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Accurate quantification of pelagic primary production is essential for quantifying the marine carbon turnover and the energy supply to the food web. Knowing the electron requirement (Κ) for carbon (C) fixation (Κ C) and oxygen (O2) production (Κ O2), variable fluorescence has the potential to quantify primary production in microalgae, and hereby increasing spatial and temporal resolution of measurements compared to traditional methods. Here we quantify Κ C and Κ O2 through measures of Pulse Amplitude Modulated (PAM) fluorometry, C fixation and O2 production in an Arctic fjord (Godthåbsfjorden, W Greenland). Through short- (2h) and long-term (24h) experiments, rates of electron transfer (ETRPSII), C fixation and/or O2 production were quantified and compared. Absolute rates of ETR were derived by accounting for Photosystem II light absorption and spectral light composition. Two-hour incubations revealed a linear relationship between ETRPSII and gross 14C fixation (R2 = 0.81) during light-limited photosynthesis, giving a Κ C of 7.6 ± 0.6 (mean ± S.E.) mol é (mol C)−1. Diel net rates also demonstrated a linear relationship between ETRPSII and C fixation giving a Κ C of 11.2 ± 1.3 mol é (mol C)−1 (R2 = 0.86). For net O2 production the electron requirement was lower than for net C fixation giving 6.5 ± 0.9 mol é (mol O2)−1 (R2 = 0.94). This, however, still is an electron requirement 1.6 times higher than the theoretical minimum for O2 production [i.e. 4 mol é (mol O2)−1]. The discrepancy is explained by respiratory activity and non-photochemical electron requirements and the variability is discussed. In conclusion, the bio-optical method and derived electron requirement support conversion of ETR to units of C or O2, paving the road for improved spatial and temporal resolution of primary production estimates.

Phytoplankton are the main food source for marine life, and accurate uantification of its productivity is essential for understanding how marine food webs function. As a novel non-invasive technology, chlorophyll fluorescence can be used to assess in situ primary production in phytoplankton - overcoming the limited spatial and temporal resolution of traditional bottle techniques. Here we present data on gross and net primary production from Pulse Amplitude Modulated (PAM) fluorescence, 14C fixation and O2 production of a natural phytoplankton community in the arctic Godthåbsfjorden, in West Greenland. Using a novel combination of PAM fluorescence and biooptical measurements we derived the electron requirement for carbon (C) fixation and oxygen (O2) production in absolute units. Both short- (2h) and long-term (24h) experiments demonstrated a strong coupling between the three techniques, especially during light-limited conditions, resulting in predicable parameters for conversion of PAM fluorescence to gross and net primary production. For instance we documented an electron requirement for gross 14C fixation of 7.7 ± 0.8 (mean ± S.E, with units of mol é (mol C)-1). Future applications using PAM fluorescence on moorings and Autonomous Underwater Vehicles (AUVs) for improved spatial and temporal resolution of primary production will be discussed.

This is a study of the optical, physical and biological parameters of sea ice and the water below it at stations ( n =25) in the central (>88 ° N) Eurasian sector of the Arctic Ocean during the summer 2012 record low sea-ice minimum extent. Results show that photosynthetically active radiation (PAR) transmittance of the ice was low (0.09) and apparently related to a high degree of backscattering by air-filled brine channels left by brine draining. The under-ice PAR was also low (8.4±4.5 SD µmol photons m −2 s −1 ) and partly related to the low transmittance. There were no significant differences in multi-year and first-year PAR transmittances. In spite of this low under-ice PAR, only 3% of the transmitted PAR through the ice was absorbed by phytoplankton in the water. On average, chlorophyll-a concentrations were low (0.34±0.69 SD mg chl-a m −3 ) in the water compared to the high ( a 375 =0.52 m −1 ) coloured dissolved organic matter (CDOM) absorption coefficient with a strong terrestrial optical signature. Two distinct clusters of stations with waters of Pacific and North Atlantic origin were identified based on significant differences in temperature, salinity and CDOM absorption coefficient between water masses. The under-ice light field for bare ice was parameterized as follows: I z = I o (1−0.55)*(0.09)*exp (−0.17*z) . Keywords: Sea ice; transmittance; PAR; CDOM; chl-a; Eurasian sector (Published: 1 September 2015) Citation: Polar Research 2015, 34 , 23978,http://dx.doi.org/10.3402/polar.v34.23978

