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Cullen, John

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  • ItemOpen Access
    Methyl iodide in the NW Atlantic; spatial and seasonal variation
    (American Geophysical Union, Washington, DC, 2009) Wang, Lu; Moore, Robert M.; Cullen, John J.
    While the global ocean is an important source of atmospheric methyl iodide (CH (sub 3) I), the major producers of CH (sub 3) I within the ocean remain unclear. During a seasonal study in the NW Atlantic, the relationship between CH (sub 3) I and some characteristic phytoplankton pigments was examined in order to identify possible phytoplankton producers of CH (sub 3) I. Although no characteristic pigments exhibited a strong positive correlation with CH (sub 3) I, in the surface mixed layer, there was a weak correlation (R=0.35, n=70, p=0.003) between the concentrations of CH (sub 3) I and zeaxanthin, a pigment characteristic of cyanobacteria in the open ocean. In this study, a moderate correlation was observed between the surface mixed layer CH (sub 3) I concentration and depth-averaged daily radiant exposure (R=0.61, n=15, p=0.02), which indicates a positive influence of solar radiation on CH (sub 3) I production. However, the results from this study do not conclusively show whether the influence was exerted through photochemistry or other pathways. A positive correlation between the CH (sub 3) I concentration and sea surface temperature was also observed (R=0.61, n=79, p<<0.001).
  • ItemOpen Access
    Inferred influence of nutrient availability on the relationship between Sun-induced chlorophyll fluorescence and incident irradiance in the Bering Sea
    (American Geophysical Union, 2000 Florida Ave., N.W. Washington DC 20009 USA, [mailto:service@agu.org], [URL:http://www.agu.org], 2008-08) Schallenberg, Christina; Lewis, Marlon R.; Dan E Kelley,; Cullen, John J.
    This study examines variability in the relationship between Sun-induced chlorophyll fluorescence and incident solar irradiance as a potential diagnostic of the nutritional status of phytoplankton. The study site is the Bering Sea, where two optical drifters were caught for more than 100 days in an anticyclonic eddy, while two others provided data from adjacent waters. Estimates of fluorescence emission normalized to the absorption of light by pigments were analyzed as a function of irradiance to describe variability of the quantum yield of fluorescence. Yields in bright sunlight and under lower light varied by a factor of 5 or more on the scale of days to weeks. For the one drifter that remained in the high-velocity region of the eddy, there was a lagged correlation between the eddy rotation period and fluorescence parameters, with higher fluorescence yields in both low and high irradiance associated with slower rotation. Since nutrient input to the photic zone may increase with increasing shear of the eddy flow, this is consistent with the established suggestion that Sun-induced fluorescence increases with nutrient stress in phytoplankton. Independent measurements of variable fluorescence (/, an indicator of photosynthetic efficiency) further support this interpretation. However, modeling shows that the established hypothesis of competition between photosynthesis and fluorescence for absorbed photons (i.e., photochemical quenching), with high fluorescence yields reflecting photosynthetic debility, does not apply near the sea surface, where photosynthesis is saturated, and dissipation of excess absorbed radiation by nonphotochemical quenching is the dominant influence on fluorescence yield.
  • ItemOpen Access
    Ocean Fertilization Science, Policy, and Commerce
    (2009-09) Strong, Aaron L.; Cullen, John J.; Chisholm, Sallie W.
    Over the past 20 years there has been growing interest in the concept of fertilizing the ocean with iron to abate global warming. This interest was catalyzed by basic scientific experiments showing that iron limits primary production in certain regions of the ocean. The approach-considered a form of "geoengineering"-is to induce phytoplankton blooms through iron addition, with the goal of producing organic particles that sink to the deep ocean, sequestering carbon from the atmosphere. With the controversy surrounding the most recent scientific iron fertilization experiment in the Southern Ocean (LOHAFEX) and the ongoing discussion about restrictions on large-scale iron fertilization activities by the London Convention, the debate about the potential use of iron fertilization for geoengineering has never been more public or more pronounced. To help inform this debate, we present a synoptic view of the two-decade history of iron fertilization, from scientific experiments to commercial enterprises designed to trade credits for ocean fertilization on a developing carbon market. Throughout these two decades there has been a repeated cycle: Scientific experiments are followed by media and commercial interest and this triggers calls for caution and the need for more experiments. Over the years, some scientists have repeatedly pointed out that the idea is both unproven and potentially ecologically disruptive, and models have consistently shown that at the limit, the approach could not substantially change the trajectory of global warming. Yet, interest and investment in ocean fertilization as a climate mitigation strategy have only grown and intensified, fueling media reports that have misconstrued scientific results, and conflated scientific experimentation with geoengineering. We suggest that it is time to break this two-decade cycle, and argue that we know enough about ocean fertilization to say that it should not be considered further as a means to mitigate climate change. But, ocean fertilization research should not be halted: if used appropriately and applied to testable hypotheses, it is a powerful research tool for understanding the responses of ocean ecosystems in the context of climate change.
