Analyzing sources to sedimentary organic carbon in the Gulf of Urabá, southern Caribbean, using carbon stable isotopes

Accepted Manuscript Analyzing sources to sedimentary organic carbon in the Gulf of Urabá, southern Caribbean, using carbon stable isotopes Alex Rúa, Gerd Liebezeit, Heazel Grajales, Jaime Palacio PII:

S0895-9811(17)30238-9

DOI:

10.1016/j.jsames.2017.06.011

Reference:

SAMES 1725

To appear in:

Journal of South American Earth Sciences

Received Date: 30 June 2016 Revised Date:

10 February 2017

Accepted Date: 15 June 2017

Please cite this article as: Rúa, A., Liebezeit, G., Grajales, H., Palacio, J., Analyzing sources to sedimentary organic carbon in the Gulf of Urabá, southern Caribbean, using carbon stable isotopes, Journal of South American Earth Sciences (2017), doi: 10.1016/j.jsames.2017.06.011. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Analyzing sources to sedimentary organic carbon in the Gulf of Urabá, southern

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Caribbean, using carbon stable isotopes

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CBATA, Departamento de Ciencias Básicas y Áreas Comunes Tecnológico de Antioquia – Institución Universitaria, 050034 Medellín, Colombia b Institut für Chemie und Biologie des Meeres (ICBM) Oldenburg Universität, 26382 Wilhelmshaven, Germany INTEGRA, Facultad de Ingeniería Tecnológico de Antioquia – Institución Universitaria, 050034 Medellín, Colombia d GAIA, Corporación Académica Ambiental Universidad de Antioquia UdeA Medellín, Colombia

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Alex Rúaa1, Gerd Liebezeitb, Heazel Grajalesc, and Jaime Palaciod

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Corresponding author. Present address: Tecnológico de Antioquia 050034. Calle 78B No. 72A - 220 Medellín – Colombia E-mail address: [email protected] (A. Rúa)

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Abstract

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Carbon stable isotopes analysis serve reconstruction of the origin of organic matter (OM)

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deposited onto sediments. They also allow tracing vegetation change at different time

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scales. This study weighs the contribution of both marine and terrestrial sources to

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sedimentary organic carbon (OC) from a southwestern Caribbean Gulf partly surrounded

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by large Musa acuminata (banana) croplands. The δ13C values in three sediment cores

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from the gulf have slightly decreased over 1000 yrs BP, indicating enhanced terrestrial

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input of detrital carbon owing to river discharge. A two-end mixing model fed with these

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δ13C values showed that averaged terrestrial contribution of OC to sediment was 52.0% at

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prodelta, 76.4% at delta front, and 64.2% at Colombia Bay. This agrees well with

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sediment dynamics. The main source of sedimentary OC within the gulf was terrestrial

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instead of marine. In fact, a distorted trend in δ13C values for one of the coring sites could

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be the result of banana crop expansion through the 20th century.

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Keywords: Carbon stable isotope, sedimentary organic carbon, banana cropland, detrital

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carbon, marine source

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1. Introduction

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Isotopic fractionation is a reaction or process by which products shift their

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isotopic compositions (δ13C values) relative to that of their precursors when a bond

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breaks or forms. For kinetic isotope effects on OM,

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faster, leaving behind remnant molecules of their precursor enriched in 13C (Emerson and

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Hedges, 2008). Owing to isotope enzymatic effects that depend on temperature and their

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metabolic pathway (C3 or C4), terrestrial plants and marine phytoplankton

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photosynthesize preferentially

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fractionation factors for these two autotrophs are different and hover at predictable

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values. While the fractionation factor for terrestrial plants is ca. –19‰, it is ca. –14‰ for

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marine phytoplankton (O'Leary, 1981). Overall, this

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euphotic zone as fitoclasts onto sediments, where it is slightly enriched in

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diagenesis (Emerson and Hedges, 2008).

