Particulate organic matter sinks and sources in high Arctic fjord

    Particulate organic matter sinks and sources in high Arctic fjord Karol Kuli´nski, Monika Kedra, Joanna Lege˙zy´nska, Marta Głuchowska, Agata Zaborska PII: DOI: Reference:

S0924-7963(14)00104-3 doi: 10.1016/j.jmarsys.2014.04.018 MARSYS 2538

To appear in:

Journal of Marine Systems

Received date: Revised date: Accepted date:

13 December 2013 27 April 2014 29 April 2014

Please cite this article as: Kuli´ nski, Karol, Kedra, Monika, Lege˙zy´ nska, Joanna, Gluchowska, Marta, Zaborska, Agata, Particulate organic matter sinks and sources in high Arctic fjord, Journal of Marine Systems (2014), doi: 10.1016/j.jmarsys.2014.04.018

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ACCEPTED MANUSCRIPT Particulate organic matter sinks and sources in high Arctic fjord Karol Kuliński(*), Monika Kędra, Joanna Legeżyńska, Marta Głuchowska, Agata Zaborska Institute of Oceanology, Polish Academy of Sciences, IO PAN, ul. Powstańców Warszawy 55, 81-

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712 Sopot, Poland

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*Corresponding author, e-mail: [email protected]

Abstract

The main aim of this paper is to present results on concentrations, fluxes and isotopic

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composition (δ13Corg) of particulate and sedimentary organic carbon (measures of particulate and sedimentary organic matter, respectively) in Kongsfjorden, Spitsbergen. The terrestrial particulate

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organic carbon (POC) input to the Kongsfjorden reached 760·106±145·106 g Corg y-1, forced mostly by the glaciers’ activity. This constituted 5-10% of the bulk POC supplied to the system. Marine primary production was the main source of the remaining 90-95% of POC. Organic carbon burial

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rates amounted to 9±1 g Corg m-2 y-1 in the central and 13±1 g Corg m-2 y-1 in the outer part of the

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fjord. Two terrestrial POM δ13Corg end members were identified: the ancient organic matter (OM) supplied by glaciers and rivers fed by water discharged from the glaciers (from -25.4‰ to -25.1‰),

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and the fresh terrestrial POM (from -26.7‰ to -26.6‰). Marine OM was characterized by a wide range of δ13Corg signatures: from ≤-26.1‰ for the phytoplankton depleted in

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Corg to ca. -15.8‰

for debris of marine phytobenthos. The lack of distinct marine δ13Corg end member and the

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resemblance of phytoplankton δ13Corg signatures to the terrestrial POM δ13Corg end member precluded the use of the two δ13Corg end members mixing model to trace terrestrial OM in Kongsfjorden, which is also very likely to happen in other Arctic regions.

Key words: POC, POM, carbon stable isotopes, organic carbon accumulation rate, organic carbon burial rate, Kongsfjorden, Spitsbergen

1. Introduction Shelf seas play an important role in the global carbon cycle by linking the terrestrial, oceanic and atmospheric carbon reservoirs (Thomas et al., 2004). Despite the fact that they make up only a little over 7% of the global sea surface and less than 0.5% of the ocean volume they are responsible for 15–30% of marine primary production and as much as 80% of organic matter (OM) burial (Borges, 2005; Bozec et al., 2005; Chen and Borges, 2009; Walsh, 1991).

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ACCEPTED MANUSCRIPT Recently, the carbon cycle in the Arctic shelf regions has received special attention, mainly due to their high sensitivity to the climate change (Bauch et al., 2000; McGuire et al., 2009; Stein and Macdonald, 2004). Arctic shelves are affected by seasonal or permanent ice cover, variable light availability and near-shore salinities (Grebmeier and Barry, 1991) and are currently

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experiencing significant changes primary due to rapid sea ice cover retreat (Comiso, 2012). Short

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productive season and resulting seasonal pulses of particulate organic matter (POM) exported to

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sediments shape the structure of local biogeochemical cycles and distribution and biomass of benthic biota (Carroll and Ambrose, 2012; Renaud et al., 2008; Wassmann et al., 2006a; Wassmann et al., 2006b). The fitness and survival of benthic communities are not only linked to the loads of POM to the sea floor but also depend on the quality of POM supplied since fresh

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marine POM is more bioavailable than the one originating from the land (Burdige, 2007; Iken et al., 2005; Kędra et al., 2012). Additionally, in the Arctic, high contribution of terrestrial POM is of

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ancient origin and therefore highly refractory for organisms (Goni et al., 2005; Kim et al., 2011). Identifying the sources of particulate and sedimentary OM is important for studying the carbon cycle. Marine POM, which is mostly phytoplankton derived, constitutes a driving force for

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the biological pump – one of the mechanisms controlling the uptake of the atmospheric CO2 by the

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marine environment. Burial of marine fraction of POM in sediments eliminates CO2 assimilated by phytoplankton during photosynthesis from the present CO2 pool (Thomas et al., 2004). However,

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shelf regions also receive significant loads of terrestrial POM, which partially may undergo mineralization in seawater releasing CO2 to the water column (Anderson et al., 2009). Therefore, determination of relative contributions of terrestrial and marine derived POM is

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often required in the biogeochemical studies conducted in the shelf regions. One of the methods used to identify the POM sources is an assessment of stable organic carbon isotopes ratio (δ13Corg). In general, marine POM is isotopically heavier than terrigenous plant material (Schubert and Calvert, 2001). Thus, a two end member mixing model is often used to distinguish between autoand allochthonous loads of POM in the system (Belicka and Harvey, 2009; Hedges et al., 1988; Schubert and Calvert, 2001; Winkelmann and Knies, 2005):

(1)

where: fterr (%) – percentage contribution of terrestrial organic carbon in the sample, δ13Corg(sample) δ13Corg measured in the sample, δ13Corg(marine) - δ13Corg of the marine end member, δ13Corg(terrestrial) δ13Corg of the terrestrial end member. The terrestrial δ13Corg end member for the Arctic regions is related to the presence of C3 plant debris since the contribution of C4 plants is of minor importance 2

ACCEPTED MANUSCRIPT in the high latitudes. The terrestrial δ13Corg end member ranges from -29.3‰ to -25.5‰ with an average range from -27.0‰ to -26.8‰ (Knies and Martinez, 2009; Naidu et al., 2000; Ruttenberg and Goni, 1997; Winkelmann and Knies, 2005). The terrestrial δ13Corg values may vary locally depending on the vegetation structure in the catchment areas. Additionally, in the high Arctic fjords

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discharge from glaciers supplies the marine environment with the ancient POM (Kim et al., 2011).

