Accepted Article This article is protected Allrights bycopyright. reserved. article asdoi:10.1111/gcb.12987

may lead to differences between differences to may lead been through the copyediting, typesetting, which and proofreading process, pagination for publicati accepted This articlehasbeen Article Type:- Research Review Accepted Date:-10-May-2015 Revised Date:-01-May-2015 Received Date:-12-Sep-2014

Takamitsu Ito, School of Earth and Atmospheric Sciences, Georgi Anna Cabre, Department of Earth & Sciences, University of Penns of Department & Earth Anna Cabre, of University Sciences, Adrian B.Burd,Department ofMa Naomi M. Levine, Department ofB Serita Frey, Department of Natural Resources & the &the of Frey,Department Resources Natural Environment, Serita Terrestrial andMarineTerrestrial Perspectiv Hampshire, Durham, NH 03824, ([email protected])USA Atlanta, GA30332, (takUSA California 90089, USA ([email protected]) 19104, ([email protected])USA DegradationPathways this version and the Version thisversionandthe USA ([email protected]) rine Sciences, University of Ge of University Sciences, rine iology, University of Southern on and undergone full peer review buthasnot review undergone full peer on and

es on Modeling OrganicMatter [email protected]) of Record. Please cite this this cite Please of Record. a Institute of Technology, orgia, Athens, GA30602, ylvania, Philadelphia, PA California, Los Angeles, University of New New of University Accepted Article determine the fateof detrital m atmosphere exceed those from fossil fuel combustion. Understand This article is protected Allrights bycopyright. reserved. cycles. The amount of carbon stored in these systems is far gre amountcarbon systems of is these stored cycles. in The role both in terrestrial and (OM)plays amajor Organic matter Abstract Modeling head: Orga Running dioxide (CO Ning Zeng, Department of Atmospheric andOceanic Unive Zeng,Department of Science, Atmospheric Ning Christian Lønborg, Australian Institute of Marine Science, PMB Brandon M. Stephens, Geosciences Research Division, Scripps Ins Research Division, Scripps M.Stephens, Geosciences Brandon Marguerite Mauritz, Center for Ecosystem Science and Society, D Mauritz,Marguerite Society, Science Ecosystem and Center for Matthew Long, Climate and Climate Long, Matthew Global R. Quinn Thomas, Department of Forest Resources Resources Environment Forest and of Department Thomas, R. Quinn University of California, San Di Tom Vanwalleghem, Department of Agronomy, University Cordoba Agronomy, of of Vanwalleghem, Tom Department 2 ) in the atmosphere, fluxes the andannual ) in CO of Sciences, Northern Arizona Uni Virginia Tech, Blacksburg, VA, Research, Boulder, Colorado, USA ([email protected]) Park, MD20742, USA ([email protected]) ([email protected]) nic Matter Degradation Australia ([email protected]) ([email protected]) Australia aterial is important for predic for important aterial is ego, LaJolla, 92093, CA ego, (b USA ([email protected]) ([email protected]) Dynamics Division, National Ce National Division, Dynamics 24061, USA ([email protected]) versity, Flagstaff, AZ 86011, USA

2 from these pools to pools from these the ting effects climate the that ater than that ofcarbon oceanic biogeochemical 3, Townsville QLD4810,MC, titution oftitution Oceanography, ing the processes that [email protected]) epartment of Biological rsity of Maryland, College Maryland, College of rsity nter for Atmospheric al Conservation, , Spain

Accepted Article (oceanic OC) the atmospheric atmospheric OC)CO the (oceanic & Duarte,1995). Globally, detrit enteringmaterial this 56% t of (Table1)with about ecosystems equally almost divided is betweent photosynthesis through (OC) resources and observational cons developing comprehensive models of these representation Accurate and biologica betweenphysical byacomplex interplay regulated Decomposition (mineralization) of detrital pools in both marine under achanging climate. so as to accurately predict how understanding the of develop to critical amechanistic it makes emissions (Ciais et climate depends partly andsystem climate understanding on quantifying coup the simulate to used (ESMs) and decomposition of organic ma feedbacks alters between oftheglobal components syste climate C y This article is protected Allrights bycopyright. reserved. Anthropogenic release of CO Introduction communities would benefit from closer collaboration. both terrestrial in and transformation systems,marine andthat arguethatenvironments. We ther and systems coastal waters to inland through soils, from moves diff the of discussion a include andexamine h systems and marine role and the understanding cycling of the current we highlight factors controlling its transformation have yet to find their w and storage of detrita of processes formulations verysimple utilize typically (ESMs) feedbacks on to willhave change terrestrial terrestrial (60 –75Pgsoils y C -1 ), with both being approximately being both ), with al., 2013). The size o l OM. Recent changes in our view of the n the viewof our in changes l OM. Recent 2 totheatmosphere perturbs th erent mineralization pathways a -1 the large natural flux ofCto ) is comparable to that from the world’s oceans world’s (70 –80Pg that the from to comparable ) is al OC pools arelarger than(s processes andfeedbacks runs a processes the global carbon cycle. Howev 2 tter (OM). Annual global product ling between physical and bioge traints ontheother. The accur reservoir (Table 1). Respiration ofdetrital OC from e is strong commonality between ow this pool of material is rep on the one hand, and the availa hand, the one on and the an order of magnitude larger t f these detrital pool s and fluxes s the magnitude of the atmosphere will bealtered e global carbon (C) cycle and ay into models. In thisreview, oil OC) or comparable to to comparable or OC) oil affecting the mineralization of detrital OMin terrestrial ature ofthis material the and processes regulating them, vailable organic as matter our respective scientific ourrespective scientific acy of Earth System Models he detrital OC pool (Cebrian (Cebrian detrital OC pool he and terrestrial systems is is andterrestrial systems ultimately into open ocean er, Earth System Models m, such as the production as theproduction m, such foul of the tension between the of tension foul l mechanisms (Box 1). errestrial and oceanic resented in ESMs. We We ESMs. in resented ochemical processes in the the mineralization ion of organic carbon carbon organic of ion bility of computational aspects of aspects OM han fossil fuel fuel fossil han Accepted Article This article is protected Allrights bycopyright. reserved. processes transforming non-living OM to CO al., 2013; Cabréetal., 2014). (Duteil etal.,2012; Anaveta accurately predicting spatial an though production, with primary annual global considerable scat and theatmosphere (Ci chemical, andbiological process Herewe ESMs. within processes mineralization of representation developme andmodel microbiology developments detrital of Recent ourwel understanding in OM,as soils (Schmidt etal., 2011) and plant of po decomposition asubstantial represent the materials main OC inputs to soils. Microbial byproducts (exudates and nec and withlitter, roots, root plants, multi-cellular long-lived, systems (Fig. 1). Primary production in terrestrial systems is terrestr to inputs both theOC organisms provide Photosynthetic represented in models differ bet andoceanic OCpools terrestrial (Hedges, 2002), butdifferences in 1). Operationally, OC can be divi a multitude ofpathway Detrital Cinthebiosphere exis Sources &Composition of Detrital Organic Matter community. either drawn from can learnfrom the other, and we communities. We highlight areas of similarity and difference, a methodological and linguistic di are currently represented in mod and soils terrestrial the in both s transforming mater ais etal.,2013). Current ESMs provide r l, 2013;Boppetal., 2013; Moor ts in a variety of chemical and chemical of avariety ts in marine environment, concentra are animportant C source for d temporal patterns of OC stora fferences thatseparate theter ded into dissolved ded dissolved andp into (DOC) es that result in the that in result degradati es ween the terrestrialween the andmarine difficult (See Box 1).difficult Box (See Consequ makerecommenda els. devoteWe attention tobri terminology and methodology nt, providethe opportunity to 2 ial between them and , andthe feedbacks be tions on fruitf -zone exudates providing the e et al.,2013; Todd-Brown et physical forms physical 1),with (Table mainly conducted by relatively mineralization by soil on and oxidation of detrital OC andoxidation detrital on of ently, the OC pools ently, the restrial and marine scientific reas where each community ge and mineralization articulate (POC) pools articulate (POC) pools easonable estimates of ting onhowthese processes rtion of the OM stored in in OM of stored the rtion dging thedistinct romass), produced during communities. ial soils and marine ter, have but difficulties l asadvances in make direct comparison of review the physical, ul approaches that can be approaches that can ul improve the the improve atmospheric C pools (Fig. tween these processes Accepted Article between terrestrial and marine ecosystems, with terrestrial ecosystems, between terrestrial andmarine OM is vital for calculating C stora C calculating vital for is 2013). Understanding the extent towhich chemical detstructure However, the composition of OMd of thecomposition However, lipid/aliphatic andlignin compo o terms in classified broadly is OC of composition The chemical built in to some recent ecosyste al., 2014), thatis notyetthe ca ec be incorporated to into starting is emerging view this While arethe predomina recalcitrance, observations demonstrate that physicochemical and biotic factor OM of soil theformation (Marín-Sp on stabilization and control systems at least, was that the molecular structure of organic m is beingcurrently re-examined divide OC pools based on chemica This article is protected Allrights bycopyright. reserved. andfundamentally a environments (e betweenThe interplay abiotic 2004). turnover times ofdecades to m resembla bearingmaterial little available OC times (secondsreadily with turnover fast years to These compounds are found atvar of (Hedges largebiopolymers 199 mixtures and humics andOades, Chemically, OC inboth Hansell, 2013). Organic C inputst terrestrial systems (~days as opposed to weeks, months or years (phytoplankton), organisms celled Incontrast, primarymicroorganisms. production in marine syste pellets, discarded animal feedin exudates, andmaterial transform systems ranges in size and complexity fr andcomplexity size ranges in systems ge dynamics both on land on andin both ge dynamics se for current Earth system for Earth current m system se (Stockmann etal., 2013). The hi illennia (Baldock etal., 2004; T m models (Wieder al.,2014).et nce thecompounds from which to g structures etc. (Nagata, 2000 unds (Kögel-Knabner, 2002; Whit .g., aggregation) and biotic pr nt controls on C cycling in soi ed byheterotrophic ( organisms o the marine environment main l lability, even though this un this though even lability, l erived production from primary ious stages of degradation, of stages froious leading toafasterleading turnover ffect degradation andmineraliz odels (Table 2), though is it theoceans (Baldock etal., ocesses can differ inthetwo ls (Schmidt etal., 2011). rumbore, 2009; Hansell, )). osystem models (Wieder et aterials aprimary was ) to highly processed ) tohighly processed derstanding of recalcitrance time of biomass than seen in seenin than biomass of time iotta, 2014). However, new

