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The oxygen deficient mesopelagic layer (ODL) off Peru has concentrations below 5 μmol O2 kg–1 and is delimited by a shallow upper oxycline with strong vertical gradient and a more gradual lower oxycline (lOx). Some regions show a narrow band of slightly increased oxygen concentrations within the ODL, an intermediate oxygen layer (iO2). CTD, oxygen and lowered Acoustic Doppler Current Profiler (LADCP, 300 kHz) profiles were taken on the shelf edge and outside down to mostly 2000 m. We evaluate here the acoustic volume backscatter strength of the LADCP signal representing organisms of about 5 mm size. Dominant features of the backscatter profiles were a minimum backscatter strength within the ODL, and just below the lOx a marked backscatter increase reaching a maximum at less than 3.0 μmol O2 kg–1. Below this maximum, the acoustic backscatter strength gradually decreased down to 1000 m below the lOx. The backscatter strength also increased at the iO2 in parallel to the oxygen concentration perturbations marking the iO2. These stable backscatter features were independent of the time of day and the organisms represented by the backscatter had to be adapted to live in this microaerobic environment. During daylight, these stable structures were overlapped by migrating backscatter peaks. Outstanding features of the stable backscatter were that at very low oxygen concentrations, the volume backscatter was linearly related to the oxygen concentration, reaching half peak maximum at less than 2.0 μmol O2 kg–1 below the lOx, and the depth-integrated backscatter of the peak below the lOx was higher than the integral above the Ox. Both features suggest that sufficient organic material produced at the surface reaches to below the ODL to sustain the major fraction of the volume backscatter-producing organisms in the water column. These organisms are adapted to the microaerobic environment so they can position themselves close to the lower oxycline to take advantage of the organic particles sinking out of the ODL.

Marine particulate organic matter (POM) supports the vertical transport of organics in the oceans, and the ecology of microbes and filter feeders. POM is collected on GFF filters and quantified as particulate organic carbon (POC) and nitrogen (PON). The filtrate contains dissolved organic matter (DOM) that partly is abiotically converted into POM and can be collected on GFF filters. We filtered seawater from cultures and the pelagic ocean, after the initial sample filtration yielding the conventional POC/PON sample (POM1), we refiltered the filtrate yielding POM2, refiltering its filtrate we obtained POM3 and so on till POMi. Refiltered POM tended to the same concentration independent of the sample depth and even after a few refiltrations, independent of the original particulate organic load. POM2/POMi for surface water ( 1000 m) was > 1.0. We considered adsorption of DOM and bacteria that had passed through the first filter but concluded that these could not explain the high POM concentration in the filtrates. We suggest that POM in filtrates represent gels formed due to hydraulic stress during filtration. The ratio of POM2/POMi will partly depend on environmental conditions like turbulent energy. We suggest that the increase of POM2/POMi with depth is related to the lower in situ turbulent energy at greater depth. We discuss aspects of POM methodology, including problems with acidification of samples, and the wider ecological implications of our results.

In the ocean, the prokaryote respiration rates dominate the oxidation of organics, but the measurements may be biased due to pre-incubation size filtration and long incubation times. To overcome these difficulties, proxies for microbial respiration rates have been proposed, such as the in vitro and in vivo estimation of electron transport system rates (ETS) based on the reduction of tetrazolium salts. INT (2-(4-Iodophenyl)-3-(4-Nitrophenyl)-5-(Phenyl) Tetrazolium Chloride) is the most commonly applied tetrazolium salt, although it is toxic on time scales of less than 1 h for prokaryotes. This toxicity invalidates the interpretation of the rate of in vivo INT reduction to formazan as a proxy for oxygen consumption rates. We found that with aquatic bacteria, the amount of reduced INT (F, &micro, mol/L formazan) showed excellent relation with the respiration rates prior to INT addition (R, O2 &micro, mol/L/hr), using samples of natural marine microbial communities and cultures of bacteria (V. harveyi) in batch and continuous cultures. We are here relating a physiological rate with the reductive potential of the poisoned cell with units of concentration. The respiration rate in cultures is well related to the cellular potential of microbial cells to reduce INT, despite the state of intoxication.

