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The hypothesis that seaweed farming contributes to carbon burial below the farms was tested by quantifying burial rates in 20 seaweed farms distributed globally, ranging from 2 to 300 years in operation and from 1 ha to 15,000 ha in size. This involved combining analyses of organic carbon density with sediment accumulation rate in sediments below seaweed farms relative to reference sediments beyond the farm and/or prior to the farm operation. One in every four farms sampled was set over environments that export, rather than retain materials. For the farms that were placed over depositional environments, where sediment accumulation could be quantified, the thickness of sediment layers and stocks of carbon accumulated below the farms increased with farm age, reaching 140 ton C ha-1for the oldest farm, and tended to exceed those in reference sediments beyond the farm and/or prior to the operation of the farms. Organic carbon burial rates in the farm sediments averaged (± SE) 1.87 ± 0.73 ton CO2equivalent (CO2-eq) ha-1year-1(median 0.83, range 0.10 – 8.99 ton CO2-eqha-1year-1), twice the average (± SE) burial rate in reference sediments (0.90 ± 0.27, median 0.64, range 0.10-3.00 ton CO2-eqha-1year-1), so that the excess organic carbon burial attributable to the seaweed farms averaged 1.06 ± 0.74 ton CO2-eqha-1year-1(median 0.09, range −0.13-8.10 ton CO2-eqha-1year-1). This first direct quantification of carbon burial in sediments below seaweed farms confirms that, when placed over depositional environments, seaweed farming tend to sequester carbon in the underlying sediments, but do so at widely variable rates, increasing with farm yield.

Kelp forests are dynamic coastal habitats that generate large amounts of carbon-rich detritus. The fate of this detritus is largely unknown and considered a missing link in global carbon budgets. Kelp detritus can serve as food for benthic invertebrates and pelagic invertebrate larvae, but we know close to nothing about the role of kelp detritus as food source for other zooplankton. Lipid-rich pelagic copepods constitute a key link from primary producers to higher trophic levels in marine boreal and arctic ecosystems, and they transport vast amounts of carbon into the deep sea. We conducted feeding experiments to test if the copepodCalanus finmarchicuscan feed on fragments of two dominant kelp species,Saccharina latissimaandLaminaria hyperborea. Such feeding would constitute an undescribed pathway from blue forests to pelagic consumers and deep-sea carbon sequestration. The experiment indicated thatC. finmarchicuscan ingest kelp particles, but the digestion is limited compared to a regular phytoplankton diet. Moreover, the results provide initial evidence thatL. hyperboreacontains substances that are toxic to copepods, an observation that warrants further research. Using specific qPCR assays to trace the consumption of kelp, we found that kelp DNA amplification signals were stronger for copepods fed withS. latissimathan L. hyperborea, but we were not able to conclusively separate consumed kelp from DNA attached to the outside of the copepods.

The paper — Seaweed ecosystems may not mitigate CO2 emissions (Gallagher et al., 2022) — claims that seaweed ecosystems are carbon sources rather than carbon sinks because ‘respiration subsidies’ (from inputs of allochthonous organic carbon) create negative net ecosystem production. That is, that seaweed ecosystems produce more CO2 than they draw down, and thus may not mitigate CO2 emissions. They make this claim using a compiled dataset which shows that, on average, seaweed ecosystems are net heterotrophic. However, their assessment is flawed and conceptually misleading as key terms are misinterpreted, the data presented are biased, and the conclusions are not supported statistically. Here we discuss four flaws in the argument presented by Gallagher et al., which we believe risk confusing further research on seaweed blue carbon and unjustifiably seeding doubt around motivations and initiatives to protect and restore seaweed forests.

