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Net community production (NCP) constrains the amount of carbon that is available for storage within or export from, the photic zone of marine ecosystems. With the aim of studying the control exerted by microbial community respiration (MCR) and gross primary production (GPP) over NCP, short-term variability in rates of MCR, GPP and NCP were measured over a 13-day sampling period (August 23–September 4, 2012) at Station ALOHA. During this period, picoplankton abundances and concentrations of photosynthetic pigments demonstrated weak to moderate decreases coincident with the passage of a low salinity water mass through the sampling area. During the same period, rates of MCR, measured using the in vivo INT method, varied by 2.7-fold. Rates of primary production (PP) were estimated based on four different methodologies: Fast Repetition Rate Fluorometry (FRRF), 14C-bicarbonate assimilation, diel changes in mixed layer O2 concentrations based on Seaglider measurements, and isotopic composition (17ΔO2) of dissolved O2. Remarkably, these different methods for measuring microbial metabolism were consistent, suggesting that collectively these different approaches provide an accurate constraint on ecosystem metabolism, despite the different time and space scales over which these measurements integrate. FRRF-derived estimates of PP, which were similar in magnitude to 14C-based-PP, were significantly correlated with variability in mixed layer MCR. None of the other independent measurements of PP demonstrated significant relationships to MCR. Day-to-day variability in MCR and bacterial growth efficiency (BGE), derived based on measurements of bacterial production (as estimated by 3H-leucine incorporation) and MCR, were related to changes in NCP estimated from O2/Ar ratios (O2/Ar-NCP), suggesting short-term variability in the efficiency with which microorganisms consume dissolved organic matter exerts direct control on rates of NCP in this ecosystem. Our results highlight internal consistency among the derived rates of ecosystem metabolism using a suite of different methodologies to estimate productivity and respiration. Moreover, we find that rates of MCR can be as variable as PP and that variability in MCR may regulate NCP in this ecosystem.

Station ALOHA (A Long-term Oligotrophic Habitat Assessment) was established in the North Pacific Subtropical Gyre (22°45′N, 158°W) as an oligotrophic ocean benchmark to improve our understanding of processes that govern the fluxes of carbon (C) into and from the surface ocean. At approximately monthly intervals, measurements of the primary production of particulate C (PC) using the 14C method, and the export of PC and particulate nitrogen (PN) using surface-tethered sediment traps deployed at 150 m have been made along with a host of complementary physical, biological, and biogeochemical measurements. Euphotic zone depth-integrated (0–200 m) primary production ranged from 220.2 (standard deviation, SD, 10.8) mg C m−2 d−1 in Feb 2018 to 1136.5 (SD = 17.1) mg C m−2 d−1 in Jun 2000, with a 30-yr (1989–2018) mean of 536.8 (SD = 135.0) mg C m−2 d−1 (n = 271). Although the monthly primary production climatology was fairly well constrained, we observed substantial sub-decadal variability and a significant 0–125 m depth-integrated increasing trend of 4.0 (p

To constrain the energy fueling photosynthesis in the North Pacific Subtropical Gyre (NPSG) we characterize the variability of phytoplankton absorption spectra in conjunction with that of the light field at Station ALOHA (22°45′N, 158°00′W). Furthermore, we decompose the phytoplankton absorption into photosynthetic and photoprotective components based on high-performance liquid chromatography pigment analysis. Between January 2006 and December 2012 the variability in chlorophyll-specific absorption ( aϕ∗) above the deep chlorophyll maximum (DCM) layer was driven by changes in photoprotective carotenoid concentrations while the chlorophyll-specific absorption of photosynthetic pigments ( aϕ(PSP)∗) remained nearly constant with a mean (± SD) value of 0.008 ± 0.001 m2 (mg chl a)−1. In contrast, below the DCM layer changes in aϕ∗ resulted from increases in the relative contribution of photosynthetic pigments with depth, suggesting that the constancy in aϕ(PSP)∗ above the DCM layer is controlled by nutrient limitation. While the daily photon fluxes absorbed by photosynthetic pigments in the upper 45 m did not vary at a seasonal scale, averaging 0.45 ± 0.12 mol quanta m−2 d−1 in winter and 0.46 ± 0.10 mol quanta m−2 d−1 in summer, when integrated over the upper 200 m these fluxes ranged from 0.64 ± 0.16 to 0.79 ± 0.19 mol quanta m−2 d−1 in winter and summer, respectively. Based on the rate of photons trapped by the photosynthetic pigments and on the seasonal euphotic zone depth integrated gross O2 evolution rates derived from H218O in situ incubations we estimate a mean photosynthetic yield of ∼0.1 mol O2 evolved per mol quanta absorbed by photosynthetic pigments.

Picophytoplankton, including photosynthetic picoeukaryotes (PPE) and unicellular cyanobacteria, are important contributors to plankton biomass and primary productivity. In this study, phytoplankton composition and rates of carbon fixation were examined across a large trophic gradient in the South East Pacific Ocean (SEP) using a suite of approaches: photosynthetic pigments, rates of 14C-primary productivity, and phylogenetic analyses of partial 18S rRNA genes PCR amplified and sequenced from flow cytometrically sorted cells. While phytoplankton >10 μm (diatoms and dinoflagellates) were prevalent in the upwelling region off the Chilean coast, picophytoplankton consistently accounted for 55–92% of the total chlorophyll a inventories and >60% of 14C-primary productivity throughout the sampling region. Estimates of rates of 14C-primary productivity derived from flow cytometric sorting of radiolabeled cells revealed that the contributions of PPE and Prochlorococcus to euphotic zone depth-integrated picoplankton productivity were nearly equivalent (ranging 36–57%) along the transect, with PPE comprising a larger share of picoplankton productivity than cyanobacteria in the well-lit (>15% surface irradiance) region compared with in the lower regions (1–7% surface irradiance) of the euphotic zone. 18S rRNA gene sequence analyses revealed the taxonomic identities of PPE; e.g., Mamiellophyceae (Ostreococcus) were the dominant PPE in the upwelling-influenced waters, while members of the Chrysophyceae, Prymnesiophyceae, Pelagophyceae, and Prasinophyceae Clades VII and IX flourished in the oligotrophic South Pacific Subtropical Gyre. Our results suggest that, despite low numerical abundance in comparison to cyanobacteria, diverse members of PPE are significant contributors to carbon cycling across biogeochemically distinct regions of the SEP.

The particle size distribution (PSD) is a critical aspect of the oceanic ecosystem. Local variability in the PSD can be indicative of shifts in microbial community structure and reveal patterns in cell growth and loss. The PSD also plays a central role in particle export by influencing settling speed. Satellite‐based models of primary productivity (PP) often rely on aspects of photophysiology that are directly related to community size structure. In an effort to better understand how variability in particle size relates to PP in an oligotrophic ecosystem, we collected laser diffraction‐based depth profiles of the PSD and pigment‐based classifications of phytoplankton functional types (PFTs) on an approximately monthly basis at the Hawaii Ocean Time‐series Station ALOHA, in the North Pacific subtropical gyre. We found a relatively stable PSD in the upper water column. However, clear seasonality is apparent in the vertical distribution of distinct particle size classes. Neither laser diffraction‐based estimations of relative particle size nor pigment‐based PFTs was found to be significantly related to the rate of 14C‐based PP in the light‐saturated upper euphotic zone. This finding indicates that satellite retrievals of particle size, based on particle scattering or ocean color would not improve parameterizations of present‐day bio‐optical PP models for this region. However, at depths of 100–125 m where irradiance exerts strong control on PP, we do observe a significant linear relationship between PP and the estimated carbon content of 2–20 μm particles., Key Points: Particle size is not correlated to productivity in the surface mixed layer of Station ALOHASeasonal changes in the vertical distribution of particle size classes are apparentThe carbon content of 2–20 μm particles is positively related to productivity rates at the DCM

