Vertical Distribution Of Chlorophyll Research Articles

Vertical distribution of chlorophyll a in the western part of the Kara Sea in autumn 2020

The aim of the work was to study the distribution of chlorophyll a (Chl-a) in the deepest part of the western Kara Sea — the Novaya Zemlya Trough and in St. Anna Trough. Materials: field studies of Chl-a, macronutrients, dissolved oxygen and physical parameters were held in September 2020 during the 81st cruise of R/V «Akademik Mstislav Keldysh».The results showed that Chl-a concentration within the upper 100 m layer ranged from 0.01 to 1.37 mg/m3 (median value of 0.23 mg/m3). The maximum concentrations of Chl-a in the Novaya Zemlya Trough (0.39–1.18 mg/m3) were observed at depths of 10–35 m, in the St. Anna Trough (0.25–1.37 mg/m3) — in the upper 15-meter layer. In the vertical distribution of Chl-a the subsurface chlorophyll maximum (SCM) was noted at depths of 10–42 m. In the southern part of the St. Anna Trough, the maximum concentrations of Chl-a were observed in the surface horizon. SCM existence depended on the runoff water distribution: well-pronounced SCM was observed at stations with high surface salinity which were characterized by a deeper euphotic depth, and a low concentration of Chl-a at the surface. In regions affected by river runoff, which had low salinity and high nutrient content in the upper layer as well as shallow depth of the photic layer, the maximum concentrations of Chl-a were observed at the surface. The share of pheophytin varied from 18 to 73% (median value of 41%) with minimum values in the layer of chlorophyll maximum. Integrated Chl-a concentration ranged from 5.75 to 24.54 mg/m2 (median value of 9.51 mg/m2), the highest values were observed in regions with deeper euphotic layer and pronounced SCM.Practical value: the data on the vertical distribution of Chl-a concentration allow to expand understanding of the conditions of organic matter formation and productivity of the Kara Sea.

Vertical patterns of chlorophyll a in the euphotic layer are related to mesoscale eddies in the South China Sea

Phytoplankton closely connects with the hydrodynamics and biogeochemical environment of the ocean. While research focusing on both the physiochemical factors and hydrodynamics regulating phytoplankton has already been conducted, the coupling mechanism between mesoscale eddies and the vertical distribution of phyto plankton in the South China Sea (SCS) is still not well understood. Here, phytoplankton was studied under one weak-cold and two warm eddies along the 18°N transect in the SCS. The results show that the vertical distribution of chlorophyll (chl-a) presented a similar pattern at all four sampling stations. The mixed layer is less than 50 m. It is the same as the meridional salinity gradients that may be distinguished above a depth of 60 m. The subsurface chlorophyll maximum at the edge of a warm (WI) and cold eddy (CI) at E413 and E411 was shallower than that at the edge of a warm eddy (WII) at E407 and E409, indicating that temperature and salinity may be the important driving factors. On the whole, mesoscale eddies had a significant influence on the vertical pattern of chl-a in the SCS during the study period.

Effects of the Three Gorges Reservoir Operation on Vertical Distribution of Chlorophyll a and Environmental Factors in Tributaries

The hydrodynamics and environmental factors in the Xiangxi River (XXR) and Shennong River (SNR), which are tributaries of the Three Gorges Reservoir (TGR), were monitored from July to August (the low water level period) and in October (the impoundment period) in 2018. The vertical distribution characteristics of chlorophyll a and other indicators of the two tributaries were analyzed during the different operation periods, and the factors that affected the vertical distribution in each period were discussed. The results showed that the vertical distribution of dissolved oxygen, water temperature, pH value, and chlorophyll a of the XXR and SNR during the low water level period was relatively consistent. The indexes 0-10 m (0-5 m for chlorophyll a) from the surface of the XXR and SNR, respectively, showed significant stratification and decreased with increasing water depth; the stability index of thermal stratification (RWCS/H) was 13.71-29.07 m-1, which was stable. After the water depth reached 10 m (5 m for chlorophyll a), the indexes tended to be stable along the water depth. During the impoundment period, there was no obvious stratification for each index; the stability index of thermal stratification was 0-0.5 m-1, the stability of the water body was weak, and the vertical variation of each index was relatively stable. The comprehensive trophic state index (TLI) of the XXR and SNR were 55 and 53 during the low water level period, respectively, indicating that they were in a slightly eutrophic state, and 39 and 46 during the impoundment period, respectively, indicating a mesotrophic state. Linear regression analysis showed that chlorophyll a, dissolved oxygen, water temperature, and pH in the two tributaries were significantly correlated in the vertical direction in the low water level period, indicating that dissolved oxygen, water temperature stratification, and pH were important factors affecting the vertical distribution of chlorophyll a. During the impoundment period, a large amount of backflow from the Yangtze River, a large fluctuation in tributary water level, and the decrease in RWCS/H were the important factors that affected the small vertical change in the water body. The enhancement of vertical mixing and the decrease in Zeu/Zmix were the key factors affecting the nutritional status of the water.