Ice algae are key contributors to primary production and carbon fixation in the Arctic, and light availability is assumed to limit their growth and productivity. We investigated photo-physiological responses in sea ice algae to increased irradiance during a spring bloom in West Greenland. During a 14 d field experiment, light transmittance through sea ice was manipulated to provide 3 under-ice irradiance regimes: low (0.04), medium (0.08), and high (0.16) transmittances. Chlorophyll a decreased with elevated light availability relative to the control. Maximum dark-adapted photosynthetic efficiency (ΦPSII_max) showed an initially healthy and productive ice algae community (ΦPSII_max > 0.6), with ΦPSII_max decreasing markedly under high-light treatments. This was accompanied by a decrease in the light utilization coefficient (α) and photosynthetic capacity (maximum relative electron transfer rate), and a decrease in the ratio of mono- to polyunsaturated fatty acids. This was partly explained by a corresponding increase of photoprotective pigments (diadinoxanthin and diatoxanthin), and a development of mycosporine-like amino acids as identified from a distinctive spectral absorption peak at 360 nm. After 14 d, in situ fluorescence imaging revealed significant differences in ΦPSII_max between treatments of dark-adapted cells (i.e. those sampled before sunrise and after sunset), during diel cycles, with clear chronic photoinhibition in high and medium treatments. Data demonstrate the high sensitivity of spring-blooming Arctic sea ice algae to elevated irradiance caused by loss of snow cover. The predicted loss of snow cover on landfast ice will negatively impact ice algae, their potential primary production, and nutritional quality for higher trophic levels.

This protocol was established for the Nordic Blue Carbon Project (2017–2020) for tracking the presence of kelp DNA in marine sediments, providing preliminary quantitative information on the original kelp biomass. Nordic blue forests are coastal vegetated habitats, such as kelp forests, eelgrass meadows and rockweed beds, that are important natural sinks for carbon and thereby climate regulation. They also play an important role in climate adaptation. Simultaneously, blue forests are at high risk from climate change and other human impacts, such as eutrophication and coastal development. The advent of eDNA methods for tracking animal or vegetal organisms in water or sediment matrices, has enabled not only geographical detection without collection of the organism but also temporal study of their presence in dated sediment cores. The fate of eDNA and its persistence in the environment is intimately related to its biophysical surroundings. eDNA entrapped in sediments may be preserved on long time scales, up to centuries, enabling historical tracking of the presence of a species on a site. The present protocol was developed for tracking eDNA of a predominant Norwegian kelp species, Laminaria hyperborea, in dated marine sediment cores. This approach enables confirmation of species specific contribution to carbon sequestration in an effort to evaluate marine sediments operating as carbon sinks. This work was financed by the Norwegian Environment Agency (Miljødirektoratet) contract #17080044 and published in a NIVA report ISBN 978-82-577-7384-7, Norwegian Environment Agency Report M-2090|2021, Blue Carbon eDNA – A novel eDNA method to trace macroalgae carbon in marine sediments. .

Compelling new evidence shows that kelp production contributes an important and underappreciated flux of carbon in the ocean. Major questions remain, however, about the controls on the cycling of this organic carbon in the coastal zone, and their implications for future carbon sequestration. Here we used field experiments distributed across 28° latitude, and the entire range of two dominant kelps in the northern hemisphere, to measure decomposition rates of kelp detritus on the seafloor in relation to environmental factors. Ocean temperature was the strongest control on detritus decomposition in both species, and it was positively related to decomposition. This suggests that decomposition could accelerate with ocean warming under climate change, increasing remineralization and reducing overall kelp carbon sequestration. However, we also demonstrate the potential for high kelp-carbon storage in cooler (northern) regions, which could be targeted by climate mitigation strategies to expand blue carbon sinks.

Nordic blue forests are coastal vegetated habitats, such as kelp forests, eelgrass meadows and rockweed beds, that are important natural sinks for carbon and thereby climate regulation. They also play an important role in climate adaptation. Simultaneously, blue forests are at high risk from climate change and other human impacts, such as eutrophication and coastal development. This report presents the main findings of the Nordic Blue Carbon Project (2017–2020) on the areal distribution and carbon budget of blue forests (kelp forests, seagrass meadows and rockweed beds) in the Nordic region. We have identified the main ecosystem effects of climate change and other human pressures on Nordic blue forests, tested the effect of moderating some of these pressures, and give scientific advice on management measures aimed at safeguarding these important coastal ecosystems for the future.

