Iron and manganese accumulation within the Eastern Tropical North Pacific oxygen deficient zone

Bolster, Kenneth; Heller, Maija; Mulholland, Margaret R.; Moffett, James W.

doi:10.1016/j.gca.2022.07.013

Cited by 11 publications

(9 citation statements)

References 72 publications

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“…31–33 provide an excellent opportunity to study cross‐shelf transport because the Heceta Bank region is a hot spot for cross‐shelf transport, revealed in an iron ROMS model applied to the region (Damien et al 2023). In contrast to Fe(II) observations off ODZs (Vedamati et al 2014; Bolster et al 2022), we did not observe evidence of Fe(II) being transported off‐shelf in waters that intersect with the continental shelf, between 26.5 and 26.6 kg m −3 (Fig. 6).…”

Section: Discussioncontrasting

confidence: 99%

“…Recent observations of deep Fe plumes in all three ocean ODZs (Thi Dieu Vu and Sohrin 2013; Resing et al 2015; Bolster et al 2022; Chinni and Singh 2022) as well as recent investigations into the mechanisms of off‐shelf Fe transport (Homoky et al 2021; König et al 2021) have prompted interest in the conditions that enhance off‐shelf Fe transport. Previous research has determined the importance of the benthic carbon oxidation rate (Elrod et al 2004) as well as bottom water oxygen concentrations (Severmann et al 2010) on influencing benthic Fe fluxes (Dale et al 2015).…”

Section: Discussionmentioning

confidence: 99%

“…This off‐shelf Fe(II) may precipitate to Fe(III), settle onto the continental slope, and be remobilized to form a deep plume of dissolved Fe(III) (Lam et al 2020). These deep plumes have been observed in all three oceanic ODZs: the Eastern Tropical North Pacific (ETNP), Eastern Tropical South Pacific (ETSP), and the Arabian Sea (Thi Dieu Vu and Sohrin 2013; Resing et al 2015; Bolster et al 2022; Chinni and Singh 2022) as well as highly productive Oxygen Minimum Zones (Noble et al 2012; Hatta et al 2015), though their appearance is not predicted by classical geochemical models (Lam et al 2020).…”

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confidence: 99%

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The role of seasonal hypoxia and benthic boundary layer exchange on iron redox cycling on the Oregon shelf

Evans,

Floback,

Gaffney

et al. 2023

Limnology & Oceanography

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Widespread hypoxia occurs seasonally across the Oregon continental shelf, and the duration, intensity, and frequency of hypoxic events have increased in recent years. In hypoxic regions, iron reduction can liberate dissolved Fe(II) from continental shelf sediments. Fe(II) was measured in the water column across the continental shelf and slope on the Oregon coast during summer 2022 using both a trace metal clean rosette and a high‐resolution benthic gradient sampler. In the summer, Fe(II) concentrations were exceptionally high (40–60 nM) within bottom waters and ubiquitous across the Oregon shelf, reflecting the low oxygen condition (40–70 μM) at that time. The observed inverse correlation between Fe(II) and bottom water oxygen concentrations is in agreement with expectations based on previous work that demonstrates oxygen is a major determinant of benthic Fe fluxes. Rapid attenuation of Fe(II) from the benthic boundary layer (within 1 m of the seafloor) probably reflects efficient cross‐shelf advection. One region, centered around Heceta Bank (~ 44°N) acts a hotspot for Fe release on the Oregon continental shelf, likely due to its semi‐retentive nature and high percent mud content in sediment. The results suggest that hypoxia is an important determinant of the inventory of iron is Oregon shelf waters and thus ultimately controls the importance of continental margin‐derived iron to the interior of the North Pacific Basin.

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Section: Discussioncontrasting

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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confidence: 99%

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The role of seasonal hypoxia and benthic boundary layer exchange on iron redox cycling on the Oregon shelf

Evans,

Floback,

Gaffney

et al. 2023

Limnology & Oceanography

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“…Results suggest that Zn/Ca and Mn/Ca in G. hexagonus can be related to macroenvironmental drivers, via concentrations of dissolved ions in ambient seawater. This is further supported by observations of an increase in dissolved Mn and Zn at OMZ depths in the ETNP, where Mn/Ca and Zn/Ca also increase in foraminiferal calcite (Bolster et al, 2022; Figure 5). The variability in Zn/Ca and Mn/Ca ratios of G. hexagonus shells and dissolved Mn and Zn are also all higher at OMZ depths (Figure 5; Supplemental Table 2).…”

