H2S events in the Peruvian oxygen minimum zone facilitate enhanced dissolved Fe concentrations

Schlösser, Christian; Streu, Peter; Lavik, Gaute; Croot, Peter; Dengler, Marcus; Achterberg, Eric P.

doi:10.1038/s41598-018-30580-w

Cited by 37 publications

(48 citation statements)

References 87 publications

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“…1). Iron concentrations were reportedly high reaching concentrations up to about 267 nmol kg -1 in the water column, mostly in the bioavailable form of Fe(II) (Schlosser et al 2018), in line with earlier reports from that same area (Hong and Kester 1986).…”

Section: Resultssupporting

confidence: 91%

Facets of diazotrophy in the OMZ off Peru revisited- what we couldn’t see from a single marker gene approach

Christiansen

Löscher

2019

Preprint

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Correspondence to cloescher@biology.sdu.dk Significance statementThis study addresses the important process of N 2 fixation, based on a whole-metagenome and -transcriptome screening, reports an increased diversity of N 2 fixing microbes in the sulfidic shelf water off Peru, as compared to previous target-gene based studies from the same waters. In addition to a generally higher diversity, genes encoding for alternative nitrogenases, which were previously not subject of any study on N 2 fixation in oxygen minimum zones, were detected. The ecological meaning and evolutionary history of those alternative nitrogenases is subject of ongoing debates, however, their presence in OMZ waters would allow for N 2 fixation at extreme anoxia, which may become important in a future ocean challenged by progressive deoxygenation. AbstractBiological dinitrogen (N 2 ) fixation is the pathway making the large pool of atmospheric N 2 available to marine life. Besides direct rate measurements, a common approach to explore the potential for N 2 fixation in the ocean is a mining based on molecular genetic methods targeting the key functional gene nifH, coding for a subunit of the nitrogenase reductase. As novel sequencing and single cell techniques improved, our knowledge on the diversity of marine N 2 fixers grew exponentially. However, to date one aspect of N 2 fixation in the ocean is commonly left aside. This is the existence of two alternative types of nitrogenases, which are besides the Mo-Fe nitrogenase Nif, the Fe-Fe nitrogenase Anf, and the V-Fe nitrogenase Vnf, which differ with regard to their metal co-enzymes, as well as regarding their operon structure and composition. nifH-based studies may thus be biased, and alternative nitrogenases could not be recovered. Here, we screened a set of 6 metagenomes and -transcriptomes from a sulfidic water patch from the oxygen minimum zone off Peru for genes involved in N 2 fixation. We identified genes related to all three nitrogenases, and generally increased diversity as compared to our previous nifH-based study from the same waters. While we could not confirm gene expression of the alternative nitrogenases from our transcriptomes, we detected additional diazotrophs involved in N 2 fixation. We suggest that alternative nitrogenases may not be used under conditions present in those waters, however, depending on trace metal limitation in the future they may become active.

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Section: Resultssupporting

confidence: 91%

Facets of diazotrophy in the OMZ off Peru revisited- what we couldn’t see from a single marker gene approach

Christiansen

Löscher

2019

Preprint

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“…Oregon and Washington shelf bottom water dFe concentrations were similar to our study under equivalent O 2 concentrations (18.7-42.4 nmol L -1 dFe, 42-61 µmol kg -1 O 2 ; Lohan and Bruland, 2008), whereas in the euxinic waters from the Peruvian shelf region, dFe concentrations were more than an order of magnitude higher, exceeding 200 to 300 nmol L -1 (Schlosser et al, 2018;Scholz et al, 2016). Similar dCo concentrations to our study were observed in the North and South Atlantic, with highest concentrations of ~0.16 nmol L -1 present within O 2 -depleted waters (Noble et al, 2012;Noble et al, 2017).…”