Knowledge of genetic diversity among wild populations is becoming increasingly important as more species are recognized for their bioeconomic value. Industrialization of natural resources, such as kelp in the marine shallow sublittoral zone through cultivation and wild-harvesting, may lead to extensive translocation and local population decimation. Without adequate resilience in the form of genetic diversity within and across populations and given the potential introduction of deleterious alleles from translocations, such anthropogenically pressured populations may not be able to sufficiently respond to future climate and other stressors. Here we provide an assessment of the genetic heterogeneity of two bioeconomically important kelp species, Laminaria hyperborea and Saccharina latissima, across the Norwegian coastal region from South (57°N) to North (78°N), by applying microsatellite genotyping. Isolation by distance was found for both kelp species when comparing genetic distance to geographic distance. L. hyperborea clustered into four distinct genetic groups corresponding to distinct geographical ecoregions, whereas S. latissima did not show equally strong geographical structuring but separated into three geographical clusters along the Norwegian coast. No genetic differentiation was found within the Norwegian Skagerrak region, corroborating previous findings. The identified genetic clustering of both kelp species supports the retention of established management regions along the Norwegian coast and argues for the continuation of a regional focused management plan for kelp resources. Further, the results demonstrate that care should be taken to prevent translocation of kelp between ecoregions in the ongoing industrialization of kelp cultivation, to maintain a healthy coastal ecosystem and sound natural population genetic diversity.

We have evaluated the cultivation potential of sugar kelp (Saccharina latissima) as a function of latitude and position (near- and offshore) along the Norwegian coast using a coupled 3D hydrodynamic-biogeochemical-kelp model system (SINMOD) run for four growth seasons (2012-2016). The results are spatially explicit and may be used to compare the suitability of different regions for kelp cultivation, both inshore and offshore. The simulation results were compared with growth data from kelp cultivation experiments and in situ observations on coverage of naturally growing kelp. The model demonstrated a higher production potential offshore than in inshore regions, which is mainly due to the limitations in nutrient availability caused by the stratification found along the coast. However, suitable locationsareas for kelp cultivation were also identified in areas with high vertical mixing close to the shore. The results indicate a latitudinal effect on the timing of the optimal period of growth, with the prime growth period being up to 2 months earlier in the south (58 °N) than in the north (71 °N). Although the maximum cultivation potential was similar in the six marine ecoregions in Norway (150-200 tons per unit area per year) in the six marine ecoregions in Norway, the deployment time of the cultures seems to matter significantly in the south, but less so in the north. The relevance of the results is discussed with a view towards use in decision support tools and a management context. The results are discussed, focusing on their potential significance for optimized cultivation and to support decision making towards sustainable management. The kelp cultivation potential in coastal and offshore regions of Norway

Most applications of laser induced fluorescence (LIF) for dissolved oxygen (DO) imaging in flowing water are based on luminescence intensity measurements of a dissolved indicator. A major limitation for applying the technique in the bottom boundary layer (BBL) is the sorption of the luminescent dye to organic surfaces at the sediment. Many sediment and soil studies have used planar optodes on transparent foils as an imaging technique for observing concentration distributions across the sediment-water interface. The presence of the foil, however, is restricting the free flow and therewith the DO concentration above the sediment surface. In this study, we applied the phosphorescence lifetime LIF (τLIF) technique in combination with nanoparticles coated with platinum complexes as DO indicators. By using a planar laser light sheet for fluorescence excitation, the three-dimensional flow field around the sampling area is not restricted. In contrast to the intensity-based LIF technique, this method extracts the lifetime of the luminescence by evaluating the exponential decrease of the phosphorescence intensity after a short excitation light pulse. The method is therefore independent of dye concentration and is not affected by spatial inhomogeneities of the excitation light intensity. We applied the technique to visualize the burrow-ventilation activity of the tube-dwelling Chironomus plumosus larvae. Sequences of the two-dimensional DO concentration distributions showed the intermittent outburst of highly-depleted plumes from the outlet of the burrows, which mixed rapidly with the ambient oxygen-rich water.