Section: -]) Would Co-occur With Decreasing Oxygenation In the Omzsupporting

confidence: 79%

“…Thus, Mn 2+ substitutions for Ca 2+ should occur more frequently and Mn/Ca should increase in shells formed at lower oxygen conditions (Barras et al, 2018;van Dijk et al, 2020). While there are other controls on Mn and Mn 2+ availability in natural systems, in the ETNP dissolved Mn shows a distinct peak specifically associated with low dissolved oxygen (Bolster et al, 2022; Figure 5). There is also evidence for an oxygenation control on the incorporation of Mn/Ca into benthic foraminiferal calcite (Munsel et al, 2010;Groeneveld and Filipsson, 2013;Koho et al, 2015;McKay et al, 2015;Nı́Fhlaithearta et al, 2018;van Dijk et al, 2020).…”

Section: Oxygen and Carbonate System Controls On Mn And Znmentioning

confidence: 98%

Trace element composition of modern planktic foraminifera from an oxygen minimum zone: Potential proxies for an enigmatic environment

et al. 2023

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Oxygen limited marine environments, such as oxygen minimum zones, are of profound importance for global nutrient cycling and vertical habitat availability. While it is understood that the extent and intensity of oxygen minimum zones are responsive to climate, the limited suite of viable proxies for low oxygen pelagic environments continues to pose a real barrier for paleoclimate interpretations. Here we investigate the proxy potential of an array of trace element (Mg, Mn, Zn, and Sr) to Ca ratios from the shells of Globorotaloides hexagonus, a planktic foraminifer endemic to tropical through temperate oxygen minimum zones. A species-specific relationship between Mg/Ca and temperature is proposed for quantitative reconstruction of oxygen minimum zone paleotemperatures. Both Mn/Ca and Zn/Ca ratios vary with oxygen concentration and could be useful for reconstructing G. hexagonus habitat where the primary signal can be d\istinguished from diagenetic overprinting. Finally, a robust correlation between Sr/Ca ratios and dissolved oxygen demonstrates a role for Sr as an indicator of oxygen minimum zone intensity, potentially via foraminiferal growth rate. The analysis of these relatively conventional trace element ratios in the shells of an oxygen minimum zone species has tremendous potential to facilitate multiproxy reconstructions from this enigmatic environment.

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Sample preservation methods for nitrous oxide concentration and isotope ratio measurements in aquatic environments

Frey,

Tang,

Ward

et al. 2024

Limnology & Ocean Methods

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The nitrogen (N) and oxygen (O) stable isotope analysis of dissolved nitrous oxide (N2O) can provide important constraints on the sources and cycling of N2O in aquatic environments. The isotopic composition of aqueous N2O, both in field (natural abundance) or experimental (15N‐labeling) samples, however, may be altered by abiotic reactions involving nitrite () or hydroxylamine (NH2OH) and microbial activity during sample storage, if samples are not adequately preserved. Here we tested five different preservatives, mercuric chloride (HgCl2), copper sulfate (CuSO4), zinc chloride (ZnCl2), hydrochloric acid (HCl) mixed with sulfamic acid (SFA), and sodium hydroxide (NaOH), for fixing natural water samples from an estuary and a lake with different concentrations over a range of different storage times for N2O analyses. ZnCl2 and CuSO4 decreased the pH, and led to abiotic N2O production from , shifting the N2O isotopic composition significantly. Removal of with a mixture of SFA and HCl did not always prevent the alteration of the original N and O isotope composition of N2O, confirming the requirement for complete removal, and underscoring the biasing effects of at very low pH, even at trace levels. At low background, HgCl2 preservation led to robust and accurate results. However, in light of its toxicity and bioaccumulation potential in food webs, this fixative should be avoided. The addition of NaOH reduced abiotic side reactions involving , and yielded the most reliable and reproducible results for N2O concentration and isotope ratio measurements across tested settings and storage times.

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Iron and manganese accumulation within the Eastern Tropical North Pacific oxygen deficient zone

Cited by 11 publications

References 72 publications

The role of seasonal hypoxia and benthic boundary layer exchange on iron redox cycling on the Oregon shelf

The role of seasonal hypoxia and benthic boundary layer exchange on iron redox cycling on the Oregon shelf

Trace element composition of modern planktic foraminifera from an oxygen minimum zone: Potential proxies for an enigmatic environment

Sample preservation methods for nitrous oxide concentration and isotope ratio measurements in aquatic environments

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