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The Arctic marine δ13Corg end member may be difficult to determine due to the heterogeneous structure of POM observed in the water column. Based on the relationship between

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organic nitrogen contribution to the total nitrogen and δ13Corg data in sediments west off Spitsbergen, Winkelmann and Knies (2005) estimated the marine δ13Corg end member to be 20.6‰. Similar results were found for the northern Norwegian coastal region (-20.3‰) (Knies et

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al., 2003) and in the Eurasian Arctic north-west off Spitsbergen (from -21.3‰ to -19.0‰) (Schubert and Calvert, 2001). However, the marine δ13Corg end member may change seasonally

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along with the changes in marine POM composition. Ice-algae, which may significantly contribute to the phytoplankton biomass, are enriched in 13Corg by 2-10‰ (Lovvorn et al., 2005; Tamelander et al., 2006). Schubert and Calvert (2001) estimated an average value of -18.3‰ for ice associated

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algae. Even higher results were found in the Chukchi Sea (-14.2‰) (Gradinger, 2009) and in the

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Canadian Arctic (-13.2‰) (Tremblay et al., 2006). Moreover, Tremblay et al. (2006) found strong positive relationship between δ13Corg results and thickness of sea ice. The marine δ13Corg end 13

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member may be also affected by the presence of phytoplankton depleted in

Corg: δ13Corg in

phytoplankton can be much lower in polar regions compared to the lower latitudes (Goericke and Fry, 1994; Rau et al., 1982; Rau et al., 1989). In the southern hemisphere there is a clear latitudinal

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trend of POM δ13Corg values: from ca. -18 to -22‰ in tropics and subtropics down to even -35‰ in the Antarctic region. Much less fractionation and less pronounced latitudinal trend were noticed in the Arctic. However, some POM samples collected in the high Arctic δ13Corg had values as low as 27‰ (Goericke and Fry, 1994). The application of the two δ13Corg end member mixing model to distinguish terrestrial OM from autochthonous OM in the Arctic is challenging due to the complexity of the carbon cycle there. The main aim of our research was to identify the δ13Corg signatures of the potential POM sources and sinks in high Arctic fjord. The obtained results were used to verify the applicability of the δ13Corg as a tracer of the organic matter sources in the Arctic marine ecosystems. Our study was conducted in Kongsfjorden – a high Arctic fjord (79 °N), strongly influenced by terrestrial and glacial supply. Additionally, we quantified the mean POC loads from land to Kongsfjorden and established Corg accumulation and burial rates in sediments. Thus, this study combine both qualitatively and quantitatively assessment of the POM cycling in the fjord and include wide range of measurements performed on terrestrial and marine POM samples and sediments. 3

ACCEPTED MANUSCRIPT 2. Study area Kongsfjorden is an open, 26 km long fjord located on the north-western coast of Spitsbergen, Svalbard (12˚E 79˚ N; Fig. 1). The fjord is divided into the outer basin with average

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depths of 200-300 m, and well separated by the chain of islands (Lovénøyane) inner basin with

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average depths of 50-60 m. Blomstrandøya is the only large island in the north–central part of the

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fjord. Landforms around Kongsfjorden are shaped by glacial activity, with active tidal glacier Kongsbreen at the head of the fjord. Located on the northern side, less active Blomstrandbreen also has a calving front, but on the southern side none of the several valley or cirque glaciers reaches the fjord. The fjord’s hydrology is influenced by relatively warm Atlantic waters of temperatures

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above 2°C and salinity of 35, carried by West Spitsbergen Current. The glacial activity causes environmental gradients in salinity, temperature, sedimentation rates and bottom sediment

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composition (Hop et al., 2002; Lefauconnier et al., 1994; Svendsen et al., 2002). The input of mineral material from Kongsbreen meltwaters into the fjord is about 2.6·105 m3 per year (Elverhoi et al., 1983) with the sedimentation rate decreasing with distance from the glacier (from about 800

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g m-2 day-1 at the glacier’s head to ca. 25 g m-2 day-1 at the mouth of the fjord) (Zaborska et al.,

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2006). Both advection of Atlantic waters and glacial input in the fjord are subjected to strong seasonal changes (Walkusz et al., 2009). The main freshwater input occurs in the summer season

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due to intensified rainfall, ice calving and melting of snow and ice. The amount of Corg in the surface sediments increases along the fjord axis from less than 2 mg g-1 in the inner bay to over 15 mg g-1 at the fjord opening (Kędra et al., 2010; Włodarska-Kowalczuk and Pearson, 2004). The

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sediments in below 30-40 m are composed of fairly uniform mud (Włodarska-Kowalczuk and Pearson, 2004). In glacial bay the deposited material is not compacted and thus frequently resuspended by iceberg scouring, sediment slides and gravity flows, but the stability of the sediments increases towards the central parts of the fjord (Dowdeswell, 1987; Syvitski et al., 1987). Ny-Ålesund is the only permanent settlement in the area, inhabited by 30–120 people depending on season, working at the local research stations. Due to the location of Kongsfjorden in the high latitudes, relatively easy access and excellent scientific base intensive studies on response of the Arctic ecosystem to climate change have been recently conducted in the region (Czerny et al., 2013; Motegi et al., 2013; Schulz et al., 2013; Silyakova et al., 2013; Tanaka et al., 2013).

3. Methods Sampling Samples were collected between 29.07 and 01.08.2011 during the r/y Oceania cruise. The sampling was performed at three marine stations, namely: KI, KM and KO located in the inner, 4

ACCEPTED MANUSCRIPT central and outer part of Kongfjorden, respectively, and at five additional locations identified as potential sources of allochthonous POM to the fjord (Tab. 1, Fig. 1). The latter included: Bayelva and NyLondon rivers (T1 and T2, respectively), a stream leaving the birds colony on the Blomstrandøya island (T3), Kongsbreen glacier discharge water (T4) and drifting icebergs from the

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Kongsbreen glacier (T5). Additionally, the random samples of living and degraded marine

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phytobenthos and land vegetation, soil and birds guano were collected from the intertidal zone and

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inland close to Bayelva and NyLondon rivers (T1 and T2 respectively) as well as close to the birds colony on Blomstrandøya island (T3).

Prior to the sampling the vertical profiles of salinity (in Practical Salinity Scale) and temperature were recorded at marine stations by means of SBE 911plus probe (Seabird Electronics

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Inc., USA). The CTD probe was deployed to the sea bottom except from the station KO (water depth: 249 m), where, due to the technical reasons, only upper 184 m were measured. Marine

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sediments were collected with GEMAX gravity corer. The upper 16 cm of the sediments cores were sliced onboard into 10 mm thick (upper 10 cm of the core) and 20 mm thick (bottom 6 cm of the core) layers and frozen at -80°C. Each slice was sampled for granulometry analysis. The coarse

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grains (>2 mm) were separated by dry sieving. Fine fraction of the sediment (0.02–2000 μm) was

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analyzed using a Malvern instrument Mastersizer 2000 (Syvitski, 1991). POM samples were taken in triplicates by filtering a volume of 0.5-2 dm3 of water (large plankton removed if present)

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through pre-combusted and pre-weighed Whatman GF/F glass fibre filters. After filtering the samples were immediately frozen at -80°C. At all stations, POM samples were collected separately for chlorophyll-a (chl-a) and organic carbon (elemental and isotopic) analyses. In case of marine

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stations POM samples were taken from three different depths: surface (1.5 m), subsurface maximum of fluorescence (located between 20 and 30 m depending on the station) and bottom water (ca. 2 m above the seabed). POM samples for chl-a were homogenized and acetone-extracted for 2 h in 4 °C in the dark. Afterwards extracts were spectrophotometrically measured. The concentrations of chl-a were calculated according to equations given by Lorenzen (1967).