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C-rich products form and diffuse

C (Fischer, 1991; Albarède, 2009). However,

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C-rich OM is deposited from the 13

C during

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Many studies have assessed sources and budget of OC within coastal

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environments through carbon stable isotope analysis (Gearing et al., 1977; Benner et al.,

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1987; Martinelli et al., 1991; Dittmar et al., 2001; Bouillon et al., 2003; Cronin et al.,

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2005; Bouillon et al., 2008; Albarède, 2009; Liebezeit and Wöstmann, 2009; Xue et al.,

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2009; Sanders et al., 2010; Zhan et al., 2011). Some of these studies underline that the

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shifts in δ13C values of decomposing fitoclasts in sediment should also be considered in

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source identification of deposited OC. In recent years, Bouillon et al. (2008) concluded

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that carbon stable isotope analysis alone fails to unambiguously assess source of OC

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contributions. However, the use of specific biomarkers for particular sources can provide

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complementary indicators of source and decomposition processes for OC (Emerson and

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Hedges, 2008; Cortes et al., 2010). Previous research on carbon stable isotopes within tropical estuaries has

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concentrated on discrimination between mangrove and terrestrial contributions to the OC

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budget (Dittmar et al., 2001; Bouillon et al., 2003; Bouillon et al., 2008; Xue et al., 2009;

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Zhan et al., 2011). Little is known about the contribution of extensive cropland to the OC

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budget within estuarine environments. This study evaluates different sources of

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sedimentary OC in a low gradient hinterland (3%), where high river discharge drains

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large M. acuminata (banana) croplands. It extends the use of the classical approach for

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prediction of the terrestrial and marine contributions to sedimentary OC, thus including

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δ13C values from M. acuminata lipids as source indicators. In addition, this study

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discusses whether contribution from M. acuminata cropland to OC is widespread onto

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gulf sediments or rather limited within the zone of direct influence of freshwater jets

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coming from agricultural land.

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Methodology

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2.1

Study area

The Darién Gulf is the biggest gulf in the Atlantic coastline of Colombia, located

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in the southwestern Caribbean Sea at the Colombian border to Panamá. The inner portion

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of the Darién Gulf, known also as the Gulf of Urabá, is a 2000 km2 incursion of the sea

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into the northern end of the Bolívar Geosyncline. About 86% of the sediment load within

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the gulf is supplied by the Atrato River and the remainder by a number of minor streams

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and flashy hydrographs (Restrepo and Kjerfve, 2004). These rivers drain consolidated

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and unconsolidated alluvial Quaternary deposits, Eocene-Pliocene marine sediments,

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basaltic lava flow, Tertiary quartz diorites, and Tertiary volcanic rocks (Thomas et al.,

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2007b). Their mouths and deltas are fringed with swamp forests and salt marshes

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dominated by mangroves and dense stands of halophytes (Fig. 1, Table 1).

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Seasonality of regional precipitation shifts the modus of surface circulation as

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well as sediment dispersion and deposition within the gulf. Total annual precipitation

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ranges from ca. 2500 mm onto the gulf to up to 11000 mm upstream (Poveda and Mesa,

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2000; Restrepo et al., 2002). Freshwater jets of the rivers meander either southerly due to

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trade winds in dry season (January–March), or northerly due to Southern winds in rainy

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season (April–November). In the dry season, the freshwater jets of the rivers are

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topographically constrained and lose energy, favouring sedimentation rates up to 1 cm/y

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in Colombia Bay (Rúa et al., 2014). The northern portion of the gulf constitutes

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otherwise a flow-through system onto which mainly terrigenous silt is slowly (0.18 cm/y)

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and steadily deposited from freshwater jets (Ospina et al., 2014).

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While the hinterland basin is a warm (19–40 ºC) transitional watershed from

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rainforest to savannah fields (Vann, 1959; Thomas et al., 2007a), much of the gulf is at

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present moving slowly towards a depositional environment. Enhanced precipitation on

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the watershed increases erosion and transport of fissile mudstones down the rivers

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(Correa et al., 2005). The Atrato River drains 35700 km2 of rainforest in the Pacific basin

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(Robins, 1978), a zone with no dry season. In the southern hinterland, at least 34000 ha of

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original vegetation has been cut and replaced by Musa acuminata (banana) plantations,

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which increased erosion rates of Quaternary mudstones drained by the León River

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(Ménanteau, 2007; Blanco, 2009).

