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Iron biogeochemistry across marine systems – progress from the past decade

Authors:
Eike Breitbarth at REZO Water+Energy, Dunedin, New Zealand
Eike Breitbarth
  • REZO Water+Energy, Dunedin, New Zealand
E. P. Achterberg at GEOMAR Helmholtz Centre for Ocean Research Kiel
E. P. Achterberg
Murat V Ardelan at Norwegian University of Science and Technology
Murat V Ardelan
Alex R. Baker
Alex R. Baker
Alex R. Baker
  • This person is not on ResearchGate, or hasn't claimed this research yet.
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Abstract

Based on an international workshop (Gothenburg, 14–16 May 2008), this review article aims to combine interdisciplinary knowledge from coastal and open ocean research on iron biogeochemistry. The major scientific findings of the past decade are structured into sections on natural and artificial iron fertilization, iron inputs into coastal and estuarine systems, colloidal iron and organic matter, and biological processes. Potential effects of global climate change, particularly ocean acidification, on iron biogeochemistry are discussed. The findings are synthesized into recommendations for future research areas.
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... In the Southern Ocean iron supply is expected to rise in the future due to aerosol dust deposition and melting ice (Hutchins and Boyd, 2016;IPCC, 2019). Also, Breitbarth et al. (2010) have suggested increased iron bioavailability due to ocean acidification. Contrary to iron, acidification is predicted to be reducing DSi availability in the euphotic zone (Taucher et al., 2022). ...
Rice husk as a potential source of silicate to oceanic phytoplankton
Article
  • Mar 2023
  • SCI TOTAL ENVIRON
Global oceans are witnessing changes in the phytoplankton community composition due to various environmental stressors such as temperature, stratification, nutrient limitation, and ocean acidification. The Arabian Sea is also undergoing changes in its phytoplankton community composition, especially during winter, with the diatoms being replaced by harmful algal blooms (HABs) of dinoflagellates. Recent studies have already highlighted dissolved silicate (DSi) limitation and change in Silicon (Si)/Nitrogen (N) ratios as the factors responsible for the observed changes in the phytoplankton community in the Arabian Sea. Our investigation also revealed Si/N < 1 in the northern Arabian Sea, indicating DSi limitation, especially during winter. Here, we demonstrate that rice husk with its phytoliths is an important source of bioavailable DSi for oceanic phytoplankton. Our experiment showed that a rice husk can release ~12 μM of DSi in 15 days and can release DSi for ~20 days. The DSi availability increased diatom abundance up to ~9 times. The major benefitted diatom species from DSi enrichment were Nitzshia spp., Striatella spp., Navicula spp., Dactiliosolen spp., and Leptocylindrus spp. The increase in diatom abundance was accompanied by an increase in fucoxanthin and dimethyl sulphide (DMS), an anti-greenhouse gas. Thus, the rice husk with its buoyancy and slow DSi release has the potential to reduce HABs, and increase diatoms and fishery resources in addition to carbon dioxide (CO2) sequestration in DSi-limited oceanic regions such as the Arabian Sea. Rice husk if released at the formation site of the Subantarctic mode water in the Southern Ocean could supply DSi to the thermocline in the global oceans thereby increasing diatom blooms and consequently the biotic carbon sequestration potential of the entire ocean.
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... Temperature affects metal-algae interactions by changes in their metabolism and in the bioavailability of metals. Thus, increasing temperatures impact the particle residence in the euphotic zone and the redox chemistry of metals by implication of photooxidation (Breitbarth et al., 2010). However, robust studies and predictions are not yet available on this regard (Hoffmann et al., 2012). ...
