Convoluted carbon cycle collection

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Image: NASA Earth Observatory/Earth Science Enterprise.
Image: NASA Earth Observatory/Earth Science Enterprise.

Of all the biogeochemical cycles that help to sustain life on Earth, the carbon cycle  is arguably the most important (although not necessarily the most straightforward!). The following collection of papers help to underline how complicated and convoluted this near-perfect cycle is. Brian Hopkinson et al. have examined the efficiency with which marine diatoms concentrate CO2 (PNAS 108: 3830–3837, 2011). Why? Because these abundant unicellular phytoplankters are extremely important in fixing CO2 – ultimately from an atmospheric source via diffusion into sea water – and exporting that fixed carbon to ocean depths, and are responsible for ‘low modern-day CO2 concentrations in surface seawater and the atmosphere’. What did they find out? Pyrenoids are implicated, but no space for more here: read the paper (a little harsh perhaps, but I view part of this column’s role as ‘enabling’ and facilitating an increase in botanical litreracy… by providing the reference I’ve enabled you to delve deeper…). If carbon acquired from consumption of marine organismss – both animal and vegetable, such as diatoms – can be locked away as carbonate-rich rocks then it is removed from the carbon cycle for millions of years, thus helping to reduce atmospheric levels of CO2. An initial step in limestone rock formation is accumulation of carbonate-rich sediment. An interesting – if slightly scatological – dimension to this has been provided by Chris Perry and co-workers [PNAS 108: 3865–3869, 2011] who investigated the disputed origins of this carbonate mud. Getting to the bottom of the problem, the team discovered that tropical marine fish excrete a range of calcium carbonates, which can account for approx. 70% of mud production in some habitats. As an aside, carbonate mud gives rise to deposits that contain unique records of changes in ocean chemistry and climate shifts in the geological past, which is in turn related to the carbon cycle. Finally, in a report at the other end of the carbon cycle – the pump-priming of ocean productivity by CO2-drawdown in the spring phytoplankton bloom – Mati Kahru et al. (Global Change Biology 17: 1733–1739, 2011) pose the question in the title of their study: ‘Are phytoplankton blooms occurring earlier in the Arctic?’. This is dramatically answered by the news item headline: ‘Arctic Blooms Occurring Earlier: Phytoplankton Peak Arising 50 Days Early, With Unknown Impacts on Marine Food Chain and Carbon Cycling’. Bloom and bust? Let’s hope not!


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