Video
Iron in the Southern Ocean Ballast has been widely Iron in marine applications recently by various marine marinne energy installations. In particular, applicatiions Iron in marine applications and floating wind turbine technologies require high-quality Hypoglycemic unawareness awareness month systems applicatipns restrict their movements, and Iroj installation and maintenance easier. Cast iron ballast responds to all these requirements and can be easily implemented into different designs with various functions. Gravity-based structures are a quite common type of tidal turbine foundation, kept in place by the additional ballast. When these foundations are made of concrete, a massive supporting structure is needed leading to high material and logistic cost.Iron in marine applications -
The inclusion of spatially varying ligand classes with different binding strengths in the model is important to explain the observed dFe pattern. We also identify the relative roles of different external dFe sources in different ocean basins. While the atmospheric deposition is an important source of dFe in the Atlantic and Indian Oceans, sedimentary and hydrothermal dFe inputs are more important in the Pacific Ocean.
In the third part of the work, we apply an unsupervised classification technique to analyze the dFe budget and the dFe distribution field simulated in different ocean Fe models. We suggest that the upper ocean dFe patterns are modulated by interior ocean processes and that without an appropriate representation of these processes, Fe models cannot reproduce observations, even with a correct magnitude of the external fluxes.
Our analysis also emphasizes a much more complex picture of the ocean Fe cycling than that of other nutrients such as phosphorus P and nitrogen N. In the last part, we incorporate our improved Fe scheme into an ocean ecosystem model to investigate the response of the Indian Ocean ecosystem to an increasing atmospheric deposition of Fe.
We found that while the diatom growth and export carbon flux are enhanced in the south of 40ͦS, they decrease in some regions in the northern Indian Ocean, compensated by increases in the coccolithophores growth and carbonate carbon flux.
These changes lead to a decrease in the carbon dioxide uptake over the Indian Ocean. Georgia Institute of Technology North Avenue, Atlanta, GA You are here: GT Home Home.
Understanding ocean iron dynamics and impacts on marine ecosystems. Dissertation Defense. Friday, October 18, - pm.
Taka Ito advisor , Dr. In the context of increasing global social—political—economic concerns associated with rapid climate change, it is necessary to examine the validity and usefulness of aOIF experimentation as a climate change mitigation strategy.
Furthermore, aOIF experiments have provided insights into the structure and function of pelagic ecosystems that cannot be acquired from observational cruises alone. Non-OIF observations provide an assortment of snapshots from which only an incomplete image of the processes involved can be rendered, while OIF experiments provide time-ordered focused frames allowing one to directly follow changes triggered by addition of an important limiting nutrient i.
That being said, it is necessary to plan and carry out the next aOIF experiments within the framework of international law. Therefore, the purpose of this paper is to 1 provide a thorough overview of the aOIF experiments conducted over the last 25 years; 2 discuss aOIF-related important unanswered questions, including carbon export measurement methods, potential side effects, and international law; 3 suggest considerations for the design of future aOIF experiments to maximize the effectiveness of the technique and begin to answer open questions; and 4 introduce design guidelines for a future Korean Iron Fertilization Experiment in the Southern Ocean KIFES.
Table 2 Summary of artificial ocean iron fertilization aOIF experiments: objectives, significant results, and limitations. A total of 13 aOIF experiments have been conducted in the following areas: 12 experiments were conducted in the three main HNLC i.
One experiment was conducted in the subtropical NA, known to be a low-nutrient and low-chlorophyll LNLC i.
These aOIF experiments have been conducted with various objectives and multiple hypotheses to investigate the biogeochemical responses of ocean environments to artificial iron additions Table 2. This overview of past aOIF experimentation begins in Sect.
The unique ocean conditions for the various experiments are described in Sect. Iron addition and tracing methods are described in Sect. The biogeochemical responses to the aOIF experiments are presented in Sect. Initially, Martin's hypothesis was supported by the results of laboratory and shipboard iron-enrichment bottle experiments Hudson and Morel, ; Brand, ; Sunda et al.
However, the extrapolation of these results based on bottle incubations that exclude higher trophic levels has been strongly criticized due to possible underestimates in grazing rates and other bottle effects.
To deal with these issues, in situ iron fertilization experiments at the whole-ecosystem level are required. Under the hypothesis that aOIF would increase phytoplankton productivity by relieving iron limitations on phytoplankton in HNLC regions, the first aOIF experiment, the iron enrichment experiment IronEx-1 , was conducted over 10 days in October in the EP where high light intensity and temperatures would promote rapid phytoplankton growth Table 1 and Fig.
However, the magnitude of the biogeochemical responses in IronEx-1 was not as large as expected Martin et al. Four hypotheses were advanced to explain the weak responses observed: 1 the possibility of unforeseen micronutrient e.
To test the four hypotheses, a second aOIF experiment, IronEx-2, was conducted in May Coale et al. The IronEx-2 research cruise investigated the same area for a longer period 17 days , providing more time to collect information about the biogeochemical, physiological, and ecological responses to the aOIF.
The SO plays an important role in intermediate and deep-water formation and has the greatest potential of any of the major ocean basins for carbon sequestration associated with artificial iron addition Martin, ; Sarmiento and Orr, ; Cooper et al. It is known as the largest HNLC region in the world ocean and models simulating aOIF have predicted that, among all HNLC regions, the effect of OIF on carbon sequestration is greatest in the SO Sarmiento and Orr, ; Aumont and Bopp, However, a simple extrapolation of the IronEx-2 results to the SO was not deemed appropriate because of the vastly different environmental conditions Coale et al.
To test the roles of iron and light availability as key factors controlling phytoplankton dynamics, community structure, and grazing in the SO, the Southern Ocean Iron Release Experiment SOIREE Table 1 and Fig.
The following year, a second aOIF experiment in the SO, EisenEx Eisen means iron in German , was performed in November within an Antarctic Circumpolar Current eddy in the Atlantic sector Smetacek, ; Gervais et al.
