Carbon cycling in a changing climate. How will the oceans respond to the rapid changes in atmospheric carbon dioxide that are ahead of us?

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1 Carbon cycling in a changing climate. How will the oceans respond to the rapid changes in atmospheric carbon dioxide that are ahead of us? pco 2(atm) pco 2(aq) CO 2(aq) + H 2 O H 2 CO 3 H2CO3 H + +HCO 3 - ph will go down pco 2 will go up Nature, v450 (Nov 2007) pp ΔC 45 µm ΔC 30 µm

2 The biological pump and organic carbon transfer to the sea floor grain-by-grain deposition is by far the most common phenomenon of pelagic sedimentation Jacobs et al. (1973) Marine Geology v14, We use filters to sample suspended POM The biological pump and organic carbon transfer to the sea floor grain-by-grain deposition is by far the most common phenomenon of pelagic sedimentation Jacobs et al. (1973) Marine Geology v14, # particles ml -1 Particle diameter (µm) We use filters to sample suspended POM

3 The biological pump and organic carbon transfer to the sea floor N = αd m Flux (µg m -2 s -1 ) Particle diameter McCave DSR(1975) v Large, rapidly sinking particles are collected with sediment traps Ioeb.whoi.edu

4 What drives carbon flux? Carbon flux Depth J = J 100 /((Z/100) ) New production Martin et al (1987) DSR v 34; C flux is closely coupled to the biological processing of organic matter

5 Geographic correlation between carbon flux and wt% C in sediments Marine snowvery fragile aggregates of organic matter and minerals that form spontaneously, or are excreted by marine biota Difficult to measure flux Wells, Nature (1998) 391 Chin et al. Nature (1998) 391:

6 Molecular-level characterization of POM in sediment traps What determines how much C makes it to the sea floor, how much is mineralized, and how much is buried?.at a molecular level, the composition of sinking POC is edited depth (degradation) Do molecular level analyses give a fair representation of POM composition? C:N = 6.6 C:N = 9.0 From Lee et al. (2004) Ambio 33,

7 The composition of organic matter in marine sediments and the mechanisms of carbon preservation What determines how much makes it to the sea floor, How much is mineralized, and how much is buried? 1) Selective preservation: Some compounds are intrinsically more labile than others, and will be preserved in sediments. 2) Physical protection/encapsulation: Organic matter can be locked up In clay minerals, cysts, etc and preserved. 3) Geopolymer model: Simple biomolecules (sugars, amino acids, lipids) recombine through unknown reactions to form complex substances that are not easy to degrade. These are not mutually exclusive.! How well do we know the composition of marine algae? CH 3 CH(N)COOH proteins I, II, III, VII C(H 2 O) carbohydrates III CH 3 (CH 2 ) n COOH lipids I, V, VII Hedges et al. (2002) Marine Chemistry v 78, pp 47-63

8 13 CNMR of phytoplankton, shallow and deep sediment trap material (Equatorial Pacific) Surface protein carbo lipid 1000 m 3500 m 13 CNMR of phytoplankton, shallow and deep sediment trap material (Arabian Sea)

9 From the small changes in the 13 CNMR spectra of sinking POM, Hedges et al. infer that the C degradation acts non-selectively, and that preservation occurs via physical protection. How well do we know the composition of marine algae? Molecular analyses of phytoplankton cannot account for the NMR distributions of functional groups Do protein/carbohydrates/lipids account for most of the C&N in algae, and are the functional group assignments correct? If C/N increases with depth from 6.6-> 9, then why isn t this reflected in the 13 CNMR?

10 Reconciling selective and nonselective preservation the effects of mineral ballast on C flux As more of the material is ballasted, the F org /EP increases F org = fraction organic carbon & EP = export production Francois et al. (2002) GBC 16 doi:10,1029/2001gb001722, 2002: Reconciling selective and nonselective preservation the effects of mineral ballast on C flux Organic matter on sinking particles is made up of protected and nonprotected forms. The nonprotected OM is lost in the upper water column, protected is not, and its flux will vary with the amount of mineral flux.

11 Testing the mineral protection hypothesis: Do mineral bound amino acids make up a large fraction of the sinking POM at at depth in the ocean?.not really, at least not in the southern ocean. NMR spectra of fresh algae. 15 N and 13 CNMR show a large fraction of the material is protein, (amide, CON, CHO & CH x ) Knicker et al Org Geo 24, N-NMR 13 CNMR O = C-C-N amide - C-C-NH = O amine

12 Physical entrapment into resistant geopolymers 13 CNMR of mixed algae From laboratory culture The same culture material After 2 months of degradation Knicker et al Org Geo 24, N- and 13 CNMR study of algal degradation Knicker et al Org Geo 24, Fresh algae Algal compost (60 d) Algaenan (nonextractable POM)

13 15 N and 13 CNMR of an algal 4000 yr old sapropel from Mangrove Lake, Bermuda Knicker et al Org Geo 24, Note presence of Amide (?) 15 N 13 C Knicker reasons that amide comes from protein, which should be labile. Preservation suggests some form of physical protection but is protein labile? The effect of aging on protein degradation Keil and Kirchman

14 Another way to think about selective preservation. What are the isotopic consequences of degradation? Acid insoluble Lipid Carbohydrate TH amino acids J. Hwang & E.R.M. Druffel (2003) Science, Another way to think about selective preservation. What are the isotopic consequences of degradation? Acid insoluble Lipid Carbohydrate TH amino acids As organic matter ages (14C) the amount of acid insoluble C increases.. J. Hwang & E.R.M. Druffel (2003) Science,

15 And the C isotope ratios of the acid insoluble fraction looks a lot like lipids. DIC Acid insoluble Lipid Carbohydrate TH amino acids J. Hwang & E.R.M. Druffel (2003) Science, Summary There is clear evidence for selective degradation of labile Organic matter in sinking particles and in fresh vs. preserved OM Selective preservation is quantitatively significant as it affects C/N ratios. It is not clear is organic matter is protected by adsorption onto mineral surfaces. Some organic matter is encapsulated into minerals and is protected, But this may or may not be quantitatively significant (globally) Other means of physical protection have been proposed, but are a matter of conjecture (in my opinion)

16 Particle dynamics and radiocarbon distribution in POC Druffel et al. DSR (1990) 45: