from bedrock to burial: the evolution of particulate organic carbon across coupled...

www.elsevier.com/locate/marchem

Marine Chemistry 92

From bedrock to burial: the evolution of particulate organic carbon

across coupled watershed-continental margin systems

Neal E. Blaira,*, Elana L. Leitholda, Robert C. Allerb

aDepartment of Marine, Earth and Atmospheric Sciences, North Carolina State University, P.O. Box 8208 Raleigh,

NC 27695-8208, United StatesbMarine Sciences Research Center, Stony Brook University, Stony Brook, NY 11794-5000, United States

Received 3 December 2003; received in revised form 12 April 2004; accepted 30 June 2004

Available online 3 October 2004

Abstract

Deltas sequester nearly half of the organic carbon (OC) buried in the marine environment. The composition of the

buried organic matter reflects both watershed and seabed processes. A conceptual model is presented that describes the

evolution of particulate organic carbon (POC) as it travels from its terrestrial source to its burial at sea. Alterations to the

POC occur primarily in bioactive reservoirs, such as soils and the surface mixed layer (SML) of the seabed, where new

organic matter can be added and older material degraded. Bypassing or rapid passage through the reservoirs is a key

parameter because it avoids change.

The Eel River of northern California and the Amazon River systems illustrate the importance of reservoir transit time

and storage in determining the character of POC delivered to the continental margin. The Eel exemplifies a bypass

system. Mass-wasting processes on land deliver unaltered bedrock along with OC derived from extant vegetation directly

to the river channel without significant storage in soils. Rapid burial on the shelf occurs as a result of flood events. As a

consequence, the buried material appears to be a simple mixture of carbon derived from kerogen (bedrock C), and modern

terrestrial and marine sources. This is predicted to be a characteristic of the many similar short rivers on active margins

that supply N40% of the fluvial sediment to the world’s ocean.

Extensive storage and processing of OC in lowland soils is a characteristic of the large Amazon watershed. Upland

POC compositions are either overprinted or replaced by lowland sources. Upon delivery to the shelf, over half of the

riverine POC is lost as a result of residence in sediment layers that are periodically reworked over time scales of days to

months. The addition of fresh reactive marine OC, exposure to oxygen, and the regeneration of metal oxidants during

resuspension events fuel the oxidation of the riverine organic matter. The nature of the watershed-shelf processes likely

produce a complex mixture of organics possessing a continuum of ages and reactivities.

The model illustrates the need to develop tools to measure residence times of particles in the various reservoirs so that

the behavior of POC can be calibrated as it moves through a sedimentary system. The ultimate goal is to be able to use

0304-4203/$ - s

doi:10.1016/j.m

* Correspon

E-mail addr

(2004) 141–156

ee front matter D 2004 Elsevier B.V. All rights reserved.

archem.2004.06.023

ding author.

ess: [email protected] (N.E. Blair).

N.E. Blair et al. / Marine Chemistry 92 (2004) 141–156142

the organic geochemistry of soils and sediments to quantitatively infer the history of processes that determine both the

composition and amount of POC present in different depositional environments.

D 2004 Elsevier B.V. All rights reserved.

Keywords: Organic carbon; Carbon isotopes; River; Continental margin; Soil; Kerogen; Delta

1. Introduction

Continental margins play a pivotal role in modu-

lating Earth’s atmospheric chemistry and global

climate over geological time scales (Berner, 1982,

1989; Hedges and Keil, 1995). Approximately 90% of

the organic carbon (OC) buried globally in the ocean

has been sequestered in shelf and slope sediments

(Hedges and Keil, 1995). Slow, continuous removal of

OC from the biosphere and storage in margin

sediments has contributed to the accumulation of O2

and depletion of CO2 in the atmosphere over the

Earth’s history (Berner, 1982, 1989). Uplift, weath-

ering and oxidation of sedimentary OC counterbal-

ance the burial process.

The mechanisms that govern OC burial in margins

are controversial and have historically focused on the

importance of marine processes. Productivity, bottom

water oxygen level, sediment accumulation rate, and

organic matter composition can all influence OC

preservation in sediments (see Hedges and Keil, 1995

for review). The protection of OC by association with

terrestrially derived, clay-sized particles has been

implicated as at least one of the key controls on such

seemingly disparate features as the OC content of

sedimentary rocks (Kennedy et al., 2002) and burial

efficiency in deltaic and continental shelf and slope

sediments (Mayer, 1994a,b; Keil et al., 1997; Hedges

and Keil, 1995). The nature of the apparent protective

process is poorly understood, although recycling of C

by particle-bound microbes and incorporation of

microscopic biogenic debris into the particle matrix

via organic glues may be important (Ransom et al.,

1997, 1999; Arnarson and Keil, 2001; Blair et al.,

2003). Sorption of dissolved OC by clays has also

been invoked as a potentially important mechanism;

however, modeling exercises, isotopic, and other

studies suggest that this is not the dominant process

in shallow water settings (Henrichs, 1995; Blair et al.,

2003; Arnarson and Keil, 2001).

Nearly half of margin OC burial occurs in deltaic

regions (Berner, 1989; Hedges and Keil, 1995). The

clay fraction of river suspensions is typically loaded

with terrestrial organic matter to a nearly uniform OC

to particle surface area ratio (OC/SA; Keil et al.,

1997). In some coupled river/delta systems, such as

the Amazon and Fly, riverine particles appear to

rapidly lose as much as 70% of their loads of

terrestrial OC upon discharge, demonstrating the

dynamic nature of the OC–clay association (Aller et

al., 1996; Keil et al., 1997). In contrast, little

detectable loss of riverine OC from the clay fraction

occurs on particles discharged to the Eel shelf offshore

of northern California (Blair et al., 2003). Watershed

and seabed processes may both contribute to the

differences.

There are literally thousands of rivers delivering

sediment and the associated OC to the ocean (Milli-

man and Syvitski, 1992). 40–70% of the sediment is

transported by the smaller, more numerous rivers

(Milliman and Syvitski, 1992; Milliman, personal

communication). Only a subset of rivers can be

studied, and, to-date, preference has been given to

those with either high fluvial sediment outputs, which

provide an easily recognizable signal on the shelf, or

to logistically convenient rivers. Important C-cycling

processes may go unappreciated if other selection

criteria are not considered. In addition, although the

sources and fates of terrestrial inputs to the seabed

have received attention in marine organic geochem-

istry (Hedges and Keil, 1995; Hedges et al., 1997),

terrestrial physical processes, such as those involved

in landscape evolution, have largely escaped scrutiny

as factors that might influence the OC signatures

buried on continental margins. Existing riverine OC

models, such as those based on the River Continuum

and Flood Pulse concepts, were developed primarily

to relate watershed C-dynamics to riverine food webs

(Vannote et al., 1980; Robertson et al., 1999) and do

not consider the nature of the OC exported from the

N.E. Blair et al. / Marine Chemistry 92 (2004) 141–156 143

river or its fate in the seabed. A conceptual model is

presented here that links the terrestrial and marine

portions of a river dispersal system and describes the

evolution of particulate OC (POC) as it passes through

the coupled watershed–seabed system. The model is

sufficiently general to be used as a template by which

to compare different river-margin systems and plan

future studies.

Fig. 1. Coupled watershed–seabed model describing the evolution

of POC. Changes in POC content occur primarily in boxes

however, transport between reservoirs can result in hydrodynamic

sorting and desorption of OC.

2. Model description

The preservation of OC requires its survival over

the time required to bury it beneath the biologically

active surface environment. This is accomplished

primarily when the kinetics of decomposition are

slowed relative to the burial rate via several mecha-

nisms: some organic materials are transported into

environments, typically anoxic, in which they are less

reactive; others are rendered unrecognizable to

enzymes by geochemical side reactions; and still

others are sequestered in protective matrices (Hedges

and Keil, 1995). In addition, certain biopolymers are

synthesized with an intrinsic resistance to degradation

(de Leeuw and Largeau, 1993). An underlying

premise of the model is that the protective mecha-

nisms may change as material moves through space

and time. History is important.

The model is composed of a series of intercon-

nected bioactive reservoirs representing locations

where the dominant changes in POC composition

occur (Fig. 1). The primary inputs into each reservoir

are the POC from an upstream reservoir, OC produced

within the reservoir, oxidants to support OC break-

down, and nutrients to support the in situ synthesis.