Recent research has shown that in aquatic systems pairs of prokaryote and eukaryote species exercise symbiotic exchanges of metabolites that are essential for the proliferation of either species. Using dinoflagellate Lingulodinium polyedrum cultures and a factorial design, we examined its growth at different concentrations of vitamin B1 (thiamine) and B12 (cobalamin). When both vitamins were at their lowest concentrations tested, 0.033 pM of B1 and 0.053 pM of B12 the growth was limited. When axenic L. polyedrum was co-cultured with the bacterium Dinoroseobacter shibae, a known B1 and B12 producer, then L. polyedrum grew at the same rate as in culture media supplemented with B1 and B12. In the L. polyedrum vitamin—limited culture (V-L), the abundance of attached and free-living D. shibae was higher than in the vitamin—replete (V-R) culture. In the V-R and V-L co-cultures the measured particulate B12 (pB12) concentration of attached and free-living D. shibae were in the range of 4.7 × 10−19 to 3 × 10−18 and 8.4 × 10−21 to1.2 × 10−19 (mol cell−1), respectively. Without B12 or B7 (biotin) added to the culture medium of a co-culture of L. polyedrum and D. shibae, the measured dissolved B12 (dB12) concentration was more than 60 pM higher than necessary for un-limited growth rates of L. polyedrum. In the same culture we measured B7 in the L. polyedrum particulate fraction (pB7; 4.7 × 10−19 to 9.4 × 10−19 mol cell−1). We suggest that in response to the production of B1 and B12 by D. shibae to supply L. polyedrum requeriments, the latter produced B7, which is required by D. shibae, and in our culture was only produced by L. polyedrum when D. shibae was present. We propose that D. shibae can control L. polyedrum through the release of B1 and B12, and L. polyedrum can control D. shibae through the release of B7. D. shibae is also auxotroph for niacin and 4-amino-benzoic acid, not provided by the culture medium. Therefore, L. polyedrum might affect a similar control through the release of these specific compounds and organic substrate necessary for the growth of D. shibae.

The fate of the Organic Matter (OM) produced by marine life controls the major biogeochemical cycles of the Earth’s system. The OM produced through photosynthesis is either preserved, exported towards sediments or degraded through remineralisation in the water column. The productive Eastern Boundary Upwelling Systems (EBUSs) associated with Oxygen Minimum Zones (OMZs) should foster OM preservation due to low O2 conditions, but their intense and diverse microbial activity should enhance OM degradation. To investigate this contradiction, sediment traps were deployed near the oxycline and in the OMZ core on an instrumented moored line off Peru, providing high temporal resolution O2 series characterizing two seasonal steady states at the upper trap: suboxic ([O2]

Bacteria are the principal consumers of dissolved organic carbon (DOC) in the ocean and predation of bacteria makes organic carbon available to higher trophic levels. The efficiency with which bacteria convert the consumed carbon (C) into biomass (i.e., carbon growth efficiency, Y) determines their ecological as well as biogeochemical role in marine ecosystems. Yet, it is still unclear how changes in temperature will affect Y and, hence, the transfer of consumed C to higher trophic levels. Here, we experimentally investigated the effect of temperature on metabolic functions of coastal microbial communities inoculated in both nutrient-limited chemostats and nutrient–unlimited turbidostats. We inoculated chemostats and turbidostats with coastal microbial communities into seawater culture medium augmented with 20 and 100 μmol L−1 of glucose respectively and measured CO2 production, carbon biomass and cell abundance. Chemostats were cultured between 14 and 26°C and specific growth rates (μ) between 0.05 and 6.0 day−1, turbidostats were cultured between 10 and 26°C with specific growth rates ranging from 28 to 62 day−1. In chemostats under substrate limitation, which is common in the ocean, the specific respiration rate (r, day−1) showed no trend with temperature and was roughly proportional to μ, implying that carbon growth efficiency (Y) displayed no tendency with temperature. The response was very different in turbidostats under temperature-limited, nutrient-repleted growth, here μ increased with temperature but r decreased resulting in an increase of Y with temperature (Q10: 2.6). Comparison of our results with data from the literature on the respiration rate and cell weight of monospecific bacteria indicates that in general the literature data behaved similar to chemostat data, showing no trend in specific respiration with temperature. We conclude that respiration rates of nutrient-limited bacteria measured at a certain temperature cannot be adjusted to different temperatures with a temperature response function similar to Q10 or Arrhenius. However, the cellular respiration rate and carbon demand rate (both: mol C cell−1 day−1) show statistically significant relations with cellular carbon content (mol C cell−1) in chemostats, turbidostats, and the literature data.

In oceanography, a near homogeneous mixed layer extending from the surface to a seasonal thermocline is a common conceptual basis in physics, chemistry, and biology. In a coastal upwelling region 3 km off the coast in the Mexican Pacific, we measured vertical density gradients with a free-rising CTD and temperature gradients with thermographs at 1, 3, and 5 m depths logging every 5 min during more than a year. No significant salinity gradient was observed down to 10 m depth, and the CTD temperature and density gradients showed no pronounced discontinuity that would suggest a near-surface mixed layer. Thermographs generally logged decreasing temperature with depth with gradients higher than 0.2 K m−1 more than half of the time in the summer between 1 and 3 m, 3 and 5 m and in the winter between 1 and 3 m. Some negative temperature gradients were present and gradients were generally highly variable in time with high peaks lasting fractions of hours to hours. These temporal changes were too rapid to be explained by local heating or cooling. The pattern of positive and negative peaks might be explained by vertical stacks of water layers of different temperatures and different horizontal drift vectors. The observed near-surface gradient has implications for turbulent wind energy transfer, vertical exchange of dissolved and particulate water constituents, the interpretation of remotely sensed SST, and horizontal wind-induced transport.

