Depth-integrated Primary Production Research Articles

Effects of river inputs on nutrient and organic-carbon conditions and net ecosystem metabolism in the Kaoping (Taiwan) coastal sea

This study aims to understand the variability of net ecosystem metabolism in a tropical sea. The contrasting pattern of metabolic state between wet and dry seasons was caused by the pronounced difference of river exports in the Kaoping coastal sea. The depth-integrated gross primary production (IGPP) through the euphotic zone ranged from 2451 to 16 230 mg C m–2 day–1 in summer, and from 844 to 5549 mg C m–2 day–1 in winter, and was apparently regulated by oceanic temperature, nutrients and organic carbon. The depth-integrated dark community respiration (IDCR), attributed largely to bacterial respiration (BR, ~69%), ranged from 861 to 12 418 mg C m–2 day–1 in summer, and from 997 to 5781 mg C m–2 day–1 in winter. GPP and DCR correlated inversely with salinity but positively with nutrients, Chlorophyll a, dissolved organic carbon (DOC) and particulate organic carbon (POC). The autotrophic state (IGPP : IDCR > 1) prevailed in most stations in summer, whereas the heterotrophic state (IGPP : IDCR < 1) occurred in all but Station B1 in winter. Bacterial production (BP) and bacterial respiration (BR) also correlated inversely with salinity but positively with nutrients and DOC. Bacterial carbon demand (BCD) was 0.15 GPP in summer and 0.64 GPP in winter, supporting the autotrophic and heterotrophic conditions in summer and winter, respectively. The metabolic state is apparently determined by seasonal variation of temperature and river exports.

How phytoplankton physiology and community structure adjust to physical forcing in a coastal ecosystem (northern Adriatic Sea)

:We investigated how variability in physicochemical properties influenced photosynthetic parameters and the phytoplankton community in the shallow coastal waters of the Adriatic Sea (Gulf of Trieste), where local rivers greatly influenced the dynamics of the system. During the study period (May 2009–July 2010), high sea-surface temperatures in summer, freshwater inputs and precipitation influenced the stability of the water column and the distribution of major nutrients. Redundancy analysis showed a significant effect of total inorganic nitrogen, silicate and salinity on the distribution of the surface phytoplankton community. The modest chlorophyll a (Chl a) concentration exhibited higher variability [coefficient of variation(C.V.) = 60–69%] compared with the photosynthetic parameters. Among them, photosynthetic capacity (PBmax) showed smallest variation (C.V. =37–45%) and no significant vertical or temporal variability was observed. PBmax significantly correlated with temperature, although indirect control by other environmental factors should not be overlooked. During the stratified period, significant vertical differences were observed in photosynthetic efficiency [αB: 0.009 and 0.014 mg C (mg Chl a)−1 h−1 (μmol photon m−2 s−1)−1 at the surface and 15 m, respectively] and in the light saturation index (Ek: 270 and 172 μmol photon m−2 s−1 at the surface and 15 m, respectively), revealing photoacclimation in the communities. Both parameters also tended to be different in the more homogenous water column during winter. Using a ratio between available light and Ek, this study demonstrated light-limited photosynthesis for the greater proportion of the water column, drawing attention to the vertical variability in αB that could, if disregarded, have a significant effect on the assessment of depth-integrated primary production.

Connections between physical, optical and biogeochemical processes in the Pacific Ocean

A new biogeochemical model has been developed and coupled to a three-dimensional physical model in the Pacific Ocean. With the explicitly represented dissolved organic pools, this new model is able to link key biogeochemical processes with optical processes. Model validation against satellite and in situ data indicates the model is robust in reproducing general biogeochemical and optical features. Colored dissolved organic matter (CDOM) has been suggested to play an important role in regulating underwater light field. With the coupled model, physical and biological regulations of CDOM in the euphotic zone are analyzed. Model results indicate seasonal variability of CDOM is mostly determined by biological processes, while the importance of physical regulation manifests in the annual mean terms. Without CDOM attenuating light, modeled depth-integrated primary production is about 10% higher than the control run when averaged over the entire basin, while this discrepancy is highly variable in space with magnitudes reaching higher than 100% in some locations. With CDOM dynamics integrated in physical-biological interactions, a new mechanism by which physical processes affect biological processes is suggested, namely, physical transport of CDOM changes water optical properties, which can further modify underwater light field and subsequently affect the distribution of phytoplankton chlorophyll. This mechanism tends to occur in the entire Pacific basin but with strong spatial variability, implying the importance of including optical processes in the coupled physical-biogeochemical model.

