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Global WarmingOceans

Iron 'Seeding' of Ocean May Promote Toxic Plankton

In the constant interplay between Humans and Nature, everything is a trade-off. As our scientists begin to consider an intervention approach to climate change and conducting large-scale experiments, this trade-off is coming into sharper resolution.

Case in point: iron ocean fertilization (or “seeding”), a geoengineering strategy making the news in recent years. Iron fertilization also occurs naturally through such actions as coastal land run-off and landslides. However it happens, it tends to have a marked impact on the growth rates of oceanic plant life, and potentially also on the ocean’s entire ecology.

The idea is to enhance  CO2 sequestration from the atmosphere by algae by seeding the oceans (or parts thereof) with iron crystals. Iron in the water acts as a metabolic catalyst for algae (single celled phytoplankton) that flourish at or near the ocean’s surface. This growth in turn requires the uptake of more CO2 from the atmosphere.*

As an added benefit, the activity is believed to limit coral-destroying acidification which occurs when too much CO2 gets dissolved in sea water, some of which is converted into carbonic acid (H2CO3).

That was the plan.  And while iron seeding does indeed promote algal blooms, not all alga are equal — some forms can be poisonous to other lifeforms. One such form of plankton — a species of diatom by the name of Pseudo-nitzschia — happens also to be strongly associated with a wide-ranging neurotoxin called domoic acid (DA). The toxin may be a metabolic by-product or perhaps an adaptation (survival strategy) of this planktonic life form.

Last Fall, a team of ocean scientists (Silver et al) sampled water from 35 stations ranging from the Pacific subarctic (58°N) to the Southern Ocean (66°S), finding P. nitzchia at 34 of them, and detected significant levels of DA in diatom cells at 14 of the 26 stations analyzed for the toxin. Similar values were found in cells from coastal waters (the presumed result of land run-off effects). Included amongst the sampling stations were the sites of the historic iron fertilization experiments SOFeX, and IronEx II.

According to the authors: “By reexamining phytoplankton samples from SOFeX and IronEx II, we found substantial amounts of DA associated with Pseudo-nitzschia. Indeed, at SOFeX in the Antarctic Pacific, DA reached 220 ng·L−1, levels at which animal mortalities have occurred on continental shelves.”

diatoms (microscopic view)

They also noted that the sinking of large quantities of the diatoms delivered significant levels of DA to the meso-pelagic depths (150 – 500 meters) of the western subarctic region.

DA is found in varying abundances in both oceanic and coastal waters and correlates positively with variations in P. nitzschia abundances. Such algal “booms and busts” have occurred a great many times over the eons, varying with glacial and climate cycles. But now, it seems that artificial iron fertilization is another co-variant in these planktonic bloom cycles, and likely a cause of them.

Given the proposed use of iron fertilization strategies to reduce atmospheric CO2 and ocean acidification, the authors caution: “…consideration of the potentially serious ecosystem impacts associated with DA is prudent.”

For more information about geo-engineering, check out my previous article on Planetsave: Geoegineering Ethics – Getting Serious & Humble About Climate Intervention [Video]

Check out the paper: Toxic diatoms and domoic acid in natural and iron enriched waters of the oceanic Pacific, by Silver et al

* Carbon remediation or sequestration occurs when the iron-enriched planktonic bloom dies and begins sinking to the bottom of the ocean.

Top Image: An oceanic phytoplankton bloom in the South Atlantic Ocean off the coast of Argentina covering an area about 300 miles by 50 miles

Diagram: derivative work: McSush (talk) CO2_pump_hg.png: Hannes Grobe 21:52, 12 August 2006 (UTC), Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany; cc –by – sa 2.5




7 comments
  1. CaptD

    The ongoing enormous amount of Fukushima ☢ will also magnify the effect of Pacific Ocean Pollution for the rest of this century if not forever… – CaptD

    1. michael R.

      to Bhaskar:

      to Bhaskar:

      This may be a viable substitution (as it will not significantly alter the ph of the water), however, as a powerful fertilizing agent, it could lead to over-nitrification of the marine habitat, creating hyper-trophic conditions…which tend to disrupt the balance between primary producers and higher (dependent) forms of marine fauna…thus disrupting ecosystems.

      That said, I would like to see or hear from those who have experimented with urea in the context of carbon remediation.

  2. Bhaskar

    In natural upwelling and dust deposition many micro nutrients in addition to Iron are mixed into the oceans and this causes blooms of healthy Diatoms and other phytoplankton.

    If ‘Iron fertilization’ or other fertilization follows the natural balance and care is taken then only healthy Diatoms would bloom and not unhealthy ones.

    1. Michael R.

      thanks for your comment.

      I’m not sure what you mean by ‘follows the natural balance” …if you mean that iron seeding should only occur in amounts that reflect the “natural’ (but ever dynamic) amounts of Fe (all forms) that are present in these waters, Ok, but the idea is to INCREASE blooms of phytoplankton to absorb MORE CO2…so, on its face, iron seeding is not “in balance” with nature (and neither is the amount of CO2 we put into the atmosphere).

      It is true that natural upwelling and sediment (water column) mixing promote “blooms” of plankton (many forms). However, which forms of plankton will benefit most from this, or gain biological advantage (in terms of growth booms and blooms), can not be predicted or controlled, as the types and amounts of nutrients from these up-wellings vary greatly from locale to locale, as do the populations of various plankton species that are most dominant.

      All forms of plankton benefit from iron fertilization, including “bad” forms, toxic-producing forms. I’m not sure how this can be controlled, mitigated, or stopped.

      Every geoengineering strategy that I have read about carries with it some ecological or climatological trade-off. Ultimately, such decisions (to seed or not to seed) will come down to the “lesser of two evils”, as they will be implemented, most likely, when we are in a state of climate crisis.

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