Eukaryotic phytoplankton and bacteria form complex trophic interactions in nature and cultures. The interaction will depend on the spatial arrangement but the architecture of these arrangements has been little investigated. Here we modified a protocol to identify and localize multiple bacterial taxa attached to phytoplankton cells in culture and natural samples, including sensitive dinoflagellates. Samples were embedded in agarose and hybridized simultaneously with different probes of distinct fluorescence properties. Embedding avoided losses or damage of host cells and preserved the attached bacteria during hybridization and washing. Embedding still allowed efficient hybridization and identification of intact host cells. After fluorescence in situ hybridization of the bacteria the phytoplankton host cells, including dinoflagellates were still intact. Digital image stacks taken with a wide field epifluorescence microscope using different excitation–emission wavelength combinations allow the location of the different bacterial groups on the host cell surface and the spatial relationship of the different bacterial groups.

Oxygen minimum zones (OMZs) are important sources of CO2 to the atmosphere when physical forces bring subsurface water with high dissolved inorganic carbon (DIC) to the surface. This study examines, for the first time, the influence of the OMZ of the coastal North Eastern Tropical Pacific off Mexico on surface CO2 fluxes. We use variations in the oxycline depth and subsurface water masses to discern physical oceanographic influences. During two cruises, in November 2009 and August 2010, DIC and total alkalinity (TA) measurements were used to estimate pCO2 and air-sea CO2 fluxes. At the OMZ layer, Subtropical Subsurface Water (StSsW) was found to have high pCO2 values (1290 ± 70 μatm). Due to strong vertical stratification, however, the relationship between ΔpCO2 at the air-sea interface and the oxycline/StSsW upper limit depth was weak. During November, the region was a weak source of CO2 to the atmosphere (up to 2.5 mmol C m−2 d−1), while during August a range of values were observed between −4.4 and 3.3 mmol C m−2 d−1). Strong stratification (>1200 J m−3) prevented subsurface mixing of water from the OMZ to the upper layer; particularly in November 2009 which was during an El Nino event. Results suggest that advection of surface water masses, reinforced by strong vertical stratification, controlled surface pCO2, and air-sea CO2 fluxes.

We measured diel migration with 11 acoustic Doppler current meter profilers and consistently found diel and lunar cycles of vertical migration from 250 m down to the bathypelagic (. 1000 m). These measurements come from year-long deployments in eight locations within the Gulf of Mexico. Diel vertical migration could be characterized, in depth and time, by a pulse of maximum vertical migration activity (PMV), which has a nearly fix phase relation to sunrise and sunset modulated by the lunar cycle. The vertical velocity of migrating biota is in the same direction as the PMV propagation, but it is significantly slower. This difference in velocity implies that the PMV cannot represent the migration pattern of one single population. The lunar cycle is evident down to 1000 m, where the upward migration delays in phase with the full moon. The extension of the diel and lunar cycles over 1000 m depth together with the difference in vertical migration velocity indicate that the surface irradiance signal is transmitted to bathypelagic depth by synchronized depth-tiered populations. A model in which particulate organics are recycled at different depths, similar to a bucket brigade, is consistent with these observations. This daily vertical connectivity is expected to affect the vertical transport of carbon down to the bathypelagic. Zooplankton is a crucial agent in pelagic ecology, linking primary production with higher trophic levels. Zooplankton diel vertical migration is a global phenomenon linking the strata in the ocean transferring organic material toward greater depth (Angel 1989; Buesseler and Boyd 2009). The diel excursion of the ‘sound scattering layer,’ from , 150 m down to , 400 m, is easily observed with echo sounders and serves as a textbook example of negative phototaxis. This migration is commonly explained by a better food supply closer to the surface and predator avoidance by migration to deeper levels during the day, where visual detection is more difficult, a hypothesis calling for strict light control of vertical migration (Cohen and Forward 2009; Ringelberg 2010). The ample literature on diel vertical migration covers aspects of physiological control of the timing, energetic balances, and the effect on vertical transport of organics forming part of the biological carbon pump. Vinogradov (1962) proposed that zooplankton play a role in the vertical transport of organic material within the mesopelagic depth range (bottom of the euphotic zone to 1000 m), suggesting the term ‘ladder of migrations’ for the diel migration of different populations of zooplankton covering different depth ranges. The literature agrees that light triggers the migration; solar eclipses perturb the cycle, and even lunar eclipses have significant effects (Tarling et

