased light penetration enhanced the efficiency of nutrient assimilation and thereby triggered the late-summer phytoplankton bloom. In contrast to the adjacent stratified areas, light rather than nutrient status appears to be the key determinant for the onset of phytoplankton blooms in the Bisan Strait.

Coupling between sediment biogeochemistry and phytoplankton development in a temperate freshwater marsh (Charente-Maritime, France): Evidence of temporal pattern

In freshwater systems, sediment can be an important source for the internal loading of PO4. The limiting character of this element in such system leads to consider this phenomenon in terms of eutrophication risks and water quality stakes. A four-months follow-up (January, March, April and May 2019) was carried out in a strong phosphate (PO4) limited secondary channel from an artificial irrigation system of Charente Maritime (France) to link the mobilization of remineralization products in the upper 6 cm layer of sediment (conventional core slicing/centrifugation and DET probes) and the phytoplankton biomass dynamics in the water column. Results showed congruent patterns between the temporal succession of the organic matter mineralization processes in the sediment and the primary biomass dynamics in the water column. In January and March (considered in winter), PO4 proved to be retained by adsorption onto iron oxides in anoxic sediment since pore water nitrate inhibited for about a month the respiration of metal oxides in the first cm of sediment, thus limiting PO4 availability and the phytoplankton growth. In April and May (early spring), after exhaustion of pore water nitrate, the dissolutive reduction of iron oxides released PO4 into pore water generated a significant diffusive outgoing flux from the sediment to the water column with a maximum in April (-1.10E-04±2.81E-05 nmol cm−2 s−1). This release coincided with the nanophytoplankton bloom (5.50 µg Chla L−1) and a potential increase of PO4 concentration in the water column. This work provides some insight on the importance of benthic-pelagic coupling in anthropogenic systems. This conceptual model has to be deployed on other sites of interest where internal loading of P takes precedence over external inputs and nitrate mitigation drives its benthic recycling and ultimately its bioavailability. This is to be essential to characterize the aquatic environment quality in order to limit eutrophication risks.

Seasonal modulation of phytoplankton biomass in the Southern Ocean

Over the last ten years, satellite and geographically constrained in situ observations largely focused on the northern hemisphere have suggested that annual phytoplankton biomass cycles cannot be fully understood from environmental properties controlling phytoplankton division rates (e.g., nutrients and light), as they omit the role of ecological and environmental loss processes (e.g., grazing, viruses, sinking). Here, we use multi-year observations from a very large array of robotic drifting floats in the Southern Ocean to determine key factors governing phytoplankton biomass dynamics over the annual cycle. Our analysis reveals seasonal phytoplankton accumulation (‘blooming’) events occurring during periods of declining modeled division rates, an observation that highlights the importance of loss processes in dictating the evolution of the seasonal cycle in biomass. In the open Southern Ocean, the spring bloom magnitude is found to be greatest in areas with high dissolved iron concentrations, consistent with iron being a well-established primary limiting nutrient in this region. Under ice observations show that biomass starts increasing in early winter, well before sea ice begins to retreat. The average theoretical sensitivity of the Southern Ocean to potential changes in seasonal nutrient and light availability suggests that a 10% change in phytoplankton division rate may be associated with a 50% reduction in mean bloom magnitude and annual primary productivity, assuming simple changes in the seasonal magnitude of phytoplankton division rates. Overall, our results highlight the importance of quantifying and accounting for both division and loss processes when modeling future changes in phytoplankton biomass cycles.

Dynamics of phytoplankton species composition, biomass and nutrients in the North Atlantic during spring and summer - A trans-Atlantic study

