Dissolved Organic Matter DOM and the Microbial loop

Dissolved Organic Matter (DOM) and the Microbial “loop” “I presume that the numerous lower pelagic animals persist on the infusoria, which are known to abound in the open ocean: but on what, in the clear blue water, do these infusoria subsist? ” Charles Darwin (1845) DOM CO 2 “Basic to the understanding of any ecosystem is knowledge of its food web, through which energy and materials flow. If microorganisms are major consumers in the sea, we need to know what kinds are the metabolically important ones and how they fit into the food web. ” - Lawrence Pomeroy (Bioscience, 1974) 2015 CMORE Agouron Repeta Lecture 2 1

Cycling and composition of marine dissolved organic matter: A primer 1) What is the global distribution of dissolved organic matter? 1) How do we approach an understanding of its cycling and reactivity? 2) What techniques are used to characterize DOM composition? 1) Can we link composition to source and putative sinks? 2015 CMORE Agouron Repeta Lecture 2 2

Typical profile of dissolved organic carbon in the ocean TOC (µM) Often measured as TOC Surface values typically 60 -80 µM Deep water values @ 35 -40 µM (implies some unknown feedback/ control of DOC values) Global inventory about 680 GT C 2015 CMORE Agouron Repeta Lecture 2 Data from Peltzer and Hayward (1996) DSR 3

Global circulation and the distribution of DOC Hansell et al. Oceanography 2009 2015 CMORE Agouron Repeta Lecture 2 4

Stable carbon (13 C) isotopes suggest a marine source d 13 C (per mil) Carbon Dioxide Particulate Organic Carbon (POC) Dissolved Organic Carbon (DOC) Druffel et al. , 1992 2015 CMORE Agouron Repeta Lecture 2 5

Mc. Nichol and Aluwihare 2007 2015 CMORE Agouron Repeta Lecture 2 6

Hansell et al. Oceanography 2009 (Inorganic carbon radiocarbon value) 2015 CMORE Agouron Repeta Lecture 2 7

DOC cycling via DO 14 C UV photooxidation Depth 14 C(‰) Age 1880 m -351 ‰ -3470+330 ybp 1920 m -341 ‰ -3350+300 ybp Williams, Oeschger, and Kinney; Nature v 224 (1969) 2015 CMORE Agouron Repeta Lecture 2 8

Radiocarbon in the Atlantic and Pacific Oceans Peter M. Williams and Ellen Druffel; Nature 1987, JGR 1992 Pacific suspended POC Pacific sinking POC Sargasso suspended POC 2015 CMORE Agouron Repeta Lecture 2 9

Radiocarbon in the Atlantic and Pacific Oceans DIC 14 C in surface waters of the Atlantic and Pacific have similar isotopic values. DOC is always older than DIC (by 2 -3 kyrs in surface water) DIC POC DOC Pacific suspended POC Pacific sinking POC Sargasso suspended POC 2015 CMORE Agouron Repeta Lecture 2 10

Radiocarbon in the Atlantic and Pacific Oceans DIC 14 C in surface waters of the Atlantic and Pacific have similar isotopic values. DOC is always older than DIC (by 2 -3 kyrs in surface water) 14 C of DIC and DOC is about the same in the deep Atlantic and Pacific suspended POC Pacific sinking POC Sargasso suspended POC 2015 CMORE Agouron Repeta Lecture 2 11

Radiocarbon based models of DOC cycling in the water column DIC POC DOC [DOC]z(C 14)z = [Deep](C 14)D+ [Z-Deep](C 14)DIC Atlantic surface water 14 C calc = -120 ‰ 14 C obs = -127 ‰ Pacific surface water 14 C calc = -147 ‰ 14 C obs = -148 ‰ 2015 CMORE Agouron Repeta Lecture 2 12

Under this perspective, DOM is produced and rendered recalcitrant by marine microbes. combined with radiocarbon and deep sea DOC gradients, it suggests no or at best very slow removal of DOM in the deep sea 2015 CMORE Agouron Repeta Lecture 2 13

Southern Ocean DOC-14 data suggests this model cannot be correct. Druffel and Bauer, 2000 GRL 2015 CMORE Agouron Repeta Lecture 2 14

Very rapid degradation of DOC in the Mediterranean Sea. If DOC is refractory, why does this happen? Depth (m) Santinelli et al. 2010. DSR LIW 40 m. M 34 m. M C. Sanitelli et al. 2013 2015 CMORE Agouron Repeta Lecture 2 15

Alternative models for DOC cycling in the deep sea 2015 CMORE Agouron Repeta Lecture 2 16

So what is DOC? 2015 CMORE Agouron Repeta Lecture 2 17

Dissolved Organic Matter Composition – The Problem Salt DOC 2015 CMORE Agouron Repeta Lecture 2 18

Cross or tangential flow filtration, Ultra- or nanofiltration Separation based on size 1 nm pore @ 1 k. D Selects for larger size (High Molecular Weight) fraction About 30 -35% TOC (now up to 60% using electrically assisted UF) Membrane effects what is collected 2015 CMORE Agouron Repeta Lecture 2 19

Ultrafiltration of high molecular weight DOM (HMWDOM) >1000 D DOM fraction < 1000 D DOM fraction 2015 CMORE Agouron Repeta Lecture 2 20

Isolation of DOM by adsorption onto hydrophobic resins Selective chemical Adsorption Seawater (filtered; p. H = 2) 10 -20% of DOC Methanol or Ammonium hydroxide wash 2015 CMORE Agouron Repeta Lecture 2 21