This region is considered to have a relatively high iron supply, which is supported by dust inputs and possibly icebergs de Baar et al. EisenEx was designed to test how atmospheric dust, an important source of iron in ocean environments, might have led to a dramatic increase in ocean productivity during the LGM due to the relief of iron-limiting conditions for phytoplankton growth Smetacek, ; Abelmann et al.
In addition to iron availability, the supply of silicate is also considered to be an important factor controlling PP in the SO.
Therefore, to address the impact of iron and silicate on phytoplankton communities and export, two aOIF experiments were conducted during January—February in two distinct regions: the Southern Ocean iron experiment north SOFeX-N and south SOFeX-S of the PF Table 1 Coale et al.
Two years later, the Surface Ocean—Lower Atmosphere Study SOLAS Air—Sea Gas Exchange SAGE experiment was conducted during March—April 15 days in sub-Antarctic waters, which are typically HNLC with low silicate concentrations HNLCLSi.
The aim was to determine the response of phytoplankton dynamics to iron addition in an HNLCLSi region Fig. SAGE was designed with the assumption that the response of phytoplankton blooms to aOIF could be detected by enhanced air—sea exchanges of climate-relevant gases e.
These early aOIF experiments resulted in clear increases in phytoplankton biomass and PP, but the impact on export production i. To determine if aOIF could increase export production, EIFEX was carried out in the closed core of a cyclonic eddy near the PF during the austral summer of Fig.
Of similar duration, the Indo-German iron fertilization experiment LOHAFEX; Loha means iron in Hindi was conducted during January—March 40 days , also in a PF cyclonic eddy in HNLCLSi waters Smetacek and Naqvi, ; Martin et al.
Figure 5 Photographs of the iron addition procedure a—f taken during the European Iron Fertilization Experiment EIFEX , Surface Ocean—Lower Atmosphere Study SOLAS Air—Sea Gas Exchange SAGE , and Indo-German iron fertilization experiment LOHAFEX. a Iron II sulfate bags. b The funnel used to pour iron and hydrochloric acid.
c Tank system used for mixing iron II sulfate, hydrochloric acid, and seawater Smetacek, e Outlet pipe connected to the tank system. f Pumping iron into the prop wash during EIFEX Smetacek, The subarctic NP shows a strong longitudinal gradient in aeolian dust deposition i.
In , the experiment was repeated SEEDS-2 in almost the same location and season. In the intervening year, the Subarctic Ecosystem Response to Iron Enrichment Study SERIES was performed in July—August 25 days in the Gulf of Alaska representing the eastern subarctic gyre ecosystem to compare the response of phytoplankton in this area with that in the western subarctic Boyd et al.
The SEEDS-1 and 2 experiments focused on changes in phytoplankton composition, vertical carbon flux, and climate-relevant gas production stimulated by artificial iron addition Tsuda et al.
The main objective of SEEDS-2 and SERIES was to determine the most significant factor i. Table 3 Initial conditions and changes Δ values in chemical parameters during the artificial ocean iron fertilization aOIF experiments.
b Δ PO 4 3 - in EIFEX was digitized from Fig. c Δ PO 4 3 - in LOHAFEX was digitized from Fig. d Δ p CO 2 in LOHAFEX was digitized from Fig. Download Print Version Download XLSX.
Table 4 Initial values of biological parameters and the values after fertilization. Note that maximum values were attained after fertilization. c PP in IronEx-2 was digitized from the Fig. d Mesozooplankton biomass in IronEx-2 was digitized from the Fig. e PP in SOIREE was digitized from the Fig.
f Mesozooplankton biomass indicates copepod biomass; values in brackets correspond to the sampling layer; after mesozooplankton biomass is the mean value averaged for the experimental period after iron addition.
g Chlorophyll a concentrations in SOFeX-N and SOFeX-S were digitized from the Supplement Fig. h PP values in SOFeX-N and SOFeX-S were digitized from the Fig. Sources are Kolber et al. Unlike HNLC regions, PP in LNLC regions, which are predominantly occupied by N 2 fixers, is generally co-limited by phosphate and iron Mills et al.
To investigate the impact of iron and phosphate co-limitation on PP, the in situ phosphate and iron addition experiment FeeP was conducted by adding both phosphate and iron in a LNLC region of the subtropical NA during April—May 21 days Rees et al.
The location of the subtropical NA experiment corresponded to a typical LNLC region Fig. The FeeP experiment reported that picoplankton 0. This experiment will, therefore, not be discussed further.
Figure 6 a Maximum bar with dotted line and initial bar with solid line patch size km 2 during artificial ocean iron fertilization aOIF experiments.
b First target iron concentrations nM. c Maximum bar with dotted line and minimum bar with solid line mixed layer depth MLD, m during aOIF experiments. e Initial nitrate concentrations µM. f Initial silicate concentrations µM. Note that the numbers on the x axis indicate the order of aOIF experiments as given in Fig.
Below we consider the similarities and differences in these environments according to the physical and biogeochemical properties of the sites Coale et al.
The first two aOIF experiments, IronEx-1 and IronEx-2, which were both conducted in the EP, were performed in different seasons i. However, the initial surface physical conditions were similar, with warm temperatures The initial surface biogeochemical conditions were high nutrients i.
The picophytoplankton community, including Synechococcus and Prochlorococcus , was dominant Martin et al. Initial surface nutrient concentrations were relatively low compared with other ocean basin aOIF sites Table 3 and Fig.
Initial photosynthetic quantum efficiency i. In the EP, initial surface partial pressure of CO 2 p CO 2 values were The initial physical conditions for the aOIF experiments in the SO SOIREE, EisenEx, SOFeX-N, SOFeX-S, EIFEX, SAGE, and LOHAFEX were very different from those found in the EP; MLDs were much deeper During SOFeX-N and SOFeX-S, which were conducted along the same line of longitude, on either side of the PF, there were distinct differences in SST: 5.
SAGE was the northernmost of the aOIF experiments in the SO Table 1 and, therefore, had the highest SST The locations for the aOIF experiments were selected following preliminary surveys to confirm the HNLC conditions, i.