Global decrease in heavy metal concentrations in brown algae in the last 90 years
Article
Full-text available
  • Nov 2022
  • J HAZARD MATER
In the current scenario of global change, heavy metal pollution is of major concern because of its associated toxic effects and the persistence of these pollutants in the environment. This study is the first to evaluate the changes in heavy metal concentrations worldwide in brown algae over the last 90 years (>15,700 data across the globe reported from 1933 to 2020). The study findings revealed significant decreases in the concentrations of Cd, Co, Cr, Cu, Fe, Hg, Mn, Pb and Zn of around 60-84% (ca. 2% annual) in brown algae tissues. The decreases were consistent across the different families considered (Dictyotaceae, Fucaceae, Laminariaceae, Sargassaceae and Others), and began between 1970 and 1990. In addition, strong relationships between these trends and pH, SST and heat content were detected. Although the observed metal declines could be partially explained by these strong correlations, or by adaptions in the algae, other evidences suggest an actual reduction in metal concentrations in oceans because of the implementation of environmental policies. In any case, this study shows a reduction in metal concentrations in brown algae over the last 50 years, which is important in itself, as brown algae form the basis of many marine food webs and are therefore potential distributors of pollutants.
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... For example, Fe oxyhydroxides have a strong affinity for trace metals and P (Du Laing et al. 2009;Miao et al. 2006;Queiroz et al. 2018aQueiroz et al. , 2021, and their reductive dissolution may release these adsorbed elements into the pore water, potentially increasing nutrient availability (Rozan et al. 2002;Reef et al. 2010) and contamination. Estuarine soils may also represent a potential Fe source to the ocean, which plays a key role in a wide range of organisms (e.g., bacteria, algae, and phytoplankton) and ocean biogeochemical cycles (Breitbarth et al. 2010;Boyd and Ellwood 2010;Taylor and Konhauser 2011;Shaked and Lis 2012). Conversely, the sulfate reduction process may act as a sink for trace metals, as the produced sulfides (e.g., mackinawite, greigite, pyrite, and other metallic sulfides) decrease the bioavailability of trace metals via co-precipitation (Lin and Morse 1991;Huerta-Diaz and Morse 1992;Liamleam and Annachhatre 2007;Ye et al. 2010;Nóbrega et al. 2013). ...
Changes in soil iron biogeochemistry in response to mangrove dieback
Article
Full-text available
  • Apr 2022
  • BIOGEOCHEMISTRY
Fe biogeochemistry is associated with important ecosystem services provided by mangrove forests, including carbon sequestration and the retention of potentially toxic elements. The biogeochemical processes controlling Fe fate in mangroves are naturally affected by the soil geochemical environment, which controls Fe dynamics. However, ongoing climate changes and the associated extreme weather events may drastically affect the biogeochemistry of this important micronutrient for both terrestrial and oceanic environments. Therefore, this study aimed to evaluate how massive mangrove mortality after an extreme weather event altered the Fe dynamics in mangrove soils. The results show a significant decrease in soil carbon stock in the dead mangrove forests (25 kg m⁻²), as compared with the undisturbed forests (37 kg m⁻²). In addition, we observed a substantial Fe loss (greater than 50% of soil Fe forms, i.e., 17,000 mg kg⁻¹) in the dead mangrove soils, which was associated with pyrite (9000 mg kg⁻¹) and low crystallinity Fe oxyhydroxides (2400 mg kg⁻¹). These impacts led to a decrease in the pyritization in soils, which resulted in a loss of 170 tons of Fe from 500 ha of dead mangrove forests within one year. Thus, the pyritization process may critically compromise a mangrove forests' ability to immobilize pollutants (e.g., metals) and sequester carbon in the long term, thereby altering their ability to provide these ecosystem services. Overall, our results revealed that the Fe biogeochemical cycle of mangrove forests is very sensitive to future climate change scenarios and increased extreme weather events.
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... OA might enhance Fe bioavailability, as was shown by Stockdale et al. (2016), who used the IPCC model to predict that OA could lead to an increase in biologically available Fe. This would increase phytoplankton carbon acquisition and promote phytoplankton productivity (Breitbarth et al., 2010). In our research, however, the response of phytoplankton and the three BSCs to the coupled influences of low pH and Fe was again different. ...