©2015. American Geophysical Union. All Rights Reserved. Time-series observations are critical to understand the structure, function, and dynamics of marine ecosystems. The Hawaii Ocean Time-series program has maintained near-monthly sampling at Station ALOHA (22°45′N, 158°00′W) in the oligotrophic North Pacific Subtropical Gyre (NPSG) since 1988 and has identified ecosystem variability over seasonal to interannual timescales. To further extend the temporal resolution of these near-monthly time-series observations, an extensive field campaign was conducted during July-September 2012 at Station ALOHA with near-daily sampling of upper water-column biogeochemistry, phytoplankton abundance, and activity. The resulting data set provided biogeochemical measurements at high temporal resolution and documents two important events at Station ALOHA: (1) a prolonged period of low productivity when net community production in the mixed layer shifted to a net heterotrophic state and (2) detection of a distinct sea-surface salinity minimum feature which was prominent in the upper water column (0-50 m) for a period of approximately 30 days. The shipboard observations during July-September 2012 were supplemented with in situ measurements provided by Seagliders, profiling floats, and remote satellite observations that together revealed the extent of the low productivity and the sea-surface salinity minimum feature in the NPSG.

During the summer of 2012, we used laser diffractometry to investigate the temporal and vertical variability of the particle size spectrum (1.25–100 µm in equivalent diameter) in the euphotic zone of the North Pacific Subtropical Gyre. Particles measured with this optical method accounted for ∼40% of the particulate carbon stocks (

Reef-building corals inhabiting the mesophotic zone (30�150 m) not only survive but thrive in light-limiting environments. Similar to shallow corals, mesophotic corals also exhibit coral fluorescence. Because fluorescent proteins (FPs) absorb high-energy light and emit lower- energy light, FPs could play an important role in mesophotic coral physiology and ecology. For 4 species of the Hawaiian mesophotic reef-building coral Leptoseris (65�125 m), we investigated the abundance of fluorescent morphs, types of FPs, fluorescence emission phenotypes, and the physiological relationship between coral fluorescence and endosymbiotic Symbiodinium (dino - flagellate; Dinophyta). Cyan/green coral fluorescence emission was widespread in mesophotic Leptoseris spp.; more than 70% of corals fluoresced, yet fluorescent and nonfluorescent corals co- occurred at all depths investigated. Coral fluorescence was attributed to 2 proteins, a cyan fluores- cent protein (CFP, λex = 424 nm, λem = 490 nm) and a green fluorescent protein (GFP, λex = 478 nm, λem = 502 nm). The type of FP in Leptoseris colonies was correlated with depth; CFP was dominant in corals from shallower depths (65�85 m), GFP was dominant in corals from deeper depths (96�125 m), and CFP and GFP were present in corals from middle depths (86�95 m). Coral FP emission was primarily localized in the coenosarc and/or the oral disc. Symbiodinium from corals with and without fluorescence emission had similar genotypes, abundances, photosynthetic pigments, photosynthetic efficiencies, photosynthetic rates, and chlorophyll excitation spectra. As such, it is unlikely that these FPs play a significant role in enhancing symbiont photosynthesis. The high abundance of fluorescent morphs (>70%) dominating this energetically limited environ- ment may suggest that FPs play an integral and conserved physiological role in corals.

ments was collected from the sea-surface in order to quantify the time-dependent rate of change in the ratio of XCP to chlorophyll a (XCP/CHLA). In situ XCP/CHLA values were measured by rapid collection of cells in the mixed layer using a diaphragm pumping system and the xanthophyll cycle activity inhibitor dithiothreitol. Turbulent transfer velocity (TTV) was estimated as the quotient of the XCP/CHLA photoadaptation rate and the XCP/CHLA gradient in the mixed layer. TTVs ranged from 0.3 to 0.5 cm s 21 , and agreed to within a factor of 2 of the Lagrangian floatderived estimate of vertical mixing at a comparable friction velocity. Coincident measurements of dissolved gases suggest that XCP dynamics may be useful for the interpretation of trace gases species distributions, such as hydrogen and carbon monoxide, in the upper ocean.

Eukaryotic phytoplankton play important roles in regulating productivity and material export in oligotrophic ocean ecosystems. In this study, we examined the vertical and temporal variability in planktonic Chromalveolate (hereafter chromophyte) assemblages over a 2-year period (2007–2009) at Station ALOHA (22°45′N, 158°W) in the North Pacific Subtropical Gyre (NPSG). Polymerase chain reaction (PCR) amplification, cloning, and sequencing of form ID rbcL genes from samples collected at nearly monthly intervals provided information on the diversity, abundances, and variability associated with chromophytic phytoplankton. Despite persistently oligotrophic conditions, the euphotic zone of this habitat supported a phylogenetically diverse assemblage of chromophytic algae, including representatives of various genera of diatoms, pelagophytes, prymnesiophytes, and dinoflagellates. Quantitative PCR (qPCR) amplification of diatom, prymnesiophyte, and pelagophyte rbcL phylotypes revealed that the population structure of these assemblages was highly variable in time, with gene abundances often varying more than an order of magnitude between successive months. Diatom rbcL genes were typically the most abundant in both the upper and lower regions of the euphotic zone, while rbcL gene abundances of the prymnesiophytes and pelagophytes were significantly greater (One-way ANOVA, P

Bioassays were performed on phytoplankton communities from the coastal waters at Grand Isle, Louisiana from February through August 2013 to determine the impact of the water-accommodated fraction of unweathered Macondo well oil on the growth rates and taxonomic composition of the phytoplankton. Pigment analysis indicated that diatoms dominated the natural phytoplankton communities, and with one exception, diatoms were the only class of phytoplankton that grew in control cultures or in artificial seawater amended with the water-accommodated fractions of Macondo well oil at a series of concentrations from 0.1 to 19.2 mg L–1. The growth rates of diatoms were enhanced by roughly 10% at oil concentrations ≤ 0.6 mg L–1 but were reduced by up to 30% at concentrations ≥ 1.0 mg L–1. Ratios of fucoxanthin to chlorophyll a were positively correlated with oil concentrations, an indication that there was some adjustment of the characteristics of the light-harvesting antennae of the diatoms in response to the stress of the oil.

β-N-methylamino-L-alanine (BMAA) is an excitotoxic neurotoxin that has been implicated in the etiology of Amyotrophic Lateral Sclerosis-Parkinsonism-Dementia Complex in the South Pacific island of Guam. BMAA has been reported to be present in a wide range of cyanobacteria taxa and aquatic invertebrates. However, there are large uncertainties in the human health risks associated with BMAA exposure because of the analytical challenges associated with the detection and quantification of BMAA. Here we describe an improved liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS) method for the analysis of BMAA in aquatic invertebrate sample matrices, and present initial findings for oysters and blue crabs collected in the southeastern United States. The LC-MS/MS method is linear over a wide range of BMAA concentrations (0.4−153.2 pg µL−1, r2 = 0.997), and analytically precise, with a relative standard deviation (RSD) of 2.4%. The on-column limit of detection (LoD) and limit of quantification (LoQ) values for this method were determined to be 5 pg (0.2 pg µL−1) and 17 pg (0.8 pg µL−1), respectively. We observed a weak ion enhancement effect of ~10% in a mollusk matrix that tested negative for BMAA. Analyte recovery for the method averaged 92% (8% RSD). BMAA concentrations for oysters and blue crabs ranged from 5 to 47 µg g−1 dry weight sample and are substantially lower than the concentrations reported previously with a nonspecific BMAA method that was based on liquid chromatography-fluorescence detection (LC-FL). We conclude that BMAA analysis via LC-MS/MS methodologies is absolutely necessary for obtaining reliable data.