Initial nitrate concentrations ranged from 7. Among the various aOIF HNLC experiment sites, the SO had the highest initial nitrate concentrations With the specific intent of investigating the co-limitation of iron and silicate, SOFeX-N, SAGE, and LOHAFEX were all conducted in HNLCLSi regions, with initial silicate concentrations less than 2.
Initial p CO 2 values were low in the SO The maximum initial chlorophyll concentrations occurred in EIFEX, which started with a community dominated by diatoms Hoffmann et al.
The subarctic NP aOIF experiments i. Compared with the other aOIF experiments, these subarctic experiments had much higher initial silicate concentrations Although SEEDS-1 and SEEDS-2 were conducted in almost the same location and season in the western basin Tsuda et al.
Unlike the latitudinal gradients seen in the aOIF experiments in the SO, there were longitudinal gradients in physical and biogeochemical properties in the subarctic NP experiments Tables 3, 4, Figs. Initial SSTs in the subarctic NP were lower in the western region 7.
Initial nutrient concentrations were much higher in the west nitrate: There was also a longitudinal gradient in chlorophyll a concentrations, with relatively high values in the west SEEDS 0.
Iron sulfate is a common inexpensive agricultural fertilizer that is relatively soluble in acidified seawater Coale et al. Therefore, all aOIF experiments have been conducted by releasing commercial iron sulfate dissolved in acidified seawater into the propeller wash of a moving ship Fig.
Iron-enrichment bottle incubation experiments performed in deck incubators using in situ seawater have indicated the maximum phytoplankton growth rates in response to iron additions of 1.
These processes occur more rapidly in warmer waters ACE CRC, For example, the first aOIF experiment, IronEx-1, showed that the dissolved iron concentration rapidly decreased from 3.
As a result, except for the single iron addition experiments of IronEx-1, SEEDS-1, and FeeP Martin et al. These experiments included two additions EIFEX, SERIES, SEEDS-2, and LOHAFEX Boyd et al.
To trace the iron-fertilized patch, aOIF experiments have used a combination of physical and biogeochemical approaches. All the aOIF experiments except EIFEX have used sulfur hexafluoride SF 6 as a chemical tracer Table 1 Martin et al. The SF 6 , which is not naturally found in oceanic waters, is a useful tracer for investigating physical mixing and advection—diffusion processes in the ocean environment due to its nontoxicity, biogeochemically inert characteristics, and low detection limit Law et al.
The injected SF 6 is continuously monitored using gas chromatography with an electron capture detector system Law et al. Furthermore, caution is required because artificially high levels of SF 6 injection may negatively impact the interpretation of low-level SF 6 signals dissolved in seawater via air—sea exchange to estimate tracer-based water mass ages for understanding physical circulation Fine, These techniques have been widely used to estimate anthropogenic carbon invasion as well as to understand ocean circulation in various ocean environments, with SF 6 being an important time-dependent tracer that has a well-recorded atmospheric history.
In addition, surface-drifting buoys equipped with Argos or GPS systems have been successfully used to track the movement of fertilized patches along with biogeochemical tracers Coale et al. However, floats tend to drift out of the fertilized patches under strong wind forcing Watson et al.
NASA airborne oceanographic lidar and ocean-color satellites have also been employed to assess the large-scale effects of iron addition on surface chlorophyll in fertilized patches, as compared to surrounding regions Martin et al.
Table 5 Initial values of the export flux and the values after fertilization mg C m - 2 day - 1 , the corresponding depth inside and outside the fertilized patch for artificial ocean iron fertilization aOIF experiments, and measurement method.
Values in brackets correspond to the day of measurement after fertilization. a Export flux in EIFEX was digitized from the Supplement Fig.
b Export flux in LOHAFEX was digitized from the Fig. c Export flux in LOHAFEX was digitized from the Fig. d Export flux in SEEDS-1 was determined from the suspended particles. e Export flux in SERIES was digitized from the Fig. Sources are Bidigare et al. The results are important, as they have been used as a basis to determine whether the aOIF is effective.
Here we address the biogeochemical response in each of the ocean basins to the aOIF experiments to date. The numbers on the x axis indicate the order of aOIF experiments as given in Fig.
The IronEx-1 and 2 experiments, which were conducted in similar initial conditions refer to Sect. On the other hand, IronEx-2 found dramatic changes in biogeochemical responses, providing support for Martin's hypothesis Coale et al.
Unexpected small responses during IronEx-1 were due to subduction of the fertilized surface layer by adjacent water Coale et al. The contrasting results from the two experiments are also likely to be associated with whether or not there were additional iron injections IronEx no extra addition; IronEx two additional injections and different experiment durations IronEx 10 days; IronEx 17 days.
During IronEx-1, chlorophyll a concentrations increased significantly 3-fold , reaching a maximum value of 0. To quantify the changes in carbon fixation following iron addition, the depth-integrated PP from the surface to the critical depth, euphotic depth, or MLD was estimated in the iron-fertilized patches.
The depth-integrated PP values increased significantly compared to the initial values. As the bloom developed, a significant nitrate uptake e. The depletion of macronutrients in fertilized patches provides indirect evidence that phytoplankton growth in surface waters was driven by aOIF Boyd and Law, Although no phytoplankton community change was observed in IronEx-1, after iron addition in IronEx-2 a shift from a picophytoplankton-dominated community to a microphytoplankton-dominated community was observed, resulting in a diatom-dominated bloom Behrenfeld et al.
Diatom biomass increased nearly 70 -fold over 8 days early in the experiment, compared to a less than a 2-fold increase for the picophytoplankton Landry et al.
However, grazing did not prevent the development of a diatom bloom over 8 days early in the IronEx-2 experiment Table 4 Coale et al.
The decline was probably associated with the combined effects of both the elevated grazing pressure and the onset of nutrient depletion i. To determine whether the biological pump i. The Th radionuclide has a strong affinity for particles, and the extent of Th removal in the water column is indicative of the export of POC associated with surface PP out of the ML Buesseler, However, no Th measurements were made in the unfertilized patch for comparison, and no measurements in the deep ocean were undertaken to demonstrate deep carbon export Bidigare et al.
