Abstract. Although the Southern Ocean is considered a high-nutrient, low-chlorophyll (HNLC) area, massive and recurrent blooms are observed over and downstream of the Kerguelen Plateau. This mosaic of blooms is triggered by a higher iron supply resulting from the interaction between the Antarctic Circumpolar Current and the local bathymetry. Net primary production, N uptake (NO − 3 and NH + 4 ), and nitrification rates were measured at eight stations in austral spring 2011 (October-November) during the KEOPS 2 cruise in the Kerguelen Plateau area. Natural iron fertilization stimulated primary production, with mixed layer integrated net primary production and growth rates much higher in the fertilized areas (up to 315 mmol C m −2 d −1 and up to 0.31 d −1 respectively) compared to the HNLC reference site (12 mmol C m −2 d −1 and 0.06 d −1 respectively). Primary production was mainly sustained by nitrate uptake, with f ratios (corresponding to NO − 3 -uptake / (NO − 3 -uptake + NH + 4 -uptake)) lying at the upper end of the observations for the Southern Ocean (up to 0.9). We report high rates of nitrification (up to ∼ 3 µmol N L −1 d −1 , with ∼ 90 % of them < 1 µmol N L −1 d −1 ) typically occurring below the euphotic zone, as classically observed in the global ocean. The specificity of the studied area is that at most of the stations, the euphotic layer was shallower than the mixed layer, implying that nitrifiers can efficiently compete with phytoplankton for the ammonium produced by remineralization at low-light intensities. Nitrate produced by nitrification in the mixed layer below the euphotic zone is easily supplied to the euphotic zone waters above, and nitrification sustained 70 ± 30 % of the nitrate uptake in the productive area above the Kerguelen Plateau. This complicates estimations of new production as potentially exportable production. We conclude that high productivity in deep mixing system stimulates the N cycle by increasing both assimilation and regeneration.

a b s t r a c tCoastal upwelling ecosystems are areas of high productivity and strong outgassing, where most gases, such as N 2 O and CH 4 , are produced in subsurface waters by anaerobic metabolisms. We describe seasonal CH 4 variation as well as potential mechanisms producing CH 4 in surface waters of the central Chile upwelling ecosystem (36°S). Surface waters were always supersaturated in CH 4 (from 125% up to 550%), showing a clear seasonal signal triggered by wind driven upwelling processes (austral springsummer period), that matched with the periods of high chlorophyll-a and dimethylsulfoniopropionate (DMSP) levels. Methane cycling experiments, with/without the addition of dimethylsulfide (including 13 C-DMS) and acetylene (a nonspecific inhibitor of CH 4 oxidation) along with monthly measurements of CH 4 , DMSP and other oceanographic variables revealed that DMS can be a CH 4 precursor. Net CH 4 cycling rates (control) fluctuated between À0.64 and 1.44 nmol L À1 d À1 . After the addition of acetylene, CH 4 cycling rates almost duplicated relative to the control, suggesting a strong methanotrophic activity. With a spike of DMS, the net CH 4 cycling rate significantly increased relative to the acetylene and control treatment. Additionally, the d 13 C values of CH 4 at the end of the incubations (after addition of 13 C enriched-DMS) were changed, reaching À32‰ PDB compared to natural values between À44‰ and À46‰ PDB. These findings indicate that, in spite of the strong CH 4 consumption by methanotrophs, this upwelling area is an important source of CH 4 to the atmosphere. The effluxes are derived partially from in situ surface production and seem to be related to DMSP/DMS metabolism.

Strain HIMB11 is a planktonic marine bacterium isolated from coastal seawater in Kaneohe Bay, Oahu, Hawaii belonging to the ubiquitous and versatile Roseobacter clade of the alphaproteobacterial family Rhodobacteraceae. Here we describe the preliminary characteristics of strain HIMB11, including annotation of the draft genome sequence and comparative genomic analysis with other members of the Roseobacter lineage. The 3,098,747 bp draft genome is arranged in 34 contigs and contains 3,183 protein-coding genes and 54 RNA genes. Phylogenomic and 16S rRNA gene analyses indicate that HIMB11 represents a unique sublineage within the Roseobacter clade. Comparison with other publicly available genome sequences from members of the Roseobacter lineage reveals that strain HIMB11 has the genomic potential to utilize a wide variety of energy sources (e.g. organic matter, reduced inorganic sulfur, light, carbon monoxide), while possessing a reduced number of substrate transporters.

The production of large amounts of algal biomass for different purposes such as aquaculture or biofuels, may cause impacts on the marine environment. One such impact is the production of radiatively active trace gases and aerosols with climate cooling (dimethyl sulfide DMS and its precursor DMSP) and warming (N₂O and CH₄) effects. Total and dissolved DMSP, N₂O and CH₄, together with other environmental variables were monitored daily for 46 days within a massive microalgae monoculture of Nannochloris (Chlorophyceae) in an open pond system. The growth of this green microalgae was stimulated by the addition of N- and P-rich salts, resulting in exponential growth (growth phase) during the first 17 days observed by cell abundance (1 × 10⁶ to 4.4 × 10⁶ cell mL⁻¹) and Chl-a levels (from 1.4 to 96 mg Chl-a m⁻³) followed by a decrease in both Chl-a and cell abundance (senescence phase). Total DMSP (from 6.3 to 142 μmol m⁻³), dissolved DMSP i.e. 5.8 to 137 μmol m⁻³ and N₂O (from 8 to 600 μmol m⁻³) abruptly peaked during the senescence phase, whereas CH₄ steadily increased between 2 and 10 μmol m⁻³ during the growth phase. Different ratios between tracers and Chl-a during both phases reveal different biochemical processes involved in the cycling of these gases and tracers. Our results show that despite the consumption of large quantities of CO₂ by the massive algal culture, a minor amount of DMS and huge amounts of greenhouse gases were produced, in particular N₂O, which has a greater radiative effect per molecule than CO₂. These findings have important implications for biogeochemical studies and for environmental management of aquaculture activities