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δ13C and δ15N variations in terrestrial and marine foodwebs of Beagle Channel in the Holocene. Implications for human paleodietary reconstructions

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ABSTRACT In this article we evaluate the isotopic variability in δ13C and δ1 N values of diets among maritime hunter-gatherers of the Beagle Channel (Southern Argentina). A system with two end members –marine and terrestrial resources– is not enough
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  Contents lists available at ScienceDirect Journal of Archaeological Science: Reports  journal homepage: www.elsevier.com/locate/jasrep δ 13 C and  δ 15 N variations in terrestrial and marine foodwebs of BeagleChannel in the Holocene. Implications for human paleodietaryreconstructions Sayuri Kochi a, ⁎ , Suray A. Pérez b , Augusto Tessone a , Andrew Ugan c , Mary Anne Tafuri d ,Jonathan Nye e , Angélica M. Tivoli f  , Atilio Francisco Zangrando f  a  Instituto de Geocronología y Geología Isotópica, UBA/CONICET, Argentina b  Facultad de Filosofía y Letras, Universidad de Buenos Aires, Argentina c  Far Western Anthropological Research Group, University of Utah, USA d  Dipartimento di Biologia Ambientale, Sapienza Università di Roma, Italy  e  Department of Earth Sciences, University of California, Riverside, USA f  Centro Austral de Investigaciones Cientí   󿬁 cas  –   CONICET, Argentina A R T I C L E I N F O  Keywords: Isotopic ecologyPaleodietHunter-gatherersTierra del FuegoPatagonia A B S T R A C T In this article we evaluate the isotopic variability in  δ 13 C and  δ 15 N values of diets among maritime hunter-gatherers of the Beagle Channel (Southern Argentina). A system with two end members  – marine and terrestrialresources –  is not enough to describe populations with diversi 󿬁 ed subsistence strategies. Moreover, these marinehunter-gatherers are characterized as highly mobile groups whose foraging ranges comprised not only nearshoreareas, but also o ff  shore spaces.As a  󿬁 rst step to distinguish the diversity of prey choices during the Late Holocene, and to improve theaccuracy of paleodietary interpretations, we conducted stable isotope analyses on zooarchaeological collectionsand modern samples of shell 󿬁 sh and plants. We observed that  δ 13 C and  δ 15 N values of aquatic animals are moreclustered than expected in comparison to modern ecological parameters. Terrestrial prey, such as the guanaco,showed considerable isotopic dispersion in both carbon and nitrogen. While zooarchaeological studies haveidenti 󿬁 ed foraging activities in o ff  shore spaces, stable isotope analyses should use di ff  erent criteria to char-acterize long-term dietary patterns.With this local isotopic frame of reference, we re-examined  δ 13 C collagen  and  δ 15 N collagen  measurements of seven adult individuals from the Beagle Channel. Most individuals had marine diets complemented with re-sources more depleted in  13 C and  15 N than aquatic prey. While previous interpretations stated that the com-plementary staple was terrestrial protein, we suggest consumption of shell 󿬁 sh as another possibility. Finally,plants should be reconsidered as a source depleted both in  13 C and  15 N for mixing models, when typicallyunderestimated in paleodiets from subpolar environments. 1. Introduction One of the earliest applications of stable isotopes in archaeologyfocused on distinguishing between the consumption of marine vs. ter-restrial resources (Tauber, 1981; Chisholm et al., 1982). These twogroups are characterized by a clear contrast in  δ 13 C and  δ 15 N dis-tributions (Schoeninger and DeNiro, 1984). However, aquatic en-vironments o ff  er a diversity of isotopically di ff  erent prey items(Richards and Hedges, 1999; Szpak et al., 2009; Coltrain et al., 2016). δ 13 C and  δ 15 N values of littoral and pelagic primary producers typicallydi ff  er strongly among habitats, and they are in 󿬂 uenced by numerousphysical and chemical factors (Casey and Post, 