Responses of Biogenic Sulfur Compound Concentrations to Dust Aerosol Enrichment and Ocean Acidification in the Western Pacific Ocean
Article
Full-text available
Deck incubation experiments were conducted to investigate how the addition of atmospheric dust aerosols and ocean acidification (OA) affects phytoplankton growth and the production of dimethylsulfide (DMS), its precursor dimethylsulfoniopropionate (DMSP), and dimethylsulfoxide (DMSO) in the oligotrophic western Pacific Ocean. The incubation experiment showed that the deposition of simulated dust aerosols greatly influenced phytoplankton growth and the release of biogenic sulfur compounds (BSCs). Furthermore, it altered the N:P ratios in seawater and phytoplankton community composition, elevating the proportions of strong DMSP and DMSO producers (mainly haptophytes). The average Chl‐a and DMS/P/O concentrations in the acidified treatment (pH 7.9) were 86.76%, 82.53%, 84.17%, and 231.06% higher than in the control. The results indicated that lower pH promoted the growth of diatoms and to a certain extent, the release of the three BSCs.
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... The current experiments were conducted at constant concentrations of biologically available dissolved inorganic Fe (Fe 0 ), but these concentrations, and hence biological uptake of Fe may also be changing with increasing CO 2 concentrations due to CO 2 -linked pH decreases in ocean water (Breitbarth et al. 2010;Shi et al. 2010;Sunda 2010). In addition, how the bacterial population associated with phytoplankton may change the effect of acidification on Fe bioavailability currently remains unknown (Amin et al. 2009). ...
Effect of increased CO2 on iron‐light‐CO2 co‐limitation of growth in a marine diatom
Article
  • Nov 2021
Light affects iron (Fe) growth requirements in marine phytoplankton while CO2 can influence energy allocation and light sensitivity. Therefore, ongoing increases in seawater CO2 concentrations could impact the growth of Fe‐ and light‐limited phytoplankton. In this study, Phaeodactylum tricornutum was used as a model diatom to examine the interactive effects of Fe, light, and CO2 on photosynthesis, growth, and protein expression in marine phytoplankton. Low concentration of biologically available inorganic iron (Fe′) and low‐light intensity decreased specific rates of carbon (C)‐fixation and growth, and the two together had an even greater effect, indicating a co‐limitation. Increased partial pressure of CO2 from its current value (400 μatm) to 750 μatm had no effect at growth sufficient levels of Fe and light, but increased C‐fixation and growth rate under Fe or light limitation, and had an even greater effect in Fe and light co‐limited cells. The results suggest that ongoing increases in CO2 may increase C‐fixation rates in Fe‐ and light‐limited and co‐limited regions, which cover at least 30% of the ocean. Measurements of photosynthetic proteins in photosystems II and I, and transcripts of proteins involved in CO2 concentrating mechanisms (CCMs), photorespiration, and antioxidant protection, suggest that the benefit of increased CO2 in the Fe‐ and light‐limited cells was from a downregulation of CCMs and resultant decreased demands for energy supplied from photosynthesis, and from decreased rates of photorespiration, which consumes photosynthetically produced ATP and NADPH. A decrease in oxidative stress with increased CO2 also contributed.
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Dissolved Fe(II) and its oxidation rates in the Kuroshio area, subarctic Pacific, and Bering Sea
Article
  • Apr 2024
Iron (Fe) in seawater is essential for marine phytoplankton. The bioavailability of Fe to phytoplankton largely depends on its chemical form in seawater. Fe(II) is an important component of surface water because photochemical reduction processes are related to the Fe acquisition mechanism of phytoplankton. However, the marine biogeochemical processes of Fe(II) have not been thoroughly investigated. This study applied the luminol chemiluminescence method to directly determine Fe(II) in acidified seawater in the Kuroshio area, subarctic Pacific, and the Bering Sea. We successfully obtained the vertical profile of Fe(II) in the Kuroshio region, where Fe oxidation has been studied; oxidation rates were consistent with previous studies. The prolonged half-life of Fe(II) in the Bering Sea suggests the possible influence of dissolved organic matter from the marginal sea on Fe(II) oxidation. The long half-life of Fe(II) in the high nutrient, low chlorophyll (HNLC) water may be crucial for supplying Fe to phytoplankton.