Parental effects have been largely unexplored in marine organisms and may play a significant role in dictating the phenotypic range of traits in coral offspring, influencing their ability to survive environmental challenges. This study explored parental effects and life-stage differences in the Hawaiian reef-building coral Montipora capitata from different environments by examining the biochemical composition of mature coral colonies and their eggs. Our results indicate that there are large biochemical differences between adults and eggs, with the latter containing higher concentration of lipids (mostly wax esters), ubiquitinated proteins (which may indicate high turnover rate of proteins) and antioxidants (e.g., manganese superoxide dismutase). Adults displayed high phenotypic plasticity, with corals from a high-light environment having more wax esters, lighter tissue δ13C signatures and higher Symbiodinium densities than adults from the low-light environment who had higher content of accessory pigments. A green-algal pigment (α-carotene) and powerful antioxidant was present in eggs; it is unclear whether this pigment is acquired from heterotrophic food sources or from endolithic green algae living in the adult coral skeletons. Despite the broad phenotypic plasticity displayed by adults, parental investment in the context of provisioning of energy reserves and antioxidant defense was the same in eggs from the different sites. Such equality in investment maximizes the capacity of all embryos and larvae to cope with challenging conditions associated with floating at the surface and to disperse successfully until an appropriate habitat for settlement is found.

The vertical zonation of dominant megabenthic, photosynthetic taxa suggests that differential photosynthetic capabilities enable specialized, low-light zooxanthellate corals to dom- inate at depths where shallow-water corals become light limited. This study examines the eco- physiology of deep-water (68�113 m) Leptoseris spp. and shallow-water (2�15 m) Porites spp. zooxanthellate corals from Hawai'i by comparing spectral absorbance properties and photosyn- thetic pigment concentrations to the available light spectra in their respective environments. Photo synthetically active radiation reaching Leptoseris spp. was 3 to 11% of surface irradiance compared to 41 to 90% reaching Porites spp. Optical measurements indicated that Leptoseris spp. exhibited lower reflectance (i.e. higher absorptance) compared to Porites spp. and were chromat- ically adapted to the wavelengths of photons available at depth. Despite the decreased spectral reflectance, deep-water Leptoseris spp. exhibited significantly lower areal photosynthetic pig- ment concentrations than did shallow-water Porites spp. Based on morphological comparisons of the skeletons of both coral genera, we hypothesize that Leptoseris spp. skeletons may cause inci- dent light to travel through the coral tissue several times, thereby increasing photon-pigment interactions without increasing pigment concentrations. This superior light harvesting efficiency exhibited by Leptoseris in an energy limited environment (enabled by skeletal design rather than pigment physiology) may in part explain why the dominant genus of reef-building corals in Hawai'i cannot compete successfully with specialized low-light corals at extreme depths.

Phytoplankton dynamics were investigated in the eastern equatorial Pacific at 32 stations sampled during two cruises (December 2004 and September 2005). Based on standing stock analyses from HPLC pigments, flow cytometry and microscopy, we used a modified 2-treatment approach of the seawater dilution method to estimate taxon-specific phytoplankton growth and mortality rates in 8-depth per station profiles. These data were complemented by contemporaneous measurements of dissolved iron (Fe). The stations encompassed an equatorial zonal gradient (110 to 140°W) of diminishing eastward Fe availability in the euphotic zone from upwelling of the Equatorial Undercurrent (EUC). Latitudinal variation was assessed by meridional transects at 110 and 140°W. Overall, euphotic zone averaged growth rates were 0.53±0.17 d −1 (total chlorophyll a ), 0.34±0.15 d −1 (divinyl chlorophyll a ) and 0.86±0.32 d −1 (fucoxanthin). Microzooplankton grazing accounted for 50-60% of daily production of eukaryotic algae, whereas essentially all growth of phototrophic prokaryotes was consumed daily. Fucoxanthin, representing diatoms, was a minor component of the accessory pigments, but diatom growth rates were both significantly higher than other taxonomically defined groups and dropped off more sharply with depth (low light level). Strikingly, no spatial or temporal trends were seen in the 256 growth rate measurements for each measured pigment. However, the diminishing eastward equatorial Fe gradient was associated with deepening subsurface pigment maxima and decreasing surface-layer pigment stocks (down to the 8% light level). In addition, integrated standing stocks of total chlorophyll a and Prochlorococcus (divinyl chlorophyll a ) were strongly correlated with integrated iron at equatorial upwelling stations, yet no correlation with Fe was seen for any of the eukaryotic groups, including diatoms. This latter result is contrary to expectations from previous Fe addition experiments ( in situ or in bottles), where diatom biomass increased relative to other phytoplankton. We hypothesize that the natural supply of Fe to the base of the euphotic zone from the EUC is less favorable for diatoms because of light limitation. Rather, new Fe is rapidly incorporated into a small phytoplankton-dominated community in the deep euphotic zone, and tightly coupled grazing control results in a system regulated by return of recycled Fe.

We investigate the hypothesis that phytoplankton growth and grazing processes are strongly balanced in high-nutrient low-chlorophyll (HNLC) waters of the equatorial Pacific using euphotic-zone estimates of rates and biomass determined for 30 stations during EB04 (December 2004) and EB05 (September 2005). As predicted by the balance hypothesis, depth-averaged instantaneous rates of phytoplankton growth and grazing losses to micro- and mesozooplankton show a net growth difference of zero. Contemporaneous estimates of phytoplankton biomass and specific rates from flow cytometry, microscopy and taxon-specific accessory pigments allow determination of constrained production-consumption trophic balances for the phytoplankton community as a whole and for major component populations. The magnitude of growth-based production (867 mg C m −2 d −1 ) is consistent with measured 14 C primary production, given methodological differences. 70% of production is utilized by protistan herbivores within the microbial community; 30% is consumed by mesozooplankton. Among picophytoplankton ( Prochlorococcus , Synechococcus and small eukaryotes), representing 40% of community biomass and 27% of daily biomass growth, microzooplankton consume almost all production. Among groups of larger eukaryote taxa, including diatoms but dominated by dinoflagellate biomass, micro-grazers consume 51–62% of production, with the remainder available to mesozooplankton. Some leakage from the balance is expected as export of sinking phytoplankton cells and aggregates, but is constrained to no more than a few percent of daily production from alternate determinations of mesozooplankton grazing. The demonstrated balance of growth and grazing processes in the equatorial Pacific is inconsistent with recent claims from inverse models that a large flux associated with ungrazed picophytoplankton production dominates euphotic zone carbon export in the region.

Biological responses to basin-scale climate forcing in the subtropical North Pacific Ocean are assessed based on temporal variations in plankton community structure observed at Station ALOHA and results of a coupled physical‐biogeochemical model. Observational data and model simulations for the period 1990‐2004 reveal distinct temporal patterns, with significant increases in net primary productivity, modeled nitrate flux into the euphotic zone and the measured downward flux of particulate nitrogen during 1999‐2004. Concurrent increases in microalgae, cyanobacteria and modeled and measured zooplankton biomass were also observed during this period. We provide evidence that these responses were a consequence of climate forcing that destratified the upper ocean, making it more susceptible to mixing events and nutrient entrainment. These findings underscore the importance of nitrate flux and plankton community structure, as modulated by climate forcing, in regulating particle export over interannual and decadal time scales.

