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The distribution of bioactive trace metals has the potential to enhance or limit primary productivity and carbon export in some regions of the world ocean. To study these connections, the concentrations of Cd, Co, Cu, Fe, Mo, Ni, and V were determined for 110 surface water samples collected during the Malaspina 2010 Circumnavigation Expedition (MCE). Total dissolved Cd, Co, Cu, Fe, Mo, Ni, and V concentrations averaged 19.0 ± 5.4 pM, 21.4 ± 12 pM, 0.91 ± 0.4 nM, 0.66 ± 0.3 nM, 88.8 ± 12 nM, 1.72 ± 0.4 nM, and 23.4 ± 4.4 nM, respectively, with the lowest values detected in the Central Pacific and increased values at the extremes of all transects near coastal zones. Trace metal concentrations measured in surface waters of the Atlantic Ocean during the MCE were compared to previously published data for the same region. The comparison revealed little temporal changes in the distribution of Cd, Co, Cu, Fe, and Ni over the last 30 years. We utilized a multivariable linear regression model to describe potential relationships between primary productivity and the hydrological, biological, trace nutrient and macronutrient data collected during the MCE. Our statistical analysis shows that primary productivity in the Indian Ocean is best described by chlorophyll a, NO3, Ni, temperature, SiO4, and Cd. In the Atlantic Ocean, primary productivity is correlated with chlorophyll a, NO3, PO4, mixed layer depth, Co, Fe, Cd, Cu, V, and Mo. The variables salinity, temperature, SiO4, NO3, PO4, Fe, Cd, and V were found to best predict primary productivity in the Pacific Ocean. These results suggest that some of the lesser studied trace elements (e.g., Ni, V, Mo, and Cd) may play a more important role in regulating oceanic primary productivity than previously thought and point to the need for future experiments to verify their potential biological functions. [ABSTRACT FROM AUTHOR]

We examined large volumes of seawater under the microscope to explore the limits of phytoplankton diversity in a highly dynamic coastal ecosystem. Our analysis showed that conventional sample volumes severely underestimate the species richness of these phytoplankton communities. The number of species observed doubled after a 10-fold increase in sample volume, implying that estimates of phytoplankton species richness depend critically on sampling effort. The volume of sample needed to detect 90% of the species varied between 0.25 and 1 L depending on the concentration of phytoplankton biomass. [ABSTRACT FROM PUBLISHER]

The universal temperature dependence of metabolic rates has been used to predict how ocean biology will respond to ocean warming. Determining the temperature sensitivity of phytoplankton metabolism and growth is of special importance because this group of organisms is responsible for nearly half of global primary production, sustains most marine food webs, and contributes to regulate the exchange of CO2 between the ocean and the atmosphere. Phytoplankton growth rates increase with temperature under optimal growth conditions in the laboratory, but it is unclear whether the same degree of temperature dependence exists in nature, where resources are often limiting. Here we use concurrent measurements of phytoplankton biomass and carbon fixation rates in polar, temperate and tropical regions to determine the role of temperature and resource supply in controlling the large-scale variability of in situ metabolic rates. We identify a biogeographic pattern in phytoplankton metabolic rates, which increase from the oligotrophic subtropical gyres to temperate regions and then coastal waters. Variability in phytoplankton growth is driven by changes in resource supply and appears to be independent of seawater temperature. The lack of temperature sensitivity of realized phytoplankton growth is consistent with the limited applicability of Arrhenius enzymatic kinetics when substrate concentrations are low. Our results suggest that, due to widespread resource limitation in the ocean, the direct effect of sea surface warming upon phytoplankton growth and productivity may be smaller than anticipated. [ABSTRACT FROM AUTHOR]

The effects of inorganicand/or organic (glucose+AAs) inputs on phytoplankton and heterotrophic bacteria were assessed, using a microcosm approach, in two contrasting marine environments: an open ocean oligotrophic site (North Atlantic Subtropical Gyre) and a highly productive coastal embayment (Ría de Vigo, NW Spain). Overall, changes in microbial plankton biomass were smaller than those of metabolic rates. The largest increases in primary production, bacterial production and community respiration were measured in response to mixed () nutrient additions in both sites. Primary production responded toadditions only in oligotrophic waters. The distinct autotrophic responses to nutrient additions measured in these environments were related to the different initial composition of phytoplankton populations and, presumably, also to differences in grazing pressures in both marine ecosystems. Heterotrophic bacteria were limited by organic substrates in both ecosystems, although mixed additions further enhanced bacterial growth in the subtropical gyre. The differences detected in bacterial responses to nutrient additions may be related to differences in nutrient limitations and to the prevalence of different relationships between components of the microbial food web (e.g. coupling between heterotrophic bacteria and phytoplankton and predation pressure) in both environments. We found a more relevant role of inorganic nutrients in controlling the efficiency of bacterial growth in oligotrophic regions as compared with highly productive systems. Our results suggest that organic matter inputs into both ecosystems might result in a tendency towards heterotrophy and in increases in bacterial growth efficiency. [ABSTRACT FROM AUTHOR]