During a return trip in May–June 2013 from Bergen, Norway, to Nuuk, Greenland, on the Institute of Marine Research's R/V “G. O. Sars”, four ocean basins, the Norwegian, Iceland, Irminger and Labrador seas, were surveyed twice. Here we analyse the phytoplankton communities and their dynamics in the four basins, winter nutrient content, potential for new production, consumption of nutrients, phenology and algae biomass (Chlorophyll a). The primary production dynamics of the four basins are compared and related to physical forcing and top-down control and discussed in relation to vertical carbon flux. We focus on the primary production dynamics in the central, mostly Atlantic, water masses of the basin-wide gyres. The survey results are put into a larger scale context by comparison with MODIS surface chlorophyll estimates.The timing of the phytoplankton bloom phase differed among the basins. In the Labrador Sea, there was a strong bloom already occurring during the first crossing in mid-May. This was confirmed by nitrate and silicate reduction, which was much larger in the Labrador Sea compared to the other seas in May. In the Irminger Sea the bloom lagged behind, whereas in the Norwegian and Iceland seas both a pre-bloom and a late bloom were observed during May–June.There was a direct relationship between the mixed layer depth and the use of nitrate at the sampling stations, and a direct relationship between chlorophyll concentrations and the use of nitrate. The two relationships suggest that the use of nitrate can serve as a measure of the developmental state of the phytoplankton bloom, phenology, and that it is related to the shallowing of the mixed layer.Flagellates were the most abundant algae in all regions, outnumbered by diatoms only at a couple of stations west of Greenland. Elevated ciliate numbers were observed in the Iceland and Norwegian seas on both sides of the Arctic front. The algae outnumbered the microzooplankton by at least an order of magnitude.

Phytoplankton Biomass Dynamics in Tropical Coastal Waters of Jakarta Bay, Indonesia in the Period between 2001 and 2019

A study of nutrients, underwater light dynamics, and their correlation with phytoplankton biomass was conducted in the tropical estuary of Jakarta Bay, Indonesia, in the dry season during the period from 2001 to 2019. This study analyzed the spatial and temporal dynamics of phytoplankton biomass and its correlation with phytoplankton biomass. There was significant increase in nutrient concentration in Jakarta Bay, with annual means of 27.97 µM dissolved inorganic nitrogen (DIN) and 11.31 µM phosphates in 2001, increasing to 88.99 µM DIN and 25.92 µM phosphates in 2019. Increased mean nutrient concentrations were accompanied by increased mean phytoplankton biomass, from 15.81 µg Chl-a L−1 in 2001 to 21.31 µg Chl-a L−1 in 2019. The eutrophication status of Jakarta Bay waters was calculated using the Tropical Index for Marine Systems eutrophication index, which showed increased areas of hyper-eutrophic and eutrophic zones, while the mesotrophic area decreased. The hyper-eutrophic zone dominated the areas around river mouths and the inner part of the bay, while eutrophic status was observed in the middle part of the bay and mesotrophic status was found in the outer part of the bay. The area of hyper-eutrophic water increased 1.5-fold, from 75.1 km2 in 2001 to 114.0 km2 in 2019. Increasing eutrophication of the bay has had negative ecological consequences including algal blooms, hypoxic conditions, and mass mortality of marine biota, and it urgently requires remediation.

A Trait-Based Clustering for Phytoplankton Biomass Modeling and Prediction

When designing models for predicting phytoplankton biomass or characterizing traits, it is useful to aggregate the myriad of species into a few biologically meaningful groups and focus on group-level attributes, the common practice being to combine phytoplankton species by functional types. However, biogeochemists and plankton ecologists debate the most applicable grouping for describing phytoplankton biomass patterns and predicting future community structure. Although trait-based approaches are increasingly being advocated, methods are missing for the generation of trait-based taxa as alternatives to functional types. Here we introduce such a method and demonstrate the usefulness of the resulting clustering with field data. We parameterize a Bayesian model of biomass dynamics and analyze long-term phytoplankton data collected at Station L4 in the Western English Channel between April 2003 and December 2009. We examine the tradeoffs encountered regarding trait characterization and biomass prediction when aggregating biomass by (1) functional types, (2) the trait-based clusters generated by our method, and (3) total biomass. The model conveniently extracted trait values under the trait-based clustering, but required well-constrained priors under the functional type categorization. It also more accurately predicted total biomass under the trait-based clustering and the total biomass aggregation with comparable root mean squared prediction errors, which were roughly five-fold lower than under the functional type grouping. Although the total biomass grouping ignores taxonomic differences in phytoplankton traits, it predicts total biomass change as well as the trait-based clustering. Our results corroborate the value of trait-based approaches in investigating the mechanisms underlying phytoplankton biomass dynamics and predicting the community response to environmental changes.