Spatial and Temporal Vertical Distribution of Chlorophyll in Relation to Submarine Wastewater Effluent Discharges

The vertical distribution of chlorophyll in coastal waters is influenced by a combination of the hydrodynamic environment and different biotic and abiotic processes. The spatial and temporal occurrences of chlorophyll profiles provide a good representation of the changes in the marine environment. The majority of studies in the Adriatic Sea have so far been conducted in areas unaffected by anthropogenic pressure. Our study site is located near two marine outfalls, which are part of the public sewage system. This study aims to characterize the chlorophyll vertical distribution and describe its variability based on the stratification conditions and the presence of a wastewater effluent plume. Based on these conditions, we identified three characteristic scenarios/types of chlorophyll profiles. The first one occurs when the vertical mixing of the water column creates the upwelling of chlorophyll and nutrients to the upper part of the water column. The second and third scenarios occur during stratified conditions and differ by the extent of the effluent plume intrusion. Using modern fluorescence techniques, we identified and described three different vertical chlorophyll profiles, characterizing them according to their physical and biological parameters and processes. For cases with a visible effluent intrusion, we confirmed the importance of the pycnocline formation in keeping the effluent below and maintaining the higher water quality status at the top of the water column.

Assimilating synthetic Biogeochemical-Argo and ocean colour observations into a global ocean model to inform observing system design

Abstract. A set of observing system simulation experiments was performed. This assessed the impact on global ocean biogeochemical reanalyses of assimilating chlorophyll from remotely sensed ocean colour and in situ observations of chlorophyll, nitrate, oxygen, and pH from a proposed array of Biogeochemical-Argo (BGC-Argo) floats. Two potential BGC-Argo array distributions were tested: one for which biogeochemical sensors are placed on all current Argo floats and one for which biogeochemical sensors are placed on a quarter of current Argo floats. Assimilating BGC-Argo data greatly improved model results throughout the water column. This included surface partial pressure of carbon dioxide (pCO2), which is an important output of reanalyses. In terms of surface chlorophyll, assimilating ocean colour effectively constrained the model, with BGC-Argo providing no added benefit at the global scale. The vertical distribution of chlorophyll was improved by assimilating BGC-Argo data. Both BGC-Argo array distributions gave benefits, with greater improvements seen with more observations. From the point of view of ocean reanalysis, it is recommended to proceed with development of BGC-Argo as a priority. The proposed array of 1000 floats will lead to clear improvements in reanalyses, with a larger array likely to bring further benefits. The ocean colour satellite observing system should also be maintained, as ocean colour and BGC-Argo will provide complementary benefits.

Vertical structure in chlorophyll profiles: influence on primary production in the Arctic Ocean.