In this study we established the B1 and B12 vitamin requirement of the dinoflagellate Lingulodinium polyedrum and the vitamin supply by its associated bacterial community. In previous field studies the B1 and B12 demand of this species was suggested but not experimentally verified. When the axenic vitamin un-supplemented culture (B-ns) of L. polyedrum was inoculated with a coastal bacterial community, the dinoflagellate’s vitamin growth limitation was overcome, reaching the same growth rates as the culture growing in vitamin B1B7B12-supplemented (B-s) medium. Measured B12 concentrations in the B-s and B-ns cultures were both higher than typical coastal concentrations and B12 in the B-s culture was higher than in the B-ns culture. In both B-s and B-ns cultures, the probability of dinoflagellate cells having bacteria attached to the cell surface was similar and in both cultures an average of six bacteria were attached to each dinoflagellate cell. In the B-ns culture the free bacterial community showed significantly higher cell abundance suggesting that unattached bacteria supplied the vitamins. The fluorescence in situ hybridization (FISH) protocol allowed the quantification and identification of three bacterial groups in the same samples of the free and attached epibiotic bacteria for both treatments. The relative composition of these groups was not significantly different and was dominated by Alphaproteobacteria (>89%). To complement the FISH counts, 16S rDNA sequencing targeting the V3–V4 regions was performed using Illumina-MiSeq technology. For both vitamin amendments, the dominant group found was Alphaproteobacteria similar to FISH, but the percentage of Alphaproteobacteria varied between 50 and 95%. Alphaproteobacteria were mainly represented by Marivita sp., a member of the Roseobacter clade, followed by the Gammaproteobacterium Marinobacter flavimaris. Our results show that L. polyedrum is a B1 and B12 auxotroph, and acquire both vitamins from the associated bacterial community in sufficient quantity to sustain the maximum growth rate.

The formation of a diurnal thermocline at few meters depth is difficult to document because of the mixing induced by research platforms. We built a free-rising CTD-platform, including sensors for chlorophyll fluorescence, turbidity, and light, that profiles to ~0.4 m below the surface with better than 0.03 m resolution and at sufficient distance from the research platform to measure an undisturbed water column. The profiler, with a practical maximum depth of 100 m is controlled mechanically using sacrificial weights and a safety tether that assures easy recovery of the instrument. The design concept is easily adapted to many commercial CTD models. Off Baja California, most profiles showed temperature stratification near the surface and some profiles showed near surface chlorophyll fluorescence thin layers; these features would be difficult to observe with normal CTD profilers.

The eastern Pacific intermediate oxygen minimum layer (OML) is particularly well-developed and shoals close to the Mexican coast. We obtained hydrographic profiles including oxygen concentration [O], measured dissolved inorganic carbon (DIC), continuous surface pCO2 in water and air and took biological data south of the Gulf of California in March 2005. The core of the OML, with close to zero [O] was centered around 475 m with a thickness of the core varying between 80 m and 700 m and the upper limit of the core ranging from 500 m to 80 m. At the surface [O] was close to air-saturation and showed no relation with the depth of the OML contrary to DIC and pCO2 concentrations. Below 50-m depth the changes in DIC and Apparent Oxygen Utilization (AOU) yielding a molar ratio of dDIC 5 0.79 3 dAOU. When the OML shoaled, surface temperature, chlorophyll concentration [CHL], and depth-integrated zooplankton increased, resulting in positive correlations among plankton biomass, pCO2, and DIC in surface waters. When [CHL] is recalculated as particulate organic carbon (POC), a linear relationship with the sum of DIC and POC is observed as expected for concomitant transport of DIC and inorganic nutrients supporting POC formation. Neglecting ventilation of carbon into the atmosphere and the production of dissolved organic carbon, the results suggested that , 16% of the carbon transported up from the OML was present in surface waters in the form of POC and the rest in inorganic form.

To model the physiological potential of marine heterotrophic bacteria, their role in the food web, and in the biogeochemical carbon cycle, we need to know their growth efficiency response within a matrix of different temperatures and degrees of organic substrate limitation. In this work, we present one part of this matrix, the carbon growth efficiencies of marine bacteria under different temperatures and nonlimiting organic and inorganic substrate supply. We ran aerobic turbidostats with glucose enriched seawater, inoculated with natural populations of heterotrophic marine bacteria at 10, 14, 18, 22, and 26 degrees C. The average cell-specific growth rates increased with temperature from 1.17 to 2.6 h-1. At steady-state total CO2 production, biomass production [particulate organic carbon (POC) and nitrogen (PON)], and viruslike particle abundance was measured. CO2 production and specific growth rate increased with increasing temperature. Bacterial carbon growth efficiency (BCGE), the particulate carbon produced per dissolved carbon utilized, varied between 0.12 and 0.70. Maximum BCGE values and decreased specific respiration rates occurred at higher temperatures (22 and 26 degrees C) and growth rates. This trend was largely attributable to an increase in POC per cell abundance; when the BCGE was recalculated, parameterizing the biomass as the product of cell concentration and a constant cellular carbon content, the opposite trend was observed.

