James R. Nelson

Benthic flux of biogenic elements on the Southeastern US continental shelf: influence of pore water advective transport and benthic microalgae

In situ, paired light and dark benthic #ux chamber incubations were used to estimate the exchange of nutrients, oxygen and inorganic carbon across the sediment } water interface of the South Atlantic Bight (SAB) continental shelf. The results indicate that physically forced non-di!usive pore water transport and benthic primary production (BPP) by sea #oor microalgae exert a major in#uence on benthic exchange rates on the mid- and outer-continental shelf (depths of 14}40 m). Light #uxes to the sea #oor and sediment photosynthetic pigment distributions determined on two, widely spaced cross-shelf transects suggest that BPP may occur over 84% of the SAB continental shelf area. Microalgal gross BPP rates at all study sites averaged 400

Microzooplankton grazing of primary production at 140°W in the equatorial Pacific

260 mg C m~2 d~1 between May and September 1996 while water column primary productivity averaged 682

Grazing, growth and mortality of microzooplankton during the 1989 North Atlantic spring bloom at 47°N, 18°W

176 mg C m~2 d~1, implying a total primary productivity for this region of approximately 1100 mg C m~2 d~1 (1.6 times the water column productivity alone). The results are also consistent with the advective transport of pore waters. Benthic #ux chambers appear to retard this exchange, a!ecting the accuracy of derived net #uxes. Given our inability to relate pore water gradients to #uxes in non-di!usive regimes and to mimic natural advective transport in intact core incubations, traditional techniques such as pore water gradient di!usion calculations or shipboard core incubations also may not provide accurate #ux estimates. Because of these limitations, fundamental questions remain concerning the

Particulate and dissolved spectral absorption on the continental shelf of the southeastern United States

Abstract Phytoplankton growth rates and the grazing impact by microzooplankton were estimated from dilution experiments during spring and fall time-series cruises in the equatorial Pacific as part of the U.S. JGOFS program. The Time-series I (TS-I) cruise occurred during El Nino conditions, while Time-series II (TS-II) coincided with a relaxation event. Deck incubation experiments were conducted using samples from the upper mixed layer (15 m) and depths coinciding with subsurface peaks in chlorophyll a (30–60m). Initial chlorophyll a concentrations were similar at 15m (0.1-0.2 μg 1−1) and at 60 m (0.2-0.4 μg 1−1) in both cruises (experiments at 30 m were conducted only in TS-II). Phytoplankton growth rates were highest at 15 m and decreased with depth. Growth rates in the mixed layer were lower in TS-I (0.4-0.6 day−1) than TS-II (0.8-1.1 day−1). The same trend was observed in phytoplankton growth in the subsurface chlorophyll a maxima (0.2 vs 0.6-0.7 day−1). Grazing rates, which also declined with depth, were higher in TS-II than in TS-I at 60 m (0.6-0.7 vs 0.2-0.4 day−1), but lower at 15 m (0.5-0.8 vs 0.7-1.0 day−1). HPLC pigment analyses indicated that microzooplankton grazing generally balanced the daily production by prymnesiophytes, and consumed much of the daily production of picophytoplankton. However, microzooplankton apparently consumed only about half the potential production by diatoms, implying that other loss processes (macrozooplankton grazing, sinking) regulate diatom abundance in these waters. Herbivory by microzooplankton, primarily by small microflagellates and dinoflagellates, averaged 133 (15 m) to 123% (60 m) of phytoplankton growth in TS-I, and 70 (15–30 m) to 105% (60 m) in TS-II. Thus, grazing of phytoplankton by microzooplankton represented a major pathway of organic carbon transformation at the equator during El Nino and non-El Nino conditions.

Composition, productivity and nutrient chemistry of a coastal ocean planktonic food web

Grazing and growth rates of nano- and microzooplankton were measured as part of the 1989 North Atlantic Bloom Experiment, an interdisciplinary research program of the Joint Global Ocean Flux Study (JGOFS). Samples for shipboard experimental incubations were collected from the mixed layer of a drogued water mass (46°20′N, 17°50′W) over a 2 week period in May. Grazing and growth rates, measured using the size fractionation and dilution techniques, were calculated from changes in chlorophylls, accessory pigments, and cell abundances. The phytoplankton community was dominated by phytoflagellates, primarily prymnesiophytes, which passed 10 μm mesh. Chlorophyll a (Chl a) increased at an average rate of 0.9 doublings day−1 when incubated at 60 % I0. Grazing by nano- and microzooplankton removed 37–100% of estimated primary production in samples from 10 m, and 100% of that at 30 m. An attempt was made to budget estimated rates of community grazing to major groups of nano- and microzooplankton, using measured biomass and specific ingestion or growth rates from laboratory studies. Aplastidic microflagellates were apparently the most important herbivores. In addition to ciliates and heterotrophic dinoflagellates, various developmental stages of copepods were abundant in the <200 μm fraction. Predation within the microzooplankton community appeared to be substantial. Given the evidence of tight coupling between production and consumption within the upper water column, little material appeared to be available for direct export from the mixed layer to depth during this phase of the spring bloom.