The effects of temperature and light on both oxygen (O2) production and gross photosynthesis were resolved in a benthic microalgal community by combining two-dimensional (2D) imaging of O2 and variable chlorophyll a (Chl a) fluorescence. Images revealed a photosynthetically active community with spatial heterogeneity at the millimeter scale. Irradiance strongly increased pore-water O2 concentration, sediment net O2 production, and gross photosynthesis. The latter was derived from measurements of the electron transfer rate (rETR) in Photosystem II. The onset of light saturation for gross photosynthesis was approximately twofold higher than for net O2 production, reflecting significant light-stimulated O2 consumption at higher light (. 75 mmol photons m22 s21). Temperature stimulated O2 consumption more than photosynthesis, turning the community more heterotrophic at elevated temperatures. Thus, the compensation irradiance (i.e., the irradiance at which community O2 production and consumption balance) increased fivefold (from 6 to 30 mmol photons m22 s21) with a temperature increase from 10u Ct o 25uC, corresponding to a temperature coefficient (Q10) of 2.9. Whereas net O2 production had a temperature optimum at , 20uC, no optimum was observed for gross photosynthesis within the investigated range (10u Ct o 25uC). The resolved 2D net O2 production and rETR exhibited a significant exponential relationship, demonstrating predictable correlations between the net community production and gross photosynthesis for a complex microbial community, at different temperatures. The present imaging approach demonstrates a great potential to study consequences of environmental effects on photosynthetic activity and O2 turnover in complex phototrophic benthic communities. Shallow-water benthic phototrophic communities have been shown to mediate a positive net community production over . 33% of the global shelf area and thereby play a crucial role in the global marine carbon cycling (Cahoon 1999; Gattuso et al. 2006). This underlines the importance of these communities as sources of organic carbon for sustaining the food web. The effects of fluctuating temperature and light on phototrophic sediments are

Due to the selective attenuation of solar light and the absorption properties of seawater and seawater constituents, free-floating photosynthetic organisms have to cope with rapid and unpredictable changes in both intensity and spectral quality. We have studied the transcriptional, metabolic and photo-physiological responses to light of different spectral quality in the marine diatom Phaeodactylum tricornutum through time-series studies of cultures exposed to equal doses of photosynthetically usable radiation of blue, green and red light. The experiments showed that short-term differences in gene expression and profiles are mainly light quality-dependent. Transcription of photosynthesis-associated nuclear genes was activated mainly through a light quality-independent mechanism likely to rely on chloroplast-to-nucleus signaling. In contrast, genes encoding proteins important for photoprotection and PSII repair were highly dependent on a blue light receptor-mediated signal. Changes in energy transfer efficiency by light-harvesting pigments were spectrally dependent; furthermore, a declining trend in photosynthetic efficiency was observed in red light. The combined results suggest that diatoms possess a light quality-dependent ability to activate photoprotection and efficient repair of photodamaged PSII. In spite of approximately equal numbers of PSII-absorbed quanta in blue, green and red light, the spectral quality of light is important for diatom responses to ambient light conditions. © 2014 Valle et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

The impact on downwelling irradiance of phytoplankton, cromophoric dissolved organic matter (CDOM) and particulate inorganic carbon (PIC) in the form of coccoliths, is described using a radiative transfer model and field data from the Barents Sea (BS). While annual Emiliania huxleyi blooms in the BS have been detected with satellite remote sensing, this is the first bio-optical field study on E. huxleyi from this area. Bio-optical variables were measured in August 2007 along a transect through the Polar Front from Arctic Water (ArW) into an E. huxleyi bloom in Atlantic Water (AW). The depth of the euphotic zone was on average 52m in ArW, 45m in frontal mixed water (FMW) and 21m in AW. At the 10% irradiance depth in AW, phytoplankton had attenuated 40%, CDOM 17% and PIC 18% of the irradiance from 400 to 700nm. Numbers from ArW were 36%, 26% and pot) in AW was 1.8× higher than in ArW, and PIC had reduced PP pot in AW by 20-40% at stations with ~100-130mg PIC m -3. A novel approach for estimating PIC based on a theoretical relationship between diffuse attenuation and irradiance reflectance is also described.

