Marine phytoplankton account for approximately half of global primary productivity , making their fate an important driver of the marine carbon cycle. Viruses are thought to recycle more than one-quarter of oceanic photosynthetically fixed organic carbon , which can stimulate nutrient regeneration, primary production and upper ocean respiration via lytic infection and the 'virus shunt'. Ultimately, this limits the trophic transfer of carbon and energy to both higher food webs and the deep ocean . Using imagery taken by the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard the Aqua satellite, along with a suite of diagnostic lipid- and gene-based molecular biomarkers, in situ optical sensors and sediment traps, we show that Coccolithovirus infections of mesoscale (~100 km) Emiliania huxleyi blooms in the North Atlantic are coupled with particle aggregation, high zooplankton grazing and greater downward vertical fluxes of both particulate organic and particulate inorganic carbon from the upper mixed layer. Our analyses captured blooms in different phases of infection (early, late and post) and revealed the highest export flux in 'early-infected blooms' with sinking particles being disproportionately enriched with infected cells and subsequently remineralized at depth in the mesopelagic. Our findings reveal viral infection as a previously unrecognized ecosystem process enhancing biological pump efficiency.

Ocean Sampling Day was initiated by the EU-funded Micro B3 (Marine Microbial Biodiversity, Bioinformatics, Biotechnology) project to obtain a snapshot of the marine microbial biodiversity and function of the world’s oceans. It is a simultaneous global mega-sequencing campaign aiming to generate the largest standardized microbial data set in a single day. This will be achievable only through the coordinated efforts of an Ocean Sampling Day Consortium, supportive partnerships and networks between sites. This commentary outlines the establishment, function and aims of the Consortium and describes our vision for a sustainable study of marine microbial communities and their embedded functional traits.

A brief review is given of the physical dynamics that occur at seamounts and the implications of these dynamics for seamount productivity highlighted. Several physical seamount characteristics, stratification and oceanic flow conditions interact to provide a number of different local dynamic responses at a seamount. These include Taylor Columns or Cones, doming of density surfaces, enclosed circulation cells and enhanced vertical mixing. Due to oceanic background flow variability, it is likely that the localised seamount dynamics, and resultant bio-physical interaction processes; will also be variable. This makes quantification of an 'idealised' response of a particular seamount to the impinging flow regime difficult. It has been widely accepted that dynamics at seamounts generate conditions such as increased vertical nutrient fl uxes and material retention, to promote productivity that fuels higher trophic levels. To date, however, there has been little consistent concrete evidence for this in observations. This is likely due to the non-steady background oceanic forcing which may disrupt the 'idealised' response, such as Taylor Cones and circulation cells generated at the seamount. In addition, the seamount may shed passive tracers such as chlorophyll downstream, providing a source of oceanic bio-physical patchiness in the surrounding ocean. Such variability provides a challenge for the environmental management of seamounts.

Phytoplankton blooms are ephemeral events of exceptionally high primary productivity that regulate the flux of carbon across marine food webs [1-3]. Quantification of bloom turnover [4] is limited by a fundamental difficulty to decouple between physical and biological processes as observed by ocean color satellite data. This limitation hinders the quantification of bloom demise and its regulation by biological processes [5, 6], which has important consequences on the efficiency of the biological pump of carbon to the deep ocean [7-9]. Here, we address this challenge and quantify algal blooms' turnover using a combination of satellite and in situ data, which allows identification of a relatively stable oceanic patch that is subject to little mixing with its surroundings. Using a newly developed multisatellite Lagrangian diagnostic, we decouple the contributions of physical and biological processes, allowing quantification of a complete life cycle of a mesoscale (∼10-100 km) bloom of coccolithophores in the North Atlantic, from exponential growth to its rapid demise. We estimate the amount of organic carbon produced during the bloom to be in the order of 24,000 tons, of which two-thirds were turned over within 1 week. Complimentary in situ measurements of the same patch area revealed high levels of specific viruses infecting coccolithophore cells, therefore pointing at the importance of viral infection as a possible mortality agent. Application of the newly developed satellite-based approaches opens the way for large-scale quantification of the impact of diverse environmental stresses on the fate of phytoplankton blooms and derived carbon in the ocean.

Western boundary currents are the locus of intense nutrient transport, or nutrient streams. The largest fraction of this transport takes place in the upper-thermocline layers, between the surface layers (where speed reaches a maximum) and the nutrient bearing strata of the subtropical gyres (where nutrient concentration is maximum). The core of the nutrient stream of the North Atlantic subtropical gyre is located slightly offshore the Gulf Stream, its density coordinate centered on the 26.5-27.30rband, approximately constant along the axis of the stream. During !ate spring 2nd wmmer the n~frient stresim reaches fhe surfare rearnnal mixed layer a t the outcropping of this isopycnal band. We argue that this must be a principal factor sustaining the seasonal high productivity of the subpolar North Atlantic Ocean. Additionally, we investigate the possibility of intermittent shearinduced diapycnal mixing in the upper-thermocline layers of the Gulf Stream, i n d~c e d by frmtegenesis t u b g p!ae during scme phase ~f ?he memderc. Uere we illustrate that diapycnal mixing has a maximum a t the location of the nutrient stream, being associated to observed nutrient anomalies. We suggest that diapycnal mixing associated to the passage of steep meanders brings nutrients from the nutrient stream to the shallow photic layers, and sustains intermittent (day-toweek) patchy (10-100 km) productivity over the stream itself.