The OC produced in situ, while potentially possessing

a wide range of reactivities (de Leeuw and Largeau,

1993), will tend to be more susceptible to turnover

because it is younger and less degraded than that

arriving from upstream. It may add to the POC pool

entering from upstream, replace a portion of the older

pool, or act as a co-metabolic primer to facilitate the

oxidation of the older POC (Canfield, 1994; Aller,

1998). The primary oxidants are higher order in

energy, i.e., O2, NO3�, Mn+4 and Fe+3. Relatively

minor bulk compositional changes are expected in

sulfate reducing and methanogenic environments

based on the apparent stabilization of POC content

;

in anoxic sediments (Hartnett et al., 1998; Hedges

et al., 1999a).

There are numerous factors that can influence POC

and oxidant inputs that will, in turn, drive POC

turnover and/or preservation. These include climate,

hydrology, geology, and biota. Variations in these

environmental parameters lead to changes in POC

composition and preservation mechanisms as one

moves through the entire system. For instance,

terrestrial soils are primarily subaerial and are subject


to downward percolation of interstitial water, whereas

the bulk of marine sediments are subaqueous and have

relatively reduced advective flow of porewater and

solutes (Hedges and Oades, 1997). O2 transport is

thus more facile in soils while anaerobic conditions

dominate marine sediments millimeters to several

centimeters below the sediment–water interface. The

oxidation of recalcitrant biochemicals, such as spor-

opollenins, might be favored in aerobic soils (Hedges

and Keil, 1995). The cross-linking of olefinic species

by sulfides (vulcanization), which may reduce the

bioreactivity of the organic compounds, is more likely

to occur in sulfate-reducing marine sediments (Koh-

nen et al., 1991; Hedges and Oades, 1997).

The relative fluxes of material through and around

reservoirs, and the residence time within reservoirs are

key controls on OC character. An extreme example

would be bypassing a reservoir completely; it avoids

change altogether. Transport between reservoirs itself

can also influence the bulk composition of the POC.

Insofar as composition typically varies with particle

grain size (Hedges and Oades, 1997; examples to

follow), processes such as selective winnowing of

fine-grained particles from hillslopes (Rosenbloom et

al., 2001) and the hydrodynamic sorting of coarse and

fine particles can alter bulk POC characteristics

(Vannote et al., 1980; Goni et al., 1997).

Approximately 80–90% of recent sediment is

derived from the erosion of uplifted sedimentary rock

(Veizer and Jansen, 1985; Wold and Hay, 1990); thus,

the starting material in the model is ancient sedimen-

tary OC (Fig. 1A). Typically, this OC will contain a

significant fossil marine component that has experi-

enced extensive diagenesis and some catagenesis. The

characteristics of the rock OC are primarily functions

of the original depositional environment and thermal

history (Tissot and Welte, 1978).

Having survived diagenesis and likely some

thermal modification, the rock OC is relatively

unreactive. Even so, upon exposure in the regolith

(Fig. 1B) some of the rock OC may be removed if

time is sufficient (Petsch et al., 2000, 2001). In

unvegetated exposures, the time scale of kerogen

oxidation appears to be thousands of years. The time

required for significant rock OC loss in vegetated soils

is unknown but may be considerably less due to the

addition of reactive OC that could fuel co-metabolism

and the subsurface injection of O2 by plant roots.

Modern C is added to soils primarily as vascular

plant debris and transformed to heterotrophically

recycled material (Baldock and Skjemstad, 2000).

Aggregates of POC with inorganic minerals create a

hierarchy of stability (Golchin et al., 1997a). Macro-

aggregates (N250 Am) consist of plant fragments

encrusted with mineral particles. Mucilaginous glues

produced by microbes and plant roots provide

cohesion (Golchin et al., 1997a). The macroaggregate

disintegrates upon the decomposition of the core plant

fragment producing remnant microaggregate POC

that is of lower reactivity and more heterotrophic in

nature (Golchin et al., 1997a). The decomposition of

rock OC may occur simultaneously, resulting in a

partial blending of the modern and ancient C sources

via microbial processing (Petsch, 2001; Agnelli et al.,

2002). Turnover times of the various OC pools range

from seasonal to millennial (Admunson, 2001; Qui-

deau et al., 2001a).

Soil mineralogy, vegetative cover, exposure to

oxidants (which is dependent on regolith permeabil-

ity), water availability, temperature, and land use will

influence the evolution of soil organics (Connin et al.,

1997; Kay, 1997; Quideau et al., 2001b). Vegetative

cover in particular represents a nexus of controlling

processes. Climate, hydrology, and anthropogenic

activities, as examples, influence the composition of

the plant community. In turn, vegetative type can

affect the composition and timing of the organics

delivered to the soil (Quideau et al., 2001b), slope

stability, and soil residence time (Gabet and Dunne,

2002).

Lithology, hydrology, relief, climate (storm events),

and land use direct mass-wasting processes such as

shallow or deep landsliding, gully formation, and

sheet wash (Kelsey, 1980; DeRose et al., 1998;

Dymond et al., 1999; Page et al., 1999; Trustrum et

al., 1999; Hicks et al., 2000; Iverson et al., 2000).

These, in turn, influence the balance between bedrock,

soil, and vegetation delivered to waterways. Material

may go directly to the river (D) or to intermediate

storage locations such as slide tailings, channel infills,

and the floodplain (C; Page et al., 1994; DeRose et al.,

1998; Gomez et al., 1998; Marutani et al., 1999;

Trustrum et al., 1999). Modification of the OC is

predicted to occur during storage with the extent of

change controlled by time and exposure to biota,

oxidants, and possibly UV light. The extent of


vegetative colonization of the stored soil/sediment and

the type of vegetative cover are predicted to signifi-

cantly influence the turnover and replacement of the

POC in a manner similar to that resulting from a

succession of plant communities caused by either

climate or land-use changes (Buyanovsky et al., 1997;

Connin et al., 1997; Golchin et al., 1997b; Quideau et

al., 2001b).

Further evolution of the POC can occur in the river

channel due to production from photosynthesis or

consumption via respiration (Richey et al., 1990;

Robertson et al., 1999; Bianchi et al., 2004). Little

change in suspended OC composition is expected to

occur within the channels of small, steep-sloped rivers

because of their short lengths and often high

turbidities (Blair et al., 2003).

Upon delivery to the shelf (E) and during transport

to the slope (F), sediment resides in the surface mixed

layer (SML) where it is subjected to repeated

resuspension–deposition cycles. SML residence time

will depend on wave, current, and tidal energy, the

slope and width of the continental shelf, bioturbation

depth, episodicity of erosion and deposition during

both floods and wave events, and the input flux of

sediment (Wright et al., 2001; Harris and Wiberg,

2002; Sherwood et al., 2002; Scully et al., 2003).

Residence time, along with water column productivity

and the intensity/frequency of reworking, are pre-

dicted to be factors controlling the extent of replace-

ment of rock and terrestrial plant-derived OC by

marine OM.

The replacement of terrestrial OC by marine-

derived material is likely facilitated, and perhaps

limited, by the disaggregation of soil particles in the

river or the marine SML. The newly exposed

terrestrial OC is thus vulnerable to enzymatic attack,

photolytic oxidation, and desorption. This is analo-

gous to the loss of POC from soils as a result of

agricultural tillage (Angers and Chenu, 1997). The

introduction of marine C proceeds via the incorpo-

ration of debris from the water column into the

sediment matrix followed by its partial reprocessing

by infauna and microbes (Blair et al., 1996, 2003;

Ransom et al., 1997, 1999; Arnarson and Keil, 2001;

Thomas and Blair, 2002). Sequestration in micro-

aggregates and mineral mesopores is hypothesized to

significantly slow the degradation kinetics of the OC,

particularly if coupled with cross-linking and con-

densation-style chemical reactions, and the production

of microbial glues (Hedges and Oades, 1997; Zimmer-

man et al., 2004).