Here we describe the design, performance and field tests of a lightweight (13.1 kg), low-cost (15.000 USD), and portable remotely operated vehicle (ROV) of dimensions 55 x 43 x 34 cm (L x H x W), with a new optical based positioning system. The ROV is designed for deployments and measurements of the irradiance field at a short distance below sea ice bottom in landfast level sea ice at calm under ice conditions. It is equipped with two cameras (front and rear) for optical positioning based on reference poles with LED lights below the ice. A third upward camera is for guiding during deployment and positioning. The ROV is equipped with spacer poles to maintain a constant distance between ROV with onboard optical sensors and bottom of the ice. All pre-tests of housing, thrusters, optical positioning, and ROV maneuverability were carried out in freshwater basins prior to field trials and tests. These were conducted at Kangerlussuaq, West Greenland on landfast first-year 79-80 cm thick ice with a variable (1-12 cm) snow cover in March 2016. The ROV was easily deployed through a hole (75 x 50 cm) in the ice and easy to maneuver below the ice. Test of positioning system showed an average deviation of 28 +/- 5 cm between optically based position and actual position with an average offset from center line of 16 +/- 5 cm. The ROV was applied for measuring the under-ice irradiance field and results demonstrated a solid negative correlation between snow depth and PAR transmittance. We derived a Normalized Differences Index (NDI) for snow depths: NDIsnow (depth) = [E(610 nm) - E(490 nm)]/[E(610 nm) + E(490 nm)] with minimum attenuation at 490 nm and maximum at 610 nm. It is discussed that the correlations for both PAR transmittance and the NDI with snow depths are due to a combination of a constant distance between optical sensor and ice bottom, and accurate positioning. A test showed that the wakes of thrusters removed parts of the ice algae biomass, but the study demonstrates the applicability of this ROV design for measurements of the under-ice irradiance field below landfast sea ice with a new optical based positioning system.

This report describes the status and trends of biodiversity and ecosystem services in the Nordic region, the drivers and pressures affecting them, interactions and effects on people and society, and options for governance. The main report consists of two volumes. Volume 1 The general overview (this report) and Volume 2 The geographical case studies. This study has been inspired by the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystems Services (IPBES). It departs from case studies (Volume 2, the geographical case studies) from ten geographical areas in the Nordic countries (Denmark, Finland, Iceland, Norway, Sweden) and the autonomous areas of Faroe Islands, Greenland, and Åland. The aim was to describe status and trends of biodiversity and ecosystem services in the Nordic region, including the drivers and pressures affecting these ecosystems, the effects on people and society and options for governance. The Nordic study is structured as closely as possible to the framework for the regional assessments currently being finalized within IPBES. The report highlights environmental differences and similarities in the Nordic coastal areas, like the inhabitants´ relation to nature and the environment as well as similarities in social and policy instruments between the Nordic countries. This study provides background material for decision-making and it is shown that Nordic cooperation is of great importance for sustainable coastal management and should be strengthened in future work.

This report contributes to a Nordic IPBES-like assessment of biodiversity and ecosystem services in Nordic coastal areas. It is based on ten geographical cases in the Nordic countries (Denmark, Fin ...

The quantification of benthic fluxes with the aquatic eddy correlation (EC) technique is based on simultaneous measurement of the current velocity and a targeted bottom water parameter (e.g., O2, temperature). High-frequency measurements (64 Hz) are performed at a single point above the seafloor using an acoustic Doppler velocimeter (ADV) and a fast-responding sensor. The advantages of aquatic EC technique are that 1) it is noninvasive, 2) it integrates fluxes over a large area, and 3) it accounts for in situ hydrodynamics. The aquatic EC has gained acceptance as a powerful technique; however, an accurate assessment of the errors introduced by the spatial alignment of velocity and water constituent measurements and by their different response times is still needed.Here, this paper discusses uncertainties and biases in the data treatment based on oxygen EC flux measurements in a large-scale flume facility with well-constrained hydrodynamics. These observations are used to review data processing procedures and to recommend improved deployment methods, thus improving the precision, reliability, and confidence of EC measurements. Specifically, this study demonstrates that 1) the alignment of the time series based on maximum cross correlation improved the precision of EC flux estimations; 2) an oxygen sensor with a response time of −1; and 3) the smallest possible distance (

