Phytoplankton iron limitation in the Humboldt Current and Peru Upwelling

Abstract

We investigated phytoplankton Fe limitation using shipboard incubation experiments in the high-nutrient South American eastern boundary current regime. Low ambient Fe concentrations (ϳ0.1 nM) in water collected from the Humboldt and Peru Currents were supplemented with a range of added Fe levels up to 2.5 nM. Phytoplankton chlorophyll a, photosystem II photosynthetic efficiency, and nitrate and phosphate drawdown increased in proportion to the amount of Fe added. The Humboldt Current algal community after Fe additions included colonial and flagellated Phaeocystis globosa and large pennate diatoms, whereas the Peru Upwelling assemblage was dominated by coccolithophorids and small pennate diatoms. Apparent half-saturation constants for growth of the two communities were 0.17 nM Fe (Humboldt Current) and 0.26 nM Fe (Peru Upwelling). Net molar dissolved Si(OH) 4 : NO drawdown ratios were low in both experiments (ϳ0.2-0.7), but net particulate silica to nitrogen production Ϫ 3 ratios were higher. Fe limitation decreased net NO : PO utilization ratios in the Humboldt Current incubation to

The effect of vitamin B12 on phytoplankton growth and community structure in the Gulf of Alaska

“…1): West of Glacier Bay at 59u0.569N, 139u50.589W (Coastal experiment) and southwest of Kodiak Island at 53u44.829N, 155u18.79W (HNLC experiment). Acidwashed, trace-metal-clean 1.1-liter polycarbonate bottles were filled with water from the GeoFish clean pumping system (Hutchins et al 2002;Bruland et al 2005) from an average depth of 1-3 m. To avoid trace-metal contamination, all manipulating and processing of experimental bottles was performed in the trace-metal-clean room using trace-metal-clean techniques. For the coastal experiment, triplicate bottles were amended with NO { 3 (20 mmol L 21 ), B 12 (100 pmol L 21 ), and both compounds.…”

“…Water was collected from near surface via a conductivity temperature depth rosette or directly from the GeoFish clean underway surface-sampling system. This system delivered water from 1-m to 3-m depth into a tracemetal-clean room via a trace-metal-clean Teflon pumping system (Hutchins et al 2002;Bruland et al 2005). Triplicate chlorophyll a (Chl a) samples were collected on 0.2-mm and 2-mm polycarbonate filters and frozen and analyzed according to Parsons et al (1984).…”

Algal and aquatic plant carbon concentrating mechanisms in relation to environmental change

“…At low latitudes, in the absence of an upwelling, the greater temperature differential between the warm upper mixed layer and the cooler deeper waters decreases the extent of eddy diffusion of nutrients from the deeper phosphate-and combined nitrogen-rich waters to the surface nutrient-poor waters. The impact on the supply of phytoplankton-available iron of such decreased eddy diffusion is much less than for phosphate and combined nitrogen, since phytoplankton-available iron input to the ocean is mainly aeolian (discussed by Archer et al 2000;Hutchins et al 2002;Parekh et al 2004;Boyd 2007;Boyd et al 2010b). The restriction on the nutrient flux from the deep ocean means even less new productivity and even less potential for continued export production from this already nutrient-limited ocean.…”

Microbial oceanography of anoxic oxygen minimum zones

“…It is not clear, however, why AMZ settings do not support other nitrogen fixers whose physiological traits are more compatible with the ambient physicochemical conditions. As another possibility, iron limitation demonstrably hinders primary production in the ETSP AMZ region (63). Severe iron limitation could exclude nitrogen-fixing cyanobacteria whose iron requirements are particularly high (64).…”