2.1. The Eel River end-member: an example of

reservoir bypass

The Eel River drains a small watershed (~9000

km2) in northern California characterized by season-

ally heavy precipitation, steep slopes, rapid rates of

mass wasting, and the highest sediment yield for any

river in the contiguous U.S. (Fig. 2; Brown and Ritter,

1971; Sommerfield et al., 2002). The basin is under-

lain by the Jurassic to Tertiary Franciscan Complex, a

heterogeneous, tectonically sheared body of rock

composed primarily of easily eroded, shale-rich

melange and secondarily of more coherent sandstone

blocks (Kelsey, 1980; Blake et al., 1988). The

melange appears to be the primary source of fine-

grained sediment to the river based on its measured

contribution (70–94%) to the suspended load of the

Van Duzen River, a major tributary of the Eel (Kelsey,

1980). The melange OC (0.5–0.9% by weight) is

predominantly a Type III kerogen (Blair et al., 2003).

Gully wall erosion, earthflows, and landslides deliver

unweathered melange and plant debris-rich surface

soils to the river. Although some sediment is depo-

sited to form alluvial terraces and floodplain soils

during overbank events and then slowly eroded, the

bulk of the suspended riverine load appears to have

bypassed intermediate storage (Kelsey, 1980; Som-

merfield and Nittrouer, 1999).

The POC transported by the Eel is heterogeneous

in composition as a function of grain size (Fig. 3).

Plant debris, principally wood, is visually evident in

the coarse (N25 Am) fraction. The y13C value

(~�26.5x) and atomic C/N ratio (N20) are consistent

with a terrestrial C3 plant source (Leithold and Blair,

2001). Wood fragments collected from post-1960

shelf sediments have 14C-contents of ~108 pMC (%

modern 14C content; Blair et al., 2003).

The finer fractions contain OC from a mixture of

sources. The b4 Am OC in soils and riverine

suspended load is derived nearly equally from the

melange (0 pMC) and modern vegetation (~110 pMC)

as indicated by isotopic mass balances of 12C, 13C and14C (Figs. 3 and 4; Blair et al., 2003). Aged (N1000

years) soil C does not appear to be a major component

Fig. 2. Maps of the Eel watershed and margin (top panels) and Amazon shelf (bottom panel). Sampling locations are shown on each. The Eel

shelf was sampled 2 weeks after a flood event in 1997. River samples were collected at Cock Robin Island (CR) and the Scotia bridge (S).

Sampling details are provided in Blair et al. (2003). Amazon shelf sampling stations are from Blair and Aller (1995) (�) and Sommerfield et al.

(1996) (o). Approximate distances to Amazon River from each station are measured to X on the map.


Fig. 3. y13C and C/N ratios of riverine POC. Isotopic compositions

suggest that fine-grained POC is derived from plant debris in the

Amazon watershed (Hedges et al., 1986a,b). The shift in y13C from

coarse to fine POC may reflect a greater compositional complexity

for the fine-grained material as a result of its age. Alteration of the

C/N ratio is apparently the result of microbial processes in soils. The

same trend is seen in the Eel watershed except that the POC is

derived from a combination of kerogen and plant debris (Blair et al.,

2003).


of the fluvial POC. The residence time of the

vegetation-derived OC in the eroding soils must be

on the order of several decades or less based on 14C-

content. The steep slopes of crushed bedrock in the

Eel watershed generates a weathering-limited situa-

tion (sensu Stallard, 1995), whereby the soil OC that

feeds the riverine suspended load has not had the

opportunity to age greatly. The POC is thus largely a

bimodal mixture of ancient and modern OC. C/N

ratios suggest microbial reprocessing of the two

sources (Fig. 3).

Greater than 80% of the sediment delivery to the

~25-km-wide shelf is associated with annual winter

storms (Sommerfield and Nittrouer, 1999; Sommer-

field et al., 1999). Sediment plumes from the river

initially travel northward and stay inshore of the 40-m

isobath (Geyer et al., 2000). Wave-induced gravity-

driven processes then transport thin fluid mud layers

to the mid-shelf depocenter within days (Ogston et al.,

2000; Traykovski et al., 2000; Scully et al., 2003).

20–25% of the fine sediment from floods accumulates

on the mid-shelf; the remainder is either trapped in

inner shelf sands or dispersed across and along shelf,

and downslope (Wheatcroft et al., 1997; Sommerfield

and Nittrouer, 1999; Mullenbach and Nittrouer, 2000;

Scully et al., 2002, 2003; Puig et al., 2003). Flood

layers are preserved on the mid-shelf as a result of

rapid burial through the surface mixed layer (Wheat-

croft and Drake, 2003).

The POC buried in the depocenter reflects the

short time spent in the surface mixed layer (Blair et

al., 2003). Portions of the flood layer may be buried

below the mixed layer nearly instantaneously (within

days) because of the volume of sediment deposited.

As a result, flood layer OC has essentially retained

the isotopic composition of riverine material (Fig. 4).

Muds not directly associated with preserved flood

layers have incorporated marine OC as result of their

longer residence in the SML and exposure to local

productivity (Leithold and Hope, 1999; Fig. 4).

Given the return frequency of major floods and the

average sediment accumulation, the residence time of

non-flood sediment in the SML is on the order of a

decade. The difference in the loading of marine OC

in the clay fraction between flood and non-flood

deposits is recorded in the seabed as each is buried

(Fig. 5). Significant loss of either modern terrestrial

C or the kerogen is not observed presumably

because the intensity and duration of surface mixing

processes are insufficient, even in the non-flood

intervals (Fig. 6).

2.2. The Amazon end-member: an example of

extensive storage in bioactive reservoirs

Whereas the bulk of the sediment buried on the Eel

shelf by a flood event can literally travel from bedrock

source to marine burial in a matter of days, suspended

sediment in the Amazon follows a more protracted

journey. The Amazon River drains nearly half of

South America or approximately 7.05�106 km2

(Hoorn, 1994). 80–90% of the suspended load

originates in the Andes (Gibbs, 1967; Meade et al.,

1985), which are composed of uplifted marine and

continental sediments, and igneous and metamorphic

rocks (Potter, 1997; Bevins et al., 2003). Large-scale

sedimentation has occurred in the adjoining foreland

basin due to the Andean uplift and erosion (Rasanen

et al., 1995; Irion et al., 1995; Potter, 1997), leading to

long-term storage of materials spanning millions of

years. Weathering of sedimentary cover and shield

bedrock has formed soils in the upper lowlands (the

terra firme) that may be tens of millions of years old

(Stallard, 1995; Irion et al., 1995). However, the low

Fig. 4. The evolution of POC on the continental margin. Both the Eel and Amazon display the same y13C trend towards more 13C-enriched

contents as one moves offshore but the underlying processes differ. On the Eel shelf and slope, marine C is added to particles with little loss of

kerogen or modern terrestrial OC. 14C ages decrease due to the addition of the marine OC (Blair et al., 2003). Shelf and slope analyses were

done on the b4 Am fraction of the 0–1-cm depth intervals of box cores. In contrast, particle age increases on the Amazon shelf as young

terrestrial OC is selectively lost. The particles are not completely reloaded with marine OC. Amazon River data are from Hedges et al. (1986a,b)

and Keil et al. (1997). Amazon shelf 14C data are from piston core tops (Sommerfield et al., 1996); the OC/SA and y13C measurements are from

the 3- to 13-cm depth interval of piston cores (Blair and Aller, unpublished data) and surface samples (Showers and Angle, 1986; see citation for

sampling locations). All samples should be representative of the surface mixed layer. The measurements were made on bulk samples, which

exhibit the same general OC/SA and y13C trends as clay fractions (Keil et al., 1997). Methods for the Blair and Aller’s unpublished data are

reported in Blair et al. (2003).


erosion rates that permit the formation of such ancient

soils also contribute little to the riverine sediment load

(Stallard, 1995).

50,000 km2 of the Amazon basin are occupied by

the floodplain (varsea), an area N5 times that of the

entire Eel watershed (Richey et al., 1990). An average

of 1.7 billion tons of sediment are deposited on the

floodplain and 1.6 billion tons are returned to the

mainstem via bank erosion per annum (Dunne et al.,

1998). Given that approximately 1.2 billion tons/year

of sediment are transported by the river to the delta

plain, where 0.3–0.4 billion tons/year are intercepted,

it is likely that much of the sediment discharged to the

ocean has resided in the floodplain for some period of

time (Dunne et al., 1998).