  • ItemOpen Access
    Primary Production Estimates from Recordings of Solar Stimulated Fluorescence in the Equatorial Pacific at 150-Degrees-W
    (1992-01) STEGMANN, PM; LEWIS, MR; DAVIS, CO; CULLEN, JJ
    Biological, optical, and hydrographical data were collected on the WEC88 cruise along 150-degrees-W and during a 6-day time series station on the equator during February/March 1988. This area was characterized by a subsurface chlorophyll maximum (SCM), located at 50-70 m depth at the equator and descending down to 120-125 m at the north and south end of the transect. Highest primary production rates were near-surface and confined to the equatorial region and stations between 7-degrees and 11-degrees-N. To determine the relationship between solar-stimulated fluorescence (centered at 683 nm wavelength) and primary production, a production-fluorescence model based on phytoplankton physiology and marine optics is described. Results of model calculations predict that there is a linear relation between production and fluorescence. A comparison between morning and midday measurements of the production-fluorescence relation showed that there was some difference between the two, whereas evening measurements, on the other hand, were distinctly different from the morning/midday ones. This seems to suggest that diurnal variations contribute significantly to variability in the quantum yield of photochemical processes. The ratio of the quantum yield of photosynthesis to the quantum yield of fluorescence (PHI(c)/PHI(f)), the parameter which will determine how well production can be estimated from optical recordings, ranged between 0.24 and 0.44 molC Ein-1 (an Einstein equals a mole of photons) for all stations. The highest value for this ratio occurred at the equatorial stations, indicating that interstation (i.e., latitudinal) variability could have an effect on the production-fluorescence relation. Measured (with C-14 incubations) and predicted production compared quite well, although high measured production rates for near-surface samples were underestimated in most cases. Since both production and fluorescence were nonlinear at high irradiance intensities, we recommend in the future that a nonlinear component be incorporated into our model to take this effect into account and thus allow us to refine our estimates of nonlinear data.
  • ItemOpen Access
    Changes in buoyancy and chemical composition during growth of a coastal marine diatom: Ecological and biogeochemical consequences
    (1995) Richardson, Tammi L.; Cullen, John J.
    Growth and sinking of the coastal marine diatom Thalassiosira weissflogii was studied during experiments in a 2.1 m tall water column. Under nutrient-replete conditions, T. weissflogii grew rapidly in the upper layer of the tank and cells exhibited nearly neutral buoyancy. Cells sank, however, after depletion of ambient nitrate. The growth and sinking of cells were well described by a simple model with nitrate-dependent growth and sinking terms. The best fit was obtained by describing the sinking response with a sigmoid function, where the time scale for increased sinking was 25 h after nitrate depletion. Smaller-scale batch culture experiments showed changes that were consistent with increased sinking upon depletion of nitrate: carbohydrate per ml of culture increased 2- to 5-fold over 3.5 d, while protein per ml did not change significantly. After re-introduction of nitrate into the medium, carbohydrate:protein ratios reverted to their original values. Calculations show that intracellular density and cell sinking rate should change substantially due to fluctuations in carbohydrate and that increased ballast of carbohydrate was sufficient to cause the sinking observed in the tank. Changes in the buoyancy of small (15 mu-m) diatoms such as T. weissflogii in response to changes in nutrient status have important ecological and biogeochemical implications. Nutrient-dependent changes in sinking rates can result in increased residence time of cells in the mixed layer of the ocean, and in enhanced transport of deep nutrients to the euphotic zone uncoupled from inputs of inorganic carbon.