Satellite observations were used to investigate the changing spatial and temporal distribution of chlorophyll a concentration in response to iron fertilization in the fertilized patches compared to the surrounding waters; for example, SOFeX-N and SOFeX-S found elevated chlorophyll a concentrations in fertilized patches after iron addition through satellite images Fig.
During SOIREE, EisenEx, SOFeX-N, and SOFeX-S, PP increased continuously throughout the duration of the experiments Boyd et al. The decrease was due to various processes such as export e. Using both microscopes and high-performance liquid chromatography pigment analysis, changes in the phytoplankton community affected by iron addition have also been investigated.
Most SO aOIF experiments have resulted in blooms of diatoms Boyd et al. During SOIREE and EisenEx, the dominant phytoplankton community shifted from pico- and nanophytoplankton e.
In SOFeX-S and EIFEX, diatoms were already the most abundant group prior to iron addition Coale et al. Although SOFeX-N was conducted under low silicate conditions Fig. This result was partly influenced by the temporary relief of silicate limitation through lateral mixing of the iron-fertilized waters with surrounding waters, with relatively higher silicate concentrations Coale et al.
Iron-mediated increases in PP resulted in a significant uptake in macronutrients and p CO 2 throughout the aOIF experiments in the SO except for SAGE Table 3, Fig.
During EIFEX, the ratio of heavily silicified diatoms e. These contrasting results were thought to be the result of entrainment through vertical and horizontal physical mixing into the iron-fertilized patch of surrounding waters with higher nutrient and p CO 2 concentrations Currie et al.
SOIREE was the first aOIF experiment in the SO to estimate the downward carbon flux into deep waters Fig. A comprehensive suite of methods was used: drifting traps, Th and the stable carbon isotope of particulate organic matter δ 13 C org estimates derived from high-volume pump sampling, and a beam transmissometer Nodder and Waite, However, no measurable change in carbon export was observed in response to iron-stimulated PP Table 5 and Fig.
During EisenEx, an increased downward carbon flux estimated from Th deficiency was observed in the iron-fertilized patch as the experiment progressed. However, there were no clear differences between in- and outside-patch carbon fluxes Buesseler et al.
During SOFeX-S, significantly enhanced POC fluxes below the MLD, similar to those observed in natural blooms, were estimated from Th measurements after iron enrichment Buesseler et al. However, it was unclear whether surface-fixed carbon was well and truly delivered below the winter MLD.
During SAGE and LOHAFEX, which were conducted under silicate-limited conditions Table 3, Figs. This result was likely due to the dominance of picoplankton and grazing that led to rapid recycling of organic matter in the ML. This value remained constant for about 24 days after iron addition. Significant changes in export production were not found in any of the other aOIF experiments and, therefore, the impact of artificial iron addition on diatom aggregate formation needs focused study in future aOIF experiments Boyd et al.
Increases in chlorophyll a concentrations were detected in the subarctic NP aOIF experiments in both basins after about the fifth day Tsuda et al.
These increases were especially apparent in SEEDS-1, where they reached a maximum value of This augmentation was the largest among all the aOIF experiments Tsuda et al. The dramatic surface chlorophyll a increase observed during SEEDS-1 was partly attributed to the particular range of seawater temperature in the region, which was conducive to diatom growth i.
During SERIES, chlorophyll a concentrations increased substantially from the initial value of 0. Although SEEDS-2 was conducted under similar initial conditions to SEEDS-1 refer to Sect.
This smaller increase was thought to be the result of strong copepod grazing SEEDS-2 had almost 5 times more copepod biomass than SEEDS-1 Table 4 Tsuda et al.
A similar range was seen in depth-integrated PP, which increased 3-fold or more after iron addition in the subarctic NP aOIF experiments e. Changes in the composition of phytoplankton groups were investigated in the subarctic NP aOIF experiments.
In SEEDS-1 there was a shift from oceanic diatoms e. The effect on the biological pump can be quite different depending on the species of diatom stimulated by the aOIF. Chaetoceros debilis , known to be widespread in coastal environments, intensifies the biological pump by forming resting spores in contrast to grazer-protected, thickly silicified oceanic species e.
and Thalassiothrix sp. that contribute silica but little carbon to the sediments. The shift in the dominant phytoplankton species during SEEDS-1 was an important contributor to the recorded increase in phytoplankton biomass. During SERIES, the phytoplankton community changed from Synechococcus and haptophytes to diatoms, and the highest SERIES chlorophyll a concentration day 17 was associated with a peak in diatom abundance Boyd et al.
However, during SEEDS-2, no significant iron-induced diatom bloom was observed. Instead, pico- and nanophytoplankton e.
In the subarctic NP experiments, significant changes in macronutrient uptake i. During SEEDS-2, the nitrate concentration decreased remarkably from Despite the formation of a massive iron-induced phytoplankton bloom during SEEDS-1, there was no large POC export flux during the observation period Table 5 Tsuda et al.
During SERIES and SEEDS-2, which allowed comprehensive time-series measurements of the development and decline of the iron-stimulated bloom, POC fluxes estimated by the drifting traps in the fertilized patch displayed temporal variations Boyd et al.
The results suggested that, subsequently, the drifting trap captured only a small part of the decrease in ML POC and POC flux losses were mainly governed by bacterial remineralization and mesozooplankton grazing Boyd et al. Each aOIF experiment has provided new results on basic processes pertaining to the relationship between pelagic ecology and biogeochemistry, such as selection of the dominant phytoplankton group or species; the effects of grazing; interactions within the plankton community; and effects of nutrient concentrations on the growth of phytoplankton.
The aOIF experiments have generally led to changes in the size of the phytoplankton community from pico- and nanophytoplankton to microphytoplankton.
This effect was particularly noticeable as diatoms became the dominant species during IronEx-2, SOIREE, EisenEx, SEEDS-1, SOFeX-S, EIFEX, and SERIES.
The shift to a diatom-dominated community appears to be related to initial availability of silicate i. As a consequence, pico- and nanophytoplankton dominated their communities and diatom growth was limited by the lack of available silicate. These results suggest that, to develop large-phytoplankton blooms, changeover to a diatom-dominated community after iron addition is needed.