2011). Moreover, someprehistoric populations consumed resources at multiple levels of thelocal food web (Maschner et al., 2009), which makes understanding thepaleodiets of coastal hunter-gatherers even more complex. As such,only with a detailed ecological frame of reference is it possible to dis-tinguish among diverse prey choices and to address broader questions:for example, patterns of foraging ranges and mobility (Weber et al.,2011) or sexual division of labor (Kusaka et al., 2010). At the southern tip of South America, hunter-gatherer populationsof the Beagle Channel (Fig. 1) developed marine foraging strategiesfrom 6400 yr BP until the arrival of European settlers to the region in https://doi.org/10.1016/j.jasrep.2017.11.036Received 20 April 2017; Received in revised form 18 September 2017; Accepted 20 November 2017 ⁎ Corresponding author.  E-mail address:  sayuri@ingeis.uba.ar (S. Kochi). Journal of Archaeological Science: Reports xxx (xxxx) xxx–xxx2352-409X/ © 2017 Elsevier Ltd. All rights reserved. Please cite this article as: Kochi, S., Journal of Archaeological Science: Reports (2017), https://doi.org/10.1016/j.jasrep.2017.11.036  the 19th century. Stable isotope analyses on archaeological human re-mains from the Beagle Channel indicated that most individuals hadmarine diets, complemented with terrestrial resources during the LateHolocene (Yesner et al., 1991; Orquera and Piana, 1996; Guichón et al.,2001; Tessone et al., 2003; Yesner et al., 2003; Panarello et al., 2006).Nevertheless, this high latitude coastal environment o ff  ered variedpotential resources, which required di ff  erent amounts of labor in theirprocurement and processing (Orquera and Piana, 1999a; Zangrando,2009a). As Yesner (1980) stated it is  “ misleading to lump coastal peo-ples into a single economic category ” , and therefore a comprehensivelocal isotopic ecology (Schwarcz, 1991; Newsome et al., 2007) is re-quired to improve the accuracy of diet reconstructions and ultimately,to identify variations among subsistence strategies of marine hunter-gatherers.Recent zooarchaeological studies in this area have demonstratedtemporal variation in human subsistence activities, showing an ex-pansion of foraging habitats, and an increase of labor investment into 󿬁 shing activities and capture of birds during the late Holocene(Zangrando, 2009a; Tivoli, 2010; Tivoli and Zangrando, 2011). Forexample, adult snoeks ( Thyrsites atun ) in the Beagle Channel appear asthe most important  󿬁 sh taxa from deep waters only during the last1000 years (Zangrando, 2009b). Recognized as pelagic predators(Gri ffi ths, 2002), adult specimens of snoeks in the Beagle Channel haveonly been recorded in deep waters (Fenucci et al., 1974).While zooarchaeological assemblages and stable isotope studies of human bone inform about di ff  erent units of analyses and temporal re-solution (Barberena and Borrero, 2005),  δ 13 C and  δ 15 N measurementson late Holocene individuals should also detect the consumption of o ff  shore animals. However, it is  󿬁 rst necessary to evaluate the amountof isotopic disparity of nearshore and o ff  shore resources as end mem-bers (Casey and Post, 2011). Often the end members of interest are notseparated enough to provide good resolution in mixing models(Hobson, 1999).If the isotopic information is not suitable to infer where diets wereobtained and, by extension, to analyze the foraging spatial range of thehunter-gatherer groups, then it can be used to discuss possible preycombinations in marine diets of the Beagle Channel. While zooarch-aeological studies identify taxon-speci 󿬁 c consumption (Barberena andBorrero, 2005; Newsome et al., 2007), isotopic analyses need to ag-gregate isotopically similar resources for paleodietary interpretations.At this point, the challenge is to combine sources in a logical fashion(Newsome et al., 2004; Phillips et al., 2005) allowing meaningful in-terpretations about past human behavior. The endmembers de 󿬁 ned inecological studies are not always appropriate to archaeological ques-tions.The aim