Add time:08/23/2019         Source:sciencedirect.com

We investigated biogeochemical cycling of dissolved copper (dCu) along the Line P transect, spanning from the coastal waters of British Columbia, Canada, to the High Nutrient, Low Chlorophyll (HNLC) open Ocean Station Papa (OSP or P26), in the subarctic Northeast Pacific. DCu concentrations ranged from 1.4–3.7 nmol kg− 1 throughout the water column along the transect, and were elevated in the upper and bottom waters near the continental margin (< 300 m and > 1100 m respectively) as well as in the upper waters offshore (< 300 m). These trends were attributed to the fluvial and sedimentary sources near the coast of BC, and upwelling of deep, dCu rich waters in the Alaska gyre offshore. In addition, we conducted a temporal investigation of dCu at OSP over three consecutive years (2010 − 2012), which revealed dynamic variability in the top 300 m that was accompanied by elevated sub-surface concentrations, indicating Cu supply from atmospheric deposition. We explore atmospheric inputs in the Gulf of Alaska and suggest that they may play a significant role in moderating dCu distribution in this region. Consistent with previous investigations in the North Pacific, dCu distributions in the nutricline throughout the transect were strongly linked to those of phosphate and silicate. However, within the Northeast Pacific Oxygen Minimum Zone (OMZ) silicate and dCu distributions were noticeably decoupled suggesting a deficit or loss of dCu in these deep, oxygen depleted waters. In this study, we also assessed the requirement for UV oxidation of our samples (pH 2) prior to dCu analysis by flow injection-chemiluminescence (FIA‐CL). We found that UV oxidation leads to a significant increase in labile Cu (up to 40%), however, the variation in this increase is largely dictated by the length of sample storage under acidic conditions. Our results suggest that UV oxidation is essential prior to FIA-CL analysis of young samples (aged for 48 h–2 months), but may not be required if samples have been stored for an extended period at low pH (≥ 4 years). We found a good agreement between dCu values at station P26 obtained with FIA-CL and those obtained with cathodic stripping voltammetry (CSV). However, comparison of our dataset with all published dCu profiles in the North Pacific revealed some discrepancies in dCu values in this region. Here, we briefly discuss the role of sample storage period, UV oxidation and differences in analytical methodologies as factors causing uncertainties in dCu values.

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