Southern Ocean Upwelling and the Marine Iron Cycle

Weber, Thomas

doi:10.1029/2020gl090737

Cited by 6 publications

(5 citation statements)

References 25 publications

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“…Our study suggests that the residence time for hydrothermal Fe is on the order of a few tens of years, which requires upper ocean ventilation to be sufficiently rapid. The conservative hydrothermal tracer 3 He has been estimated to emerge in Southern Ocean surface waters within 99 ± 18 years (Jenkins, 2020), similar to the median re-exposure timescale from the deep Southern Ocean calculated from data constrained ocean physical models (DeVries and Holzer, 2019;Weber, 2020). Estimates from particle tracking models at higher spatial resolution suggest more rapid ventilation timescales of around 20 years, which slow to many decades in coarser resolution configurations (Tamsitt et al, 2017;Drake et al, 2018).…”

Section: Wider Implicationssupporting

confidence: 57%

Constraining the Contribution of Hydrothermal Iron to Southern Ocean Export Production Using Deep Ocean Iron Observations

et al. 2022

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Hydrothermal iron supply contributes to the Southern Ocean carbon cycle via the regulation of regional export production. However, as hydrothermal iron input estimates are coupled to helium, which are uncertain depending on whether helium inputs are based on ridge spreading rates or inverse modelling, questions remain regarding the magnitude of the export production impacts. A particular challenge is the limited observations of dissolved iron (dFe) supply from the abyssal Southern Ocean ridge system to directly assess different hydrothermal iron supply scenarios. We combine ocean biogeochemical modelling with new observations of dFe from the abyssal Southern Ocean to assess the impact of hydrothermal iron supply estimated from either ridge spreading rate or inverse helium modelling on Southern Ocean export production. The hydrothermal contribution to dFe in the upper 250 m reduces 4–5 fold when supply is based on inverse modelling, relative to those based on spreading rate, translating into a 36–73% reduction in the impact of hydrothermal iron on export production. However, only the spreading rate input scheme reproduces observed dFe anomalies >1 nM around the circum-Antarctic ridge. The model correlation with observations drops 3 fold under the inverse modelling input scheme. The best dFe scenario has a residence time for hydrothermal iron that is between 21 and 34 years, highlighting the importance of rapid physical mixing to surface waters. Overall, because of its short residence time, hydrothermal Fe supplied locally by circum-Antarctic ridges is most important to the Southern Ocean carbon cycle and our results highlight decoupling between hydrothermal iron and helium supply.

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Section: Wider Implicationssupporting

confidence: 57%

Constraining the Contribution of Hydrothermal Iron to Southern Ocean Export Production Using Deep Ocean Iron Observations

et al. 2022

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“…In the subarctic North Atlantic and North Pacific Ocean, where dust provides 15%–50% of the Fe demand, additional Fe may be transported through western boundary currents from regions of high deposition. Near the Antarctic coastline in the Southern Ocean, shallow shelves (Abadie et al., 2017) and upwelling deep water carrying hydrothermally sourced Fe (Jenkins, 2020; Resing et al., 2015; Weber, 2020) may provide the additional Fe required to support export. In the Tropical and Eastern Pacific, where the Fe supply from dust falls furthest short of the demand (<10%), upwelling of sediment‐sourced Fe, especially from oxygen minimum zones (John et al., 2018), may make up the deficit.…”

Section: Discussionmentioning

confidence: 99%

Ocean Dust Deposition Rates Constrained in a Data‐Assimilation Model of the Marine Aluminum Cycle