of this paper is to generate isotopic reference values forcombination of resources in human paleodiets. We determine if thecomposition of marine diets can be related to the exploitation of dif-ferent environments by hunter-gatherers, or if is better to analyze thecomposition of diets according to di ff  erent criteria. To accomplish this,we characterize isotopic variability in  δ 13 C and  δ 15 N throughout marineand terrestrial food webs of the Beagle Channel by analyzing modernand zooarchaeological samples. First, we describe the ecological settingof this region and expectations about the natural distribution of   δ 13 Cand  δ 15 N. Then we introduce the samples and methods used in thisstudy. Finally, we present the isotopic results and we discuss the im-plications for human paleodiet reconstructions. 1.1. Ecological setting  The Beagle Channel is located at 55° S, along the southern coast of the Isla Grande de Tierra del Fuego. One hundred sixty- 󿬁 ve kilometerslong, it connects the Paci 󿬁 c and Atlantic Oceans. The Andean Cordillerais situated parallel to the coast in an E-W direction. The climate isclassi 󿬁 ed as oceanic, dominated by a polar maritime air massthroughout the late Holocene (Heusser, 1988). Mean annual tempera-ture is 6 °C and precipitation ranges between 500 and 600 mm(Coronato, 2014).The subpolar marine ecosystem contains a wide range of speciesthat were consumed by prehistoric populations. Previous Fig. 1.  A map of Southern South America showing the Beagle Channel, where specimens with stable isotopic values srcinated.  S. Kochi et al.  Journal of Archaeological Science: Reports xxx (xxxx) xxx–xxx  2  zooarchaeological studies (e.g. Zangrando, 2009a, 2009b; Tivoli andZangrando, 2011), sorted taxonomic groups according to modern eco-logical parameters, to test hypothesis on landscape use for hunting, 󿬁 shing or gathering activities in human populations. Nevertheless,isotopic studies need to generate their own frame of reference due toseveral reasons. Species may have experienced changes in their fora-ging ecology (Burton et al., 2001) by natural and/or anthropogenicfactors, di ff  ering present distributions from the past (Szpak et al., 2012;Zangrando et al., 2014a). On the other hand, baseline  δ 13 C and  δ 15 Nvalues  󿬂 uctuate over time (Post, 2002), a ff  ecting isotopic valuesthrough the food web. Then, to interpret human paleodiets in relationto subsistence strategies in di ff  erent ecozones, we need to understandthe degree of isotopic variation within and among the resources(Phillips, 2012) in the prehistoric environment.As some marine species change their habitat through their life cycle(Barnes and Hughes, 1999), it may not be suitable to classify faunalspecies according to where they could be obtained by the hunter-gatherers; but instead, to also take into account general descriptionsabout the ecological niche of the species (Newsome et al., 2007). Weconsider the di ff  erences between inshore and o ff  shore primary produ-cers in marine systems (France, 1995; Hobson, 1999), the trophic levelof the species (Minagawa and Wada, 1984; Forero et al., 2004; Hedgesand Reynard, 2007; Ciancio et al., 2008). For terrestrial resources, weinclude traits of Patagonian forests and herbivores (Tessone, 2010;Fernández and Tessone, 2014; Barberena et al., 2011). This informationis useful to model the expectations about di ff  erences in  δ 13 C and  δ 15 Ndistributions in the Beagle Channel environment. 