Low colloidal associations of aluminium and titanium in surface waters of the tropical Atlantic

The distribution of dissolved, soluble and colloidal fractions of Al and Ti was assessed by ultrafiltration studies in the upper water column of the eastern tropical North Atlantic. The dissolved fractions of both metals were found to be dominated by the soluble phase smaller than 10 kDa. The colloidal associations were very low (0.2–3.4%) for Al and not detectable for Ti. These findings are in some contrast to previous estimations for Ti and to the predominant occurrence of both metals as hydrolyzed species in seawater. However, low tendencies to form inorganic colloids can be expected, as in seawater dissolved Al and dissolved Ti are present within their inorganic solubility levels. In addition, association with functional organic groups in the colloidal phase is unlikely for both metals. Vertical distributions of the dissolved fractions showed surface maxima with up to 43 nM of Al and 157 pM of Ti, reflecting their predominant supply from atmospheric sources to the open ocean. In the surface waters, excess dissolved Al over dissolved Ti was present compared to the crustal source, indicating higher solubility and thus elevated inputs of dissolved Al from atmospheric mineral particles. At most stations, subsurface minima of Al and Ti were observed and can be ascribed to scavenging processes and/or biological uptake. The dissolved Al concentrations decreased by 80–90% from the surface maximum to the subsurface minimum. Estimated residence times in the upper 100 m of the water column ranged between 1.6 and 4 years for dissolved Al and between 14 and 17 years for dissolved Ti. The short residence times are in some contrast to the low colloidal associations of Al and Ti and the assumed role of colloids as intermediates in scavenging processes. This suggests that either the removal of both metals occurs predominantly via direct transfer of the hydrolyzed species into the particulate fraction or that the colloidal phase is rapidly turned over in the upper water column.

Methanol acetaldehyde and acetone in the surface waters of the Atlantic Ocean

Oceanic methanol, acetaldehyde, and acetone concentrations were measured during an Atlantic Meridional Transect (AMT) cruise from the UK to Chile (49°N to 39°S) in 2009. Methanol (48–361 nM) and acetone (2–24 nM) varied over the track with enrichment in the oligotrophic Northern Atlantic Gyre. Acetaldehyde showed less variability (3–9 nM) over the full extent of the transect. These oxygenated volatile organic compounds (OVOCs) were also measured subsurface, with methanol and acetaldehyde mostly showing homogeneity throughout the water column. Acetone displayed a reduction below the mixed layer. OVOC concentrations did not consistently correlate with primary production or chlorophyll-a levels in the surface Atlantic Ocean. However, we did find a novel and significant negative relationship between acetone concentration and bacterial leucine incorporation, suggesting that acetone might be removed by marine bacteria as a source of carbon. Microbial turnover of both acetone and acetaldehyde was confirmed. Modeled atmospheric data are used to estimate the likely air-side OVOC concentrations. The direction and magnitude of air-sea fluxes vary for all three OVOCs depending on location. We present evidence that the ocean may exhibit regions of acetaldehyde under-saturation. Extrapolation suggests that the Atlantic Ocean represents an overall source of these OVOCs to the atmosphere at 3, 3, and 1 Tg yr−1 for methanol, acetaldehyde, and acetone, respectively.

Pattern of benthic biomass size spectra from shallow waters in the East China Seas

Benthic biomass size spectra (BSS) and normalized biomass size spectra were constructed, and benthic secondary production was estimated by a size spectrum equation in the shallow waters in the East China Sea, ranging latitudinally from 40A degrees N to 29A degrees N. The BSS patterns were bimodal, two biomass peaks corresponding to meiofauna and macrofauna, respectively, separated by a trough of low biomass at 8-256 mu g individual dry weight which varied in position with median sediment particle size. The BSS also displayed bimodality within meiofauna size ranges, which in most stations was due to the relative proportions of nematodes and other meiofauna taxa. Re-analysis of data from sites in the UK, South Africa, and Antarctic showed a similar bimodality in the adult species body size distribution within the meiofauna size range. Macrofaunal production estimated by the size spectrum equation was very similar to the results of Brey90 empirical equation. However, these production values were much lower than those calculated by Brey01. Different individual dry-to-wet conversion ratios, temperature deviation, and macrofauna taxonomic composition might be responsible for the between-model differences. The macrofaunal P/B ratios calculated by this equation ranged from 0.3 to 3.4 which were in accordance with values from Northern Hemisphere mid-latitudes. Meiofaunal production estimates will need further empirical support.

