The flux of dissolved iron from sediments to the water column was measured with flux chambers along the California coast over a five‐year period. High fluxes were observed from sediments on the continental shelf. The measured fluxes were an average of 75 times larger than flux values derived from pore‐water iron gradients. The iron flux was significantly correlated with the oxidation of organic matter, which allows an extrapolation to the global shelf. The input from shelf sediments is at least as significant as the global input of dissolved iron from aerosols, which has been presumed to be the dominant external iron source. Evidence of this input is seen 100's of kilometers offshore where it can enable the high productivity of broad coastal regions seen in satellite images.

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B vitamins are some of the most commonly required biochemical cofactors in living systems. Therefore, cellular metabolism of marine vitamin-requiring (auxotrophic) phytoplankton and bacteria would likely be significantly compromised if B vitamins (thiamin B 1 , riboflavin B 2 , pyridoxine B 6 , biotin B 7 , and cobalamin B 12 ) were unavailable. However, the factors controlling the synthesis, ambient concentrations, and uptake of these key organic compounds in the marine environment are still not well understood. Here, we report vertical distributions of five B vitamins (and the amino acid methionine) measured simultaneously along a latitudinal gradient through the contrasting oceanographic regimes of the southern California-Baja California coast in the Northeast Pacific margin. Although vitamin concentrations ranged from below the detection limits of our technique to 30 pM for B 2 and B 12 and to ∼500 pM for B 1 , B 6 , and B 7 , each vitamin showed a different geographical and depth distribution. Vitamin concentrations were independent of each other and of inorganic nutrient levels, enriched primarily in the upper mesopelagic zone (depth of 100-300 m), and associated with water mass origin. Moreover, vitamin levels were below our detection limits (ranging from ≤0.18 pM for B 12 to ≤0.81 pM for B 1 ) in extensive areas (100s of kilometers) of the coastal ocean, and thus may exert important constraints on the taxonomic composition of phytoplankton communities, and potentially also on rates of primary production and carbon sequestration.T he evolution of organic catalysts (enzymes and coenzymes) that accelerated biochemical reactions by orders of magnitude compared with inorganic catalysis alone was a critical step for the emergence of major cellular processes (1). Well-known coenzyme molecules include the B vitamins, which catalyze many important biochemical reactions in central metabolism (2). Those reactions include rearrangement-reduction of C-C bonds and methyl transfer reactions, synthesis of deoxyribose/fatty acids/ carbohydrates/branched-chain amino acids, electron transfer in oxidation-reduction reactions, and CO 2 fixation (2). This means that without an exogenous source of B vitamins, central metabolism in vitamin-requiring (auxotrophic) organisms would be compromised and the cells would not be able to grow, a situation that could have great bearing on many biological processes in the ocean, including the biological carbon pump.In the marine environment, vitamins have been implicated as important factors regulating the growth and succession of phytoplankton species (3). This inference was based on the fact that many species of eukaryotic phytoplankton require vitamins when they are cultured in the laboratory (3-7). Although it was thought that marine prokaryotes were the major producers of vitamins in the sea (4), genomic data indicate that it is common for both eukaryotic phytoplankton and bacterioplankton to be auxotrophic for at least one B vitamin, mainly because they lack the complete biosynthetic...

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[1] The global CaCO 3 budget is constrained by new estimates of standing stocks, fluxes through the water column, and dissolution in the water column and on the sea floor. Previous estimates of carbonate production and export are indistinguishable within a large range of values, 0.4-1.8 Gt PIC yr À1 . Globally, excess alkalinity (TA*) and water mass tracers indicate dissolution of 1.0 Gt PIC yr À1 between 200 and 1500 m, suggesting production and export must at least equal this amount. Most water column dissolution occurs at high latitudes, and alkalinity fluxes from outer shelf and upper slope sediments (100-1500 m) only support 5-10% of the TA* inventory. Below 2000 m, the sinking flux of PIC (0.6 Gt PIC yr À1 ) is consistent with the rate of sea floor dissolution (0.4 Gt PIC yr À1 ) plus burial (0.1 Gt PIC yr À1 ). This rain rate constrains the export value to >1.6 Gt PIC yr À1 . Satellite-based estimates of standing stocks of CaCO 3 indicate a decrease equatorward, which is opposite in trend to sediment trap fluxes. This observation may be explained by an equatorward decrease in sinking particle dissolution, systematic changes in PIC residence time with latitude, or satellite retrieval problems. Globally averaged euphotic zone standing stock (5.4 mmol m À2 ) and export estimates indicate PIC residence times of 5-18 days.

Climate warming is expected to reduce oxygen (O2) supply to the ocean and expand its oxygen minimum zones (OMZs). We reconstructed variations in the extent of North Pacific anoxia since 1850 using a geochemical proxy for denitrification (δ(15)N) from multiple sediment cores. Increasing δ(15)N since ~1990 records an expansion of anoxia, consistent with observed O2 trends. However, this was preceded by a longer declining δ(15)N trend that implies that the anoxic zone was shrinking for most of the 20th century. Both periods can be explained by changes in winds over the tropical Pacific that drive upwelling, biological productivity, and O2 demand within the OMZ. If equatorial Pacific winds resume their predicted weakening trend, the ocean's largest anoxic zone will contract despite a global O2 decline.

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