  • ItemOpen Access
    Effect of Uv-Radiation on Phytoplankton
    (1995) SMITH, RC; CULLEN, JJ
    No abstract available.
  • ItemOpen Access
    Inhibition of marine photosynthesis by ultraviolet radiation: Variable sensitivity of phytoplankton in the Weddell-Scotia Confluence during the austral spring
    (1998-05) Neale, PJ; Cullen, JJ; Davis, RF
    To assess the potential impacts of ozone depletion on photosynthesis in the Southern Ocean, we need to know more about effects of ultraviolet radiation (UV) on phytoplankton in Antarctic waters, where, in addition to variable stratospheric ozone, temporal and regional differences in vertical mixing might influence photosynthesis and photoacclimation of phytoplankton assemblages. Toward this end, we quantified the responses to UV of Antarctic phytoplankton in the Weddell-Scotia Confluence during the austral spring of 1993. Experimental results on spectral sensitivity of photosynthesis were fit statistically to a model-that incorporated uninhibited photosynthesis as a function of photosynthetically available radiation (PAR), wavelength-dependence of inhibition, and the kinetics of photosynthesis during exposure to UV. In contrast to previous results on UV-induced photoinhibition in a diatom culture at 20 degrees C, natural phytoplankton from open waters of the Antarctic showed no ability to counter UV-induced inhibition of photosynthesis during exposures of 0.5-4 h: the rate of photosynthesis declined exponentially as a function of cumulative exposure, and inhibition was not reversed during incubations for up to 3.5 h under benign conditions. The results suggest that nonlinear exposure-response relationships are necessary for modeling UV-dependent photosynthesis in the surface mixed layer of the springtime Weddell-Scotia Confluence. Consequently, we modified our laboratory-based model of photosynthesis and photoinhibition to describe photoinhibition as a nonlinear function of biologically weighted cumulative exposure to damaging irradiance. The model described similar to 90% of the spectrally dependent experimental variation in photosynthetic rate, and yielded six biological weighting functions (BWFs) for phytoplankton in the Weddell-Scotia Confluence. Assemblages from different stations showed substantial variability in sensitivity to UV. Tolerance of UV was generally highest in assemblages from shallower mixed layers, which presumably had experienced higher irradiance, including W, prior to sampling. The BWFs of assemblages that seemed acclimated to low irradiance showed the highest sensitivity to UV yet seen for Southern Ocean phytoplankton. The pattern of UV sensitivity was consistent with acclimation, but also with selection against less tolerant species.
  • ItemOpen Access
    Fine-Scale Vertical Resolution of Chlorophyll and Photosynthetic Parameters in Shallow-Water Benthos
    (1995-06) MACINTYRE, HL; CULLEN, JJ
    The vertical distributions of chlorophyll concentration and photosynthetic parameters of sediment-associated microalgae were measured with a resolution of 1 mm. Sediment and the overlying water were sampled at 3 sandy, shallow-water sites near Corpus Christi Bay, Texas, USA. All sediment samples had a floc in the surficial millimeter that contained as much as or more chlorophyll than the 0.2 to 0.6 m of water overlying them. The photosynthetic responses of the sediment-associated microalgae were comparable with those of the suspended phytoplankton. Below the surficial floc, constancy of chlorophyll concentration and photosynthetic-irradiance (PI) responses indicated the existence of a physically mixed layer in the underlying 8 to 15 mm. Photosynthetically competent algae were found below the mixed layer and well below the depth to which Light penetrates the sediment (ca 1 mm). Primary production was more or less equally distributed between the surficial millimeter of benthos and the overlying water. The surficial flee and some of the underlying sediment may be readily resuspended so that 'benthic' microalgae can contribute significantly to both water column and benthic primary production.