35 páginas, A small hydrological basin (Lerma, NE Spain), transformed from its natural state (steppe) to rain-fed agriculture and recently to irrigation agriculture, has been monitored across four seasons of an agricultural year. The goal of this study was to assess how and whether agricultural activities impacted the nearby freshwater ecosystems via runoff. Specifically, we assessed the toxicity of three triazine herbicides, terbuthylazine, atrazine and simazine on the photosynthetic efficiency and structure of algal benthic biofilms (i.e., phototropic periphyton) in the small creek draining the basin. It was expected that the seasonal runoff of the herbicides in the creek affected the sensitivity of the periphyton in accord with the rationale of the Pollution Induced Community Tolerance (PICT): the exposure of the community to pollutants result in the replacement of sensitive species by more tolerant ones. In this way, PICT can serve to establish causal linkages between pollutants and the observed biological impacts. The periphyton presented significantly different sensitivities against terbuthylazine through the year in accord with the seasonal application of this herbicide in the crops nowadays. The sensitivity of already banned herbicides, atrazine and simazine does not display a clear seasonality. The different sensitivities to herbicides were in agreement with the expected exposures scenarios, according to the agricultural calendar, but not with the concentrations measured in water, which altogether indicates that the use of PICT approach may serve for long-term monitoring purposes. That will provide not only causal links between the occurrence of chemicals and their impacts on natural communities, but also information about the occurrence of chemicals that may escape from traditional sampling methods (water analysis). In addition, the EC50 and EC10 of periphyton for terbuthylazine or simazine are the first to be published and can be used for impact assessments., This work was supported by the National Research Plan from the Spanish Ministry of Economy and Competitiveness and FEDER funds (EU), projects BFU2010-22053 and CGL-2012-32395. D. Merchán holds a fellowship from the same Ministry (Ref. BES2010-034124). We also acknowledge Dr. Marta Luścińska for the algal taxonomic analysis.

Burrow ventilation by tube-dwelling benthic animals affects solute exchange between sediments and water by 2 means. Drawing of O2-rich water into the burrow increases O2 availability in the sediment and stimulates biogeochemical and microbial processes, whereas flushing of the burrow creates a 3-dimensional flow field above the burrow, which induces mixing. Previous studies have revealed the role of the diffusive boundary layer (DBL) thickness on the exchange of solutes between the sediment and overlying water. Mapping the O2 gradient within the DBL is a challenging task in the presence of benthic faunal activities. We used a novel lifetime-based laser induced fluorescence (τLIF) technique that enables unobstructed observations of spatial and temporal O2 dynamics above burrows inhabited by midge larvae (Chironomus plumosus). We observed instantaneous plumes of O2-depleted water released from the outlet of the burrows and drawdown of O2-rich water above the inlet caused by peristaltic pumping of C. plumosus larvae. Vertical O2 gradients changed dynamically during burrow ventilation relative to in a control tank without animals. The advective transport of O2 above the opening caused by burrow ventilation degraded the O2-concentration gradient. For a range of larvae densities that is frequently observed in ponds and lakes, the advective transport caused by burrow ventilation was the dominant transport mechanism.

Colored Dissolved Organic Matter (CDOM) is an important optical constituent in seawater, which significantly attenuates the violet to blue portion of visible light. Thus, CDOM reduces the radiation energy available to phytoplankton and affects remote-sensing signals. We present data from two cruises transecting the Polar Front from Atlantic to Arctic waters in the Barents Sea, in 2007 and 2008. The latter took place during the spring bloom of phytoplankton in May (0.2-3) and the former during August (max. [Chl a]-3). Absorption by CDOM at 443nm ranged from 0.004 to 0.080m -1 during May and from 0.006 to 0.162m -1 during August. Surprisingly, CDOM absorption differed little across the Polar Front, but was higher during August than during May (P-1 (mean=0.015nm -1) including both cruises, and varied little across the Front (P>0.05). The CDOM remote sensing product from GlobColour correlated well with sampled data (R 2=0.73) during May. However, during August the satellite product performed poorly (R 2=0.02) due to extensive scattering caused by coccolithophorids in the Atlantic Water. The CDOM pool was of autochthonous (marine) origin as characterized from its S vs. absorption relationship. Modeling showed that CDOM, on average, contributed equally to the light absorption as did phytoplankton (at 1mg Chl a m -3), and thereby reduces the amount of light available for primary production.