Parameterization of vertical chlorophyll <i>a</i> in the Arctic Ocean: impact of the subsurface chlorophyll maximum on regional, seasonal, and annual primary production estimates

Abstract. Predicting water-column phytoplankton biomass from near-surface measurements is a common approach in biological oceanography, particularly since the advent of satellite remote sensing of ocean color (OC). In the Arctic Ocean, deep subsurface chlorophyll maxima (SCMs) that significantly contribute to primary production (PP) are often observed. These are neither detected by ocean color sensors nor accounted for in the primary production models applied to the Arctic Ocean. Here, we assemble a large database of pan-Arctic observations (i.e., 5206 stations) and develop an empirical model to estimate vertical chlorophyll a (Chl a) according to (1) the shelf–offshore gradient delimited by the 50 m isobath, (2) seasonal variability along pre-bloom, post-bloom, and winter periods, and (3) regional differences across ten sub-Arctic and Arctic seas. Our detailed analysis of the dataset shows that, for the pre-bloom and winter periods, as well as for high surface Chl a concentration (Chl asurf; 0.7–30 mg m−3) throughout the open water period, the Chl a maximum is mainly located at or near the surface. Deep SCMs occur chiefly during the post-bloom period when Chl asurf is low (0–0.5 mg m−3). By applying our empirical model to annual Chl asurf time series, instead of the conventional method assuming vertically homogenous Chl a, we produce novel pan-Arctic PP estimates and associated uncertainties. Our results show that vertical variations in Chl a have a limited impact on annual depth-integrated PP. Small overestimates found when SCMs are shallow (i.e., pre-bloom, post-bloom > 0.7 mg m−3, and the winter period) somehow compensate for the underestimates found when SCMs are deep (i.e., post-bloom < 0.5 mg m−3). SCMs are, however, important seasonal features with a substantial impact on depth-integrated PP estimates, especially when surface nitrate is exhausted in the Arctic Ocean and where highly stratified and oligotrophic conditions prevail.

Reevaluating the Generality of an Empirical Model for Light-Limited Primary Production in the San Francisco Estuary

Depth-integrated primary production (ΣP, in grams of carbon per square meter per day) was measured using 14C in the northern San Francisco Estuary (SFE) from March through August of 2006 and 2007. Determinations of ΣP were then used to calibrate a published light-utilization model that relates ΣP to a composite parameter of chlorophyll, solar irradiance, and photic zone depth. The resultant calibration coefficient, Ψ, varied by a factor of nearly two between 2006 and 2007 and was lower than determined in previous calibrations for the estuary. The now chronically low chlorophyll concentrations in the SFE have resulted in lower predictive power of the light-utilization model. The variation in Ψ was likely the result of interannual variation in phytoplankton assimilation number. These results suggest that using a single Ψ may yield large errors in estimated estuarine production when applied overbroad spatial and temporal scales. Given the food-limited condition of the SFE, it appears that direct measurements of primary production are necessary for accurately characterizing the base of the estuarine food web.

Variations in phytoplankton dynamics and primary production associated with ENSO cycle in the western and central equatorial Pacific during 1994–2003