f polysaccharide, protein, storical view, interrestrial om simple monomers to inputs inputs a larger containing m recently-deposited, recently-deposited, m ermines the stability of OC s, rather than chemical ratherthan chemical s, ms is is dominatedms bysingle ) (Trumbore, 2009; ly include cells and their andtheir ly include cells e.g. zooplankton fecal itwas derived, having ehead etal. 2008). ation rates. Most ESMs 7; Hedges et al.,2000). differs substantially Accepted Article This article is protected Allrights bycopyright. reserved. Grandy &Neff,2008). In the majority ofwhich are prefer Primary producers in both ecosystems are enriched in labile sug protein-rich material (Nelson of fraction carbohydrate-rich structural components, whereas ma with depth. The average radiocar gen and in datingshows OC oceans that, soils of in Radiocarbon Transformations Processesand Mineralization: thousands of years. degrada those with to of with residence minutes times compounds time scal these though turnover on OC scales, those controlling years (Bauer etal.,1992; Schmi (deep soil OM, marine sediments, 2011, Dungait etal., 2012). Thed availabi and nutrient structure, composition and factors such as temperature, physical accessibi interplay andare betweenthe bythe controlled and time depth terrestrial andmarin in compounds organic rates of Degradation the watercolumn (Benner, fatty relat polyunsaturated acids OC in both soils and marine both syst soils in OC soils to to3000yearsup in tem deep, ages the of Similarly, of component f stable soils varies nature takes on chemical recalcitrant the oceans atruly in DOC Oceans ranges from 4000 – 6000ye the average residence times, det (Boudreau andRuddick, 1991,Vähä a which of themajority species, consist thepool However, OC kinetics. order first using models marine environments 2002; Wakeham etal., 1997). & Baldock, 2005; Arrigo, 2005;Wh lity (Healet al., 1997; Jobbag perate soils (Hsieh, 1996). Mic re uncharacterized de which and dt etal., 2011), suggesting si entially mineralized by microor ems, altering the chemical comp ermined by radiocarbon dating, dating, byradiocarbon ermined ive tosuspended OM andtends egradation pattern ofdetrita bon age of deep ocean DOC in th ageof in deepoceanbon DOC deep oceanic DOC)deep t oceanic areallon talo etal, 2010). Although res ars (Bauer etal., 1992),sugg , sinking OM isenr milarities in the factors y &Jackson,2000; Kujawinski, rom a few centuries in tropical robes rapidly degrade labile labile degrade rapidly robes l OC is often described in s of many distinct molecular es es averages, combiningare (Kujawinski, 2011). eral, theage of ganisms (Benner, 2002; he scale of thousands of lity, microbial community OC biochemical biochemical OC osition of the OC and grade atdifferent rates esting thattheesting of majority ars, starches andproteins, to berapidly degradedin of the largest the pools OC of itehead et al., 2008). e systems decrease with iched in amino acids and acids amino in iched idence times of OC vary, OC of times idence e Atlantic and Pacific ande Atlantic Pacific rine OM contains more tion timescales of tion timescales OC increases increases OC Accepted Article physical protection (Kleber, microbial ecology, diffusion limitations, enzyme kinetics, envi bebetterviewedas a “logisti OMin might of soils degradation led has (Fig. surfaces 1).This mineral to OMbinding areas of an important control on lateral fluxes on through role control OC in an important their comprised primarily of mineral p regardless of presumed chemical recalcitrance (Marín-Spiotta et (Ekschmitt etal., 2005;F conditions (Schmidt et al., 2011) orenergy limitation ofthem a Knabner etal.,2008) protected by or within physically being min to bybinding likely more be stabilized to is (SOC) OC Soil This article is protected Allrights bycopyright. reserved. soils (Marschner et al., 2008; S not th recalcitrance is chemical ocean is alteration intoa chemi Whereas there is some evidence t (Hertkorn etal.,2006). structure to be predominantly microbial derived carboxylic-rich Benner, 2012).Further, studies o substrateimportant for microbes dissolved sug these that decreases with depth indicating DOC in Kögel-Knabner, 2003; Schmidt et produceexample, microbes polysa (Grandy 20 depth OC &Neff, ageandwith with which increase of leaving a mixture ofless labile releasing CO warming event whereotherwise re feedbacks. This is currently hypothesized to have occurred duri pools C vulnerabledegradatio to long-lived maymake conditions provide stability to OC in either system, then changes in bioti 2 into the atmosphere andraising the atmosphere into ontaine etal.,2007) 2010; Stockmann etal., 2013).Mor material and microbial-derived chmidt, etal., 2011). If chemi e primary process that process stabiliz e primary cally recalcitrant form, there f deep ocean DOM suggest the p articles, provide regions of ph thedeep in ocean, albeit atv hat the dominant stabil process al., 2011). Inthe oceans, the ccharides that, in soils canpe calcitrant pools DOC marine of