A necessary, but not sufficient, condition for such a change to occur is the availability of silicate. Silicate alone is not expected to be sufficient because diatom-dominated blooms were not observed in all experiments with high initial silicate concentrations. Taken together, the aOIF results suggest that both mesozooplankton grazing rates and initial silicate concentrations play a role in limiting the stimulation of diatom-dominated blooms after artificial iron enrichment.
However, influence of iron addition on the phytoplankton growth extends from surface to euphotic depth as added iron is mixed within the ML by physical processes Coale et al. Therefore, to quantify the exact changes in phytoplankton biomass in response to iron addition, it would be appropriate to consider the MLD-integrated PP for comparison.
However, changes in the carbon export varied substantially and differed from experiment to experiment. In SEEDS-1 and SOIREE there was little increase in export flux. These two experiments were conducted over only about 2 weeks. The short duration of these experiments could have prevented the detection of downward carbon export.
However, the changes in export flux, after iron addition, were not dramatic compared to natural values Buesseler et al. This high flux was due to aggregate formation with fast sinking rates Smetacek et al. EIFEX observed an entire cycle i. It should also be noted that the rates of bacterial remineralization and grazing pressure on the diatoms were in the same range inside the fertilized patch as outside, which might have assisted the delivery of iron-induced POC from the ML to deep layers Smetacek et al.
These results suggest that to detect significant carbon exported below the winter MLD following an increase in PP, at least three conditions are necessary: 1 a shift to a diatom-dominated community; 2 low bacterial respiration and grazing pressure rates within the ML; and 3 a sufficient experimental duration, enabling both immediate and delayed responses to iron addition to be observed.
OIF has been proposed as a potential technique for rapidly and efficiently reducing atmospheric CO 2 levels at a relatively low cost Buesseler and Boyd, , but there is still much debate. Over the past 25 years, controlled aOIF experiments have shown that substantial increases in phytoplankton biomass can be stimulated in HNLC regions through iron addition, resulting in the drawdown of DIC and macronutrients de Baar et al.
However, the impact on the net transfer of CO 2 from the atmosphere to below the winter MLD through the biological pump Fig. There have also been a wide range of the estimates of atmospheric CO 2 drawdown resulting from large-scale and long-term aOIF based on model simulations Joos et al.
While it is generally agreed that OIF effectiveness needs to be determined through quantification of export fluxes, there has been no discussion about which export flux measurement techniques are the most effective.
Meanwhile, concern has been expressed regarding possible environmental side effects in response to iron addition Fuhrman and Capone, These side effects include the production of greenhouse gases e. These unwanted side effects could lead to negative climate and ecosystem changes Fuhrman and Capone, ; Sarmiento and Orr, ; Jin and Gruber, ; Schiermeier, ; Oschlies et al.
Model studies suggested that the unintended ecological and biogeochemical consequences in response to large-scale aOIF might cancel out the effectiveness of aOIF. Core unanswered questions remain concerning the different carbon export flux results from different measurement techniques Nodder and Waite, ; Aono et al.
With the design of future aOIF experiments in mind, the following section discusses these core questions: 1 which of the methods are optimal for tracking and quantifying carbon export flux, 2 which of the possible side effects have negative impacts on aOIF effectiveness, and 3 what are the international aOIF experimentation laws and can they be ignored?
A traditional, direct method for estimating POC export fluxes in the water column is a sediment trap that collects sinking particles Suess, Sediment traps are generally deployed at specific depths for days to years to produce estimates of total dried mass, POC, particulate inorganic carbon PIC , particulate organic nitrogen PON , particulate biogenic silica, δ 13 C org , and Th.
A basic assumption for the use of a sediment trap is that it exclusively collects settling particles, resulting from the gravitational sinking of organic matter produced in surface waters.
However, although they are designed to ensure the well-defined collection and conservation of sinking particles, they have accuracy issues due to 1 interference of the hydrodynamic flow across the trap i.
The application of sediment traps for the determination of the carbon export flux is relatively more biased in the ML where ocean currents are generally faster and zooplankton are much more active than deep water. These issues suggest that sediment traps alone may not accurately determine carbon export fluxes within the ML.
Even when used at the same depth, traditional sediment traps, such as the surface-tethered drifting trap and bottom-moored trap, can greatly over- or underestimate particulate Th fluxes compared to water-column-based estimates Buesseler, The water-column-based total Th deficiency method the sum of dissolved and particulate activities is less sensitive than sediment traps to the issues mentioned above and provides better spatial and temporal resolution in flux estimates Buesseler, For these reasons, traditional sediment trap POC flux estimates have often been calibrated using the total Th deficiency measured using rosette bottle or high-volume pump samples Coale and Bruland, ; Buesseler et al.
However, the water-column-based Th method is sensitive to the characterization of the POC to Th ratio on sinking particles and the choice of Th flux models Buesseler et al. Therefore, sampling to estimate the POC to Th ratio should be conducted below MLD to accurately detect downward carbon export flux into intermediate—deep waters.
Several aOIF experiments have used both sediment traps and Th deficiency to estimate the iron-induced POC export flux Table 5.
While there was no measurable change in Th -based POC fluxes during the 13 days of the SOIREE experiment Fig. It was later discovered that the sediment-trap-based sampling biases caused this supposed increase Nodder et al.
This large discrepancy between the two methods might be caused by the under-sampling of POC into the drifting traps Aono et al. To resolve the potential biases in traditional sediment traps, a neutrally buoyant and freely drifting sediment trap NBST was developed Valdes and Price, ; Valdes and Buesseler, Through preliminary experiments conducted in June and October at the Bermuda Atlantic Time-series Study site, Buesseler et al.
However, the PELAGRA sediment traps did not detect aOIF-induced carbon export even though PP did increase within the ML. It should be noted that both sediment traps and water-column-based Th measurements have a limited ability to fully scan the vertical profile of POC fluxes and, therefore, these methods should ideally be complemented with additional techniques that can measure particle stocks at high depth resolution throughout the water column.
