require continued iron additions forever. The project seemed so unpromising that the
environmentalist furor around OIF blew itself out for a time.
(^) Starting about 1994, a sequence of commercial OIF schemes has appeared (Strong
et al. 2009b). Various companies have formed, then dissolved, prominently including
GreenSea Ventures (led by Michael Markels), Planktos (Russ George) and Climos
(Dan Whaley and Margaret Leinen). Their schemes have had different details, but all
included the hope of making money by selling “carbon credits”. GreenSea proposed a
tropical addition using slow-release capsules of major nutrients as well as iron.
Climos, while still extant, has mostly gone quiet since late 2008. Climos is/was
principally interested in the potential of the unutilized major nutrients of the Southern
Ocean. Substantive arguments can be made that OIF would not remove sufficient CO 2
from the atmosphere to be worth the bother.
(^) First, for OIF to work significantly, the gain would come almost entirely from the
Southern Ocean, the site of the most significant availability of residual (southern
autumn) nitrate and phosphate in the euphotic zone (see NOAA–NODC World Ocean
Atlas 2009 April–June surface nitrate map at:
http://www.nodc.noaa.gov/OC5/WOA09F/pr_woa09f.html). . ) However, the
subantarctic sector does not have significant unused amounts of silicic acid (compare
the April–June surface silicate map in the World Ocean Atlas 2009) to match its “left
over” NO 3 − and PO 4 3−. Two iron-ex studies, the more northerly trial of “SoFex” and
the 2009 “LohaFex” study have both shown that chlorophyll increases induced by
added iron were not due to diatoms and export was minimal. It is essential for OIF to
work that it induce diatom blooms that sink mostly unconsumed by grazers. Without
silicate, microflagellates increase but do not sink. That pushes the OIF potential south
of 55° to 60°S, depending upon latitude. A more difficult and remote ocean area does
not exist.
(^) Second, the potential of OIF for CO 2 sequestration must be evaluated by models.
Among the best available is that by Zahariev et al. (2008), a global circulation model
(GCM) including vertical mixing and incorporating primary production controlled by
spatial variation in temperature, nitrogen, mixing depth, and iron limitation (modeled
from the spatial distributions of annual minima of residual nitrate). Alleviating all iron
limitation in the model (i.e. using all nitrate everywhere, every year) removes 0.9 GtC
in the first year, but that drops progressively to only 0.2 GtC yr−1 after 30 years of
OIF. The reason for the drop is that vertical resupply would not fully replenish the
removed nitrate during the seasons of low production. Actually, the estimate is too
large by a factor of ∼2, since the model neglected the silicate “problem” in the
subantarctic. Sequestering 0.1 GtC yr−1 by repeated spreading of iron (say as
Fe 2 (SO 4 ) 2 ) across the entire sector south of the polar front every year until fossil fuel
runs out or can be replaced, does not seem a promising strategy in the face of >8 GtC