1.1.1. Marine environment  In cold temperate coasts, pinnipeds are described as major toppredators worldwide (Vales et al., 2017). The South American fur seal(  Arctocephalus australis ) dominates zooarchaeological assemblages fromthis area (Schiavini, 1993; Orquera and Piana, 1999a). They travel longdistances and mostly feed on anchovy, sardines, crustaceans and ce-phalopod mollusks (Sielfeld, 1999; Falabella et al., 2009). While adultand young male seals spend more time in the water than on land, fe-male fur seals continuously return to the breeding colonies to nursetheir pups. However, there are not signi 󿬁 cant di ff  erences between sexesin  δ 13 C values since 5000 BP (Zangrando et al., 2014b).The seabirds of Patagonia have a relatively high trophic position(Forero et al., 2004). Migratory birds like the Magellanic penguin(  Spheniscus magellanicus ) forage over 500 km from their colonies. Theirdiet is mixed, based on  󿬁 sh and squid (Raya Rey and Schiavini, 2000;Silva et al., 2014). Albatrosses (  Diomedea  sp.) are o ff  shore species,which spend most of their time  󿬂 ying over the shelf slope. They feed oncrustaceans, squid,  󿬁 sh and carrion (Couve and Vidal, 2003). They onlyoccasionally come to the coast (Falabella et al., 2009).Fish species with pelagic habits were also consumed by hunter-gatherers, mainly snoeks ( Thyrsites atun ), hake (  Merluccius  sp.) andPatagonian grenadier (  Macruronus magellanicus ). The latter may comecloser to the coast in their juvenile stage, and it is a generalist predatorwith a lower trophic position than the snoeks and hakes. These twoepipelagic species are described as consumers of intermediate size  󿬁 shand squid (Ciancio et al., 2008; Zangrando et al., 2016). In the near-shore marine ecosystem, kelp forests of   Macrocystis pyrifera  constitutean important habitat for several consumers (Riccialdelli et al., 2016).Small  󿬁 shes of the Nototheniidae family, like the Southern cod (Pata-gonotothen  sp. ) and Magellanic rockcod (  Paranotothenia magellanica )inhabit these shallow waters. They are detritivore and small crustaceanfeeders (Moreno and Jara, 1984; Zangrando, 2009b). Cormorants(  Phalacrocorax   sp.) also feed nearshore, with interspeci 󿬁 c di ff  erences inforaging behavior (Raya Rey and Schiavini, 2000). The rocky ridges of the intertidal zone are colonized by shell 󿬁 sh communities. The bluemussel (  Mytilus edulis ) is a suspension feeder. They comprise more than96% of the shell middens of Beagle Channel, being the most commonspecies in these deposits (Orquera, 1999; Orquera and Piana, 2000,2001; Zangrando et al., 2017).Typical of estuarine zones is the Patagonian blenny (  Eleginops ma-clovinus ). It consumes  󿬁 shes, amphipods and kelps (Lloris andRucabado, 1991). The Southern river otter (  Lontra provocax  ) reliesheavily on benthic marine resources like crustaceans and  󿬁 sh (Gomezet al., 2010). 1.1.2. Terrestrial environment  The dominant vegetation types in the terrestrial environment areevergreen and deciduous forests. The most characteristic species arefrom the  Nothofagus  genera. These trees grow on acidic soils with a poordrainage, rich in organic matter but depleted in nitrogen and othernutrients. However, species of   Nothofagus  in Tierra del Fuego havemycorrhizal associations providing plants with nitrogen (Frangi et al.,2004).Guanaco (  Lama guanicoe ) was the main terrestrial staple (Orqueraand Piana, 1999a). This camelid is de 󿬁 ned as an adaptable mixedfeeder (Barberena et al., 2009), and analysis of feces found a constantand abundant presence of   Nothofagus  spp. throughout the year (Soleret al., 2013; Arias et al., 2015). A native carnivore is the Fuegian fox(  Lycalopex culpaeus ). They mainly feed on rodents, but aquatic prey isfrequent in their diet (Gomez et al., 2010). Neither foxes nor rodentswere consumpted by humans, and their presence in archaeologicaldeposits is attributed to taphonomic processes (Santiago and Vázquez,2012). 1.2. Expectations about the natural distribution of   δ  13 C and  δ  15  N values From the data summarized above, considerable isotopic variabilityshould characterize resources consumed by prehistoric populations of Beagle Channel. Marine ecosystems typically show strong spatial gra-dients in the distribution of carbon stable isotope values, with near-shore primary producers more enriched in  13 C than o ff  shore ones(Clementz and Koch, 2001; France, 1995; Hemminga and Mateo, 1996).In low turbulence areas like kelp forests there is high di ff  usional re-sistance to CO 2 , which leads to an increased assimilation of heavier  13 Cisotopes by aquatic