Natural iron fertilization by shallow hydrothermal sources fuels diazotroph blooms in the ocean

Bonnet, Sophie; Guieu, Cécile; Taillandier, Vincent; Boulart, Cédric; Bouruet-Aubertot, Pascale; Gazeau, Frédéric; Scalabrin, Carla; Bressac, Matthieu; Knapp, Angela N.; Cuypers, Yannis; González-Santana, David; Forrer, Heather J.; Grisoni, Jean-Michel; Grosso, Olivier; Habasque, Jérémie; Jardin-Camps, Mercedes; Leblond, Nathalie; Le Moigne, Frédéric A. C.; Lebourges-Dhaussy, Anne; Lory, Caroline; Nunige, Sandra; Pulido-Villena, Elvira; Rizzo, Andrea L.; Sarthou, Géraldine; Tilliette, Chloé

doi:10.1126/science.abq4654

Cited by 27 publications

(33 citation statements)

References 93 publications

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“…Taken together, these data illustrate the high biological productivity previously reported in the Lau Basin during the austral summer season and mainly supported by calcareous (i.e., CaCO 3 ) and diazotrophic (i.e., OM) species (Bonnet, Guieu et al., 2023). These biological particles were intimately linked to the influx of lithogenic material largely originating from the Tonga Arc, renowned for its shallow hydrothermal activity (e.g., Massoth et al., 2007; Tilliette et al., 2022).…”

Section: Discussionsupporting

confidence: 83%

“…Sediment cores were collected at around 10 p.m. using a MC-8/100 multi-corer (Oktopus GmbH, Kiel, Germany) at the mooring positions and at the deep-sea reference site (station 8; 20°23.33' S, 166°25.4' W; Figure 1). The Bonnet, Guieu et al, 2023). Different oceanic regions were occupied during the cruise: the South Pacific gyre (station 8; sediment coring only) and the Lau Basin (stations 5 and 10), where a drifting mooring line was deployed for 5 and 4 days, respectively, as well as station 12 where a fixed mooring line was deployed for 1 year.…”

Section: Fieldworkmentioning

confidence: 99%

“…Figure 1. (a) Cruise transect superimposed on surface chlorophyll-a concentrations (mg m −3 ;Bonnet, Guieu et al, 2023). Different oceanic regions were occupied during the cruise: the South Pacific gyre (station 8; sediment coring only) and the Lau Basin (stations 5 and 10), where a drifting mooring line was deployed for 5 and 4 days, respectively, as well as station 12 where a fixed mooring line was deployed for 1 year.…”

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confidence: 99%

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Significant Impact of Hydrothermalism on the Biogeochemical Signature of Sinking and Sedimented Particles in the Lau Basin

Tilliette,

Gazeau,

Chavagnac

et al. 2023

JGR Oceans

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Iron (Fe) is an essential micronutrient for diazotrophs, which are abundant in the Western Tropical South Pacific Ocean (WTSP). Their success depends on the numerous trace metals, particularly Fe, released from shallow hydrothermal vents along the Tonga Arc. This study aimed to explore the spatio‐temporal impact of hydrothermal fluids on particulate trace metal concentrations and biological activity. To identify the composition of sinking particles across a wide area of the WTSP, we deployed sediment traps at various depths, both close and further west of the Tonga Arc. Seafloor sediments were cored at these deployment sites, including at a remote location in the South Pacific Gyre. The sinking particles were composed of a large amount of biological material (up to 88 mg d−1), indicative of the high productivity of the region. A significant portion of this material (∼21 ± 12 wt.%) was lithogenic of hydrothermal origin, as revealed through Al‐Fe‐Mn tracing. The sinking material showed similar patterns between lithogenic and biogenic fractions, indicating that hydrothermal input within the photic layer triggered surface production. A hydrothermal fingerprint was suggested in the sediments due to the high sedimentation rates (>47 cm kyr−1) and the presence of large, heterogeneous, metal‐rich particles. The presence of nearby active deep hydrothermal sources was suspected near the Lau Ridge due to the large particle size (1–976 μm) and the significant excess of Fe and Mn (2–20 wt.%). Overall, this study revealed that hydrothermal sources have a significant influence on the biogeochemical signature of particles in the region.

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Section: Discussionsupporting

confidence: 83%

Section: Fieldworkmentioning

confidence: 99%

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confidence: 99%

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Significant Impact of Hydrothermalism on the Biogeochemical Signature of Sinking and Sedimented Particles in the Lau Basin

Tilliette,

Gazeau,

Chavagnac

et al. 2023

JGR Oceans

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“…Gradients in both metrics suggest that phytoplankton experience less iron stress in the Western than Eastern Pacific Ocean, consistent with observations that iron limits phytoplankton growth (Mahowald et al., 2005; Moore et al., 2013; Ustick et al., 2021) and nitrogen fixation rates (Dekaezemacker et al., 2013; Knapp et al., 2016) in the Eastern Pacific Ocean. We note that hydrothermal vents along the Tonga‐Kermadec Ridge in the Western South Pacific Ocean are another potential source of iron in addition to dust deposition (Bonnet et al., 2023; Guieu et al., 2018). Increased iron supply in the Western South Pacific Ocean favors nitrogen fixation, which adds new nitrogen to the ocean and enhances PO 4 3− stress, highlighting DOP as an alternative P source to support primary production and nitrogen fixation.…”