Light fluctuations are key in modulating plankton trophic dynamics and their impact on primary production

AbstractSurface‐ocean mixing creates dynamic light environments with predictable effects on phytoplankton growth but unknown consequences for predation. We investigated how variations in average mixed‐layer (ML) irradiance shaped plankton trophic dynamics by incubating a Northwest‐Atlantic plankton community for 4 days at high (H) and low (L) light, followed by exposure to either sustained or reversed light intensities. In deep‐ML (sustained L), phytoplankton biomass declined (μ = −0.2 ± 0.08 d−1) and grazing was absent. In shallow‐ML (sustained H), growth exceeded grazing (μ = 0.46 ± 0.07 d−1; g = 0.32 ± 0.04 d−1). In rapidly changing ML‐conditions simulated by switching light‐availability, growth and grazing responded on different timescales. During rapid ML‐shoaling (L to H), μ immediately increased (0.23 ± 0.01 d−1) with no change in grazing. During rapid ML‐deepening (H to L), μ immediately decreased (0.02 ± 0.09 d−1), whereas grazing remained high (g = 0.38 ± 0.05 d−1). Predictable rate responses of phytoplankton growth (rapid) vs. grazing (delayed) to measurable light variability can provide insights into predator‐prey processes and their effects on spatio‐temporal dynamics of phytoplankton biomass.

Variation in phytoplankton community and its implication to dimethylsulphide production at a coastal station off Goa, India

Seasonal hypoxia/suboxia (at times anoxia) towards the end of Southwest monsoon (SWM; June to September) at the coastal time series site off Goa, West coast of India was found to influence the dynamics of phytoplankton biomass, community structure and production of climatically active gas, dimethylsulphide (DMS). In this diatom dominated study region, high DMS production in the subsurface waters during late SWM might possible be attributed to the stress experienced by micro- and macro-algae from the prevailing low oxygen subsurface waters through different pathways specifically believed to be via methylation pathway (see Schafer et al., 2010). Based on laboratory experiments, we hypothesize presence of floating seaweeds mostly Sargassum species washed from the shore to the study site to contribute sizably to DMS production in the water column as they sink and degrade during the senescence phase. However, we are yet to address its loss/emission processes across the oxic-hypoxic boundary of seasonal (and permanent) oxygen minimum zone of the northern Indian Ocean, which is important from the viewpoint of global climate change.

Enhancement of phytoplankton biomass leeward of Tahiti as observed by Biogeochemical-Argo floats

Abstract The South Pacific Subtropical Gyre (SPSG) is a vast and remote oceanic system where the variability in phytoplankton biomass and production is still largely uncertain due to the lack of in situ biogeochemical observations. The SPSG is an oligotrophic environment where the ecosystem is controlled predominantly by nutrient depletion in surface waters. However, this dynamic is altered in the vicinity of islands where increased biological activity occurs (i.e. the island mass effect, IME). This study mainly focuses on in situ observations which show evidence of an IME leeward of Tahiti (17.7°S - 149.5°W), French Polynesia. Physical and biogeochemical observations collected with two Biogeochemical-Argo profiling floats are used to investigate the dynamics of phytoplankton biomass. Data from the first float, drifting from April 2015 to November 2016 over >1000 km westward of Tahiti, describe the open ocean conditions. The second float, deployed leeward of Tahiti in October 2015, stayed within 45 km off Tahiti for three months before it stopped communicating. In the oligotrophic central SPSG, our observations show that the deepening of the deep chlorophyll maximum (DCM) from winter to summer is light-driven and that the wintertime increase in chlorophyll a concentration in the upper layer is likely to be due to the process of photoacclimation, consistent with previous observations in oligotrophic environments. In contrast, leeward of Tahiti, the DCM widens toward the surface during late spring in association with a biological enhancement in the upper layer. Using Biogeochemical-Argo data, meteorological data from Tahiti, Hybrid Coordinate Ocean Model outputs and satellite-derived products (i.e., horizontal currents and associated fronts), the physical mechanisms involved in producing this biological enhancement leeward of Tahiti have been investigated. The IME occurs during a period of strong precipitation and in a zone of weak currents downstream of the island. We conjecture that the land drainage induces a significant supply of nitrate in the ocean upper layer (down to ~100 m) while a zone of weak currents in the southwestern zone behind Tahiti allows an accumulation zone to form, hence increasing phytoplankton growth up to 20 km away from the coastlines. A bio-optical-based community index suggests that the composition of the phytoplankton community differs leeward of Tahiti from that in the open ocean area, with more microphytoplankton within the IME, which is associated with an increase in the carbon export to the deeper ocean.