The VERtical Transport In the Global Ocean (VERTIGO) study examined particle sources and fluxes through the ocean’s ‘‘twilight zone’’ (defined here as depths below the euphotic zone to 1000 m). Interdisciplinary process studies were conducted at contrasting sites off Hawaii (ALOHA) and in the NW Pacific (K2) during 3-week occupations in 2004 and 2005, respectively. We examine in this overview paper the contrasting physical, chemical and biological settings and how these conditions impact the source characteristics of the sinking material and the transport efficiency through the twilight zone. A major finding in VERTIGO is the considerably lower transfer efficiency (Teff) of particulate organic carbon (POC), POC flux 500/150 m, at ALOHA (20%) vs. K2 (50%). This efficiency is higher in the diatomdominated setting at K2 where silica-rich particles dominate the flux at the end of a diatom bloom, and where zooplankton and their pellets are larger. At K2, the drawdown of macronutrients is used to assess export and suggests that shallow remineralization above our 150-m trap is significant, especially for N relative to Si. We explore here also surface export ratios (POC flux/primary production) and possible reasons why this ratio is higher at K2, especially during the first trap deployment. When we compare the 500-m fluxes to deep moored traps, both sites lose about half of the sinking POC by 44000 m, but this comparison is limited in that fluxes at depth may have both a local and distant component. Certainly, the greatest difference in particle flux attenuation is in the mesopelagic, and we highlight other VERTIGO papers that provide a more detailed examination of the particle sources, flux and processes that attenuate the flux of sinking particles. Ultimately, we contend that at least three types of processes need to be considered: heterotrophic degradation of sinking particles, zooplankton migration and surface feeding, and lateral sources of suspended and sinking materials. We have evidence that all of these processes impacted the net attenuation of particle flux vs. depth measured in VERTIGO and would therefore need to be considered and quantified in order to understand the magnitude and efficiency of the ocean’s biological pump.

As part of the VERTIGO program, we collected and analyzed sinking particles using tethered and neutrally buoyant sediment traps at three depths in the oceanic mesopelagic zone and at two biogeochemically contrasting sites (N. Central Pacific at ALOHA; N. Pacific Western Subarctic Gyre at K2). This effort represented the first large-scale use of neutrally buoyant traps and represents a significant step forward in the study of the marine biological pump. In this paper, we present the results of mass, macronutrient, biominerals and phytoplankton pigment determinations made on these samples. The impact of a variety of potential collection biases were examined, including those from in-trap particle degradation, zooplankton swimmers and poisons. Though these factors have been observed to affect results in other programs, we found them to have relatively little impact on measured fluxes in this study. There was evidence, however, that the neutrally buoyant traps performed better than the tethered traps in terms of flux accuracy during one deployment, possibly because of improved large particle collection efficiency. Fluxes of material exhibited three different patterns through the mesopelagic: increasing, decreasing and constant with depth. Decreasing fluxes with depth were observed for all biogenic material formed in the euphotic zone. The attenuation of flux with depth was not the same for all components, however, with phytoplankton pigments exhibiting the greatest degradation with depth and particulate inorganic carbon the least. Organic carbon and nitrogen showed a very high correlation in these samples, with little evidence of different attenuation length scales. Increasing fluxes with depth were observed for particulate Ba at both sites and Al at K2. The increases in Ba are attributed to the formation of barite in degrading particles, while increasing Al at K2 was the result of lateral inputs from a continental shelf/slope. Constant fluxes with depth were observed for Al at ALOHA, where fluxes appeared to be in steady state with atmospheric dust deposition. The mesopelagic zone at K2 was observed to attenuate particle flux less than at ALOHA, and with a higher POC/PIC (“rain”) ratio. These two factors combine to imply that the Subarctic province had a much more efficient biological pump than had the subtropical gyre during our occupations. This could be the result of either faster sinking particles, generated from grazing by large zooplankton, or inherently slower particle degradation rates.

A central question addressed by the VERtical Transport In the Global Ocean (VERTIGO) study was ‘What controls the efficiency of particle export between the surface and subsurface ocean’? Here, we present data from sites at ALOHA (N Central Pacific Gyre) and K2 (NW subarctic Pacific) on phytoplankton processes, and relate them via a simple planktonic foodweb model, to subsurface particle export (150–500 m). Three key factors enable quantification of the surface–subsurface coupling: a sampling design to overcome the temporal lag and spatial displacement between surface and subsurface processes; data on the size partitioning of net primary production (NPP) and subsequent transformations prior to export; estimates of the ratio of algal- to faecal-mediated vertical export flux. At ALOHA, phytoplankton were characterized by low stocks, NPP, Fv/Fm (N-limited), and were dominated by picoplankton. The HNLC waters at K2 were characterized by both two-fold changes in NPP and floristic shifts (high to low proportion of diatoms) between deployment 1 and 2. Prediction of export exiting the euphotic zone was based on size partitioning of NPP, a copepod-dominated foodweb and a ratio of 0.2 (ALOHA) and 0.1 (K2) for algal:faecal particle flux. Predicted export was 20–22 mg POC m−2 d−1 at ALOHA (i.e. 10–11% NPP (0–125 m); 1.1–1.2×export flux at 150 m (E150). At K2, export was 111 mg C m−2 d−1 (21% NPP (0–50 m); 1.8×E150) and 33 mg POC m−2 d−1 (11% NPP, 0–55 m); 1.4×E150) for deployments 1 and 2, respectively. This decrease in predicted export at K2 matches the observed trend for E150. Also, the low attenuation of export flux from 60 to 150 m is consistent with that between 150 and 500 m. This strong surface–subsurface coupling suggests that phytoplankton productivity and floristics play a key role at K2 in setting export flux, and moreover that pelagic particle transformations by grazers strongly influence to what extent sinking particles are further broken down in the underlying waters of the Twilight Zone.

As part of the E-Flux project, we documented spatial variability and temporal changes in plankton community structure in a cold-core cyclonic eddy in the lee of the Hawaiian Islands. Cyclone Opal spanned 200 km in diameter, with sharply uplifted isopycnals (80–100 m relative to surrounding waters) and a strongly expressed deep chlorophyll a maximum (DCM) in its central core region of 40 km diameter. Microscopic and flow cytometric analyses of samples from across the eddy revealed dramatic transitions in phytoplankton community structure, reflecting Opal's well-developed physical structure. Upper mixed-layer populations in the eddy resembled those outside the eddy and were dominated by picophytoplankton. In contrast, the DCM was composed of large chain-forming diatoms dominated by Chaetoceros and Rhizosolenia spp. Diatoms attained unprecedented levels of biomass (nearly 90 μg C l−1) in the center of the eddy, accounting for 85% of photosynthetic biomass. Protozoan grazers displayed two- to three-fold higher biomass levels in the eddy center as well. We also found a distinct and persistent layer of senescent diatom cells overlying healthy populations, often separated by less than 10 m, indicating that we were sampling a bloom in a state of decline. Time-series sampling over 8 days showed a successional shift in community structure within the central diatom bloom, from the unexpected large chain-forming species to smaller forms more typical of the subtropical North Pacific. The diatom bloom of Cyclone Opal was a unique, and possibly extreme, example of biological response to physical forcing in the North Pacific subtropical gyre, and its detailed study may therefore help to improve our predictive understanding of environmental controls on plankton community structure.

Persistent northeasterly trade winds have a substantial impact on the oceanic circulation around the Hawaiian Islands. A regional ocean model is applied to understand the effect of different temporal and spatial resolutions of surface momentum forcing on the formation of strong mesoscale vortices and on the simulation of realistic levels of eddy kinetic energy. The higher spatial and temporal resolutions of wind forcing is shown to substantially affect the vorticity and deformation field in the immediate lee of the Hawaiian Islands and produce patterns of eddy kinetic energy similar to observations. This suggests that the surface eddy field in the region is mostly dominated by the local surface momentum forcing. Mesoscale cyclones and anticyclones formed in the lee of the Island of Hawaii are shown to have different propagation patterns. Mesoscale cyclones are more confined to the lee and are hence subject to interactions with the strong wind forcing and deformation field as well as smaller vortices formed in the wake of the other islands. Mesoscale anticyclones show not only a tendency to propagate further westward, but also to persist as coherent features as they propagate, even at relatively lower values of relative vorticity. The large strain rates that affect the propagation of the cyclones cause them to break down into filaments of positive vorticity. Rossby numbers of O(1) within vortices and filaments indicate that nonlinear interactions between the wind stress and the vertical component of the relative vorticity field is potentially important in producing large vertical velocities. Modeled cyclonic eddies show a good resemblance to observations both in terms of vertical structure and propagation patterns.