Above-water reflectance for the evaluation of adjacency effects in Earth observation data: initial results and methods comparison for near-coastal waters in the Western Channel, UK

Un-supervised hyperspectral remote-sensing reflectance data (<15 km from the shore) were collected from a moving research vessel. Two different processing methods were compared. The results were similar to concurrent Aqua-MODIS and Suomi-NPP-VIIRS satellite data.

Nitrogen uptake of phytoplankton assemblages under contrasting upwelling and downwelling conditions: The Ría de Vigo, NW Iberia

Regenerated production (including organic nitrogen) is shown here to be important in the Ria de Vigo (Galicia, NW Iberia) in supporting both harmful algal bloom communities during the downwelling season, but also (to a lesser extent) diatom communities during stratified periods of weak to moderate upwelling. The Galician Rias, situated in the Iberian upwelling system, are regularly affected by blooms of toxic dinoflagellates, which pose serious threats to the local mussel farming industry. These tend to occur towards the end of summer, during the transition from upwelling to downwelling favourable seasons, when cold bottom shelf waters in the rias are replaced by warm surface shelf waters. Nitrate, ammonium and urea uptake rates were measured in the Ria de Vigo during a downwelling event in September 2006 and during an upwelling event in June 2007. In September the ria was well mixed, with a downwelling front observed towards the middle of the ria and relatively high nutrient concentrations (1.0-2.6 mu mol L-1 nitrate; 1.0-5.6 mu mol L-1 ammonium; 0.1-0.8 mu mol L-1 phosphate; 2.0-9.0 mu mol L-1 silicic acid) were present throughout the water column. Ammonium represented more than 80% of the nitrogenous nutrients, and the phytoplankton assemblage was dominated by dinoflagellates and small flagellates. In June the water column was stratified, with nutrient-rich, upwelled water below the thermocline and warm, nutrient-depleted water in the surface. At this time, nitrate represented more than 80% of the nitrogenous nutrients, and a mixed diatom assemblage was present. Primary phytoplankton production during both events was mainly sustained by regenerated nitrogen, with ammonium uptake rates of 0.035-0.063 mu mol N L-1 h(-1) in September and 0.078-0.188 mu mol N L-1 h(-1) in June. Although f-ratios were generally low (<0.2) in both June and September, a maximum of 0.61 was reached in June due to higher nitrate uptake (0.225 mu mol N L-1 h(-1)). Total nitrogen uptake was also higher during the upwelling event (0.153-0.366 in June and 0.053-0.096 mu mol N L-1 h(-1) in September). Nitrogen uptake kinetics demonstrated a strong preference for ammonium and urea over nitrate in June.

Competition Drives Clumpy Species Coexistence in Estuarine Phytoplankton

Understanding the mechanisms that maintain biodiversity is a fundamental problem in ecology. Competition is thought to reduce diversity, but hundreds of microbial aquatic primary producers species coexist and compete for a few essential resources (e.g., nutrients and light). Here, we show that resource competition is a plausible mechanism for explaining clumpy distribution on individual species volume (a proxy for the niche) of estuarine phytoplankton communities ranging from North America to South America and Europe, supporting the Emergent Neutrality hypothesis. Furthermore, such a clumpy distribution was also observed throughout the Holocene in diatoms from a sediment core. A Lotka-Volterra competition model predicted position in the niche axis and functional affiliation of dominant species within and among clumps. Results support the coexistence of functionally equivalent species in ecosystems and indicate that resource competition may be a key process to shape the size structure of estuarine phytoplankton, which in turn drives ecosystem functioning.