Abstract
AbstractConcentrations of polychlorinated biphenyls (PCBs), organochlorine pesticides (OC pesticides), and polybrominated diphenyl ethers (PBDEs) are reported in surficial sediments sampled along cruise transects from the Bering Sea to the central Arctic Ocean. OCs and PCBs all had significantly higher concentrations in the relatively shallow water (<500 m depth) of the Bering‐Chukchi shelf areas (e.g., ΣPCB 286 ± 265 pg g−1 dw) compared to the deeper water regions (>500 m) of the Bering Sea and Arctic Ocean (e.g., Canada Basin ΣPCB 149 ± 102 pg g−1 dw). Concentrations were similar to, or slightly lower than, studies from the 1990s, indicating a lack of a declining trend. PBDEs (excluding BDE‐209) displayed very low concentrations (e.g., range of median values, 3.5–6.6 pg/g dw). In the shelf areas, the sediments comprised similar proportions of silt and clay, whereas the deep basin sediments were dominated by clay, with a lower total organic carbon (TOC) content. While significant positive correlations were observed between persistent organic pollutant (POP) concentrations and TOC (Pearson correlation, r = 0.66–0.75, p <0.05), the lack of strong correlations, combined with differing chemical profiles between the sediments and technical formulations (and/or marine surface waters), indicate substantial chemical processing during transfer to the benthic environment. Marked differences in sedimentation rates between the shallow and deeper water regions are apparent (the ∼5 cm‐depth grab samples collected here representing ∼100 years of accumulation for the shelf sediments and ∼1000 years for the deeper ocean regions), which may bias any comparisons. Nonetheless, the sediments of the shallower coastal arctic seas appear to serve as significant repositories for POPs deposited from surface waters.
Highlights
Persistent organic pollutants are globally distributed chemicals that are present in the Polar Regions and remote ocean environments [MacDonald et al, 2000]
For (iii), there are relatively few studies that have measured concentrations in deep ocean waters or bottom sediments [Iwata et al, 1994; Schulz-Bull et al, 1998], processes for transferring persistent organic pollutant (POP) from surface to deep waters are varied and include subduction of surface ocean currents via the thermohaline circulation [Lohmann et al, 2006], the transfer of sediments in coastal regions to continental shelf areas [Jonsson et al, 2003], and particle settling from well-mixed surface waters [Dachs et al, 1999; Dachs et al, 2002]
Recent work in a trans Arctic Ocean assessment has revealed only a very small fraction of the global inventory of polychlorinated biphenyls (PCBs) reside in surface ocean media across the Arctic [Carrizo and Gustafsson, 2011]
Summary
Persistent organic pollutants are globally distributed chemicals that are present in the Polar Regions and remote ocean environments [MacDonald et al, 2000]. Recent work in a trans Arctic Ocean assessment has revealed only a very small fraction of the global inventory of PCBs reside in surface ocean media across the Arctic [Carrizo and Gustafsson, 2011] This indicates that the majority of PCBs reside closer to source regions and/or intra-Arctic transfer processes are efficient at removing chemicals from surface media to other sinks such as the deep ocean environment [Sobek and Gustafsson, 2014]. To examine this further, this study presents the results of ocean sediment measurements conducted on a ship-based transect from the North Pacific to the central Arctic Ocean (via the Bering Strait). The aim was to examine spatial variations in sediment-bound concentrations, comparing different regions as well as deep ocean versus shallow water sites, and to explore the influence of sediment properties on chemical concentrations and composition
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