Sediments as a Source of Iron, Manganese, Cobalt and Nickel to Continental Shelf Waters (Louisiana, Gulf of Mexico)

Lenstra, Wytze K.; Helmond, Niels A. G. M. van; Żygadłowska, Olga M.; Zummeren, Roosmarijn van; Witbaard, Rob; Slomp, Caroline P.

doi:10.3389/fmars.2022.811953

Cited by 13 publications

(14 citation statements)

References 71 publications

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“…Further benthic chamber experiments in diverse sedimentary environments (such as that by Ghaisis et al. (2019)) as well as constraining porewater and bottom water vertical gradients in dissolved Fe (e.g., Lenstra et al., 2022) will help narrow this range in expected deep benthic Fe flux in the future. In terms of global context, our Gulf of Mexico dissolved Fe flux (based on 232 Th) of about 2 mmol Fe/m 2 /yr (1,000 m reference depth) is relatively high compared to other remote oceanic regions such as the northwestern Pacific (0.2 mmol/m 2 /yr; Hayes et al., 2013) and subtropical North Pacific (0.08 mmol/m 2 /yr; Hayes, Fitzsimmons et al., 2015), but similar to that found in Kerguelen Plateau region (1.5–2 mmol/m 2 /yr; Perez‐Tribouilier et al., 2020).…”

Section: Resultsmentioning

confidence: 99%

Toward Constraining Sources of Lithogenic Metals in the Northern Gulf of Mexico

2022

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North African dust is known to be deposited in the Gulf of Mexico, but its deposition rate and associated supply of lithogenic dissolved metals, such as the abiotic metal thorium or the micronutrient metal iron, have not been well‐quantified. 232Th is an isotope with similar sources as iron and its input can be quantified using radiogenic 230Th. By comparing dissolved 232Th fluxes at three sites in the northern Gulf of Mexico with upwind sites in the North Atlantic, we place an upper bound on North African dust contributions to 232Th and Fe in the Gulf of Mexico, which is about 30% of the total input. Precision on this bound is hindered by uncertainty in the relative rates of dust deposition in the North Atlantic and the northern Gulf of Mexico. Based on available radium data, shelf sources, including rivers, submarine groundwater discharge, and benthic sedimentary releases are likely as important if not more important than dust in the budget of lithogenic metals in the Gulf of Mexico. In other words, it is likely there is no one dominant source of Th and Fe in the Gulf of Mexico. Finally, our estimated Fe input in the northern Gulf of Mexico implies an Fe residence time of less than 6 months, similar to that in the North Atlantic despite significantly higher supply rates in the Gulf of Mexico.

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Section: Resultsmentioning

confidence: 99%

Toward Constraining Sources of Lithogenic Metals in the Northern Gulf of Mexico

2022

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“…During hypoxic conditions, high riverine discharge can facilitate the rapid burial of OM. Nevertheless, sediment accumulation rates found on the Louisiana shelf ranged from ∼ 1.5 cm yr −1 on the shallow shelf, towards 0.2-0.3 cm yr −1 on the slope (Lenstra et al, 2022). Therefore, the upper 0-2 cm sediment analyzed, which represents at least 1-year deposition time, integrates multiple years of seasonally varying oxygen conditions.…”

Section: Sample Collectionmentioning

confidence: 97%

The dispersal of fluvially discharged and marine, shelf-produced particulate organic matter in the northern Gulf of Mexico

