Description: The Joint Global Ocean Flux Study (JGOFS) has completed a decade of intensive process and time-series studies on the regional and temporal dynamics of biogeochemical processes in five diverse ocean basins. Its field program also included a global survey of dissolved inorganic carbon (DIC) in the ocean, including estimates of the exchange of carbon dioxide (CO2) between the ocean and the atmosphere, in cooperation with the World Ocean Circulation Experiment (WOCE). This report describes the principal achievements of JGOFS in ocean observations, technology development and modelling. The study has produced a comprehensive and high-quality database of measurements of ocean biogeochemical properties. Data on temporal and spatial changes in primary production and CO2 exchange, the dynamics of of marine food webs, and the availability of micronutrients have yielded new insights into what governs ocean productivity, carbon cycling and export into the deep ocean, the set of processes collectively known as the "biological pump." With large-scale, high-quality data sets for the partial pressure of CO2 in surface waters as well for other DIC parameters in the ocean and trace gases in the atmosphere, reliable estimates, maps and simulations of air-sea gas flux, anthropogenic carbon and inorganic carbon export are now available. JGOFS scientists have also obtained new insights into the export flux of particulate and dissolved organic carbon (POC and DOG), the variations that occur in the ratio of elements in organic matter, and the utilization and remineralization of organic matter as it falls through the ocean interior to the sediments. JGOFS scientists have amassed long-term data on temporal variability in the exchange of CO2 between the ocean and atmosphere, ecosystem dynamics, and carbon export in the oligotrophic subtropical gyres. They have documented strong links between these variables and large-scale climate patterns such as the El Nino-Southern Oscillation (ENSO) or the North Atlantic Oscillation (NAO). An increase in the abundance of organisms that fix free nitrogen (N-2) and a shift in nutrient limitation from nitrogen to phosphorus in the subtropical North Pacific provide evidence of the effects of a decade of strong El Ninos on ecosystem structure and nutrient dynamics. High-quality data sets, including ocean-color observations from satellites, have helped modellers make great strides in their ability to simulate the biogeochemical and physical constraints on the ocean carbon cycle and to extend their results from the local to the regional and global scales. Ocean carbon-cycle models, when coupled to atmospheric and terrestrial models, will make it possible in the future to predict ways in which land and ocean ecosystems might respond to changes in climate.

Description: An overview is given of the multinational investigations carried out at 47°N 20°W for the period 24 April–31 May, with the main emphasis on the succession of plankton communities and the flux of organic carbon through various plankton components. The depth of the upper mixed layer decreased rapidly after 25 April, triggering the start of the spring bloom that developed within a 2-week period. Chlorophyll a stocks integrated to 80 m water depth reached peak concentrations during the first 10 days in May. The observed decline was partly due to the seasonal development, but also may have been influenced by changes in water masses associated with a cyclonic eddy. Primary production ranged from 50 to 150 mmol C m−2 day−1 with highest values in the first half of May. After the first bloom phase, dominated by diatoms, nanophytoplankton gained more importance as primary producers when silicate was depleted. Stocks of bacteria, microzooplankton and mesozooplankton increased in the second half of May. Bacterial production averaged 30% of primary production and probably metabolized a large amount of dissolved organic carbon (DOC) per day, but due to uncertain carbon conversion efficiencies total bacterial carbon consumption is difficult to estimate. Largely daily changes in the DOC standing stock could not be reconciled with the measured primmary production and are probably an expression of spatial rather than temporal variations. Microzooplankton was found to consume around 64% of primary production in the second half of May. Grazing estimates for mesozooplankton varied but seem to be small (〈5% of primary production) for most of the investigation period. The small mesozooplankton size classes (〈1 mm) dominated biomass and grazing. Vertical particulate organnic carbon (POC) flux measured by sediment traps in 150 m depth was around 9.8 mmol C m−2 day−1 representing approximately 11% of primary production. The spring bloom pulse of particle flux reached the deep ocean and benthos 4–6 weeks after the surface water peak.

Description: The cold-water coral Lophelia pertusa (Scleractinia, Caryophylliidae) is a key species in the formation of cold-water reefs, which are among the most diverse deep-sea ecosystems. It occurs in two color varieties: white and red. Bacterial communities associated with Lophelia have been investigated in recent years, but the role of the associated bacteria remains largely obscure. This study uses catalyzed reporter deposition fluorescence in situ hybridization to detect the in situ location of specific bacterial groups on coral specimens from the Trondheimsfjord (Norway). Two tissue-associated groups were identified: (i) bacteria on the host's tentacle ectoderm, “Candidatus Mycoplasma corallicola,” are flasklike, pointed cells and (ii) endoderm-associated bona fide TM7 bacteria form long filaments in the gastral cavity. These tissue-bound bacteria were found in all coral specimens from the Trondheimsfjord, indicating a closer relationship with the coral compared to bacterial assemblages present in coral mucus and gastric fluid.

Description: Previous studies have suggested that phytoplankton play an important role in the biogeochemical cycling of iodine, due to the appearance of iodide in the euphotic zone. Changes in the speciation of iodine over the course of the growth cycle were examined in culture media for a variety of phytoplankton taxa (diatoms, dinoflagellates and prymnesiophytes). All species tested showed the apparent ability to reduce iodate to iodide, though production rates varied considerably between species (0.01 to 0.26 nmol l–1 µg–1 chl a d–1), with Eucampia antarctica the least and Pseudo-nitzschia turgiduloides the most efficient iodide producers. Production was found to be species specific and was not related to biomass (indicated by e.g. cell size, cell volume, or chl a content). In all species, except for the mixotrophic dinoflagellate Scrippsiella trochoidea, iodide production commenced in the stationary growth phase and peaked in the senescent phase of the algae, indicating that iodide production is connected to cell senescence. This suggests that iodate reduction results from increased cell permeability, which we hypothesize is due to subsequent reactions of iodate with reduced sulphur species exuded from the cell. A shift from senescence back to the exponential growth phase resulted in a decline in iodide and indicated that phytoplankton-mediated oxidation of iodide to iodate was likely to be occurring. Iodide production could not be observed in healthy cells kept in the dark for short periods. Bacterial processes appeared to play only a minor role in the reduction of iodate to iodide.

Description: Headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography-mass spectrometry (GC-MS) has been developed, optimized, and applied to investigate the dimethylsulfide (DMS) emissions from eight marine phytoplankton species, namely, Calcidiscus leptoporus, Emiliania huxleyi, Phaeodactylum tricornutum, Chaetoceros neogracilis, Dunaliella tertiolecta, Synechococcus, Prochlorococcus, and Trichodesmium. Four SPME fiber coatings (PDMS, PDMS-DVB, PDMS-CAR, and CW-DVB) were tested for linearity and limit of detection. Key parameters such as equilibrium and extraction times, desorption temperature and time, and headspace volume were optimized to make extraction as efficient as possible using the PDMS-DVB fiber coating. This fiber enabled the characterization of DMS in seawater under 0.005 nM levels and within 1 min exposure time. Among the different algae groups, the two coccolithophorids, C. leptoporus and E. huxleyi, were the strongest emitters of DMS. Within the cyanobacteria, Prochlorococcus and Trichodesmium expressed no DMS emission, whereas Synechococcus showed very low DMS emission. The DMS emission of C. leptoporus, however, was several orders of magnitude higher than all other algae, including E. huxleyi, which is known to be a prolific emitter of DMS.