Through an analysis of particle size distributions, the UVP also allowed particles to be classified into fecal pellets, aggregates, and live zooplankton.
Interestingly, large particles i. Improving on this method, SOFeX-N applied autonomous carbon explorers equipped with transmissometers, designed to float along with the currents. Three autonomous carbon explorers were deployed, two explored the iron-fertilized patch and one acted as a control outside the patch.
Carbon explorers could continuously monitor carbon flux in the field for up to 18 months beyond the initial deployment, which allowed SOFeX-N to observe episodic raining in the iron-fertilized waters Bishop et al.
Furthermore, recent studies also reported that use of optical spike signals in particulate backscattering and fluorescence, measured from autonomous platforms such as gliders and floats, can provide high-resolution observations of POC flux Briggs et al.
The combination of multiple approaches is essential to the successful detection of POC produced in response to iron addition and its fate. NBST systems e. This technique is improved when accompanied by calibration using water-column-based Th. Particle profiling systems e.
They are therefore useful for indirectly identifying deep carbon transport. Autonomous carbon explorers are an excellent alternative, allowing for continuous observation of POC fluxes during and after an aOIF experiment.
The purpose of aOIF is to reduce the atmospheric CO 2 level by stimulating the sequestration of oceanic carbon through artificial iron additions in the HNLC regions, mitigating the global warming threat. Beyond the benefits of aOIF experimentation, scientists have debated the unintended secondary consequences of aOIF, such as production of climate-relevant gases and ocean ecosystem changes.
Therefore, it is important to consider the possible negative consequences of aOIF to evaluate whether the aOIF experiments are effective i. However, CH 4 has been considered to be relatively low risk because most of the CH 4 formed in the ocean is used as an energy source for microorganisms and is converted to CO 2 before reaching the sea surface Smetacek and Naqvi, ; Williamson et al.
The SO nOIF experiment conducted in year i. During the SOFeX-N experiment, measurements of dissolved CH 4 indicated concentrations were slightly elevated, i.
Hence, additional CH 4 production from aOIF experiments is not likely to be significant. The ocean is already a significant source of atmospheric N 2 O Nevison et al.
Oceanic N 2 O is mainly produced by bacterial remineralization. Therefore, increases in N 2 O production after iron additions are expected and, in the long run, contribute to an increase rather than a decrease in the greenhouse effect Fuhrman and Capone, However, the SO nOIF experiment i.
Excess N 2 O was not found after iron addition in EIFEX, where significant vertical export through the formation of rapidly sinking aggregates was found Walter et al. Based on the results of previous studies, no consensus has yet been reached on the exact extent of additional N 2 O production after iron additions.
However, because there is the potential for excessive N 2 O production that would not only impact the effectiveness of aOIF experiments but also positively contribute to global warming, further studies are required to reach a conclusion.
Unlike N 2 O emissions, which have the potential to offset the effectiveness of aOIF, DMS, a potential precursor of sulfate aerosols that cause cloud formation, may contribute to the homeostasis of the Earth's climate by countering the warming due to increased CO 2 emissions Charlson et al.
DMS is produced by the enzymatic cleavage of planktonic dimethylsulfoniopropionate DMSP. Microzooplankton grazing on nanophytoplankton e. The production of DMS in response to iron addition was measured during all aOIF experiments.
In the EP and SO, DMS production increased, but, in the subarctic NP, it remained constant or decreased Boyd et al. There were significant short-term increases in DMS production in IronEx-2 from 2.
The maximum DMS production observed was a 6. During the SOIREE experiment, the initial dominant phytoplankton species were haptophytes and they remained dominant until day 7.
Since then, DMS production was increased by microzooplankton grazing on DMSP-rich haptophyte groups e. Similarly, a 4. On the other hand, the SO nOIF experiment KEOPS-1 conducted in year Table 1 and Fig. In addition, a year aOIF simulation through a three-dimensional ocean biogeochemical model did not show significant increase in DMS emissions from the SO Bopp et al.
Interestingly, there were no significant changes in DMS production after iron additions in the western subarctic NP SEEDS-1 and 2 experiments, despite increases in PP Takeda and Tsuda, ; Nagao et al. Furthermore, in the eastern subarctic NP, SERIES DMS production increased from 8.
It is therefore difficult to predict the iron-induced DMS response, because OIF itself is not the only source of DMS. Based on the results of previous aOIF experiments, DMS production was sensitive in the EP and SO, but was less sensitive in the subarctic NP Law, These results indicate that further process and modeling studies for each region are required to determine the production and degradation of DMS, both following iron fertilization and in the natural environment.
HVOCs, such as CH 3 Cl , CH 3 Br , and CH 3 I , are well known for their ability to destroy ozone in the lower stratosphere and marine boundary layer Solomon et al. However, no consistent results have been reported for HVOCs production Liss et al.
Such a complicated response suggests that, as for DMS, further study is needed to fully understand natural cycling of HVOCs and their responses to aOIF. Another important consideration is the extent to which the effectiveness of aOIF is canceled out by its tendency to lead to ocean ecosystem changes such as a decrease in dissolved oxygen and an increase in domoic acid DA levels.
The decomposition of iron-addition-enhanced biomass may cause decreased oxygen concentrations in subsurface waters, but midwater oxygen depletion has not been reported from aOIF experiments to date Williamson et al. Keller et al. Clearly, the circumstances under which a substantial decline in oxygen inventory can be caused by large-scale aOIF need further study.
The changes in phytoplankton community composition after iron addition discussed in Sect. For example, such changes could lead to potentially toxic species dominating plankton assemblages Silver et al.
Some aOIF experiments e. Some Pseudo-nitzschia species have the capacity to produce the neurotoxin DA that can detrimentally affect marine ecosystems. However, no DA was found during EisenEx and SERIES, even though Pseudo-nitzschia were dominant Gervais et al.
However, phytoplankton samples used to estimate DA production have sometimes been stored for a long time before the analysis, for example, 12 years in IronEx-2 and 4 years in SOFeX-S Silver et al.