permits, evenold SOC turn overcan rapidly global temperatures (Sexton et temperatures (Sexton global cal recalcitrance not does is increasing evidence that c communities and climate to the suggestion that that thesuggestion to eral complexes (Kögel- ronmental factors, and es onlongC scales time in icrobial community transport bywater selective cal problem” involving proportion of carbohydrates compounds, the proportions ery low rates (Kaiser & ggregates, and if climatic ysical protection forOMand eover, soil aggregates exert ng an Eocene ng anEocene global ars can serve as an rsist for decades (Kiem & alicyclic molecules al,2014). Soil aggregates, 08; Jiao etal, 2010). For redominant biomolecular redominant biomolecular n andthus result climate in izing DOM in the deep were mineralized, 2011).al., Accepted Article to inorganic forms (e.g.CO forms inorganic to detrital therateof degr penetration. OC Sunlight alters light ecosystems, though it ecosystems, may bemor Photodegradation also contributes to OC decomposition in marine explain changes in SOC mineraliz Environmental drivers can affect (Hansell, 2013). surface-derived semi-labile OMp marine environment, seasonal water column stratification and/or stratification environment, watercolumn seasonal marine that dr processes help byaffecting physical or mineralization, Reinthaler, 2013). The stability the rates atwhich organisms can the mineralization of nowa this systems, becomes material soil may also provide physical prot mineralized. being without Calci 2011). Diffusion limitation ofC OM to limit m beensuggested also has diffusionlow, limitation composition (Kujawinski, 2011). Carlson etal.,1994), as can mac transport awayfrom re This article is protected Allrights bycopyright. reserved. individual particles caught upi feeding structures. The effect o fecal pellets, bein of formation through bythe or aggregation, components (e.g.algalcells, fe aggregates, mari soil to contrast viewed interms ofreducing the d slightly is aggregatessystems in role of marine erosion. The OC chemical composition (Rozem species (ROS) changing degrader gions of origin can alter mineralization 2 ) andindirectly bypr cal pellets etc.) brought toget ection (Hedges etal., 2001; Arms n theaggregate, allowing it to f aggregation is to increase th within soils has also beensug of deep ocean DOC makes the pa ronutrient availability andmi ne aggregates areprimarily co exposure of OC to to OC of heterotrophic exposure um carbonate and um carbonate mineralization rates byeither findandproces ation when dry soils arewetted drysoils when ation ool, andadeep recalcitrant OM In the deepocean where OM conc a etal., 1997; Searles et al., 2 and primary producer communitie e important in the former becau theformer in e important oducing free radicals andreactive oxygen s these sinking biogenic silic biogenic her through physical adation directly by oxidizing it e settling velocity velocity e settling the of travel deeper into theocean gested as a mechanism to g trapped on discarded crobial community ifferent, but ifferent, but be can also ive mineralization. In the 001; etal.,Xue 2005; King et mposed of biological ineralization (Kattneret al, times of oceanic OM(e.g. forming physical barriers to barriers physical forming logistical problem involving particles (Herndl particles and trong et al., 2002). Aswith a, parts of many algal cells, rtitioning of DOM into a of into DOM rtitioning pool of particular interest interest particular of pool microbial communities. In communities. microbial (Xiang et al., 2008). horizontal and vertical se ofthe greater depth of andterrestrial entrations aregenerally s, andalterings, detrital

Accepted Article The OM The a of mineralization exchang the is component in critical Representing Respiration/Mineralization inGlobal Models substantial OC losses from leaf ecosystems, but recent work suggests that similar effects of UV exchange (Anavetal.,2013). How and, to a lesser extent,and, toalesser hemisph cycle and Earth’s climate. In ge OCdetrital andtheprocesses affecting them importantis forp atmosphere, the land,and oceans Gt CO In marine systems, direct photo-oxidation of OC to inorganic C (Scully etal.,2003; an decomposition bycompeting for microbial substrates decrease microbial decomposition (Moran & This article is protected Allrights bycopyright. reserved. increase decomposition rates(Se versus terrestrially derived O rates documentedof the photo-oxidation differencesclearly in al., 2012). The best-documented e (CMIP5) ranged from 510 to 3040 example, SOC predictedstocks bythelatest Climate Model Inter influence projections of future carbon-climate feedbacks (Todd- the global distribution of existing OC stocks is highly variabl regions. In comparison, current SOC stocks based on soil databa on based soil stocks SOC current Incomparison, regions. condensation of OMinto materials recalcitrant of condensation decomposers (Sepp etal., 2011). bleached anddegraded, providing absorbing wavelengths,UV such a through the water column, itpro 2 annually, and indirect photo-oxidation produces an additional produces photo-oxidation andindirect annually, Lesser, 2006). M (Obernosterer and Benner, 2004) neral, current ESMs neral, current ESMs are ableto litter (King et al.,2012) and eric patterns atmosphere-laneric of duces free radicals ROStha and Sunlight alsocan induce biolo pp etal.,2011). Organic carbo . Consequently, being able toa ever, the ability of these mod ffects come from aquatic ecosy s chromophoric dissolved organi a large influx of alarge of bioavailable influx Pg Cglobally and from60 to34 Zepp, 1997). No global estimat

(Harvey etal.,1983, etMopper al,2015)and soil (Rutledge et al., 2010). e, and this variability could could variability e, andthis reasonably reproduce global redictions theof globalC OC to microbial to OC microbial produces anestimated 12-16 radiation account for for account radiation gical polymerization and els to accurately represent of aquatically-derivedof OM d andatmosphere-ocean CO n compounds capable of of capable n compounds ccurately model thepools of e ofCO -comparison Project ses are estimated tobe Brown etal., 2013). For t destabilize andcan OC stems, where are there stems, . As UV penetrates 0 Pg C in circumpolar circumpolar in 0 PgC d causing oxidative stress es exist for exist terrestrial es c matter (CDOM), are matterc (CDOM), 1 GtC 2 between the

available to to available 2

Accepted Article thermodynamic constraints of carbonate chemistry CO on corresponding land-atmosphere flu 2013; Jiang etal.,2014), and unde Most CMIP5 models reproducepools. o the failto of seasonality context of simulated marine primary productivity andfluxes of This article is protected Allrights bycopyright. reserved. variability in CMIP5 predictions for ocean-atmosphere CO the fluxesGenerally, climate for ocean C report realms models Brown etal.,2013). 1260 Pg Cglobally with an addition primary productionprimary (e. estimates include multiple nutri including temperature, light, an functio multiplicative a as parameterized usually is production patterns and thepatterns magnitude ofpri phytoplanktonseparate intomult traced in part to how OM pools an The differences between terrestri phytoplankton (Cabré etal., 2014). largelayer, as phytoplankton si Moore etal., 2013; Cabré al et turnover time), and a passive OC pool that is stable stable longer on thatis OC andapassive pool time), turnover physically or that chemically is pool OC,aslow soil degrading biomass and rapi live pool that includes active microbial fast, based on soil properties and predefined turnover times (Dungait two widelyused soil OC models, (terrestrial), and content oxyge ratesMineralization used of are te functions models in atbest explici being than are used, with processes being parameterized using semi-empiric tly represented. ent limitations (nitrate,ent limitations phosphate, and , 2014). Typically n content (marin n content nk faster andare more likelyt d a limiting nutrient. The most The nutrient. d alimiting CENTURY and RothC, partition OC g. Moore et al2002b, Cabré et al and marine model results an mary productionmary and exportof iple size types, usually small d degradation processes are re restimate oceanic primary pr al 500Pg Cin circumpolar p x (Anav etal.,2013), which i , only veryco e), and atwors 2 2 flux. Models Models diverge flux. the more in flux is smaller than for the the than smaller for is flux arse classifications of OC pools dly yearturnover) (1-5 protected (20-40 year o form aggregates than small time scales (200-1500 years) iron) which typically improve mperature, soil moisture advanced ecological routines and large, affecting the rather than stocks. The n of limiting factors, t a constant. Forexample, oduction. Primary cean production (Anavetal., al, 2014). Some models OC into various OC into detrital ermafrost soils (Todd- s due in part to the strong due the partto s in d observations canbe al., 2012)et (Table2):a presented (e.g. in ESMs OM out of the euphotic theOM out of euphotic al relationships rather into discrete pools