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The trace metal economy of the coral holobiont: supplies, demands and exchanges
Article
  • Nov 2022
The juxtaposition of highly productive coral reef ecosystems in oligotrophic waters has spurred substantial interest and progress in our understanding of macronutrient uptake, exchange, and recycling among coral holobiont partners (host coral, dinoflagellate endosymbiont, endolithic algae, fungi, viruses, bacterial communities). By contrast, the contribution of trace metals to the physiological performance of the coral holobiont and, in turn, the functional ecology of reef‐building corals remains unclear. The coral holobiont's trace metal economy is a network of supply, demand, and exchanges upheld by cross‐kingdom symbiotic partnerships. Each partner has unique trace metal requirements that are central to their biochemical functions and the metabolic stability of the holobiont. Organismal homeostasis and the exchanges among partners determine the ability of the coral holobiont to adjust to fluctuating trace metal supplies in heterogeneous reef environments. This review details the requirements for trace metals in core biological processes and describes how metal exchanges among holobiont partners are key to sustaining complex nutritional symbioses in oligotrophic environments. Specifically, we discuss how trace metals contribute to partner compatibility, ability to cope with stress, and thereby to organismal fitness and distribution. Beyond holobiont trace metal cycling, we outline how the dynamic nature of the availability of environmental trace metal supplies can be influenced by a variability of abiotic factors (e.g. temperature, light, pH, etc.). Climate change will have profound consequences on the availability of trace metals and further intensify the myriad stressors that influence coral survival. Lastly, we suggest future research directions necessary for understanding the impacts of trace metals on the coral holobiont symbioses spanning subcellular to organismal levels, which will inform nutrient cycling in coral ecosystems more broadly. Collectively, this cross‐scale elucidation of the role of trace metals for the coral holobiont will allow us to improve forecasts of future coral reef function.
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Low source-inherited iron solubility limits fertilization potential of South American dust
Article
Full-text available
  • Oct 2022
  • GEOCHIM COSMOCHIM AC
Where atmospheric processing is weak due to low anthropogenic emissions, fertilization of iron-limited oceans by non-volcanic mineral dust aerosols strongly depends on iron solubility at the sources. Southern South America (SSA) is a pristine environment and the main dust supplier to the southern oceans, the most sensitive to iron fertilization. Thus, the present-day lack of SSA dust fertilization of the southern oceans is hypothesized to reflect low source-inherited iron bioavailability. However, a dearth of geochemical studies on SSA dust prevents testing this hypothesis. To remedy this, we conducted the first systematic sampling of SSA dust sources. Iron leaching experiments showed fractional solubilities of close-to-source dust (bulk) and dust-emitting surface sediments (<63 µm) in pure water (0.05 ± 0.05%), seawater (0.03 ± 0.04%) and 1% nitric acid (5 ± 6%) that imply a low mass-normalized fertilization potential of SSA dust compared to dust from other regions. Based on grain size, size-resolved mineralogy, elemental chemistry and iron speciation determinations, we found that variability in labile iron is enhanced by high clay contents, small grain size and higher proportions of paramagnetic versus non-paramagnetic iron, irrespective of oxidation state. The independence of the most labile, water-soluble iron on grain size and its strong negative correlation to the Chemical Index of Alteration may imply that we currently underestimate the role of coarse glaciogenic dust as a supplier of bioavailable iron during drier-than-present ice ages when continental chemical weathering was reduced, and during which enhanced supply of dust-borne bioavailable iron to the southern oceans is observed.
