Nanoplankton: The dominant vector for carbon export across the Atlantic Southern Ocean in spring.

Across the Southern Ocean, large (≥20 µm) diatoms are generally assumed to be the primary vector for carbon export, although this assumption derives mainly from summertime observations. Here, we investigated carbon production and export potential during the Atlantic Southern Ocean's spring bloom from size-fractionated measurements of net primary production (NPP), nitrogen (nitrate, ammonium, urea) and iron (labile inorganic iron, organically complexed iron) uptake, and a high-resolution characterization of phytoplankton community composition. The nanoplankton-sized (2.7 to 20 µm) diatom, Chaetoceros spp., dominated the biomass, NPP, and nitrate uptake across the basin (40°S to 56°S), which we attribute to their low iron requirement, rapid response to increased light, and ability to escape grazing when aggregated into chains. We estimate that the spring Chaetoceros bloom accounted for >25% of annual export production across the Atlantic Southern Ocean, a finding consistent with recent observations from other regions highlighting the central role of the phytoplankton "middle class" in carbon export.

Dataset from a mesocosm experiment on brownification in the Baltic Sea.

Climate change is projected to cause brownification of some coastal seas due to increased runoff of terrestrially derived organic matter. We carried out a mesocosm experiment over 15 days to test the effect of this on the planktonic ecosystem. The experiment was set up in 2.2 m3 plastic bags moored outside the Tvärminne Zoological Station at the SW coast of Finland. We used four treatments, each with three replicates: control (Contr) without any manipulation; addition of a commercially available organic carbon additive called HuminFeed (Hum; 2 mg L-1); addition of inorganic nutrients (Nutr; 5.7 µM NH4 and 0.65µM PO4); and a final treatment of combined Nutr and Hum (Nutr+Hum) additions. Water samples were taken daily, and measured variables included water transparency, organic and inorganic nutrient pools, chlorophyll a (Chla), primary and bacterial production and particle counts by flow cytometry.

Brownification affects phytoplankton community composition but not primary productivity in eutrophic coastal waters: A mesocosm experiment in the Baltic Sea.

Climate change is projected to cause brownification of some coastal seas due to increased runoff of terrestrially derived organic matter. We carried out a mesocosm experiment (15 d) to test the effect of this on the planktonic ecosystem expecting reduced primary production and shifts in the phytoplankton community composition. The experiment was set up in 2.2 m3 mesocosm bags using four treatments, each with three replicates: control (Contr) without any manipulation, organic carbon additive HuminFeed (Hum; 2 mg L-1), inorganic nutrients (Nutr; 5.7 µM NH4 and 0.65 µM PO4), and combined Nutr and Hum (Nutr + Hum) additions. Measured variables included organic and inorganic nutrient pools, chlorophyll a (Chla), primary and bacterial production and particle counts by flow cytometry. The bags with added inorganic nutrients developed a phytoplankton bloom that depleted inorganic N at day 6, followed by a rapid decline in Chla. Brownification did not reduce primary production at the tested concentration. Bacterial production was lowest in the Contr, but similar in the three treatments receiving additions likely due to increased carbon available for heterotrophic bacteria. Picoeukaryotes clearly benefited by brownification after inorganic N depletion, which could be due to more effective nutrient recycling, nutrient affinity, light absorption, or alternatively lower grazing pressure. In conclusion, brownification shifted the phytoplankton community composition towards smaller species with potential effects on carbon fluxes, such as sinking rates and export to the sea floor.

Dinophysiales (Dinophyceae) no extremo Sul do Brasil (inverno de 2005, verão de 2007) / Dinophysiales (Dinophyceae) in the farthest Southern region of Brazil (Winter 2005, Summer 2007)

The dinoflagellates of the Dinophysiales order are a morphologically diverse and ecologically heterogeneous group that includes autotrophic, mixotrophic and heterotrophic species and others containing endosymbionts or phycotoxin producers. In this research Dinophysis, Ornithocercus, Histioneis and Amphisolenia species have been identified in both coastal and oceanic waters of the Southern region of Brazil next to Santa Marta Grande Cape, SC and Albardão-Chuí, RS. Vertical hauls were performed with plankton nets (20 µm) on board of the R. V. Atlântico Sul at 33 oceanographic stations sampled in August/September 2005 (Winter) and February 2007 (Summer). The plankton was fixed with formaldehyde (4 percent) and analyzed with the help of an inverted microscope. A total of 43 Dinophysiales species were identified, most of them widely distributed in the coastal, continental and oceanic areas such as Dinophysis acuminata, D. exigua, D. ovata and Histioneis hyalina in the Summer of 2007 and D. acuminata, D. caudata, D. fortii e D. schroederi in the Winter of 2005. The distribution of some species was restricted to the oceanic region under the influence of the Brazil Current as it was observed for Dinophysis dubia, D. exigua, D. schuetti, Histioneis para, Ornithocercus thumii and O. splendidus in the Winter of 2005 and D. similis, D. rapa, H. megalocopa, H. milneri, O. heteroporus and O. splendidus in the Summer of 2007. Six potentially toxic species were registered, Dinophysis acuminata, D. caudata, D. fortii, D. mitra, D. tripos and D. rotundata.

Os dinoflagelados da ordem Dinophysiales representam um grupo morfologicamente diverso e ecologicamente heterogêneo, incluindo espécies autotróficas, mixotróficas e heterotróficas, outras contendo endossimbiontes ou ainda produtoras de ficotoxinas. No presente trabalho, foram identificadas as espécies de Dinophysis, Ornithocercus, Histioneis e Amphisolenia em águas costeira e oceânica na região Sul do Brasil, ao largo do Cabo de Santa Marta Grande, SC e Albardão-Chuí, RS. Arrastos verticais foram realizados com rede de plâncton (20 µm) à bordo do N. O. Atlântico Sul em 33 estações oceanográficas visitadas em agosto/setembro de 2005 (inverno) e fevereiro de 2007 (verão). As amostras de plâncton foram fixadas com formol (4 por cento) e analisadas com o auxílio de microscópio invertido. Ao todo, 43 espécies de Dinophysiales foram identificadas, a maioria com ampla distribuição nas regiões costeira, de plataforma continental e oceânica, como Dinophysis acuminata, D. exigua, D. ovata e Histioneis hyalina no verão de 2007, e D. acuminata, D. caudata, D. fortii e D. schroederi no inverno de 2005. Algumas espécies apresentaram distribuição restrita à região oceânica, sob influência da Corrente do Brasil, como Dinophysis dubia, D. exigua, D. schuetti, Histioneis para, Ornithocercus thumii e O. splendidus no inverno de 2005, e D. similis, D. rapa, H. megalocopa, H. milneri, O. heteroporus e O. splendidus no verão de 2007. Seis espécies potencialmente tóxicas foram encontradas, Dinophysis acuminata, D. caudata, D. fortii, D. mitra, D. tripos e D. rotundata.