Trick et al. Nevertheless, discernable changes in DA production were found in IronEx-2 and SOFeX-S experiments Silver et al. However, large uncertainties remain as Trick et al.
Here again, existing research indicates that the processes involved need to be better understood in the natural environment before the ramifications of aOIF can be fully understood.
Whether aOIF is a viable carbon removal strategy is still under debate Boyd et al. The production of climate-relevant gases such as N 2 O , DMS, and HVOCs, which is influenced by the remineralization of sinking particles that follows OIF-induced blooms; the decline in oxygen inventory; and the production of DA are particularly important to understand.
These processes can directly and indirectly modify the effectiveness of carbon sequestration, with either positive or negative effects. Therefore, monitoring declines in oxygen content and production of climate-relevant gases and DA to evaluate the effectiveness of aOIF as a geoengineering approach is essential.
The processes discussed here represent the current state of knowledge concerning aOIF side effects. The direct and indirect environmental consequences remain largely unresolved due to the inconsistent and highly uncertain outcomes of the experiments conducted so far, as well as our poor understanding of the processes involved under both nOIF and aOIF conditions Chisholm et al.
However, considering the increasing evidence for the necessity to keep warming at or below 1. Figure 9 Assessment framework for scientific research involving ocean fertilization OF modified from Resolution LC-LP. To prevent pollution of the sea from human activities, the international Convention on the Prevention of Marine Pollution by Dumping of Wastes and Other Matter London Convention, was amended in In , contracting parties to the London Convention adopted the Protocol to the London Convention London Protocol, In , several commercial companies e.
As discussed earlier, these small-scale experiments have left many unanswered scientific questions regarding both the effectiveness and the potential impacts of aOIF Lawrence, ; Buesseler and Boyd, This resolution prohibited ocean fertilization activities until such time that specific guidance could be developed to justify legitimate scientific research.
In the meantime, there was a call to develop an assessment framework for ocean fertilization experiments to assess, accurately, scientific research proposals Resolution LC-LP. This framework demands preliminary scientific research prior to any aOIF experimentation.
Monitoring is also required as an integral component of all approved i. intended geoengineering benefits ACE CRC, This means that large-scale i. Scientific aOIF research has focused on improving our understanding of the effectiveness, capacity, and risks of OIF as an atmospheric CO 2 removal strategy both in the future and the past in particular glacial periods.
Although the first aOIF experiments took place more than 20 years ago, the legal and economic aspects of such a strategy in terms of the international laws of the sea and carbon offset markets are not yet clear ACE CRC, Nonetheless, previous small-scale aOIF experiments have demonstrated a considerable potential for easily and effectively reducing atmospheric CO 2 levels.
Accordingly, physical—biogeochemical—ecological models and nOIF experiments long-term have been conducted in an effort to overcome some of the limitations of short-term aOIF experiments e. These results suggest that the amount of carbon sequestration resulting from aOIF represents only a modest offset, i.
The nOIF experiments have also produced much higher carbon sequestration rates than the small-scale aOIF experiments Morris and Charette, Furthermore, the results from nOIF experiments do not support the potential negative impacts proposed for OIF experiments, even at larger scales Belviso et al.
However, these nOIF results do not guarantee that aOIF as a geoengineering approach is able to achieve the high effectiveness associated with carbon sequestration and enables a simple scaling up as a prediction tool, because the nOIF experiments differ from the aOIF experiments in the mode of iron supply.
In particular, nOIF is a continuous and slow process and its iron source is based on the upwelling of iron-rich subsurface waters to the surface layer, whereas aOIF is intended to be episodic, with massive short-term iron additions Blain et al.
In addition, in nOIF it is difficult to accurately identify iron sources due to the complexity of the system, whereas in aOIF there is quantitative and qualitative information about iron additions and sources Blain et al.
Contrary to the results of aOIF experiments in the SO e. There is also a broad swath of hypotheses in the fields of pelagic ecology—biogeochemistry that can be tested with OIF experiments using the correlations between temperature, CO 2 concentrations, and dust over the past four glacial—interglacial cycles on the one hand and bottle experiments showing iron limitation of phytoplankton growth in HNLC regions on the other.
Therefore, it is important to continue undertaking small-scale studies to obtain a better understanding of natural processes in the SO as well as to assess the associated risks and so lay the groundwork for evaluating the potential effectiveness and impacts of large-scale aOIF as a geoengineering solution to anthropogenic climate change.
It is therefore of paramount importance that future aOIF experiments continue to focus on the effectiveness and capacity of aOIF as a means of reducing atmospheric CO 2 , but they should also carefully consider the location i.
They should build on the results of previous aOIF experiments to develop our understanding of the magnitude and sources of uncertainties and provide confidence in our ability to reproduce results.
The first consideration for a successful aOIF experiment is the location. The dominance of diatoms in phytoplankton communities plays a major role in increasing the biological pump because diatom species can sink rapidly as aggregates or by forming resting spores to efficiently bypass the intense grazing pressure of mesozooplankton e.
Previous aOIF experiments have shown that silicate concentration and mesozooplankton stocks i. Therefore, to obtain the greatest possible carbon export flux in response to iron addition, aOIF experiments should be designed in regions with high silicate concentrations and low grazing pressure. It will be important to conduct initial surveys to measure the degree of grazing pressure in HNLC regions with high silicate concentrations such as in the subarctic NP e.
In selecting sites for aOIF, it is also important to distinguish the iron-fertilized patch from the surrounding unfertilized waters to easily and efficiently observe iron-induced changes Coale et al.
Ocean eddies provide an excellent setting for aOIF experimentation because they tend to naturally isolate interior waters from the surrounding waters. Eddy centers tend to be subject to relatively slow current speeds, with low shear and high vertical coherence, providing ideal conditions for tracing the same water from the surface to below the winter MLD, while simultaneously minimizing lateral stirring and advection Smetacek et al.
Finding an appropriate eddy setting in a study area should be a high priority consideration when designing an aOIF experiment Smetacek and Naqvi, Mesoscale eddies can be reliably identified and tracked with satellite sea surface height anomalies Smetacek et al. The second consideration for a successful aOIF experiment is timing, which includes when an experiment starts.