Recent discrepancies between geochemical and biological approaches for determining whether ocean ecosystems are net heterotrophic or net autotrophic have led to uncertainty in the net metabolic state of open ocean ecosystems. Geochemical approaches indicate that the oceans are net positive autotrophic, but direct observations based on short-term incubation techniques suggest that the ocean is in a state of net heterotrophy. One hypothesis for the apparent discrepancy is that net autotrophic production occurs in aperiodic “bursts,” which are superimposed on a more constant background state of net heterotrophy. Mixing events, which introduce new nutrients to the surface ocean, provide one mechanism for fueling such aperiodic bursts of net production. In conjunction with the Eddy Flux (E-Flux) program in the lee of the Hawaiian Islands during winter 2004–2005, we examined the relationship between photosynthesis and irradiance ( P vs. E ) in surface waters inside and outside of two cold-core, cyclonic eddies, and conducted five incubation experiments to examine the metabolic response of mixed-layer plankton communities to nutrient-rich deep-sea water additions. Our results showed that in the mixed layer, maximum rates of light-saturated photosynthesis, derived from photosynthesis–irradiance experiments were not significantly different inside vs. outside the eddies ( p =0.35 and 0.44 for E-Flux I and E-Flux III, respectively). Addition of nutrients to mixed-layer water showed that (1) gross primary production (GPP) became decoupled from a more constant rate of respiration and (2) net system metabolism shifted from approximate balance, or slight net heterotrophy, to a demonstrably net autotrophic system. From these results, we determined that the threshold GPP for net autotrophic production for the mixed layer of the study region was 1.65 mmol O 2 m −3 d −1 , which is consistent with previous estimates for the oligotrophic open ocean.

Macronutrients, photosynthetic pigments, and particle export were assessed in two eddies during the E-Flux I and III cruises to investigate linkages between biogeochemical properties and export flux in Hawaiian lee cyclonic eddies. Cyclone Noah (E-Flux I), speculated to be in the 'decay' stage, exhibited modest increases in macronutrients and photosynthetic pigments at the eddy center compared to ambient waters. Cyclone Opal (E-Flux III) also exhibited modest increases in macronutrient concentrations, but a 2-fold enhancement in total chlorophyll a (TChl a) concentration within the eddy center. As indicated by fucoxanthin concentrations, the phytoplankton community in the deep chlorophyll maximum (DCM) of Opal was comprised mainly of diatoms. During an 8-day time series in the center of Opal, TChl a concentration and fucoxanthin in the DCM decreased by � 50%, which was potentially triggered by silicic acid limitation. Despite the presence of a substantial diatom bloom, Opal did not deliver the expected export of particulate carbon and nitrogen, but rather a large biogenic silica export (� 4-fold increase relative to export in surrounding waters). Results suggest that controls on the life cycle of a Hawaiian lee cyclone are likely a combination of physical (eddy dynamics), chemical (nutrient limitation), and biological (growth and grazing imbalance) processes. Comparisons between Noah and Opal and previously studied cyclones in the region point to a relationship between the spin-up duration of a cyclone and the resulting biological response. Nonetheless, Hawaiian lee cyclones, which strongly influence the biogeochemistry of areas 100's of km in scale in the subtropical North Pacific Ocean, still remain an enigma.

The dynamics of dissolved inorganic carbon (DIC) and processes controlling net community production (NCP) were investigated within a mature cyclonic eddy, Cyclone Opal , which formed in the lee of the main Hawaiian Islands in the subtropical North Pacific Gyre. Within the eddy core, physical and biogeochemical properties suggested that nutrient- and DIC-rich deep waters were uplifted by ∼80 m relative to surrounding waters, enhancing biological production. A salt budget indicates that the eddy core was a mixture of deep water (68%) and surface water (32%). NCP was estimated from mass balances of DIC, nitrate+nitrite, total organic carbon, and dissolved organic nitrogen, making rational inferences about the unobserved initial conditions at the time of eddy formation. Results consistently suggest that NCP in the center of the eddy was substantially enhanced relative to the surrounding waters, ranging from 14.1±10.6 (0–110 m: within the euphotic zone) to 14.2±9.2 (0–50 m: within the mixed layer) to 18.5±10.7 (0–75 m: within the deep chlorophyll-maximum layer) mmol C m −2 d −1 depending on the depth of integration. NCP in the ambient waters outside the eddy averaged about 2.37±4.24 mmol C m −2 d −1 in the mixed layer (∼0–95 m). Most of the enhanced NCP inside the eddy appears to have accumulated as dissolved organic carbon (DOC) rather than exported as particulate organic carbon (POC) to the mesopelagic. Our results also suggest that the upper euphotic zone (0–75 m) above the deep chlorophyll maximum is characterized by positive NCP, while NCP in the lower layer (>75 m) is close to zero or negative.

As part of E-Flux III cruise studies in March 2005, we investigated phytoplankton community dynamics in a cyclonic cold-core eddy (Cyclone Opal) in the lee of the Hawaiian Islands. Experimental incubations were conducted under in situ temperature and light conditions on a drift array using a two-treatment dilution technique. Taxon-specific estimates of growth, grazing and production rates were obtained from analyses of incubation results based on phytoplankton pigments, flow cytometry and microscopy. Cyclone Opal was sampled at a biologically and physically mature state, with an 80–100 m doming of isopycnal surfaces in its central region and a deep biomass maximum of large diatoms. Depth-profile experimentation defined three main zones. The upper (mixed) zone (0–40 m), showed little compositional or biomass response to eddy nutrient enrichment, but growth, grazing and production rates were significantly enhanced in this layer relative to the ambient community outside of the eddy. Prochlorococcus spp. dominated the upper mixed layer, accounting for 50–60% of its estimated primary production both inside and outside of Opal. In contrast, the deep zone of 70–90 m showed little evidence of growth rate enhancement and was principally defined by a ∼100-fold increase of large (>20-μm) diatoms and a shift from Prochlorococcus to diatom dominance (∼80%) of production. The intermediate layer of 50–60 m marked the transition between the upper and lower extremes but also contained an elevated biomass of physiologically unhealthy diatoms with significantly depressed growth rates and proportionately greater grazing losses relative to diatoms above or below. Microzooplankton grazers consumed 58%, 65% and 55%, respectively, of the production of diatoms, Prochlorococcus and the total phytoplankton community in Cyclone Opal. The substantial grazing impact on diatoms suggests that efficient recycling was the major primary fate of diatom organic production, consistent with the low export fluxes and selective export of biogenic silica, as empty diatom frustules, in Cyclone Opal.