The coarse (N63 Am) POC fraction of the

Amazon’s suspended load is dominated by leaf

(70–80%) and woody (15–25%) debris (Hedges et

al., 1986a, 2000). Varsea C4 grasses contribute

V10%. Breakdown of the coarse POC and incorpo-

ration into soils appears to be the primary source of

the fine (b63 Am) POC (Fig. 3; Hedges et al.,

1986a, 1994). The respective 14C contents of the

coarse and fine pools, 123 and 102 pMC, are

consistent with the diagenetic flow of coarseYfine

(Hedges et al., 1986b). Neither POC fraction

undergoes extensive changes within the river chan-

nel in part because of low primary production rates

there (Richey et al., 1990). In-channel respiration

rates seem to be preferentially fueled by a reactive

Fig. 5. y13C and OC/surface area of Eel shelf b4 Am sediment.

Samples are from a core collected at the 70-m depocenter of the

shelf (K70 station). Flood layers were identified by their higher clay

content (Leithold and Blair, 2001). Marine OC is added to the b4

Am fraction as particles reside in the surface mixed layer. Non-flood

sediment spends more time in the mixed layer and thus has a more

marine signature.

Fig. 6. POC sources downcore on the Eel shelf. 13C/12C and 14C/12C

abundances were used to resolve kerogen, modern terrestrial, and

marine OC sources at the K70 site using an isotopic mass balance

approach (Blair et al., 2003). Deposition is post-1964. y13C end-

member values were �24.3x, �26.5x and �21x for the kerogen,

terrestrial and marine sources. D14C values were �1000x for the

kerogen and +100x for the terrestrial and marine OC. The

terrestrial isotopic end-member values were verified using wood

isolates from the core. Those of the kerogen and marine sources

were assumed to be the same as at present (Blair et al., 2003). Data

are from Perkey (2003) and Leithold et al. (2004).


subset of dissolved OC and POC that turns over

rapidly.

Downstream y13C gradients of the fine POC argue

for an overprinting or replacement of Andean-derived

OC by that from the lowlands (Quay et al., 1992).

This is analogous to the overprinting of the original

tectonic (upland) signature of quartz sands (and

presumably many other inorganic minerals) by long-

term storage and intense chemical weathering in the

alluvial sediments and soils of the Orinoco drainage

basin (Johnsson et al., 1988). Much of the OC

transformation may occur during storage in the

floodplain (Richey et al., 1991). Deposition on varsea

surfaces and erosion of banks creates a slowly moving

solid bed reactor for the processing of the OC. Given

that the length and speed of the reactor will vary

throughout the floodplain, a continuum of ages is

predicted for the fine POC. In addition, the age

distribution should be skewed toward younger mate-

rial because in general the slower erosion rates that

would allow the OC to age would also contribute less

to the total sediment budget (Fig. 7). The exceptions

would be if the slower cycling region were suffi-

ciently large in area to compensate for the lower

sediment flux, or non-steady-state processes such

land-use perturbations greatly accelerated erosion of

previously stable soils. The mean residence time in

the watershed estimated for the suspended fine POC,

b600 years based on 14C age (Hedges et al., 1986b;

Richey et al., 1990), may thus reflect the preferential

delivery of younger, more rapidly eroded material to

the river. Residence times for the material remaining

in the varsea deposits must be longer, particularly

given that sediment deposition in the floodplains is

controlled in part by sea-level changes (Irion et al.,

1995). This is an important consideration when

comparing residence times of OC retained within soil

profiles to those of the soil C that escaped to the river.

A suite of physical processes act on the Amazon

sediment discharged to the ocean to create z1-m-thick

suspensions of fluid mud (N10 g l�1) that cover large

Fig. 7. Hypothetical 14C age distributions of riverine POC before and after deposition on the shelf. Short, mountainous rivers, such as the Eel,

are predicted to discharge POC predominantly composed of modern OC and kerogen. If deposition is sufficiently rapid, the POC will be largely

recalcitrant in the shelf environment. The modern component is augmented by the addition of marine OC on the shelf. Extensive storage, as

exhibited in the Amazon watershed, is predicted to lead to a more continuous range of POC ages that is skewed to the modern. Total OC

decreases and modern OC will be preferentially lost in the energetic regions of wide shelves. Reloading of particles with modern OC can occur

in deeper, more quiescent margin zones, provided that a source of fresh marine organic matter is present. The predicted age distribution may be

more like that of the river, except that the modern component will have a marine source.


areas of the shelf adjacent the river mouth (Kineke

and Sternberg, 1995; Kuehl et al., 1995). These fluid

muds overlie and exchange with a more consolidated

but still highly mobile zone of the seabed. During

neap tides, water column salinity is stratified and

resuspended sediment is trapped in turbidity max-

imum regions to form fluid muds (Kineke and

Sternberg, 1995). These fluid muds are dispersed

during the more energetic spring tides and become

temporarily incorporated into the underlying seabed.

The tidal excursion of the front is ~30 km.

Seasonal fluctuations in river discharge cause the

turbidity maximum-sediment mobilization zone to be

displaced either landward or seaward (Kineke and

Sternberg, 1995; Nittrouer et al., 1995). A combina-

tion of surface waves, tidal currents, and riverine

supply influence the thickness and expanse of the

fluid mud; winds tend to accentuate across-shelf

transport in both seaward and shoreward directions

(Kineke and Sternberg, 1995).

Mobilized sediment is transported northward

along-shelf, forming a reworked surface layer in the

relatively consolidated seabed that is as much as 1.5 m

thick between the 10- and 30-m isobaths (Kuehl et al.,

1995). Portions of the seabed are exhumed and

resuspended into overlying fluid muds during periods

when intense surface waves are superimposed upon

tidal currents (Cacchione et al., 1995; Kuehl et al.,

1995). Overall, ~31�109 tons of sediment are

reworked annually on daily to seasonal time scales

(Aller, 1998). Given the riverine discharge of

0.8�109–0.9�109 tons/year, the mean residence time

of material in the physically reworked zone is ~30–40

years.

More than 50% of the fluvial OC disappears on the

Amazon shelf (Aller et al., 1996; Keil et al., 1997).

Normalization of OC content to particle surface area

(OC/SA) indicates that this is not a result of hydro-

dynamic sorting, but instead that of desorption and/or

oxidation (Keil et al., 1997; Aller, 1998; Fig. 4). y13Cvalues indicate a seaward trend toward increasing

proportions of marine OC (Showers and Angle, 1986;

Keil et al., 1997; Fig. 4). Isotopic mass balance

calculations, assuming terrestrial and marine y13Cend-members of �28x and �20x, respectively

(Showers and Angle, 1986; Hedges et al., 1986a;

Sommerfield et al., 1996), indicate a nearly constant

marine loading but a net loss of terrestrial material

(Fig. 4). 14C ages of the POC increase with distance

from the river mouth, which is consistent with the

preferential loss of a younger, more reactive fraction

(Fig. 4; Sommerfield et al., 1996). Porewater dis-

solved inorganic y13C values converge over much of

the delta topset region to near �23x, reflecting an

oxidized mixture of ~40% terrestrial and ~60% ma-

rine C (Fig. 8). A trend towards a greater marine

contribution is seen as one moves seaward and

downdrift of the river mouth (Fig. 8). Modeling

indicates that the average y13C values of DIC added to

the porewater over the upper 5 m at these sites are


�23.4F0.1 (RMT-2), �23.5F0.4 (OST-2), and

�22.0F0.7x (OST-3). A similar, albeit better re-

solved pattern is observed in the mobile deltaic topset

muds on the Fly River shelf offshore of Papua New

Guinea, where the 13C, 14C contents of porewater DIC

and the POC clearly indicate selective oxidation of

younger marine OC over the riverine input both with

distance from the river mouth and downcore within

the seabed (Aller and Blair, 2004).

Periodic regeneration of oxidants coupled with the

admixing of reactive marine OC likely fuels the loss of

the otherwise recalcitrant terrestrial material in a

manner analogous to what occurs during sewage

treatment (Graf, 1992; Canfield, 1994; Aller, 1998).

Although a large flux of marine carbon enters the

seabed, little is preserved in the highly dynamic

environment. Not until sediment moves out to the

more physically stable foreset region of the subaqu-

eous delta does the organic content increase with the

addition of marine carbon (Showers and Angle, 1986).