Subsurface chlorophyll maximum (SCM) layers are prevalent throughout the Arctic Ocean under stratified conditions and are observed both in the wake of retreating sea ice and in thermally stratified waters. The importance of these layers on the overall productivity of Arctic pelagic ecosystems has been a source of debate. In this study, we consider the three principal factors that govern productivity within SCMs: the shape of the chlorophyll profile, the photophysiological characteristics of phytoplankton and the availability of light in the layer. Using the information on the biological and optical parameters describing the vertical structure of chlorophyll, phytoplankton absorption and photosynthesis–irradiance response curves, a spectrally resolved model of primary production is used to identify the set of conditions under which SCMs are important contributors to water-column productivity. Sensitivity analysis revealed systematic errors in the estimation of primary production when the vertical distribution of chlorophyll was not taken into account, with estimates of water-column production using a non-uniform profile being up to 97% higher than those computed using a uniform one. The relative errors were shown to be functions of the parameters describing the shape of the biomass profile and the light available at the SCM to support photosynthesis. Given that SCM productivity is believed to be largely supported by new nutrients, it is likely that the relative contribution of SCMs to new production would be significantly higher than that to gross primary production. We discuss the biogeochemical and ecological implications of these findings and the potential role of new ocean sensors and autonomous underwater vehicles in furthering the study of SCMs in such highly heterogeneous and remote marine ecosystems.This article is part of the theme issue ‘The changing Arctic Ocean: consequences for biological communities, biogeochemical processes and ecosystem functioning'.

Effect of cloudiness on the vertical distribution of chlorophyll a and zooplankton in Barguzin Bay of Lake Baikal: a numerical experiment

The objectives of this article are to describe the effect of cloudiness on the content of chlorophyll a and zooplankton on an example of Barguzin Bay of Lake Baikal using mathematical modeling. In this study, numerical experiments with various values of cloud coverage have been implemented. Simulations demonstrate that cloudiness essentially influences the vertical distribution of chlorophyll a and zooplankton in the open lake.

URRENT STATE OF THE ECOSYSTEM OF LAKE UROZERO, KARELIA, ASSESSED THROUGH PRIMARY PRODUCTION AND DESTRUCTION INDICATORS

Lake Urozero has the status of a regional-level state hydrological nature monument in the Republic of Karelia. Up until the mid-2000’s, the lake have been noted for very high water transparency and the ultra-oligotrophic state of the ecosystem. In 2018, the prima-ry production and destruction characteristics of the Urozero ecosystem were studied as integral indicators of the current state and direction of its functioning. Such assessments are necessitated by the modified climatic conditions in Karelia, which affect catchments. These changes result in enlarged flow of allochtonous organic matter to water bodies. The values of photosynthesis (average 22 μg C/l per day), chlorophyll a(average 1.6 μg/l), daily assimilation number (on average 21 μg C/μg Chl), P/B factor (average 1.2 days-1) and water transparency (average 9.8 m) were measured in May, July and September. These measurements confirm that the lake ecosystem has retained its ultra-oligotrophic state. In spring and summer, when solar radiation is excessive and water transparency is high, the vertical distribution of chlorophyll ashowed a pattern unusual for Karelia, with maximum values found at the depth of one transparency. The change in the values of or-ganic matter destruction down the water column corresponds to the vertical dynamics of chlorophyll a. This vertical distribution of the values of destruction, as well as the con-sistently high transparency of the lake water, indicates that allochtonous organic mat-ter does not affect the water ecosystem. The natural ecological state of Lake Urozero in the current circumstances of climate change in the catchment area and human pres-sure is retained owing to the absence of surface inflows and nature conservation mea-sures to counteract pollution.

Vertical distribution of chlorophyll in dynamically distinct regions of the southern Bay of Bengal