plants and more positive  δ 13 C values among thoseplants and their secondary consumers.Conversely, primary producers found in the open water or pelagichabitats have primary producers with lower di ff  usion resistance andmore negative values of   δ 13 C (Newsome et al., 2010). We expect the carbon isotopic values of animals feeding in the open ocean carbon tobe depleted by up to 6 ‰  relative to the nearshore animals, due to asmaller boundary layer for di ff  usion. Higher concentrations of dissolvedCO 2  and less HCO 3 – in subpolar waters relative to lower latitudesshould increase the likelihood of observing depleted carbon isotopevalues for open ocean animals (Casey and Post, 2011).Therefore, we expect consumers that are associated with benthichabitats such as littoral  󿬁 shes like notothenids to have higher  δ 13 Cvalues than seabirds, pelagic  󿬁 shes and pinnipeds, which forage acrosswider areas. Estuarine species should have lower  δ 13 C values thannearshore animals, due to C 3  terrestrial plant material at the base of thefood web. However, the isotopic di ff  erence should be minimal, as theyalso feed frequently in the nearshore area.In contrast to notothenids closely associated to kelp forests, weexpect for intertidal suspension-feeders to be depleted in  13 C. Themussel beds may rely mainly on the pelagic production (Jack and Wing,2011), although they are exposed to a variety of food sources on rockyshores (Richoux et al., 2014). Therefore, mussels also could have  δ 13 Cdi ff  erences with o ff  shore animals closer to open ocean water. While inecological studies gastropods are usually analyzed to evaluate benthicsources in a foodweb, we do not include them. Benthic invertebrateswere less eaten by hunter-gatherers of the Beagle Channel (Orquera andPiana, 2000, 2001).Among the many factors which in 󿬂 uence the  δ 15 N values of marineorganisms, we focus on the trophic discrimination factor (Minagawa  S. Kochi et al.  Journal of Archaeological Science: Reports xxx (xxxx) xxx–xxx  3  and Wada, 1984; Schoeninger and DeNiro, 1984; Post, 2002; Wolf et al., 2009). Taking into account the stepwise increase in  δ 15 N valuesup food chains, primary consumers like mussels should exhibit thelowest values of   δ 15 N. From modern ecological studies, we expect thehighest  δ 15 N values for seabirds and fur seals. Finally, food sources of estuarine environments are similar to nearshore systems in their ni-trogen isotopic composition (Michener and Kaufman, 2007). Knowingthat Southern river otter and Patagonian blenny feed on marine prey,they should have  δ 15 N values similar to those of nearshore predators.We are aware of the complexity of marine food webs, and that co-existing species could feed along a continuum of trophic levels (Hobsonet al., 1994; Link, 2002). However, after evaluating the isotopicvariability between sources, our aim is to narrow down the diversity of prey in groups useful to re 󿬁 ne paleodietary interpretations. The con-sideration of some di ff  erences between nearshore and o ff  shore re-sources makes sense ecologically, and it is pertinent to archaeologicalquestions (Phillips et al., 2005).In terms of the terrestrial fauna, we expect to  󿬁 nd guanacos de-pleted in  15 N to the same degree as other herbivores of the PatagonianAndean Forest (Tessone, 2010; Tessone et al., 2014; Fernández andTessone, 2014; Méndez et al., 2014). This pattern was related to theclosed nature of the nitrogen cycle in these environments. If this is thecase, previous isotopic references for terrestrial foods in the BeagleChannel needs to be reconsidered. Those guanaco bones in previousstudies were obtained from archaeological sites situated in the steppezone (Guichón et al., 2001), which is a drier environment than theforest. 