The Ocean's Biological Carbon Pump as Part of the Global Carbon Cycle.

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The Biological Carbon Pump includes all those processes in the ocean that cause photosynthetically formed organic carbon (primary production) by phytoplankton to sink out of the sunlit surface layer (the euphotic zone) into the deep sea and eventually to the ocean floor. It is a mechanism which sequesters carbon dioxide (CO2) from contact with the atmosphere for decades or hundreds or even millions of years, and even geological time-scales. The biological carbon pump together with the physical carbon pump of the ocean constitutes the ocean's CO2 sink. Together these two major processes in the global carbon cycle have removed about 2- 2.5 Pg Carbon per year (last decade average). What used to be a process in steady state (i.e., ocean emitted as much CO2 as it took up) is now changing on time scales of a few decades. The Ocean's net CO2 uptake has increased by about 1 Pg in the last 50 years due to anthropogenic increase of atmospheric CO2 levels; this offsets the natural balance of CO2 production and uptake. Since the industrial revolution in 1750, the atmospheric concentration of carbon dioxide has risen from the pre-industrial level at 280 ppm to almost 400 ppm (2013), a more than 40% increase in some 260 years. Today, about half of the CO2 emitted due to fossil fuel burning and land use changes stays in the atmosphere, and the other half goes into land sinks and the ocean, in about the same parts if you look at a decade long average. In this interdisciplinary lecture, we focus on the processes related to the biological carbon pump and how it functions, with close attention to the relevant time-scales and to the global carbon cycle. Topics include an introduction to the different carbon pumps (biological, carbonate, physical), followed by a detailed process-oriented introduction to the biological carbon pumps. This also includes the organismal aspects, such as an introduction to phytoplankton, primary production, distribution of primary producers in the global ocean, and the role of zooplankton in particle formation, transformation, removal and active transport. More mechanistic aspects follow, such as the concepts of new and export production, the flux attenuation and the role of mineral ballasting, as well as different measurements to determine export production (particle collection with traps, thorium budget, nutrient budgets, geochemical tracers, modeling, etc.). The lecture is intended for senior undergraduate and graduate students, and can be used in courses such as Oceanography, Biogeochemistry, Geology, Biogeochemistry and Environmental Life Sciences.

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DOI 10.4319/lol.2014.sneuer.miversen.gfischer.9

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Neuer, S. , Iversen, M. and Fischer, G. (2014): The Ocean's Biological Carbon Pump as Part of the Global Carbon Cycle. , Limnology and Oceanography e-Lectures, 4 (4), pp. 1-51 . doi: 10.4319/lol.2014.sneuer.miversen.gfischer.9

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