Table 1. Coordinates and characteristics of the sampling stations.

Fig. 1. Sampling locations in Kongsfjorden.

Elemental and isotopic analyses Prior to the analyses, both sediments and POM samples were freeze dried, homogenized and weighted into silver capsules (with 1-μg accuracy). Afterwards samples were soaked in 2 M 5

ACCEPTED MANUSCRIPT HCl to remove inorganic carbon species and dried at 60 °C for 24 h (both steps were repeated until constant weight was reached). The analyses were performed on an Elemental Analyzer Flash EA 1112 Series combined with an Isotopic Ratio Mass Spectrometer IRMS Delta V Advantage (Thermo Electron Corp., Germany). The quantitative measurements were calibrated against the

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certified reference materials consisting of environmental samples (including marine sediments)

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provided by HEKAtech GmbH (Germany) and yielded a precision better than ±1.0% (n=7). For

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sediments the results are presented as Corg concentration in dry weight of the sample, whereas for POM they are given as POC concentration per both water volume (POCV) and dry weight of suspended matter (POCM). Organic carbon stable isotopes ratios (δ13Corg) were calculated using the laboratory working pure reference CO2 calibrated against IAEA standards: CO-8 and USGS40.

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Results of δ13Corg are given in the conventional delta notation versus Pee Dee Belemnite as parts

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per thousand (‰) according to the following equation:

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than 0.16‰ (n=7).

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Corg/12Corg. The precision of the measurements was better

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where: R is a corresponding ratio of

Sediment dating

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(2)

Pb method was used to determine the sediment mass accumulation rates (MAR). 210Pb is

particularly reactive and readily sorbs to sinking particles in marine waters. Since bottom

additional

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sediments also contain

Pb from the in situ decay of radium-226 (supported

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Pb is known as excess

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210

Pb (210Pbex). The activity of

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Pb,

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Pbsupp), the

Pbex decreases exponentially

Pbsupp activity remains constant. In this study the

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Po by alpha spectrometry. The secular equilibrium between

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over time since deposition while measured indirectly as

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210

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Pb was Po and

Pb was assumed. Sediment samples were frieze-dried and ground. Sediment moisture and porosity was

calculated. Radiochemical separation of 210Po was performed according to the method presented by Zaborska et al. (2007). Shortly, sediment samples were spiked with

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Po (chemical yield tracer)

and digested. Polonium isotopes were spontaneously deposited onto silver disks. Discs were analysed for 210Po and

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Po in a multi-channel analyser (Canberra) equipped with Si/Li detectors.

The samples were counted for 1 day. The activity of

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Po in the sample was determined based on

chemical recovery by comparing the measured and spiked activities of

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Po. Blanks and standards

were measured to verify the efficiency of the separation procedure and detection. 6

ACCEPTED MANUSCRIPT The 210Pbsupp activity was calculated as the average of several

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210

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sediment layers (below the zone of

Pb exponential decline). The

Pb determinations in deep

Pbex versus depth profiles

were corrected for compaction based on measurements of sediment porosity. Sediment mass accumulation rates (MAR) were calculated using Constant Initial Concentration model. Calculated

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rates represent upper limit values for sediment accumulation because the approach assumes no

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sediment mixing.

Corg accumulation and burial in sediments

The contemporary total organic carbon accumulation rate (CorgAR) was derived by

(3)

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multiplying MAR by the Corg concentration of surface-most sediment layer (0-1 cm) – Corg(0-1):

Organic matter accumulated at the bottom undergoes mineralization and/or is buried and preserved in the sediments. Organic carbon burial rate (CorgBR) was determined by multiplying MAR by the

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Corg concentration of the deepest sediment layer (14-16 cm) of the collected cores (Eq. 4). It was

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assumed that only refractory Corg exists at this depth and its mineralization, if such occurs, is

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negligible.

(4)

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4. Results and discussion

Seawater and sediment properties During the sampling campaign seawater temperature in the inner part of the Kongsfjorden was lower by ca. 1-1.5 ºC at all depths, except from 40 m, than the temperatures recorded at stations KM and KO (Fig. 2A). The whole area of the fjord was strongly influenced by freshwater originating from the glaciers’ discharge and/or river runoff. Salinity gradually increased from 31.7 at the sea surface to 34.5 at the depth of 70 m (Fig. 2B). Such hydrological regime is typical for the Kongsfjorden in summer (Hop et al., 2002). Mud prevailed at all stations (Tab. 1) which is coincident with study of (WłodarskaKowalczuk and Pearson, 2004) who found fairly uniform mud at depths greater than 30-40 m in Kongsfjorden.

Fig. 2. Temperature (A) and salinity (B) profiles at KI (blue), KM (red) and KO (green) stations. 7

ACCEPTED MANUSCRIPT 4.1. Organic carbon concentrations and fluxes POC in marine samples The highest concentrations of POCV were observed at the surface layer, with values

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between 0.170±0.003 and 0.498±0.067 mg dm-3 at KM and KO stations, respectively (Fig. 3A).

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The POCV concentration in the Kongsfjorden decreased towards the sea bottom except from its

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central part (station KM), where minimum values (0.091±0.006 mg dm-3) were observed in the subsurface water layer. The POM content in the suspended matter (POCM ) concentrations, increased from the inner to the outer part of the fjord (Fig. 3B). The highest POCM concentrations were observed in the subsurface layer at all investigated stations and ranged between 9.6±0.4 mg g(station KI) and 61.2±6.8 mg g-1 (station KO). Such POCM horizontal distribution is typical for

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the basins affected by the active glacier fronts (Svendsen et al., 2002). The glacier discharge water,

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which is enriched with mineral material and have low OM content, is diluted in seawater usually richer in POM. However, the combination of both low POCM and relatively high POCV (comparable to POCV at station KO) suggests that extremely high amount of suspended matter

POC in terrestrial samples

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originating from the glacier occurred in the inner part of the fjord during the sampling campaign.

