Phaeocystis colony distribution in the North Atlantic Ocean since 1948, and interpretation of long-term changes in the Phaeocystis hotspot in the North Sea

Monitoring of Phaeocystis since 1948 during the Continuous Plankton Recorder survey indicates that over the last 5.5 decades the distribution of its colonies in the North Atlantic Ocean was not restricted to neritic waters: occurrence was also recorded in the open Atlantic regions sampled, most frequently in the spring. Apparently, environmental conditions in open ocean waters, also those far offshore, are suitable for complete lifecycle development of colonies (the only stage recorded in the survey).In the North Sea the frequency of occurrence was also highest in spring. Its southeastern part was the Phaeocystis abundance hotspot of the whole area covered by the survey. Frequency was especially high before the 1960s and after the 1980s, i.e., in the periods when anthropogenic nutrient enrichment was relatively low. Changes in eutrophication have obviously not been a major cause of long-term Phaeocystis variation in the southeastern North Sea, where total phytoplankton biomass was related significantly to river discharge. Evidence is presented for the suggestion that Phaeocystis abundance in the southern North Sea is to a large extent determined by the amount of Atlantic Ocean water flushed in through the Dover Strait.Since Phaeocystis plays a key role in element fluxes relevant to climate the results presented here have implications for biogeochemical models of cycling of carbon and sulphur. Sea-to-air exchange of CO2 and dimethyl sulphide (DMS) has been calculated on the basis of measurements during single-year cruises. The considerable annual variation in phytoplankton and in its Phaeocystis component reported here does not warrant extrapolation of such figures.</p

58. INTERACTION BETWEEN SEDIMENT AND INTERSTITIAL WATER NEAR THE JAPAN TRENCH, LEG 57, DEEP SEA DRILLING PROJECT

ABSTRACT Analyses of water samples taken by means of an in-hole sampler generally show good agreement with analyses of samples collected by routine shipboard squeezing techniques. At Sites 438 and 439, a decrease in salinity with depth is related to former freshwater flow from an aquifer that crops out at an anticline on a deep sea terrace between Japan and the top of the trench slope of the Japan Trench. This former subaerial recharge suggests significant late Cenozoic subsidence of the terrace, because it now lies at a water depth of 1500 meters. Samples from the trench slope at Site 440 have extremely high values of alkalinity and ammonia, presumably because of a favorable combination of high sedimentation rate and organic carbon content. Diagenetic conditions on the trench slope favor formation of the Fe-Mg carbonate mineral, ankerite; at Site 440 it first occurs at a depth below the sea floor of only 29 meters in late Pleistocene strata. Undissolved diatoms persist to relatively great depth at the sites of Leg 57 because of a low geothermal gradient caused by subduction. Secondary silica lepispheres first appear at 851 meters at the most landward and warmest site, Site 438, in strata 16 million years old with an ambient temperature of 31 °C. SAMPLING AND ANALYTICAL PROCEDURES During Leg 57 Shipboard in-hole data on pH, alkalinity, chlorinity, calcium, and magnesium (except Mg from Site 438) generally show good agreement with the samples obtained by routine shipboard squeezing techniques The results for ammonia and silica were obtained from the overflow water of the in-hole sampler and had to be corrected for dilution by distilled water. Agreement for Site 438 with routinely collected samples is good In general, however, we conclude that the in-hole samples essentially confirm the validity of the interstitial water sample data collected by routine squeezing, even for the minor constituents, silica and ammonia. This is in agreement with the conclusions of Barnes and others (1979). SALINITY DECREASE WITH DEPTH An interesting phenomenon at Sites 438 and 439 (water depth about 1600 m) is a downhole decrease in salinity and chlorinity. The chlorinity at the deepest sample at Site 438 is only about 50 per cent of that of seawater. These data imply that fresh water has been advected to the sites from an outcrop area. A possible source of fresh water is through sandstone and conglomerate layers in the deeper strata of the sites. Because boulders in the conglomerate are very large, 126

Evidence for inhibition of bacterial luminescence by allelochemicals from Fibrocapsa japonica (Raphidophyceae), and the role of light and microalgal growth rate