Accepted Article 1983; Enriquez etal., 1993), usin of explain OMcan ratios C:N:P et al.,2000; Kaiser &Benner, com in chemical similarity greater a suggesting systems, marine DOMsimilarly deplet However, is average C:N:P ratio of changes incarbon and (e.g. lignin) andasi of alargercomponent terrestrialC- POMhas because ecosystems Sarmiento, 1994). Acorrespondin carbon, ratios of (atomic ratios followmodels a element (usuallysingle nitrogen or phosphorus) wellrepresented not inmodels. material this of is complexity number alimited With such ofde translatelaws into different depths. mineralization atmosphere for longer for timescales atmosphere asoceanic sequestration, deeperC tend watermasses be out to OC that mineralizes at shallower depths. The depth of mineraliz silicate frustules) that mineral (Armstrong etal.,2002): arapidl CESM1(BGC) uses two classes of sinking POC based on the commonl functions combination of these h depth, flux with POC in fit observed changes to beenused have only particul consider the pools though (POC), particulate some This article is protected Allrights bycopyright. reserved. power law(Kriest andOschlies whereas if sinking speed increas depth former the (Table 2).Inthe with case, flux of decre POC e is speed that a POC sinking with ratecombined mineralization mineralization rate. Most CMIP5 marine biogeochemical models us assig lability, according their to thesepools models subdivide (Parton etal.,1987). Marine mod gnificantly wider rang 106:16:1, though many nitrogen. Particulate organic matter int 2012; Lønborg &Álvarez-Salgado, izes deeper thewaterin column >80% thevariance of minerali in nitrogen, and phosphorus) to c to andphosphorus) nitrogen, , 2008). Both simple exponential es linearly with depth, POC depth,flu es POC linearly with ave also been used (Marsay et a y sinking class associated wi associated class y sinking g constant stoichiometric rat els typically divide detrital trital OM pools, it trital withou OMpools, it goes . Forexample, the commonly use ed in nitrogen and phosphorus i nitrogen andphosphorus ed in g benchmark ratio isless appli e ofnutrient ratio use a use rati revised s (Sterner &Elser, 2002). OM dissolvedinto and th ballast mineral (e.g.diatom ning each sub-pool a fixed afixed sub-pool each ning Many marine biogeochemical ases with depth exponentially, ios in models is problematic alculate corresponding , andnon-mineral associated he globalocean an has x decreases according to a though more sophisticated though more sophisticated o of117:16:1 (Anderson & t saying that the chemical thatthet chemical saying zation rates (Coleman etal., of contact with the ate pool(Table 2012). Although initial initial 2012). Although ation is a key control on on akey is ation control ither constant orincreases position than for POM(Neff and power-law functions and power-law functions l., 2014). For example, cable to terrestrial and use stoichiometric anduse stoichiometric rich structural compounds compounds structural rich n both terrestrial and terrestrial n both d exponential and power andpower d exponential e a constant POC y used ballast model 2), andsome Accepted Article suggests aglobal convergence onQ 2013). It isunclear whether using asingle global Q increase in arate following a10°C rise in temperature) and soil moisture (Todd-Brown etal., mineralization rates for sinking OC (Moore etal., 2006),(Moore OC which rates for sinking mineralization For the marine components of ESMs it is important to accurately mineralization at agiven low oxygen threshold (Maier-Reimer etal., 2005) (Table 2). processes mineralization regimes inlow oxygen zones, asmost models shift from oxic to anoxic oceans are predicted to change underawarming climate, and this will affect heterotrophic production distributions (Taucher & Oschlies, 2011). Dissolved oxygen concentrations in the modest change in C export from thesurface to the deep ocean, but shifted nutrient andprimary rates into the Max Planck Institut Earth System Model (MPI-ESM) using Q (4°C) temperatures (Iversen & Ploug, 2013). Incorporating temperature dependent degradation decrease inC-specific respiration rates when changing from average surface (15°C) todeep ocean mineralization rates (Table 2). Temperature effects have been shown to produce a 3.5-fold In contrast, not all existing global ocean C cycle models incorporate temperature dependent Weintraub, 2003). realistic when substrates are highly abundant, a condition that is rare in nature (Schimel & order degradation functions that represent temperature responses and enzyme kinetics are only (Giardina & Ryan, 2000; Davidson et al., 2006; Isse & Moorcroft, 2006). In addition, the first enzymekinetics, microbial community dynamics, and SOC stabilization respond to temperature understanding of the conditions under which temperature is the main rate-limiting factor, and how Despite the potential convergence of temperature sensitivity, wehave an incomplete This article is protected Allrights bycopyright. reserved. degradation rates based on temperature sensitivity (using asingle temperature factor Q is crucial tomaking accurate predictions of the global C cycle. Models of SOC typically employ Accurately modeling howrates ofOM degradati 2004). tends tooccur interrestrial s tends increase to systems, o C:N:P ratios marine mineralization because the ratios change due to ystems (Blair, 1988; Adams &Ang preferential mineralization (P 10 =1.4 for terrestrial ecosystems (Mahecha et al., 2010). on might change under future climate scenarios 10 value isrealistic, althoughrecent evidence affectcan atmospheric CO aulmeier etal., 2000).In radi, 1996; Badcock etal., f POM, whereas the opposite opposite the f POM, whereas predict depth-dependent 10 =2 produced a 10 ; the 2

Accepted Article terrestrial and terrestrial waterinland sink 2013) andalso combine terrestrial atmospheric inversion methods represent processes on continenta terrestrial and waterinland C increase is subtracted from the sum of fossil fuel and land use This article is protected Allrights bycopyright. reserved. deep ocean, affecting the profil resulting mesopelagic undere the in mineralization in of amount concentrations (Kwon etal.,2009) the degree of oxygen depletion. D thermocline anddeep of alterretention also waters biolcan of (Moore et al.,zones 2013). Uncertainti minimum observed oxygen biogeochemical models show littl Depth dependence been s also has Depth etal., (Duteil observations 2012; etal., Bopp with consistent biologically sequestered nutrien example to calculate theland C 2). However, models and C budget andu rivers, lakes, streams, within “downstream” or deposited, derivedTerrestrially OC can bem Mineralization from terrestrial to marine systems al, 2013). dynamics compared well with site-level comparisons of soil radi realis more with biogeochemistry soil depth-resolved with model 2007) anddeep-rooting plants can large po can SOM contain soils be not correct. Subsurface might plays deep in layersthe cy a negligible role of SOM C soils in layerbox single afix model and of heatand transport moisture i etal.,2013).(Koven include models avertically soil Although sinks (e.g. LeQuéré et al.,201 es ofes dissolved inorganic C, an sink, the sum of the uptaocean ed profile of SOM. The assumpti ofed profile The SOM. n soils, soil biogeochemistry i ts, eventhough total nutrient s. However, global budgets tha e agreement in terms of their o their of terms in agreement e ue tothese uncertainties, the ineralized within the soil whe hown to be important in models models in be important to hown s oftens treatthe fate ofthis . For example, the CESM1(BGC) CandNdeepinput intothe s and waterinland Csinks. ES 4). Carbonsinks inferred from cling. However, this assumption 2013). d contributes d contributes to than larger resolved submodel for the for submodel resolved s s usually dealt with using a emissions and combines the the and combines emissions material differently. For inventories are relatively ogically sequestered Cand CMIP5 marine ke andatmospheric CO t are ableto include more on in this approach is that that is approach this in on re it producedis and ols (Baisden and Parfitt, ltimately, the oceans (Figure Ms also implicitly combine oils. from Results aglobal ocarbon profiles (Koven et et (Koven profiles ocarbon stimates of OM fluxes to the xygen content and xygen content tic twentieth century C C century twentieth tic overestimates the overestimates es in the ventilation rates rates theventilation in es l scales (Peylin etal., of soil biogeochemistry biogeochemistry soil of 2

Accepted Article CO conditio sustaining OC terrestrial input with of mineralization andrivers streams communities within thetransport also impact etal., 2008; protected(Hilton and OC Yoon of bioavailability Moore, 2006;Monteith etal.,200 area (Evans contribution major that catchment soils consensus and whilst the mechanisms leading to this increase remain unkno DOC concentr that indicated have exported annually Sweden’sinto lakes andrivers (Weyhenmeyer e Swedenrivers in estimates a of that 0.03–0.87%minimum the of (Seitzinger etal., 2010;Laudon fu arenot transformations these occur which through mechanisms so that are with that a well-mixed contact sediments in so water column for understanding of thecycling v that the in like the lakes oceans actsense, more In this OC. input (0.45PgCyr input amount appro ocean to coastal of terrestrial the OC inputs into the coastal ocean (Battin et a extreme precipitation events tha waters is spatially and tempora temperature (Ludwig et al, 1996), to of OC the inland factors water soil transport Several impact 2011). allow additional transformaalso (Cowan etal., 2002). Thus, inland This article is protected Allrights bycopyright. reserved. Approximately 1.9Pg Cyr C sinks (e.g. Ciai processes use a variety of metho Lakes, ponds, andimpoundments a transformed, stored, ortranspor 2 supersaturation found in most inland waters (Raymond etal., inland 2 most found in supersaturation s etal., 2013). -1 ) (Bauer etal.,2013), with appr -1 of total soil C finds its way into inland waters where it is waters is waywhere inland its it finds into C soil total of l., 2008; Regnier etal., 2013;B lly variable. However amo lly variable. exact et al,2012). Acomprehensive OC.Most lakes are ands small tion and storage along the way tion along andstorage the ds toexplicitly separate outt ted downstream such that only~ t act to physically disrupt soi disrupt to physically t act 7). Erosion canplay asignifi waters notonlytransportte ations generallyare increasing so thatthe amount ofsoil-de re efficient at retaining sedim retaining at efficient re oximately 60% theformin ofD auer etal.,2013). Riverine ertical dimension is important Raymond, 2012).Raymond, Microbial cant role, particularly during cant l aggregates and increase the he terrestrial and inlandwater s, including basin slope and basinslope s, including study of boreal lakes and ns ofns netheterotrophy and rrestrially derived OM,but hallow (Downing etal.,2006) ximately half of the total C C half total ofximately the rived OC entering inland (Battin etal., 2008; Bianchi unts and precise unts and precise et al., 2005; Rouletand over time in time over in waters, inland , conditions that favour favour that , conditions ents, allowing forburialof of soil derived soil through OC of surface SOC pool is wn, there is general 0.9 Pg C yr 0.9 PgC lly understood t al, 2012). Otherstudies 013). -1 is input into OC OC Accepted Article al., 2008). Similar gradients wi ( present material theorganic of composition chemical changing communities have been observed to resuspended, potentially alterin have consequences for models. Smaller particles will also settl be as high as 0.53 Pg C yr 0.53 PgC as high be as sedimentation fluxes sedimentation DOCof thro et al.,2013). Asinthe oceans, (Cole etal., 2007; Battinet a Amazon river basin alone beenestimated alone basin river Amazon has at0.5 yr Pg C Pg of OC, with estimates 0 rates with ranging OC, of from Pg of storage global et al., 2009), which can be compared with 0.2 Pg C yr with be 0.2PgC et al.,2009), compared can which indicates that indicates ofthe CO most Estimates ofEstimates globalCO shallow-water ecotypes (e.g. Ivars-Martinez etal., 2008). living large on for adaptation p example, For deep-water ecotypes organism. of same large particles will bedeposited gravitationally settle beaf OC Particulate will also these waters. within communities beadvected OC bythe and will water flow Dissolved components. and par dissolved both waters in Soil andtheoceans. in transport ofsoils vertical role the on Lateral transport ofOC is impor affect regional Cbudgets. th that affect practices landuse in that changes suggests This theatmosphere to being lost 1.2–2.2% netprimary of production This article is protected Allrights bycopyright. reserved. mineralization ofOC burial over CO streams (Raymond etal recentof larger estimates from the valuesmore arising higher 2