Nuclear Magnetic Resonance Spectroscopy (NMR) Can be tuned to different Nuclei of interest (C, N, P…). Gives information on functional groups which, combined with a knowledge of biochemicals can be used to deduce composition and origin. 2015 CMORE Agouron Repeta Lecture 2 22

13 C Nuclear Magnetic Resonance Spectrum of high molecular weight dissolved organic matter (C/N = 15) Frequency Abundance H-C-OH O=C-O or O=CN O-C-O CH 3 200 150 100 50 2015 CMORE Agouron Repeta Lecture 2 0 23

13 CNMR of plankton tows 13 CNMR of HMWDOM Sargasso Sea (surface) Chemical shift (ppm) Hedges et al GCA 2001 2015 CMORE Agouron Repeta Lecture 2 24

13 CNMR spectra of HMWDOM Sargasso Sea North Pacific Subtropical Gyre 3 m 3 m 2015 CMORE Agouron Repeta Lecture 2 25

13 CNMR Lake Superior (USA) 3 m spectra of HMWDOM North Pacific Subtropical Gyre 3 m 2015 CMORE Agouron Repeta Lecture 2 26

HMWDOM in the deep sea Sargasso Sea North Pacific 3 m 3 m 2500 m 1800 m 2015 CMORE Agouron Repeta Lecture 2 27 5. 17 Slide

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Degradation of DOM by marine microbes Pedler et al. PNAS 2014 2015 CMORE Agouron Repeta Lecture 2 29

Utilization of DOM polysaccharide by Marine microbes using dilution-to-extinction Sosa et al ISME 2015 CMORE Agouron Repeta Lecture 2 30

Isolation of DOM by adsorption onto hydrophobic resins Selective chemical Adsorption Seawater (filtered; p. H = 2) 20 -30% of DOC Methanol or Ammonium hydroxide wash 2015 CMORE Agouron Repeta Lecture 2 31

http: //antoine. frostburg. edu/chem/senese/101/glossary/m. shtml 2015 CMORE Agouron Repeta Lecture 2 32

2015 CMORE Agouron Repeta Lecture 2 33

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Elemental Analysis of DOM in Weddell Seawater Hertkorn 2015 CMORE Agouron Repeta Lecture 2 35

Unusual molecular masses in DOM Surprisingly, there is a population of very low H/C and O/C organic matter 2015 CMORE Agouron Repeta Lecture 2 36

Source-specific studies Different responses to productivity levels in-situ SAR 11 stays consistent Roseobacter and Bacteroidetes prefer high productivity Lability varies on a population scale Alonso-Saez et al AME 2007 Radiolabeled DOC derived from various phytoplankton sources Uptake of substrate by various heterotrophic groups shows connections between specific autotrophic & heterotrophic groups 2015 CMORE Agouron Repeta Lecture 2 Sarmento et al EM 2012 4. 37

Cottrell & Kirchman AEM 2000 2015 CMORE Agouron Repeta Lecture 2 4. 38

Cottrell & Kirchman AEM 2000 2015 CMORE Agouron Repeta Lecture 2 4. 39

Composition, reactivity, flux and distribution of DOM Non-reactive DOM Semi-reactive DOM Very reactive DOM -C-N- HO O -C-N- O O -C-NCH 3 CH 2 O Biopolymers Aliphatic or “Humic” substances (polysaccharides, proteins)* Simple biomolecules Concentration 40 µM Concentration 0 -40 µM (amino acids, sugars)* Inventory = 640 GT C Inventory = 10 -20 GT C Concentration 1 -2 µM 14 C= -400 to -600‰ 14 C= modern (DIC) Inventory = 0. 1 -0. 3 GT C Annual flux = 0. 1 GTC Annual flux = 10’s GT C? 14 C= modern (DIC) * = 80% of cell C, N Annual flux = 10’s GT C? * = 10 -20% of cell C, N 2015 CMORE Agouron Repeta Lecture 2 40 5. 38 Slide

Lecture 2. Summary There is a large vertical gradient in DOC between surface and deep waters. Net production in the euphotic zone, net respiration in the mesopelagic zone. Stable carbon isotopes suggest most DOC originates from marine microbes, but this is not certain, as the isotopic values are open to interpretation. Radiocarbon measurements show that there is “new” DOC in the surface ocean, very “old” DOC at depth. Loss of about 30% of deep DOC between the North Atlantic and the North Pacific, along the path of deep water drift. Studies of chemical composition are handicapped with by our ability to sample DOM is sampled by two techniques, ultrafiltration which is based on the larger molecular size of some DOM relative to water and salt (high molecular weight DOM; HMWDOM) and solid phase extraction (SPE) that relies on chemical adsorption onto a hydrophobic surface. 2015 CMORE Agouron Repeta Lecture 2 41

Lecture 2. Summary Of the ~ 50 -60% of DOM that can be recovered, and therefore characterized. Major techniques used to characterized DOM are nuclear magnetic resonance spectroscopy (NMR) and high resolution mass spectrometry (HR-MS). HMWDOM is largely “new” DOC and has a modern radiocarbon age when purified. HMWDOM is largely carbohydrate with a small amount of protein. HMWDOM carbohydrate has an unusual composition that has not been fully characterized. The source of the carbohydrate is not known. DOM extracted by adsorption onto a solid phase has an old radiocarbon age. So far this is very hard to analyze and characterize. It is clearly a complex mixture of organic matter with a significant amount of aliphatic character. The source of this DOM and the pathways that lead to its formation and removal are not known. 2015 CMORE Agouron Repeta Lecture 2 42

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