2 cycles | Carbon Cycle | Photosynthesis - Scribd
Photosynthesis Cellular Respiration Lab Key2 - Scribd
An additional pathway for CO2 uptake involves photosynthesis by phytoplankton. The organic carbon produced by phytoplankton moves up the food chain and about 90% is converted eventually to CO2(aq) by respiration and decay within the oceanic mixed layer. The 10% fraction that precipitates (fecal pellets, dead organisms) represents a biological pump transferring carbon to the deep ocean. The biological productivity of the surface ocean is limited in part by upwelling of nutrients such as nitrogen from the deep (), so that the efficiency of the biological pump is again highly dependent on the vertical circulation of the ocean water. It is estimated that the biological pump transfers 7 Pg C yr-1 to the deep ocean, as compared to 40 Pg C yr-1 for CO2(aq) transported by deep water formation.
Photosynthesis Cellular Respiration Lab Key2
This cycling of O2 with the lithosphere is illustrated in . Atmospheric O2 is produced during the formation of reduced sedimentary material, and the consumption of O2 by weathering when this sediment is eventually brought up to the surface and oxidized balances the O2 source from sediment formation. Fossil records show that atmospheric O2 levels have in fact not changed significantly over the past 400 million years, a time scale much longer than the lifetime of O2 against loss by weathering. The constancy of atmospheric O2 suggests that there must be stabilizing factors in the O2-lithosphere cycle but these are still poorly understood. One stabilizing factor is the relative rate of oxidation vs. burial of organic carbon in the ocean. If sediment weathering were to increase for some reason, drawing down atmospheric O2, then more of the marine organic carbon would be buried (because of slower oxidation), which would increase the source of O2 and act as a negative feedback.