Phytoplankton dynamics and bloom formation in the oligotrophic Eastern Mediterranean: Field studies in the Aegean, Levantine and Ionian seas

This study attempts to elucidate the dynamics of phytoplankton biomass (as Chl-a), productivity, community structure and bloom formation in different regions of the oligotrophic Eastern Mediterranean (EMed). With this scope, several chemical and phytoplankton parameters were studied along a transect of 1300 km across different pelagic environments from North (N) Aegean to South (S) Aegean, Levantine and Ionian seas during spring and summer 2008. An exceptional spring phytoplankton bloom was detected in the S Aegean Sea, dominated by large sized diatoms and spreading almost throughout the euphotic zone. This unprecedented bloom was triggered by the nutrient enrichment of surface water masses due to cyclonic formations and a strong convection event that caused deep mixing. There was a clear decreasing trend of phytoplankton biomass and productivity from the Aegean towards the Levantine and Ionian seas. The same trend was recorded for N:P ratios and increasing P limitation from the Aegean to the Levantine and Ionian seas. Si:N ratio indicated an overall deficiency of N in relation to the available Si. Picoplankton was the dominant and most productive size fraction, except for the S Aegean in spring due to the diatom bloom. Chl-a maxima in the N Aegean were constrained within the surface layer occupied by modified Black Sea water, deepening progressively towards the Levantine and Ionian seas, especially during the stratified period. Nanoflagellates and small-sized dinoflagellates were important phytoplankton components in the N Aegean inter-seasonally, whereas in the S Aegean the large diatoms associated with the spring blooming shifted to nanoflagellates and small dinoflagellates in the stratified period. Coccolithophores and small diatoms were significant components in the Levantine and Ionian seas, whereas the overall microplankton community structure did not demonstrate prominent seasonal patterns. These results confirm that oligotrophy is the main driving force for the distribution of phytoplankters, but also offer evidence of how the low nutrient-low chlorophyll EMed system can occasionally support high phytoplankton biomass and generate prominent blooms. This work will help elucidate the structure and functioning of EMed pelagic food webs and contribute to the analysis of signals related to structural and functional ecosystem changes.

Temporal and spatial phytoplankton biomass dynamics in southern Gulf of Lake Tana, Northwestern Ethiopia

Southern Gulf of Lake Tana is southern part of Lake Tana in Northwestern Ethiopia. Water samples were obtained from eight sites of the gulf for six months during November to April 2010/11 twice a month to determine temporal and spatial variation in phytoplankton biomass of the gulf. Phytoplankton biomass data was estimated following total chlorophyll-a concentrations determination methods. There was no significant difference in sampling sites and interactions between sampling sites and months ( P >0.05). However, there is a significant difference in sampling months ( P <0.05). The absence of significant difference in sampling sites and the interactions might be due to the similarity in human or natural impacts, and phytoplankton growth and decline. But, the presence of significant difference among sampling months might be due to the difference in growth/decline periods of the phytoplankton. Southern Gulf of Lake Tana subparts are similarly impacted naturally or by humans who passed their time around the gulf. The Ethiopian government and concerned non-governmental organizations in general and local communities, in particular, have better cooperate their efforts for conservation and sustainable use of the gulf. Similarly, they have to play in awareness creation for stakeholders to reduce natural/human impacts to the lake gulf.