2.3. Implications and conclusions

The Eel is an example wherein the original

upland-generated organic carbon signal is transmitted

with some fidelity to the seabed. Modification of the

Fig. 8. Profiles of porewater dissolved inorganic carbon y13C (filled

symbols) and POC y13C (open symbols) on the Amazon shelf. POC

y13C values reflect the dominance of the terrestrial OC in the buried

solid phase. DIC y13C profiles record not only the co-oxidation of

terrestrial and marine OC but also the preferential oxidation of the

more reactive marine component. DIC y13C values at depthsz6 m

are impacted by anaerobic methane oxidation and are not shown

(Blair and Aller, 1995).

signal is accomplished by simple additions of

modern OC. In contrast, upstream signals from the

Amazon are erased and overprinted by successive

downstream reservoirs, primarily the floodplain soils

and the shelf surface muds. These two riverine

systems represent end-members in a continuum of

behaviors, yet their characteristics are far from

atypical. For instance, a number of highly turbid

rivers in addition to the Eel, including the Santa

Clara of southern California, the Lanyang Hsi of

Taiwan, and the Waipaoa of New Zealand, transport

kerogen loads on the order of 0.5% by weight

(Meybeck, 1993; Masiello and Druffel, 2001; Kao

and Liu, 1996; Gomez et al., 2003). This concen-

tration is the same as the mean OC content of

sedimentary rocks (Ronov, 1976), which may

explain the uniformity in fluvial kerogen load and

argues for an even greater and more widespread

occurrence than what has been reported to date. The

bimodal age distribution of POC (modern and

ancient) exported by the Eel is predicted to be

typical for short, steep, high sediment yield systems

(Fig. 7).

As on the Amazon shelf, distinctively low OC/

surface area ratios exist in the deltaic sediments of

other rivers, such as the Fly, Johnstone, and Mis-

sissippi, when compared to the riverine output or other

continental margin locations (Keil et al., 1997; Aller,

1998; Aller and Blair, 2004). The intensity (depth

within seabed), frequency and duration of physical

mixing coupled with sediment accumulation rate are

hypothesized to be factors in controlling the extent of

OC loss (Aller, 1998). Duration will be controlled in

part by shelf width and morphology. Narrow shelves,

such as those characteristic of the Eel and other small,

active margin rivers, facilitate sediment bypass to the

slope (Sommerfield and Nittrouer, 1999; Nittrouer et

al., 2001); thus, the material buried on them will have

spent relatively less time in the surface mixed layer

than on wider margins, particularly if sediment

accumulation rates are high. Partially enclosed coastal

embayments, such as the Columbia and Gironde

estuaries, would facilitate the exchange of marine for

terrestrial OC because of the retention of particles in an

environment subject to repeated deposition–resuspen-

sion cycles and the supply of reactive marine

production (Keil et al., 1997; Abril et al., 1999; Crump

and Baross, 2000). Given the complex resuspension–


deposition histories that are likely experienced by

sediment in deltas, determining the total residence time

of POC in the mixed layer and its frequency of

resuspension is a crude exercise at best. This lack of

constraint has limited our ability to evaluate quantita-

tively the relationship between OC preservation and

sediment transport processes. Determining the resi-

dence time of POC in its various reservoirs, especially

in the seabed mixed layer, poses a significant challenge

for the future.

Understanding the dynamics of both the watershed

and shelf processes is key to interpreting the preserved

OC record. For example, soil C can appear older

(more 14C-depleted) than co-buried marine material as

a result of various processes as illustrated by the

model. In short Eel-like systems, OC sources differing

in age by millions of years are mixed producing a

material with an apparent intermediate age. Where

sources of OC are lowland-dominated as in the

Amazon system, terrestrial OC is aged by storage in

soils. Further 14C-loss occurs via the preferential loss

of the younger, more reactive terrestrial component

during diagenesis (Raymond and Bauer, 2001; Aller

and Blair, 2004; Fig. 7). Not considering these factors

may lead to erroneous interpretations of 14C-sedimen-

tary profiles (Sommerfield et al., 1996; Aller and

Blair, 2004).

The global CO2 and O2 cycles are linked by a

tectonically driven, mineral conveyor belt that both

buries and exhumes sedimentary OC (Hedges et al.,

1999b). The present-day burial flux of OC in marine

sediments has been estimated to be 12–13 Tmol C/

year (Hedges and Keil, 1995; Schlunz and

Schneider, 2000). The oxidation rate of the exhumed

rock OC is assumed to equal the burial flux so as to

maintain near constant O2 levels (Berner, 1989;

Hedges, 1992). If 40–70% of the global fluvial

sediment flux to the ocean (~20,000 Tg/year) is

delivered by small, mountainous rivers (Milliman

and Syvitski, 1992; Milliman, personal communica-

tion), and those rivers transport material that is on

average 0.5% kerogen C by weight, then 40–70 Tg

kerogen C/year (3.3–5.8 Tmol C/year) escape imme-

diate oxidation and may be reburied. This calculation

does not include export of kerogen from larger

drainage basins where it is more likely to be

oxidized during long-term storage. The riverine

kerogen flux is ~25–50% of the presumed kerogen

oxidation rate and total OC burial term. The net

effect of widespread kerogen reburial would be to

buffer the atmosphere against dramatic changes in

pO2 (Hedges, 1992). However, comparisons of OC

burial fluxes with kerogen oxidation rates must be

done with the acknowledgment that they have been

impacted anthropogenically and not equally. Human

activities have accelerated mass-wasting rates (Milli-

man and Syvitski, 1992; Foster and Carter, 1997;

Sommerfield et al., 2002), which should increase

kerogen export and OC burial fluxes while decreasing

kerogen oxidation or at least displacing it from the

continents to the deep-sea. As a result, a steady-state

balance between OC burial and kerogen oxidation

should not be assumed for the present.

Acknowledgements

This article was written to commemorate John

Hedges for his substantial contributions and leader-

ship in the field of organic geochemistry. John opened

many doors for us and his impact on the field will be

felt for many years. In addition, we wish to thank the

many individuals involved in the AmasSeds and

STRATAFORM projects who made the marine

sample collection and analyses possible. Special

thanks go to C.A. Nittrouer for his leadership on both

projects. An early version of this model was prepared

for a research proposal and the co-PIs, J. Bauer, E.

Canuel, C. Harris, and S. Kuehl, are acknowledged for

their assistance in its development. Funding has been

provided by NSF grants OCE-8812907, OCE-

9115709, OCE-9809553, OCE-0219919, and EAR-

0222584, the American Chemical Society Petroleum

Research Fund (33207-AC2), and the Office of Naval

Research. The comments offered by P. Raymond and

an anonymous reviewer were appreciated, as were the

efforts of R. Benner, C. Lee, and S. Wakeham in the

organization of the symposium and editorial handling

of the manuscripts.

References

Abril, G., Etcheber, H., Le Hir, P., Bassoullet, P., Boutier, B.,

Frankignoulle, M., 1999. Oxic/anoxic oscillations and organic

carbon mineralization in an estuarine maximum turbidity zone

(the Gironde, France). Limnol. Oceanogr. 44, 1304–1315.


Admunson, R., 2001. The carbon budget of soils. Annu. Rev. Earth

Planet. Sci. 29, 535–562.

Agnelli, A., Trumbore, S.E., Corti, G., Ugolini, F.C., 2002. The

dynamics of organic matter in rock fragments in soil inves-

tigated by 14C dating and measurements of 13C. Eur. J. Soil Sci.

53, 147–159.

Aller, R.C., 1998. Mobile deltaic and continental shelf muds as

suboxic, fluidized bed reactors. Mar. Chem. 61, 143–155.

Aller, R.C., Blair, N.E., 2004. Early diagenetic remineralization of

sedimentary organic C in the Gulf of Papua deltaic complex

(Papua New Guinea): net loss of terrestrial C and diagenetic

fractionation of C isotopes. Geochim. Cosmochim. Acta 68,

1815–1825.

Aller, R.C., Blair, N.E., Xia, Q., Rude, P.D., 1996. Remineralization

rates, recycling, and storage of Corg in Amazon Shelf sedi-

ments. Cont. Shelf Res. 16, 753–786.