Photosynthetic diatoms are exposed to rapid and unpredictable changes in irradiance and spectral quality, and must be able to acclimate their light harvesting systems to varying light conditions. Molecular mechanisms behind light acclimation in diatoms are largely unknown. We set out to investigate the mechanisms of high light acclimation in Phaeodactylum tricornutum using an integrated approach involving global transcriptional profiling, metabolite profiling and variable fluorescence technique. Algae cultures were acclimated to low light (LL), after which the cultures were transferred to high light (HL). Molecular, metabolic and physiological responses were studied at time points 0.5 h, 3 h, 6 h, 12 h, 24 h and 48 h after transfer to HL conditions. The integrated results indicate that the acclimation mechanisms in diatoms can be divided into an initial response phase (0–0.5 h), an intermediate acclimation phase (3–12 h) and a late acclimation phase (12–48 h). The initial phase is recognized by strong and rapid regulation of genes encoding proteins involved in photosynthesis, pigment metabolism and reactive oxygen species (ROS) scavenging systems. A significant increase in light protecting metabolites occur together with the induction of transcriptional processes involved in protection of cellular structures at this early phase. During the following phases, the metabolite profiling display a pronounced decrease in light harvesting pigments, whereas the variable fluorescence measurements show that the photosynthetic capacity increases strongly during the late acclimation phase. We show that P. tricornutum is capable of swift and efficient execution of photoprotective mechanisms, followed by changes in the composition of the photosynthetic machinery that enable the diatoms to utilize the excess energy available in HL. Central molecular players in light protection and acclimation to high irradiance have been identified. © 2009 Nymark et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Short-term temperature effects on photosynthesis were investigated by measuring O-2 production, PSII-fluorescence kinetics, and C-14-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 degrees C and 80 mu mol photons . m(-2) . s(-1). Photosynthesis versus irradiance curves were measured at seven temperatures (0 degrees C-30 degrees C) by all three approaches. The maximum photosynthetic rate (P-max(C)) was strongly stimulated by temperature, reached an optimum for Pro. minimum only (20 degrees C-25 degrees C), and showed a similar relative temperature response for the three applied methods, with Q(10) ranging from 1.7 to 3.5. The maximum light utilization coefficient (alpha(C)) was insensitive or decreased slightly with increasing temperature. Absolute rates of O-2 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 O-2 production and measured O-2 production and C-14 assimilation showed a species-specific correlation, with 1.2-3.3 times higher absolute values of P-max(C) and alpha(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 O-2 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.

Photosynthetic diatoms that live suspended throughout the water column will constantly be swept up and down by vertical mixing. When returned to the photic zone after experiencing longer periods in darkness, mechanisms exist that enable the diatoms both to survive sudden light exposure and immediately utilize the available energy in photosynthesis and growth. We have investigated both the response to prolonged darkness and the re-acclimation to moderate intensity white irradiance (E = 100 µmol m−2 s−1) in the diatom Phaeodactylum tricornutum, using an integrated approach involving global transcriptional profiling, pigment analyses, imaging and photo-physiological measurements. The responses were studied during continuous white light, after 48 h of dark treatment and after 0.5 h, 6 h, and 24 h of re-exposure to the initial irradiance. The analyses resulted in several intriguing findings. Dark treatment of the cells led to 1) significantly decreased nuclear transcriptional activity, 2) distinct intracellular changes, 3) fixed ratios of the light-harvesting pigments despite a decrease in the total cell pigment pool, and 4) only a minor drop in photosynthetic efficiency (ΦPSII_max). Re-introduction of the cells to the initial light conditions revealed 5) distinct expression profiles for nuclear genes involved in photosynthesis and those involved in photoprotection, 6) rapid rise in photosynthetic parameters (α and rETRmax) within 0.5 h of re-exposure to light despite a very modest de novo synthesis of photosynthetic compounds, and 7) increasingly efficient resonance energy transfer from fucoxanthin chlorophyll a/c-binding protein complexes to photosystem II reaction centers during the first 0.5 h, supporting the observations stated in 6). In summary, the results show that despite extensive transcriptional, metabolic and intracellular changes, the ability of cells to perform photosynthesis was kept intact during the length of the experiment. We conclude that P. tricornutum maintains a functional photosynthetic apparatus during dark periods that enables prompt recovery upon re-illumination. © 2013 Nymark et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Vegetated coastal and marine habitats in the Nordic region include salt marshes, eelgrass meadows and, in particular, brown macroalgae (kelp forests and rockweed beds). Such habitats contribute to storage of organic carbon (Blue Carbon – BC) and support coastal protection, biodiversity and water quality. Protection and restoration of these habitats therefore have the potential to deliver climate change mitigation and co-benefits. Here we present the existing knowledge on Nordic BC habitats in terms of habitat area, C-stocks and sequestration rates, co-benefits, policies and management status to inspire a coherent Nordic BC roadmap. The area extent of BC habitats in the region is incompletely assessed, but available information sums up to 1,440 km2 salt marshes, 1,861 (potentially 2,735) km2 seagrass meadows, and 16,532 km2 (potentially 130,735 km2, including coarse Greenland estimates) brown macroalgae, yielding a total of 19,833 (potentially 134,910) km2. Saltmarshes and seagrass meadows have experienced major declines over the past century, while macroalgal trends are more diverse. Based on limited salt marsh data, sediment C-stocks average 3,311 g Corg m-2 (top 40-100 cm) and sequestration rates average 142 g Corg m-2 yr-1. Eelgrass C-stocks average 2,414 g Corg m-2 (top 25 cm) and initial data for sequestration rates range 5-33 g Corg m-2, quantified for one Greenland site and one short term restoration. For Nordic brown macroalgae, peer-reviewed estimates of sediment C-stock and sequestration are lacking. Overall, the review reveals substantial Nordic BC-stocks, but highlights that evidence is still insufficient to provide a robust estimate of all Nordic BC-stocks and sequestration rates. Needed are better quantification of habitat area, C-stocks and fluxes, particularly for macroalgae, as well as identification of target areas for BC management. The review also points to directives and regulations protecting Nordic marine vegetation, and local restoration initiatives with potential to increase C-sequestration but underlines that increased coordination at national and Nordic scales and across sectors is needed. We propose a Nordic BC roadmap for science and management to maximize the potential of BC habitats to mitigate climate change and support coastal protection, biodiversity and additional ecosystem functions.