(Wachenfeldt and Tranvik, 2008). (Hu and Kuhn,2014). 2 outgassing from streams and rivers vary from 0.5 and streams from yr –1.8PgC rivers outgassing ., 2013). Outgassing ofCO -1 (Tranviketal.,2009) and lake l., 2009;Aufdenkampe al.,20 et 2 evadedfrom theselakes arrives flocculation can be important flocculation canbeimportant th depth are seen theocean,in articles and degrading more rec anddegradingarticles more tant instreams and rivers, and close to the region the the to close where g the residence time ofOCint in the sediments. Globally, CO sediments. the in ticulate forms and transport ra andtransport forms ticulate ugh flocculation canbesimilar flocculation ugh change as one as one downstrea moves change A study of20 lakes in theEng There are several c 2 from the rivers and wetlands of the andwetlands the rivers from of -1 Alteromonas macleodii Alteromonas for burial in marine sediments (Ciais sediments store an estimated 8 -1 OM finds its way into inland 11; Raymondet al, 2013),with in boreal lakes where , anorderofmagnitude greater e mobilization of SOMcan even among ecotypes ofthe y were mobilized and this can can andthis y weremobilized he system. Stream microbial microbial Stream he system. from streams and rivers, with e, but can be readily bereadily can e, but .03 to0.07 Pg C yr 2 onsequences of this. Firstly, can be thought of as taking as of bethought can role oftemperate rivers and alcitrant compounds that fected by the ability to emissions from lakes could emissions tes differ forthese two to the flux of outgassing flux the of to outgassing Winter etal, 2007; Battinet (Maberly et al.,2012). acted upon by microbial acted upon bymicrobial lish Lake District m, adapting to the adapting the to m, show greater greater show -1 (Tranvik (Tranvik -1

20 Accepted Article CO Pg C yr Pg C Inland waters transport terrestri 2012). residence times (e.g. slower ru transported material as selectively is lost this DOC is this of increased (e.g. become evident lateral has the it inputdecade, that DO soil of exceed the microbial mineralizat increased propensity for photochemical oxidation which in some Another change to the potential terrestrial origin. of theCoutgassed bythe rivers int from soils of DOC export basin, Amazon River the comprising e (Raymond of besignificant terrestrial could SOM contribution uncertain; however, the higher r combined tidal wetland this Csees different environmen efficiency ofparticulate materi result exchangew the of is Some aggregation andsinking of clays 2013). Partof this is theresult a (estuaries deposited coastal sediments in then is C inorganic by the highly productive tidal productive and wetlands, respired highly is (about by the equal amount of inorganic C (Bau estuaries onto the coastal the coastal andapproximately 0.3onto Pgyr shelf estuaries This article is protected Allrights bycopyright. reserved. contribution that respiration of soil OM makes to riverine outg etal., 2 oceans (Richey the to by the Amazon OC of export than fresh, through brackish, to saline. At the high salinity high end, s At the to saline. brackish, through fresh, Coastal systems are dynamic and complex environments with water 2 and methane production. production. andmethane -1 of total OC being carried by rivers into estuaries, along with along estuaries, into byrivers carried being OC total of Evans etal. 2005;Monteit s and estuaries). Appr the of increased ionic streng nning rivers) result inagreate result rivers) nning al. This re-deployment ofterre (Richey etal,2002), and80% minerals andtheOC associated for mineralization of soil OMi ates found in low order low ates found streams in ts where differencests where in mineral ith tidal wetlandsith wherevegeta ion of soil-derived OC (Cory et (Cory soil-derived OC of ion ally derived OC to wat coastal er etal.,2013). This carbon c h.et al.2007). Inad oximately 0.5PgC y alt marshes and mangrove th of seawater allowing for rapid to thecoasts such that longer -1 dition, the coloured component of OC and0.15Pgyr OC of r loss (Weyhenmeyerr loss etal, C into inland waters has inlandC into waters strial-derived POC that means of the CO the of n inland waters is the n inland waters is nd shelf) (Reigner etal. ombines with that produced produced that with ombines 0.35 yr PgC 002). The precise ers with approximately 0.45 assing of CO of assing al.2014). Over thelast ization processes can affect t al, 2013). For rivers with them (e.g. Dyer1985). tion trapping increases the suggests that the o rivers accounts for 15% for accounts rivers o r lakes has been shown to -1 is transported from salinity varying from anapproximately 2 outgassed is of of is outgassed 2 -1 remains highly highly remains from the from -1 of of Accepted Article significant improvement over current models. Traditional soil andmarine models implicitly Explicitly incorporatingmicrobial populations and dynamics into ESMs could provide a Improving mineralization inESMs. and long DOC DOCterrestrial concentrations marine residence ti terrestrial plants (Hernes et al (Stubbins al,2010),et and bacter can transform thearomatic fract material anareais ofactive re c at low surprisingly occurs DOC region exported or shelf tocoastal o is the estuaries, and the compared with other wetland ecos C content of estuarine wetlands leads to a C sequestration rate i these systems in sequestration estuaries (Cai, 2011; Regnier e limited available on t wetlands data,coastal areBased thought on impact a have significant will methane outof the sediments (We This article is protected Allrights bycopyright. reserved. yr atleast C 44.6Tg swamps sequester decomposition of OM, increasing rates of sulphate reduction and 2002). Similarly, saltwater intru iron-redu bystimulating sediments marsh salt in mineralization Bioturbation by plant roots and seawater,an import reduction in sulphate component is sulphate mineralization occurs under anoxic conditions (Howarth, 1993). se thesurface rapidly quite in utilized is oxygen saltmarshes, affect C mineralizat processes andbiological physical Multiple Mcleod etal.,2011). vegetated coastal frequently in sequestered system is referred search. Photochemical reactions ., 2003). Such reaction pathway t al.2013; Bauer etal., 2013). s highly efficient; the high se thehigh efficient; highly s sion intidal freshwater marsh invertebrates (e.g. crabs)affe coastal wetlands and their se oncentrations in the open ocean ion of terrestrial DOC into terrestrial DOC into mor of ion ia found ia found shelf in arewaters ston etal., 2011). These resul ystem on an areal basis (Bridgh