Wind-driven cyclonic eddies are hypothesized to relieve nutrient stress and enhance primary production by the upward displacement of nutrient-rich deep waters into the euphotic zone. In this study, we measured nitrate (NO 3 − ), particulate carbon (PC), particulate nitrogen (PN), their stable isotope compositions ( δ 15 N-NO 3 − , δ 13 C-PC and δ 15 N-PN, respectively), and dissolved organic nitrogen (DON) within Cyclone Opal , a mature wind-driven eddy generated in the lee of the Hawaiian Islands. Sampling occurred in March 2005 as part of the multi-disciplinary E-Flux study, approximately 4–6 weeks after eddy formation. Integrated NO 3 − concentrations above 110 m were 4.8 times greater inside the eddy (85.8±6.4 mmol N m −2 ) compared to the surrounding water column (17.8±7.8 mmol N m −2 ). Using N-isotope derived estimates of NO 3 − assimilation, we estimated that 213±59 mmol m −2 of NO 3 − was initially injected into the upper 110 m Cyclone Opal formation, implying that NO 3 − was assimilated at a rate of 3.75±0.5 mmol N m −2 d −1 . This injected NO 3 − supported 68±19% and 66±9% of the phytoplankton N demand and export production, respectively. N isotope data suggest that 32±6% of the initial NO 3 − remained unassimilated. Self-shading, inefficiency in the transfer of N from dissolved to particulate export, or depletion of a specific nutrient other than N may have led to a lack of complete NO 3 − assimilation. Using a salt budget approach, we estimate that dissolved organic nitrogen (DON) concentrations increased from eddy formation (3.8±0.4 mmol N m −2 ) to the time of sampling (4.0±0.09 mmol N m −2 ), implying that DON accumulated at rate of 0.83±1.3 mmol N m −2 d −1 , and accounted for 22±15% of the injected NO 3 − . Interestingly, no significant increase in suspended PN and PC, or export production was observed inside Cyclone Opal relative to the surrounding water column. A simple N budget shows that if 22±15% of the injected NO 3 − was shunted into the DON pool, and 32±6% is unassimilated, then 46±16% of the injected NO 3 − remains undocumented. Alternative loss processes within the eddy include lateral exchange of injected NO 3 − along isopycnal surfaces, remineralization of PN at depth, as well as microzooplankton grazing. A 9-day time series within Cyclone Opal revealed a temporal depletion in δ 15 N-PN, implying a rapid change in the N source. A change in NO 3 − assimilation, or a shift from NO 3 − fueled growth to assimilation of a 15 N-deplete N source, may be responsible for such observations.

Interdisciplinary observations of mesoscale eddies were made to the west of the island of Hawai’i. A central goal of the studies is to improve our understanding of the coupling of physical, biological, and biogeochemical processes that occur within these eddies. A specific objective was to test the hypothesis that the physical mechanisms of mesoscale eddies result in increases in nutrient availability to the euphotic layer, increases in primary production, changes in biological community compositions and size distributions, and increases in carbon flux to the deep sea. Data were obtained from ships, surface drifters, and satellite sensors during three separate field experiments. Variability was associated with two well-developed cyclonic, cold-core mesoscale eddies, Cyclone Noah and Cyclone Opal, which were observed during the E-Flux I (survey November 6–20, 2004) and E-Flux III (survey March 10–27, 2005) field campaigns, respectively. No mesoscale eddies were found during E-Flux II (survey January 10–19) when winds were erratic in magnitude and direction, supporting the hypothesis that persistent trade winds drive the production of cold-core mesoscale eddies in the lee of the Hawaiian Islands. Cold-core eddies were present in the E-Flux study area for about 2/3 of a year beginning May 1, 2004 and trade winds prevailed for about 3/4 of the same year. Both Cyclone Noah and Cyclone Opal were generated during strong, persistent northeasterly trade wind conditions and appeared downwind of the ’Alenuihaha Channel separating the islands of Maui and Hawai’i. The likely production mechanism for both mesoscale cold-core eddies involves localized wind-stress-curl-induced upwelling produced by trade wind forcing. Cyclone Noah was likely spun up by strong trade winds just to the southwest of the ’Alenuihaha Channel ( ∼ 20 . 10 ∘ N , 156 . 40 ∘ W ) between August 13 and 21, 2004 based on MODIS satellite sea-surface temperature (SST) imagery and QuikScat satellite wind data, and apparently began to dissipate by mid-December 2004. Cyclone Opal was likely spun up by strong trade winds between February 2 and 18, 2005 southwest of the ’Alenuihaha Channel ( ∼ 20 . 30 ∘ N , 156 . 30 ∘ W ), but was no longer evident in April 2005. Both Cyclone Noah and Cyclone Opal had strong physical, chemical, and biological expressions and displayed similar maximum tangential current speeds of ∼ 60 cm s - 1 . However, Cyclone Opal was more symmetric and larger in scale (roughly 180–200 km in diameter compared to ∼ 160 km in horizontal scale for Cyclone Noah). Both mesoscale eddies displayed significant doming in their centers and in some cases outcroppings of isothermal, isopycnal, nutrient, and chlorophyll a isopleths. After formation and a slow drift southward, Cyclone Noah remained in nearly the same location (roughly 19 . 60 ∘ N , 156 . 50 ∘ W ) during the 3-week in situ sampling period, whereas Cyclone Opal drifted southward by ∼ 165 km over a similar time span of sampling. Interestingly, the physical manifestations of both features were relatively unchanged during the ship-based surveys; however, the biology appears to have evolved within Cyclone Opal. The present report sets the context for several other E-Flux studies.

E-Flux III (March 10–28, 2005) was the third and last field experiment of the E-Flux project. The main goal of the project was to investigate the physical, biological and chemical characteristics of mesoscale eddies that form in the lee of Maui and the Island of Hawai’i, focusing on the physical–biogeochemical interactions. The primary focus of E-Flux III was the cyclonic cold-core eddy Opal, which first appeared in the NOAA GOES sea-surface temperature (SST) imagery during the second half of February 2005. During the experiment, Cyclone Opal moved over 160 km, generally southward. Thus, the sampling design had to be constantly adjusted in order to obtain quasi-synoptic observations of the eddy. Analyses of ship transect-depth profiles of CTD, optical and acoustic Doppler current profiler (ADCP) data revealed a well-developed feature characterized by a fairly symmetric circular shape with a radius of about 80 km. Depth profiles of temperature, salinity and density were characterized by an intense doming of isothermal, isohaline and isopycnal surfaces. Isopleths of nutrient concentrations were roughly parallel to isopycnals, indicating the upwelling of deep nutrient-rich water. The deep chlorophyll maximum layer (DCML) shoaled from a depth of about 130 m in the outer regions of the eddy to about 60 m in the center. Chlorophyll concentrations reached their maximum values in Opal's core region (about 40 km in diameter), where nutrients were upwelled into the euphotic layer. ADCP velocity data clearly showed the cyclonic circulation associated with Opal. Vertical sections of tangential velocities were characterized by values that increased linearly with radial distance from near zero close to the center to a maximum of about 60 cm s - 1 at roughly 25 km from the center, and then slowly decayed. The vertical extent of the cyclonic circulation was primarily limited to the upper mixed layer, as tangential velocities decayed quite rapidly within a depth range of 90–130 m. Potential vorticity analysis suggests that only a relatively small (about 50 km in diameter) and shallow (to a depth of approximately 70 m) portion of the eddy is isolated from the surrounding waters. Radial movements of water can occur between the center of the eddy and the outer regions along density surfaces within an isopycnal range of σ – t 23.6 ( σ t = 23.6 kg m - 3 ) and σ – t 24.4 ( σ t = 24.4 kg m - 3 ). Thus the biogeochemistry of the system might have been greatly influenced by these lateral exchanges of water at depth, especially during Opal's southward migration. While the eddy was translating, deep water in front of the eddy might have been upwelled into the core region, leading to an additional injection of nutrients into the euphotic zone. At the same time, part of the chlorophyll-rich waters in the core region might have remained behind the translating eddy and, thus contributed to the formation of an eddy wake characterized by relatively high chlorophyll concentrations.