A PHYTOL‐SUBSTITUTED CHLOROPHYLL C FROM EMILIANIA HUXLEYI (PRYMNESIOPHYCEAE)1

Visible absorption spectra of particulate and dissolved materials were characterized on the continental shelf off the southeastern United States (the South Atlantic Bight), emphasizing cross-shelf and seasonal variability. A coastal front separates turbid coastal waters from clearer midshelf waters. Spatial and seasonal patterns were evident in absorption coefficients for phytoplankton, detritus, and colored dissolved organic matter (CDOM); spectral shape parameters for CDOM and detritus; and phytoplankton chlorophyll-specific absorption. The magnitude of CDOM absorption reflected seasonal differences in freshwater discharge and the salinity of the midshelf waters. In the spring of 1993 (high discharge), CDOM absorption at 443 nm was >10 times that of total particulate absorption between 12 and 50 km offshore (0.28–0.69 m−1 versus 0.027–0.062 m−1) and up to 10 times the CDOM absorption measured in the previous summer (low discharge). Phytoplankton chlorophyll-specific absorption in the blue increased with distance from shore (from <0.03 m2 mg−1 in inner shelf waters to ∼0.1 m2 mg−1 at the most seaward stations in summer) and, for similar chlorophyll concentrations, was higher in summer than in the winter-spring. These spatial and seasonal patterns in phytoplankton chlorophyll-specific absorption can be attributed to a shift in phytoplankton species composition (from predominantly diatoms inshore to a cyanobacteria-dominated assemblage midshelf in summer), pigment packaging, and higher carotenoid:chlorophyll with distance from shore.

Evaluation of microalgal clones for mass culture in a subtropical greenhouse bivalve hatchery: growth rates and biochemical composition at 30 °C

A 3 year field study was conducted to investigate patterns, magnitude and variability of primary production; the abundance, biomass and composition of producers and consumers; and the relative importance of physical and chemical variables associated with these parameters, in inner shelf waters of the South Atlantic Bight. Discrete interval, time series and continuous measurements were made along a transect and at two process-oriented stations during summer and winter 1985–1988. A quasi-permanent density front constrains low salinity (<34‰) waters to within ca 10 km of the coast. These waters contain abundant autotrophic and heterotrophic communities. Primary production is high, 6–7 × 102gC m−2 year−1, and is apparently subsidized by rapid nutrient recycling in the water column, sediments and adjacent salt marshes. Silicate is notable for its excess concentrations year-round and supports substantial diatom productivity. Correlation analyses suggest that Si strongly influences phytoplankton biomass, whereas growth rates are coupled to availability of light and NH4. Despite evidence of considerable variability in primary production over daily to interannual scales, plankton biomass is relatively constant. Experimental studies suggest a tight coupling between primary producers and microconsumers, and support the hypothesis that substantial fractions of primary and secondary production are recycled within the water column.

Waves Initiative within SEACOOS

A nonpolar chlorophyll c‐like pigment was isolated by semi‐preparative high performance liquid chromatography from the coccolithophorid Emiliania huxleyi (Lohm.) Hay and Mohler. The visible absorption spectrum of this pigment was similar to that of chlorophyll c2. However, its nonpolar chromatographic properties were quite different from those of the relatively polar chlorophylls c2 and c3 in E. huxleyi and similar to those of chlorophyll a. Analyses by gas chromatography and gas chromatography‐mass spectrometry showed that the nonpolar character of this new chlorophyll c was due to the presence of phytol, most likely on the acid side chain of the porphyrin macro‐cycle. This is the first example of a phytol‐substituted chlorophyll c‐like pigment.

In Situ Observations and Satellite Remote Sensing in SEACOOS: Program Development and Lessons Learned

Abstract Eleven microalgal clones were screened for their ability to grow at temperatures of 30–35 °C as a preliminary test of their suitability for greenhouse mass culture in a bivalve hatchery located in the southeastern United States. Five potential candidate clones, Isochrysis aff. galbana (TISO), Isochrysis sp. (CISO), Chaetoceros muelleri (CHAET10), Tetraselmis suecica (TETRA1), and Ellipsoidon sp. (ELLIP1), were further characterized for growth rates and biochemical composition (particulate organic carbon and nitrogen, chlorophyll a, total protein, total carbohydrate, and major lipid classes) at various stages of batch culture at 30 °C. Experiments were conducted under two light regimes, which represent the approximate range of daily irradiance that can be achieved in the greenhouse mass culture facility. Only clone CHAET 10 showed good growth at 35 °C. Other clones may be suitable for mass culture at temperatures up to 32–33 °C. Total protein at 30 °C was highest for TISO and CISO. Changes in the relative proportions of protein, carbohydrate and lipid between batch culture phases were minor for the Isochrysis clones, while the proportion of carbohydrate increased in CHAET10 and TETRA 1 from exponential to stationary phases. Lipid production in clone ELLIP1 was strongly influenced by growth irradiance, with substantial production of triacylglycerols under higher light. The biochemical composition of microalgal clones, and hence the diet supplied to larval and juvenile bivalves, may be manipulated to some extent by control of the growth irradiance and the stage of batch culture at which the cells are harvested.

SEACOOS program management

This article describes the efforts and progress in the area of surface waves, detailing the development of the in situ measuring stations operating in the SEACOOS region. The development and operation of 2 cabled near-shore directional wave installations are described, with some results on near-shore wave climatology developed from those stations. This is followed by a description of a wave buoy observational activity that included an intercomparison of surface wave parameters measured by the buoy with those measured by an RD Instruments acoustic Doppler current profiler. Lastly, a large section of the article is dedicated to describing research and development activities designed to evaluate the use of HF Radar technology for wave measurements.