The Jan Mayen Front is located in the Norwegian Sea to the east of the Jan Mayen Ridge and separates warm, salty Atlantic water and colder, less salty Arctic water. The effects of the light regime, hydrographical conditions and nutrients on the variations of chlorophyll a (chl a), quantum efficiencies of photochemistry in PSII (F v:F m) and effective absorption cross-section of PSII (σ PSII) at the Front were studied in June 2007. Stratified waters were seen on both sides of the Front and lowered nutrient concentrations were seen shallower than 10-20m. The lowest values of the spectral diffuse attenuation coefficient, K d (λ), were found at 500-550nm (0.07-0.16m -1), while K d (465nm) ranged between 0.08 and 0.17m -1 and K d (380nm) between 0.13 and 0.20m -1. Chl a concentrations seldom exceeded 1.0mgm -3 outside pure Atlantic Water, while elevated concentrations (3-4mgm -3) developed at depth (20-30m) east of the Front in Atlantic Water. For the upper 100m N/P, Si/P, N/Si and POC/PON ratios were 15.2, 8.0, 1.7 and 6.2, respectively. The quantum efficiency was strongly influenced by nutrients, suggesting nutrient limitation of phytoplankton biomass at the Front in June, but also light inhibition probably was a contributing factor in the upper part of the water column. High quantum efficiencies (0.5) and effective absorption cross sections (>700Å 2 quanta -1) were seen to the east of the Front and at depth (20-40m) in stratified Atlantic waters. We therefore conclude that the Jan Mayen Front did not have a stimulatory effect on phytoplankton biomass enhancement and photosynthetic performance. This is in part due to the weak horizontal density front caused by density compensation of temperature and salinity characteristics of the adjacent water masses, and the associated weak vertical mixing.

Light is the primary energy source fuelling the primary production in the ocean, and an accurate representation of the light's propagation in the water column is important for ecological models that seek to estimate primary production. Ecological models typically use a non-spectral representation of light, meaning that information about the wavelength-specific absorption and scattering properties of the optical components in the water is lost. In this work, a spectrally-resolved light field propagation model (SINMOD Light, or SL) has been developed for the purpose of providing reliable estimates of primary production, while keeping the computational load low enough to be acceptable for 3D ecological models. The model is tested against the radiative transfer model Ecolight as well as in situ data from the Barents Sea. Compared to Ecolight, SL has much simpler dynamics and requires around 1% of the computation time. The spectral downwelling irradiances predicted by SL are highly correlated (≥ 0.95) with the measurements for the four tested scenarios. The correlations are similar to those seen between Ecolight and measurements. For upwelling irradiances, the match is stronger (≥ 0.98) between SL and Ecolight than between the data and either model. Comparing primary production estimates, there is good agreement between SL and the in situ data, with average prediction errors within 5% of the maximum production rate. The spectral model predicts primary production slightly more accurately than a non-spectral model normalized to equal SL near the surface (on average within 6%). A spectral model allows more sophisticated treatment of phytoplankton and other components with differing optical characteristics in ecosystem modelling. Furthermore, the model allows an estimate of the water-leaving radiance to be computed along with the underwater irradiance distribution. This can be developed further into a powerful tool for verification of remote sensing products as well as validation of ecosystem models using high-accuracy water-leaving radiance measurements.

Coastal and shelf systems likely exert major influence on Arctic Ocean functioning, yet key ecosystem processes remain poorly quantified. We employed the aquatic eddy covariance (AEC) oxygen (O2) flux method to estimate benthic primary production and mineralization in a High Arctic Greenland fjord. Seabed gross primary production (GPP) within the 40 m deep photic zone was highest at 10 m (29 mmol O2 m-2 d-1) and decreased to 5 mmol O2 m-2 d-1 at 40 m, while nighttime community respiration (CR) ranged from 11 to 25 mmol O2 m-2 d-1. CR decreased to ∼2.5 mmol O2 m-2 d-1 at 80 m and remained constant with further depth. Fauna activity accounted for ∼50% of the CR at depths ≤60 m but was -1), and here the seabed was twice as important as the pelagic compartment for primary production. However, when scaled to the entire outer fjord area of which 80% is >40 m, benthic GPP was 26% of the pelagic production. CR was 2-fold higher than GPP over this region (5.7 t C d-1) and thus net heterotrophic. By scaling AEC-derived Arctic benthic GPP to the entire Arctic Ocean using modelled seabed light data, we estimate an annual Arctic Ocean benthic GPP of 11.5 × 107 t C yr-1. On average, this value represents 26% of the Arctic Ocean annual net phytoplankton production estimates. This scarcely considered component is thus potentially important for contemporary and future Arctic ecosystem functioning.