  • ItemOpen Access
    Mapping coastal optical and biogeochemical variability using an autonomous underwater vehicle and a new bio-optical inversion algorithm
    (2004-08) Brown, CA; Huot, Y.; Purcell, MJ; Cullen, JJ; Lewis, MR
    Autonomous underwater vehicles (AUVs) can map water conditions at high spatial ( horizontal and vertical) and temporal resolution, including under cloudy conditions when satellite and airborne remote sensing are not feasible. Applications of this technology are numerous, and harnessing the full potential of AUV platforms for oceanographic research will require innovative sampling and data processing techniques, particularly in shallow littoral environments. We deployed a passive radiometer on a small AUV called the Remote Environmental Monitoring UnitS (REMUS; Hydroid) to demonstrate a novel method that uses one optical sensor at depth to characterize variability in underwater clarity and the constituents of coastal seawater (i.e., dissolved organic material, algal biomass, and other particles). This approach uses spectral differences between attenuation coefficients that are computed from ratios of downwelling irradiance measured at one depth assuming a constant shape, but not magnitude, for the solar irradiance spectrum at the surface. A spectral inversion model provides estimates of the absorption coefficients ( m(-1)) of the constituents above the sensor. There is no requirement for sensors at the ocean surface using this approach and, compared to inversion methods for subsurface reflectance, the effects of bottom reflectance in shallow waters are minimal. Maps of biooptical properties at high spatial resolution demonstrate that our approach can be used for characterizing shallow and highly variable coastal waters. This simple and robust technique is also applicable to other in situ sampling platforms ( e. g., gliders, moorings, Argo floats).
  • ItemOpen Access
    Relationships between vertical mixing and photoadaptation of phytoplankton: Similarity criteria
    (1984-03) Lewis, M. R.; Cullen, J. J.; Platt, T.
    In their natural environment phytoplankton are exposed to fluctuations in incident irradiance due to vertical displacements in the water column induced by turbulent fluid motion. A reaction-diffusion model is analyzed to determine the physical conditions under which a given physiological adaptation would be of ecological importance.
  • ItemOpen Access
    Biooptical Inferences from Chlorophyll-a Fluorescence - what Kind of Fluorescence is Measured in Flow-Cytometry
    (1989-12) NEALE, PJ; CULLEN, JJ; YENTSCH, CM
    No abstract available.
  • ItemOpen Access
    Spectrally weighted transparency in models of water-column photosynthesis and photoinhibition by ultraviolet radiation
    (2004) Lehmann, Moritz K.; Davis, Richard F.; Huot, Yannick; Cullen, John J.
    We present a simple method for describing the influence of variable attenuation of spectral irradiance, Kd(lambda), on water-column photosynthesis and its inhibition by ultraviolet radiation (UV). The approach is based on weighted water transparency, a calculation introduced by Vincent et al. 1998 (Ann Glaciol 27:691-696). Key results of a depth- and spectrally-resolved model of photosynthesis can be reproduced for a broad range of water types by simple parameterizations using a reference solar irradiance spectrum at the surface and water transparency (1/Kd(lambda)) weighted spectrally for biological effectiveness. Transparency that has been weighted spectrally by the normalized product of irradiance and photosynthetic absorption (PUR-weighted transparency, TPURW) describes spectral effects on photosynthesis in the water column. An empirical parameterization of transparency weighted by the product of surface irradiance and the biological weighting function for inhibition of photosynthesis (TPIRW), along with TPURW, describes the inhibition of water-column photosynthesis relative to the uninhibited rate. Our approach is directly compared with an analysis that used weighted transparency as an indicator of the potential for inhibition of photosynthesis by UV as influenced by variations in chromophoric dissolved organic matter associated with climate change over the past 6000 yr (Pienitz & Vincent 2000, Nature 404:484-487). Results demonstrate how weighted transparency, used as an indicator of potential inhibition, can be transformed into a predictor of biological effects.
  • ItemOpen Access
    Vertical migration, nutrition and toxicity in the dinoflagellate Alexandrium tamarense
    (1997) Macintyre, J. Geoff; Cullen, John J.; Cembella, Allan D.