[1] We examined spatial and temporal variations in phytoplankton distribution and primary production on the equator between 143°E and 160°W during 1994–2003. The study area extended from the nitrate-depleted western Pacific warm pool (WPWP) to the nitrate-replete upwelling region in the central equatorial Pacific. Whereas depth-integrated chlorophyll a concentrations did not differ greatly between the WPWP (30.5 ± 5.7 mg m−2) and upwelling region (34.4 ± 5.4 mg m−2), depth-integrated primary production in the upwelling region was approximately double (990 ± 61 mg C m−2 d−1) that in the WPWP region (435 ± 158 mg C m−2 d−1), owing to the presence of deep chlorophyll maximum in the former and higher nutrient availability in the latter. Marked differences in water column structure were observed in the WPWP region between El Nino and La Nina: eastward advection of the WPWP region with development of El Nino led to thermocline shoaling in the WPWP region, resulting in a significant nitracline uplift (P < 0.01). In this region, the isopleth of 1-μM nitrate in the nitracline was brought up from an average of 103 m during La Nina to 61 m during El Nino. When the uplift reached the lower part of the euphotic zone, primary production was enhanced. The enhancement occurred at 4% to 10% light depths relative to that at the surface. However, the magnitude of the enhancement was not large, and there was no substantial difference in depth-integrated primary production between El Nino and La Nina.

Phytoplankton biomass and primary production responses to physico-chemical forcing across the northeastern New Zealand continental shelf

Phytoplankton biomass and primary production were monitored in the Hauraki Gulf and on the northeastern continental shelf, New Zealand – using ship surveys, moored instruments and satellite observations (1998–2001) – capturing variability across a range of space and time scales. A depth-integrated primary production model (DIM) was used to predict integrated productivity from surface parameters, enabling regional-specific estimates from satellite data. The shelf site was dominated by pico-phytoplankton, with low chlorophyll- a (<1 mg m −3) and annual production (136 g C m −2 yr −1). In contrast, the gulf contained a micro/nano-phytoplankton-dominated community, with relatively high chlorophyll- a (>1 mg m −3) and annual production (178 g C m −2 yr −1). Biomass and productivity responded to physico-chemical factors; a combination of light, critical mixing depths and/or nutrient limitation—particularly new nitrate-N. Relatively low biomass and production was observed during 1999. This coincided with inter-annual variability in the timing and extent of upwelling- and downwelling-favourable along-shelf wind-stress, influencing the fluxes of new nitrate-N to the shelf and gulf. Relationships with the Southern Oscillation Index are also discussed. Our multi-scaled sampling highlighted details associated with stratification and de-stratification events, and deep sub-surface chlorophyll- a not visible to satellite sensors. This study demonstrates the importance of multi-scaled sampling in gaining estimates of regional production and its responses to physico-chemical forcing.

Temporal variability in physicochemical properties, phytoplankton standing crop and primary production for 7 years (2002–2008) in the neritic area of Sagami Bay, Japan

Seasonal and interannual variations in physicochemical properties (i.e., temperature, salinity, dissolved oxygen and dissolved inorganic nutrients), chlorophyll a (Chl-a), particulate carbon and nitrogen (PC and PN, respectively), and primary production were investigated in the neritic area of Sagami Bay, Kanagawa, Japan, from January 2002 to December 2008. These abiotic/biotic variables, except for NH4 +–N, repeated similar seasonal variations for all 7 years. On the basis of the analysis of data obtained on 167 sampling dates, depth-integrated primary production in this water can be easily estimated from Chl-a at the surface using the regression equations obtained in the present study. Intermittently high values of dissolved inorganic nutrients, Chl-a, PC, PN and primary productivity at the surface during the summer stratified period were induced by high freshwater discharge from the rivers after rainfalls and by the expansion of nutrient-rich Tokyo Bay Water. Temperature, salinity and dissolved inorganic nutrients showed drastic variations within a scale of a few days and/or weeks, and these variations were related to sea levels that represent the intrusion of the Kuroshio Water, Intermediate Oyashio Water or deep water from the continental slope. However, there was no consistent trend in the variations in Chl-a, PC, PN and primary production due to the complex effects of these waters.