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3.2.2

Sampling Within the Gulf of Urabá, three sediment cores (2.0–2.7 m in length) were drilled

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on board R/V ARC-Quindío with a piston/gravity corer with 6.3 cm internal diameter

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PVC tubing in December 2009 (Fig. 1). Every core was stored at 4°C while awaiting

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analysis. Temperature, salinity, dissolved oxygen, and pH were measured in the water

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column every meter until 10 m depth and then every 5 m. Later, an erosive foothill of a

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Holocene terrace as well as leaves from two C4 and ten C3 plant species were sampled

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around some rivers that drain into the gulf (Atrato, Caimán Nuevo, and Caimán Viejo) in

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February 2011 (Table 1).

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2.3

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Sample analysis

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δ13C was analysed because it is a reliable way to estimate the OC budget within

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depositional environments (Sackett et al., 1965; Zhan et al., 2011) . Further, this method

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can help in source identification of deposited sediments (Benner et al., 1987; Sanders et

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al., 2010). All sediments studied were late Holocene in age (Ospina et al., 2014). Three

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charcoal bulk samples were dated for each of the cores prodelta and Colombia Bay at the

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Scottish Universities Environmental Research Centre by accelerator mass spectrometry.

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Ages were calibrated using OxCal v3.1 program from the University of Oxford.

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Chronology for the core Atrato Delta front was approximated by contrasting the history

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of both mercury usage during the Spanish colonization and cataclysmic volcanic

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eruptions against mercury content in well preserved sediments (Rúa et al., 2014).

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Chronology dates were used mainly for estimating constant sedimentation rates between

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dated horizons.

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2.3.1 Sample preparation

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The sediment cores were cut into 5-cm-slices that totalled 134 samples. Sediment

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and soil samples were lyophilized (Christ Alpha 1-4 LSC) at –40°C and ground in a

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planetary ball mill (Fritsch Pulverisette 5). Prior to oven dry (60ºC) and homogenise,

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inorganic carbonate was removed (HCl 2N) from the sediment and soil samples. Plant

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leaves were thoroughly washed, oven dried at 40°C, crushed with an impact mill (IKA A

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11), and sieved over a 0.125 mm mesh.

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To study patterns of isotopic fractionation from M. acuminata, its lipids were

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Soxhlet extracted for 24 h using dichloromethane/methanol (99:1 v/v). The extract was

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subdivided into n-alkanes, aromatic hydrocarbons, and polar heterocomponents (NSO)

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using an experimental set up similar to the one proposed by Liebezeit and Wöstmann

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(2009). In short, the three fractions were separated by column chromatography with

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activated silica gel (100–200 mesh) using solvent mixtures of sequentially increasing

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polarity:

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dichloromethane/methanol (90:10 v/v). These resulting fractions along with the rest of

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the samples were finally weighted and packed in tin capsules prior to assessment of δ13C

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values. Each tin capsule contained 20–50 µg OC. All samples were prepared per

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triplicate.

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(2)

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n-hexane,

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2.3.2 Carbon isotope analysis

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δ13C value of each sample was assessed by means of combustion isotope-ratio-

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monitoring mass spectrometry (C-irmMS) using a Carlo Erba EA 1108 elemental

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analyzer connected to a Finnigan MAT 252 mass spectrometer via a Finnigan MAT

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Conflo II split interface (Böttcher et al., 1998) in batches of 50 positions. The liberated

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sample gas (CO2) was transported in a continuous stream of helium (5.0 grade). Every

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batch included five positions with WS2 standard (–25.65‰) and four blanks. Results

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were reported in standard delta notation (δ) in per mil (‰) relative to V-PDB. They were

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tested for normality (Kolmogorov-Smirnov) and variance heterogeneity (Levene) and

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thus estimated by mean ± standard deviation.

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2.3.3 Geochemical model for deposited organic carbon

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In an attempt to assess terrigenous and marine contribution of OC to the gulf

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sediments, we adapted the method proposed by Dittmar et al. (2001). Specifically, in our

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approach variation of δ13C values in sediments was described by a two-end mixing model

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taking tropical marine plankton and C3 plants as end-members. The first end-member was

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averaged δ13C value (–20.5‰) of tropical marine plankton off Brazil and Uruguay

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(Fischer, 1991). The second was averaged δ13C value (–29.4‰) of the nine C3 plants in

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this study plus 28 species from the Siak Estuary in Indonesia (Liebezeit, unpubl. data).

