Trace metals and organic carbon in sediments of the northeastern Chukchi Sea John H. Trefry a,n , Robert P. Trocine a , Lee W. Cooper b , Kenneth H. Dunton c a Department of Marine & Environmental Systems, Florida Institute of Technology,150 West University Boulevard, Melbourne, FL 32901, USA b Chesapeake Biological Laboratory, University of Maryland Center for Environmental Science, Solomons, MD 20688, USA c Marine Science Institute, The University of Texas at Austin, Port Aransas, TX 78373, USA article info Available online 20 July 2013 Keywords: Chukchi Sea Sediments Metals Organic carbon 137 Cesium and 210 Pb dating abstract Concentrations of Al, Fe and selected trace metals (As, Ba, Be, Cd, Cr, Cu, Hg, Mn, Ni, Pb, Sb, Se, Sn, V, Zn) in surface sediments from the northeastern Chukchi Sea (NECS) varied considerably as a function of sediment texture (i.e., grain size); however, essentially all metals, when normalized to Al, were present at natural, background values. Total organic carbon content ranged from 0.06–1.56% with a marine origin for at least two-thirds of the organic matter at each station based on δ 13 C values and C/N ratios. Recent sedimentation rates from 137 Cs and 210 Pb dating were 0.03–0.14 cm yr 1 . Corresponding vertical distributions for most metals in age-dated sediment cores showed 4100-yr records of uniform metal/Al ratios, including Pb and Hg. Concentrations of As, Mn and Cd were modified in surface sediments at a few stations by early chemical diagenesis. Surveys around two exploratory oil and gas drilling sites that were occupied in 1989 showed that Ba concentrations were as high as 10,000 mgg 1 within 200 m of one drilling site relative to background values of 700 mgg 1 . Barium enrichment was from barite, a drilling mud additive that was discharged to the seafloor. Above background concentrations of Cu, Hg, Pb and Zn also were found in sediments from 3–4 stations within 200 m of the two drilling sites. At present, sediments in the NECS are essentially pristine with respect to trace metals of anthropogenic origin, excluding small areas around drilling sites. These data should be of value for detecting and tracking future chemical changes in the sediments of the NECS, particularly in light of planned oil and gas exploration and production as well as environmental changes that may be associated with climate change. & 2013 Elsevier Ltd. All rights reserved. 1. Introduction Sea ice retreat, increased coastal erosion, enhanced primary productivity and planned oil and gas exploration foreshadow impending changes to the biologically-rich benthic environment of the northeastern Chukchi Sea (NECS) (Post et al., 2009; Rowland et al., 2010). These impacts carry with them the possibility for increased inputs of sediment, particulate organic carbon and potentially toxic metals, as well as a shift to a more reducing sedimentary environment. Limited information on the distribution of trace metals in sediments is available for the NECS, making it important to determine background concentrations as a reference point for tracking any future changes from human activities and climate change. Sediment texture varies greatly throughout the NECS with a range of o10% to 490% silt+clay (mud) in surface sediments (Naidu, 1988; Naidu et al., 1997). Gravelly-sand is found along the nearshore pathway of the Alaska Coastal Current and around Hanna and Herald shoals (McManus et al., 1969). Sand and gravel have remained on the shoals after winnowing of the fine fraction by currents following resuspension due to ice gouging of the seafloor (Tomil and Grantz, 1976). Silt and clay are more abundant in the central Chukchi Basin (McManus et al., 1969; Naidu, 1988). Provenance for much of the fine-grained sediment is the Yukon River with transport from the Bering Sea to the eastern Chukchi Sea via the Alaska Coastal Current (McManus et al., 1969). The sediments of the Chukchi Sea support diverse assemblages of abundant infaunal and epifaunal commu- nities that are partly linked with sediment texture (Feder et al., 1994; Grebmeier et al., 2006). Concentrations of total organic carbon (TOC) also vary greatly in sediments from the NECS with a range of 0.1% to 42% and a spatial pattern driven by sediment texture and the flux of phytodetritus (Naidu et al., 2000, 2004). The mass ratio of C/N for organic matter (OM) decreases from 410 to o5 with increased distance offshore, a trend that correlates significantly with the stable carbon isotope composition (δ 13 C) of sediment OM Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/dsr2 Deep-Sea Research II 0967-0645/$ - see front matter & 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.dsr2.2013.07.018 n Corresponding author. Tel.: +1 321 674 7305. E-mail address: jtrefry@fit.edu (J.H. Trefry). Deep-Sea Research II 102 (2014) 18–31