Trace metals (manganese, iron, nickel, copper, zinc, and cadmium) are essential micronutrients for phytoplankton and can be used as tracers of oceanic processes. The supply of trace metals to the Western Arctic was thought to be dominated by macronutrient-rich Pacific waters entering through the Bering Strait and modified by uptake and regeneration on the Chukchi Shelf. However, the first high resolution (~6km) trace metal measurements in the strait (July 2021) show large variability in trace metal concentrations across the strait and a close relationship with salinity. The previously unsampled Alaskan Coastal Water has unexpectedly high trace metal concentrations, while the macronutrient-rich Anadyr Water has surprisingly low trace metal concentrations. We make the first estimates of trace metal flux from the Pacific to the Arctic through the Bering Strait and find they are elevated despite the comparatively small volume transport and, for some metals, exceed the Arctic to Atlantic export.

Trace metal and macronutrient samples were collected July 10-16, 2021, from the R/V Norseman II during an annual Bering Strait (BS) mooring and hydrographic cruise, which sampled the eastern Bering Strait (eBS) and the A3 line (AL) sections at 6-10km resolution. Water was collected using an air-diaphragm pump (PTFE, Wilden) with inline filtration (0.2 um, Acropak), pumping water from ~5m (“surface”) or ~25-45m depth (“bottom”), sufficient resolution to define the strait’s typically two-layer stratification (Woodgate et al., 2015). Samples were collected into acid-cleaned 250 mL low density polyethylene bottles and acidified to pH 1.8 following established protocols (Jensen et al., 2020). Additionally, filtered macronutrients (nitrate (N), phosphate (P), and silicate (Si)) samples were taken from the same depths and frozen (-20°C) immediately after collection until analysis at the University of Washington Marine Chemistry Lab in October 2021, following WOCE/JGOFS protocols (Gordon et al., 1993; Knap et al., 1996). Trace metal samples were run using a seaFAST-pico and an Element XR ICP-MS at Texas A&M University (Jensen et al., 2020).

Nutrient data was QA/QCed following WOCE/JGOFS protocols by the UW Marine Chem Lab. Trace metal data was derived from isotope ratios and standard curve slopes (Jensen et al., 2020) and compared to seawater certified reference materials provided by the GEOTRACES program (GSP and GSC water).

Gordon, L. I., J. C. Jennings Jr, A. A. Ross, and J. M. Krest (1993), A suggested protocol for continuous flow automated analysis of seawater nutrients (phosphate, nitrate, nitrite and silicic acid) in the WOCE Hydrographic Program and the Joint Global Ocean Fluxes Study, WOCE hydrographic program office, methods manual WHPO(68/91), 1-52.

Jensen, L. T., N. J. Wyatt, W. M. Landing, and J. N. Fitzsimmons (2020), Assessment of the stability, sorption, and exchangeability of marine dissolved and colloidal metals, Marine Chemistry, 220, 103754.

Knap, A., A. Michaels, A. Close, H. Ducklow, and A. Dickson (1996), Protocols for the joint global ocean flux study (JGOFS) core measurements, JGOFS, Reprint of the IOC Manuals and Guides No. 29, UNESCO 1994, 19.

Woodgate, R. A., K. M. Stafford, and F. G. Prahl (2015), A synthesis of year-round interdisciplinary mooring measurements in the Bering Strait (1990–2014) and the RUSALCA years (2004–2011), Oceanography, 28(3), 46-67.