PP in the SO, a representative HNLC region, is subject to co-limitation by micro- or macronutrients i. To the south of the SO PF, phytoplankton blooms usually occur during early summer i.
Weekly and monthly climatological maps of chlorophyll a concentrations derived from satellite data could provide the necessary information for determining the timing of blooms in the SO PF Westberry et al.
Prior to December, phytoplankton growth is mainly limited due to light availability Mitchell et al. The grazing pressure of mesozooplankton on large diatoms was also a major limiting factor in diatom production Schultes et al. Considering the key factors i.
Sources are Gall et al. How long. The third consideration for a successful aOIF experiment is the duration. Although the first 2 weeks have a decisive effect on the development and demise of the bloom, it has been suggested that most aOIF experiments did not cover the full response times from onset to termination Boyd et al.
For example, SOIREE and SEEDS-1 had relatively short observation periods 13 days and saw increasing trends in PP throughout the experiments Fig. This indicates that short experimental durations may not be sufficient for detecting the full influence of aOIF on PP and the ecosystem Figs.
SOFeX-S also resulted in relatively low export production despite the high PP due to the experimental duration being insufficient to cover the termination of the phytoplankton bloom.
However, SERIES, SEEDS-2, EIFEX, and LOHAFEX did fully monitor all phases of the phytoplankton bloom from onset to termination. EIFEX, the third-longest aOIF experiment, at 39 days, was the only one that observed iron-induced deep export production between day 28 and 32 Table 5 and Fig.
Furthermore, long-term observations covering the later stage of bloom development during nOIF experiments resulted in much higher C:Fe export efficiencies compared to the short-term aOIF Blain et al. Based on previous aOIF experiments, it would, therefore, be important to detect the full phase of a phytoplankton bloom to determine accurately the amount of iron-induced POC exported out of the winter ML.
The observation period is, therefore, an important consideration with regard to budget and effectiveness estimates. In addition, autonomous observation platforms are essential to monitor post-assessment of effectiveness, capacity, and risks of aOIF for at least 12 months after experiment termination.
First, the chemical form for iron addition should be acidified iron sulfate, which is less expensive and more bioavailable than other iron compounds. As a consequence of expansion and dilution, previous aOIF experiments also produced similar results to this model study.
Therefore, it would be more appropriate to fertilize a large area e. For example, in SOIREE it was found that four additions of iron at intervals of about 3 days led to persistently high levels of both dissolved and particulate iron within the ML, with a rapid reduction at the end of the experiment, combined with an increase in the concentration of iron-binding ligands Bowie et al.
In both EIFEX and SOFeX-S, it was also found that multiple iron II infusions in particular, two infusions with intervals of 13 days in EIFEX and four infusions with intervals of 4 days in SOFeX-S allowed iron to persist in the ML longer than its expected oxidation kinetics.
The relatively low oxidation rates were related to a combination of photochemical production; slow oxidation; and, possibly, organic complexation Croot et al. Blain et al. Large amounts of iron addition at one time can lead to a substantial loss of artificially added iron.
The fifth consideration for a successful aOIF experiment is the effective tracing of the fertilized patch, including the detection of carbon sequestration Buesseler and Boyd, The first step in tracing a fertilized patch is to investigate in advance the development and fate of natural blooms appearing as chlorophyll patches using satellite data from pre-experiment investigations.
All aOIF experiments used physical tracers to follow the iron-fertilized patches, in particular GPS- and Argos-equipped drifting buoys that provide the tracked positions of a fertilized patch as a passive system moving with local currents. GPS- and Argos-equipped drifting buoys should be released before fertilization to provide a baseline , and ensuing aOIF experiments should be carried out in the region described by the drifting buoys deployed.
Drifting buoys are, however, not perfect representations of water motion and due to the effects of winds are likely to escape a fertilized patch within a few days to a week regardless of how deep their drogues are Watson et al.
An inert chemical tracer, such as SF 6 , would also be an excellent option for following the fertilized patch after iron addition. Previous aOIF experiments have shown that the SF 6 measurements based on underway sampling systems can be used to accurately determine time-dependent vertical and lateral transport of iron-fertilized patches.
Direct measurements of carbon export fluxes to determine the effectiveness of aOIF should be conducted by deploying an NBST at two depths: 1 just below the in situ MLD to detect increases in iron-induced POC in the surface layer along with the calibration of the water-column-based Th method and 2 at the winter MLD to detect iron-induced carbon export fluxes below winter MLD Bidigare et al.
Sinking-particle profiling systems e. Repeat casts with UVPs mounted on the rosette could also serve a similar purpose providing a photographic history of the water column Martin et al.
Future aOIF experiments would benefit from these technological advances, enabling a more efficient tracing of the carbon export flux and particle size and composition at higher vertical and temporal resolution than has been possible in the past. Hence, the application of an NBST system and water-column-based Th method to direct flux estimates, combined with autonomous sinking-particle profilers of a transmissometer and an UVP, will enable the quantitative and qualitative evaluation of the effectiveness of aOIF and direct observation of iron-induced carbon export fluxes after artificial iron additions.
What concerns.
Oceanic phytoplankton species Irn highly Iron in marine applications mechanisms of iron acquisition, as Iron in marine applications can take marins iron applicatikns environments in Iron in marine applications it is application at subnanomolar concentrations. In eukaryotes, three main models were proposed for iron transport into Teenagers and mealtime family connection cells by applictions studying the kinetics marinw iron uptake in different algal species and then, more recently, by using modern biological techniques on the model diatom Phaeodactylum tricornutum. In the first model, the rate of uptake is dependent on the concentration of unchelated Fe species, and is thus limited thermodynamically. In this strategy the cells are able to take up iron from very low iron concentration. This strategy allows the cells to take up iron from a great variety of ferric species. In a third model, hydroxamate siderophores can be transported by endocytosis dependent on ISIP1 after binding to the FBP1 protein, and iron is released from the siderophores by FRE2-dependent reduction.
0 thoughts on “Iron in marine applications”