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3

Results

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Marked shifts in some physical and chemical parameters were found throughout

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the water column from the Darién Gulf. At the Atrato Delta front, dissolved oxygen

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remained fairly constant through the water column, while pH values varied considerably

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(Fig. 2a). Although bottom water was hypoxic (0.03 mmol O2/ l) in the Colombia Bay, its

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surface water was oxygen saturated. Brackish water comprised ca. 930 km2 of the

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southern portion of the gulf, where runoff overlaid marine water with different

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proportions. The delta front was essentially polyhaline (2.9–22.0 PSU), while

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mixoeuhaline conditions (21.1–35.4 PSU) were found at the northerly prodelta (Fig. 2b).

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δ13C values of the three cores showed that contribution of terrigenous sediment to

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the seafloor decreased with distance from the Atrato Delta front (Fig. 3). These δ13C

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values tended to be relatively

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delta front, and intermediate on the Colombia Bay (Table 1). In fact, relatively lighter

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carbon has been deposited onto the three drilling sites in a long term trend from 960 ± 35

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cal yrs BP to present (Fig. 3b). δ13C values of sediment including the Holocene terrace

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ranged from –28.50‰ to –24.30‰.

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C enriched on the prodelta, generally depleted on the

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It is interesting to note that the δ13C values of sediments varied with gulf

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geometry and sediment regimes in each drilling site (Fig. 3c). This finding validates the

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usefulness of δ13C values as a tracer for sediment dynamics (sources and transport). The

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intermediate δ13C values found in core Colombia Bay are consistent with direction of

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wind driven currents in shallow water during dry season. The relatively heavier δ13C

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values found in the northerly prodelta highlight the role of a compensating outflow in

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transporting fine grained sediment seaward. On average, terrestrial contribution of OC to

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sediment was 52.0% at prodelta, 76.4% at delta front, and 64.2% at Colombia Bay.

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Typical δ13C values for plants inhabiting brackish wetlands were found (Table 1).

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As expected, bulk δ13C values for higher plants following the C3 metabolic pathway were

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considerably lighter than those of the C4 plants. Further analysis showed that detrital

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products of M. acuminata litter could be relatively 13C-depleted as its leaves decompose.

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Total reproducibility of the measuring procedure was better than 0.1‰.

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Discussion

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Lateral variation of δ13C values in cored sediments agreed well with changes in

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surface salinity (Fig. 2 and 3). This finding is consistent with earlier studies conducted in

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transitional environments (Allen and Keith, 1965). However, the effect of salinity on

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isotopic fractionation must be tested for particular environmental settings (Bouillon et al.,

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2008). Within the gulf, seasonal changes in salinity owing to rainfall and wind forcing

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have caused sediment focusing to alternate temporarily. Through 3070 cal yrs BP, the

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gulf has shifted to a regressive environment where sediments display decreasing clay to

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silt ratios towards present (Ospina et al., 2014). These muddy sequences seem to imply

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an underlying tendency for

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time.

C, and presumed salinity, to have slightly decreased with

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It is fundamental to note that enhanced preservation of OC varied with

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sedimentation rates onto the gulf. Sediment coring was sparse, but results agreed with

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rheology, seemingly unbiased. Input of terrigenous OC decreased with sedimentation

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rates onto the delta front (up to 3cm/yr), Colombia Bay (2 cm/yr), and prodelta (0.18

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cm/yr), as well as with distance from the delta (Table 1). This dilution of terrigenous OC

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along seaward transects has been found to be typical for coastal sediments (Gearing et al.,

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1977; Goñi et al., 1997; Marinoni et al., 2000). Within the gulf, this finding is also

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consistent with modern hydrodynamics, mud deposition from river flumes, and delta

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progradation through 3070 cal yrs BP (Montoya, 2010; Ospina et al., 2014; Rúa et al.,

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2016). The OC origin of sediments in the continental margin within the gulf was

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dominated by terrestrial detritus, rather than from local marine biomass.