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Characteristics of suspended matter found in the samples from Bayelva River (T1) and Kongsbreen glacier discharge water (T4) (Fig. 3C and D) were similar to those recorded at KI station (high POCV and low POCM) indicating that both river and glacier discharge are important

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terrestrial sources of POM and generally suspended matter in the fjord. Samples of drifting icebergs (T5) had similar POCV to both T1 and T4 (Fig. 3C), but had significantly higher POCM. This may suggest that the mineral material is released faster from the melting icebergs than OM. Drifting icebergs might be settled by marine organisms, likely contributing to the higher POCM. The water entering Kongsfjorden from Blomstradøya (T2 and T3) carried suspended matter richer in POM (higher POCM) than water coming from Bayelva River and glacier discharge (Fig. 3D). Nevertheless, the POCV concentration in NyLondon river (T2) was significantly lower (0.226±0.055 mg dm-3) than in other terrestrial samples (Fig. 3C). The highest POCV (1.132±0.468 mg dm-3) and POCM (95.6±2.5 mg g-1) were noticed in the stream leaving the bird colony on Blomstrandøya island (T3). This is probably due to the high contribution of the fresh OM originating from both the bird colony and in situ production in the stream. Fig. 3. Concentrations of POCV and POCM [mg dm-3] and SD in seawater (A and B, respectively) and in potential terrestrial sources of POM (C and D, respectively) 8

ACCEPTED MANUSCRIPT Allochthonous POC input vs. primary production Model estimations suggest that glaciers around the Kongsfjorden supply the basin annually with 842·106 m3 of freshwater on average (Svendsen et al., 2002). Svendsen et al. (2002) showed

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that bulk of freshwater originates from glaciers located in the eastern part of the fjord, including

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Kongsbreen. Thus, we used POCV concentrations obtained for the discharge water from

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Kongsbreen (T4) as representative and calculated the mean annual load of POC to the Kongsfjorden from glaciers (Lg) using the following formula:

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(5)

where: Vg is the mean freshwater volume supplied by the glaciers to Kongsfjorden annually and

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POCV(T4) is the POCV concentration in the Kongsbreen glacier discharge water measured in our study. Thus, Lg amounts to 738·106±142·106 g POC y-1. Using similar approach we determined the

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mean POC load from the Bayelva River (LB):

(6)

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where: VB is the mean, annual freshwater discharge from Bayelva River and POCV(T1) is the POCV concentration found in the samples of the Bayelva River water (this study). Svendsen et al. (2002) estimated VB to be of 32·106 m3 y-1. This volume multiplied by POCV(T1) of 686±103 mg m-3

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according to equation 6 results in load of 22·106±3·106 g POC y-1 from Bayelva. The sum of both Lg and LB gives the total input from land (LT) to Kongsfjorden of 760·106±145·106 g POC y-1. This result is likely underestimated since it does not take into account other rivers entering Kongsfjorden. However, LT seems to be controlled by the freshwater volume and not by the POCV concentrations, which do not differ significantly among the potential terrestrial POC sources (Fig. 3C). According to Svendsen et al. (2002) glaciers are the major source of freshwater in Kongsfjorden. This is reflected by the relatively low (2.9%) contribution of LB to LT though Bayelva is the largest river draining the Kongsfjorden catchment. Some POC may be additionally deposited from the atmosphere, yet the atmospheric POC deposition in high latitudes is believed to be minor (Jurado et al., 2008). The mean primary production in Kongsfjorden amounts to 35-50 g C m-2 y-1 (Hop et al., 2002). Assuming that the area of Kongsfjorden is 231 km2 (Hop et al., 2002), the mean bulk POC produced in the fjord varies between 8,085·106 and 11,550·106 g y-1. Therefore, LT constitutes from 5% to 10% of the sum of LT and primary production in the fjord (8,700·106-12,455·106 g y-1). This 9

ACCEPTED MANUSCRIPT range may be even higher since both LT and primary production are subjected to significant interannual variations due to changing ice cover, light, nutrient and temperature conditions as well as freshwater discharge to the fjord (Hop et al., 2002; Iversen and Seuthe, 2011; Svendsen et al.,

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2002).

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Sediment accumulation rates

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An excess of 210Pb decreased exponentially from the sediment surface to the depth of 9 cm at station KO (Fig. 4A). The maximum linear sediment accumulation rate (LAR) was estimated to be 0.14±0.01 cm y-1, whereas a mass sediment accumulation rate (MAR) amounted to 0.13±0.01 g cm-2 y-1 (1350±130 g m-2 y-1). The mean deposition year of the deepest sediment layer was 1871

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(Tab. 2). MAR at KO station was slightly higher than MAR reported previously for outer Kongsfjorden (Papucci et al., 1998). The reason for that is likely different location of sampling

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station in study of Papucci et al. (1998), located farther from the glaciers compared to the station KO (this study). Svendsen et al. (2002) reported only 0.02 g cm-2 y-1 (200 g m-2 y-1) of sedimentary material to be accumulated at the bottom of the fjord mouth. 210

Pb was present (Fig. 4A). Therefore, we used supported

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supported

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The sediment core taken at station KM was not long enough to reach layers where only 210

Pb value of 32.3 Bq kg-1

measured at station located in the central Kongsfjorden by Zaborska et al. (2006). The estimation

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of accumulation rate was mathematically forced considering an exponential decrease of

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Pbex

activity observed in the profile. The maximum sediment accumulation rate was estimated at 0.24±0.02 cm y-1 whereas MAR amounted to 0.32±0.03 g cm-2 y-1 (3200±320 g m-2 y-1). The

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deepest layer of the sediment core was dated to 1959 (Tab. 2). The obtained MAR was similar to the values reported by Svendsen et al. (2002) and Aliani et al. (2004) for the central part of Kongsfjorden (0.18-0.38 g cm-2 y-1 or 1,800-3,800 g m-2 y-1). The accumulation rate estimated by Zaborska et al. (2006) for the central Kongsfjorden was an order higher (about 2.5 cm y-1 or 5.6 g cm-2 y-1), however, this result was obtained for the station located closer to the Kongsbreen glacier. Station KI was located very close to the Kongsbreen glacier front, where enormous quantities of mineral material were transported from the glacier to the bottom. Unfortunately, sedimentation rate was too high there to use

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Pb method for determination of the accumulation

rate. Svendsen et al. (2002) observed the MAR even higher than 20,000 g m-2 y-1 in the 400 m distance from the glacier front. Sediment accumulation rates estimated from acoustic records in this area ranged from 6 to 8 cm y-1 (Elverhoi et al., 1983).

Table 2. Mean deposition year and Corg concentration in sediments from KM and KO stations. 10

ACCEPTED MANUSCRIPT Sedimentary organic carbon Organic carbon concentrations in sediments decreased significantly from outer to inner part of Kongsfjorden (Fig. 4B), where the lowest Corg concentrations (about 2.0 mg g-1) have been

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found. This horizontal gradient followed the distribution of POCM concentrations in the bulk

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suspended matter in the water column (Fig. 3B) and suggested a dilution of allochthonous material

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in POM-rich seawater with the increasing distance from the glacier.