Abstract. The Bay of Bengal (BoB) generally exhibits surface oligotrophy due to nutrient limitation induced by strong salinity stratification. Nevertheless, there are hotspots of high chlorophyll in the BoB where the monsoonal forcings are strong enough to break the stratification; one such region is the southern BoB, east of Sri Lanka. A recent field programme conducted during the summer monsoon of 2016, as a part of the Bay of Bengal Boundary Layer Experiment (BoBBLE), provides a unique high-resolution dataset of the vertical distribution of chlorophyll in the southern BoB using ocean gliders along with shipboard conductivity–temperature–depth (CTD) measurements. Observations were carried out for a duration of 12–20 days, covering the dynamically active regions of the Sri Lanka Dome (SLD) and the Southwest Monsoon Current (SMC). Mixing and upwelling induced by the monsoonal wind forcing enhanced surface chlorophyll concentrations (0.3–0.7 mg m−3). Prominent deep chlorophyll maxima (DCM; 0.3–1.2 mg m−3) existed at intermediate depths (20–50 m), signifying the contribution of subsurface productivity to the biological carbon cycling in the BoB. The shape of chlorophyll profiles varied in different dynamical regimes; upwelling was associated with sharp and intense DCM, whereas mixing resulted in a diffuse and weaker DCM. Within the SLD, open-ocean Ekman suction favoured a substantial increase in chlorophyll. Farther east, where the thermocline was deeper, enhanced surface chlorophyll was associated with intermittent mixing events. Remote forcing by the westward propagating Rossby waves influenced the upper-ocean dynamics and chlorophyll distribution in the southern BoB. Stabilizing surface freshening events and barrier-layer formation often inhibited the generation of surface chlorophyll. The pathway of the SMC intrusion was marked by a distinct band of chlorophyll, indicating the advective effect of biologically rich Arabian Sea waters. The region of the monsoon current exhibited the strongest DCM as well as the highest column-integrated chlorophyll. Observations suggest that the persistence of DCM in the southern BoB is promoted by surface oligotrophy and shallow mixed layers. Results from a coupled physical–ecosystem model substantiate the dominant role of mixed layer processes associated with the monsoon in controlling the nutrient distribution and biological productivity in the southern BoB. The present study provides new insights into the vertical distribution of chlorophyll in the BoB, emphasizing the need for extensive in situ sampling and ecosystem model-based efforts for a better understanding of the biophysical interactions and the potential climatic feedbacks.

Vertical distributions of chlorophyll and nitrogen and their associations with photosynthesis under drought and rewatering regimes in a maize field

In this study, we characterize the vertical leaf distribution of chlorophyll (Chl) and nitrogen (N) content and their associations with leaf photosynthetic responses in Zea mays L. under field watering regimes. We simulated five precipitation patterns, including a drought-rewatering sequence using an electric-powered, rainproof shelter. The results indicate the vertical leaf Chl and N distribution versus the cumulative leaf-area index (LAIc) fit well into a significant quadratic function. The simulated precipitation patterns significantly influenced the parabolic curve trajectory patterns and their parameters. Chlorophyll and N contents had the same trend, with a close and positive relationship. Drought stress followed by rewatering increased the slopes of the linear equations but narrowed the parabolic opening of the quadratic functions. This finding implies that the relationship between Chl and N content can be used to estimate responses to drought and rewatering. The findings also suggested that the relationship patterns between Chl and N levels could be an assessment tool for N-fertilizer managements under different drought conditions to maintain high yields in maize production. Principal component analysis indicated the correlations between functional traits in maize leaves and the responses to drought and rehydration. These findings help to improve drought management and cultivar selection, which will be important in coping with the severe intensity and high frequency of episodic drought events expected from climate change.

Variability in the vertical distribution of chlorophyll in a spill-managed temperate reservoir

Perkins KR, Rollwagen-Bollens G, Bollens SM, Harrison JA. 2019. Variability in the vertical distribution of chlorophyll in a spill-managed temperate reservoir. Lake Reserve Manage. 35:119–126.Phytoplankton form the base of pelagic food webs, and as aquatic systems come under increasing pressure from environmental stressors, managers are becoming more concerned about how these pressures may result in changes to phytoplankton distribution and abundance. The vertical distribution of phytoplankton, including the phenomenon of subsurface chlorophyll a (Chl-a) maxima (SCM), is known to vary widely, with a combination of biotic and abiotic processes hypothesized to be driving this variation. We examined how the vertical distribution of Chl-a generally, and SCM specifically, varied over 4 years (2013–2016) in a managed temperate reservoir (Lacamas Lake, Washington, USA) that experiences rapid (2–3 weeks) release of water from within the epilimnion each autumn. Seasonally, a strong thermocline developed each spring at depths of 5–10 m, and persisted throughout summer and early autumn. Although temperature varied somewhat between years, elevated concentrations of Chl-a occurred in spring and summer of each year. In addition, pronounced SCM of 30–60 µg/L at depths of 2–8 m were observed each year, and were nearly always above the thermocline. There was no “seasonal deepening” of SCM in Lacamas Lake, as has been observed in several other lakes and oceans, and annual drawdown events in early fall had little to no effect on SCM in Lacamas Lake. We recommend that more process-oriented studies be undertaken to fully understand which biotic and abiotic processes are driving the formation and maintenance of SCM in lakes and reservoirs, and how SCM are modulated by different reservoir drawdown practices.