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δ13C values in sediment within the gulf appear to be preserved during transport

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and deposition (Fig. 3c). In our view, this result emphasizes the validity of our model.

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Indeed, two-end-member models describe adequately

C stocks in coastal zones with

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zones of accumulation and exchange of carbon (Bouillon et al., 2003). Local differences

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in δ13C values in sediment can reflect distinctive production of terrestrial OC and also

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influence interpretation of OC sources if selective assimilation and degradation occurs

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(Benner et al., 1987; Schlesinger and Bernhardt, 2013).

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Particularly, δ13C values in core Colombia Bay showed a distorted trend

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compared with the remaining two cores (Fig. 3b). These results could imply that input

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rate of OC to sediment have equaled diagenesis in Colombia Bay through 300 cal yrs BP.

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The latter hypothesis cannot be rejected based on our data. It can nevertheless be argued

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that this distorted trend is the result of altered vegetation by agricultural practices, as put

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forward by Cerling et al. (1989). In fact, soils surrounding the gulf have a complex

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vegetational history attributable to extensive cultivation of banana (Blanco, 2009;

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Arroyave-Rincón et al., 2012; Rúa et al., 2014). Input differences in compound-specific

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δ13C values through time in this core may thus not be disregarded.

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This study offers unprecedented insight into OC contribution from banana

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cropland to coastal sediments. Mean δ13C for M. acuminata kerogen was lighter than any

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of the sedimentary samples, whereas mean δ13C values for its aromatic hydrocarbons

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were much closer to values observed in sediments from the cores Atrato Delta front and

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Colombia Bay. Therefore M. acuminata kerogen can be discounted as the main

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sedimentary carbon source to sediments in this bay. On the other hand, aromatic

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hydrocarbons could significantly contribute to sedimentary carbon budget in the gulf. In

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fact, refractory compounds like aromatic hydrocarbons in terrestrial OM are

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preferentially preserved (de Leeuw and Largeau, 1993). Based on the isotopic signature

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of the fractions of M. acuminata extractable lipids, it seems likely that selectivity with

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which consumers would exploit this carbon source follows the order N-S-O compounds

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and lastly aromatic hydrocarbons alkanes. This is in line with the acknowledged

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biodegradability of biomacromolecules in marine sediments(Arndt et al., 2013). Actually,

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a slight degree of 13C enrichment is often observed between the dominant inputs and the

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resulting sediment OM (Bouillon et al., 2003). Further, recent studies have offered

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compelling evidence for slower mineralization rates of OC in M. acuminata (C3) than in

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C4 croplands under warming scenarios (Sierra et al., 2010).

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The relatively heavier OC found in the cores from the prodelta (Fig. 3) suggested

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a mild marine productivity towards the shelf that could be attributed to marine

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phytoplankton. This supports previous findings in the literature that propose an increasing

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gradient of marine productivity from the hinterland to the Caribbean atolls of Colombia

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(Howard et al., 2003). Besides, it also fits well with

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with increased productivity (Gearing et al., 1977; Fischer, 1991). Since primary

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productivity at the surface oceans is dominated by phytoplankton (–25‰), deposition of

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OC assimilated in its live tissue reflect the intensity of this enrichment (Emerson and

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Hedges, 2008; Albarède, 2009). Of course, brackish waters within the gulf have been

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C-enrichment of phytoplankton

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C-enriched through the last 960 ± 35 cal yrs BP.

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Plant habitat displayed no distinctive effect on δ13C values of plant leaves (Table 12

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1). However, results confirmed preferential assimilation of

C for all plants and

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the great isotope fractionation during photosynthesis compared to litter respiration

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regardless the metabolic pathway (Martinelli et al., 1991; Emerson and Hedges, 2008).

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Shifts in δ13C values of decomposing litter may depend on the type, diversity, and

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abundance of microbial decomposers colonizing the sedimentary OM (Bouillon et al.,

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2008). The δ13C of ca. –25‰ found in sediments for bitumen is inherited from its vegetal

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precursors (Albarède, 2009). Therefore down-core δ13C values from dated sediments are

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used in palaeoecology reconstructions of depositional systems (Cerling et al., 1989).