Dynamics of size-fractionated phytoplankton biomass in a monsoonal estuary: Patterns and drivers for seasonal and spatial variability

Phytoplankton size-fractionated biomass is an important determinant of the type of food web functioning in aquatic ecosystems. Knowledge about the effect of seasonal salinity gradient on the size-fractionated biomass dynamics is still lacking, especially in tropical estuaries experiencing monsoon. The phytoplankton size-fractionated chlorophyll a biomass (>3 μm and <3 μm) and picophytoplankton community structure were characterized in the monsoonal Zuari estuary, along the west coast of India, from October 2010 to September 2011 across the salinity gradient (0–35). On an annual scale, >3 μm size-fraction was the major contributor to the total phytoplankton chlorophyll a biomass with the ephemeral dominance of <3 μm size-fraction. During monsoon season, freshwater runoff and shorter water residence time resulted in a size-independent response. The lowest annual chlorophyll a biomass concentration of both size-fractions showed signs of recovery with increasing salinity downstream towards the end of the monsoon season. In contrast, the chlorophyll a biomass response was size-dependent during the non-monsoon seasons with the sporadic dominance (>50%) of <3 μm chlorophyll a biomass during high water temperature episodes from downstream to middle estuary during pre-monsoon and at low salinity and high nutrient conditions upstream during post-monsoon. These conditions also influenced the picophytoplankton community structure with picoeukaryotes dominating during the pre-monsoon, phycoerythrin containing Synechococcus during the monsoon and phycocyanin containing Synechococcus during the post-monsoon. This study highlights switching over of dominance in size-fractionated phytoplankton chlorophyll a biomass at intra, inter-seasonal and spatial scales which will likely govern the estuarine trophodynamics.

Abiotic and biotic controls of phytoplankton biomass dynamics in a freshwater tributary, estuary, and large lake ecosystem: Sandusky Bay (Lake Erie) chemostat

The classic view of tributary–lake interactions solely considers tributaries as sources of nutrients for phytoplankton growing offshore. We tested how river input of phytoplankton affected dynamics in a lacustrine estuary and how these phytoplankters could, upon discharge, affect offshore phytoplankton dynamics. In addition, we explored whether phytoplankton biomass was controlled by bottom-up abiotic factors (stream flow, temperature, light attenuation, and nutrient concentrations) or top-down biotic factors (zooplankton herbivory) and the role the lacustrine estuary played in modifying the quality of the water discharged into the lake. We tested these possibilities using field sampling over 2 years in the Sandusky River, Sandusky Bay, and the Sandusky subbasin of Lake Erie in conjunction with river flow and nutrient monitoring and multivariate statistical analysis of the relationships among the various datasets. Nutrient loading to the estuary corresponded with watershed input; nutrients were used within the estuary, decreasing nutrient loads to the lake. Phytoplankton biomass, however, was extremely high in the estuary and was much higher at the bay–subbasin interface than offshore, indicating that the estuary likely discharges phytoplankton to the nearshore area, not offshore. An information-theoretic analysis of 15 candidate models showed that phytoplankton biomass was best predicted by the ratio of total inorganic nitrogen to total phosphorus, indicating bottom-up control. The lacustrine estuary therefore functions as a chemostat, using incoming nutrients to grow large amounts of phytoplankton. Our results indicate that the classic model of tributary–bay interactions needs revision to include phytoplankton load and its subsequent effects within the lake.

Student's tutorial on bloom hypotheses in the context of phytoplankton annual cycles

Phytoplankton blooms are elements in repeating annual cycles of phytoplankton biomass and they have significant ecological and biogeochemical consequences. Temporal changes in phytoplankton biomass are governed by complex predator–prey interactions and physically driven variations in upper water column growth conditions (light, nutrient, and temperature). Understanding these dependencies is fundamental to assess future change in bloom frequency, duration, and magnitude and thus represents a quintessential challenge in global change biology. A variety of contrasting hypotheses have emerged in the literature to explain phytoplankton blooms, but over time the basic tenets of these hypotheses have become unclear. Here, we provide a “tutorial” on the development of these concepts and the fundamental elements distinguishing each hypothesis. The intent of this tutorial is to provide a useful background and set of tools for reading the bloom literature and to give some suggestions for future studies. Our tutorial is written for “students” at all stages of their career. We hope it is equally useful and interesting to those with only a cursory interest in blooms as those deeply immersed in the challenge of understanding the temporal dynamics of phytoplankton biomass and predicting its future change.