Quasi-synoptic observations of the horizontal and vertical structure of a cold-core cyclonic mesoscale eddy feature (Cyclone Noah) were conducted in the lee of Hawai’i from November 4–22, 2004 as part of the E-Flux interdisciplinary collaborative research program. Cyclone Noah appears to have spun up to the southwest of the ‘Alenuihaha Channel (between Maui and Hawai’i) as a result of strong and persistent northeasterly trade winds through the channel. Shipboard hydrographic surveys 2.5 months later suggest that Noah weakened and was in a hypothesized spin-down phase of its life cycle. Although the initial surface expression of Noah was limited in scale to ∼40 km in diameter and, as evidenced by surface temperatures, 2–3 °C cooler than the surrounding waters, depth profiles revealed a fully developed semi-elliptical shallow feature (∼200 m), ∼144 km long and ∼90 km wide (based on sigma-t=23 kg m−3) with tangential speeds of 40–80 cm s−1, and substantial isopycnal doming. Potential vorticity distribution of Noah suggests that radial horizontal flow of the core water was inhibited from the surface to depths of ∼75 m, with high vorticity confined above the sigma-t=23.5 kg m−3 isopycnal surface. Upward displacements of isopycnal surfaces in the eddy's center (∼50 m) were congruent with enhanced pigment concentrations (0.50 mg m−3). Comparisons of the results obtained for E-Flux I (Noah) and E-Flux III (Opal) suggest that translation characteristics of cyclonic Hawaiian lee eddies may be important in establishing the biogeochemical and biological responses of the oligotrophic ocean to cyclonic eddies.

Mesoscale eddies may play a critical role in ocean biogeochemistry by increasing nutrient supply, primary production, and efficiency of the biological pump, that is, the ratio of carbon export to primary production in otherwise nutrient-deficient waters. We examined a diatom bloom within a cold-core cyclonic eddy off Hawai`i. Eddy primary production, community biomass, and size composition were markedly enhanced but had little effect on the carbon export ratio. Instead, the system functioned as a selective silica pump. Strong trophic coupling and inefficient organic export may be general characteristics of community perturbation responses in the warm waters of the Pacific Ocean.

Two in situ iron-enrichment experiments were conducted in the Pacific sector of the Southern Ocean during summer 2002 (SOFeX). The ‘‘north patch,’’ established within the Subantarctic Zone (� 561S), was characterized by high nitrate (� 21 mmol m � 3 ) but low silicic acid (2 mmol m � 3 ) concentrations. North patch iron enrichment increased chlorophyll (Chl) by 12-fold to 2.1 mg m � 3 and primary productivity (PPEU) by 8-fold to 188 mmol C m � 2 d � 1 . Surprisingly, despite low silicic acid concentrations, diagnostic pigment and size-fraction composition changes indicated an assemblage shift from prymnesiophytes toward diatoms. The ‘‘south patch,’’ poleward of the Southern Boundary of the Antarctic Circumpolar Current (SBACC) (� 661S), had high concentrations of nitrate (� 27 mmol m � 3 ) and silicic acid (64 mmol m � 3 ). South patch iron enrichment increased Chl by 9-fold to 3.8 mg m � 3 and PPEU 5-fold to 161 mmol C m � 2 d � 1 but, notably, did not alter the phytoplankton assemblage from the initial composition of � 50% diatoms. South patch iron addition also reduced total particulate organic carbon:Chl from � 300 to 100; enhanced the presence of novel non-photosynthetic, but fluorescent, compounds; and counteracted a decrease in photosynthetic performance as photoperiod decreased. These experiments show unambiguously that in the contemporary, high nitrate Southern Ocean increasing iron supply increases primary productivity, confirming the initial premise of the Martin Iron Hypothesis. However, despite a 5-fold increase in PPEU under iron-replete conditions in late summer, the effect of iron on annual productivity in the Southern Ocean poleward of the SBACC is limited by seasonal ice coverage and the dark of polar winter. r 2007 Elsevier Ltd. All rights reserved.

Understanding the natural variability of photosynthetic pigment ranges and distributions in healthy corals is central to evaluating how useful these measurements are for assessing the health and bleaching status of endosymbiotic reef-building corals. This study examined the photosynthetic pigment variability in visibly healthy Porites lobata and Porites lutea corals from Kaneohe Bay, Hawaii and explored whether pigment variability was related to the genetic identity or phenotypic characteristics of the symbionts. Concentrations of the photosynthetic pigments chlorophyll a, peridinin, chlorophyll c 2 , diadinoxanthin, diatoxanthin, β,β-carotene and dinoxanthin were quantified using high-performance liquid chromatography (HPLC). Pigment concentrations were found to range 1.5–10 fold in colonies of each species at similar depths (0–2, 2–4, 10–15 and 19–21 m). Despite the high pigment variability, pigment ratios for each species were relatively conserved over the 0–21 m depth gradient. The genetic identity of the symbiont communities was examined for each colony using 18S nuclear ribosomal DNA (nrDNA) restriction fragment length polymorphisms. All colonies contained symbionts belonging to clade C. The density and phenotypic characteristics of the symbionts were explored using flow cytometry, and fluorescence and side scatter (cell size) properties revealed phenotypically distinct symbiont subpopulations in every colony. The symbiont subpopulations displayed pigment trends that may be driven by acclimatization to irradiance microenvironments within the host. These results highlight the biological complexity of healthy coral–symbiont associations and the need for future research on pigments and symbiont subpopulation dynamics.

Dissolved and particulate concentrations of the biogenic thiols cysteine (Cys), arginine–cysteine (Arg–Cys), glutamine–cysteine (Gln–Cys), γ-glutamate–cysteine (γ-Glu–Cys) and glutathione (GSH) were measured in the subartic Pacific Ocean in the summer of 2003 using high performance liquid chromatography (HPLC) with precolumn derivatization as reported in previous work. In this study, a preconcentration protocol for the derivatized thiols was utilized to extend detection limits of dissolved thiols to picomolar levels. The measured concentrations of particulate and dissolved thiols were uncoupled, with distinctive depth profiles and large differences in the particulate to dissolved ratios between individual compounds. Glutathione was the most abundant particulate thiol whereas the most abundant dissolved thiol was γ-Glu–Cys, with concentrations as high as 15 nM. Given the relatively small pool of intracellular γ-Glu–Cys and the very low dissolved concentrations of GSH, we hypothesize that glutathione released from cells is rapidly converted to the potentially degradation resistant γ-Glu–Cys outside the cell. The relatively high concentrations of other dissolved thiols compared to particulate concentrations implies both biological exudation and slow degradation rates. Some thiols appear to vary with changes in nutrient availability but this effect is difficult to decouple from changes in community structure inferred from pigment analyses. Dissolved thiol concentrations also exceed typical metal concentrations in the subartic Pacific, supporting previous arguments that they may be important in metal speciation.

The marine photoheterotroph Erythrobacter longus Strain NJ3Y was grown in continuous culture under variable light:dark (L:D) regimes of 24:0, 12:12 and 0:24 h to examine the influence of photoperiod on pigmentation and metabolic efficiency. Average carbon mass balances for each light regime closed to within 5 %, giving confidence in the measured variables as well as calculations of physiological parameters. Significant differences in photosynthetic pigmentation were observed for the experimental light treatments, with highest and lowest pigment concentrations measured in the 0:24 and 24:0 h L:D regimes, respectively, indicating that the photosynthetic pigments of E. longus Strain NJ3Y are preferentially synthesized in the dark. These differences are consistent with the strategy that photosynthetic pigments are produced during periods of darkness, for use in energy harvesting during subsequent light periods. In contrast, concentrations of the photoprotective pigment caloxanthin sulfate were highest for cells grown under a 12:12 h L:D cycle, indicating that this carotenoid is synthesized in the light and the dark. It is concluded that the 12:12 h L:D regime provides the maximum opportunity for E. longus Strain NJ3Y to derive a metabolic advantage from light availability (i.e. by enabling it to both synthesize and utilize its light harvesting apparatus). The corresponding carbon-specific glucose uptake rate was similar to 30% higher than that measured for the 0:24 and 24:0 h L:D regimes. It is hypothesized that light-stimulated rates of dissolved organic carbon uptake by bacteriochlorophyll a containing bacteria confer a slight competitive advantage over bacteria that lack this photosynthetic machinery. Lowest glucose-specific biomass yields (Y-x/s, g dry cell wt g(-1) glucose) were observed for the 12:12 h L:D treatment, suggesting that under the culture conditions used in this study, photosynthesis does not contribute significantly to the growth of E. longus Strain NJ3Y.