At station KM Corg concentrations decreased along the sediment depth profile from 5.2 mg -1

g in the upper most layer to 2.8 mg g-1 in the deeper zone (Tab. 2, Fig 4B). Generally, two uppermost cm of sediment were enriched in organic carbon. Below 2nd cm depth Corg

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concentrations fluctuated around 3 mg g-1. Less variable and much higher organic carbon concentrations were measured at station KO where Corg concentrations decreased from 12.5 mg g-1

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at the top of the core to 10.0 mg g-1 in the layer of 14-16 cm depth (Tab. 2, Fig. 4B). Smaller decrease of Corg concentrations with sediment depth noticed in the mouth of the fjord may result from greater water depth (249 m) and thus higher residence time of POM in the

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water column. This extends the exposure of POM to pelagic mineralization and consequently less

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bioavailable POM reaches the sea bottom (Wassmann et al., 2006a). On the other hand, the relatively shallow water depths in the central and inner parts of the fjord favour utilization of POM

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in surface sediments. However, the effect is less pronounced at KI station. This is very likely due to enormous supply of glaciers’ material to sediments in the inner fjord hindering the development of

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the benthic communities.

Fig. 4. 210Pbex (A) and Corg (B) concentrations in sediments: KI (blue), KM (red), KO (green). Organic carbon accumulation and burial rates Due to lack of mass accumulation rate (MAR) for the KI station organic carbon accumulation and burial rates were determined only for the KM and KO stations. Although both KM and KO stations were characterized by different MARs and Corg(0-1) concentrations, the CorgAR values were similar at both locations: 16.6±2 g Corg m-2 y-1 and 16.8±2 g Corg m-2 y-1 at KM and KO, respectively. At station KM much lower Corg(0-1) concentration was compensated by the significantly higher MAR than at station KO. The combination of high MAR and low C org(0-1) in sediments at KM station resulted from the proximity to the very active glaciers’ fronts which supply the fjord with significant loads of sedimentary material originating from the local bedrock scratched by the glacier and thus being enriched with mineral fraction. On the other hand, low MAR at KO station was accompanied by high contribution of OM to the material accumulated in 11

ACCEPTED MANUSCRIPT sediments. Similar CorgAR were reported by Winkelmann and Knies (2005) in Storfjorden. They estimated that 5-7 g m-2 y-1 of marine organic carbon and similar amount of terrigenous organic carbon is deposited in surface-most sediments (dated for 2001). Comparable rates ranging from 18 to 34 g Corg m-2 y-1 were measured in Saguenay Fjord (St-Onge and Hillaire-Marcel, 2001).

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Organic carbon accumulation rates in fjords are higher than in modern shelf environment (Tyson,

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1995). For instance, Carroll et al. (2008) measured 2-4 times lower CorgAR ranging from 3.7 to 8.4 g Corg m-2 y-1 in the Barents Sea sediments.

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Organic carbon burial rates amounted to 9±1 g Corg m-2 y-1 and 13±1 g Corg m-2 y-1 at stations KM and KO, respectively. Although CorgAR were found similar at both locations, the lower CorgBR at KM station suggested more intensive recycling of OM in the surface sediments of the central

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Kongsfjorden than in its outer part. High irregularities observed in

210

Pbex profile at KM station

(Fig. 4A) indicated that those sediments were bioturbated. Since bioturbation contributes to better

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supply of sediments with oxidants, it may be the reason of more effective degradation of sedimentary organic matter and thus also lower CorgBR noticed at KM station than at KO station, where

210

Pbex profile suggested only minor relocation of sediments (Fig. 4A). Organic carbon

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burial rates obtained in this study were relatively high compared to the results reported for other

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Arctic shelf seas (Tab. 3). Higher burial rates measured for Shelikof Strait (Alaska) resulted from higher MAR, ranging from 900 to 6000 g m-2 yr-1 (Corg content was similar, ranging from 3 to 11

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mg g-1) (Rember and Trefry, 2005). Increased sediment accumulation for Shelikof Strait were explained by high river material input and occasional volcanic ash (Mont Katmai) input. Elevated organic CorgBR at some stations of the Mackenzie Shelf (Beaufort Sea) were caused by very high

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sedimentary material loads from Mackenzie river (Macdonald et al., 1998). Assuming the CorgBR of 9-13 g Corg m-2 y-1 as representative for the whole area of Kongsfjorden (231 km2) the total amount of Corg buried in the fjord ranged between 2079·106 and 3003·106 g y-1. This constituted from 17% to 34% of the total Corg supplied to the system both from LT and primary production (8,700·106-12,455·106 g y-1). However, the marine OM is expected to be more labile than the terrestrial one and thus to undergo more easily remineralisation. Therefore, the given above range of the Corg burial efficiency (17-34%) in Kongsfjorden is very likely the combination of lower percentage attributed to the burial efficiency of Corg originating from primary production and higher percentage related to the burial efficiency of the terrigenous Corg. To obtain the burial rates of the autochthonous OM in Kongsfjorden, we multiplied CorgBR results calculated in our study (9-13 g Corg m-2 y-1) by the marine OM shares in the bulk sedimentary OM estimated by Kim et al. (2011). They suggested that marine OM constitutes from 50% to 55% of the total sedimentary OM in a gradient from the central to the outer part of the fjord and as low as 9% in the vicinity of the glacier’s front. Hence, the burial rates of marine OM were 12

ACCEPTED MANUSCRIPT 4.5 g Corg m-2 y-1 and 7.1 g Corg m-2 y-1 in the central and outer part of the fjord, respectively. This constituted 9-20% of the mean primary production in Kongsfjorden reported by Hop et al. (2002). These numbers would be probably lower if phytobenthos production was included together with primary production as the source of marine organic carbon. However, there are no available data

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on benthic production in Kongsfjorden. The obtained carbon burial efficiency was significantly

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higher than in any other Arctic regions. For instance, in the Barents Sea burial efficiency amounts

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to 5-7% (Carroll et al., 2008) while in the Beaufort Sea to ca. 4% (Goni et al., 2005) (Tab. 3). Higher results were reported for the temperate areas (Tab. 3) where up to 50 % of organic carbon from primary production was buried in sediments. Generally, our results suggest low efficiency of the OM recycling in the water column and at the sea bed of Kongsfjorden. However, such

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conclusions should be drawn cautiously since all the input data used for this assessment are subject

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to significant uncertainty and seasonal variations.

Table 3. The organic carbon burial rates (CorgBR) and organic carbon burial efficiency (share of primary production buried in sediments). The comparison of results for Arctic and

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temperate shelf areas.