Phytoplankton size structure is key for the ecology and biogeochemistry of pelagic ecosystems, but the relationship between cell size and maximum growth rate (μmax) is not yet well understood. We used cultures of 22 species of marine phytoplankton from five phyla, ranging from 0.1 to 106 μm3 in cell volume (Vcell), to determine experimentally the size dependence of growth, metabolic rate, elemental stoichiometry and nutrient uptake. We show that both μmax and carbon-specific photosynthesis peak at intermediate cell sizes. Maximum nitrogen uptake rate ( VmaxN) scales isometrically with Vcell, whereas nitrogen minimum quota scales as Vcell0.84. Large cells thus possess high ability to take up nitrogen, relative to their requirements, and large storage capacity, but their growth is limited by the conversion of nutrients into biomass. Small species show similar volume-specific VmaxN compared to their larger counterparts, but have higher nitrogen requirements. We suggest that the unimodal size scaling of phytoplankton growth arises from taxon-independent, size-related constraints in nutrient uptake, requirement and assimilation. [ABSTRACT FROM AUTHOR]

We conducted a meta-analysis of temperature, phytoplankton size structure, and productivity in cold, temperate, and warm waters of the world's oceans. Our data set covers all combinations of temperature and resource availability, thus allowing us to disentangle their effects. The partitioning of biomass between different size classes is independent of temperature, but depends strongly on the rate of resource use as reflected in the rate of primary production. Temperature and primary production explained 2% and 62%, respectively, of the variability in the contribution of microphytoplankton to total biomass. This contribution increases rapidly with total biomass and productivity, reaching values > 80% when chlorophyll a concentration is > 2 µg L-1 or primary production is > 100 µg C L-1 d-1, irrespective of water temperature. Conversely, picophytoplankton contribution is substantial (> 40%), at all temperatures, only when chlorophyll a concentration is < 1 µg L-1 or primary production is < 50 µg C L-1 d-1. The temperature--size rule cannot explain these changes, which instead reflect fundamental reorganizations in the species composition of the assemblage, arising from taxon- and size-dependent differences in resource acquisition and use. Given that resource availability, rather than temperature per se, is the key factor explaining the relative success of different algal size classes, there will be no single, universal effect of global warming on phytoplankton size structure. [ABSTRACT FROM AUTHOR]

To determine the effects of Saharan dust on the abundance, biomass, community structure, and metabolic activity of oceanic microbial plankton, we conducted eight bioassay experiments between ca. 30°N and 30°S in the central Atlantic Ocean. We found that, although bulk abundance and biomass tended to remain unchanged, different groups of phytoplankton and bacterioplankton responded differently to Saharan dust addition. The predominant type of metabolic response depended on the ecosystem's degree of oligotrophy and was modulated by competition for nutrients between phytoplankton and heterotrophic bacteria. The relative increase in bacterial production, which was the dominant response to dust addition in ultraoligotrophic environments, became larger with increasing oligotrophy. In contrast, primary production, which was stimulated only in the least oligotrophic waters, became less responsive to dust as the ecosystem's degree of oligotrophy increased. Given the divergent consequences of a predominantly bacterial vs. phytoplanktonic response, dust inputs can, depending on the ecosystem's degree of oligotrophy, stimulate or weaken biological CO2 drawdown. Thus, the biogeochemical implications of changing dust fluxes might not be universal, but variable through both space and time. [ABSTRACT FROM AUTHOR]

We have determined the relationship between carbon-specific photosynthesis and phytoplankton cell size in a coastal ecosystem. The normalized size spectra of carbon (C) biomass and photosynthesis allow to determine both biomass and photosynthesis within any size class along the community size spectrum. By dividing the size spectra of photosynthesis and biomass, the size spectrum of C-specific photosynthesis is derived. Our results indicated a high variability in the slope of the C-specific photosynthesis size spectrum. Under favourable conditions for growth, in the upper euphotic layer, the slope was positive, indicating that larger phytoplankton attained higher C-specific photosynthesis rates than the smaller cells. This pattern represents a significant departure from the expected, literature value of −0.25 for the size-scaling of biomass-specific metabolism. We suggest that this change in the slope may be caused by the changes in the taxonomic composition along the community size spectrum. Towards the bottom of the euphotic layer, we observed a decrease in the slope of the C-specific photosynthesis size spectrum, which could be associated with an enhanced package effect in larger cells under light-limited conditions. These results question the applicability of single and overall exponents to describe the size scaling of photosynthesis in natural phytoplankton assemblages. [ABSTRACT FROM AUTHOR]