Multi-model approach to predict phytoplankton biomass and composition dynamics in a eutrophic shallow lake governed by extreme meteorological events

A multi-model approach to predict phytoplankton biomass and composition was performed in a eutrophic Uruguayan shallow lake which is the second drinking water source of the country. We combined statistical (spectral analysis and Machine learning techniques) and physically based models to generate, for the first time in this system, a predictive tool of phytoplankton biomass (chlorophyll-a) and composition (morphology-based functional groups). The results, based on a 11-year time series, revealed two alternating phases in the temporal dynamics of phytoplankton biomass. One phase is characterized by high inorganic turbidity and low phytoplankton biomass, and the other by low inorganic turbidity and variable (low and high) phytoplankton biomass. A threshold of turbidity (29 TNU), above which phytoplankton remains with low biomass (<15–20ug/l) was established. The periods of high turbidity, which in total cover 30% of the time series, start abruptly and are related to external forcing. Meteorological conditions associated with the beginning of these periods were modeled through a regression tree analysis. These conditions consist of moderate to high wind intensities from the SW direction, in some cases combined with high antecedent precipitation or low water level. The results from the physically-based modeling indicated that the long decaying time-scale of turbidity and intermediate resuspension events could explain the prolonged length of the high turbidity periods (∼1.5 years). Random Forests models for the prediction of phytoplankton biomass and composition in periods of low turbidity resulted in a proportion of explained variance and a classification error over a test sample of 0.46 and 0.34 respectively. Turbidity, conductivity, temperature and water level were within the most important model predictors. The development and improvement of this type of modeling is needed to provide management tools to water managers in the current water supply situation.

On the use of optical remote sensing to assess phytoplankton biomass dynamics in the Pelagos Sanctuary (Ligurian-Provençal Sea)

If Marine Protected Areas (MPAs) are to aid in protecting and conserving marine ecosystems in the face of extensive and severe impacts of human activities, underpinning scientific knowledge and understanding of MPAs are imperative. This study aims to describe and evaluate phytoplankton dynamics in a pelagic Mediterranean MPA (The Pelagos International Marine Mammals Sanctuary) in the north-western Mediterranean Sea as a means to understand better the spatial and temporal distribution of basal ecosystem resources. Ocean colour data collected by orbital remote sensing (Sea-viewing Wide Field-of-view Sensor [SeaWiFS] data) were analysed to elucidate spatial and temporal variations in the concentration of chlorophyll-like pigments (chl). Mean chl images were generated for consecutive 10-day periods, to provide quasi-continuous coverage of the study area, combined with a Principal Component Analysis and analysis of a time series ​(1998–2004). The chl surface patterns traced seasonal upwelling events recurring annually, demonstrating the critical role of physical oceanography in sustaining the food web of the PelagosSanctuary. Phytoplankton blooms, however, differ in terms of peak timing, spatial distribution and chl concentration, due in part to the influence of broad-scale environmental factors that are beyond direct and regional control. Further research is needed to elucidate the relationship between the biomass of primary and secondary producers to understand better the implications of phytoplankton biomass distribution in space and time for charismatic and protected biota such as cetaceans.

A Statistical Algorithm for Estimating Chlorophyll Concentration in the New Caledonian Lagoon

Spatial and temporal dynamics of phytoplankton biomass and water turbidity can provide crucial information about the function, health and vulnerability of lagoon ecosystems (coral reefs, sea grasses, etc.). A statistical algorithm is proposed to estimate chlorophyll-a concentration ([chl-a]) in optically complex waters of the New Caledonian lagoon from MODIS-derived “remote-sensing” reflectance (Rrs). The algorithm is developed via supervised learning on match-ups gathered from 2002 to 2010. The best performance is obtained by combining two models, selected according to the ratio of Rrs in spectral bands centered on 488 and 555 nm: a log-linear model for low [chl-a] (AFLC) and a support vector machine (SVM) model or a classic model (OC3) for high [chl-a]. The log-linear model is developed based on SVM regression analysis. This approach outperforms the classical OC3 approach, especially in shallow waters, with a root mean squared error 30% lower. The proposed algorithm enables more accurate assessments of [chl-a] and its variability in this typical oligo- to meso-trophic tropical lagoon, from shallow coastal waters and nearby reefs to deeper waters and in the open ocean.

