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Diatoms are one of the most ecologically successful classes of photosynthetic marine eukaryotes in the contemporary oceans. Over the past 30 million years, they have helped to moderate Earth's climate [...]

Author(s): Michael J. Behrenfeld (corresponding author) [1]; Robert T. O'Malley [1]; David A. Siegel [3]; Charles R. McClain [4]; Jorge L. Sarmiento [5]; Gene C. Feldman [4]; Allen J. Milligan [...]

Author(s): Antonietta Quigg (corresponding author) [1]; Zoe V. Finkel [1]; Andrew J. Irwin [1]; Yair Rosenthal [1, 2]; Tung-Yuan Ho [5]; John R. Reinfelder [3]; Oscar Schofield [1, 4]; Francois [...]

The evolution of biogeochemical cycles are examined to determine the factors that influence total oceanic primary productivity. For the past two million years, the rise in the transportation of organic carbon from surface waters into marine sediments were linked to the decline in atmospheric carbon dioxide concentrations. This indicates that fixed nitrogen is a variable that controls primary productivity on geological timescales.

In situ measurements of fluorescence during IronEx II, when dissolved iron was infused into the surface layer of a square patch of ocean in the eastern equatorial Pacific Ocean in 1995, are reported. They show that the iron enrichment induced dramatic biophysical changes of phytoplankton's photosynthetic mechanisms, leading to increased photosynthetic capacities and hence, the massive phytoplankton bloom. Findings offer proof that iron limits the bioavailability of phytoplanktons in high nitrate, low-chlorophyll waters.

Evaluation of the variations in the photochemical energy conversion efficiency of natural phytoplanktons prior and subsequent to artificial fertilization of an area with high nitrate and low chlorophyll in the equatorial Pacific Ocean with iron using a fast repetition rate fluorometer reveals that physiological proliferation of phytoplanktons is restricted by iron. Inhibition diminishes the potential of phytoplankton to photochemically convert light to stored chemical energy, preventing phytoplanktons from entirely consuming the available nutrients in the water.

Records of changes in phytoplankton biomass in the North Pacific ocean since 1900 revealed that these changes were negligible and will therefore not slow the increase in atmospheric carbon dioxide (CO2) due to human industry. The data on marine phytoplankton productivity were obtained using Secchi disks. Hence it is unlikely that increased oceanic productivity will erase the environmental effects of rising anthropogenic CO2 levels.

Diatoms are one of the most ecologically successful classes of photosynthetic marine eukaryotes in the contemporary oceans. Over the past 30 million years, they have helped to moderate Earth's climate by absorbing carbon dioxide from the atmosphere, sequestering it via the biological carbon pump and ultimately burying organic carbon in the lithosphere. The proportion of planetary primary production by diatoms in the modern oceans is roughly equivalent to that of terrestrial rainforests. In photosynthesis, the efficient conversion of carbon dioxide into organic matter requires a tight control of the ATP/NADPH ratio which, in other photosynthetic organisms, relies principally on a range of plastid-localized ATP generating processes. Here we show that diatoms regulate ATP/NADPH through extensive energetic exchanges between plastids and mitochondria. This interaction comprises the re-routing of reducing power generated in the plastid towards mitochondria and the import of mitochondrial ATP into the plastid, and is mandatory for optimized carbon fixation and growth. We propose that the process may have contributed to the ecological success of diatoms in the ocean. [ABSTRACT FROM AUTHOR]