Angers, D.A., Chenu, C., 1997. Dynamics of soil aggregation and C

sequestration. In: Lal, R., Kimble, J.M., Follett, R.F., Stewart,

B.A. (Eds.), Soil Processes and the Carbon Cycle. CRC Press,

NY, pp. 199–206.

Arnarson, T., Keil, R.G., 2001. Organic–mineral interactions in

marine sediments studied using density fractionation and X-ray

photoelectron spectroscopy. Org. Geochem. 32, 1401–1415.

Baldock, J.A., Skjemstad, J.O., 2000. Role of the soil matrix and

minerals in protecting natural organic materials against bio-

logical attack. Org. Geochem. 31, 697–710.

Berner, R.A., 1982. Burial of organic carbon and pyrite sulfur in the

modern ocean: its geochemical and environmental significance.

Am. J. Sci. 282, 451–473.

Berner, R.A., 1989. Biogeochemical cycles of carbon and sulfur and

their effect on atmospheric oxygen over Phanerozoic time.

Palaeogeogr. Palaeoclimatol. Palaeoecol. 75, 97–122.

Bevins, R.E., Robinson, D., Aguirre, L., Vergara, M., 2003.

Episodic burial metamorphism in the Andes—a viable model?

Geology 31, 705–708.

Bianchi, T.S., Filley, T., Dria, K., Hatcher, P.G., 2004. Temporal

variability in sources of dissolved organic carbon in the lower

Mississippi River. Geochim. Cosmochim. Acta 68, 959–967.

Blair, N.E., Aller, R.C., 1995. Anaerobic methane oxidation on the

Amazon shelf. Geochim. Cosmochim. Acta 59, 3707–3715.

Blair, N.E., Levin, L.A., DeMaster, D.J., Plaia, G., 1996. The short-

term fate of fresh algal carbon in continental slope sediments.

Limnol. Oceanogr. 41, 1208–1219.

Blair, N., Leithold, E., Ford, S., Peeler, K., Holmes, J., Perkey, D.,

2003. The persistence of memory: the fate of ancient sedimen-

tary organic carbon in a modern sedimentary system. Geochim.

Cosmochim. Acta 67, 63–73.

Blake Jr., M.C., Jayko, A.S., McLaughlin, R.J., Underwood, M.B.,

1988. Metamorphic and tectonic evolution of the Franciscan

Complex, northern California. In: Ernst, W.G. (Ed.), Meta-

morphism and Crustal Evolution of the Western United States.

Prentice-Hall, Upper Saddle River, NJ, pp. 1036–1060.

Brown, W.M. III, Ritter, J.M., 1971. Sediment Transport and

Turbidity in the Eel River basin, California. Water Supplemental

Paper No. 1986. U.S. Geological Survey.

Buyanovsky, G.A., Brown, J.R., Wagner, G.H., 1997. Sanborn

field: effect of 100 years of cropping on soil parameters

influencing productivity. In: Paul, E.A., Elliott, E.T., Paustian,

K., Cole, C.V. (Eds.), Soil Organic Matter in Temperate

Agroecosystems. CRC Press, NY, pp. 205–225.

Cacchione, D.A., Drake, D.E., Kayen, R.W., Sternberg, R.W.,

Kineke, G.C., Tate, G.B., 1995. Measurements in the bottom

boundary layer on the Amazon subaqueous delta. Mar. Geol.

125, 235–257.

Canfield, D.E., 1994. Factors influencing organic carbon preserva-

tion in marine sediments. Chem. Geol. 114, 315–329.

Connin, S.L., Virginia, R.A., Chamberlain, C.P., 1997. Carbon

isotopes reveal soil organic matter dynamics following arid land

shrub expansion. Oecologia 110, 374–386.

Crump, B.C., Baross, J.A., 2000. Characterization of the bacterially-

active particle fraction in the Columbia River estuary. Mar.

Ecol., Progr. Ser. 206, 13–22.

de Leeuw, J.W., Largeau, C., 1993. A review of macromolecular

organic compounds that comprise living organisms and their

role in kerogen, coal, and petroleum formation. In: Engel, M.H.,

Macko, S.A. (Eds.), Organic Geochemistry Principles and

Applications. Plenum, New York, pp. 23–72.

DeRose, R.C., Gomez, B., Marden, M., Trustrum, N.A., 1998.

Gully erosion in Mangatu Forest, New Zealand, estimated

from digital elevation models. Earth Surf. Process. Landf. 23,

1045–1053.

Dunne, T., Mertes, L.A.K., Meade, R.H., Richey, J.E., Forsberg,

B.R., 1998. Exchanges of sediment between the floodplain

and channel of the Amazon River in Brazil. GSA Bull. 110,

450–467.

Dymond, J.R., Jessen, M.R., Lovell, L.R., 1999. Computer

simulation of shallow landsliding in New Zealand hill country.

JAG 1, 122–131.

Foster, G., Carter, L., 1997. Mud sedimentation on the continental

shelf at an accretionary margin—Poverty Bay, New Zealand.

N.Z. J. Geol. Geophys. 40, 157–173.

Gabet, E.J., Dunne, T., 2002. Landslides on coastal sage-scrub and

grassland hillslopes in a severe El Nino winter: the effects of

vegetation conversion on sediment delivery. Geol. Soc. Amer.

Bull. 114, 983–990.

Geyer, W.R., Hill, P.S., Milligan, T.G., Traykovski, P., 2000. The

structure of the Eel River plume during floods. Cont. Shelf Res.

20, 2067–2093.

Gibbs, R.J., 1967. Amazon River: environmental factors that control

its dissolved and suspended load. Science 156, 1734–1737.

Golchin, A., Baldock, J.A., Oades, J.M., 1997a. A model linking

organic matter decomposition, chemistry, and aggregation

dynamics. In: Lal, R., Kimble, J.M., Follett, R.F., Stewart,

B.A. (Eds.), Soil Processes and the Carbon Cycle. CRC Press,

pp. 245–266.

Golchin, A., Clarke, P., Baldock, J.A., Higashi, T., Skjemstad, J.O.,

Oades, J.M., 1997b. The effects of vegetation and burning on

the chemical composition of soil organic matter in a volcanic

ash soil as shown by 13C NMR spectroscopy. I: whole soil and

humic fraction. Geoderma 76, 155–174.

Gomez, B., Eden, D.E., Peacock, D.H., Pinkney, E.J., 1998.

Floodplain construction by recent, rapid vertical accretion:

Waipaoa River, New Zealand. Earth Surf. Process. Landf. 23,

405–413.


Gomez, B., Trustrum, N.A., Hicks, D.M., Rogers, K.M., Page, M.J.,

Tate, K.R., 2003. Production, storage and output of particulate

organic carbon: Waipaoa River basin, New Zealand. Water

Resour. Res. 39, ESG 2-1–ESG 2-8.

Goni, M.A., Ruttenberg, K.C., Eglinton, T.I., 1997. Sources and

contribution of terrigenous organic carbon to surface sediments

in the Gulf of Mexico. Nature 389, 275–278.

Graf, G., 1992. Benthic–pelagic coupling: a benthic view. Ocean-

ogr. Mar. Biol. Annu. Rev. 30, 149–190.

Harris, C.K., Wiberg, P.L., 2002. Across-shelf sediment transport:

interactions between suspended sediment and bed sediment.

J. Geophys. Res. 107 (C1), 8-1–8-12.

Hartnett, H.E., Keil, R.G., Hedges, J.I., Devol, A.H., 1998.

Influence of oxygen exposure time on organic carbon

preservation in continental margin sediments. Nature 391,

572–574.

Hedges, J.I., 1992. Global biogeochemical cycles: progress and

problems. Mar. Chem. 39, 67–93.

Hedges, J.I., Keil, R.G., 1995. Sedimentary organic matter

preservation: an assessment and speculative synthesis. Mar.

Chem. 49, 81–115.

Hedges, J.I., Oades, J.M., 1997. Comparative organic geochemistries

of soils and marine sediments. Org. Geochem. 27, 319–361.

Hedges, J.I., Clark, W.A., Quay, P.D., Richey, J.E., Devol, A.H.,

Santos, U. de M., 1986a. Compositions and fluxes of particulate

organic material in the Amazon River. Limnol. Oceanogr. 31,

717–738.