2. Materials and methods Analyses of   δ 13 C and  δ 15 N were conducted on the collagen of 180zooarchaeological samples, comprising 13 di ff  erent taxa. Additionally,we collected 15modern samples of blue mussels (  Mytilus edulis ) and 8plants from the Magellanic forest ( n  = 13) in order to estimate theisotopic base line of marine and terrestrial food webs. In total weanalyzed 208 samples is.The faunal bones come from archaeological sites on the north coastof the Beagle Channel, spanning the Middle to Late Holocene. Theoldest samples were selected from Second Component of Túnel I site,between 6400 and 4600 yr BP, and Lower Component of Imiwaia I,dated between 6390 ± 50 yr BP and 4900 ± 120 yr BP (Orquera andPiana, 1999a). Late Holocene samples are from the upper layers of thesetwo sites plus  󿬁 ve sites postdating 3500 yr BP. Detailed data for eachsample is presented in Table A, supplementary material. Specimenswere identi 󿬁 ed at the species or genus level, and were di ff  erentiated byanatomical units and side.The subset of aquatic animals includes 10 samples of albatross( Thalassarche  sp.), 10 magellanic penguin (  Spheniscus magellanicus ), 11cormorants (  Phalacrocorax   sp.), 5 Magellanic rockcod (  Paranototheniamagellanica ), 5 Southern cods (  Patagonotothen  sp.), 2 samples of Southern river otter (  Lontra provocax  ) and 2 Patagonian blenny(  Eleginops maclovinus ). We also included isotopic data from 46 southernfur seals (  Arctocephalus australis ) analyzed by Zangrando et al. (2014b),and 45 pelagic  󿬁 shes published in Zangrando et al. (2016). Its samplecomprised Patagonian grenadiers (  Macruronus magellanicus ), snoeks( Thyrsites atun ) and hakes (  Merluccius  sp.). The terrestrial group consistsof 38 zooarchaeological and 3 modern samples of guanaco (  Lama gua-nicoe ), and 3 red foxes (  Lycalopex culpaeus ).Both  δ 13 C and  δ 15 N measurements on bone collagen of seven adulthuman individuals from the Beagle Channel have been published(Yesner et al., 1991; Guichón et al., 2001; Panarello et al., 2006). Mostof them (Table 1,  n  = 5) belong to museum collections with scarcecontextual information (Yesner et al., 1991; Guichón et al., 2001).According to their associated documents, the remains postdate 1500 yrBP. Only two individuals were recovered in situ. One was AMS dated to1536 ± 46 yr BPS (Suby et al., 2011); the other was dated to the post-contact period (Panarello et al., 2006).Bone fragments were cleaned with abrasive elements and ultrasonicbaths. Mammal and bird samples of approximately 1 g were 󿬁 rst treatedwith NaOH (0.1 M) for 24 h and demineralized in HCl (2%) for 72 h,changing the acid every 24 h. Subsequently, bone fragments weretreated again with NaOH for approximately 24 h. The resulting materialwas then dried in an oven at 40 °C for 20 h (Tykot, 2004). Approxi-mately 0.3 g of each  󿬁 sh sample was repeatedly soaked in very diluteHCl (0.5%) every 24 – 48 h (Sealy, 1986). Then, it was rinsed withdeionized water and treated with NaOH (0.125%) for 20 h. The col-lagen extracted was  󿬁 nally dried at 40 °C during 24 h. Plants and softtissues of mussels were cleaned, dried at 40 – 50 °C and ground using amortar and a pestle.Dried samples were weighed into tin cups and analyzed at theInstituto de Geocronología y Geología Isotópica laboratory (INGEIS,CONICET-UBA), Buenos Aires, Argentina. The isotopic analysis of col-lagen fraction and soft tissue was performed with a Carlo Erba EA1108Elemental Analyzer (CHN), connected to a continuous  󿬂 ow ThermoScienti 󿬁 c Delta V Advantage mass spectrometer through a ThermoScienti 󿬁 c ConFlo IV interface.The conservation status of isotopic signal was evaluated by ele-mental analysis C/N (DeNiro, 1985). Results are expressed as the ratioof the heavier isotope to the lighter isotope and reported as delta ( δ )values in parts per thousand ( ‰ ) relative to internationally acceptedstandards for carbon (VPDB) and nitrogen (AIR). The analytical preci-sion was± 0.3 ‰ .Modern mussel samples were adjusted for oceanic Suess E ff  ect usingEq. (1) below, from Misarti et al. (2009): = ∗ ∗ a exp b Suess Effect correction factor(0.027)  (1) a  is the maximum annual rate of   δ 13 C decrease ( − 0.015 ‰ ) due toSuess E ff  ect in the Sub-Antarctic zone (McNeil et al., 2001; Hilton et al.,2006).  