Short-term temperature effects on photosynthesis were investigated by measuring O2 production, PSII-fluorescence kinetics, and 14C-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 oC and 80 umol photons m-2 s-1. Photosynthesis versus irradiance curves were measured at seven temperatures (0oC to 30oC) by all three approaches. The maximum photosynthetic rate (PCmax) was strongly stimulated by temperature, reached an optimum for Pro. minimum only (20oC–25oC), 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 (alfaC) 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 14C assimilation showed a species-specific correlation, with 1.2–3.3 times higher absolute values of PCmax and alfaC 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.

Short-term temperature effects on respiration and photosynthesis were investigated in intact diatom-dominated benthic communities, collected at 2 temperate and 1 high-arctic subtidal sites. Areal rates of total (TOE) and diffusive (DOE) O2 exchange were determined from O2-microsen- sor measurements in intact sediment cores in the temperature range from 0 to 24°C in darkness and at 140 µmol photons m -2 s -1 . In darkness, the O2 consumption increased exponentially with increas- ing temperature for both TOE and DOE, and no optimum temperature was observed within the applied temperature range. Q10 was calculated from the linear slope in Arrhenius plots and ranged between 1.7 and 3.3 at the respective sites. The volume-specific rate (Rdark,vol) solely representing the biological temperature response was somewhat stronger, with Q10 values of 2.6 to 5.2. The Q10 values were overall not correlated to the in situ water temperature or geographical position. Accordingly, no difference in the temperature acclimation or adaptation strategy of the microbial community was observed. Slurred oxic sediment samples showed a Q10 of 1.7 and were, hence, lower than estimates based on intact sediment core measurements. This can be ascribed to changes in physical and biolog- ical controls during resuspension. Gross photosynthesis was measured with the light-dark shift method at the 2 temperate sites. Both areal (Pgross) and volumetric (Pgross,vol) rates increased with tem- perature to an optimum temperature at 12 and 15°C, with a Q10 for Pgross of 2.2 and 2.6 for the 2 sites, respectively. The gross photosynthesis response could be categorised as psychrotrophic for both sites and no temperature adaptation was observed between the 2 sites. Our measurements document that temperature stimulates heterotrophic activity more than gross photosynthesis, and that the benthic communities gradually become heterotrophic with increasing temperature. This has implications for C-cycling in shallow water communities experiencing seasonal and diel temperature fluctuations.

There is an increasing focus on ecosystem services provided by macroalgae worldwide, many which depend on its structural and morphological characteristics. Here we investigated how characteristics of canopy kelp plants of Laminaria hyperborea varies along the Norwegian part of the NE Atlantic. Ten characteristics related to size, allometry, density, biomass and epiphytes were analyzed along wide gradients of depth, wave exposure and latitude. The analyses were performed on a compiled dataset of 630 scuba samples from different research and monitoring projects along the Norwegian coast (58-71°N). The largest kelps, highest biomass, and highest biomass of epiphytic algae was found in Mid-Norway (63-65°N). While most size-related kelp characteristics were reduced with water depth, they were enlarged with wave exposure. The developed statistical models can be used to calculate site-specific values (and their variation) of the different characteristics at any location based on latitude, depth and wave exposure. These can further be used to map kelp derived ecosystem services. We predicted region-specific estimates of total plant weight, kelp density and kelp biomass. Moreover, the models were applied to estimate living biomass (56 million tonnes fresh weight), carbon standing stock (2.6 million tonnes carbon or 9.5 million tonnes CO2), and carbon sequestration potential (0.46 million tonnes per year) for the Norwegian kelp forests, that were estimated to cover about 5 355 km2. The site- and region-specific estimates are relevant to kelp forest management and for blue carbon accountings.