Effect of natural iron fertilization on carbon sequestration in the Southern Ocean

By S. Blain, B. Quéguiner, L. Armand, S. Belviso, B. Bombled, L. Bopp, A. Bowie, C. Brunet, C. Brussaard, F. Carlotti and 37 more. Nature, 2007

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The availability of iron limits primary productivity and the associated uptake of carbon over large areas of the ocean. Iron thus plays an important role in the carbon cycle, and changes in its supply to the surface ocean may have had a significant effect on atmospheric carbon dioxide concentrations over glacial–interglacial cycles. To date, the role of iron in carbon cycling has largely been assessed using short-term iron-addition experiments. It is difficult, however, to reliably assess the magnitude of carbon export to the ocean interior using such methods, and the short observational periods preclude extrapolation of the results to longer timescales. Here we report observations of a phytoplankton bloom induced by natural iron fertilization—an approach that offers the opportunity to overcome some of the limitations of short-term experiments. We found that a large phytoplankton bloom over the Kerguelen plateau in the Southern Ocean was sustained by the supply of iron and major nutrients to surface waters from iron-rich deep water below. The efficiency of fertilization, defined as the ratio of the carbon export to the amount of iron supplied, was at least ten times higher than previous estimates from short-term blooms induced by iron-addition experiments. This result sheds new light on the effect of long-term fertilization by iron and macronutrients on carbon sequestration, suggesting that changes in iron supply from below—as invoked in some palaeoclimatic and future climate change scenarios—may have a more significant effect on atmospheric carbon dioxide concentrations than previously thought.

Subfields: Atmospheric Science, Environmental Chemistry, Oceanography

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Citations in the corpus

Microbial control of diatom bloom dynamics in the open ocean (2012, background): “[2] Diatoms are important bloom-forming phytoplankton that contribute 40% of global ocean productivity [Falkowski et al., 1998] and represent a major vector of carbon sequestration via downward particle export [Blain et al., 2007].”
Mesoscale eddies as foraging area of a deep-diving predator, the southern elephant seal (2010, background): “(1) At a larger scale, a previous study showed that phytoplankton blooms occur in the vicinity of many topographic structures, particularly around Kerguelen Island and its adjacent plateau (Blain et al. 2007).”
Iron limitation across chlorophyll gradients in the southern Drake Passage: Phytoplankton responses to iron addition and photosynthetic indicators of iron stress (2007, background): “Examining the influence of the Kerguelen Islands on phytoplankton distributions, Blain et al. (2001, 2007) found elevated levels of iron and chlorophyll in the island wake, but lower chlorophyll and iron outside, indicating that iron supply was responsible for the large phytoplankton blooms in the…”
Late summer diatom biomass and community structure on and around the naturally iron-fertilised Kerguelen Plateau in the Southern Ocean (2008, background): “The KERFIX study nonetheless revealed the recurrent summer bloom was dominated by Fragilariopsis kerguelensis and Thalassionema nitzschioides in the HNLC waters southwest of Kerguelen Plateau.”
The spatial structure of Antarctic biodiversity (2014, result): “The fertilization efficiency (an index of carbon export divided by iron input) in this area was up to an order of magnitude greater than in artificial fertilization studies (Blain et al. 2007).”
Man and the Last Great Wilderness: Human Impact on the Deep Sea (2011, background): “Although iron fertilisation looks attractive in theory [132,133] and is generating commercial interest, the amount of surface production sequestered is in the same order of”
Rapid bacterial mineralization of organic carbon produced during a phytoplankton bloom induced by natural iron fertilization in the Southern Ocean (2008, background): “Continuous supply of low quantities of iron and major nutrients above the Kerguelen Plateau sustained a massive phytoplankton bloom over roughly three months (Blain et al., 2007).”
The fate of biogenic iron during a phytoplankton bloom induced by natural fertilisation: Impact of copepod grazing (2008, background): “…fe ratio of 0.49 above the Kerguelen plateau suggests that new sources of Fe, such as winter mixing, Sarthou et al., Deep Sea Research II, 55, 734-751 28/50 diapycnal diffusive flux, and particulate Fe dissolution (Blain et al. 2007; this issue b) are available to sustain the massive bloom.”