    The effect of nitrate-N availability on paralytic shellfish toxin production by the dinoflagellate Alexandrium tamarense was studied in a vertically stratified laboratory water column (tank) where swimming behavior could influence photosynthesis and nutrition. Results were compared with those from batch and semi-continuous cultures in which migratory behavior was not a factor. The batch and semi-continuous cultures demonstrated a direct positive relationship between N availability and toxin content. Steady-state cultures, maintained at 2 contrasting rates of semi-continuous N supply, also demonstrated significantly different cellular toxin profiles (relative proportion of toxins). The tank experiment was carried out in a 2.1 m PVC cylinder (0.29 m internal diameter) and lasted for 24 d. Initially, nitrate was replete throughout the water column (50 mu-M) and the highly toxic cells formed a thin surface layer which persisted throughout the 14 h light:10 h dark cycle. When nitrate was depleted in the surface layer as a result of uptake by the phytoplankton, the cells began a nocturnal migration to the nitracline. During this phase the toxin content of the cells decreased gradually as the C:N of the cells increased. In the third phase, the deep nitrate pool was exhausted and the cells penetrated deeper during the dark period. The toxin content of the cells reached the lowest level during this phase. When nitrate was added to the deep layer, a fourth phase began, during which nocturnal descent of the migrating cells was again restricted to the nitracline; toxicity of the cells increased and C:N declined. Finally, N was added to the surface layer. During this fifth and final phase, cellular toxicity continued to rise, C:N declined further, and the cells continued to migrate to the thermocline during the dark period. The toxicity of the cells during the N-stratified phases of the water column experiment was intermediate between the N-replete and N-depleted phases, indicating that A. tamarense is capable of producing PSP toxins from N acquired during a nocturnal descent. It is concluded that toxic dinoflagellates inhabiting N-depleted coastal waters are likely capable of sustaining growth and a moderate level of toxicity through nocturnal migrations to deep N pools.
  • ItemOpen Access
    New production in the warm waters of the Tropical Pacific Ocean
    (1994) Pena, MA; Lewis, M. R.; Cullen, J. J.
    The average depth-integrated rate of new production in the tropical Pacific Ocean was estimated from a calculation of horizontal and vertical nitrate balance over the region enclosed by the climatological 26 degree C isotherm. The net turbulent flux of nitrate into the region was computed in terms of the climatological net surface heat flux and the nitrate-temperature relationship at the base of the 26 degree C isotherm. The net advective transport of nitrate into the region was estimated using the mean nitrate distribution obtained from the analysis of historical data and previous results of a general circulation model of the tropical Pacific. The rate of new production resulting from vertical turbulent fluxes of nitrate was found to be similar in magnitude to that due to advective transport. Most (about 75%) of the advective input of nitrate was due to the horizontal transport of nutrient-rich water from the eastern equatorial region rather than from equatorial upwelling.
  • ItemOpen Access
    Distributions of Pigments and Primary Production in a Gulf-Stream Meander
    (1993-08) LOHRENZ, SE; CULLEN, JJ; PHINNEY, DA; OLSON, DB; YENTSCH, CS
    An investigation was made of physical effects of Gulf Stream meandering on the vertical and horizontal distributions of photosynthetic pigments and primary production. Cruises were conducted in the vicinity of a meander east of 73-degrees-W and north of 37-degrees-N from September 21 to October 5 (leg 1) and October 12-21, 1988 (leg 2), on the R/V Cape Hatteras. Relationships of photosynthesis (normalized to chlorophyll) to irradiance (P-1) did not show large horizontal variation, and water column composite P-I curves from leg 1 and leg 2 were similar. Therefore a single P-I curve derived from pooled data was used to model distributions of primary production. Distributions of photosynthetic pigments were characterized on the basis of in vivo fluorescence profiles and empirical relationships with extracted pigment concentrations. Subsurface irradiance was described using a spectral irradiance model. Cross sections of the Gulf Stream revealed consistently higher pigment concentrations and primary production on the slope water side. Along-stream variations in pigment distributions and primary production were apparently related to density structure influenced by meander circulation. Such variations were less pronounced during leg 2. which came after a transition from a well-defined meander interacting with a warm-core ring (leg 1) to a more linear stream (leg 2). Higher water-column-integrated primary production during leg 2 was attributed to mixing-induced nutrient injection and redistribution of chlorophyll in the photic zone.