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Marine algae produce isotopically heavy carbon, but the ratios found in sediments from

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the gulf confirmed dominance of broad leaved (C3) plants.

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Mangrove area around the gulf amounts to ca. 1% and decrease continually due to

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logging (Thomas et al., 2007a). Mangroves bear a potentially high impact on the OC

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budget of global coastal zones (Bouillon et al., 2008). Mangrove litter contribution to

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sedimentary OM in wetlands varies (6.36–36.88%) depending on the species (Xue et al.,

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2009). The most extensive areas of mangrove forests occur on sedimentary shorelines

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(Bouillon et al., 2003), amounting to 60-75% of tropical coasts (Xue et al., 2009).

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Dittmar et al. (2001) traced mangrove, terrestrial, and marine-derived OM in a Brazilian

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estuary based on

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Remarkably, they found that mangrove contribution to the estuarine OM exceeds several

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times the terrigenous input from hinterland, although mangrove coverage was only ca.

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6%.

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C isotopes and lignin-derived phenols and mixing models.

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δ13C values of marine organic sediments can be controlled by the amount of

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terrestrially derived OC and the amount of cold-warm-water plankton preserved in the

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sediment (Sackett et al., 1965). That is, the δ13C of marine-derived sedimentary OC

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should also vary with the local water temperature in the overlying photic zone (Gearing et

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al., 1977). Despite the relatively constant temperatures found in the gulf, however,

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temperature variations in the Caribbean Current might have altered the isotopic profile in

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prodelta core during the Little Ice Age and Medieval Warm Period. Indeed, spatial and

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temporal changes in δ13C values in deltas, estuaries, and marginal bays may result from

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rainfall seasonality, patterns of bars and distributaries, as well as from long-term

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advances and retreats of the sea (Allen and Keith, 1965)

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Since the Atrato River is the major tributary draining into the gulf, input of

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terrestrial OC should be at a maximum at the prodelta. Dilution of seawater by

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freshwater, as in many other estuaries, results in

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13

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enriched algae (Bouillon et al., 2003) like G. dichotoma (Table 1). Given the shallow

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waters, and the similarity between δ13C value for the Holocene terrace and sediment, it

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appears likely that δ13C values were only modified after burial. We suggest that the

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respiration rate of sediments within the gulf decreases from North to South based upon

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sediment focusing and delta progradation. Naturally, the extent of

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deposition depends on the mode of benthic respiration and major components of plant

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tissues (Benner et al., 1987; Fischer, 1991). In fact, selective assimilation and degradation

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may occur as shown for banana litter.

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C depletion (Bouillon et al., 2008).

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C-

C depletion after

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C-enriched values are attributed to inwelling of marine OM including relatively

Conclusions

The rainforest and banana plantations are the Quaternary source of sediment to the

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gulf. Here, bulk OC is of terrestrial origin, though limited by contribution of marine

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plankton and algae. Gradients in δ13C values in sediment within the Darién Gulf are

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ascribed to incremental physical and chemical changes. First, hydrodynamics impinges

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on sediment delivery towards the South, where δ13C values are lighter than in the inner

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shelf. Second, sediment profiles were slightly

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C-enriched downcore following early

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diagenesis, i.e., loss to respiration. The extent of respiration in Colombia Bay may be

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limited by sediment focusing or alteration of vegetation cover for agricultural ends. This

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study has gone some way towards enhancing our understanding of OC delivery from

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banana cropland to the Caribbean. However, further work should be devoted to tracking

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and comparing the available sediment data with the history of land use around the gulf.

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315 Acknowledgements

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This research was made possible by a grant from the Colombian Administrative

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Department of Science, Technology and Innovation (COLCIENCIAS) and was partly

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sponsored by the Centre of Excellence in Marine Sciences (CEMarin). We thank the

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Universities Antioquia, Eafit, and Nacional de Colombia for donating the sediment cores

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to the CEMarin. We warmly thank Dr. I. Correa, L.C. Giraldo, J.B. Ospina, and C.A.

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Vélez for helping out with data collection. Thanks are also due to Dr. M.T. Flórez, who

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gave us much valuable advice in early stages of this work.