-1 globally (Chmura etal., 2003). Carbon C This either settles inthe pen ocean. Terrestrial-derived dimentation ratesdimentation soil and high diments, sothat OM diments, most able todegrade cts the pathways of OC questration of of questration C. s may helptoexplains thelow ion incoastal marshes. In es es stimulates microbial s that are that s 10-fold higher inthe surface shelf waters o be a net source of be anetsource of o to C to as “blue carbon” (e.g. e stable components ts indicate that sealevel rise cing bacteria (Kostka et al., flux rates flux rates of CO s, fate s, this the and of mes. Because of the high the high of Because ant microbial process. am etal., 2006). Carbon lignins fromlignins 2 and Accepted Article global scale processes. For exam but adequately not c models are typically global represented in response to hot spots and/or hot moments) to regional scales (e resolution is important because crucial processes occur at the considerable attention within the modeling community over the l the availability ofrepresentati from uncertainties arising from two major issues: (1) scaling a with process associated representa uncertainties to In addition models, the results from whichcould inform ESMs through newparameterizations. seen in recent years could provide detailed genomic and transcriptomic information for single-cell can informmore traditional ESMs.For example, the rapid development of “omic” techniques more computationally intensive techniques with amore focused scope may provide insights than a common platform for the terrestrial and marine modeling communities. Results from novel, issue. For example, trait-based models (Follows & Dutkiewicz, 2011;Allison 2012) complexity of these models. However, developments in modeling techniques may alleviate this (Wider et al., 2013). Explicitly incorporating microbial dynamics intoESMs will increase the SOC, showgreater agreement with actual observations ofsoil Cpools than models without them microbial processes inESMs using Michaelis-Menton kinetics to represent their interactions with more parameters (Manzoni and Porporato, 2009). Yet, initial attempts to explicitly represent soil accurate than simple models, possibly because greater mechanistic accuracy is needed, rather than has improved predictions of OCcycling, but at larger scales complex models are often nomore 2010). At small spatial and short temporal scales, explicit representation of microbial populations functions change with depth inboth the ocean and in soils (Fierer et al., 2003; Robinson et al., and so cannot be used to address questions related to changes i related questions changes to to beused address cannot and so parameterizations and I scaling. Bernard etal,2011) for systems,shelf estuarine but processes resolution eddy resolving models transformation of OC to the coastal shelves are not currently i This article is protected Allrights bycopyright. reserved. to be impacted by climate (Allison et al., 2010; Frey et al.,2013) environment. However, in both systems, theefficiency ofmicrobial processes have been shown 2). This assumes that the microbes are effectively not responding oradapting tochanges in their include microbial populations anduse first-order kinetics to represent OMmineralization (Table ve measurements. The scaling is Thescaling ve measurements. ple, estuarine and coastal proc coastal and estuarine ple, n addition, these models canno do allow some ofthese process

ncluded in models. High and microbial populations and local (e.g., soil respiration in require sub-grid nd model resolution, and(2) resolution, nd model sue has received received has sue esses such as delivery and an substantially impact tion, global C models suffer n climate. The opposite t be run at the global scale at thet berun scale global .g. ocean upwelling), that es to es (e.g. be captured to ast decade. Model

may provide Accepted Article the flux from soils to to from flux the inland has by0.8PgC soils increased waters respiration and emissions. However, estimates of anthropogenic c be small still would of two flux byafactor this in decrease 2013), which is approximately 3%o OC mineralization vary between soils and aquatic environments. andaquatic environments. vary between mineralization soils OC However, OC mineralize ESMs the within factors soil. affecting There is also aproblem involved doubling thenaturalalmost fl soils to aquatic systems h systems aquatic could to soils This article is protected Allrights bycopyright. reserved. from to OC flux of inland the estimates soils report b water to terms in ESMs would significantly affect model projections. For through watersinland to coastal terrestrial general t do in consider ESMs not The of components 2007). Similar arguments can also be made formarine biogeochemical models. are imprecise and often disrupt more than one stabilizingmechanism atonce (von Lutzow etal., specific soil fractions (Six et al., 2002), and partly because isolation and fractionation methods fractions, have been unsuccessful, partly because the conceptual pools do not correspond to Attempts to experimentally isolate soil OC fractions, which correspond to conceptual model deconstruct and test the mechanisms that produce certain model outputs (Six et al., 2002). to ability the is models OC soil of dynamics internal the verifying for challenges biggest the efficiency, or adsorption-desorption dynamics underlie soil OC-temperature relationships. Oneof focusing onmechanisms thatdistinguish how changes in microbial substrate use, enzyme observational constraints.Conant etal(2011) The development, validation, andverification ofmodels depends crucially onthe availability of marine fields. model accurate for represents a key building challenge problems atlargerrepresentative scales, madeat local scal arise the also whenmeasurements problem can ux (Regnier etal., 2013). are create global to used esti ave different tu systems. However, it is unclea is it However, systems. in neglecting lateral neglecting in fluxe OC f terrestrial net primary pro suggested that models will be improved by rnover times, a ompared toterrestrial mates. Resolving these scaling scaling these Resolving mates. yr e 1.7Pg Cyr s between systems. Currently, ffecting the overall feedback the rates and availability of r atpresent if including such example, the latest IPCC IPCC latest the example, -1 he lateral he of transport SOM duction. An increase or or Anincrease duction. since pre-industrial times, times, pre-industrial since s for bothterrestrials and perturbations suggest that Thus, OC released from e, which are not -1 (Ciais et al., (Ciais Accepted Article database ofsoil respiration (Bo andmarineof especially OMdegrad forsoil aproblem models is datasets global constraining of problems andv in A lack causes water column andterrestrial relationsh asuite OMproviding of ratethatdecay are w consistent by aggregates (e.g. Rothman and reaction-diffusion models of OM decay in marine sediments that This article is protected Allrights bycopyright. reserved. be may which effects confounding datatofield allows realism bekepti and interactions complex debated inthe literature (e.g C andturnover) (e.g.of relevant the cycle storage aspects for The relative merits ofvarious m obtained. andPOC derived DOC soil have to t approach apossible indicating respiration an soil between total 2009) which could beused todeve there are many detailed models o developed from more mechanistically detailed, but spatially res processes into global On models. models. This raises the problem of how to incorporate suitable The spatial resolution of ESMs limits the processes that can be lateral how of implications the to theatmosphere (Carvalhais etal.,2014). Further research i 2013), and some estimates forah entering from of inland Measures tota waters and DOC POC soils. wewer addition, In conclusions. primarily focus on sur databases (e.g. http://www.socat face waters(often < ., Wienhold, 2007; Gasol etal., transport ofOCwith re is ESMs nd-Lamberty &Thomson, 2010, 20 o improving model parameterizat ith sediment core data. Such mo ethods terrestrial in used and e unable to find sufficient dat find to sufficient e unable Forney,2007)predict resimple d heterotrophic soil respirati e possible approache possible beto might f soil OC OC f soil (e.g.mineralization .info/about.html) have started different fates, reliable esti andful of lakes (e.g. Tranvik hard to discern and account fo and account hard discern to lop simpler parameterizations 100 m depth) making 2008; Burdetal.,2010). Use of ESMs are still vigorously mates of both need to be a tomake global estimates of on for multiple biomes, s neededto fully understand ntact, but ntact, is subject to Manzoni and Poprorato, et al,2009). Since weexpect marine science to measure measure to science marine explicitly included in these these included in explicitly presented. alidating global models. This parameterizations of these these of parameterizations ips that becan used inESMs. tricted Forexample, models. dels could be extended to ation. Arecent global to emerge, but these but emerge, these to use parameterizations use include physical protection it difficult to to difficult general it derive l OC exist (eg Ciais etal., (eg Ciais l OC exist lationships lationships for theOM r. Laboratory experiments ions. For oceans, oceans, For similar ions. for ESMs. Similarly, 12) showed acorrelation Accepted Article that mechanisms specific capture results and observations show li both benefit terrestrial would and that modelingmarine communi allowing different model perform and Taylor diagrams; however, diagrams; th and Taylor metrics include model-data residuals, root-mean-square-error, t ongoi an also is benchmarking for suitable measures statistical themselves have tobe evaluated observational data and associated uncertainties. This means tha availability su efforts the of is that with such arises problem spatial andtemporal p 2009; Luoetal., 2012). Models can benchmarking framework have been developed for terrestrial mode and satellite observations (e.g. upper biogeochemica ocean of skill assessing the for frameworks In marine systems, efforts have b Quantifying and unders effects of future processes, in both terrestrial and marine systems, is essential POC sinking out of the surface thesurface vary of ocean out sinking POC production and degradation, as w require times andturnover reliable oceanestimates of stocks C Trull, 2007;Henson etal., 2012,M This article is protected Allrights bycopyright. reserved. the sea andbetween the ESM representation has derived from different data sour measurements: global C stocks an requiresESMs variables information derived from fi main two on investigate simple cause-effect r havetheadvan hand other the on climate change. atterns seen inobservational datasets. tanding model performance is also a cruci proven to be highly variable (Todd-Brown proven behighly to upper anddeepocean Doneyetal.,2009). Similar e elationships, butrealism may ces vary by a factor (Hi two of vary byafactor ces ttle correlation atscales of1 in the formulation of suitable the formulationin suitable of een made todevelop systematic create spatial ance to be compared (Luo etal. (Luo be compared ance to tage of being able to isolate i isolate able to being of tage ell as o the physical transport ere is yetas nogenerally acce d turnover rates, respectively. arsay etal., 2014). Anincr becompared not onlywithd

