Spatial variability in dissolved iron concentrations in the marginal and open waters of the Indian Ocean

A nutrient limitation mosaic in the eastern tropical Indian Ocean

“…Dissolved and particulate Fe concentrations were also extremely low in surface waters, particularly in the SIO gyre and EqIO to the south of BoB, where both remained below 0.2 nmoL/L. These concentrations match those measured previously in the BoB and eastern tropical IO (Chinni et al, 2018;Grand et al, 2015b). They also agree with the modeling results of Wiggert et al (2006), which suggested dFe remains at or below 0.1 nmoL/L in surface waters south of the equator.…”

“…The biogeochemistry of the Indian Oceanparticularly the eastern sectoris less constrained than that of the North Atlantic or Pacific Oceans. The Indian Ocean tropical waters are extremely low in macronutrients (Wiggert et al, 2006), and recent measurements of Fe have shown low dFe levels in surface waters, as well (Chinni et al, 2018;Grand et al, 2015b). Measurements of autotrophic biomass, community composition, and primary production indicate an oligotrophic system similar to other basins: one dominated by cyanobacteria and Prochlorococcus in particular (Baer et al, 2018;Bouman et al, 2006).…”

“…In the BoB, the nearby Indian subcontinent serves as an abundant source of lithogenic and anthropogenic aerosols (Prospero et al, 2002), and dust inputs approach those found to the west of the Saharan desert in the North Atlantic (Grand et al, 2015a). Despite these inputs, dissolved iron (dFe) in surface waters of the eastern Indian Ocean south of the BoB are thought to be low (<0.2 nmoL/L), whereas BoB surface waters have shown higher dFe along with lower dissolved oxygen concentrations (Chinni et al, 2018;Grand et al, 2015b;Thi Dieu Vu and Sohrin, 2013). Thus, there appear to be 3 biogeochemical regions in the eastern Indian Ocean: a potentially N-and Fe-stressed SIO gyre; an area of upwelling and somewhat higher macronutrientsbut still low dFein the EqIO; and the BoB characterized by higher-Fe waters and an elevated nutrient supply.…”

Shelf Inputs and Lateral Transport of Mn, Co, and Ce in the Western North Pacific Ocean

“…Redox mobilized shelf inputs of dissolved trace elements can be preserved and transported offshore when the overlying waters are also low in oxygen, especially in regions like the northern Indian Ocean, the eastern Atlantic Ocean, and the eastern North and South Pacific Oceans (Breitburg et al, 2018;Scholz, 2018). In the northern Indian Ocean, the depths of the minimum oxygen concentrations coincide with plumes of dissolved trace elements like Mn (Saager et al, 1989;Lewis and Luther, 2000), Fe (Saager et al, 1989;Kondo and Moffett, 2013;Vu and Sohrin, 2013;Grand et al, 2015a,b;Chinni et al, 2019), Co (Vu and Sohrin, 2013), and Ce (German and Elderfield, 1990). In the eastern South Atlantic, during the CoFeMUG cruise (Noble et al, 2012;Zheng et al, 2016), Mn, Co, Fe, and Ce were all enriched in subsurface plumes within the depth range of the oxygen minimum zone.…”

Supplementary material to &quot;No nitrogen fixation in the Bay of Bengal?&quot;

“…This leads to a modification of the previous OMZ model (Boyle et al, 2013) with the Redfield control of N2 fixation being replaced by a phosphorous only control with P > 0 constantly allowing for N2 fixation and export production scaling with phosphate and Nox + NR upwelling. Tables Tab M1: Concentrations used in the model experiment, data taken from Bristow et al (2017), Grand et al (2015) and (Chinni et al 2019) Table S1: CO2 and N2 fixation rates based on triplicate measurements at stations 1 (17.9970°N, 88.9968°E), 4 (16.9828°N, 89.2063°E) and 5 (17.2075°N, 89.4282°E). N2 fixation was only measurable in two individual samples, but only in one out of three technical replicates.…”