Diel variability of vertical distributions of chlorophyll a at the SEATS and ALOHA stations: implications on remote sensing interpretations

ABSTRACTThe effects of the diel (involving a 24 hour period) variations in the surface concentrations of chlorophyll a (C) on the use of once-daily remotely sensed C as the diel average were assessed from the diel records in the derived depth-weighted C (Cd) that should be detected by remote sensing and the in situ surface C at two time-series stations in the North Pacific: the SEATS (SouthEast Asian Time-series Study) station in the northern South China Sea and the ALOHA (A Long-Term Oligotrophic Habitat Assessment) station in the North Pacific subtropical gyre. In situ surface C varied by a factor of about 2.0 and 1.3 over a diel cycle, and by ±20% and ±9% over the diel average at the SEATS and ALOHA stations, respectively. As the overpass-times of the different satellites were not identical, Cd was satellite-dependent. While the Cd corresponding to MODerate resolution Imaging Spectroradiometer on Aqua (MODIS-Aqua) and Sea-viewing Wide Field-of-view Sensor (SeaWiFS) overpass-times agreed to ±10%, the Cd corresponding to MEdium Resolution Imaging Spectrometer (MERIS) overpass-time could differ from the other two by −22% to +28% at the SEATS station and −1% to +12% at the ALOHA station. In addition, Cd corresponding to the overpass-times of the three satellites deviated from the observed diel average in situ surface C by −19% to +32% at the SEATS station and by −6% to +13% at the ALOHA station. These results indicate that, as a result of diel variations, neither a one-time remotely-sensed nor a one-time observed in situ surface C can represent the diel average in situ surface C accurately. Furthermore, diel variations are an inherent source of uncertainty when data from multiple satellites are pooled for use. The magnitudes of these discrepancies can be comparable to the commonly claimed uncertainties in remotely sensed C and thus should be taken into consideration in its interpretation and use.

Response of phytoplankton to heavy cloud cover and turbidity in the northern Bay of Bengal

An interesting physiological response of phytoplankton to large fluctuations in underwater photosynthetically active radiation (PAR) levels in the northern Bay of Bengal has been presented here. This study is primarily based on a 12-day time series observation in the northern Bay of Bengal during the peak Southwest Monsoon (July 2012), when the study region was recurrently exposed to alternating cloudy and sunny sky conditions. On overcast days, the PAR available underwater at the time series location (TSL) drastically decreased, with the noontime PAR at the surface water (2 m) usually being ~600 µmol m−2 s−1 on sunny days and declining to ~50 µmol m−2 s−1 on heavily overcast days. Closely linked with the sunny and cloudy days at TSL, chlorophyll a concentration in the water column showed noticeable features; it increased in the upper water column (surface-40 m) and decreased in the lower water column (41–80 m) on cloudy days, while the reverse was the case on sunny days. Based on in-situ and laboratory experimental data, it was observed that these temporal changes in the vertical distribution of chlorophyll a in the northern Bay of Bengal were due to the short-term physiological acclimation of phytoplankton to large changes in underwater PAR.

Vertical Distribution of Chlorophyll in the Upper Volga Reservoirs

The vertical distribution of phytoplankton (chlorophyll a, CHL) was investigated in August 2015 at 25 sampling stations in the Ivankovo, Uglich, and Rybinsk reservoirs (Upper Volga, Russia) using a bbe Moldaenke Fluoroprob submersible fluorimeter. Three types of CHL vertical distribution were identified under homothermy. There was a gradual CHL decline in the water column at the upper part of reservoirs; a sharp decline at a certain depth in most riverine sections; and uniform distribution opposite the mouth of a small river (the Kashinka River, Uglich Reservoir), as well as at the open lacustrine sites of the Rybinsk Reservoir under wind-driven mixing. The average CHL content in the euphotic layer at the stations of three groups were 25.0 ± 6.3, 44.1 ± 4.0, and 20.8 ± 2.9 μg/L, respectively; the CHL contributions to the PAR absorption were 47 ± 9%, 66 ± 4%, and 38 ± 6%. Under thermal stratification the vertical distribution of CHL corresponds to the course of the temperature dynamics (r = 0.85).