from 4 Pg C y 4PgC from . Estimates of, for. Estimates complexity (Tod -1 to more than 12PgCy than more to fforts to arrive at consistent a fficiently complete eased understanding of these 00s as 00s the km fail of to models to accurately predict the predict the accurately to ndividual mechanisms and However, one significant However, one significant ederer &Köchy, 2011) and be sacrificed. Validation of benchmarks. Agreement of ng problem. Commonly used used ng problem. Commonly f POCandDOC from landto accurate of estimates pted choice of metric Globalsoil OC estimates t the chosen datasets ata values, but alsowith example, the amount of ime andspace correlations, d-Brown et 2013).al., 2012). This issomething l against data field models and quantitative andquantitative eld and laboratory al area for development. ties. Moreover, ESM etal., 2013). Similarly, ls (Randersonls etal., -1 (Boyd & Accepted Article This article is protected Allrights bycopyright. reserved. comparisons with data,and whatd bymo predicted arebest variables which determining practices, This means thatthere dialog needs to beaniterative betweenc and experimental scientists is t in uncertainties globa the Given quantitative metrics allowing fordifferent models to be compared against a standard suite of data. practices for benchmarking models. This should lead to thedevelopment of anaccepted suite of there should be agreement between both terrestrial and marine modeling communities onbest formulations with observations from field studies and constraints. Arobust model verification test bed should endeavor to confront model rates. Better microbial representations in models will rely onobservations of metabolic processes mechanistic representations ofmicrobial physiology andecology thatdetermine degradation decomposition is microbiallymediated. A primary area ofcrossover, therefore, is to develop One key similarity between OC degradation in the marine and terrestrial systems is that from scarce and highly variable data. based approaches) anddegradation pathways; and parameterization and validation ofmodels composition; betterrepresentation heterotrop of sensitivity ofdegradation rates to environmental variables and heterotrophic community (e.g. Burd,2013) and its implications for altering OMdegradation rates; understanding the dialogue wouldbe particularly useful include: improving representations ofparticle aggregation making adialogue between the two communities potentially fruitful. Some areas where we think similar. Moreover, similar challenges in modeling these processes are faced by both communities, between marine and terrestrial systems, themetabolic processes mediating OMdegradation are 2013; Moore et al., 2013; Todd-Brown etal., 2013 important that ESMs get OC dynamics right for the right reasons (Anav etal., 2013; Bopp et al., production, nutrient inputs, ocean stratification, land management practices, etc. change, it is conditions are likely to alter multiple ecosystem components simultaneously. As primary ESMs. But, there is considerable concern that model projections are biased. Changing climate Organic matter degradation isakey process in both the terrestrial and marine components of Conclusions & Recommendations o determine which estimates and o determine estimates which l estimates, a major task for m for task major a estimates, l ata needtobe collected for i hic microbial communities (perhaps through trait- and experimental manipulations. In addition, ). Although the physical environment differs odelers, andobservational ommunities on best- ommunities mproving the models. the models. mproving dels for meaningful variables are used. best Accepted Article occurs more or less in place in soil systems, with deep roots, deep with roots, systems, soil in place less in or more occurs and air.Incontrast, theoceans complex matrix of minerals, organic materials, and pore spaces different structure. physical intrinsically due their to oceans Conflict of Interest manuscript. preparation. Allauth manuscript layer (top 10s of m). This 10s of This rap layer (top m). primarily in the rooting zone (top 10 – 20 cm) and in the ocean organ byheterotrophic respired it of andsome consumed months) Most organic (OC) carbon enterin Soils. and Oceans in Mineralization Carbon Organic 1: Box the of of authors with interest have None materi conflict a the over long (years centuries)- ti A variablefraction ofthe organ factors (e.g., temperature, soil the of organic partby mat in composition controlled and is the This article is protected Allrights bycopyright. reserved. ABBandSDFconceived the manusc Author Contribution part byNSFgrant OCE0645485 (ABB). Working Group (CCIWG) (Thomas Foundation, Ocean Carbon Biogeoc Variability and Predictability Research Program (US-CLIVAR), th Agricu of Department bythe andsponsored U.S. USA CO, Boulder, At for National andCenter bythe andA.Bracco hosted Deutsch, Carbon Cycle” in Augus “Key Unce workshop of article amultidisciplinary grewout This Acknowledgements

t 2013 organized byN.Levine, R.Q.Thoma id mineralization returns CO me-scales, with important diffe moisture, soil texture/mineral are occa waterwith the mainly ic ic matter escapes input rapid m ors contributed to the writing writing to the contributed ors g the surface ocean orsoil is et al., 2014). The hemistry (OCB), and theCarbon ript andprepare work behindth d Fig. 1,2and d Fig. 2 back to the atmosphere quickly quickly theatmosphere to back Forexample, soils area water percolation, and ogy). rences between soils and betweenrences soils al in this article. this al in sional particle. Mineralization rapidly (~ hours – days rapidly (~or hours –days ter inputs and ter inputs environmental ineralization and is stabilized s within the the mixed surface within s and editing of the mospheric Research, variably filled with water rtainties in the Global rtainties Global the in e U.S. National Science lture, U.S. Climate s, M. Long, G. M.Long, C. McKinley, s, Box 1.ABB led isms. In soils this occurs occurs this Insoils isms. is article funded in is was Cycle Interagency Accepted Article its chemical structure or physical/chemical protection. Recalcitrant: organisms. C: organic Labile literature) consumption and respiration ( Mineralization: whether it is in dissolved particulateor form. Organic Carbon: Organic Matter: thecarbon. of composition atmosphere within hours to days; OC layer the bee mixed in surface mineralized can mineralized; partly determined by is carbon of sequestration Ocean currents. bein DOC andPOC with both andmixing, byconvection deep ocean excursions. Particulate material sinks to the ocean floor and D In marine systems, organic material can undergo significant ver organo-mineral associations (Fig. 1). decomposition, against par OC processes thaton protect depends times of 100s to1000s of years. significan contains subsurface the activity, greatest microbial motion of thewater, sinking of motion oceans, long-term for storage the of So, sediments. depends OC This article is protected Allrights bycopyright. reserved. as CO andrespired beconsumed can sediment mineralized below 1000 m toretur th ~20cm) has (top surface soil bioturbation (e.g., earthworm activity) moving OC deeper down t . Organic resista Organic that is material The oxidation of organic C to inorganic C through heterotrophic This refers to the sum of all relevant organic of allrelevant thesum refers compounds. to organic This This refers to just the carbon contained within the organic ma theorganic within contained carbon the just to refers This Organic C that is rapidly (hours Cthatis Organic often termed “remineralization” in the aquatic/marine Organic formationmatter ands speed of particulate speed of material, e highest OCconcentrations and whereas, it may n tothe atmosphere. Organic C nt to consumption andmineraliz consumption nt to 2 by organisms on the surface and within the within and the surface on byorganisms to days) utilized by heterotro takecenturies t OC stocks with turnover turnover with stocks OC t and the protection and protection the and OC betransported can tothe on the circulation and xchanged with the tical andhorizontal tabilization in soils largely tabilization insoils the depth at which OC is OC is depth which at the is considered the zone of of considered zone is the to millennia for OC millennia to OC for he soil profile. While the profile. the While he soil ticularly aggregation and that reaches the g carried on ocean ation, due to due to ation, phic phic tter,

