Dissolved organic matter dynamics in the sea DOC distributions in the Atlantic Marine Microplankton Ecology OCN 626 Matthew Church Figures from Dennis Hansell DOC distributions in the Pacific Basin scale gradients in deep ocean DOC concentrations: slow degradation and transport of organic carbon Figures from Dennis Hansell Hansell and Carlson, (1998, 2001) 1
DOC distributions in the Pacific Total organic carbon at BATS Remember that DOC = ~98% of the TOC. Note the build up in DOC through the spring and summer, with subsequent export the following winter. Figures from Dennis Hansell Figure courtesy of Craig Carlson, UCSB Contribution of different sources to marine DOC Sources of DOM to ocean ecosystems 1. Direct algal excretion 2. Zooplankton (sloppy feeding, excretion) 3. Viral lysis 4. Bacterial release 5. Solubilization of POM % carbon released 100 80 60 40 20 0 Amino acids Identified DOM compound classes Peptides Nucleotides and nucleic acids Lipids Exudation Zooplankton Viral Solubilization Bacterial Vitamins Exudation % 14 C primary production, zooplankton % carbon ingested, solubilization % C released from aggregates, bacterial % release from 14 C labeled organic substrate. Sources: Nagata (2001), Carlson (2002). Monosaccharides Polysaccharides 2
Carbohydrates, neutral sugars, amino acids, and amino sugars together make up ~20% of the bulk DOC pool in the upper ocean Isolation of DOM by ultrafiltration The vast majority of organic matter in the sea remains chemically uncharacterized Benner (2002) Dan Repeta Size selective concentration of DOM Typically solutes > 1nm are concentrated for subsequent analyses Selects for HMW fraction (about 30 35% TOC) Some salts collected also Ultrafiltration high molecular weight DOM (HMWDOM) Final product 30 35% of total DOC membrane filter >1000 D DOM fraction 30 35% TOC < 1000 D DOM fraction 65 70% TOC Photos from Dan Repeta Photos from Dan Repeta 3
Spectral and chemical analyses of HMWDOC NMR and carbohydrate analyses of deep sea HMWDOC 13 CNMR Carbohydrate 50-70% of HMWDOC Acid hydrolysis O O Acid hydrolysis followed by Monosaccharide analyses yields 7 major neutral sugars that represent 5-10% of surface water DOM surface deep monosaccharide distribution relative % relative % 200 150 100 50 0 Courtesy of Dan Repeta R F A X Gl M Ga Courtesy of Dan Repeta Labile: simple sugar monomers, amino acidstypically nanomolar concentrations Semi labile: amino sugars (ex. N acetyl glucosamine) typically ~1 10 of micromolar Refractory: largely unknown composition, rich in C relative to other nutrients (N, P); 10s of micromolar Carlson (2002) Jiao et al., (2010) Nature Reviews, Microbiology 4
Bomb 14 C Cosmogenic 14 C production Fossil fuel dilution Atmosphere Air Sea Exchange Surface Ocean Deep Ocean Jiao et al., (2010) Nature Reviews, Microbiology Factors controlling 14 C in atmospheric and oceanic reservoirs 14 C half life is 5730 years History of Radiocarbon in the Atmosphere and Ocean Bauer (2002) DOC cycling via DO 14 C Williams, Oeschger, and Kinney; Nature v224 (1969) UV photooxidation 1000L Depth 14C( ) Age Pre-bomb 14 C ~-80 1880m -351-3470+330 ybp 1920m -341-3350+300 ybp 5
Radiocarbon in the Atlantic and Pacific Oceans Peter M. Williams and Ellen Druffel; Nature 1987, JGR 1992 DIC 14 C in surface waters of the Atlantic and Pacific has the same isotopic value. DOC is always older than DIC (by 4 kyrs in surface water) Deep ocean values of DOC are equal to a radiocarbon age of 4000 5000 yrs Either there is a source of old DOC, or DOC persists for several ocean mixing cycles Prebomb organic matter: 14 C < 50 Post bomb organic matter production: 14 C > ~ 50 and <200 Bauer (2002) Plankton Suspended particles Sinking particles Surface DOM Deep DOM Plankton Suspended particles Sinking particles Surface DOM Deep DOM 0 5 10 15 20 C:N ratio Stoichiometry of POM and DOM During degradation of organic material, nutrient elements are preferentially removed. Bulk pools of DOM tend to be carbon rich, and nitrogen and phosphorus poor Regeneration versus assimilation of N and P Factors controlling whether nutrients are regenerated or assimilated: C:N:P ratio of the bacterial biomass C:N:P ratio of the substrate supporting growth Growth efficiency In general, the C:N:P ratio of the biomass must be greater than the C:N:P ratio of the substrate for regeneration of N or P to occur. 0 100 200 300 400 500 C:P ratio 6
Major components of the biological pump: 1. Sinking particles 2. DOC Major controls on the pump efficiency: 1. Plankton production and respiration, zooplankton repackaging 2. Particulate and dissolved material stoichiometry 3. Physics (stratification and mixing) 7