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Health and Safety Effects of Airborne Soil Dust in the Americas and Beyond
Article
Full-text available
Risks associated with dust hazards are often underappreciated, a gap between the knowledge pool and public awareness that can be costly for impacted communities. This study reviews the emission sources and chemical, physical, and biological characteristics of airborne soil particles (dust) and their effects on human and environmental health and safety in the Pan-American region. American dust originates from both local sources (western United States, northern Mexico, Peru, Bolivia, Chile, and Argentina) and long-range transport from Africa and Asia. Dust properties, as well as the trends and interactions with criteria air pollutants, are summarized. Human exposure to dust is associated with adverse health effects, including asthma, allergies, fungal infections, and premature death. In the Americas, a well-documented and striking effect of soil dust is its association with Coccidioidomycosis, commonly known as Valley fever, an infection caused by inhalation of soil-dwelling fungi unique to this region. Besides human health, dust affects environmental health through nutrients that increase phytoplankton biomass, contaminants that diminish water supply and affect food (crops/fruits/vegetables and ready-to-eat meat), spread crop and marine pathogens, cause Valley fever among domestic and wild animals, transport heavy metals, radionuclides and microplastics, and reduce solar and wind power generation. Dust is also a safety hazard to road transportation and aviation, in the southwestern US where blowing dust is one of the deadliest weather hazards. To mitigate the harmful effects, coordinated regional and international efforts are needed to enhance dust observations and prediction capabilities, soil conservation measures, and Valley fever and other disease surveillance.
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Natural iron enrichment around the Antarctic Peninsula in the Southern Ocean
Article
Full-text available
  • Jan 2010
As part of the US-AMLR program in January-February of 2006, 99 stations in the South Shetland Islands-Antarctic Peninsula region were sampled to understand the variability in hydrographic and biological properties related to the abundance and distribution of krill in this area. Concentrations of dissolved iron (DFe) and total acid-leachable iron (TaLFe) were measured in the upper 150 m at 16 of these stations (both coastal and pelagic waters) to better resolve the factors limiting primary production in this area and in downstream waters of the Scotia Sea. The concentrations of DFe and TaLFe in the upper mixed layer (UML) were relatively high in Weddell Sea Shelf Waters (~0.6 nM and 15 nM, respectively) and low in Drake Passage waters (~0.2 nM and 0.9 nM, respectively). In the Bransfield Strait, representing a mixture of waters from the Weddell Sea and the Antarctic Circumpolar Current (ACC), concentrations of DFe were ~0.4 nM and of TaLFe ~1.7 nM. The highest concentrations of DFe and TaLFe in the UML were found at shallow coastal stations close to Livingston Island (~1.6 nM and 100 nM, respectively). The ratio of TaLFe:DFe varied with the distance to land: ~45 at the shallow coastal stations, ~15 in the high-salinity waters of Bransfield Strait, and ~4 in ACC waters. Concentrations of DFe increased slightly with depth in the water column, while that of TaLFe did not show any consistent trend with depth. Our Fe data are discussed in regard to the hydrography and water circulation patterns in the study area, and with the hypothesis that the relatively high rates of primary production in the central regions of the Scotia Sea are partially sustained by natural iron enrichment resulting from a northeasterly flow of iron-rich coastal waters originating in the South Shetland Islands-Antarctic Peninsula region.
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Sources and transport of dissolved iron and manganese along the continental margin of the Bay of Biscay
Article
  • Jan 2007
  • BG
Dissolved iron (DFe; <0.2µm) and dissolved manganese (DMn; <0.2µm) concentrations were determined in the water column of the Bay of Biscay (eastern North Atlantic Ocean) in March 2002. The samples were collected along a transect traversing from the European continental shelf over the continental slope. The highest DFe and DMn concentrations (2.39nM and 6.10 nM, respectively) were observed in the bottom waters on the shelf at stations closest to the coast. The release of trace metal from resuspended particles and the diffusion from pore waters were probably at the origin of elevated DFe and DMn concentrations in the Bottom Boundary Layer (BBL). In the slope region, the highest total dissolvable iron (TDFe), DFe and DMn values (24.6 nM, 1.58nM and 2.12nM, respectively) were observed close to the bottom at depth of ca. 600–700 m. Internal wave activity and slope circulation are thought to be at the origin of this phenomenon. These processes were also very likely the cause of elevated concentrations (DFe: 1.27 nM, DMn: 2.34 nM) measured in surface waters of stations located in the same area. At stations off the continental slope, the vertical distribution of both metals were typical of open ocean conditions, indicating that inputs from the continental margin did not impact the metal distributions in the offshore waters.