Accepted Article Allison SD (2012) A trait-based approach for (2012) for approach Atrait-based SD modeling microbial Allison collected as pore water obtained from centrifugation of sedimen as pore of waterobtained centrifugation from collected bacteriaincludes some and Inmar wellas colloids. viruses, as defined themateriala passingas through 0.7 pore 0.2 to μm si In foranalysis a filter to (usually DOC. prior 0.7through µm) andextracted lysimeter-collected sol samples, Inboth samples. Anav A, Friedlingstein P, Kidston M Allison SD, Wallenstein MD, Bra Adams MB,Angradi TR (1996) Decom References This article is protected Allrights bycopyright. reserved. solution collected bylysimeters Dissolved organic matter (DOM): aggregates, andincludes photosy retained with a afilter between 0.7on 0.2to wit size μm pore separate mineral particles. In marine systems, POM is typically c after sieve µm 53 a on retained Particulate organic matter (POM): byproducts from decomposition. plant material variousin stages Soil organic matter (SOM): time (e.g. 100years, 1000 years). Sequestration: 6801–6843. cycle global CMIP5 the the Eart carbon of in System Jou Models. dependent on microbial physiology. Nature Geoscience, Ecology Letters, Management, litter in the Fernow Whole-Watershed Acidification Experiment. Removal of C from exchange with with exchange from C Removal of 83 15 , 61–69. , 1058–1070. Allorganic matter insoils sma of decay, living microbial bio dford MA(2010) Soil-carbon resp installed inthe soil profile omplete dispersion ofthesoil nthetic bacteria, particle atta In terrestrial systems, DOM is sampled either as soil et al. et al. Operationally defined terrestrialin systems as SOM position and nutrient dynamics (2013) Evaluation the land and ocean components (2013) landandocean Evaluation the components the atmosphere atmosphere apredefinedthe for or as a wateror as extract offresh soil 3 ller than 2 mm, including dead including ller than2mm, marine systems, DOM is , 336–340. mass, and microbial h care taken not to disrupt takennot care disrupt h to ine sediments, DOM is ched bacteria etc. ze filter. This typically ze This filter. todisrupt aggregates and considered the material utions are typically passed are passed typically utions ts. litter decomposition. onse to warming rnal ofClimate, Forest Ecology Ecology Forest of leaf hardwood 26 length of length of , Accepted Article Aufdenkampe, AK,MayorgaAufdenkampe, E,Raym Armstrong RA, LeeC,H This article is protected Allrights bycopyright. reserved. Baldock JA,Masiello GelinasCA, Aumont O,Maier-Reimer Blain E, cycl andglobal nutrient KR(2005) MarineArrigo microorganisms Anderson LA,Sarmiento JL (1994)R Battin TJ,Kaplan LA,F Bauer JE,Cai WJ, Raymond PA,Bi Bauer JE,Williams PM, Druffel Baisden WT, Parfitt RL(2007)Bom Benner R(2002)Chemical composit Luyssaert, TJ, S,KaplanBattin, FF (2008).Biophysical controls o Geoscience, doi:10.1029/2001GB001745. Frontiers Environment, atmosphere. in andthe Ecology (2011) Rivering coupling biog of ballast.mineral oce the in fluxes carbon organic nutrient dataanalysis. Gl Biogeochemistry, Biogeochemistry, matter in terrestrial andmarine ecosystems. Marine Chemistry, ocean including Fe, Si, P colimi Press, NY, USA. USA. NY, Press, matter organic marine dissolved carbon cycle ofthe coastal ocean. Nature, Sea. Nature andSargasso north-central Pacific the in fractions boundless boundless cycle. carbon Nature Geoscience, 1 , 95–100.

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Accepted Article This article is protected Allrights bycopyright. reserved. organic matter. affecting (in t italics) theprimaryprocesses along with ocean Figure 2: Center forEnvironmental Sciences (ian.umces.edu/symbols/). of courtesy symbols (some oceans Figure 1: Xue LG,Zhang Y, Zhang TG, An Xiang S-R, Doyle A,Holden PA,S Yoon B, Raymond PA (2012) Dissolved organic organic PA(2012) from matter export Dissolved B,Raymond Yoon Soil Biology andBiochemistry, Biology Soil act andmicrobial mineralization doi:10.1029/2012GL052785. during Hurricane Irene. Geophysical Research Letters, algaeand on radiation cyanobact Schematic showing the main conduits of organic matter from soil processes main the of Schematic LZ, Wang XL(2005)Effects of enh chimel JP(2008)D 40 Integration and Application Ne andApplication Integration ivity in surface and subsurface eria. Critical Reviews in Micro , 2281–2289. affecting detrital organic matt rying and wet 39 , L18402, he mineralization of that ting effects on C and N effects andN C ting on anced ultraviolet-B twork, Maryland twork, of Univ. biology, California grassland soils. a forested watershed er in soils and the 31 s to the open open to the s , 79–89. Accepted Article Net uptake(Pg Net C y This article is protected Allrights bycopyright. reserved. marine systems. 1: Table Ocean Land Atmosphere ufc eietognccro 575 Surface organic carbon sediment isle nrai abn 37800 Dissolved inorganic carbon atclt rai abn 15 Particulate organic carbon Values of uptake and stock in various organic mattercomponent organic various ofin uptake and stock Values isle rai abn 662 Dissolved organic carbon ologncmte -- matter organic Soil nrai abn 744 Inorganic carbon oliogncC-- C inorganic Soil eeain07 .7 550 0.75–1.17 Vegetation it .3–23 3 –2.33 1.73 Biota

Table 1 Table -1 ) Stock (PgC) Stock ) 924 (?) 1760 s of terrestrial and Table 2.

Model Mineralization Rate Detrital OC pools Physical Heterotrophic References Protection microbes/fungi

Ocean

Article Article Article Article Article BEC Temperature DOM (labile & semi-labile) Implicit Implicit (1) dependent, 2 rates (ballast associated & 2 POM classes (ballast associated & soft) soft) & O2 dependent (lower rate through denitrification in anoxic zones)

PELAGOS Temperature No 1 explicit (2) dependent (through DOM (C,N,P), POM bacterial growth) & (C,N,P,Si,Fe)

O2 dependent

TOPAZ2 2 rates (ballast DOM (labile & semi-labile) Yes Implicit (3) associated & soft) & O2 dependent (lower 2 POM classes (ballast rate through associated & soft) denitrification in anoxic zones)

Had-OCC Constant (shallow & POM No Implicit (4) This article is protected by copyright. All rights reserved.

Accepted Accepted Accepted Accepted Accepted deep)

Pisces Temperature & O2 Semi-labile DOM No Implicit (5) dependent (same rate but through Small & large POM denitrification in anoxic zones)

HAMOCC O2 dependent (lower DOM No Implicit (6) Article rate through denitrification in POM anoxic zones)

Soil

CENTURY Temperature & 5 litter pools No Implicit (assumed (7,8) moisture dependent steady state) 1 surface microbial pool

3 SOM pools (active, slow and passive)

DOC pool

RothC Temperature, soil 2 litter pools No 1 explicit (9) moisture 2 SOM pools

1 pool inert OM This article is protected by copyright. All rights reserved.

Accepted Biome-BGC Temperature, 4 litter, 4 SOM No Implicit (assumed (10) moisture steady state)

DNDC Soil texture, nitrogen, 3 litter pools No Explicit (11) soil temperature & moisture 2 microbial pools 3 SOM pools Article 1 DOC pool

ORCHIDEE Temperature, 4 litter No Implicit (12) humidity 3 soil C

Table 2: Comparison of different model formulations used for representing processes affecting detrital OC in terrestrial and marine systems. References: (1) Moore et al., 2002; (2) Vichi et al., 2007; (3) Dunne et al., 2010; (4) Palmer & Totterdell, 2001; (5) Aumont et al.,

2003; (6) Ilyina et al., 2013; (7) Parton et al., 1993; (8) Parton et al., 1996; (9) Coleman & Jenkinson, 1999; (10) Thornton & Rodenbloom

2005; (11) Li et al., 1994; (12) Krinner et al., 2005 This article is protected by copyright. All rights reserved.

Accepted

CO2 CO2 Surface Run-off

Grazing Aggregation CO2 CO2 CO2 POC Aggregation

POC DOC CO2 CO2 DOC Grazing Soil fauna 100 m 20 cm Leaching Mixing & CO2 Advection Sinking DOC POC

Microbes Migration Vertical 100 cm DOC POC Microbes

CO2

Organo-mineral Mixing & Advection Associations CO2 Leaching

1000 m 200 cm

DOC POC

CO2 CO2

Sediments

This article is protected by copyright. All rights reserved. Accepted Article This article is protected Allrights bycopyright. reserved. INLAND WATERS EIET EIET EIET SEDIMENTS SEDIMENTS SEDIMENTS SEDIMENTS Photodegradation Microbial Activity Resuspension Disruption Flocculation Aggregate SOILS Sedimentation Groundwater Surface runoff Surface Lateral flow Erosion

ESTUARIES Photodegradation WETLANDS Microbial Activity Resuspension Flocculation TIDAL Tidal Exchange eietto Sedimentation Sedimentation Saltwater intrusion Saltwater Deposition

COASTAL SHELF Food web processes Photodegradation Microbial Activity Flocculation

OPEN OCEAN Food web processes Microbial Activity Flocculation Sedimentation