Hedges, J.I., Ertel, J.R., Quay, P.D., Grootes, P.M., Richey, J.E.,

Devol, A.H., Farwell, G.W., Schmidt, F.W., Salati, E., 1986b.

Organic Carbon-14 in the Amazon River System. Science 231,

1129–1131.

Hedges, J.I., Cowie, G.L., Richey, J.E., Quay, P.D., 1994. Origins

and processing of organic matter in the Amazon River as

indicated by carbohydrates and amino acids. Limnol. Oceanogr.

39, 743–761.

Hedges, J.I., Keil, R.G., Benner, R., 1997.What happens to terrestrial

organic matter in the ocean? Org. Geochem. 27, 195–212.

Hedges, J.I., Hu, F.S., Devol, A.H., Hartnett, H.E., Tsamakis, E.,

Keil, R.G., 1999a. Sedimentary organic matter preservation: a

test for selective degradation under oxic conditions. Am. J. Sci.

299, 529–555.

Hedges, J.I., Keil, R.G., Lee, C., Wakeham, S.G., 1999b. Atmos-

pheric O2 control by a dmineral conveyor beltT linking the

continents and ocean. In: Armannsson, H. (Ed.), Geochemistry

of the Earth’s Surface. A.A. Balkema, Rotterdam, pp. 241–244.

Hedges, J.I., Mayorga, E., Tsamakis, E., McClain, M.E.,

Aufdenkampe, A., Quay, P., Richey, J.E., Benner, R., Opsahl,

S., Black, B., Pimental, T., Quintanilla, J., Maurice, L., 2000.

Organic matter in Bolivian tributaries of the Amazon River: a

comparison to the lower mainstream. Limnol. Oceanogr. 45,

1449–1466.

Henrichs, S.M., 1995. Sedimentary organic matter preservation—an

assessment and speculative synthesis—a comment. Mar. Chem.

49, 127–136.

Hicks, D.M., Gomez, B., Trustrum, N.A., 2000. Erosion thresholds

and suspended sediment yields, Waipaoa River basin, New

Zealand. Water Resour. Res. 36, 1129–1142.

Hoorn, C., 1994. An environmental reconstruction of the palaeo-

Amazon River system (middle–late Miocene, NW Amazonia).

Palaeogeogr. Palaeoclimatol. Palaeoecol. 112, 187–238.

Irion, G., Mqller, J., deMello, J.N., Junk, W.J., 1995.

Quaternary geology of the Amazonian lowland. Geo Mar.

Lett. 15, 172–178.

Iverson, R.M., Reid, M.E., Iverson, N.R., LaHusen, R.G., Logan,

M., Mann, J.E., Brien, D.L., 2000. Acute sensitivity of landslide

rates to initial soil porosity. Science 290, 513–516.

Johnsson, M.J., Stallard, R.F., Meade, R.H., 1988. First-cycle

quartz arenites in the Orinoco River basin, Venezuela and

Columbia. J. Geol. 96, 263–277.

Kao, S.J., Liu, K.K., 1996. Particulate organic carbon export from a

subtropical mountainous river (Lanyang Hsi) in Taiwan.

Limnol. Oceanogr. 41, 1749–1757.

Kay, B.D., 1997. Soil structure and organic carbon: a review. In:

Lal, R., Kimble, J.M., Follett, R.F., Stewart, B.A. (Eds.), Soil

Processes and the Carbon Cycle. CRC Press, NY, pp. 169–197.

Keil, R.G., Mayer, L.M., Quay, P.D., Richey, J.E., Hedges, J.I.,

1997. Loss of organic matter from riverine particles in deltas.

Geochim. Cosmochim. Acta 61, 1507–1511.

Kelsey, H.M., 1980. A sediment budget and an analysis of

geomorphic process in the Van Duzen River basin, north coastal

California, 1941–1975: summary. Geol. Soc. Amer. Bull. 91,

190–195.

Kennedy, M.J., Pevear, D.R., Hill, R.J., 2002. Mineral surface

control of organic carbon in black shale. Science 295, 657–660.

Kineke, G.C., Sternberg, R.W., 1995. Distribution of fluid muds on

the Amazon continental shelf. Mar. Geol. 125, 193–233.

Kohnen, M.E.L., Sinninghe Damste, J.S., Kock-van Dalen, A.C.,

de Leeuw, J.W., 1991. Di- or polysulphide-bound biomarkers in

sulphur-rich geomacromolecules as revealed by selective

chemolysis. Geochim. Cosmochim. Acta 55, 1375–1394.

Kuehl, S.A., Pacioni, T.D., Rine, J.M., 1995. Seabed dynamics of

the inner Amazon continental shelf: temporal and spatial

variability of surficial strata. Mar. Geol. 125, 283–302.

Leithold, E., Blair, N., 2001. Watershed control on the carbon

loading of marine sedimentary particles. Geochim. Cosmochim.

Acta 65, 2231–2240.

Leithold, E.L., Hope, R.S., 1999. Deposition and modification of a

flood layer on the northern California shelf: lessons from and

about the fate of terrestrial particulate organic carbon. Mar.

Geol. 154, 183–195.

Leithold, E., Perkey, D.W., Blair, N.E., Creamer, T.N., 2004.

Sedimentation and carbon burial on the northern California

continental shelf: the signatures of land-use change. Cont. Shelf

Res, in press.

Marutani, T., Kasai, M., Reid, L.M., Trustrum, N.A., 1999.

Influence of storm-related sediment storage on the sediment

delivery from tributary catchments in the upper Waipaoa River,

New Zealand. Earth Surf. Process. Landf. 24, 881–896.

Masiello, C.A., Druffel, E.R.M., 2001. Carbon isotope geochemis-

try of the Santa Clara River. Glob. Biogeochem. Cycles 15,

407–416.

Mayer, L.M., 1994a. Surface area control of organic carbon

accumulation in continental shelf sediments. Geochim. Cosmo-

chim. Acta 58, 1271–1284.


Mayer, L.M., 1994b. Relationships between mineral surfaces and

organic carbon concentrations in soils and sediments. Chem.

Geol. 114, 347–364.

Meade, R.H., Dunne, T., Richey, J.E., Santos, U. de M., Salati, E.,

1985. Storage and remobilization of suspended sediment in the

lower Amazon River of Brazil. Science 228, 488–490.

Meybeck, M., 1993. C, N, P and S in rivers: from sources to global

inputs. In: Wollast, R., Mackensie, F.T., Chou, L. (Eds.),

Interactions of C, N, P and S Biogeochemical Cycles and

Global Change. Springer-Verlag, Berlin, pp. 163–193.

Milliman, J.D., Syvitski, J.P.M., 1992. Geomorphic/tectonic control

of sediment discharge to the ocean: the importance of small

mountainous rivers. J. Geol. 100, 525–544.

Mullenbach, B.L., Nittrouer, C.A., 2000. Rapid deposition of fluvial

sediment in the Eel canyon, northern California. Cont. Shelf

Res. 20, 2191–2212.

Nittrouer, C.A., Kuehl, S.A., Sternberg, R.W., Figueiredo Jr., A.G.,

Faria, L.E.C., 1995. Mar. Geol. 125, 177–192.

Nittrouer, C.A., Mullenbach, B.L., Walsh, J.P., Puig, P., Ogston,

A.S., Kuehl, S.A., Kineke, G.C., 2001. Mechanisms for

substantial sediment and associated carbon to escape seaward

from present continental shelves. 2001 Aquatic Sciences Meet-

ing Abstracts, Am. Soc. Limnol. Oceanogr., pp. 104.

Ogston, A.S., Cacchione, D.A., Sternberg, R.W., Kineke, G.C.,

2000. Observations of storm and river flood-driven sediment

transport on the northern California continental shelf. Cont.

Shelf Res. 20, 2141–2162.

Page, M.J., Trustrum, N.A., Dymond, J.R., 1994. Sediment budget

to assess the geomorphic effect of a cyclonic storm, New

Zealand. Geomorphology 9, 169–188.

Page, M.J., Reid, L.M., Lynn, I.H., 1999. Sediment production from

Cyclone Bola landslides, Waipaoa catchment. J. Hydrol., N.Z.

38, 289–308.

Perkey, D.W., 2003. Long-term sediment accumulation rates and

organic carbon burial on the middle Eel shelf, northern

California. MS thesis, North Carolina State University, Raleigh.

