The experimental coordinates near 48°N, 165–166°E are high-seas locations in the western subarctic Pacific, not Japanese EEZ sites.
Repeat mesoscale field experiments
Ocean iron fertilisation: SEEDS and SEEDS-II
Two Japan-led experiments near the same season and location produced sharply different outcomes, exposing the importance of seed stock, grazing and physical state.
Repeat mesoscale field experiments
Which initial ecological and physical measurements explain a SEEDS-like bloom versus a SEEDS-II-like grazing response?
The scientific case
Why it matters
SEEDS and SEEDS-II are rare repeat experiments at nearly the same location and season with sharply different outcomes. SEEDS produced a very large centric-diatom response; SEEDS-II produced a much smaller biomass response despite renewed iron enrichment. The contrast makes this the clearest public demonstration that iron concentration alone does not predict bloom size, community structure, export or removal.
Physical setting
Oceanography
The western subarctic gyre is an HNLC system influenced by Asian dust, Sea of Okhotsk intermediate water, Kuril mixing, Oyashio circulation, fronts and eddies. SEEDS was conducted near 48.5°N, 165°E and SEEDS-II near 48°N, 166°E. These reported coordinates lie in high seas outside the relevant EEZ. Natural iron supplied through Okhotsk/Kuril intermediate waters changes seasonally and spatially; it belongs in the baseline and transport model.
Biological response
Phytoplankton and algae
SEEDS was dominated by the centric diatom Chaetoceros debilis and showed large nutrient and biomass changes. In SEEDS-II, higher copepod biomass and grazing helped suppress accumulation; the community returned toward picophytoplankton dominance. Initial diatom seed stock, iron speciation, mixed-layer conditions and grazing state were decisive.
Evidence record
Experiments and observations
- SEEDS confirmed strong iron limitation and a large centric-diatom bloom.
- SEEDS-II, designed in a similar region and season, produced a much weaker accumulation and documented copepod control.
- Particle studies conclude that high initial diatom seed abundance helped explain the large SEEDS response.
- Western subarctic observations show that Okhotsk intermediate waters transport iron through the Kuril system into the North Pacific, complicating any static iron baseline.
Accounting boundary
Carbon fate and permanence
Neither a large SEEDS bloom nor the smaller SEEDS-II response establishes durable removal. SEEDS ended while high biomass was still present, limiting full decline/export accounting. SEEDS-II shows that grazing can keep biomass low and redirect carbon through the food web. The scientific comparison covers fixed carbon, upper-ocean particle loss, deep export, food-web transfer and respiration rather than comparing chlorophyll peaks.
Observation system
Measurement and MRV priorities
- Initial seed populations and resting stages; Chaetoceros and other diatoms at species level.
- Copepod biomass, development, vertical migration and grazing alongside microzooplankton and bacterial processes.
- Iron speciation/ligands and supply from dust, Okhotsk intermediate water and Kuril mixing.
- Oyashio/front/eddy position, mixed-layer history, silica and patch dilution.
- Multi-method export observations extending through bloom demise and winter ventilation.
Field reality
Operations and cost drivers
Open-ocean vessel time; trace-metal-clean work; repeat occupations under comparable seasonal states; current and patch tracking; deep traps/profilers; plankton taxonomy and grazing experiments; dust and intermediate-water source sampling; and long follow-up. Historical Japanese research capability is relevant operational experience, not a current permission or cost estimate.
Uncertainty and exposure
Ecological and social risk pathways
Outcome sensitivity to initial ecology; grazing and food-web redistribution; harmful species/toxins; silica depletion; natural iron-source variability; downstream nutrient changes; oxygen/N2O effects; fisheries exposure; severe weather and loss of patch coherence.
Social and ocean-use baseline: fisheries, potentially affected coastal, Indigenous and local communities, protected species and existing ocean users follow the actual and downstream footprint rather than the nearest port alone.
Institutions and protection
Governance and protection context
The SEEDS coordinates lie in high seas outside Japan’s EEZ. This was Japan-led research in the western subarctic Pacific, not an experiment in Japanese waters. Exact high-seas location, vessel flag, ports, nationality of operators, BBNJ, LC/LP/OFAF and applicable domestic law require a new, activity-specific analysis. The cited sources establish no Japanese permission pathway.
Research agenda
Open questions
- Which initial community metrics predict a SEEDS-like versus SEEDS-II-like outcome?
- Can grazing, seed stock and iron chemistry be measured early enough to explain response without post-hoc fitting?
- What fraction of carbon reaches deep water after bloom decline and winter mixing?
- How does natural Okhotsk/Kuril iron supply affect the counterfactual?
- How far do food-web and nutrient effects propagate beyond the tracked patch?
Evidence trail
Primary and official sources
- Tsuda et al. (2003), SEEDS, DOI 10.1126/science.1082000 ↗.
- Tsuda et al. (2007), SEEDS-II grazing hypothesis, DOI 10.1007/s10872-007-0082-x ↗.
- Tsuda et al. (2009), meso-/microzooplankton in SEEDS-II, DOI 10.1016/j.dsr2.2009.06.004 ↗.
- Aono et al. (2010), SEEDS/SEEDS-II particles and seed population, DOI 10.1016/j.dsr2.2009.07.005 ↗.
- Nishioka et al. (2007), Okhotsk iron supply, DOI 10.1029/2006JC004055 ↗.
- Yoshida et al. (2020), phytoplankton physiology near Kurils, DOI 10.1029/2019JG005525 ↗.
Results vary by location, season, intervention, method and observation window.