  • ItemOpen Access
    Primary production by suspended and benthic microalgae in a turbid estuary: Time-scales of variability in San Antonio Bay, Texas
    (1996-12) MacIntyre, HL; Cullen, JJ
    The within-day, between-day and month-to-month variability of light attenuation and microalgal chlorophyll a (chl a) and photosynthetic response was measured in San Antonio Bay, Texas, USA. Waters were shallow (<2 m) and turbid (attenuation coefficients of 0.7 to 15.3 m(-1), yet daily rates of primary production (0.1 to 2.5 g C m(-2) d(-1)) were comparable to those in much deeper and clearer estuaries. Chl a concentrations in the sediment (459 to 7837 mg m(-3) in the surficial millimeter) were much higher than those in the water column (4 to 48 mg m(-3)). The benthic assemblages were photosynthetically competent, but daily benthic primary productivity was low (0.00 to 0.09 g C m(-2) d(-1); an average of 2 % of productivity in the water column) because of the very low irradiances at the sediment-water interface. The high rates of production by the suspended microalgae were largely due to high chlorophyll-specific light-saturated rates of photosynthesis, P-m(chl) [3.0 to 24.4 g C (g chl a)(-1) h(-1)], which were correlated positively with temperature and inversely with the mean irradiance in the water column. The between-day and temperature-independent variation in P-m(chl) was also correlated with F(v)Chl(-1), an index of the proportion of functional photosystem II reaction centers. In turn, within-day variability in F(v)Chl(-1) was inversely correlated with the mean irradiance in the water column in 8 of 10 observations, a pattern consistent with photoinhibition. A depression of P-m(chl) caused by photoinhibition throughout the water column may therefore be responsible for the inverse trend of P-m(chl) with mean irradiance in the water column. Short-term (h) variability in suspended chl a and turbidity was high (coefficient of variation = 13 to 75 %), but estimates of daily productivity could be predicted with reasonable fidelity (mean error 27 %) from a single midday determination of chl a, the photosynthesis versus irradiance response and the attenuation coefficient, along with daily incident radiation. The predictive power of a single observation was due to coherence in the variation of chl a, P-m(chl) and the attenuation coefficient in the water column: the decrease in mean irradiance caused by resuspension was compensated for by concomitant increases in P-m(chl) and suspended chl a. Between-day variability in productivity of 15 to 52% approached month-to-month differences, so the optimal use of resources in monitoring productivity would be to take single samples daily.
  • ItemOpen Access
    Impact of ultraviolet radiation on marine crustacean zooplankton and ichthyoplankton: a synthesis of results from the estuary and Gulf of St. Lawrence, Canada
    (2000) Browman, HI; Rodriguez, CA; Beland, F.; Cullen, JJ; Davis, RF; Kouwenberg, JHM; Kuhn, PS; McArthur, B.; Runge, JA; St-Pierre, JF; Vetter, RD
    The objectives of the research program reported upon here were (1) to measure ambient levels of UV radiation and determine which variables most strongly affected its attenuation in the waters of the estuary and Gulf of St. Lawrence, Canada; and (2) to investigate the potential direct impacts of UV radiation on species of crustacean zooplankton and fish whose early life stages are planktonic. In this geographic region, productivity-determining biophysical interactions occur in the upper 0 to 30 m of the water column. Measurements of the diffuse attenuation coefficients forultraviolet-B radiation (UV-B, 280 to 320 nm) at various locations in this region indicated maximum 10% depths (the depth to which 10% of the surface energy penetrates at a given wavelength) of 3 to 4 m at a wavelength of 310 nm. Organisms residing in this layer-including the eggs and larvae of Calanus finmarchicus and Atlantic cod Gadus morhua- are exposed to biologically damaging levels of UV radiation. As a result of these physical and biological characteristics, this system offered a relevant opportunity to assess the impacts of UV on subarctic marine ecosystem. Eggs of C. finmarchicus were incubated under the sun, with and without the W-B and/or UV-A (320 to 400 nm) wavebands. UV-exposed eggs exhibited low percent hatching compared to those protected from UV: UV radiation had a strong negative impact on C. finmarchicus eggs. Further, percent hatching in UV-B-exposed eggs was not significantly lower than that in eggs exposed to UV-A only: under natural sunlight, UV-A radiation appeared to be more detrimental to C. finmarchicus embryos than was UV-B. In analogous experiments with Atlantic cod eggs, exposure to UV-B produced a significant negative effect. However, W-A had no negative effect on cod eggs. Additional experiments using a solar simulator (SS) revealed high