Organic Matter Cycling in the Upper Ocean

Organic matter cycling in the upper ocean THE REDFIELD PAPER (Redfield et al. 1963) REDFIELD STOICHIOMETRY 1P:16N:106C:138O2 Graphs of N vs. P and N vs. O2 utilized removed due to copyright restrictions. Redfield, A.C. (1934), On the proportions of organic derivatives in seawater and their relation to the composition of plankton, James Johnston Memorial Volume, 176-192 THE REDFIELD PAPER (Redfield et al. 1963) ¾ ¾ ¾ ¾ Redfield ratios: N and P are available in the ocean in the same ratios in which they are utilized Preformed vs. remineralized nutrients Preferential remineralization of P Nutrient limitation (Excess P in surface waters, therefore N ultimate limiting nutrient) Table of ratio of change in the atomic concentration of products of decomposition of organic matter in the presence of oxygen and under anoxic conditions removed due to copyright restrictions. A BIOLOGIST’S PERSPECTIVE (Azam et al. 1983) ¾ MICROBIAL LOOP “Energy released as DOM by plankton is rather inefficiently returned to the main food chain via a microbial loop of bacteria-flagellatesmicrozooplankton” ¾ Bacteria consume 10-50% fixed carbon. ¾ Correlation between chl, DOM and bacterial abundance A BIOLOGIST’S PERSPECTIVE (Azam et al. 1983) ¾ MICROBIAL LOOP “Energy released as DOM by plankton is rather inefficiently returned to the main food chain via a microbial loop of bacteria-flagellatesmicrozooplankton” ¾ Bacteria consume 10-50% fixed carbon. ¾ Correlation between chl, DOM and bacterial abundance Graphic showing trophic level vs. length removed due to copyright restrictions. A BIOLOGIST’S PERSPECTIVE (Azam et al. 1983) ¾ MICROBIAL LOOP “Energy released as DOM by plankton is rather inefficiently returned to the main food chain via a microbial loop of bacteria-flagellatesmicrozooplankton” ¾ ¾ ¾ Bacteria consume 10-50% fixed carbon. Correlation between chl, DOM and bacterial abundance Bacteria grazed by heterotrophic microflagellates (preditor-prey cycles) Defining “new” vs “regenerated” production (Dugdale and Goering, 1967) ¾ ¾ NEW PRODUCTION uses NO3 and N2 REGENERATED PRODUCTION uses NH4+ and Norg Graphic depicting new production, regenerated production and export production after Casciotti. Defining “new” vs “regenerated” production (Dugdale and Goering, 1967) ¾ ¾ ¾ ¾ ¾ NEW PRODUCTION uses NO3- and N2 REGENERATED PRODUCTION uses NH4+ and Norg Measure nitrogen uptake using 15N additions Light and dark assimilation of NH4+ and NO3Suggest Nitrogen limiting primary production in Bermuda N2 fixation Graph for 1962 and 1963 removed due to copyright restrictions. Defining “new” vs “regenerated” production (Dugdale and Goering, 1967) ¾ ¾ ¾ ¾ ¾ NEW PRODUCTION uses NO3- and N2 REGENERATED PRODUCTION uses NH4+ and Norg Measure nitrogen uptake using 15N additions Light and dark assimilation of NH4+ and NO3Suggest Nitrogen limiting primary production in Bermuda RICH SEAS ARE RICHER, POOR SEAS ARE POORER Poor Seas are RICHER (Jenkins and Goldman, 1985) ¾ New Estimates of primary production in oligotrophic regions ¾ Three independent methods all show significantly higher levels of productivity. Poor Seas are RICHER (Jenkins and Goldman, 1985) ¾ If system looks like a steady state system on long time scales, then inputs=losses ¾ Method 1: Heat fluxes. To account for temperature changes at 50m, there has to be a downward transport of heat through mixing. Flux brings head down, Brings O2 up -> escapes “leaky system” Poor Seas are RICHER (Jenkins and Goldman, 1985) ¾ If system looks like a steady state system on long time scales, then inputs=losses ¾ Method 2: Deep Oxygen profiles. Changes due to O2 consumption during remineratlization. Integrate oxygen utilization rates to estimate O2 consumption rate Graph of oxygen anomaly vs. January removed due to copyright restrictions. Poor Seas are RICHER (Jenkins and Goldman, 1985) ¾ If system looks like a steady state system on long time scales, then inputs=losses ¾ Method 3: Tritium-3He dating. Calculate O2 loss. Graph of depth vs. oxygen anomaly removed due to copyright restrictions. Poor Seas are RICHER (Jenkins and Goldman, 1985) ¾ New Estimates of primary production in oligotrophic regions ¾ Three independent methods all show significantly higher levels of productivity. ¾ Nutrient fluxes are event-dominated- short time periods of rapid mixing. ¾ “Spinning Wheel”- rapid regeneration in the upper ocean Poor Seas are RICHER (Jenkins and Goldman, 1985) ¾ New Estimates of primary production in oligotrophic regions “the independent oligiotrophic ocean is not steady ¾ Three methods all at show state, that far higher new primary significantly higher levels of productivity. production occurs than previously ¾ Nutrient fluxes are -dominated - short measured, andevent that this increased time periods ofisrapid mixing. productivity fueled by heterogenous ¾ “Spinninginputs Wheelof ”- new rapidnutrients. regeneration in ” the upper ocean ∆O 2 Table depicting the ratio of change in the atomic concentration of products of decomposition of organic matter in the presence of oxygen and under anoxic conditions removed due to copyright restrictions. Other discussion questions ¾ Affect of cycling on 15N uptake measurements ¾ How does ignoring nitrigication affect Dugdale’s arguments?