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Notes on Ocean biogeochemical cycles in the Anthropocene, a presentation by J. Dore (07/17/09)ΒΆ

  • The other carbon dioxide (CO2) problem: acidification of the ocean observed over 20 years at station ALOHA
  • Human effect on global nitrogen cycle: Gruber and Galloway (2008, Nature)
  • Peak in phosphorus near 2050
  • Effect of deforestation on global warming varies regionally: cutting trees at mid-latitudes actually reduce global warming (higher albedo) while cutting trees in the tropics greatly enhances global warming (Bala et al. 2007)
  • For the oceanic biogeochemical cycle, coupled with the climate, there are several feedbacks, positive and negative, that makes difficult the prediction and net effect.
  • Deep sea mixing –bringing deep water to the surface: deep water has a larger C:N ratio than the surface layer and CO2 is released into the atmosphere
  • Natural P, Fe fertilization at station ALOHA? Hypothetically, the net effect can be CO2 sequestration
  • In 2001 thru 2003, pCO2 was going down and pH was going up at station ALOHA. This event seems to be correlated with the deepening of mixed layer (see Dore et al. 2009, PNAS in press). Could this be an example of natural P, Fe fertilization? This is an exciting observation. So with increasing warming, stronger stratification and shallower mixed layer, and less likely the P, Fe fertilization process. Question: What caused a deepening of the mixed layer from 2001 to 2003? Related to Pacific Decadal variability; Ask R. Lukas. The key point is that the interannual anomaly we are talking about is much smaller (about 10-20 m difference) than the seasonal deepening (100-200 m). Thus, this subtle variability can have large consequences on the biogeochemical budget of the upper layer.