wavelength-dependent mortality in both C, finmarchicus and cod embryos exposed to UV. The strongest effects occurred under exposures to wavelengths below 312 nm. At the shorter wavelengths (<305 nm) W-B-induced mortality was strongly dose-dependent, but (for both C, finmarchicus and cod) not significantly influenced by dose-rate. Thus, at least within the Limits of the exposures under which the biological weighting functions (BWFs) were generated, reciprocity held. The BWFs derived for UV-B-induced mortality in C. finmarchicus and cod eggs were similar in shape to the action spectrum for UV-B effects on naked DNA. Further, the wavelength-dependence of DNA damage was similar to that for the mortality effect. These observations suggest that W-induced mortality in C, finmarchicus and cod eggs is a direct result of DNA damage. There was no evidence of a detrimental effect of UV-A radiation in these SS-derived results. A mathematical model that includes the BWFs, vertical mixing of eggs, meteorological and hydrographic conditions, and ozone depletion, indicates that UV-induced mortality in the C, finmarchicus egg population could be as high as 32.5%, while the impact on the cod egg population was no more than 1.2%. Variability in cloud cover, water transparency (and the variables that affect it), and vertical distribution and displacement of planktonic organisms within the mixed layer can all have a greater effect on the flux of W-B radiation to which they are exposed than will ozone layer depletion at these latitudes. Our observations indicate that C. finmarchicus and cod eggs present in the first meter of the water column (likely only a small percentage of the total egg populations) are susceptible to UV radiation. However, although exposure to UV can negatively impact crustacean zooplankton and ichthyoplankton populations, these direct effects are Likely minimal within the context of all the other environmental factors that produce the very high levels of mortality typically observed in their planktonic early Life stages. The impact of indirect effects - which may well be of much greater import - has yet to be evaluated.
  • ItemOpen Access
    Phytoplankton Growth and Light-Absorption as Regulated by Light, Temperature, and Nutrients
    (1991-12) KIEFER, DA; CULLEN, JJ
    Numerous studies of the growth of phytoplankton in the laboratory have demonstrated the dependence of cellular pigment concentration and growth rate upon light intensity, photoperiod, temperature, and nutrient supply. These same environmental parameters vary with season in thc polar seas and presumably affect the growth rate and cellular pigment concentration of the phytoplankton crop. Unfortunately, there has not been a complete mathematical description of the interaction of ali four environmental parameters. This study presents an approach to describing these interactions. It can reasonably be assumed that the gross specific growth rate, g, is a function of the specific rate of light absorption: g = PI-GAMMA (1-exp(-a(p) phi(max) E0/PI-theta)). The dependent variables in this equation are g, the gross specific growth rate, PI, the maximum carbon-specific photosynthetic rate, and, theta, the ratio of carbon to chlorophyll. The value of all three dependent variables is constrained. The independent variables are E0, the light intensity (assumed constant during the photoperiod), and GAMMA, the photoperiod (as a fraction of 24 hours) that the cells are illuminated. n is the instantaneous capacity of thc dark reactions to assimilate electrons, while thc product a(p) phi(max) E0/theta is the instantaneous capacity of the light reactions to supply electrons. If the capacity for photochemistry exceeds the capacity for assimilation, dissipative processes occur, and the quantum yield is low. We have applied this equation to thc analysis of the growth and light absorption by Skeletonema costatum cultured under light, temperature, and nutrient limitation. Decreases in nutrient supply and temperature pause decreases in PI and increases in theta; thus both thc capacity for electron supply and utilisation decrease. However, decreases in temperature decrease the capacity for electron assimilation more rapidly than thc capacity for supply; quantum yield drops. Decreases in nutrient supply cause the capacity for supply and assimilation to drop in parallel; quantum yeield is maintained. Decreases in day length cause decreases in theta and increases in PI. Thc capacity to assimilate electrons and the capacity to supply electrons increase in parallel; quantum yield is maintained. Decreases in light intensity cause decreases in both theta and the capacity to supply electrons. Although the changes in PI with light intensity are difficult to assess, the capacity to assimilate electrons appears to ec little changed by light limitation. Quantum yields increase with decreasing light levels.