Light absorption by phytoplankton is both species specific and affected by photoacclimational status. To estimate oxygenic photosynthesis from pulse-amplitude-modulated (PAM) fluorescence, the amount of quanta absorbed by PSII needs to be quantified. We present here three different biooptical approaches to estimate the fraction of light absorbed by PSII: (1) the factor 0.5, which implies that absorbed light is equally distributed among PSI and PSII; (2) the fraction of chl a in PSII, determined as the ratio between the scaled red-peak fluorescence excitation and the red absorption peak; and (3) the measure of light absorbed by PSII, determined from the scaling of the fluorescence excitation spectra to the absorption spectra by the "no-overshoot" procedure. Three marine phytoplankton species were used as test organisms: Prorocentrum minimum (Pavill.) J. Schiller (Dinophyceae), Prymnesium parvum cf. patelliferum (J. C. Green, D. J. Hibberd et Pienaar) A. Larsen (Haptophyceae), and Phaeodactylum tricornutum Bohlin (Bacillariophyceae). Photosynthesis versus irradiance (P vs. E) parameters calculated using the three approaches were compared with P versus E parameters obtained from simultaneously measured rates of oxygen production. Generally, approach 1 underestimated, while approach 2 overestimated the gross O2 -production rate calculated from PAM fluorescence. Approach 3, in principle the best approach to estimate quanta absorbed by PSII, was also superior according to observations. Hence, we recommend approach 3 for estimation of gross O2 -production rates based on PAM fluorescence measurements.

Short-term temperature effects on photosynthesis were investigated by measuring O2 production, PSII-fluorescence kinetics, and (14) C-incorporation rates in monocultures of the marine phytoplankton species Prorocentrum minimum (Pavill.) J. Schiller (Dinophyceae), Prymnesium parvum f. patelliferum (J. C. Green, D. J. Hibberd et Pienaar) A. Larsen (Coccolithophyceae), and Phaeodactylum tricornutum Bohlin (Bacillariophyceae), grown at 15°C and 80 μmol photons · m(-2) · s(-1) . Photosynthesis versus irradiance curves were measured at seven temperatures (0°C-30°C) by all three approaches. The maximum photosynthetic rate (P(C) max ) was strongly stimulated by temperature, reached an optimum for Pro. minimum only (20°C-25°C), and showed a similar relative temperature response for the three applied methods, with Q10 ranging from 1.7 to 3.5. The maximum light utilization coefficient (α(C) ) was insensitive or decreased slightly with increasing temperature. Absolute rates of O2 production were calculated from pulse-amplitude-modulated (PAM) fluorometry measurements in combination with biooptical determination of absorbed quanta in PSII. The relationship between PAM-based O2 production and measured O2 production and (14) C assimilation showed a species-specific correlation, with 1.2-3.3 times higher absolute values of P(C) max and α(C) when calculated from PAM data for Pry. parvum and Ph. tricornutum but equivalent for Pro. minimum. The offset seemed to be temperature insensitive and could be explained by a lower quantum yield for O2 production than the theoretical maximum (due to Mehler-type reactions). Conclusively, the PAM technique can be used to study temperature responses of photosynthesis in microalgae when paying attention to the absorption properties in PSII.

Dissolved oxygen (DO) concentration is a key indicator of the health and productivity of an aquatic ecosystem. This paper presents a new method for high-resolution characterization of DO as a function of both space and time. The implementation of a new oxygen optode in an Iver2 autonomous underwater vehicle (AUV) is described, which enables the system to measure both absolute oxygen concentration and percentage saturation. Also described are details of AUV missions in Hopavagen Bay, Norway, which consisted of a series of repeated undulating lawnmower patterns that covered the bay. Through offline postprocessing of data, sensor characteristic models were developed, as well as a 3D lattice time series model. The model was constructed by estimating DO at each 3D lattice node location using a 1D Kalman filter that fused local measurements obtained with the AUV. By repeating model construction for several missions that spanned 24 h, estimates of DO as a function of space and time were calculated. Results demonstrated (1) the AUVs ability to repeatedly gather high-spatial-resolution data (2) significant spatial and temporal variation in DO in the water body investigated, and (3) that a 3D model of DO provides better estimates of total DO in a volume than extrapolating from only a single 2D plane. Given the importance of oxygen within an ecosystem, this new method of estimating the quantity of DO per volume has the potential to become a reliable test for the health of an underwater ecosystem. Also, it can be refined for detecting and monitoring a range of soluble gases and dispersed particles in aquatic environments, such as dissolved O2 and CO2 around production facilities such as fish farms, or dispersed hydrocarbons and other pollutants in fragile ecosystems. © 2012 Wiley Periodicals, Inc. © 2013 Wiley Periodicals, Inc.

