Upper ocean total organic carbon at BATS Remember DOC = ~98% of the TOC. Note the build up in DOC through the spring and summer, with subsequent export the following winter. Figure courtesy of Craig Carlson, UCSB 1
TOC Profiles at BATS Figure courtesy of Craig Carlson, UCSB 2
Typical DOC profile : elevated in near surface water, decreasing through the thermocline, stable at depth. Labile pools cycle over time scales of hours to days. Semi labile pools persistfor weeks to months. Refractory material cycles over on time scales ranging from decadal to multi decadal perhaps longer 3
Contribution of different sources to marine DOM 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 Ex udation Zoop lankton Viral Solubil lization Bacterial 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). 4
Amino acids Identified DOM compound classes Peptides Nucleotides and nucleic acids Lipids Vitamins Monosaccharides Polysaccharides 5
The vast majority of organic matter in the sea remains chemically uncharacterized Carbohydrates, neutral sugars, amino acids, and amino sugars make up ~20% of the bulk DOC pool in the upper ocean 6
Isolation of DOM by ultrafiltration 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 7
Ultrafiltration high molecular weight DOM (HMWDOM) filter membrane >1000 D DOM fraction 30 35% TOC < 1000 D DOM fraction 65 70% TOC Photos from Dan Repeta 8
Final product 30 35% of total DOC 9
Spectral and chemical analyses of HMWDOC 13 CNMR Carbohydrate 50-70% of HMWDOC O O Acid hydrolysis followed by Monosaccharide analyses yields 7 major neutral sugars that represent 5-10% of surface water DOM Acid hydrolysis 200 150 100 50 0 R F A X Gl M Ga 10
NMR and carbohydrate analyses of deep sea HMWDOC surface monosaccharide distribution relative % relative % deep 11
Bomb 14 C Fossil fuel dilution Atmosphere Cosmogenic 14 C production Air Sea Exchange Surface Ocean Deep Ocean Factors controlling 14 C in atmospheric and oceanic reservoirs 14 C half life is 5730 years 12
DOC cycling via DO 14 C Williams, Oeschger, and Kinney; Nature v224 (1969) UV photooxidation 1000L Depth 14C( ) Age 1880m -351-3470+330 ybp 1920m -341-3350+300 ybp 13
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 14
Where does primary production go? Export Bacteria Grazing Dissolved organic matter 15
The Microbial Loop Classic Food web Phytoplankton Inorganic Nutrients A simplified depiction of the microbial loop Ht Heterotrophic t hibacteria Herbivores Dissolved organic matter Higher trophic levels (zooplankton, fish, etc.) Protozoa 16
Remember what life is all about: Energy (ATP) Reducing power (NADPH) Nutrients (C, N, P, S, Fe, etc., etc.) Photosynthetic organisms get these from: Sunlight, H 2 O, and dissolved nutrients Heterotrophic organisms get these from: Dissolved nutrients both organic and inorganic (with some energy from sunlight) 17
Bacterial Production Bacterial production (BP) is the rate of bacterial biomass synthesis. This describes the net movement of organic matter from a nonliving pool (DOM) to a living pool (bacterial biomass). Mathematically P = B = specific growth rate (time 1 ) B = bacterial biomass (mg C L 1 ) P= bacterial production (mg C L 11 d 11 ) Thus, P has units of mg C L 1 d 1 18
Production ( biomass/time) (mg C L 1 d 1 ) No direct measure of carbon production; rely on proxies of cell production: DNA synthesis ( 3 H thymidine, Bromodeoxyuridine) Protein synthesis ( 3 H or 14 C leucine) 19
Measuring Bacterial Production SW + isotope 3 H thymidine 3 H or 14 C leucine Concentrate t plankton or nucleic acids Whole SW Incubate at in situ temperature, typically in the dark SW + isotope Extract DNA and protein. Count radioactivity and convert to rate of incorporation (nmol leu L 1 hr 1 ) 20
Common Methods for Measuring Bacterial Production 3 H Thymidine nucleoside of thymine; DNA precursor (see Fuhrman and Azam 1980). Measures DNA production rates. Pros: specific to heterotrophic bacteria Cons: difficult to measure intracellular dilution, undergoes catabolism 3 H/ 14 C Leucine amino acid; incorporated into protein (see Kirchman et al. 1992). Measures Protein production rates. Pros: more sensitive than thymidine (intracellular protein>>dna) Cons: some cyanobacteria can utilize; difficult to measure isotope dilution. Thymidine Leucine 21
Vertical Profiles of Bacterial Production Depth (m) 0 200 400 600 800 1000 1200 Polar NABE Front Eq-Pac HOT Arabian Sea 0 500 1000 1500 2000 2500 Bacterial production in the sea is greatest in the euphotic zone reflects the dependence of heterotrophs on photosynthetically produced organic matter. Bacterial Production (ng C L -1 d -1 ) 22