Figure 1.
With 60 full depth stations over 17500Pelagia and 74JC057 on the RRS James Cook covered the complete West Atlantic Ocean GEOTRACES GA02 transect.
Numbers show the locations 1) Irminger Sea, 2) Labrador Sea, 3) the Grand Banks, and 4) Bermuda.
Table 1.
The values of SAFe and GEOTRACES reference samples for DFe, DAl and DMn measured during the cruises 64PE319, 64PE321 & 64PE358 in the western North Atlantic Ocean and cruise 74JC057 in the western South Atlantic Ocean.
Figure 2.
Section plots of A) the absolute salinity (SA), B) oxygen, C) silicate, D) phosphate, and E) nitrate as measured during the GEOTRACES cruise 64PE319, 64PE321, 64PE358 and 74JC057 in the west Atlantic Ocean.
Water masses indicated are Labrador Sea Water (LSW), North East Atlantic Deep Water (NEADW), Denmark Strait Overflow Water (DSOW), North Atlantic Deep Water (NADW), AntArctic Intermediate Water (AAIW), Upper Circumpolar Deep Water (UCDW), and AntArctic Bottom Water (AABW). Section plots of the salinity, oxygen and nutrients from the GEOTRACES GA02 transect without the results of 64PE358 have been published before [72], [97].
Figure 3.
Distribution of DFe in the western Atlantic Ocean.
A) 17500 km long full depth section plot of DFe (nM) in the western Atlantic Ocean measured on board ship in May–June 2010 and March–April 2011. B) Summary of the vertical distribution of all DFe concentrations measured during this study in the western Atlantic Ocean showing the median DFe (solid line with dots). The interquartile range defined as the range around the median containing 50% of the data is given between the two dotted lines. The number of samples per depth region (n) is shown in the plot. The 10 sampling depths in the upper water column have each on average 54±2 data points. C) A boxplot of the DFe concentrations in each of the water masses as encountered along our transect in alphabetical order Antarctic Bottom Water (AABW), Antarctic Intermediate Water (AAIW), the Amazon plume, Denmark Strait Overflow Water (DSOW), Labrador Sea Water (LSW), Mediterranean Sea Outflow Water (MSOW), North Atlantic Central Water (NACW), North Atlantic Deep Water (NADW), the lower, middle and upper NADW (NADWl, NADWm, NADWu), the North East Atlantic Deep Water (NEADW), the South Atlantic Central Water (SACW), the Upper Circumpolar Deep Water (UCDW) and the upper LSW (uLSW). Median values are indicated by a vertical line within the box, the box represents the interquartile range, and the whiskers extend to the 5th and 95th percentile values. Outliers, defined as data points more than 1.5 times the interquartile range above the third quartile and points more than 1.5 times the interquartile range below the first quartile, are not shown.
Figure 4.
The surface distributions of DFe, DAl and DMn, and their relationships.
A) Concentrations of DFe, DAl and DMn at 10 m depth along the complete western Atlantic Ocean transect. B–D) Excluding stations above the shelf and impacted by rivers, significant exponential correlations between DFe, DAl and DMn were found. The DFe correlated exponentially with B) DAl; DFe = 5.12×10−2 e0.074 DAl, R2 = 0.72, p = 1.9 10−14, n = 48 and with C) DMn; DFe = 3.43×10−2 e1.06 DMn, R2 = 0.78, p = 2.2 10−14, n = 48. DMn correlated linearly with D) DAl; DMn = 6.26×10−2 DAl+0.52, R2 = 0.78, p = 2.2 10−14, n = 49. Error bars represent standard deviations.
Figure 5.
Distribution of DFe in the Amazon plume.
A) The three-week composite image (12 June–5 August 2010) of sea surface salinity at 25 km resolution by the ESA SMOS satellite during the 64PE321 research cruise on the RV Pelagia showing the Amazon plume. Black dots represent the stations occupied during this cruise. This image was produced by the CNES/IFREMER Centre Aval de Traitement Des Données SMOS (CATDS, France). B) Fluorescence in the upper 40 m of the water column versus latitude. C) Section plot of CTD downcast salinity including salinity contour lines between the equator and 20°N showing the low saline Amazon plume. The black dots represent measurements. D) Section plot of DFe between the equator and 20°N showing the relatively high DFe concentrations in the Amazon River plume at 5°N and in comparison lower concentrations of DFe at the lower salinities of the Amazon River plume between 12–18°N.
Figure 6.
The DFe, DMn and DAl between 0–40 m depth and 3–9°N as function of salinity in the Amazon river plume.
A) The significant linear correlation between DFe and salinity. B) The significant linear correlation between DMn and salinity. C) DAl as function of salinity. D) DFe as function of DAl. Error bars represent standard deviations.
Figure 7.
Distribution of DFe in the upper 1000
Salinity is depicted as contour lines. A steep gradient in salinity in the first 800°S and 40°S indicates the subtropical shelf front (STSF) formed by the colliding of the southward flowing Brazil Current and the northward flowing Malvinas Current. Note that the color scale is between 0–6 nM in this section plot.
Figure 8.
The DFe depth profiles in the subtropical shelf front between 30°S and 40°S.
Full depth profiles of DFe measured during cruise 74JC057 with the RRS James Cook at station 6 (39°58′05″S, 42°27′32″W), station 7 (37°50′33″S, 41°07′57″W), station 8 (35°00′36″S, 39°26′21″W) and station 9 (32°05′16″S, 37°27′41″W). High DFe concentrations were found in the upper 400 m at station 7 and 8 indicating a lateral supply and partial dissolution of particulate Fe by the subtropical shelf front resulting in enhanced concentrations of DFe. Error bars represent standard deviations.
Figure 9.
The DFe concentration as function of the Apparent Oxygen Utilization (AOU).
There is a strong linear correlation between the DFe concentration and the AOU in the oxygen minimum zone between the equator and 20°N at a depth of 70–1100 m: DFe = 4.7×10−3 AOU+0.17, R2 = 0.77, p = 2.2×10−16, n = 129. Error bars represent standard deviations.
Figure 10.
The DFe concentration as function of PO43−.
A) There is a strong linear correlation between the DFe concentration and the PO43− in the oxygen minimum zone between the equator and 20°N at a depth of 70–1100 m, and B) in comparison the correlation between DFe and PO43− over the whole West Atlantic between 50–1000 m depth where remineralization of organic matter is the dominant source of DFe. The high DFe data in the STSF were left out. Error bars represent standard deviations.
Figure 11.
Section plot of the Fe* tracer in the western Atlantic Ocean.
Negative values indicate potential growth limiting DFe concentrations and positive values indicate an excess in DFe after complete biological uptake of PO43−. A contour line of 0 separates areas of negative Fe* from areas with positive Fe*.