Kristen N. Buck

Developing standards for dissolved iron in seawater

In nearly a dozen open- ocean fertilization nexperiments conducted by more than 100 nresearchers from nearly 20 countries, adding niron at the sea surface has led to distinct nincreases in photosynthesis rates and biomass. nThese experiments confirmed the nhypothesis proposed by the late John Martin n[Martin, 1990] that dissolved iron concentration nis a key variable that controls phytoplankton nprocesses in ocean surface waters. nHowever, the measurement of dissolved iron nconcentration in seawater remains a difficult ntask [Bruland and Rue, 2001] with significant ninterlaboratory differences apparent at times. nThe availability of a seawater reference solution nwith well- known dissolved iron (Fe) nconcentrations similar to open- ocean values, nwhich could be used for the calibration of nequipment or other tasks, would greatly alleviate nthese problems [National Research nCouncil (NRC), 2002]. nThe Sampling and Analysis of Fe (SAFe) ncruise was staged from Honolulu, Hawaii, to nSan Diego, Calif., between 15 October and n8 November 2004 to collect data and samples nthat were later used to provide this reference nmaterial. Here we provide a brief report on the ncruise results, which have produced a tenfold nimprovement in the variability of iron measurements, nand announce the availability of the nSAFe dissolved Fe in seawater standards.

The integral role of iron in ocean biogeochemistry

The micronutrient iron is now recognized to be important in regulating the magnitude and dynamics of ocean primary productivity, making it an integral component of the ocean’s biogeochemical cycles. In this Review, we discuss how a recent increase in observational data for this trace metal has challenged the prevailing view of the ocean iron cycle. Instead of focusing on dust as the major iron source and emphasizing iron’s tight biogeochemical coupling to major nutrients, a more complex and diverse picture of the sources of iron, its cycling processes and intricate linkages with the ocean carbon and nitrogen cycles has emerged.

Editorial: Organic Ligands—A Key Control on Trace Metal Biogeochemistry in the Ocean

1 Trace Metal Biogeochemistry, College of Marine Science, University of South Florida, Tampa, FL, United States, Department of Earth and Ocean Science, National Oceanography Centre, University of Southampton, Southampton, United Kingdom, Department of Chemistry, University of Otago, Dunedin, New Zealand, Department F.-A. Forel for Environmental and Aquatic Sciences, Université de Genève, Geneva, Switzerland, Division for Marine and Environmental

Copper toxicity response influences mesotrophic Synechococcus community structure.

Picocyanobacteria from the genus Synechococcus are ubiquitous in ocean waters. Their phylogenetic and genomic diversity suggests ecological niche differentiation, but the selective forces influencing this are not well defined. Marine picocyanobacteria are sensitive to Cu toxicity, so adaptations to this stress could represent a selective force within, and between, species, also known as clades. Here, we compared Cu stress responses in cultures and natural populations of marine Synechococcus from two co-occurring major mesotrophic clades (I and IV). Using custom microarrays and proteomics to characterize expression responses to Cu in the lab and field, we found evidence for a general stress regulon in marine Synechococcus. However, the two clades also exhibited distinct responses to copper. The Clade I representative induced expression of genomic island genes in cultures and Southern California Bight populations, while the Clade IV representative downregulated Fe-limitation proteins. Copper incubation experiments suggest that Clade IV populations may harbour stress-tolerant subgroups, and thus fitness tradeoffs may govern Cu-tolerant strain distributions. This work demonstrates that Synechococcus has distinct adaptive strategies to deal with Cu toxicity at both the clade and subclade level, implying that metal toxicity and stress response adaptations represent an important selective force for influencing diversity within marine Synechococcus populations.