The marine microalga Fibrocapsa japonica Toriumi and Takano (Raphidophyceae) produces haemolysins, neurotoxins and reactive oxygen species (ROS). To quantify potential effects of such bioactive compounds on surrounding organisms the marine bacterium Vibrio fischeri was exposed to F. japonica culture samples. Inhibition of V. fischeri 's natural luminescence, indicative of impaired metabolism, was related to the number of F. japonica cells added. The effect was fast, within 15 min. It was caused by one, possibly several, excreted substances that were less active after heating. Freezing of culture supernatant partly inactivated these substances, but ROS-scavenging enzymes had no effect. Light enhanced the V. fischeri luminescence inhibition in two ways. The direct effect of light on the action of F. japonica luminescence inhibiter(s) could be described by a saturation curve with maximum effect above 20 mu mol photons m(-2) s(-1). Light also had an indirect effect: biomass production, dependent on light availability, was closely related to the amount of inhibiting compound(s) produced by the alga. Algal growth rate, rather than its cell density, determined the bacterial luminescence inhibition per F. japonica cell, resulting in a 5-fold stronger inhibition at maximum growth rates compared to cells that barely grew during the stationary growth phase. The bioassay with F. japonica and V. fischeri has allowed quantification of the negative effects on bacteria in the microalgal microenvironment. The results presented here suggest that at favourable growth conditions F. japonica releases bioactive compounds that improve its competitive abilities

14C labelling of algal pigments to estimate the contribution of different taxa to primary production in natural seawater

Several attempts have been made in the past to measure taxon-specific growth rates in natural phytoplankton populations in order to evaluate the conditions leading to success of individual taxa, to estimate the specific role of the various taxonomic components of algae in the food web and in nutrient cycling, and to explain succession. The method of Redalje and Laws, who studied the pattern of l4C labelling of Chi a (the pigment common to all microalgae), has now been adapted by following 14C incorpor­ ation into the carotenoids that are tags of taxonomic groups. The results obtained so far indicate that even in oligotrophic regions different species co-occurring in one sample usually incorporate 14C at a very different rate, which suggests that it is not only eutrophic pelagic plankton communities that are subject to rapid shifts in growth conditions. The pigment labelling method is still open to challenge from several directions. More research must be done to transform this approach into a technique that is undeniably accurate and reliable for the assessment of growth rates of algal taxa-o r to show when and under what circumstances it cannot be used. Special care should be taken to avoid radioactive contamination of pigments separated by HPLC, and isotope dilution during experiments. The methods that are available now can also be applied directly to studies of the turnover and eventual fate of the various pigments synthesized by algae, be they photosyntheticaliy active or photoprotective, e.g., in studies of photoadaptation, for example the response of algae to increased ultraviolet radiation. I4C labelling of both chlorophylls and carotenoids may even become a tool in studies of large-scale carbon cycling because a considerable part of phytoplankton carbon biomass in the sea and in sediments is associated with pigments or their degradation products

Fluxes and gas transfer rates of the biogenic trace gas DMS derived from atmospheric gradients

Author Posting. © American Geophysical Union, 2004. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 109 (2004): C08S10, doi:10.1029/2003JC001795.Gas transfer rates were determined from vertical profile measurements of atmospheric dimethylsulfide (DMS) gradients over the equatorial Pacific Ocean obtained during the GasEx-2001 cruise. A quadratic relationship between gas transfer velocity and wind speed was derived from the DMS flux measurements; this relationship was in close agreement with a parameterization derived from relaxed eddy accumulation measurements of DMS over the northeastern Pacific Ocean. However, the GasEx-2001 relationship results in gas transfer rates that are a factor 2 higher than gas transfer rates calculated from a parameterization that is based on coincident eddy correlation measurements of CO2 flux. The measurement precision of both the profiling and eddy correlation techniques applied during GasEx-2001 is comparable; the two gas transfer data sets are in agreement within their uncertainty. Differences in the number of samples and the wind speed range over which CO2 and DMS fluxes were measured are likely causes for the observed discrepancy.Funding for this work came from the Netherlands Organization for Scientific Research (NWO) and from the NOP project 951203: ‘‘Micrometeorology of air/sea fluxes of carbon dioxide. This work was supported by the Global Carbon Cycle project of the NOAA Office of Global Programs grant NA17RJ1223, National Science Foundation grant OCE-9986724, and NSF grant ATM-0120569

An unexpected nitrate distribution in the tropical North Atlantic at 18°N, 30°W—implications for new production

During a R.V. Meteor JGOFS-NABE cruise to a tropical site in the northeast Atlantic in spring 1989, three different vertical regimes with respect to nitrate distribution and availability within the euphotic zone were observed. Besides dramatic variations in the depth of the nitracline, a previously undescribed nose-like nitrate maximum within the euphotic zone was the most prominent feature during this study. Both the vertical structure of phytoplankton biomass and the degree of absolute and relative new production were related to the depth of the nitracline, which in turn was dependent on the occurrence/non-occurrence of the subsurface subtropical salinity maximum (S(max)). The mesoscale variability of the nitracline depth, as indicated from a pre-survey grid, and published data on the frequent occurrence of the S(max) in tropical waters suggest higher variability of new production and F-ratio than usually expected for oligotrophic oceans. The importance of salt fingering and double diffusion for nitrate transport into the euphotic zone is discussed