Weber

2021

Global Biogeochemical Cycles

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The formation of organic matter in the surface ocean and its sinking and remineralization through the water column lead to a net carbon (C) transfer to depth that is known as the biological carbon pump (Ducklow, 2001). Changes in strength of the biological pump can repartition carbon dioxide (CO 2 ) between the atmosphere and ocean (Passow & Carlson, 2012), and have likely contributed to major climatic shifts through Earth's history, including the Pleistocene glacial-interglacial cycles (Martinez-Garcia et al., 2014). Production of organic matter by marine phytoplankton requires a suite of nutrient elements, each with their own unique biogeochemical cycles, which can limit primary production and regulate biological C storage in the ocean (Moore et al., 2013).Dust deposition on the surface ocean is an important source of trace metal micronutrients like iron (Fe), which serves as a cofactor in various algal pigments and enzymes (Morel et al., 1991). Dissolved Fe (dFe) scarcity directly limits phytoplankton growth and prevents the utilization of the major nutrients nitrate (NO 3 ) and phosphate (PO 4 ) at high latitudes (Moore et al., 2013), and limits the growth of nitrogen-fixation planktons that add new NO 3 to the system in low-latitude systems where NO 3 is the primary limiting nutrient (Moore et al., 2009). Therefore, Fe availability is an important factor regulating C export to depth in most ocean regions (Moore et al., 2013). There are three major external sources of Fe to the global ocean: (a) aeolian transport of dust particles, mostly from desert regions (Jickells et al., 2005); (b) release from continental margin sediments (Elrod et al., 2004); (c) injection of metal-rich hydrothermal fluids along mid-ocean ridges (Tagliabue, 2014). However, the magnitude of these sources and their relative importance in fueling phytoplankton growth remains highly uncertain (Tagliabue et al., 2016), which limits our understanding of the biological pump's sensitivity to perturbation of the marine Fe budget. Because dust is the only process that delivers Fe directly to the euphotic zone in the open ocean, it is often considered the most important Fe source to phytoplankton communities, suggesting that changing dust fluxes can drive global climate change through the biological pump (Martin, 1990).

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“…Investigations using a helium‐3 mass balance model indicated that upwelling of hydrothermal dFe from deep waters may occur over a ∼100‐year period (Jenkins, 2020; Weber, 2020). However, these estimates are subject to scavenging times of dFe that span several orders of magnitude (Bergquist & Boyle, 2006; Weber, 2020). The generally lower dFe concentrations in CDW of the Antarctic zone compared with that of the subantarctic zone (Figure 3c) indicated that this hydrothermal source may have a greater impact on subantarctic waters.…”

Section: Discussionmentioning

confidence: 99%

“…Tagliabue et al (2022) suggested that dFe enriched CDW from this hydrothermal activity may influence southern surface water dFe concentrations due to the shoaling of CDW approaching the Antarctic continental shelf (Figure 2). Investigations using a helium-3 mass balance model indicated that upwelling of hydrothermal dFe from deep waters may occur over a ∼100-year period (Jenkins, 2020;Weber, 2020). However, these estimates are subject to scavenging times of dFe that span several orders of magnitude (Bergquist & Boyle, 2006;Weber, 2020).…”

Section: Bathypelagic 1000-2000 M Depthmentioning

confidence: 99%

Mechanistic Constraints on the Drivers of Southern Ocean Meridional Iron Distributions Between Tasmania and Antarctica

Traill,

Conde‐Pardo,

Rohr

et al. 2024

Global Biogeochemical Cycles

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While modeling efforts have furthered our understanding of marine iron biogeochemistry and its influence on carbon sequestration, observations of dissolved iron (dFe) and its relationship to physical, chemical and biological processes in the ocean are needed to both validate and inform model parameterization. Where iron comes from, how it is transported and recycled, and where iron removal takes place are critical mechanisms that need to be understood to assess the relationship between iron availability and primary production. To this end, hydrographic and trace metal observations across the GO‐SHIP section SR3, south of Tasmania, Australia, have been analyzed in tandem with the novel application of an optimum multiparameter analysis. From the trace‐metal distribution south of Australia, key differences in the drivers of dFe between oceanographic zones of the Southern Ocean were identified. In the subtropical zone, sources of dFe were attributed to waters advected off the continental shelf, and to recirculated modified mode and intermediate water‐masses of the Tasman Outflow. In the subantarctic zone, the seasonal replenishment of dFe in Antarctic surface and mode waters appears to be sustained by iron recycling in the underlying mode and intermediate waters. In the southern zone, the dFe distribution is likely driven by dissolution and scavenging by high concentrations of particles along the Antarctic continental shelf and slope entrained in high salinity shelf water. This approach to trace metal analysis may prove useful in future transects for identifying key mechanisms driving marine dissolved trace metal distributions.

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Southern Ocean Upwelling and the Marine Iron Cycle

Cited by 6 publications

References 25 publications

Constraining the Contribution of Hydrothermal Iron to Southern Ocean Export Production Using Deep Ocean Iron Observations

Constraining the Contribution of Hydrothermal Iron to Southern Ocean Export Production Using Deep Ocean Iron Observations

Ocean Dust Deposition Rates Constrained in a Data‐Assimilation Model of the Marine Aluminum Cycle

Mechanistic Constraints on the Drivers of Southern Ocean Meridional Iron Distributions Between Tasmania and Antarctica

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