Chemostats with glucose-enriched seawater and inoculated with natural populations of heterotrophic marine bacteria were run at different dilution rates (0.05 to 1.0 d -1 ), at constant temper- ature (22°C) and with low organic substrate medium (20 μM glucose). The following parameters were measured: cell abundance, POC, PON and total CO2 produced. The results demonstrated an increase in growth efficiency with higher specific growth rates within the growth rate range investigated here that is typical for oceanic samples. The results were parameterized according to the Pirt model, with a maximum efficiency of substrate conversion (e = 0.57) and a specific rate of maintenance metabo- lism (a = 0.41 d -1 ), although the experimental results within the limited growth rate range investi- gated here are not statistically different from a linear relationship. On first principals it can be argued that the growth efficiency has to pass through the origin and have a maximum efficiency below 1.0, thus suggesting an asymptotic relationship like the Pirt model. Applying the iterative method of model parameter adjustment to previously published data, similar growth efficiency versus growth rate relationships were arrived at. Our results confirm that at a particular temperature a proportion- ately higher fraction of dissolved organic material is remineralized in oligotrophic oceans that sup- port lower growth rates than in waters supporting higher growth rates. Consequently, in the latter waters, the efficiency of transfer of dissolved organic material into the particulate form is supposed to be higher.

espanolSe presentan algoritmos que utilizan la profundidad optica de los sensores remotos, 1/K490, para estimar la profundidad de la zona eufotica y las profundidades donde la irradiancia espectral a 490 nm se encuentra a 10%, 3%, 1% y 0.3% del valor incidente en la superficie. Los modelos empiricos lineales resultan de los datos de los perfiles radiometricos medidos en diferentes localidades del Golfo de California durante unos cruceros realizados en 1995, 1997 y 1998. Los modelos se aplicaron en tres provincias bioopticas separadas geograficamente del golfo: la cuenca norte, la zona de las islas y la cuenca sur. La incertidumbre relativa de los modelos de regresion para estimar la profundidad de 1% de luz tanto para la irradiancia espectral (490 nm) como para la EPAR es de aproximadamente 5% en la cuenca norte y de 10% en la cuenca sur. EnglishAlgorithms are presented using remote sensing optical depth, 1/K490, to estimate the depth of the euphotic zone and depths where spectral irradiance at 490 nm are 10%, 3%, 1% and 0.3% of incident surface value. The linear empirical models are derived using data from radiometric profiles measured at various locations in the Gulf of California during cruises in 1995, 1997 and 1998. The models apply to three geographically and temporally separate bio-optical provinces of the gulf: the northern basin, the Midriff Islands and the southern basins. Relative uncertainties of the regression models for the 1% light depths for both spectral irradiance (490 nm) and EPAR range from approximately 5% in the northern basinto 10% in the southern basins.

The abundance of coccoid cyanobacteria was counted within the euphotic zone at a station in Delfín Basin, in the northern Gulf of California, and at a station in the California Current, off Todos Santos Bay, during 1993. The abundance of cyanobacteria at both stations was between 107 and 108 cells L–1. Comparison with other concomitantly sampled parameters, i.e., irradiance, temperature, nutrients and chlorophyll a, showed no significant correlation with the cyanobacterial abundance. The contribution of cyanobacteria to the total in situ chlorophyll a concentration was calculated using the cyanobacterial abundance, an average published value of 1.0fgChl a cell–1 and a reduced pigment extraction efficiency in cyanobacteria. Cyanobacteria contributed, in half of the cases, more than 10% and more than 4% of the total chlorophyll in Delfín Basin and the California Current, respectively. Again, this relative contribution was not related to the other concomitantly measured in situ parameters. In Synechococcus (WH-7803) cultures, the cellular chlorophyll a concentration was measured after extraction by soaking the samples in different solvents: 90% acetone and dimethylsulfoxide/acetone/water (DMSO/acetone). The cellular chlorophyll of WH-7803 extracted with DMSO/acetone was a factor of 1.9 times higher than the cellular chlorophyll concentration extracted with 90% acetone without sonication. Assuming that only the cyanobacteria would yield higher chlorophyll concentrations with DMSO/acetone extraction, then the chlorophyll a concentrations measured with 90% acetone extraction without sonication underestimated, in half of the cases, the real concentrations of in situ chlorophyll a by more than 5% in the northern Gulf of California and more than 2% in the California Current.