Petsch, S.T., Berner, R.A., Eglinton, T.I., 2000. A field study of the

chemical weathering of ancient sedimentary organic matter. Org.

Geochem. 31, 475–487.

Petsch, S.T., Eglinton, T.I., Edwards, K.J., 2001. 14C-dead living

biomass: evidence for microbial assimilation of ancient organic

carbon during shale weathering. Science 292, 1127–1131.

Potter, P.E., 1997. The Mesozoic and Cenozoic paleodrainage of

South America: a natural history. J. South Am. Earth Sci. 10,

331–344.

Puig, P., Ogston, A.S., Mullenbach, B.L., Nittrouer, C.A.,

Sternberg, R.W., 2003. Shelf-to-canyon sediment transport

processes on the Eel continental margin. Mar. Geol. 193,

129–149.

Quay, P.D., Wilbur, D.O., Richey, J.E., Hedges, J.I., Devol, A.H.,

1992. Carbon cycling in the Amazon River: implications from

the 13C compositions of particles and solutes. Limnol. Ocean-

ogr. 37, 857–871.

Quideau, S.A., Chadwick, O.A., Benesi, A., Graham, R.C.,

Anderson, M.A., 2001a. A direct link between forest

vegetation type and soil organic matter composition. Geo-

derma 104, 41–60.

Quideau, S.A., Chadwick, O.A., Trumbore, S.E., Johnson-May-

nard, J.L., Graham, R.C., Anderson, M.A., 2001b. Vegetation

control on soil organic matter dynamics. Org. Geochem. 32,

247–252.

Ransom, B., Bennett, R.H., Baerwald, R., Shea, K., 1997. TEM

study of in situ organic matter on continental margins:

occurrence and the bmonolayerQ hypothesis. Mar. Geol. 138,

1–9.

Ransom, B., Bennett, R.H., Baerwald, R., Hulbert, M.H., Burkett,

P.J., 1999. In situ conditions and interactions between microbes

and minerals in fine-grained marine sediments: a TEM micro-

fabric perspective. Am. Mineral. 84, 183–192.

R7s7nen, M.E., Linna, A.M., Santos, J.C.R., Negri, F.R., 1995. Late

Miocene tidal deposits in the Amazonian foreland basin.

Science 269, 386–390.

Raymond, P.A., Bauer, J.E., 2001. Riverine export of aged

terrestrial organic matter to the North Atlantic Ocean. Nature

409, 497–500.

Richey, J.E., Hedges, J.I., Devol, A.H., Quay, P.D., Victoria, R.,

Martinelli, L., Forsberg, B., 1990. Biogeochemistry of carbon in

the Amazon River. Limnol. Oceanogr. 35, 352–371.

Richey, J.E., Victoria, R.L., Salati, E., Forsberg, B.R., 1991. The

biogeochemistry of a major river system: the Amazon case

study. In: Degens, E.T., Kempe, S., Richey, J.E. (Eds.),

Biogeochemistry of Major World Rivers, SCOPE. J. Wiley

and Sons, pp. 57–74. Ch 3.

Robertson, A.I., Bunn, S.E., Boon, P.I., Walker, K.F., 1999.

Sources, sinks and transformations of organic carbon in

Australian floodplain rivers. Mar. Freshw. Res. 50, 813–829.

Ronov, A.B., 1976. Global carbon geochemistry, volcanism,

carbonate accumulation, and life. Geochem. Int. 13, 172–195.

(translation of Geokhimiya).

Rosenbloom, N.A., Doney, S.C., Schimel, D.S., 2001. Geomorphic

evolution of soil texture and organic matter in eroding

landscapes. Glob. Biogeochem. Cycles 15, 365–381.

Schlqnz, B., Schneider, R.R., 2000. Transport of terrestrial organiccarbon to the oceans by rivers: re-estimating flux- and burial

rates. Int. J. Earth Sci. 88, 599–606.

Scully, M.E., Friedrichs, C.T., Wright, L.D., 2002. Application of an

analytical model of critically stratified gravity-driven sediment

transport and deposition to observations from the Eel River

continental shelf, Northern California. Cont. Shelf Res. 22,

1951–1974.

Scully, M.E., Friedrichs, C.T., Wright, L.D., 2003. Numerical

modeling of gravity-driven sediment transport and deposition on

an energetic continental shelf: Eel River, northern California.

J. Geophys. Res. 108 (C4), 3120.

Sherwood, C.R., Drake, D.E., Wiberg, P.L., Wheatcroft, R.A.,

2002. Prediction of the fate of p,pV-DDE in sediment on the

Palos Verdes shelf, California, USA. Cont. Shelf Res. 22,

1025–1058.

Showers, W.J., Angle, D.G., 1986. Stable isotopic characterization

of organic carbon accumulation on the Amazon continental

shelf. Cont. Shelf Res. 6, 227–244.

Sommerfield, C.K., Nittrouer, C.A., 1999. Modern accumulation

rates and a sediment budget for the Eel shelf: a flood-dominated

depositional environment. Mar. Geol. 154, 227–241.


Sommerfield, C.K., Nittrouer, C.A., DeMaster, D.J., 1996. Sedi-

mentary carbon-isotope systematics on the Amazon shelf. Geo

Mar. Lett. 16, 17–23.

Sommerfield, C.K., Nittrouer, C.A., Alexander, C.R., 1999. 7Be as a

tracer of flood sedimentation on the northern California

continental margin. Cont. Shelf Res. 19, 335–361.

Sommerfield, C.K., Drake, D.E., Wheatcroft, R.A., 2002. Shelf

record of climatic changes in flood magnitude and frequency,

north-coastal California. Geology 30, 395–398.

Stallard, R.F., 1995. Relating chemical and physical erosion. Rev.

Miner. 31, 543–564.

Thomas, C.J., Blair, N.E., 2002. Transport and digestive alteration

of uniformly 13C-labeled diatoms in mudflat sediments. J. Mar.

Res. 60, 517–535.

Tissot, B.P., Welte, D.H., 1978. Petroleum Formation and Occur-

rence. Springer-Verlag, New York. 538 pp.

Traykovski, P., Geyer, W.R., Irish, J.D., Lynch, J.F., 2000. The role

of wave-induced density-driven fluid mud flows for cross-shelf

transport on the Eel River continental shelf. Cont. Shelf Res. 20,

2113–2140.

Trustrum, N.A., Gomez, B., Page, M.J., Reid, L.M., Hicks, D.M.,

1999. Sediment production, storage and output: the relative role

of large magnitude events in steepland catchment. Z. Geomorph.

N.F. 115, 71–86.

Vannote, R.L., Minshall, G.W., Cummins, K.W., Sedell, J.R.,

Cushing, C.E., 1980. The river continuum concept. Can. J.

Fish. Aquat. Sci. 37, 130–137.

Veizer, J., Jansen, S.L., 1985. Basement and sedimentary recycling:

2. Time dimension to global tectonics. J. Geol. 93, 625–664.

Wheatcroft, R.A., Drake, D.E., 2003. Post-depositional alteration

and preservation of sedimentary event layers on continental

margins: I. The role of episodic sedimentation. Mar. Geol. 199,

123–137.

Wheatcroft, R.A., Sommerfield, C.K., Drake, D.E., Borgeld, J.C.,

Nittrouer, C.A., 1997. Rapid and widespread dispersal of

flood sediment on the northern California margin. Geology 25,

163–166.

Wold, C.N., Hay, W.W., 1990. Estimating ancient sediment fluxes.

Am. J. Sci. 290, 1069–1089.

Wright, L.D., Friedrichs, C.D., Kim, S.C., Scully, M.E., 2001.

Effects of ambient currents and waves on gravity-driven

sediment transport on continental shelves. Mar. Geol. 175,

25–45.

Zimmerman, A.R., Goyne, K.W., Chorover, J., Komarneni, S.,

Brantley, S.L., 2004. Mineral mesopore effects on nitrogenous

organic matter adsorption. Org. Geochem. 35, 355–375.

Further reading

Wheatcroft, R.A., Borgeld, J.C., 2000. Oceanic flood deposits on

the northern California shelf: large scale distribution and small-

scale physical properties. Cont. Shelf Res. 20, 2163–2190.

from bedrock to burial: the evolution of particulate organic carbon across coupled...

Documents