Terrestrial POM

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4.2. δ13Corg as a tracer of OM origin

The mean terrestrial POM δ13Corg signatures ranged between -26.7±0.1‰ and -24.4±0.8‰ at T2 and T5 stations, respectively (Fig. 5). The fresh POM δ13Corg values supplied by the

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NyLondon river (T2) and a stream leaving the birds colony (T3) were comparable to each other (26.7±0.1‰ and -26.6±0.4‰, respectively) and similar to the mean range of terrestrial δ13Corg end member reported for the Arctic regions, namely from -27.0‰ to -26.8‰ (Knies and Martinez, 2009; Naidu et al., 2000; Ruttenberg and Goni, 1997; Winkelmann and Knies, 2005). Higher δ13Corg were measured in samples from Bayelva River (T1; -25.4±0.2‰) and from Kongsbreen glacier discharge water (T4; -25.1±0.8‰). Similarity of both those results may suggest the same POM source. Bayelva River is mainly fed by the melting glaciers (Svendsen et al., 2002). Thus δ13Corg found at T1 and T4 made up the end member characterizing the ancient OM. POM samples collected from drifting icebergs were expected to have similar δ13Corg signatures as POM from Kongsbreen glacier discharge water (T4). However, they were higher (-24.4±0.8‰) which was probably due to the presence of enriched in 13Corg plankton organisms on the ice surface. Kim et al. (2011) found δ13Corg even higher values (from -23.8‰ to -20.3‰) for POM from drifting icebergs in Kongsfjorden and related them entirely to the ancient OM supplied by the glaciers. 13

ACCEPTED MANUSCRIPT Fig. 5. Mean δ13C signatures in POM and sediments samples. Error bars represent standard deviation (SD) of all replicates of the single sample. For sediments and POM collected at

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marine stations the mean values and SD include all the samples from the vertical profiles.

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Point sources

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In the relatively shallow and surrounded by land water body like Kongsfjorden additional point sources of OM (except primary production, river runoff and glacier discharge) like organic material flushed from the coast directly to the sea by rain or water from melting snow and/or debris of marine phytobenthos may contribute to the sedimentary material and influence its δ13Corg. They

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may be especially important in the shallow, euphotic coastal zone. However, such material can be carried by water currents to deeper regions of the fjord though the transport processes are not

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quantified yet in Kongsfjorden. This study suggests a high range of δ13Corg signatures in OM collected from the intertidal zones and shores close to the T1, T2 and T3 locations (Tab. 4). The δ13Corg in terrestrial OM ranged from -35.2‰ to -24.9‰, which were noticed in the samples

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collected from the shores of T3 and T2, respectively. Much higher δ13Corg signatures were observed

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in marine OM sampled from the intertidal zones that ranged from -21.6‰ to -16.0‰ at T1 and from -23.9‰ to -15.8‰ at T3. Especially high δ13Corg (>-20‰) were found in debris of marine

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phytobenthos at both locations.

Table 4. The range of δ13Corg and mean δ13Corg values in the random organic matter samples

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collected at T1, T2, and T3 locations.

Marine POM

The mean δ13Corg signatures of the POM samples collected at the marine locations ranged between -26.0±0.4‰ and -25.6±0.5‰, at KM and KI stations, respectively (Fig. 5). These values were lower than the average range of δ13Corg in POM (-24‰ and -22‰) reported for the Arctic (Iken et al., 2010). However, similar or even lower δ13Corg values were measured in Arctic POM (Gradinger, 2009; Hobson et al., 1995; Iken et al., 2005; Karlsson et al., 2011; Zhang et al., 2012). Low δ13Corg signatures and their high seasonal variability (-30.5‰ in summer and -26.2‰ in winter) were also found in POM samples from Kongsfjorden (Kędra et al., 2012). Convergence of δ13Corg results in POM samples from marine locations with δ13Corg signatures of ancient POM (T1, T4) and fresh, terrestrial POM (T2, T3) may suggest that during the sampling campaign POM in Kongsfjorden was almost entirely dominated by land-derived material. The salinity profiles (Fig. 2) also showed a strong input of freshwater and its spread to the 14

ACCEPTED MANUSCRIPT whole area of the fjord. However, there was a strong negative relationship between chl-a concentrations and δ13Corg signatures in POM at KO station (Fig. 6A). The chl-a concentrations of 0.72 and 1.11 mg m-3 at the depths of 1.5 and 30 m, respectively, suggested a relatively high activity of phytoplankton in the upper water column of the outer part of the fjord. This in turn

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caused an increase of the OM content in the suspended matter, which was reflected by the positive

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relationship between chl-a and POCM results (Fig. 6B). A drop of δ13Corg accompanying the increase of chl-a concentrations (Fig. 6A) indicated that phytoplankton cells were depleted in

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Corg. Similar relationships were not found in the inner and central parts of the fjord. Although

pelagic phytoplankton depleted in 13Corg might occur in the whole Kongsfjorden, its presence at KI and KM stations was probably masked by the large amounts of terrestrial POM having similar

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isotopic characteristics.

Low δ13Corg signatures in the marine phytoplankton were noticed in high latitudes

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especially in the southern hemisphere (Goericke and Fry, 1994; Rau et al., 1982; Rau et al., 1989). The fractionation of the carbon isotopes by phytoplankton during photosynthesis depends on the cell growth rate, size of organisms, cell membrane CO2 permeability and CO2 concentration in

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seawater [CO2(aq)] (Burkhardt et al., 1999a; Burkhardt et al., 1999b; Laws et al., 1995; Rau et al.,

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1997). Low temperatures in polar regions enhance solubility of atmospheric CO2 in seawater. Additionally, the rising CO2 concentrations in the atmosphere in the last decades caused by

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anthropogenic emissions strengthen the invasion of the atmospheric CO2 into the marine regions resulting in an increase of [CO2(aq)] (Wanninkhof et al., 2013). Atmospheric CO2, and especially the fraction originated from fossil fuels combustion, is isotopically lighter than marine inorganic

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carbon. Thus the higher availability of the light CO2 for marine phytoplankton causes a decrease of δ13Corg in POM (Cullen et al., 2001; Quay et al., 2003; Quay et al., 1992; Zhang et al., 2012). Yet, this phenomenon is rarely discussed for the Arctic although relatively high number of δ13Corg measurements in POM and sediments have been performed. The low δ13Corg signatures in POM and sediments are often attributed here to the high input of isotopically light terrigenous OM (Iken et al., 2010; Karlsson et al., 2011; Morata et al., 2008; Nagel et al., 2009; Winkelmann and Knies, 2005). This would suggest that the lowest δ13Corg should be observed in the coastal regions highly influenced by freshwater discharge from land. However, Zhang et al. (2012) noticed a reversed spatial distribution of δ13Corg in POM in the western Arctic Ocean. They found a gradual decrease of δ13Corg from -21.1‰ to -28.5‰ accompanied by the rising [CO2(aq)] observed in the transect from the shallow coastal waters to the open Arctic Ocean (79-80° N). This suggests that similar phenomenon may occur in other high Arctic regions.