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Captions to figures Fig. 1. Location of the Darién Gulf showing sampling sites for sediment cores, soil, and plants. • This figure fits one column

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Fig. 2. Physical and chemical parameters measured in situ in the Darién Gulf during dry season 2009-2010. (a) O2 vs. pH plot. The shaded area shows typical pH values of rivers. (b) T vs. S plot with 95% confidence interval for measured values at Delta front. The shaded area shows typical surface salinity of the Caribbean Sea. • This figure fits one column

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Fig. 3. (a) Effect of geographical position on fractionation of carbon isotopes through the last 960 ± 35 cal yrs BP in the Darién Gulf. Numbers atop background bars show sample number. (b) Late Holocene depletion of δ 13C in three sediment cores from the Darién Gulf from 960 ± 35 cal yrs BP to present. (c) Mixing model for sedimentary OC using δ13C values as tracer for terrigenous contributions. • This figure fits two columns

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Captions to tables

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Table 1. Location, distance from Atrato River mouth, and isotopic composition of sediment, soil, and plant samples.

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8.501 8.167 7.996 8.218 8.662 8.348 8.348 8.015 8.018 8.018 8.015 8.133 8.133 8.077 8.015 8.024 7.809 N/A N/A N/A N/A

76.908 76.859 76.757 76.754 77.365 76.759 76.759 76.919 76.846 76.846 76.847 76.815 76.815 76.873 76.919 76.840 76.698 N/A N/A N/A N/A

a

WGS84 from Atrato River mouth c Plant ID as seen in Fig. 1 N/A Not applicable

40.0 3.3 22.1 16.2 77.8 25.9 25.9 15.6 15.3 15.3 15.5 7.7 7.7 8.2 15.6 14.9 43.0

N/A N/A N/A N/A

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Habitat

Metabolic pathway

N/A N/A N/A N/A

N/A N/A N/A N/A

N/A N/A N/A N/A

1 2 2 5 6 6 7 3 3 4 5 8 9

N/A N/A N/A N/A

Average δ13C [‰] –25.14 ± 0.33 –27.29 ± 0.35 –26.21 ± 0.24 –25.25 ± 0.11 –17.35 ± 0.69 –12.79 ± 0.36 –27.76 ± 0.09 –36.64 ± 0.23 –30.31 ± 0.04 –27.29 ± 0.11 –28.99 ± 0.12 –29.02 ± 0.08 –29.29 ± 0.09 –27.90 ± 0.03 –30.21 ± 0.02 –26.89 ± 0.23 –27.60 ± 0.03 –30.13 ± 0.09 –29.58 ± 0.06 –27.44 ± 0.38 –29.57 ± 0.02

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Plant IDc

Marine Limnetic Limnetic Limnetic Limnetic Limnetic Limnetic Estuarine Estuarine Estuarine Estuarine Estuarine Terrestrial N/A N/A N/A N/A

C4 C4 C3 C3 C3 C3 C3 C3 C3 C3 C3 C3 C3 C3 C3 C3 C3

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Core prodelta Core Atrato Delta front Core Colombia Bay Holocene terrace Grateloupia dichotoma Pennisetum purpureum Typha latifolia 1 Ceratophyllum demersum Polygonum ferrugineum Typha latifolia 2 Eichhornia heterosperma Avicenia germinans1 Avicenia germinans2 Acrostichum aureum Rhizophora mangle Montrichardia arborescens Musa acuminata M. acuminata kerogen M. acuminata alkanes M. acuminata aromatics M. acuminata NSO compounds

N

Distanceb [km]

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Sample

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Highlights for Analyzing sources to sedimentary organic carbon in the Gulf of Urabá, southern Caribbean, using carbon stable isotopes

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Contribution of terrigenous sediment to the seafloor decreased with distance from the Atrato Delta front Isotopic composition (δ13C) of the sediments varied with sediment dynamics related to gulf geometry Relatively lighter carbon has been deposited onto the gulf sediments in a long term trend over the last millennium Averaged terrestrial contribution of organic carbon to sediment was 52.0% at prodelta, 76.4% at delta front, and 64.2% at Colombia Bay

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