Photosynthetic features and primary productivity of phytoplankton in the Oyashio and Kuroshio-Oyashio transition regions of the northwest Pacific

Diel and seasonal changes in the photosynthetic physiology of phytoplankton and primary productivity were investigated during 2005, together with community composition in the Oyashio (OY) and Kuroshio – Oyashio transition (TR) regions of the northwest Pacific. In both regions, diel changes in the maximum photosynthetic rate (P* max) and the light saturation index (Ek) in the photosynthesis – irradiance (P –E) curve were observed, due to diel differences in photo-physiology. In the OY region, the highest values of chlorophyll a concentration, depth-integrated primary production and the maximum quantum yield of carbon fixation in photosynthesis (Fc max) were observed in May when diatom blooms occurred. Furthermore, a higher water-column light utilization efficiency (C) of photosynthesis for phytoplankton was found in the OY region in both May and September. In contrast, in the TR and warm-core ring regions, Fc max was nearly constant, while depth-integrated primary production in May was significantly lower than in the OY region. These results show that the spring phytoplankton assemblages in OY waters had a higher light utilization ability during photosynthesis. Such a high photosynthetic property would contribute to the highest seasonal biological drawdown of surface pCO2 among the world’s oceans (Takahashi, T., Sutherland, S. C., Sweeney, C. et al. (2002) Global sea – air CO2 flux based on climatological surface ocean pCO2, and seasonal biological and temperature effects. Deep-Sea Res. II, 49, 1601– 1622).

Seasonal and interannual variability of primary and export production in the South China Sea: a three-dimensional physical–biogeochemical model study

Abstract Liu, G., and Chai, F. 2009. Seasonal and interannual variability of primary and export production in the South China Sea: a three-dimensional physical–biogeochemical model study. – ICES Journal of Marine Science, 66: 420–431. To investigate the seasonal and interannual variations in biological productivity in the South China Sea (SCS), a Pacific basin-wide physical–biogeochemical model has been developed and used to estimate the biological productivity and export flux in the SCS. The Pacific circulation model, based on the Regional Ocean Model Systems (ROMS), is forced with daily air–sea fluxes derived from the NCEP (National Centers for Environmental Prediction) reanalysis between 1990 and 2004. The biogeochemical processes are simulated with a carbon, Si(OH)4, and nitrogen ecosystem (CoSiNE) model consisting of silicate, nitrate, ammonium, two phytoplankton groups (small phytoplankton and large phytoplankton), two zooplankton grazers (small micrograzers and large mesozooplankton), and two detritus pools. The ROMS–CoSiNE model favourably reproduces many of the observed features, such as Chl a, nutrients, and primary production (PP) in the SCS. The modelled depth-integrated PP over the euphotic zone (0–125 m) varies seasonally, with the highest value of 386 mg C m−2 d−1 during winter and the lowest value of 156 mg C m−2 d−1 during early summer. The annual mean value is 196 mg C m−2 d−1. The model-integrated annual mean new production (uptake of nitrate), in carbon units, is 64.4 mg C m−2 d−1, which yields an f-ratio of 0.33 for the entire SCS. The modelled export ratio (e-ratio: the ratio of export to PP) is 0.24 for the basin-wide SCS. The year-to-year variation of biological productivity in the SCS is weaker than the seasonal variation. The large phytoplankton group tends to dominate over the smaller phytoplankton group, and likely plays an important role in determining the interannual variability of primary and new production.

Physical properties and processes in the Perth Canyon, Western Australia: Links to water column production and seasonal pygmy blue whale abundance

The oceanography of the Perth Canyon, off southwestern Australia, was examined through two major field excursions in austral spring/summer 2003/2004 combined with previous results from field analysis and numerical simulations. Water properties were used to identify water masses and vertical displacement. The field cruises and numerical simulation indicated unique circulation features of the Leeuwin Current and Undercurrent within the canyon associated with the topographic features. The input of nutrients to the euphotic zone occurred sporadically as the Leeuwin Current generally suppressed upwelling, although the Perth Canyon had increased nutrient concentrations within its rims. The distribution of chlorophyll in the surface layers indicated high spatial variability, with a prevalent deep chlorophyll (and phytoplankton biomass) maximum at ~ 80 m. Depth-integrated primary production within the study region ranged from 360 to 760 mg C m − 2 d − 1 , which was on average 2.5 times higher than rates measured in continental shelf and offshore waters north of the canyon. Aggregations of krill and other acoustic backscatter targets were concentrated near the head of the canyon at a range of depths, which may have been promoted by the circulation. The findings here are consistent with seasonal variations in wind and insolation, along with variations in the Leeuwin Current, influencing the seasonal changes and mesoscale features within the region, while the canyon promotes localised upwelling, and enhances both pelagic production and physical aggregation of plankton to attract the whales. Canyon processes must be combined with outside factors to allow upwelled nutrients to reach the photic zone. It is concluded that a combination of factors, rather than one factor alone, contributes favourably to the appearance of feeding blue whales in the Perth Canyon during the summer.

