Deep carbon export from a southern ocean iron-fertilized diatom bloom

Fertilization of the ocean by adding iron compounds has induced diatom-dominated phytoplankton blooms accompanied by considerable carbon dioxide drawdown in the ocean surface layer. However, because the fate of bloom biomass could not be adequately resolved in these experiments, the timescales of carbon sequestration from the atmosphere are uncertain. Here we report the results of a five-week experiment carried out in the closed core of a vertically coherent, mesoscale eddy of the Antarctic Circumpolar Current, during which we tracked sinking particles from the surface to the deep-sea floor. A large diatom bloom peaked in the fourth week after fertilization. This was followed by mass mortality of several diatom species that formed rapidly sinking, mucilaginous aggregates of entangled cells and chains. Taken together, multiple lines of evidence-although each with important uncertainties-lead us to conclude that at least half the bloom biomass sank far below a depth of 1,000 metres and that a substantial portion is likely to have reached the sea floor. Thus, iron-fertilized diatom blooms may sequester carbon for timescales of centuries in ocean bottom water and for longer in the sediments

Association of light-to-moderate alcohol drinking in pregnancy with preterm birth and birth weight: elucidating bias by pooling data from nine European cohorts

Women who drink light-to-moderately during pregnancy have been observed to have lower risk of unfavourable pregnancy outcomes than abstainers. This has been suggested to be a result of bias. In a pooled sample, including 193 747 live-born singletons from nine European cohorts, we examined the associations between light-to-moderate drinking and preterm birth, birth weight, and small-for-gestational age in term born children (term SGA). To address potential sources of bias, we compared the associations from the total sample with a sub-sample restricted to first-time pregnant women who conceived within six months of trying, and examined whether the associations varied across calendar time. In the total sample, drinking up to around six drinks per week as compared to abstaining was associated with lower risk of preterm birth, whereas no significant associations were found for birth weight or term SGA. Drinking six or more drinks per week was associated with lower birth weight and higher risk of term SGA, but no increased risk of preterm birth. The analyses restricted to women without reproductive experience revealed similar results. Before 2000 approximately half of pregnant women drank alcohol. This decreased to 39% in 2000–2004, and 14% in 2005–2011. Before 2000, every additional drink was associated with reduced mean birth weight, whereas in 2005–2011, the mean birth weight increased with increasing intake. The period-specific associations betw

Deep carbon export from a Southern Ocean iron-fertilized diatom bloom.

Fertilization of the ocean by adding iron compounds has induced diatom-dominated phytoplankton blooms accompanied by considerable carbon dioxide drawdown in the ocean surface layer. However, because the fate of bloom biomass could not be adequately resolved in these experiments, the timescales of carbon sequestration from the atmosphere are uncertain. Here we report the results of a five-week experiment carried out in the closed core of a vertically coherent, mesoscale eddy of the Antarctic Circumpolar Current, during which we tracked sinking particles from the surface to the deep-sea floor. A large diatom bloom peaked in the fourth week after fertilization. This was followed by mass mortality of several diatom species that formed rapidly sinking, mucilaginous aggregates of entangled cells and chains. Taken together, multiple lines of evidence—although each with important uncertainties—lead us to conclude that at least half the bloom biomass sank far below a depth of 1,000 metres and that a substantial portion is likely to have reached the sea floor. Thus, iron-fertilized diatom blooms may sequester carbon for timescales of centuries in ocean bottom water and for longer in the sediments

Variation in particulate C and N isotope composition following iron fertilization in two successive phytoplankton communities in the Southern Ocean

Surface d15NPON increased 3.92 ± 0.48‰ over the course of 20 days following additions of iron (Fe) to an eddy in close proximity to the Antarctic Polar Front in the Atlantic sector of the Southern Ocean. The change in d15NPON was associated with an increase in the >20 µm size fraction, leading to a maximal difference of 6.23‰ between the >20 µm and <20 µm size fractions. Surface d13CPOC increased 1.18 ± 0.31‰ over the same period. After a decrease in particulate organic matter in the surface layer, a second phytoplankton community developed that accumulated less biomass, had a slower growth rate and was characterized by an offset of 1.56‰ in d13CPOC relative to the first community. During growth of the second community, surface d13CPOC further increased 0.83 ± 0.13‰. Here we speculate on ways that carboxylation, nitrogen assimilation, substrate pool enrichment and community composition may have contributed to the gradual increase in d13CPOC associated with phytoplankton biomass accumulation, as well as the systematic offset in d13CPOC between the two phytoplankton communities