The ultraviolet (UV) spectral component of daylight on a clear day at mid-latitudes can significantly reduce phytoplankton pigments within a daylight period. Phytoplankton samples from Redberry Lake, Saskatchewan, dominated by cyanobacteria were incubated in quartz bottles under optical long band-pass filters (cutoff wavelength 420n305 nm) in daylight in June. After incubation, samples were filtered, and in vivo particle light absorption (380n700 nm) and pigment concentrations were measured. Solar ultraviolet-B irradiance (UV-B; 280n320 nm) was measured radiometrically. On sunny days the samples that were exposed to daylight UV light showed a relative decrease in particle absorption and pigment concentration after the incubation compared with samples exposed only to visible daylight. No such decrease was observed during an overcast day. The UV-B data did not show a clear relation with the degree of pigment reduction, suggesting that other environmental factors or the state of adaptation partially controlled the pigment decrease of phytoplankton under UV-B exposure. Neither specific spectral components of the absorption spectrum nor specific pigments were more easily degraded than others by solar UV light, although the ratio of zeaxanthin to chlorophyll a probably increased in cyanobacteria as a result of UV exposure. Resume : La composante spectrale ultraviolet (UV) de la lumire par un jour clair, aux latitudes moyennes, peut rOduire de faAon significative les pigments du phytoplancton au cours diune pOriode diurne. Des Ochantillons de phytoplancton du lac Redberry (Saskatchewan) dominOs par des cyanobactOries ont OtO incubOs dans des bouteilles de quartz sous filtres optiques passe-bande (longueur dionde critique de 420 ‡ 305 nm) ‡ la lumire du jour en juin. Aprs incubation, les Ochantillons ont OtO filtrOs, et on a mesurO in vivo liabsorption de la lumire par les particules (380n700 nm) et les concentrations de pigments. LiOclairement OnergOtique solaire par les ultraviolets B (UV-B; 280n320 nm) a OtO mesurO par radiomOtrie. Les journOes ensoleillOes, on observait dans les Ochantillons exposOs ‡ la lumire ultraviolette du jour une diminution relative de liabsorption par les particules et de la concentration de pigments aprs liincubation par rapport aux Ochantillons exposOs seulement ‡ la lumire visible. Aucune diminution de ce type nia OtO observOe pendant une journOe oo le ciel Otait couvert. Les donnOes sur les UV-B niont pas rOvOlO de relation claire avec le degrO de rOduction des pigments, ce qui permet de penser que diautres facteurs environnementaux, ou le degrO diadaptation, rOgissent en partie la diminution des pigments du phytoplancton exposO aux UV-B. Les UV solaires ne semblaient pas dOgrader certaines composantes spOcifiques du spectre diabsorption ni certains pigments plutUt que diautres, mais le rapport de la zOaxanthine ‡ la chlorophylle a augmentait probablement chez les cyanobactOries ‡ cause de liexposition aux UV. (Traduit par la ROdaction)

Solar-stimulated natural chlorophyll a fluorescence measured by upwelling radiance in the red spectral band could be a fast and noninvasivc method to estimate primary production in aquatic environments if the relationship of primary production to natural fluorescence can be described as a function of easily measured environmental variables, We compared data of natural fluorescence and primary production (14C incubation for 2 h) from the California Current and the Gulf of California. The data confirm that the quantum yield ratio of fluorescence to primary production (4, : $f) is a function of in situ irradiance, but not of nutrient concentration or temperature, as has been reported in the literature. Published data from the subtropics and tropics and our data yield empirical constants that define the irradiance function of the quantum yield ratio, but variability results from ambiguity of the constant determination caused by high variance of the data. Data from the Antarctic are significantly different from the low latitude data. Below a photosynthetic rate of 300 nmol C m-3 s-l, our natural fluorescence data arc useful as a proxy of primary production with a correlation coefficient, r*, of 0.85. Of the unexplained variance (15%), a major portion is due to the C.V. of the primary production method (9.2%). The r2 value of predicted primary production is similar to other published results, which suggests that without further information about the physiology of the phytoplankton it will be difficult to improve the quality of the primary production estimate.

A time series of seston, Secchi depth and chlorophyll a data at a station in Kiel Bight, Western Baltic is evaluated. The time series include 19 years of seston data from 1957 to 1975, 20 years of chlorophyll a data between 1960 and 1989 and 5 years of Secchi depth data between 1965 and 1989. The published chlorophyll a data were corrected according to the results of a comparison of the historic chlorophyll methods with the HPLC method using samples from the location of the reference station. Annual medianLs calculated from logtransformed data from 0 to 15m and between 15 April and 15 October were calculated. The annual medianL seston concentration increased approximately 3.5-fold from 1957 to 1975. The medianLs of Secchi depth decreased from 8.3 m to about 6.1 m between 1965 and 1989 but this trend has low statistical significance because of intra-annual variability. The medianL chlorophyll a concentration shows very strong interannual variation which makes it difficult to quantify a trend in the data, but nevertheless a rank correlation of the chlorophyll medianLs does indicate an increase. The intraannual variability in the chlorophyll data is related to the method used and to the number of data taken per year. It can be concluded that the ecosystem of Kiel Bight has undergone a major change during the period 1957–1975 as demonstrated by seston.

The goal of our project is the bio-optical characterization of dinoflagellate and other red-tide blooms, to facilitate the optical detection and monitoring of these blooms from above the sea surface.