Bacterial production and microbial food web structure in a large arctic river and the coastal Arctic Ocean

Globally significant quantities of organic carbon are stored in northern permafrost soils, but little is known about how this carbon is processed by microbial communities once it enters rivers and is transported to the coastal Arctic Ocean. As part of the Arctic River-Delta Experiment (ARDEX), we measured environmental and microbiological variables along a 300 km transect in the Mackenzie River and coastal Beaufort Sea, in July–August 2004. Surface bacterial concentrations averaged 6.7 × 10 5 cells mL − 1 with no significant differences between sampling zones. Picocyanobacteria were abundant in the river, and mostly observed as cell colonies. Their concentrations in the surface waters decreased across the salinity gradient, dropping from 51,000 (river) to 30 (sea) cells mL − 1 . There were accompanying shifts in protist community structure, from diatoms, cryptophytes, heterotrophic protists and chrysophytes in the river, to dinoflagellates, prymnesiophytes, chrysophytes, prasinophytes, diatoms and heterotrophic protists in the Beaufort Sea. Size-fractionated bacterial production, as measured by 3H–leucine uptake, varied from 76 to 416 ng C L − 1 h − 1 . The contribution of particle-attached bacteria (> 3 µm fraction) to total bacterial production decreased from > 90% at the Mackenzie River stations to < 20% at an offshore marine site, and the relative importance of this particle-based fraction was inversely correlated with salinity and positively correlated with particulate organic carbon concentrations. Glucose enrichment experiments indicated that bacterial metabolism was carbon limited in the Mackenzie River but not in the coastal ocean. Prior exposure of water samples to full sunlight increased the biolability of dissolved organic carbon (DOC) in the Mackenzie River but decreased it in the Beaufort Sea. Estimated depth-integrated bacterial respiration rates in the Mackenzie River were higher than depth-integrated primary production rates, while at the marine stations bacterial respiration rates were near or below the integrated primary production rates. Consistent with these results, P CO2 measurements showed surface water supersaturation in the river (mean of 146% of air equilibrium values) and subsaturation or near-saturation in the coastal sea. These results show a well-developed microbial food web in the Mackenzie River system that will likely convert tundra carbon to atmospheric CO 2 at increasing rates as the arctic climate continues to warm.

Phytoplankton community structure and primary production in small intertidal estuarine-bay ecosystem (eastern English Channel, France)

From May 2002 to October 2003, a fortnightly sampling programme was conducted in a restricted macrotidal ecosystem in the English Channel, the Baie des Veys (France). Three sets of data were obtained: (1) physico-chemical parameters, (2) phytoplankton community structure illustrated by species composition, biovolume and diversity, and (3) primary production and photosynthetic parameters via P versus E curves. The aim of this study was to investigate the temporal variations of primary production and photosynthetic parameters in this bay and to highlight the potential links with phytoplankton community structure. The highest level of daily depth-integrated primary production Pz (0.02–1.43 g C m−2 d−1) and the highest maximum photosynthetic rate PB max (0.39–8.48 mg C mg chl a−1 h−1) and maximum light utilization coefficient αB [0.002–0.119 mg C mg chl a−1 h−1 (μmol photons m−2 s−1)] were measured from July to September. Species succession was determined based on biomass data obtained from cell density and biovolume measurements. The bay was dominated by 11 diatoms throughout the year. However, a Phaeocystis globosa bloom (up to 25 mg chl a m−3, 2.5 × 106 cells l−1) was observed each year during the spring diatom bloom, but timing and intensity varied interannually. Annual variation of primary production was due to nutrient limitation, light climate and water temperature. The seasonal pattern of microalgal succession, with regular changes in composition, biovolume and diversity, influenced the physico-chemical and biological characteristics of the environment (especially nutrient stocks in the bay) and thus primary production. Consequently, investigation of phytoplankton community structure is important for developing the understanding of ecosystem functioning, as it plays a major role in the dynamics of primary production.

