Abstract
Abstract. As a shelf-dominated basin, the Arctic Ocean and its biogeochemistry are heavily influenced by continental and riverine sources. Radium isotopes (226Ra, 228Ra, 224Ra, and 223Ra), are transferred from the sediments to seawater, making them ideal tracers of sediment–water exchange processes and ocean mixing. As the two long-lived isotopes of the radium quartet, 226Ra and 228Ra (226Ra with a t1∕2 of 1600 years and 228Ra with a t1∕2 of 5.8 years) can provide insight into the water mass compositions, distribution patterns, as well as mixing processes and their associated timescales throughout the Canadian Arctic Archipelago (CAA). The wide range of 226Ra and 228Ra activities, as well as of the 228Ra∕226Ra, measured in water samples collected during the 2015 GEOTRACES cruise, complemented by additional chemical tracers – dissolved inorganic carbon (DIC), total alkalinity (AT), barium (Ba), and the stable oxygen isotope composition of water (δ18O) – highlight the dominant biogeochemical, hydrographic, and bathymetric features of the CAA. Bathymetric features, such as the continental shelf and shallow coastal sills, are critical in modulating circulation patterns within the CAA, including the bulk flow of Pacific waters and the inhibited eastward flow of denser Atlantic waters through the CAA. Using a principal component analysis, we unravel the dominant mechanisms and apparent water mass end-members that shape the tracer distributions. We identify two distinct water masses located above and below the upper halocline layer throughout the CAA and distinctly differentiate surface waters in the eastern and western CAA. Furthermore, we highlight water exchange across 80∘ W, inferring a draw of Atlantic water (originating from Baffin Bay) into the CAA. This underscores the presence of an Atlantic water “U-turn” located at Barrow Strait, where the same water mass is seen along the northernmost edge at 80∘ W as well as along the southeasternmost confines of Lancaster Sound. Overall, this study provides a stepping stone for future research initiatives within the Canadian Arctic Archipelago, revealing how quantifying disparities in the distributions of radioactive tracers can provide valuable information on water mass distributions, flow patterns, and mixing within vulnerable areas such as the CAA.
Highlights
1.1 General backgroundOver the past 30 years, major research initiatives have been undertaken within the Arctic, highlighting this region’s global importance and vulnerability to climate change (Prinsenberg and Bennett, 1987; Shadwick et al, 2013)
A calibration of the instrument was performed against certified reference materials (CRMs) provided by Andrew Dickson (Scripps Institution of Oceanography), and the reproducibility of the dissolved inorganic carbon (DIC) and AT measurements was better than 0.1 %
This is both the widest and shallowest section of the Canadian Arctic Archipelago (CAA). It is responsible for restricting the eastward flow of deep Atlantic layer (ATL) waters found in the western Canada Basin and inhibiting high salinity (SP > 33.1) ATL water within Baffin Bay from venturing westward (Hamilton and Wu, 2013; Jones, 2003; Prinsenberg, 1982; Prinsenberg and Bennett, 1987; Shadwick et al, 2011a; Yamamoto-Kawai et al, 2010)
Summary
1.1 General backgroundOver the past 30 years, major research initiatives have been undertaken within the Arctic, highlighting this region’s global importance and vulnerability to climate change (Prinsenberg and Bennett, 1987; Shadwick et al, 2013). C. Mears et al.: Using 226Ra and 228Ra isotopes to distinguish water mass distribution ern parts of the Canadian Arctic Archipelago (CAA) and being dispersed into Baffin Bay. Previous studies have shown that these eastward-flowing waters contribute significantly to carbon sequestration and instigate deep-water formation in the North Atlantic (e.g., Aagaard and Carmack, 1989; Burt et al, 2016a; Curry et al, 2011; Hamilton and Wu, 2013; Holland et al, 2001; Ingram and Prinsenberg, 1998; Rahmstorf, 2002; Shadwick et al, 2011a). The various water masses delivered to Baffin Bay play a role in establishing and maintaining the global thermohaline circulation, little is known about the distribution, composition, and modes of delivery of water through the Canadian Arctic Archipelago. We hope that this study will provide a foundation for further investigations of how changes in environmental conditions within this vulnerable area will affect the distribution of these tracers, as well as biogeochemical cycles and circulation in the CAA
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