Surface distribution of dissolved trace metals in the oligotrophic ocean and their influence on phytoplankton biomass and productivity

Abstract

The distribution of bioactive trace metals has the potential to enhance or limit primary productivity and carbon export in some regions of the world ocean. To study these connections, the concentrations of Cd, Co, Cu, Fe, Mo, Ni, and V were determined for 110 surface water samples collected during the Malaspina 2010 Circumnavigation Expedition (MCE). Total dissolved Cd, Co, Cu, Fe, Mo, Ni, and V concentrations averaged 19.0 ± 5.4 pM, 21.4 ± 12 pM, 0.91 ± 0.4 nM, 0.66 ± 0.3 nM, 88.8 ± 12 nM, 1.72 ± 0.4 nM, and 23.4 ± 4.4 nM, respectively, with the lowest values detected in the Central Pacific and increased values at the extremes of all transects near coastal zones. Trace metal concentrations measured in surface waters of the Atlantic Ocean during the MCE were compared to previously published data for the same region. The comparison revealed little temporal changes in the distribution of Cd, Co, Cu, Fe, and Ni over the last 30 years. We utilized a multivariable linear regression model to describe potential relationships between primary productivity and the hydrological, biological, trace nutrient and macronutrient data collected during the MCE. Our statistical analysis shows that primary productivity in the Indian Ocean is best described by chlorophyll a, NO3, Ni, temperature, SiO4, and Cd. In the Atlantic Ocean, primary productivity is correlated with chlorophyll a, NO3, PO4, mixed layer depth, Co, Fe, Cd, Cu, V, and Mo. The variables salinity, temperature, SiO4, NO3, PO4, Fe, Cd, and V were found to best predict primary productivity in the Pacific Ocean. These results suggest that some of the lesser studied trace elements (e.g., Ni, V, Mo, and Cd) may play a more important role in regulating oceanic primary productivity than previously thought and point to the need for future experiments to verify their potential biological functions.

Coccolithophore calcification is independent of carbonate chemistry in the tropical ocean

“…The mean value of the coefficient of variation for triplicate samples was 18% for primary production and 33% for calcification. Primary production rates measured with the micro‐diffusion technique showed good agreement (Spearman's r = 0.85, p < 0.01, n = 95) with those measured with the conventional 14 C‐uptake technique during parallel, independent experiments (Pinedo‐González et al ). Areal rates of primary production and calcification (mgC m −2 d −1 ) were calculated by trapezoidal integration over the depth of the euphotic zone.…”

“…Previous reports have already described the geographical variability of temperature, salinity, nutrient concentration and chlorophyll a (Chl a ) concentration (Pinedo‐González et al ), as well as that of the nutrient vertical diffusive fluxes (Fernández‐Castro et al ), during the Malaspina 2010 expedition. Excluding two stations located to the south of Australia, all the stations where calcification was measured (Fig.…”

Temperature regulation of marine heterotrophic prokaryotes increases latitudinally as a breach between bottom‐up and top‐down controls

“…High nutrient concentrations would result in higher bioavailable DOM from enhanced primary production, thereby potentially allowing temperature to have a major impact on heterotrophic prokaryotes productivity. However, no significant relationships were found between the temperature control index and phytoplankton biomass or production rates (Estrada et al., ; Marañón et al., ; Pinedo‐González et al., ) during the Malaspina circumnavigation ( p > .30, n = 96 and 106, respectively). This can be explained by the fact that the high nutrient, high phytoplankton biomass and productivity stations located between 20°N and 10°S were also characterized by very high top‐down or bottom‐up control indices (Fig.…”

In situ measurements of micronutrient dynamics in open seawater show that complex dissociation rates may limit diatom growth

“…Concentrations of many nutrients and micronutrients in the oceans are potentially close to co-limiting 11 , 62 , but our predictive ability is largely clouded by the large uncertainties surrounding the diversity of the chemical species of each nutrient, and the diversity of biological strategies phytoplankton use to acquire those various chemical forms 11 . Since the diffusion domain thickness is a critical parameter in setting lability ranges and DGT uniquely allows easy variation of this parameter, a detailed speciation of highly labile and moderately labile complexes can be performed in situ .…”