The distribution of dissolved iron in the West Atlantic Ocean.

Micha J A Rijkenberg,Jeroen T M De Jong,Patrick Laan,Loes J A Gerringa,Véronique Schoemann,Hein J W De Baar,Hendrik M Van Aken,Rob Middag,Fanis Missirlis

doi:10.1371/journal.pone.0101323

Micha J A Rijkenberg, Jeroen T M De Jong + Show 7 more

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https://doi.org/10.1371/journal.pone.0101323

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Abstract

Iron (Fe) is an essential trace element for marine life. Extremely low Fe concentrations limit primary production and nitrogen fixation in large parts of the oceans and consequently influence ocean ecosystem functioning. The importance of Fe for ocean ecosystems makes Fe one of the core chemical trace elements in the international GEOTRACES program. Despite the recognized importance of Fe, our present knowledge of its supply and biogeochemical cycle has been limited by mostly fragmentary datasets. Here, we present highly accurate dissolved Fe (DFe) values measured at an unprecedented high intensity (1407 samples) along the longest full ocean depth transect (17500 kilometers) covering the entire western Atlantic Ocean. DFe measurements along this transect unveiled details about the supply and cycling of Fe. External sources of Fe identified included off-shelf and river supply, hydrothermal vents and aeolian dust. Nevertheless, vertical processes such as the recycling of Fe resulting from the remineralization of sinking organic matter and the removal of Fe by scavenging still dominated the distribution of DFe. In the northern West Atlantic Ocean, Fe recycling and lateral transport from the eastern tropical North Atlantic Oxygen Minimum Zone (OMZ) dominated the DFe-distribution. Finally, our measurements showed that the North Atlantic Deep Water (NADW), the major driver of the so-called ocean conveyor belt, contains excess DFe relative to phosphate after full biological utilization and is therefore an important source of Fe for biological production in the global ocean.

Highlights

In the ancient oxygen free and sulphidic ocean, high abundances of first row transition metals led to their implementation in many metabolic functions during biological evolution [1,2]
The importance of Fe for marine ecosystems makes Fe perhaps the most wanted chemical trace element for study in the international GEOTRACES program that aims to measure the distribution of important trace elements and isotopes in the global oceans [14]
We explain the distribution of dissolved Fe (DFe) with respect to Fe sources, sinks and internal processes occurring in the Western Atlantic Ocean (GEOTRACES GA02 section)

Summary

Introduction

In the ancient oxygen free and sulphidic ocean, high abundances of first row transition metals led to their implementation in many metabolic functions during biological evolution [1,2]. The western South Atlantic Ocean receives less dust, mainly originating from Patagonia [36] River input is another important source of DFe to the surface ocean. Model simulations show that deep hydrothermal input enhances surface water concentrations of DFe with an estimated 3% of the global mean [59] This modeled estimate may be an underestimation as hydrothermal vents along the Mid Atlantic Ridge appear to contribute a significant hydrothermal Fe flux to the South Atlantic Basin [60]. We explain the distribution of DFe with respect to Fe sources, sinks and internal processes occurring in the Western Atlantic Ocean (GEOTRACES GA02 section)

Materials and Methods

Results and Discussion

Conclusions