Quantifying uncertainties associated with the measurement of primary production

Depth-integrated primary production was estimated in the Celtic Sea (European Shelf) by 2 independent methods. Daily production rates were derived from photosynthetic parameters determined by photosynthesis/irradiance (P/E) experiments on samples incubated with 14 C-bicarbonate ( 14 C method) and from in situ profiles with the fast repetitive rate fluorometer (FRRF) method. Production was estimated to be between 332 and 910 mg C m -2 d -1 by the 14 C method and from 351 to 1278 mg C m -2 d -1 by the FRRF method. The uncertainty, or error, of these estimates was determined by calculating 95% confidence intervals using Taylor series and Monte Carlo modelling approaches. Both approaches revealed significant uncertainty in estimates. The Taylor series analysis of the 14 C method indicated that 95% confidence interval widths were between 4 and 20% of the estimated production. The smallest error in this study, calculated using a Taylor series analysis, gave a 95% confidence interval of (578, 622) mg C m -2 d -1 for an estimated production rate of 600 mg C m -2 d -1 . The largest error was calculated using a Monte Carlo analysis and found that a production rate of 377 mg C m -2 d -1 had 95% confidence limits of (300, 453) mg C m -2 d -1 . Larger uncertainties were associated with the FRRF method, but reflect only the increased complexity of equations used to derive photosynthetic parameters and not a known greater degree of error in the approach. The precision of primary production measurements is a neglected but important factor that should be considered in primary production experiments and in testing satellite remote sensing algorithms.

Seasonal dynamics of primary and new production in the northern South China Sea: The significance of river discharge and nutrient advection

Biochemical and productivity measurements and nutrient enrichment experiments were conducted on three cruises in summer and two cruises in winter on the shelf and the basin of the northern South China Sea (SCS) between 2001 and 2004. Phytoplankton production, in terms of depth-integrated new production (INP) or depth-integrated primary production (IPP), was higher in winter than in summer and on the shelf than in the basin. In winter, with deepening of the mixed layer, nitrate from the shallow nitracline that characterized the SCS waters was made available in the surface and supported the highest production of the year. Averaged INP measured in winter (0.25 g C m −2 d −1) was about twice the summer average (0.12 g C m −2 d −1) and was 0.19 g C m −2 d −1 on the shelf compared with 0.15 g C m −2 d −1 in the basin. In winter, average INP on the shelf was higher than the basin (0.34 versus 0.21 g C m −2 d −1); whereas in summer, averaged INP on the shelf (0.13 g C m −2 d −1) and the basin (0.11 g C m −2 d −1) were similar. While averaged IPP measured in the basin was higher in winter than in summer (0.53 versus 0.35 g C m −2 d −1), IPP on the shelf showed little temporal variation (0.82 in winter versus 0.84 g C m −2 d −1 in summer). Considerable spatial and inter-annual variation in production was measured in the shelf waters during summer, which could be linked to discharge volume and plume flow direction of the Zhujiang River. While the shelf waters in summer were mostly nitrogen starved or nitrogen and phosphorus co-limited, excessive river runoff may cause the nutritive state to shift to phosphorus deficiency. Waters with low surface salinities and high fluorescence from riverine mixing could be found extending from the Zhujiang mouth to as far as offshore southern Taiwan after a typhoon passed the northern SCS and brought heavy rainfall. Overall, both nutrient advection in winter and river discharge from the China coast in summer made new nitrogen available and shaped the dynamics of phytoplankton production in these oligotrophic waters.

