Aerosol deposition from the 2010 eruption of the Icelandic volcano Eyjafjallajökull resulted in significant dissolved iron (DFe) inputs to the Iceland Basin of the North Atlantic. Unique ship‐board measurements indicated strongly enhanced DFe concentrations (up to 10 nM) immediately under the ash plume. Bioassay experiments performed with ash collected at sea under the plume also demonstrated the potential for associated Fe release to stimulate phytoplankton growth and nutrient drawdown. Combining Fe dissolution measurements with modeled ash deposition suggested that the eruption had the potential to increase DFe by >0.2 nM over an area of up to 570,000 km2. Although satellite ocean color data only indicated minor increases in phytoplankton abundance over a relatively constrained area, comparison of in situ nitrate concentrations with historical records suggested that ash deposition may have resulted in enhanced major nutrient drawdown. Our observations thus suggest that the 2010 Eyjafjallajökull eruption resulted in a significant perturbation to the biogeochemistry of the Iceland Basin.

The high-latitude North Atlantic (HLNA) is characterized by a marked seasonal phytoplankton bloom, which removes the majority of surface macronutrients. However, incomplete nitrate depletion is frequently observed during summer in the region, potentially reflecting the seasonal development of an iron (Fe) limited phytoplankton community. In order to investigate the seasonal development and spatial extent of iron stress in the HLNA, nutrient addition experiments were performed during the spring (May) and late summer (July and August) of 2010. Grow-out experiments (48-120 h) confirmed the potential for iron limitation in the region. Short-term (24 h) incubations further enabled high spatial coverage and mapping of phytoplankton physiological responses to iron addition. The difference in the apparent maximal photochemical yield of photosystem II (PSII) (F v : F m ) between nutrient (iron) amended and control treatments (D(F v : F m )) was used as a measure of the relative degree of iron stress. The combined observations indicated variability in the seasonal cycle of iron stress between different regions of the Irminger and Iceland Basins of the HLNA, related to the timing of the annual bloom cycle in contrasting biogeochemical provinces. Phytoplankton iron stress developed during the transition from the prebloom to peak bloom conditions in the HLNA and was more severe for larger cells. Subsequently, iron stress was reduced in regions where macronutrients were depleted following the bloom. Iron availability plays a significant role in the biogeochemistry of the HLNA, potentially lowering the efficiency of one of the strongest biological carbon pumps in the ocean.

The oceans sequester carbon from the atmosphere partly as a result of biological productivity. Over much of the ocean surface, this productivity is limited by essential nutrients and we discuss whether it is likely that sequestration can be enhanced by supplying limiting nutrients. Various methods of supply have been suggested and we discuss the efficacy of each and the potential side effects that may develop as a result. Our conclusion is that these methods have the potential to enhance sequestration but that the current level of knowledge from the observations and modelling carried out to date does not provide a sound foundation on which to make clear predictions or recommendations. For ocean fertilization to become a viable option to sequester CO 2 , we need more extensive and targeted fieldwork and better mathematical models of ocean biogeochemical processes. Models are needed both to interpret field observations and to make reliable predictions about the side effects of large-scale fertilization. They would also be an essential tool with which to verify that sequestration has effectively taken place. There is considerable urgency to address climate change mitigation and this demands that new fieldwork plans are developed rapidly. In contrast to previous experiments, these must focus on the specific objective which is to assess the possibilities of CO 2 sequestration through fertilization.

Little is known about the distribution of coccolithophores in Arctic regions, or the reasons why they are absent from certain locations but thrive in others. Factors thought to affect coccolithophore distribution include nutrients, salinity, temperature and light, as well as carbonate chemistry parameters. Here we present data collected in summer 2008 along a transect between the North Sea and Svalbard (Arctic). Coccolithophore abundance and diversity were measured and compared with a set of environmental variables that included macronutrients, salinity, temperature, irradiance, pH and Ω calcite . Eighteen coccolithophore species were found in the southern North Sea where coccolithophores were previously thought to be absent. In the ice-covered region north of Svalbard, coccolithophores were scarce and dominated by the family Papposphaeraceae. A multivariate approach showed that changes in pH and mixed layer irradiance explained most of the variation in coccolithophore distribution and community composition (Spearman's r S = 0.62). Differences between the Svalbard population and those from other regions were mostly explained by pH (r S = 0.45), whereas mixed layer irradiance explained most of the variation between the North Sea, Norwegian Sea and Arctic water assemblages (r S = 0.40). Estimates of cell specific calcification rates showed that species composition can considerably affect community calcification. Consequently, future ocean acidification (changes in pH) and stratification due to global warming (changes in mixed layer irradiance) may influence pelagic calcification by inducing changes in the species composition of coccolithophore communities.KEY WORDS: Coccolithophore · Emiliania huxleyi · Arctic Ocean · pH · Irradiance · Ocean acidification Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 431: [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43] 2011 concentrations and light conditions (Bopp et al. 2001, Sarmiento et al. 2004, as well as ocean acidification (Orr et al. 2005). Extensive experimental and field research on Emiliania huxleyi, the most common cocco litho phore, indicates that calcification in this species depends strongly on irradiance and is stimulated by nutrient stress, even though cells grow well under high nutrient concentrations and low irradiance (see review by Zondervan 2007). However, elevated pCO 2 levels have varying effects on the calcifying ability of different E. huxleyi strains (Riebesell et al. 2000, Iglesias-Rodriguez et al. 2008, Langer et al. 2009) and different coccolithophore species (Langer et al. 2006). Moreover, effects of simultaneous changes in multiple environmental variables are diverse. For example, light saturation for E. huxleyi growth depends on temperature (Paasche 2001, Zondervan 2007 whereas the sensitivity of E. huxleyi calcification and organic C fixation to elevated pCO 2 depend on their replete or depleted nutrient status (Sciandra et al. 2003, Delille et al. 2005, E...

This paper presents analysis of nitrate, phosphate and silicate data from the Benguela upwelling system. Evidence is presented that suggests denitrification occurring close to shore, and also nutrient trapping. Denitrification leaves an imprint on the water properties in terms of a nitrate deficit, that is to say nitrate concentrations that are significantly less than predicted by multiplying the phosphate concentrations by the Redfield ratio. It is probable that denitrification also causes a decoupling of nitrate and carbon compared to Redfield processes, and large-scale losses of nitrate in the Benguela which are not accompanied by losses of carbon. Nitrate-driven CO 2 drawdown following upwelling will be less than it might otherwise be, because of denitrification.Nutrient trapping (secondary remineralisation) is apparent as enhanced phosphate concentrations, some of which are several mmol higher than in the offshore source waters for upwelling. Waters also become enriched in silicate and to a lesser extent nitrate as they advect across the shelf. By implication the same process should also ''supercharge'' waters in dissolved inorganic carbon, leading to stronger outgassing of CO 2 immediately after upwelling. The effect is again to increase the size of the estimated Benguela upwelling system CO 2 source. r