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ocean biogeochemistry.docx

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Life Sciences
Luc Bernier

February 25 , 2013 Life Sci 2H03: Environmental Life Sciences Ocean Biogeochemistry The Organic Carbon SubCycle - component of the carbon cycle which is rapidly moving in terms of the rate of exchange between vegetation in the atmosphere and the ocean an the atmosphere - burial and recycling in the earth’s rocks is much slower, erosion and volcanoes - importance of the subcycle: reacts quickly to any changes in global environment - 20% of carbon cycle involves the organic carbon sybcycle Chemical Weathering and CO U 2 - transfer into ocean - longer time period - leads to regulation of carbon in the atmosphere - incorporated in the biomass of algae - leads to formation of carbonic acid that leads to the weathering of silicate rocks - material will be recycled at the boundaries for ocean and continental plates, released over the years through volcanic activity - ocean plays a crucial role in mediating the amount of CO we f2nd in the atmosphere What is the Ocean’s Role as a Control on CO in t2e Atmospehre? - diffused in the ocean and used by photoplankton - can lead to the formation of carbonic acid - carbonic acid will dissociate:  release a hydrogen ion leads to acidification of the ocean  bicarbonate ion - calcite compensation depth: if the shells of organisms fall beneath this zone we won’t se any material on the sea floor as they decompose - shells of calcite at higher depths - what happens as a result of more carbon dioxide in the atmosphere:  acidification of the ocean due to the formation of carbonic acid - plankton that forms carbon based shells (calcite shells): coccolithophores - diatoms: different types of algae use silicon to form their shells, silicon will be recycled when the organisms die Photosynthesis in the Ocean - diatoms use carbon dioxide to form a lot of their biomass: restricted to areas where there is enough sunlight for photosynthesis - euphotic zone: where photosynthesis is possible, limited by the availability of nutrients such as nitrogen and phospore - disphotic zone: not enough energy for photosynthesis but can warm zone - aphotic zone: no sunlight, no photosynthesis below 600 meters to much greater depths - nutrients plays a large role in controlling the rates of transfer Productivity of Ocean in Upwelling Regions - upwelling: movement of deep water that resurfaces near continental coast brings up cold water with nutrients - no longer limited nutrients - important rates of algal production near the coast - water temperature is not a major control on growth of algae, ex.: algal blooms of the coast of Alaska Polar Ocean Productivity - winter darkness: photosynthetic organisms do not thrive under these conditions - summer sunlight: high rates of photosynthesis, begins in the spring when there is just enough sunlight to begin the process - E.g.: Arctic Ocean - Concentration of nutrients - Amount of photoplankton - Amount of zooplankton (consumers of photoplankton) - With sunlight increasing in the spring we see an important phytoplankton bloom growing without any limits during the beginning of spring until there predators start feeding on them - Doesn’t necessarily coincide with amount of sunlight - Decrease in zooplankton allows for another bloom in the fall - No barrier to vertical mixing - Whales move into the ocean and feed when there is a high availability of food Regional Primary Productivity - in the norht polar, we see the highest productivity peak from may-october when there is the greatest amount of sunlight - in lower latitudes: peak in spring and fall - tropical: low productivity throughout the year Antarctic Ocean Productivity - deep currents resurfacing - upwelling of nutrient rich water - favours growth of algae and various consumers and benthic invertebrates - isothermal profile: no obstacle for resurfacing of deep water as the temperatures are virtually the same - food source for krill, penguins, killer whales and seals Energy Flow in Marine Ecosystem - eventually decomposers, and nutrients return to the ocean Biogeochemical Cycling in Marine Systems - nutrient cycled from one chemical form to another - in marine food web: moved from one trophic level to another - tends to happen primarily in coastal regions, specifically close to the polar regions Tropical Ocean Productivity - permanent thermocline: barrier to vertical mixing - surface is warm, compared to cooler denser bottom water - we have a very sharp thermocline preventing - low rate primary productivity: excludes coastal regions where up wheeling is happening, or where overturning is happening - tropical ocean has a low productivity as a result of this, exception: coral reefs - for the most part, coastal areas tend to be productive - in the open ocean not much productivity - polar waters (less difference between surface and deep waters) favours productivity - exception: due to the normal process of atmospheric circulation of the trade waters bringing warm surface waters from the coast also for upwelling of cold water and nutrients along the equator - varies from season to season Seasonal Variations in Primary Productivity Ocean Sources and Sinks of CO 2 - which parts of the ocean are able to fix CO vs 2he areas that tend to be sources (net transfer from the surface to the bottom) - carbon sinks: critical in terms of net transfer of carbon dioxide from the atmosphere to the ocean through algal production and through the golf stream circulation (sinking of water entrains carbon in the process) The Ocean Carbon Pump - with sunlight and nutrients: photosynthesis is accelerated in the ocean surface water - when plankton dies: organic matter d
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