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ACCEPTED MANUSCRIPT Fig. 6. Mean δ13Corg (A) and POCM (B) plotted against chl-a concentrations in POM collected at KI (blue), KM (red) and KO (green) stations. δ13Corg in sediments

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All sediment samples had significantly higher δ13Corg than POM samples collected from

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both marine and terrestrial locations (Fig. 5 and 7). Mean δ13Corg values for upper 16 cm of the sediments core were similar at all the locations and ranged between -22.7±0.3‰ (KM) and -

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22.4±0.3‰ (KI). Similar results (from -22.9‰ to -21.4‰) found in surface sediments of Kongsfjorden were attributed to the high contribution of isotopically heavy, autochtnonous OM in sedimentary material (Winkelmann and Knies, 2005). Lower values were noticed by Kędra et al.

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(2012) who found δ13Corg within the range from -24.0‰ to -22.7‰, possibly because their study concentrated in shallow areas (15 m) exposed to the direct input of POM from the land.

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We did not observe a horizontal gradient of δ13Corg in Kongsfjorden sediments. The sources of isotopically light ancient POM are located mostly in the eastern, inner part of the fjord. Thus, we expected an increase of δ13Corg signatures in sediments towards the mouth of the fjord. Such

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hypothesis could be supported by the findings of Kim et al. (2011), who, based on analysis of the

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retene concentrations and Δ14C data, noticed a significant decrease of marine OM contribution in Kongsfjorden sediments along the fjord axis, from 55% in the mouth down to 9% in the vicinity of

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the glacier’s front. The lack of spatial variability in sedimentary δ13Corg observed in this study may suggest that a decrease of marine OM contribution towards the inner part of the fjord is compensated by a simultaneous increase of its δ13Corg signatures. The latter may be caused by the

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higher importance of phytobenthos and/or ice algae in the shallow central and inner parts of the fjord characterized by relatively long-lasting sea ice cover. Both phytobenthos and ice algae are enriched in

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Corg because they live in a more CO2-limited environment than pelagic algae where

carbonates and bicarbonates, enriched in 13C are important carbon source. Although we did not find the ice algae δ13Corg end member, several studies (Gradinger, 2009; Lovvorn et al., 2005; Tamelander et al., 2006; Tremblay et al., 2006) indicated that these organisms may have high δ13Corg signatures. Moreover, pelagic algae, when trapped in a shallow melt water layer, may also temporarily become enriched in

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Corg, especially in an exponential growth phase, when due to

local depletion of [CO2(aq)] a decrease of discrimination against 13C occurs (Soreide et al., 2006). Although contributions of both phytobenthos and ice-algae to the sedimentary material are not quantified yet in Kongsfjorden, their significance on the annual scale as a carbon source to sediments may explain the differences observed in our study between δ13Corg signatures in POM and sediments. Debris of phytobenthos enters sediments directly whereas ice algae were not noticed during our summer sampling campaign due to lack of ice cover. Moreover, it is supposed 16

ACCEPTED MANUSCRIPT that phytoplankton depleted in

13

Corg was present in the water column, especially in the outer part

of the fjord. However, a full understanding of the sedimentary δ13Corg signatures requires higher interseasonal resolution of δ13Corg measurements in pelagic POM, preferably combined with biomass estimations. Kongsfjorden was usually sampled for carbon stable isotopes in summer,

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however, study performed in October by Renaud et al. (2011) in the central part of the fjord (the

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δ13Corg of -21.6‰) showed that high seasonal variability of the POM isotopic composition is enrichment in

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envisaged. The differences between POM and sedimentary δ13Corg may result also from the Corg during the diagenetic processes, but these changes are believed to be minor

though yet not fully understood (Schulz and Zabel, 2006).

The vertical profiles of δ13Corg in sediments were scattered (Fig. 7A and B), especially at

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stations KI and KM, where δ13Corg ranged from -23.0‰ to -21.9‰ and from -23.3‰ to 22.0‰, respectively. Less variability and clear negative trend towards sediments surface was noticed at

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station KO. The δ13Corg values decreased there from -22.4‰ at 14-16 cm or even -22.2‰ at 12-14 cm to -22.8‰ in the upper most layer (0-1 cm). The age of the sediments at station KO suggested that these changes were sustained at least from the start of the industrial era, i.e. from the mid-

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nineteenth century (Fig. 7B). These shifts in the quality of the sedimentary POM in the mouth of

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Kongsfjorden may be caused by several different processes. However, based on our own results and discussion presented above we consider the following three as the most likely: (i) an increase

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of input of the terrigenous, isotopically light POM, (ii) a decrease of the biomass of 13Corg-enriched ice algae and/or shifts in their δ13Corg signatures and (iii) a depletion of pelagic phytoplankton in 13

Corg due to rising concentration of atmospheric CO2 and its invasion to the marine environment.

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However, based on our data, it is impossible to define more precisely the reason of the shift in the isotopic composition of sedimentary material. It is expected that similar changes have occurred also in the inner and central parts of the fjord. However, the eventual long-term shifts might be masked there by high interannual variability of environmental conditions (e.g. sea ice cover or discharge from glaciers), which result in changes of δ13Corg signatures in POM. Moreover, the sediment core collected at KI station was not long enough to conclude about the long-term variability in the inner part of the fjord. Fig. 7. Vertical profiles of δ13Corg in sediments from KI (blue), KM (red) and KO (green) stations plotted against depth (A) and deposition year (B).

5. Conclusions This study showed that marine primary production was the major source of POM in Kongsfjorden on the annual scale. The terrestrial POM input, dominated by the glaciers’ discharge, 17

ACCEPTED MANUSCRIPT influences especially the inner and central parts of the fjord. The obtained results suggested high retention of OM in sediments. High δ13Corg signatures noticed in sediments indicate that isotopically heavy marine OM (e.g. debris of marine phytobethos and/or ice algae) was on average the key source of sedimentary OM in Kongsfjorden. However, more comprehensive interpretation

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of the sedimentary OM composition requires higher interseasonal resolution of δ13Corg

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measurements in pelagic POM, preferably combined with application of additional tracers of OM matter origin.

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A decrease of δ13Corg towards the surface most layers in the sediments’ core at the mouth of the fjord indicated that continuous changes in the composition of the sedimentary OM occurred there in the last few decades. This may be the consequence of an increasing discharge of istopically

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light terrestrial POM and/or a decreasing biomass (or δ13Corg signatures) of isotopically heavy icealgae due to retreat of sea ice cover. However, rising availability of the isotopically light

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anthropogenic CO2 as a carbon source for pelagic phytoplankton may contribute to these shifts as well. The results suggested presence of pelagic phytoplankton depleted in 13Corg in the mouth of the fjord, but this finding requires further experimental confirmation.