Phytoplankton biomass dynamics and environmental variables around the Rocas Atoll Biological Reserve, South Atlantic

Abstract The Rocas Atoll Biological Reserve is located in the Atlantic Ocean, at 3º 51' S and 33º 49' W. It lies 143 nautical miles from the City of Natal, Rio Grande do Norte (Brazil). The purpose of this study was to analyze the hydrology, water masses, currents and chlorophyll a content to determine the dynamics of phytoplankton biomass around the Rocas Atoll. Samples were collected in July 2010 in the area around the Atoll, using the Research Vessel Cruzeiro do Sul of the Brazilian Navy. Two transects were established according to the surface currents, one of which at the southeast of the Atoll (SE) and the other at norwest (NW). Three collection points were determined on each of these transects. Samples were collected at different depths (surface and DCM - Deep Chlorophyll Maximum) and different times (day and night). According to PCA (Principal Component Analysis), the nutrients analyzed, DIN (dissolved inorganic nitrogen), DIP (dissolved inorganic phosphorus) and silicate, were inversely correlated with temperature and dissolved oxygen. Most environmental variables showed a significant increase due to the turbulence on the Northwest transect. There was an increase in the concentration of chlorophyll a and nutrients when the temperature and oxygen in the mixed layer was reduced due to the influence of the SACW (South Atlantic Central Water). Despite the increase observed in some variables such as nutrient salts and chlorophyll a, the temperature in the mixed layer attained a mean value of 23.23 ºC due to the predominance of Tropical Water. The increase of the phytoplankton biomass on the NW transect was, therefore, caused by the "island effect" and not by upwelling.

Bathymetrical influences on spatial and temporal characteristics of chlorophyll-a concentrations in the Southern Ocean from 2002 to 2012 (October to March) using MODIS

Phytoplankton blooms, particularly in the Southern Ocean, can have significant impact on global biogeochemistry cycling. To investigate the accuracy of chlorophyll-a distribution, and to better understand the spatial and temporal dynamics of phytoplankton biomass, we examine chlorophyll-a estimates (October–March from 2002 to 2012) derived from Moderate Resolution Imaging Spectrometer (MODIS) data following the ocean chlorophyll-a 3 model (OC3M) algorithm. Noticeable seasonality occurs in the temporal distribution of chlorophyll-a concentrations, which shows the highest value in December and January and an increasing tendency during the 2002–2012 period. The spatial distribution of chlorophyll-a varies greatly with latitude, as higher latitudes experience more phytoplankton blooms (chlorophyll-a concentration larger than 1 mg/m3) and marginal seas (Ross Sea and Amundsen Sea) show different bloom anomalies caused by two dominant algae species. Areas at higher latitudes and shallow water (<500 m) experience the shorter ice-free periods with greater seasonality. A noticeable bathymetry gradient exists at 2500-m isobaths, while water at the 500–2500-m depth experiences quite long ice-free periods with a stable water environment. Blooms generally occur near topographic features where currents have strong interactions when the water depth is more than 2500 m. Based on these findings, we can classify the Southern Ocean into two bloom subregions, 0–500 m as an enhanced bloom zone (EBZ), and 500–2500 m as a moderate bloom zone (MBZ). The EBZ has a quite high-bloom probability of about 30%, while the MBZ has only 10%.

Relative contribution of persistent organic pollutants to marine phytoplankton biomass dynamics in the North Sea and the Kattegat

In this paper, we use concentrations of persistent organic pollutants (POPs) and of chlorophyll a to infer POP-induced effects on marine primary production in the Kattegat and the North Sea between the 1990s and the 2000s. To do so, we modelled phytoplankton dynamics using four classical drivers (light and nutrient availability, temperature and zooplankton grazing) and tested whether extending this model with a POP-induced phytoplankton growth limitation term improved model fit to observed chlorophyll a concentrations. Including monitored concentrations of PCBs and pesticides did not lead to a better model fit, suggesting that POP-induced growth limitation of marine phytoplankton in the North Sea and the Kattegat is small compared to the limitations caused by the classical drivers. In an attempt to more fully represent the multitude of POPs in the marine environment, the monitored concentrations were multiplied with a factor 10 and 100. Under these two configurations, region-specific contributions of POPs in the phytoplankton growth limitation were found. The inferred contribution of POPs to phytoplankton growth limitation was ca. 1% in Belgian marine waters, but in the Kattegat POPs explained ca. 10% of the phytoplankton growth limitation. These results suggest that there are regional differences in the contribution of POPs to the phytoplankton growth limitation.