Section: Spatial Distributions Of Dissolved and Leachable Particulatesupporting

confidence: 84%

Controls on redox-sensitive trace metals in the Mauritanian oxygen minimum zone

Rapp¹,

Schlösser²,

Barraqueta³

et al. 2018

Preprint

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Abstract. The availability of the micronutrient iron (Fe) in surface waters determines primary production, N2 fixation and microbial community structure in large parts of the world's ocean, and thus plays an important role in ocean carbon and nitrogen cycles. Eastern boundary upwelling systems and the connected oxygen minimum zones (OMZs) are typically associated with elevated concentrations of redox-sensitive trace metals (e.g. Fe, manganese (Mn) and cobalt (Co)), with shelf sediments typically forming a key source. Over the last five decades, an expansion and intensification of OMZs has been observed and this trend is likely to proceed. However, it is unclear how trace metal (TM) distributions and transport are influenced by decreasing oxygen (O2) concentrations. Here we present dissolved (d; <&#8201;0.2&#8201;&#956;m) and leachable particulate (Lp; >&#8201;0.2&#8201;&#956;m) TM data collected at 7 stations along a 50&#8201;km transect in the Mauritanian shelf region. We observed enhanced concentrations of Fe, Co and Mn corresponding with low O2 concentrations (<&#8201;50&#8201;&#956;mol&#8201;kg&#8722;1), which were decoupled from major nutrients and nutrient-like and scavenged TMs (cadmium (Cd), lead (Pb), nickel (Ni) and copper (Cu)). Additionally, data from repeated station occupations indicated a direct link between dissolved and leachable particulate Fe, Co, Mn, and O2. An observed dFe decrease from 10 to 5&#8201;nmol&#8201;L&#8722;1 coincided with an O2 increase from 30 to 50&#8201;&#956;mol&#8201;kg&#8722;1 and with a concomitant decrease in turbidity. The changes in Fe (Co and Mn) were likely driven by variations in their release from sediment pore water, facilitated by lower O2 concentrations and longer residence time of the water mass on the shelf. Variations in organic matter remineralization and lithogenic inputs (atmospheric deposition or sediment resuspension) only played a minor role in redox-sensitive TM variability. Vertical dFe fluxes from O2-depleted subsurface to surface waters (0.08&#8211;13.5&#8201;&#956;mol&#8201;m&#8722;2&#8201;d&#8722;1) were driven by turbulent mixing and vertical advection, and were an order of magnitude larger than atmospheric deposition fluxes (0.63&#8211;1.43&#8201;&#956;mol&#8201;m&#8722;2&#8201;d&#8722;1). Benthic fluxes are therefore the dominant dFe supply to surface waters on the continental margins of the Mauritanian upwelling region. Overall, our results indicated that the projected future decrease in O2 concentrations in OMZs may result in increases in Fe, Mn and Co concentrations.

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“…µM from 20 m, just below the mixed layer, all the way to the bottom. There was no evidence for any sulfide formation at this time, though a later expedition in the same region would detect sulfide and enhanced benthic Fe fluxes 123 . Fe(II) was detectable at all stations throughout the water column with highest concentrations in the BBL which decreased with proximity from the sediments consistent with a benthic source of Fe(II).…”

Section: O 2 Distributionmentioning

confidence: 74%

Redox Processes Impacting the Flux of Iron(II) from Shelf Sediments to the OMZ along the Peruvian Shelf

Croot

Heller

Wuttig

2019

ACS Earth Space Chem.

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Iron (Fe) is a limiting nutrient in many regions of the open ocean and can also play a key role in controlling primary productivity in Eastern Boundary Upwelling Systems (EBUS). In EBUS regions, where intense oxygen minimum zones (OMZs) contact the continental shelf, significant iron inputs can result from the supply of Fe(II) from reducing sediments. How much of this iron makes it to the photic zone depends on physical processes mixing over different time scales (minutes to decades) and the kinetics of redox and complexation processes impacting the biogeochemical cycling of iron. In this work we examine the controls on Fe(II) release from shelf sediments across the Peruvian OMZ by measuring Fe(II) and hydrogen peroxide (H 2 O 2 ) in the water column and benthic boundary layer (BBL) and applying a simple 1D mixing model, with either 1 or 2 layers, where the flux of Fe(II) to the water column is treated as analogous to radon, that the decay rate is constant within the mixing layer. Our modeling approach then allows us to compare our estimated decay rate against published oxidation rates for specific oxidants of Fe(II) in OMZ waters and check the validity of our approach. Our data indicate that throughout the OMZ, Fe(II) decay rates may be partially influenced by H 2 O 2 , but it is most likely that nitrate-dependent anaerobic Fe(II) oxidizing (NDFO) bacteria are the main oxidizers. In the secondary nitrite maxima (SNM), abiotic NO 2 − or biotic-mediated processes may also be important. This work highlights the importance and uses of redox species in understanding biogeochemical cycles in the ocean.

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H2S events in the Peruvian oxygen minimum zone facilitate enhanced dissolved Fe concentrations

Cited by 37 publications

References 87 publications

Facets of diazotrophy in the OMZ off Peru revisited- what we couldn’t see from a single marker gene approach

Facets of diazotrophy in the OMZ off Peru revisited- what we couldn’t see from a single marker gene approach

Controls on redox-sensitive trace metals in the Mauritanian oxygen minimum zone

Redox Processes Impacting the Flux of Iron(II) from Shelf Sediments to the OMZ along the Peruvian Shelf

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