The Distribution of Dissolved Iron in the West Atlantic Ocean

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.

An Intercomparison of Dissolved Iron Speciation at the Bermuda Atlantic Time-series Study (BATS) Site: Results from GEOTRACES Crossover Station A

“…Dissolved Fe concentrations differed through the water column between the two occupations (Figure 2A; Rijkenberg et al, 2014;Sedwick et al, 2015). In both cases, however, organic Fe-binding ligands were reported in excess of DFe concentrations throughout the water column, and thermodynamically stable ("strong") organic DFe complexes were the dominant chemical form of DFe at all depths (Figures 2A-F; Buck et al, 2015;Gerringa et al, 2015).…”

“…Indeed, the DFe concentrations were quite different between the two GEOTRACES occupations of BATS/GEOTRACES Crossover Station A (Figure 2A; Rijkenberg et al, 2014;Buck et al, 2015;Gerringa et al, 2015;Sedwick et al, 2015). The analytical methods used for the DFe analyses were very similar Buck et al, 2015;Sedwick et al, 2015) and the DFe concentrations results from the two occupations were successfully intercalibrated and were included in the GEOTRACES Intermediate Data Product (Mawji et al, 2015).…”

“…These samples were filtered through the same filters (<0.2 µm, see details below) used for the collection of speciation samples. DFe samples were acidified to 0.024 M hydrochloric acid (HCl) with high purity HCl (Johnson et al, 2007) and DFe concentrations were determined by flow injection analysis (FIA: Rijkenberg et al, 2014;Sedwick et al, 2015). Applying these analyses to reference standards from the SAFe (Johnson et al, 2007) and GEOTRACES programs resulted in DFe concentrations within the range of consensus values reported for each reference sample Sedwick et al, 2015).…”

Latitudinal distributions of particulate carbon export across the North Western Atlantic Ocean

“…Although the Amazon River estuary is located further south, within the equatorial domain, the riverine outflow was encountered between 11ºN and 18ºN, as evidenced by low salinity (< 34) in the upper 30 -40 m and silicate concentrations reaching as high as 8 PM at 10 m ( Figure S1) (Reul et al, 2014;Rijkenberg et al, 2014). Fluorescence and beam attenuation also reflect the intrusion of the river plume as well as high satellite-derived Chl-a concentrations (Figure 1).…”

“PRISTINE”, a new high volume sampler for ultraclean sampling of trace metals and isotopes

“…The results of the analysis of the reference samples and their consensus values are reported elsewhere (Middag et al, 2015;Rijkenberg et al, 2014). 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 14…”