Abstract
B-vitamins are recognized as essential organic growth factors for many organisms, although little is known about their abundance and distribution in marine ecosystems. Despite their metabolic functions regulating important enzymatic reactions, the methodology to directly measure different B-vitamins in aquatic environments has only recently been developed. Here, we present the first direct measurements of two B-vitamins, thiamin (B1), and pyridoxine (B6), in the Amazon River plume-influenced western tropical North Atlantic (WTNA) Ocean, an area known to have high productivity, carbon (C) and dinitrogen (N2) fixation, and C sequestration. The vitamins B1 and B6 ranged in concentrations from undetectable to 230 and 40 pM, respectively. Significantly higher concentrations were measured in the surface plume water at some stations and variation with salinity was observed, suggesting a possible riverine influence on those B-vitamins. The influences of vitamins B1 and B6 on biogeochemical processes such as C and N2 fixation were investigated using a linear regression model that indicated the availability of those organic factors could affect these rates in the WTNA. In fact, significant increases in C fixation and N2 fixation were observed with increasing vitamin B1 concentrations at some low and mesohaline stations (stations 9.1 and 1; p value <0.017 and <0.03, respectively). N2 fixation was also found to have a significant positive correlation with B1 concentrations at station 1 (p value 0.029), as well as vitamin B6 at station 9.1 (p value <0.017). This work suggests that there can be a dynamic interplay between essential biogeochemical rates (C and N2 fixation) and B-vitamins, drawing attention to potential roles of B-vitamins in ecosystem dynamics, community structure, and global biogeochemistry.
Highlights
The Amazon River has the largest freshwater discharge of any river into the world ocean, resulting in an influx of lowsalinity, nutrient-rich water into the western tropical North Atlantic (WTNA) Ocean (Subramaniam et al, 2008)
The lowest concentrations of vitamin B1 were measured at the oceanic stations followed by low-salinity stations (2.5–184 pM), and the highest concentrations were observed at mesohaline stations
There was no clear spatial trend observed between the two vitamins suggesting they function and behave differently from one another, and the high variability suggests a dynamic behavior influenced by sources and sinks
Summary
The Amazon River has the largest freshwater discharge of any river into the world ocean, resulting in an influx of lowsalinity, nutrient-rich water into the western tropical North Atlantic (WTNA) Ocean (Subramaniam et al, 2008). The environmental conditions resulting from the river plume, influencing approximately two million km in the WTNA, contributes to phytoplankton species succession, high rates of primary production, and a significant carbon (C) sink (Subramaniam et al, 2008). A shift in community composition occurs beginning with diatom-diazotroph associations (DDAs) as N becomes limited but sufficient supplies of Si are still present. This is followed by a subsequent community shift to more typical oceanic N2 fixing organisms such as Trichodesmium spp.
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