A model is presented that allows the prediction of percent photosynthetically available radiation (PAR) levels from measured profiles of the absorption coefficient at 490 nm in the Gulf of California. Percent PAR levels depend on the diffuse attenuation coefficients of the wavelengths that make up PAR, which in turn depend on the absorption coefficient. The emphasis is on developing a simple but robust model that can be used by researchers to plan deployments of photosynthesis experiments in the Gulf of California.

In order to be able to invert optical remote sensing data, it is necessary to understand the absorption, scattering and attenuation spectra. In this paper we present a study of the vertical distribution and spectra of the inherent optical properties by the particulate and dissolved materials in the Gulf of California. Most of the optical properties in the gulf are dominated by phytoplankton and their by-products (Case I waters). Only in the extreme northwestern region of the gulf were the optical properties dominated by inorganic materials. Typical spectra for the various components are presented. The distribution of the components and their relative contribution to the total optical properties are discussed.

A model is presented which predicts the diffuse attenuation coefficient of downwelling irradiance as a function of depth and the depth of the euphotic zone as based on the one percent level of photosynthetically active radiation from vertical profiles of spectral absorption and attenuation. The model is tested using data obtained in the Gulf of California. The modeled diffuse attenuation coefficients and PAR levels ar shown to have average errors of less than five percent when compared to the measured values.

Remote sensing reflectances measured underwater and above- water in the Gulf of California are compared to evaluate the equivalence between methods. Each form of reflectance is also compared to concurrently measured ratios of scattering to absorption, and the mean backscattering fraction is estimated. Above-water and in-water remote sensing reflectance estimates differ by more than 20 percent, with absolute RMS difference ranging from 0.001 to 0.005. Standard deviations of estimated backscattering fractions are between 15 percent nd 20 percent of the mean at each wavelength.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Thalassiosira gravida was rapidly displaced from ammonium-limited chemostats at moderate (D = 0.03. h-‘) and low (D = 0.01 *h-l) dilution rates by Skeletonema costatum or Chaetoceros septentrionalis. Reduced temperature or reduced light did not favor Thalassiosira. Chaetoceros displaced Skeletonema at D = O.O3*h-’ but the two species coexisted at D = 0.01-h-‘. A brief temperature increase triggered changes in population densities in chemostats with coexisting species, leading to an increase in the less abundant species. Reduced turbulence did not change the pattern of coexistence. Nutrient-dependent growth-rate kinetics for the three species were deduced from rates of displacement in competition experiments and from published uptake kinetic and chemical composition data. The kinetics deduced by the two methods were qualitatively similar. Nutricrit kinetics apparently do not explain the survival of natural populations of T. gruvida in the field. On the basis of these results, a nutrient-based functional group of phytoplankton is defined to include S. costatum and C. septentrionalis and exclude T. gravidu.

Spectral absorption of phytoplankton from cultures and natural samples was measured by means of an integrating-sphere photometer. Measurements on suspension yielded specific absorption coefficients for healthy phytoplankton cultures in collimated light at 675 nm between 0.007 and 0.0 13 m2 (mg Chl a) I. These values were independent of cell density and cell wall material. Natural samples of Kiel harbor water yielded specific absorption coefficients at 675 nm of 0.009 and 0.017 m2 (mg Chl a)- I. The specific absorption coefficients in suspension were dependent on the optical properties of the individual cells (packaging effect), decreasing (ca. l/r) with increasing cell size (r radius) and increasing chlorophyll a content per cell as predicted by theory, but are significantly lower than theoretically expected. Comparison with published values shows that specific absorption coefficients of cell suspensions are often overestimated, presumably because of methodological problems.

The physiological response of ammonium-limited continuous cultures of Skeletonema costatum (Grev.)Cleve to steady-state and transient conditions was tested and compared to simulations with a Droop-type quota model and a four-state variable model (internal amino acid pool added to the quota model). External ammonium, free internal amino acids, protein, silicate and culture-cell volume were measured.All cultures showed reproducible changes in growth and uptake kinetics due to spontaneous cell-cycle synchronization of the populations. Under steady-state conditions protein decreased with increasinggrowth rate from 82%; cell-nitrogen to 52% and free internal amino acids increased from 2·5% cell-nitrogen to 8%. Under transient conditions amino acids could reach 25% of cell-nitrogen.A comparison of model and culture results yielded the following information: Both models could simulate steady-state and most transient conditions. The dependence of the quota on steady-state growth rate is not the result of changes in amino acid or protein pool size. The amino acid pool, an intermediary step in the nitrogen assimilation, does not serve to increase the time lag in growth response significantly. The four-state variable model reproduced under most conditions the behaviour of theamino acid pool without the use of feedback control mechanisms on the rate of uptake. The models could simulate a strong increase in growth rate except when it was initiated by impulse dilution of the culture. Then growth response was controlled by epigenetic mechanisms induction of enzyme synthesis). (6) The maximum nutrient uptake rate per culture cell volume of Skeletonema is inversely related to cell size.