b  derives from the year of death of the animal (2013) minus1850. Therefore, isotopic  δ 13 C values were corrected for 1.2 ‰ . Modernplants were adjusted by adding 1.5 ‰  to  δ 13 C measurements (Petersonand Fry, 1987).To compare the isotopic composition of diets we estimated  δ 13 C and δ 15 N values of animal protein from bone collagen values. O ff  sets are Δ 13 C protein – collagen  = − 2 ‰  and  Δ 15 N protein – collagen  = +2 ‰  for all ani-mals except  󿬁 sh, in which we applied  Δ 13 C protein – collagen  = − 1 ‰  and Δ 15 N protein – collagen  = +2 ‰  (Fernandes, 2016). Instead of averagingindividual samples, we averaged across taxon means to avoid bias to-wards better represented species.For protein diet to human bone collagen, we applied discriminationfactors of +5 ‰  for  δ 13 C and +5.5 for  δ 15 N (Fernandes, 2016). 3. Results The  δ 13 C and  δ 15 N results, %C and %N, C:N ratios and collagenyields are presented in the Supplementary material, Table A.Descriptive statistics for  δ 13 C and  δ 15 N values are in Table 2. Onesample of   P. magellanica  (code 36630) was eliminated from the analysis,because the C/N presents a value higher than the normal range of 2.9 – 3.6 (DeNiro, 1985). The rest of the bone samples produced C/Nratios characteristic of well-preserved collagen, assuring primary iso-topic signals.Fig. 2 displays stable isotopes results for di ff  erent groups of aquaticanimals. Data obtained for avian fauna shows a dispersion of 2.8 ‰  in δ 13 C values (Fig. 2a). There are no statistical di ff  erences between sea-birds (One-way ANOVA test, Table 3). However, as the most o ff  shorespecies among the seabirds analyzed, albatrosses have the most nega-tive average  δ 13 C values ( − 13.1 ‰  ± 0.5 ‰ ). In the other extreme,cormorants display the most enriched mean ( − 12.7 ‰  ± 0.3 ‰ ). Thisis in agreement with their feeding in shallow waters and colonies nearthe coast. Penguins occupy an intermediate position between these twospecies ( − 12.9 ‰  ± 0.7 ‰ ).  S. Kochi et al.  Journal of Archaeological Science: Reports xxx (xxxx) xxx–xxx  4  The dispersion is wider among  δ 15 N values, with a range of 6 ‰ ,more than one trophic level. The pattern is similar to that observed incarbon isotopes: the heavier mean corresponds to the albatross(18.6 ‰  ± 0.9 ‰ ), whereas penguins have an intermediate average(17.1 ‰  ± 0.9 ‰ ), and cormorants are the most depleted in  15 N(15.4 ‰  ± 0.6 ‰ ). Di ff  erences are statistically signi 󿬁 cant (Table 3).Considering  󿬁 shes, the input of distinct primary producers in thefood web is more likely (Fig. 2b).  δ 13 C values are dispersed in a con-siderable range of 4.2 ‰ . The most enriched means are observed inbenthic nearshore species as rockcod ( − 11.2 ‰  ± 1.3 ‰ ) andSouthern cod ( − 11.2 ‰  ± 1.1 ‰ ). They have signi 󿬁 cant di ff  erencescompared to more o ff  shore species as hakes and snoeks (Table 4). Bothhave the most negative averages ( − 12.8 ‰  ± 0.7 ‰  and − 12.6 ‰  ± 0.7 ‰ , respectively). The Patagonian grenadier has ahigher mean than epipelagic  󿬁 shes ( − 11.6 ‰  ± 0.4 ‰ ). The blennywas not included in the ANOVA test, as we have only two samples. Ithas an average of   − 12.1 ‰  ± 0.6 ‰ , intermediate between the o ff  -shore and nearshore  󿬁 shes. It could be explained by the mixing of de-pleted terrestrial carbon from the freshwater ecosystem, and the inputof more enriched sources from the marine environment.Although some signi 󿬁 cant statistical di ff  erences are also observed in δ 15 N values between di ff  erent  󿬁 sh species, this does not show a clearpattern. There is a range of 4.3 ‰  in the  δ 15 N values, which is expectedby the diversity of   󿬁 sh species analyzed. The rockcods have the lightestmean of 14.9 ‰  ± 0.6 ‰ , followed by the snoeks (15.3 ‰  ± 0.9 ‰ )and Patagonian grenadiers (15.8 ‰  ± 0.9 ‰ ). Patagonian blenny,Southern cod and hake are the most enriched in the heavier isotope,with a mean of 16.4 ‰  ± 0.1 ‰ , 16.5 ‰  ± 0.5 ‰  and 17 ‰  ± 0.9 ‰ ,respectively.In aquatic mammals (Fig. 2c), fur seals occupy