A comparison of global estimates of marine primary production from ocean color

The third primary production algorithm round robin (PPARR3) compares output from 24 models that estimate depth-integrated primary production from satellite measurements of ocean color, as well as seven general circulation models (GCMs) coupled with ecosystem or biogeochemical models. Here we compare the global primary production fields corresponding to eight months of 1998 and 1999 as estimated from common input fields of photosynthetically-available radiation (PAR), sea-surface temperature (SST), mixed-layer depth, and chlorophyll concentration. We also quantify the sensitivity of the ocean-color-based models to perturbations in their input variables. The pair-wise correlation between ocean-color models was used to cluster them into groups or related output, which reflect the regions and environmental conditions under which they respond differently. The groups do not follow model complexity with regards to wavelength or depth dependence, though they are related to the manner in which temperature is used to parameterize photosynthesis. Global average PP varies by a factor of two between models. The models diverged the most for the Southern Ocean, SST under 10 degrees C, and chlorophyll concentration exceeding 1 mg Chlm(-3). Based on the conditions under which the model results diverge most, we conclude that current ocean-color-based models are challenged by high-nutrient low-chlorophyll conditions, and extreme temperatures or chlorophyll concentrations. The GCM-based models predict comparable primary production to those based on ocean color: they estimate higher values in the Southern Ocean, at low SST, and in the equatorial band, while they estimate lower values in eutrophic regions (probably because the area of high chlorophyll concentrations is smaller in the GCMs). Further progress in primary production modeling requires improved understanding of the effect of temperature on photosynthesis and better parameterization of the maximum photosynthetic rate. (c) 2006 Elsevier Ltd. All rights reserved.

Biological and physicochemical factors controlling short-term variability in phytoplankton primary production and photosynthetic parameters in a macrotidal ecosystem (eastern English Channel)

Links between short-term variability of phytoplankton primary production and community structure changes have been studied rarely. This has been examined in a macrotidal ecosystem, the Baie des Veys (eastern English Channel, France), in 2003 and 2004, over the complete tidal cycle (semi-diurnal mode, 12 h). Within this area, primary production and photosynthetic parameter estimates, according to the 14C incorporation technique, were supported by an exhaustive taxonomic study and measurements of physicochemical factors to illustrate the environmental framework. Related to the river Vire discharge, daily interactions between estuarine and bay waters were demonstrated. Depth-integrated primary production P z was maximal around noon in the bay (48.7–68.0 mg C m −2 h −1) and decreased through the day in the mouth of the river. Photosynthetic parameters' variations and photoacclimation were influenced by the ecosystem variability level: short-term photoacclimation was possible in low mixing conditions. Changes in taxonomic composition according to tidal forcing led to variations in primary production levels. Large species, associated with high photosynthetic parameters, were observed in the bay, whereas small ones were present in the mouth of the river, when low primary production was measured. On a short-time scale, a positive relationship was observed between species diversity and primary production. This work emphasizes the need to focus on changes in phytoplankton community structure in order to understand short-term variability in primary production.

UV effects on photosynthesis, growth and acclimation of an estuarine diatom and cryptomonad

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 300:53-62 (2005) - doi:10.3354/meps300053 UV effects on photosynthesis, growth andacclimation of an estuarine diatom and cryptomonad Elena Litchman1,2,3,*, Patrick J. Neale1 1Smithsonian Environmental Research Center, PO Box 28, Edgewater, Maryland 21037, USA2School of Biology, 310 Ferst Drive, Georgia Institute of Technology, Atlanta, Georgia 30332, USA3Present address: Kellogg Biological Station, Michigan State University, Hickory Corners, Michigan 49060, USA *Email: litchman@msu.edu ABSTRACT: Ultraviolet (UV) radiation is a significant stressor in aquatic environments and can inhibit primary productivity of phytoplankton. The effects of UV depend on many factors, including phytoplankton community composition and acclimation status. Using spectrally resolved biological weighting functions (BWFs), we determined sensitivity of photosynthesis and acclimation to UV in a common estuarine diatom, Thalassiosira pseudonana (Hustedt) Hasle et Heimdal, and cryptomonad, Cryptomonas sp. Cryptomonas sp. grown under high PAR (photosynthetically active radiation) (250 µmol quanta m–2 s–1) was significantly more sensitive to photoinhibition in the UV-B part of the spectrum (280 to 320 nm) than T. pseudonana under high PAR. Growth under low irradiance (25 µmol quanta m–2 s–1) increased sensitivity of T. pseudonana. After a week-long exposure to moderate UV radiation, sensitivity of Cryptomonas sp. declined, while sensitivity of T. pseudonana did not change. Growth rates and chlorophyll a-specific absorption decreased in both species. Based on the BWFs obtained in this study, we predict 11 to 26% UV inhibition of depth-integrated primary production by these species under summer conditions in a shallow, turbid temperate estuary. KEY WORDS: Estuarine phytoplankton · UV radiation · Photosynthesis · Photoinhibition · Biological weighting functions · Acclimation · Thalassiosira pseudonana · Cryptomonas sp. Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 300. Online publication date: September 16, 2005 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2005 Inter-Research.