Preliminary results of bio-optical investigations at Lake Baikal

The preliminary results of complex bio-optical investigations carried out at Lake Baikal in July 2018 showed high variability in the light absorption properties of all optically active components, as well as their relation with hydrophysical characteristics. Vertical distribution of chlorophyll a was characterized by the presence of a maximum near the bottom of the euphotic zone. In this deep chlorophyll maximum layer, there were specifc features of phytoplankton light absorption spectra reflecting the abundance of phycobilin-containing blue-green algae in the phytoplankton community.

Patterns and drivers of deep chlorophyll maxima structure in 100 lakes: The relative importance of light and thermal stratification

AbstractThe vertical distribution of chlorophyll in stratified lakes and reservoirs frequently exhibits a maximum peak deep in the water column, referred to as the deep chlorophyll maximum (DCM). DCMs are ecologically important hot spots of primary production and nutrient cycling, and their location can determine vertical habitat gradients for primary consumers. Consequently, the drivers of DCM structure regulate many characteristics of aquatic food webs and biogeochemistry. Previous studies have identified light and thermal stratification as important drivers of summer DCM depth, but their relative importance across a broad range of lakes is not well resolved. We analyzed profiles of chlorophyll fluorescence, temperature, and light during summer stratification from 100 lakes in the Global Lake Ecological Observatory Network (GLEON) and quantified two characteristics of DCM structure: depth and thickness. While DCMs do form in oligotrophic lakes, we found that they can also form in eutrophic to dystrophic lakes. Using a random forest algorithm, we assessed the relative importance of variables associated with light attenuation vs. thermal stratification for predicting DCM structure in lakes that spanned broad gradients of morphometry and transparency. Our analyses revealed that light attenuation was a more important predictor of DCM depth than thermal stratification and that DCMs deepen with increasing lake clarity. DCM thickness was best predicted by lake size with larger lakes having thicker DCMs. Additionally, our analysis demonstrates that the relative importance of light and thermal stratification on DCM structure is not uniform across a diversity of lake types.

Seasonal Variation in the Vertical Distribution of Chlorophyll in East-Hiuchi-Nada, Seto Inland Sea

Seasonal Variation in the Vertical Distribution of Chlorophyll in East-Hiuchi-Nada, Seto Inland Sea

Vertical distribution of suspended particulate matter in the Caspian Sea in early summer

The features of the vertical distribution of chlorophyll a, particulate organic carbon and its isotopic composition, total suspended particulate matter (SPM), and the structure of the phytoplankton community in the Middle and South Caspian Sea in May–June 2012 are discussed. The subsurface chlorophyll a maximum (SCM) was found everywhere at depths of ~20 to 40–60 m. The position of this layer is confined to the depth of the seasonal thermocline, which is determined by the development of a cold-water (dark) phytocenosis. The genesis of this layer was studied. The increase in chlorophyll a concentration in this layer is caused by an abundance of phytoplankton or an increased concentration of this phytopigments per algal cell. The highest values of the studied organic compounds and phytoplankton biomass are revealed as close to the seasonal thermocline extending from the southern periphery of the Derbent Depression to the Apsheron Sill, which is determined by the bottom topography. The presence of chlorophyll a at depths exceeding 300 m (up to ≥1 mg/m3) was revealed. This was supported by findings of individual algal cells containing chlorophyll a and even their accumulations in the deep water layer. The most probable mechanisms responsible for the presence of these cells at the deep water level are discussed in the paper. The vertical distribution of the values of the organic carbon isotopic composition is primarily controlled by the vertical structure of phytoplankton and chlorophyll a in the water column up to ~500 m and by biogeochemical processes at the redox barrier (~600 m layer). The relative stability of chlorophyll a and the stability of pheophytin a in anaerobic environments were verified. A significant amount of weakly transformed chlorophyll a was found close the sea bottom.