National Science Foundation grants OCE-9986306 and OCE-0094637 (B.N.P., R.R.B., E.A.L.), OCE-0094272 (B.N.P.), OCE-9986306 and OCE-0094329 (F.G.P.). SOEST contribution no. 6738.

The spectral reflectance of coral is inherently related to the amounts of photosynthetic pigments present in the zooxanthellae. There are no studies, however, showing that the suite of major photosynthetic pigments can be predicted from optical reflectance spectra. In this study, we measured cm-scale in vivo and in situ spectral reflectance for several colonies of the massive corals Porites lobata and Porites lutea, two colonies of the branching coral Porites compressa, and one colony of the encrusting coral Montipora flabellata in Kaneohe Bay, Oahu, Hawaii. For each reflectance spectrum, we collected a tissue sample and utilized high-performance liquid chromatography to quantify six major photosynthetic pigments, located in the zooxanthellae. We used multivariate multiple regression analysis with cross-validation to build and test an empirical linear model for predicting pigment concentrations from optical reflectance spectra. The model accurately predicted concentrations of chlorophyll a, chlorophyll c 2, peridinin, diadinoxanthin, diatoxanthin and β-carotene, with correlation coefficients of 0.997, 0.941, 0.995, 0.996, 0.980 and 0.984, respectively. The relationship between predicted and actual concentrations was 1:1 for each pigment, except chlorophyll c 2. This simple empirical model demonstrates the potential for routine, rapid, non-invasive monitoring of coral-zooxanthellae status, and ultimately for remote sensing of reef biogeochemical processes.

A carbon mass balance methodology employing minimal measurements was applied to heterotrophic and photoheterotrophic marine bacteria grown under constant dilution and exposed to 12-h intervals of light or darkness. Carbon mass balance calculations using measurements taken every 3 h closed to within 93-103% using dissolved organic carbon, biomass carbon and CO2 production data only, indicating that background interference from dissolved inorganic carbon variations in the amended seawater medium was not significant. Neither strain was observed to sustain a net CO2 fixation using paramagnetic measurement of oxygen uptake rates (OUR), indicating a need for more sensitive on-line measurement techniques for OUR. Photoheterotrophic growth demonstrated lower carbon-mole biomass yields (0.41+/-0.026 vs. 0.64+/-0.013 mol mol(-1)) despite higher specific glucose uptake rates (0.025 vs. 0.02 mol mol(-1) h(-1)), suggesting that bioreactor-based study of marine bacteria can present growth modes that are different from those encountered in the marine environment.

The availability of iron is known to exert a controlling influence on biological productivity in surface waters over large areas of the ocean and may have been an important factor in the variation of the concentration of atmospheric carbon dioxide over glacial cycles. The effect of iron in the Southern Ocean is particularly important because of its large area and abundant nitrate, yet iron-enhanced growth of phytoplankton may be differentially expressed between waters with high silicic acid in the south and low silicic acid in the north, where diatom growth may be limited by both silicic acid and iron. Two mesoscale experiments, designed to investigate the effects of iron enrichment in regions with high and low concentrations of silicic acid, were performed in the Southern Ocean. These experiments demonstrate iron's pivotal role in controlling carbon uptake and regulating atmospheric partial pressure of carbon dioxide.

The euphotic zone below the deep chlorophyll maximum layer (DCML) at Station ALOHA (a long-term oligotrophic habitat assessment; 228459N, 1588009W) transects the nearly permanently stratified upper thermocline. Hence, seasonal changes in solar radiation control the balance between photosynthesis and respiration in this lightlimited region. Combining profiles of radiance reflectance, algal pigments, and inorganic nutrients collected between January 1998 and December 2000, we explore the relationships between photosynthetically available radiation (PAR), phytoplankton biomass (chlorophyll a), and the position of the upper nitracline in the lower euphotic zone. Seasonal variations in the water-column PAR attenuation coefficient displace the 1% sea-surface PAR depth from approximately 105 m in winter to 121 m in summer. However, the seasonal depth displacement of isolumes (constant daily integrated photon flux strata) increases to 31 m due to the added effect of changes in sea-surface PAR. This variation induces a significant deepening of the DCML during summertime with a concomitant increase in chlorophyll a and the removal of 36 mmol m 22 inorganic nitrogen [NO 1 NO ] in the 90‐200-m depth range, 22 32 equivalent to approximately 34% of the annual flux of particulate nitrogen collected in sediment traps placed at 150 m. We conclude that in this oceanic region the annual light cycle at the base of the euphotic zone induces an increase in the phototrophic biomass analogous to a spring bloom event.

Seven strains of marine aerobic anoxygenic phototrophs belonging to the genus Erythrobacter were isolated. The strains were characterized regarding their physiological and biochemical properties, 16S rDNA and pufM gene sequences, morphological features, substrate preference, as well as pigment and lipid composition. All strains had functional type-2 reaction centers containing bacteriochlorophyll, served by small, light-harvesting complex 1, and were photosynthetically competent. In addition, large pools of carotenoids were found, but only some of the accessory pigments transfer energy to the reaction centers. All of the isolates were facultative photoheterotrophs. They required an organic carbon substrate for growth; however, they are able to supplement a significant fraction of their metabolic requirements with photosynthetically derived energy.

A synoptic spatial examination of the eddy Haulani (17–20 November 2000) revealed a structure typical of Hawaiian cyclonic eddies with divergent surface flow forcing the upward displacement of deep waters. Hydrographic surveys revealed that surface water in the eddy center was ca. 3.5°C cooler, 0.5 saltier, and 1.4 kg m −3 denser than surface waters outside the eddy. Vertically integrated concentrations of nitrate+nitrite, phosphate and silicate were enhanced over out-eddy values by about 2-fold, and nitrate+nitrite concentrations were ca. 8× greater within the euphotic zone inside the eddy than outside. Si:N ratios were lower within the upper mixed layer of the eddy, indicating an enhanced Si uptake relative to nitrate+nitrite. Chlorophyll a concentrations were higher within the eddy compared to control stations outside, when integrated over the upper 150 m, but were not significantly different when integrated over the depth of the euphotic zone. Photosynthetic competency, assessed using fast repetition-rate fluorometry, varied with the doming of the isopycnals and the supply of macro-nutrients to the euphotic zone. The physical and chemical environment of the eddy selected for the accumulation of larger phytoplankton species. Photosynthetic bacteria ( Prochlorococcus and Synechococcus ) and small ( 3 μm diameter) were more abundant inside the eddy than outside. Diatoms of the genera Rhizosolenia and Hemiaulus outside the eddy contained diazotrophic endosymbiontic cyanobacteria, but these endosymbionts were absent from the cells of these species inside the eddy. The increase in cell numbers of large photosynthetic eukaryotes with hard silica or calcite cell walls is likely to have a profound impact on the proportion of the organic carbon production that is exported to deep water by sinking of senescent cells and cells grazed by herbivorous zooplankton and repackaged as large fecal pellets.