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- Continental-shelf sediment as a primary source of iron for coastal phytoplankton,
- The availability of iron, an essential nutrient, controls rates of phytoplankton primary productivity in the open-ocean, upwelling ecosystems of the equatorial Pacific. Upwelling injects large amounts of macronutrients into the euphotic zone of eastern boundary currents, such as the California Current System (CCS), where iron can become the limiting factor on productivity. Iron addition to samples from some areas of the CCS has been shown to increase rates of biomass production, but the processes that control iron availability in these systems remain poorly understood. Here we report measurements of dissolvable iron (that is, dissolved plus leachable iron at pH 3) in transects across the CCS in March of 1997 and 1998. We found high concentrations of iron in 1997 during strong upwelling conditions. During the 1998 El Nino, the concentration of dissolvable iron in surface waters was low, even though that year was marked by high river flow and low offshore salinity. These results indicate that the primary source of iron in the CCS is resuspension of particles in the benthic boundary layer, followed by upwelling of this iron-rich water, rather than direct riverine input. This source of iron must be an essential but variable component of the high productivity found in upwelling ecosystems., Cited By (since 1996):172 Oceanography, CODEN: NATUA, ,
- Johnson, Chavez, Friederich
- Surface ocean-lower atmosphere interactions in the Northeast Pacific Ocean Gyre: Aerosols, iron, and the ecosystem response,
- Here we report measurements of iron and aluminum in surface and subsurface waters during late March and late May of 2001 on transects between central California and Hawaii. A large cloud of Asian dust was detected during April 2001, and there was a clear signal in surface water iron due to aerosol deposition on the May transect. Iron and aluminum concentrations increased synchronously by 0.5 and 2 nM along the southern portion of the transect, which includes the Hawaii Ocean Time series (HOT) station, from background values in March (0.1 to 0.2 nM Fe). These changes occured in a ratio that is close to the crustal abundance ratio of the metals, which indicates a soil aerosol source. A vertical profile of dissolved iron was also measured at the HOT station in late April and this profile also shows a large increase near the surface. Direct observations of aerosol iron concentration at Mauna Loa Observatory on Hawaii indicate that aerosol concentrations were significantly lower than climatological values during this period. Soil aerosol concentrations along the transect were estimated using the real-time Navy Aerosol Analysis and Prediction System (NAAPS). The NAAPS results show a large meridional gradient with maximum concentrations in the boundary layer north of 30°N. However, the deposition of iron and aluminum to surface waters was highest south of 25°N, near Hawaii. There were only weak signals in the ecosystem response to the aerosol deposition., Cited By (since 1996):64, Oceanography, , , Downloaded from: http://onlinelibrary.wiley.com/doi/10.1029/2002GB002004/pdf (16 June 2014).
- Johnson, Elrod, Fitzwater, Plant, Chavez, Tanner, Gordon, Westphal, Perry, Wu, Karl