Stratification and residence time as factors controlling the seasonal variation and the vertical distribution of chlorophyll‐a in a subtropical irrigation reservoir

Reservoir trophic state is controlled by light and nutrient availability, as well as by hydraulic management and stratification pattern. In arid zone reservoirs, the inflow and outflow discharges have extreme seasonal variations which produce well‐defined cycles of filling and draining. Moreover, since stratification often occurs, epilimnion and hypolimnion renewal rates may vary producing different environmental conditions throughout the water column. These variation patterns may affect phytoplankton growth at both temporal and spatial scales. For two hydrological years, we analyzed the influence of light climate, nutrients, residence time (Tw), and stratification on phytoplankton biomass (as chlorophyll‐a [Chl‐a]) in an irrigation reservoir (276 hm3) in the arid central Andes in Argentina (33°S). The reservoir was turbid (ZSecchi: 1.4 m) with relatively high levels of dissolved nitrogen and phosphorus (60 μgP L−1 and 560 μgN L−1, respectively). Stratification occurred from mid‐spring to late‐summer, when hypolimnetic oxygen and pH decreased whereas dissolved nutrients increased. The reservoir was mesotrophic (Chl‐a: 4.6–10.8 μg L−1) and showed two semi‐annual peaks of Chl‐a (summer and winter). Depending on the water column circulation, Chl‐a was directly related to Tw for 60 > Tw > 200 and inversely to ammonia, during mixing and stratification periods, respectively. Phytoplankton development was strongly influenced by the seasonal variations of inflow/outflow and stratification. Chl‐a peaked in summer, when inflow plunged into the hypolimnion of the stratified reservoir and in the warm and mixed epilimnion algae proliferated until nutrients depletion. Alternatively, the winter Chl‐a maximum is likely to be produced by the higher concentration of nutrients combined with the turbulent mixing in the water column which acts as a mechanism that helps to overcome light‐limitation. Since stratification modifies the vertical distribution of Tw, the use of a single annual value of this hydraulic parameter to assess its effect on the reservoir trophic state results inadequate. This paper constitutes the first description of hydrologic effects on Chl‐a dynamics in a reservoir in arid central western Argentina.

Vertical distribution of chlorophyll <I>a</I> concentration and phytoplankton community composition from in situ fluorescence profiles: a first database for the global ocean

Abstract. In vivo chlorophyll a fluorescence is a proxy of chlorophyll a concentration, and is one of the most frequently measured biogeochemical properties in the ocean. Thousands of profiles are available from historical databases and the integration of fluorescence sensors to autonomous platforms has led to a significant increase of chlorophyll fluorescence profile acquisition. To our knowledge, this important source of environmental data has not yet been included in global analyses. A total of 268 127 chlorophyll fluorescence profiles from several databases as well as published and unpublished individual sources were compiled. Following a robust quality control procedure detailed in the present paper, about 49 000 chlorophyll fluorescence profiles were converted into phytoplankton biomass (i.e., chlorophyll a concentration) and size-based community composition (i.e., microphytoplankton, nanophytoplankton and picophytoplankton), using a method specifically developed to harmonize fluorescence profiles from diverse sources. The data span over 5 decades from 1958 to 2015, including observations from all major oceanic basins and all seasons, and depths ranging from the surface to a median maximum sampling depth of around 700 m. Global maps of chlorophyll a concentration and phytoplankton community composition are presented here for the first time. Monthly climatologies were computed for three of Longhurst's ecological provinces in order to exemplify the potential use of the data product. Original data sets (raw fluorescence profiles) as well as calibrated profiles of phytoplankton biomass and community composition are available on open access at PANGAEA, Data Publisher for Earth and Environmental Science. Raw fluorescence profiles: http://doi.pangaea.de/10.1594/PANGAEA.844212 and Phytoplankton biomass and community composition: http://doi.pangaea.de/10.1594/PANGAEA.844485