Section: Discussionmentioning

confidence: 93%

Global Patterns of Surface Ocean Dissolved Organic Matter Stoichiometry

Liang,

Letscher,

Knapp

2023

Global Biogeochemical Cycles

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Surface ocean marine dissolved organic matter (DOM) serves as an important reservoir of carbon (C), nitrogen (N), and phosphorus (P) in the global ocean, and is produced and consumed by both autotrophic and heterotrophic communities. While prior work has described distributions of dissolved organic carbon (DOC) and nitrogen (DON) concentrations, our understanding of DOC:DON:DOP stoichiometry in the global surface ocean has been limited by the availability of DOP concentration measurements. Here, we estimate mean surface ocean bulk and semi‐labile DOC:DON:DOP stoichiometry in biogeochemically and geographically defined regions using newly available marine DOM concentration databases. Global mean surface ocean bulk (C:N:P = 387:26:1) and semi‐labile (C:N:P = 179:20:1) DOM stoichiometries are higher than Redfield stoichiometry, with semi‐labile DOM stoichiometry similar to that of global mean surface ocean particulate organic matter (C:N:P = 160:21:1) reported in a recent compilation. DOM stoichiometry varies across ocean basins, ranging from 251:17:1 to 638:43:1 for bulk and 83:15:1 to 414:49:1 for semi‐labile DOM C:N:P, respectively. Surface ocean DOP concentration exhibits larger relative changes than DOC and DON, driving surface ocean gradients in DOC:DON:DOP stoichiometry. Inferred autotrophic consumption of DOP helps explain intra‐ and inter‐basin patterns of marine DOM C:N:P stoichiometry, with regional patterns of water column denitrification and iron supply influencing the biogeochemical conditions favoring DOP use as an organic nutrient. Specifically, surface ocean marine DOM exhibits increasingly P‐depleted stoichiometries from east to west in the Pacific and from south to north in the Atlantic, consistent with patterns of increasing P stress and alleviated iron stress.

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“…For example, iron supply from atmospheric deposition has been hypothesized to favor N 2 fixation in the North Atlantic (Moore et al, 2009;Wu et al, 2000) and North Pacific (Browning et al, 2022;Hashihama et al, 2009;Kitajima et al, 2009;Wen et al, 2022;. Additionally, the iron supply from the ocean interior has also been identified as a potential driving mechanism for a hotspot for N 2 fixation in the nitrate-depleted Angola Gyre of the South Atlantic (Marshall et al, 2022) and western tropical South Pacific (Bonnet et al, 2017(Bonnet et al, , 2023.…”

Section: Mechanisms Controlling Phosphate Drawdownmentioning

confidence: 99%

Enhanced Phosphate Consumption Stimulated by Nitrogen Fixation Within a Cyclonic Eddy in the Northwest Pacific

Yuan,

Browning,

et al. 2023

JGR Oceans

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Mesoscale eddies are common in the subtropical Northwest Pacific, however, relatively little is known about their spatial variability and temporal evolution, and how these impact upper ocean biogeochemistry. Here we investigate these using observations of a cyclonic eddy carried out along four sequential transects. Consistent with previous observations of cyclonic eddies, the eddy core had doming isopycnals, bringing elevated nutrient waters nearer to the surface. However, we also found that the upper layer of the eddy above the nutricline had significantly lower phosphate concentrations within its core relative to its edge. We attributed this to elevated N2 fixation within the eddy core, which was likely driven by enhanced subsurface iron supply, ultimately resulting in increased phosphate consumption. Eddy‐enhanced N2 fixation was additionally supported by the elevation of nitrate + nitrite to phosphate ratios below the euphotic zone. Moreover, we observed that while the upward displacement of isopycnals within the eddy core led to an increase in phytoplankton biomass in the lower euphotic zone, there was no significant increase in total phytoplankton biomass across the entire euphotic zone. Cyclonic eddies in the subtropical North Pacific are projected to be becoming more frequent, implying that such dynamics could become increasingly important for regulating nutrient biogeochemistry and ultimately productivity of the region.

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Natural iron fertilization by shallow hydrothermal sources fuels diazotroph blooms in the ocean

Cited by 27 publications

References 93 publications

Significant Impact of Hydrothermalism on the Biogeochemical Signature of Sinking and Sedimented Particles in the Lau Basin

Significant Impact of Hydrothermalism on the Biogeochemical Signature of Sinking and Sedimented Particles in the Lau Basin

Global Patterns of Surface Ocean Dissolved Organic Matter Stoichiometry

Enhanced Phosphate Consumption Stimulated by Nitrogen Fixation Within a Cyclonic Eddy in the Northwest Pacific

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