  • ItemOpen Access
    Retrieval of phytoplankton biomass from simultaneous inversion of reflectance, the diffuse attenuation coefficient, and Sun-induced fluorescence in coastal waters
    (2007-06) Huot, Yannick; Brown, Catherine A.; Cullen, John J.
    [1] A model has been developed to retrieve phytoplankton absorption, a proxy for phytoplankton biomass, from observations of reflectance ( R) and the diffuse attenuation coefficient (K-d) collected by moored radiometers in coastal waters, where high concentrations of chromophoric dissolved organic matter ( CDOM) confound conventional ocean color algorithms. The inversion uses simultaneously two forward models: ( 1) a look-up table (LUT) that accounts for instrument geometry and the effect of the solar angle on both R and Kd and ( 2) an analytical function describing the effects of Sun-induced fluorescence (SIF) of chlorophyll on R. Estimates of phytoplankton biomass ( mostly from SIF), the absorption by colored matter, and the particulate backscattering coefficients ( mostly from the LUT) are obtained by optimizing the amplitude and shape of the absorption and backscattering coefficients in the forward model to best match the observations. An equation describing the quantum yield of fluorescence ( photons fluoresced/photons absorbed) as a function of incident irradiance constrains the model and allows estimates of phytoplankton absorption. Innovations include: the utilization of both R and K-d, providing good separation of the effects of backscattering from absorption; avoidance of reflectance bands between 400 and 600 nm, thereby avoiding interference from bottom reflection and CDOM fluorescence; utilization of the full emission band of SIF; and accounting for the irradiance-dependence of its quantum yield. The model effectively retrieved chlorophyll concentration from an independent data set - r = 0.76, n = 93, with a mean absolute percent error (MAPE) of 24%; this is better than a modern ocean color algorithm (OC4V4) on its validation data set, when restricted to the same range of chlorophyll ( r = 0.67, n = 384, MAPE = 51%).
  • ItemOpen Access
    Modeling the effects of ultraviolet radiation on embryos of Calanus finmarchicus and Atlantic cod (Gadus morhua) in a mixing environment
    (2000-12) Kuhn, Penny S.; Browman, Howard I.; Davis, Richard F.; Cullen, John J.; McArthur, Bruce L.
    It is well established that ultraviolet radiation (UVR, 280-400 nm) harms aquatic organisms. Reductions in productivity have been reported for phytoplankton, ichthyoplankton, and zooplankton in incubations exposed to UVR. It is difficult, however, to estimate the effects of UVR in natural waters. Quantitative assessments of UVR effects on aquatic organisms require high-resolution measurements of solar irradiance and its attenuation in the water, spectral weighting functions for biological effects, and realistic descriptions of the distributions and vertical movements of particles in the water column. Using experimentally determined biological weighting functions for UV-induced mortality along with measurement-based models of solar irradiance and of vertical distributions of embryos as influenced by mixing, we modeled UVR-induced mortality in the early life stages of two key species in the upper estuary and Gulf of St. Lawrence, Atlantic cod (Gadus morhua) and the planktonic copepod, Calanus finmarchicus. G. morhua embryos are insensitive to UVR, with an average daily survival of apprx99% over numerous environmental conditions. C. finmarchicus are considerably more vulnerable, with an average survival of 90% +- 12% (SD). Lowest modeled daily survival was 59% under ambient ozone and 49% under 50% ozone loss. A sensitivity analysis allowed us to examine the relative influences of hydrographic variability, meteorological conditions, and ozone depletion on UVR-induced mortality in C. finmarchicus embryos. The modeled hydrographic and meteorological conditions are a representative range of natural variability for the St. Lawrence region during the 1997 field season, with the exception of extreme ozone depletion (50%). Effects are expressed as relative change of survival normalized to survival under a reference simulation. Similar to other studies, water column mixing and water clarity have the most significant influence on embryo survivorship, with a 3%-80% increased chance of survival when in static, compared with mixed waters, and a 3%-46% increased chance of survival when in the darkest, compared with the clearest waters. Cloudy skies increase survivorship between 1%-30%, and ozone depletion of 50% can decrease survivorship by 9%. On average, ozone depletion decreases survival by 3% and of the factors considered has the smallest influence on mortality of C. finmarchicus embryos.