Yedema¹,

Sangiorgi²,

Sluijs³

et al. 2023

Biogeosciences

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Abstract. Rivers play a key role in the global carbon cycle by transporting terrestrial organic matter (TerrOM) from land to the ocean. Upon burial in marine sediments, this TerrOM may be a significant long-term carbon sink, depending on its composition and properties. However, much remains unknown about the dispersal of different types of TerrOM in the marine realm upon fluvial discharge since the commonly used bulk organic matter (OM) parameters do not reach the required level of source- and process-specific information. Here, we analyzed bulk OM properties, lipid biomarkers (long-chain n-alkanes, sterols, long-chain diols, alkenones, branched and isoprenoid glycerol dialkyl glycerol tetraethers (brGDGTs and isoGDGTs)), pollen, and dinoflagellate cysts in marine surface sediments along two transects offshore the Mississippi–Atchafalaya River (MAR) system, as well as one along the 20 m isobath in the direction of the river plume. We use these biomarkers and palynological proxies to identify the dispersal patterns of soil–microbial organic matter (SMOM), fluvial, higher plant, and marine-produced OM in the coastal sediments of the northern Gulf of Mexico (GoM). The Branched and Isoprenoid Tetraether (BIT) index and the relative abundance of C32 1,15-diols indicative for freshwater production show high contributions of SMOM and fluvial OM near the Mississippi River (MR) mouth (BIT = 0.6, FC321,15 > 50 %), which rapidly decrease further away from the river mouth (BIT < 0.1, FC321,15 < 20 %). In contrast, concentrations of long-chain n-alkanes and pollen grains do not show this stark decrease along the path of transport, and especially n-alkanes are also found in sediments in deeper waters. Proxy indicators show that marine productivity is highest close to shore and reveal that marine producers (diatoms, dinoflagellates, coccolithophores) have different spatial distributions, indicating their preferred niches. Close to the coast, where food supply is high and waters are turbid, cysts of heterotrophic dinoflagellates dominate the assemblages. The dominance of heterotrophic taxa in shelf waters in combination with the rapid decrease in the relative contribution of TerrOM towards the deeper ocean suggest that TerrOM input may trigger a priming effect that results in its rapid decomposition upon discharge. In the open ocean far away from the river plume, autotrophic dinoflagellates dominate the assemblages, indicating more oligotrophic conditions. Our combined lipid biomarker and palynology approach reveals that different types of TerrOM have distinct dispersal patterns, suggesting that the initial composition of this particulate OM influences the burial efficiency of TerrOM on the continental margin.

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“…Water column dissolved and particulate Fe, Mn and Mo were measured by ICP mass spectrometry (ICP-MS, Nexion (Perkin Elmer)). The water column samples were concentrated and the seawater matrix was removed using a SC-DX SeaFAST S2 (Elemental Scientific) prior to analysis (Lenstra et al, 2022). Samples acidified to pH 2 were buffered with 4.8 M glacial acetic acid 99.7% (Baseline, Seastar) and 4.1 M ammonium hydroxide 29% (Baseline, Seastar) and subsequently loaded onto the pre-concentration column for 20 seconds (Lagerström et al, 2013).…”

Section: Concentrations Of Nh +mentioning

confidence: 99%

Pathways of methane removal in the sediment and water column of a seasonally anoxic eutrophic marine basin

et al. 2023

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Methane (CH4) is a key greenhouse gas. Coastal areas account for a major proportion of marine CH4 emissions. Eutrophication and associated bottom water hypoxia enhance CH4 production in coastal sediments. Here, we assess the fate of CH4 produced in sediments at a site in a seasonally anoxic eutrophic coastal marine basin (Scharendijke, Lake Grevelingen, the Netherlands) in spring (March) and late summer (September) in 2020. Removal of CH4 in the sediment through anaerobic oxidation with sulfate (SO42-) is known to be incomplete in this system, as confirmed here by only slightly higher values of δ13C-CH4 and δD-CH4 in the porewater in the shallow sulfate-methane-transition zone (~5-15 cm sediment depth) when compared to deeper sediment layers. In March 2020, when the water column was fully oxygenated, CH4 that escaped from the sediment was at least partially removed in the bottom water through aerobic oxidation. In September 2020, when the water column was anoxic below ~35 m water depth, CH4 accumulated to high concentrations (up to 73 µmol L-1) in the waters below the oxycline. The sharp counter gradient in oxygen and CH4 concentrations at ~35 m depth and increase in δ13C-CH4 and δD-CH4 above the oxycline indicate mostly aerobic water column removal of CH4. Water column profiles of particulate and dissolved Fe and Mn suggest redox cycling of both metals at the oxycline, pointing towards a potential role of metal oxides in CH4 removal. Water column profiles of NH4+ and NO3- indicate removal of both solutes near the oxycline. Analyses of 16S rRNA gene sequences retrieved from the water column reveal the presence of aerobic CH4 oxidizing bacteria (Methylomonadaceae) and anaerobic methanotrophic archaea (Methanoperedenaceae), with the latter potentially capable of NO3- and/or metal-oxide dependent CH4 oxidation, near the oxycline. Overall, our results indicate sediment and water column removal of CH4 through a combination of aerobic and anaerobic pathways, which vary seasonally. Some of the CH4 appears to escape from the surface waters to the atmosphere, however. We conclude that eutrophication may make coastal waters a more important source of CH4 to the atmosphere than commonly assumed.

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Sediments as a Source of Iron, Manganese, Cobalt and Nickel to Continental Shelf Waters (Louisiana, Gulf of Mexico)

Cited by 13 publications

References 71 publications

Toward Constraining Sources of Lithogenic Metals in the Northern Gulf of Mexico

Toward Constraining Sources of Lithogenic Metals in the Northern Gulf of Mexico

The dispersal of fluvially discharged and marine, shelf-produced particulate organic matter in the northern Gulf of Mexico

Pathways of methane removal in the sediment and water column of a seasonally anoxic eutrophic marine basin

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