Vertical profiles of particulate organic matter and its relationship with chlorophyll- a in the upper layer of the NE Mediterranean Sea

Particulate organic matter (POM), nutrients, chlorophyll- a (CHL) and primary production measurements were performed in the upper layer of three different regions (cyclonic, anticyclonic and frontal+peripherial) of the NE Mediterranean Sea in 1991–1994. Depth profiles of bulk POM exhibited a subsurface maximum, coinciding with the deep chlorophyll maximum (DCM) established near the base of the euphotic zone of the Rhodes cyclone and its periphery, where the nutricline was situated just below the euphotic zone for most of the year. Moreover, the POM peaks were broader and situated at shallower depths in late winter–early spring as compared to its position in the summer–autumn period. Under prolonged winter conditions, as experienced in March 1992, the characteristic POM feature disappeared in the center of the Rhodes cyclone, where the upper layer was entirely occupied by nutrient-rich Levantine deep water. Deep convective processes in the cyclonic gyre led to the formation of vertically uniform POM profiles with low concentrations of particulate organic carbon (POC) (2.1 μM), nitrogen (0.21 μM), total particulate phosphorus (PP) (0.02 μM) and chlorophyll- a (0.5 μg/L) in the euphotic zone. Though the Levantine deep waters ascended up to the surface layer with the nitrate/phosphate molar ratios (28–29) in March 1992, the N/P molar ratio of bulk POM in the upper layer was low as 10–12, indicating luxury consumption of phosphate during algal production. Depth-integrated primary production in the euphotic zone ranged from 38.5 for oligotrophic autumn to 457 mg C m −2 day −1 for moderately mesotrophic cool winter conditions.

Seasonal and interannual variability of chlorophyll a and primary production in the Equatorial Atlantic: in situ and remote sensing observations

The seasonal variability of phytoplankton in the Equatorial Atlantic was analysed using Sea-viewing Wide Field-of-view Sensor (SeaWiFS)-derived chlorophyll a (Chl a) concentration data from 1998 to 2001, together with in situ Chl a and primary production data obtained during seven cruises carried out between 1995 and 2000. Monthly averaged SeaWiFS Chl a distributions were in agreement with previous observations in the Equatorial Atlantic, showing marked differences between 10° W in the Eastern Tropical Atlantic (ETRA) and 25° W in the Western Tropical Atlantic (WTRA) provinces (Longhurst et al. 1995. J. Plankton Res., 17, 1245–1271). The seasonal cycle of SeaWiFS-derived Chl a concentration calculated for 0–10° S, 0–20° W (ETRA) is consistent with in situ Chl a measurements, with values ranging from 0.16 mg m−3, from February to April, to 0.52 mg m−3 in August. Lower variability was observed in 10° N−10° S, 20–30° W (WTRA) where minimum and maximum concentrations occurred in April (0.15 mg m−3) and in August (0.24 mg m−3), respectively. A significant empirical relationship between depth-integrated primary production and in situ measured sea surface Chl a was found for ETRA, allowing us to estimate the seasonal cycle of depth-integrated primary production from SeaWiFS-derived Chl a. As for Chl a, this model was verified in a small area of the Eastern Equatorial Atlantic (0–10° S, 0–20° W), although in this instance it was not completely able to describe the magnitude and temporal variability of in situ primary production measurements. The annual euphotic depth-integrated primary production rate estimated for ETRA by our empirical model was 1.4 Gt C year−1, which represents 16% of the open ocean primary production estimated for the whole Atlantic Ocean.