a tightly clusteredisotopic space. They have mean  δ 13 C values of  − 11.8 ‰  ± 0.5 ‰  and δ 15 N values of 17.3 ‰  ± 0.6 ‰ . One sample of otter is similar to furseals in both markers ( δ 13 C = − 12 ‰ ,  δ 15 N = 18.1 ‰ ). The secondsample appears as an outlier, and has the highest  δ 15 N values among allthe specimens analyzed ( δ 13 C = − 9.4 ‰ ,  δ 15 N = 24 ‰ ). Despite thefact that it does not have evidence of contamination or degradation, asmodern river otters are more depleted in  δ 15 N (Riccialdelli et al., 2016), we exclude this extremely enriched sample from the subsequent ana-lysis.Finally, the mussels show the most depleted isotopic values (Fig. 3).The  δ 13 C mean is − 16.5  ‰  ± 0.6  ‰ . The results are on muscle tis-sues, having di ff  erent discrimination factors from diet compared tofaunal bone collagen. However, they are considerably lighter than therest of the samples analyzed, probably due to an intake from a di ff  erentsource of primary producers. In previous studies, similar isotopic valuesof   󿬁 lter feeders were interpreted as showing a large consumption of pelagic producers by this group, with a great in 󿬂 uence of phyto-plankton and suspended particulate organic matter or SPOM(Riccialdelli et al., 2016). Also the  δ 15 N average is lower than the rest of the marine samples (11.1 ‰  ± 0.5 ‰ ), which is related to their lowtrophic level as  󿬁 lter feeders.Stable isotopes results for terrestrial plants are plotted in Fig. 4.While the primary producers fall in the range expected for C 3  plants,there is a considerable variability between the samples, which can beclearly divided in two groups. Lichens are the samples enriched in  13 C,with an average of   − 22.6 ‰  ± 1.2 ‰ . At the same time, they aremarkedly depleted in  15 N. The  δ 15 N mean is − 16.2 ‰  ± 1.3 ‰ . Therest of the specimens are C 3  grasses and they display the oppositepattern.  δ 13 C mean is more negative than the lichens( − 27.9 ‰  ± 1.1 ‰ ) and they have a higher  δ 15 N mean of 0.7 ‰  ± 2.4 ‰ .With respect to terrestrial animals (Fig. 5), the linear dispersion of  Table 1 Available  δ 13 C coll  and  δ 15 N measurements on human remains from Beagle Channel.Provenience Lab code Sex  δ 13 C collagen  δ 15 N C/N ReferencesUshuaia Without date (Geochron) Indet.  − 12.6 18.8 Without data (Geochron) Yesner et al. (1991) Isla Hoste  Male  − 13.3 17.2 Isla Hoste  Male  − 16.8 13.2 Isla Navarino  Male  − 18.5 10.6Lauta 2 USF 360 Female  − 12.3 17.3 Without data Guichón et al. (2001)Shamakush Entierro AIE 27573 Male  − 12.4 18.3 3.3 Panarello et al. (2006) Ea. Harberton  EILAB 87920 Male  − 11.6 18.6 3.2 Table 2 Descriptive statistics for  δ 13 C and  δ 15 N values of all taxa from Beagle Channel. With the exception of mussels and plants, values were measured on bone collagen.Taxa n  δ 13 C  ‰  δ 15 N  ‰ Mean (± SD) Minimum Maximum Mean (± SD) Minimum MaximumMarineSouthern fur seal 46  − 11.8 ± 0.5  − 12.8  − 10.8 17.3 ± 0.6 15.5 18.7Albatross 10  − 13.1 ± 0.5  − 14.5  − 12.7 18.6 ± 0.9 17.3 20.6Penguin 10  − 12.9 ± 0.7  − 13.7  − 11.7 17.1 ± 0.9 14.8 18Cormorant 11  − 12.7 ± 0.3  − 13.3  − 12.2 15.5 ± 0.6 14.6 16.6Patagonian grenadier 14  − 11.6 ± 0.4  − 12.2  − 10.8 15.8 ± 1 14.7 18.3Snoek 14  − 12.6 ± 0.7  − 13.5  − 11.6 15.3 ± 0.9 14 17.7Hake 17  − 12.8 ± 0.7  − 13.7  − 11 17 ± 0.9 14.8 18.3Rockcod 4  − 11.2 ± 1.3  − 12.7  − 9.6 14.9 ± 0.6 14.2 15.6Southern cod 5  − 11.2 ± 1.1  − 12.3  − 9.5 16.5 ± 0.5 15.7 17.1Mussel 15  − 16.5 ± 0.6  − 17.3  − 15.2 11.1 ± 0.5 10.1 11.7Southern river otter 2  − 10.7 ± 1.8  − 12  − 9.4 21.1 ± 4.2 18.1 24Patagonian blenny 2  − 12.1 ± 0.6  − 12.5  − 11.7 16.5 ± 0.1 16.4 16.5TerrestrialGuanaco 41  − 20.9 ± 1.9  − 23.6  − 15.3 1.1 ± 2.3  − 5.3 4.3Red fox 3  − 18.3 ± 2.3  − 19.9  − 15.7 9 ± 3.4 6.3 12.8C 3 plants 10  − 27.9 ± 1.1  − 30.3  − 26.7 0.7 ± 2.4  − 3.6 3.3Lichens 3  − 22.6 ± 1.2  − 23.4  − 21.2  − 16.2 ± 1.3  − 17.4  − 14.9  S. Kochi et al.  Journal of Archaeological Science: Reports xxx (xxxx) xxx–xxx  5
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