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Both fresh and ancient terrestrial POM had distinct δ13Corg signatures. However, high range

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of marine δ13Corg end member and especially the resemblance of δ13Corg signatures in phytoplankton depleted in 13Corg to the δ13Corg end member of the terrestrial POM precluded the use

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of the two δ13Corg end members mixing model to trace the terrestrial OM in Kongsfjorden. Since the occurrence of phytoplankton depleted in

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Corg is expected (or was already reported) also in

other high Arctic regions, the estimations of the terrigenous OM contribution in POM and

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sediments based on this method may require reconsideration.

Acknowledgements

The study was completed thanks to funding provided by Polish National Science Centre grant nr 2011/01/B/ST10/06985. A. Zaborska was funded by Ministry of Science and Higher Education grant nr N/N306/066634. Special thanks to Aleksandra Winogradow and Anna Maciejewska for help in samples analyses and to Emilia Trudnowska for CTD measurements.

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Table captions: Table 1. Coordinates and characteristics of the sampling stations.

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Table 2. Mean deposition year and Corg concentration in sediments from KM and KO stations.

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Table 3. The organic carbon burial rates (CorgBR) and organic carbon burial efficiency (share of

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primary production buried in sediments). The comparison of results for Arctic and temperate shelf areas.

Table 4. The range of δ13Corg and mean δ13Corg values in the random organic matter samples

Figure captions:

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Fig. 1. Sampling locations in Kongsfjorden.

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collected at T1, T2, and T3 locations.

Fig. 2. Temperature (A) and salinity (B) profiles at KI (blue), KM (red) and KO (green) stations. Fig. 3. Concentrations of POCV and POCM [mg dm-3] and SD in seawater (A and B, respectively)

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and in potential terrestrial sources of POM (C and D, respectively)

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Fig. 4. 210Pbex (A) and Corg (B) concentrations in sediments: KI (blue), KM (red), KO (green). Fig. 5. Mean δ13C signatures in POM and sediments samples. Error bars represent standard

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deviation (SD) of all replicates of the single sample. For sediments and POM collected at marine stations the mean values and SD include all the samples from the vertical profiles. Fig. 6. Mean δ13Corg (A) and POCM (B) plotted against chl-a concentrations in POM collected at

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KI (blue), KM (red) and KO (green) stations. Fig. 7. Vertical profiles of δ13Corg in sediments from KI (blue), KM (red) and KO (green) stations plotted against depth (A) and deposition year (B).

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ACCEPTED MANUSCRIPT Table 1. Coordinates and characteristics of the sampling stations. Station

Station type

Date

Coordinates

name

KI

31.07.2011

Marine: 77 m

29.07.2011

Marine: 80 m

29.07.2011

11⁰37.932' E

Mud – all layers (except

79⁰00.654’ N

1-2 cm: sandy mud)

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Marine: 249 m

12⁰08.673’ E

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characteristics

Mud – all layers (except

78⁰55.792’ N

10-12 cm: sandy mud)

12⁰28.051’ E

Mud – all layers

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KO

Sediment

78⁰53.615’ N

T1

Terrestial: Bayelva river

31.07.2011

11⁰54.356’ E

T3

Terrestial: NyLondon river

Terrestial: stream near birds

31.07.2011

1.08.2011

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T2

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78⁰55.727’N

colony (Blomstrandøya island) T4

Glacial: Kongsbreen glacier

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Glacial: drifting icebergs from

11⁰58.384’ E 78⁰59.191’ N 12⁰30.765’ E 78⁰52.501’ N

29.07.2011

12⁰30.129’ E 78⁰53.129’ N

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the Kongsbreen glacier

78⁰57.872’ N

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T5

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discharge water

29.07.2011

12⁰02.745’ E

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ACCEPTED MANUSCRIPT Table 2. Mean deposition year and Corg concentration in sediments from KM and KO stations. Layer [cm]

KM

KO

Mean deposition year Corg [mg g-1] Mean deposition year Corg [mg g-1] 2009

5.2

2007

12.5

1-2

2005

4.3

2000

12.3

2-3

2001

3.4

1994

12.4

3-4

1998

3.8

1987

11.3

4-5

1994

3.1

5-6

1991

3.4

6-7

1988

3.5

7-8

1984

3.5

8-9

1981

9-10

1978

10-12

1973

12-14

1966

14-16

1959

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0-1

10.8

1975

11.5

1968

10.8

1962

11.0

2.9

1957

10.4

2.8

1951

10.4

3.0

1938

10.2

3.0

1912

10.3

2.8

1871

10.0

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1981

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ACCEPTED MANUSCRIPT Table 3. The organic carbon burial rates (CorgBR) and organic carbon burial efficiency (share of primary production buried in sediments). The comparison of results for Arctic and temperate shelf areas. Corg burial

[g Corg m-2 y-1]

efficiency [%]

9-13

9-20

this study

4

(Goni et al., 2005)

4-5

(Silverberg et al., 2000)

-

(Cranston, 1997)

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Arctic Kongsfjorden, Svalbard

References

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CorgBR

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Shelf regions

-

Gulf of St. Lawrence

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Central Arctic Ocean

0.01-0.13

Shelikof Strait, Alaska

3.4-48.6

-

(Rember and Trefry, 2005)

0-29

-

(Macdonald et al., 1998)

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Beaufort Sea

Beaufort Sea (Mackenzie

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Shelf)

Temperate

Sea

-

3.7-8.4

5-7

(Carroll et al., 2008)

1-5

0.6-47.7

(Epping et al., 2002)

1-25

1.0-19.7

(Giordani et al., 2002)

2006)

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Adriatic Sea

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Iberian margin of Atlantic

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Barents Sea

(Rysgaard and Nielsen,

7.2

D

Greenland Sea (shelf part)

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ACCEPTED MANUSCRIPT Table 4. The range of δ13Corg and mean δ13Corg values in the random organic matter samples collected at T1, T2, and T3 locations. δ13Corg range

No. of

(mean δ13Corg)

samples

-21.6‰ to -16.0‰

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debris of marine phytobenthos and plankton

(-18.3‰)

-28.1‰ to -25.5‰

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T1 (intertidal zone)

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Type of samples

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Location

T1 (inland)

soil, moss, debris of land vegetation

soil, debris of land vegetation

debris of marine phytobenthos and plankton

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T3 (intertidal zone)

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T2 (inland)

soil, moss, debris of land vegetation,

T3 (inland)

(-26.3‰)

-30.0‰ to -24.9‰

8

(-28.4‰)

-23.9‰ to -15.8‰

5

(-19.0‰) -35.2‰ to -26.4‰

9

(-29.2‰)

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bird guano

8

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ACCEPTED MANUSCRIPT Highlights Terrestrial POC input to Kongsfjorden of 760·106 g y-1 originates mostly from glaciers.



Organic carbon burial rate amounts to 9-13 g Corg m-2 y-1 in Kongsfjorden.

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Marine δ13Corg end member has a very broad range in the high Arctic.

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Tracing of terrestrial OM by δ13Corg is limited in marine regions of the high Arctic.

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

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