The aim of my thesis is to elucidate the different pathways of light in the marine environment, from underwater irradiance to the absorption of photons in microalgae. The pathway is followed through light harvesting and the subsequent electron transfer, to the fuelling of the photosynthetic process (Fig. 1.1, Papers 1, 2 & 3). In addition, the effect of temperature on photosynthesis and respiration in pelagic and benthic microalgae has been investigated (Papers 3 & 4). A novel approach to estimate the light absorption in Photosystem II (PSII) is evaluated in combination with Pulse Amplitude Modulated (PAM) fluorescence measurements, to calculate the rate of photosynthetic oxygen production (Paper 2). The approach was evaluated against measured rates of oxygen production and 14C-assimilation, as a function of temperature (Papers 2 & 3).

PSII-fluorescence kinetics, and 14 C-incorporation rates in monocultures of the marine phytoplankton species Prorocentrum minimum (Pavill.) J. Schiller (Dinophyceae), Prymnesium parvum f. patelliferum (J. C. Green, D. J. Hibberd et Pienaar) A. Larsen (Coccolithophyceae), and Phaeodactylum tricornutum Bohlin (Bacillariophyceae), grown at 15� C and 80 lmol photons AEm )2 AEs )1 . Photosynthesis versus irradiance curves were measured at seven temperatures (0� C‐30� C) by all three approaches. The maximum photosynthetic rate (P C max) was strongly stimulated by temperature, reached an optimum for Pro. minimum only (20� C‐25� C), and showed a similar relative temperature response for the three applied methods, with Q10 ranging from 1.7 to 3.5. The maximum light utilization coefficient (a C ) was insensitive or decreased slightly with increasing temperature. Absolute rates of O2 production were calculated from pulse-amplitude-modulated (PAM) fluorometry measurements in combination with biooptical determination of absorbed quanta in PSII. The relationship between PAM-based O2 production and measured O2 production and 14 C assimilation showed a species-specific correlation, with 1.2‐3.3 times higher absolute values of P C max and a C when calculated from PAM data for Pry. parvum and Ph. tricornutum but equivalent for Pro. minimum. The offset seemed to be temperature insensitive and could be explained by a lower quantum yield for O2 production than the theoretical maximum (due to Mehler-type reactions). Conclusively, the PAM technique can be used to study temperature responses of photosynthesis in microalgae when paying attention to the absorption properties in PSII. Key index words: 14 C assimilation; microalgae; O2

In spring 2005, monthly sampling was carried out at a sublittoral site near Tautra Island. Microphytobenthic identification, abundance (ABU), and biomass (BIOM), were performed by microscopic analyses. Bacillariophyceae accounted for 67% of the total ABU, and phytoflagellates constituted 30%. The diatom floristic list consisted of 38 genera and 94 species. Intact light-harvesting pigments chl a, chl c, and fucoxanthin and their derivatives were identified and quantified by HPLC. Photoprotective carotenoids were also observed (only as diadinoxanthin; no diatoxanthin was detected). Average fucoxanthin content was 4.57 ± 0.45 μg fucoxanthin · g sediment dry mass⁻¹, while the mean chl a concentration was 2.48 ± 0.15 μg · g⁻¹ dry mass. Both the high fucoxanthin:chl a ratio (considering nondegraded forms) and low amounts of photoprotective carotenoids indicated that the benthic microalgal community was adapted to low light. Microphytobenthic primary production was estimated in situ (MPPs, from 0.15 to 1.28 mg C · m⁻² · h⁻¹) and in the laboratory (MPPp, from 6.79 to 34.70 mg C · m⁻² · h⁻¹ under light saturation) as ¹⁴C assimilation; in April it was additionally estimated from O₂-microelectrode studies (MPPO₂) along with the community respiration. MPPO₂ and the community respiration equaled 22.9 ± 7.0 and 7.4 ± 1.8 mg C · m⁻² · h⁻¹, respectively. A doubling of BIOM from April to June in parallel with a decreasing photosynthetic activity per unit chl a led us to suggest that the microphytobenthic community was sustained by heterotrophic metabolism during this period.