Spectra1 absorption of phytoplankton from cultures and natural samples was measured on filters with various optical setups including collimated and diffuse irradiation and measurements ofwetted filters within an integrating sphere. In suspensions within an integrating sphere, specific absorption coefficients for laboratory cultures varied by a factor of only two. Measurements on filters yielded values dependent on filter load. Specific absorption coefficients derived from measurements of sample filters were considerably higher than values obtained from suspensions in an integrating sphere due to increased diffuseness of irradiance and to pathlength amplification by filter-particle and particle-particle interactions. Measured absorption of phytoplankton in the blue can be increased greatly by absorption of detritus, evident from absorption spectra of depigmented samples on filter. After subtracting detrital absorption, absorption spectra of phytoplankton are qualitatively similar to the corresponding quantum-corrected fluorescence excitation spectra. The detritus-corrected ratio of absorption at 440 vs. 675 nm shows average values between 1 and 1.5. Comparison with published values shows that specific in vivo absorption coefficients of phytoplankton arc mostly overestimated as a result of the methodology applied. In the blue region of the spectrum, overestimation of phytoplankton absorption in field samples is possible if detrital absorption is neglected.

SINCE the review on glucagon that appeared in this journal a year ago1 and recent review articles from the foreign literature2 3 4 a considerable number of interesting new findings on the subject h...

Verschiedene Beobachtungen bei Untersuchungen über den Dithizon- und Alloxan-Diabetes gaben Hinweise dafür, daß dem in den Langerhansschen Inseln des Pankreas histochemisch nachweisbaren Zink eine physiologische Bedeutung zukommt. Das Ziel der vorliegenden Arbeit war, weitere Hinweise für eine solche Rolle des Inselzinks zu gewinnen. 1. Es wurde an Kaninchen gefunden, daß das in den Granula vorliegende Inselzink morphologisch und funktionell auf das engste mit dem Insulin oder dessen unmittelbarer Vorstufe verknüpft ist. 2. Bei hungernden Tieren und nach funktionellen Belastungen in Form von intensiven protrahierten Glucosebelastungen verhielten sich die Insulingranula und das Inselzink gleich. 3. Die histochemisch mit Sicherheit beobachteten Differenzen zwischen dem Inselzink hungernder und mit Glucose belasteter Kaninchen waren durch quantitative Bestimmungen des Gesamtpankreaszinks nicht nachzuweisen; eine Erklärung dafür wurde mit der Tatsache gegeben, daß die Inseln nur etwa 2% des Gesamtpankreas ausmachen, so daß selbst stärkere Schwankungen nicht in Erscheinung treten müssen. Dagegen wird ein Anhalt für den tatsächlichen maximalen Zinkgehalt der Inseln gewonnen, der sich innerhalb der biologischen Schwankungsbreite des Gesamtpankreaszinks bewegen muß. 4. Aus der topographischen Verteilung in den Inselzellen und nach dem Verhalten des Inselzinks unter extremen physiologischen Bedingungen wird geschlossen, daß dem Zink jedenfalls beim Kaninchen eine Bedeutung bei der sogenannten basalen Insulinregulation zukommt. 5. Auf Grund bekannter Tatsachen über den Einfluß von Zink auf die physikalisch-chemischen Eigenschaften vom Insulin ist anzunehmen, daß das physiologische Insulindepot in den Inselzellen als Zinkkomplex vorliegt. 6. Da die Voraussetzung für eine Abgabe des Hormons an das Blut dessen Überführung in eine lösliche Form ist, wird eine primäre Änderung der Zinkbindung durch konkurrierende Komplexbildner postuliert.

1. Das histochemisch nachweisbare Zink in den Langerhansschen Inseln des Pankreas wurde mit der vonOkamoto angegebenen und einer neuen Nativmethode bei verschiedenen Funktionszustanden der Inseln untersucht. 2. Die Inseln hungernder Kaninchen enthalten mehr Zink als die normaler Tiere. Durch intensive Glucosebelastungen last sich das Inselzink weitgehend eliminieren. 3. Durch das intrazellular gelegene Zink werden das diabetogen wirksame Dithizon sicher und Alloxan sehr wahrscheinlich nach der intravenosen Injektion in den Langerhansschen Inseln angereichert. Die Anreicherung der Diabetes erzeugenden Verbindungen ist eine Voraussetzung fur ihre spezifisch zellzerstorende Wirkung. 4. Nachdem das Inselzink weitgehend entfernt wurde, last sich infolgedessen auch kein Alloxandiabetes mehr erzeugen. 5. Auf Grund der Beobachtungen wird angenommen, das das Inselzink eine integrierende Funktion bei dem Vorgang der gesteuerten Insulinausschuttung besitzt.

1. Durch protrahierte Glucosebelastungen konnte das histochemisch nachweisbare Inselzink bei Kaninchen fast vollstandig eliminiert werden.