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A shipboard natural community continuous culture system for ecologically relevant low-level nutrient enrichment experiments: Shipboard chemostats
Article
Inputs of low concentrations of new and regenerated forms of nitrogen (≤1 µM) have large impacts on phytoplankton community structure and ocean biogeochemistry in the oligotrophic central gyres. However, current manipulative experimental methods cannot effectively simulate low‐level, continuous supplies of nitrate, such as those from upwelling or eddy events, or steady‐state inputs of regenerated ammonium and dissolved organic nitrogen from zooplankton grazing. Using a new shipboard continuous culture system based on laboratory chemostat methodology, we compared the effects of a continuous supply of 1 µM nitrate, ammonium, and urea‐N at a dilution rate of 0.5 d ⁻¹ on algal community composition in the North Atlantic. In the Gulf Stream, continuous inputs of 1 µM nitrate dramatically changed phytoplankton community structure from dominance by cyanobacteria to dominance by diatoms. Equimolar continuous supplies of ammonium resulted in much smaller increases in total phytoplankton biomass, and favored a community co‐dominated by diatoms and cyanobacteria, and promoted the growth of pelagophytes. In the Sargasso Sea, continuous 1 µM urea‐N inputs greatly increased the biomass and dominance of Synechococcus relative to the initial community and compared with control and 1 µM nitrate additions. The shipboard natural community continuous culture system is uniquely suited for realistically simulating inputs of low levels of limiting nutrients, allowing new types of prognostic enrichment experiments that give novel insights into the processes that control phytoplankton community structure in the ocean.
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Iron and macronutrients in California coastal upwelling regimes: Implications for diatom blooms
Article
  • Nov 2001
The supply of iron, relative to that of the macronutrients nitrate, phosphate, and silicic acid, plays a critical role in allowing extensive diatom blooms to develop in coastal upwelling regimes. The presence or absence of a broad continental shelf influences the supply of iron, The iron input to central California upwelling waters varies spatially and can be characterized by two end-member regimes. One end member, which includes Monterey Bay and extending north to Pt. Reyes, is an iron-replete regime where upwelling occurs over a relatively broad continental shelf that results in waters with high concentrations of dissolved and particulate iron (>10 nM) entrained together with high concentrations of nitrate and silicic acid. In these iron-replete regions, extensive blooms of large diatoms deplete macronutrient concentrations, which results in correspondingly high chlorophyll a concentrations. The other end member, located to the south of Monterey Bay off the Big Sur coast, is an iron-deplete regime where upwelling is focused offshore of a narrow continental shelf. Upwelled waters in the Big Sur region are characterized by low dissolved and particulate iron concentrations (<1 nM), together with high concentrations of nitrate and silicic acid. Extremely low iron concentrations, unused nitrate and silicic acid, and a low abundance of large diatoms characterize surface waters in these iron-deplete regions, and thus represent coastal upwelling, high-nutrient, low-chlorophyll systems limited by the micronutrient iron.
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Modeling regional responses by marine pelagic ecosystems to global climate change
Article
  • Aug 2002
Current coupled ocean-atmosphere model (COAM) projections of future oceanic anthropogenic carbon uptake suggest reduced rates due to surface warming, enhanced stratification, and slowed thermohaline overturning. Such models rely on simple, bulk biogeochemical parameterisations, whereas recent ocean observations indicate that floristic shifts may be induced by climate variability, are widespread, complex, and directly impact biogeochemical cycles. We present a strategy to incorporate ecosystem function in COAM's and to evaluate the results in relation to region-specific ecosystem dynamics and interannual variability using a template of oceanic biogeographical provinces. Illustrative simulations for nitrogen fixers with an off- line multi-species, functional group model suggest significant changes by the end of this century in ecosystem structure, with some of the largest regional impacts caused by shifts in the areal extent of biomes.
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