Radium Inputs Into the Arctic Ocean From Rivers: A Basin‐Wide Estimate

Abstract

Radium isotopes have been used to trace nutrient, carbon, and trace metal fluxes inputs from ocean margins. However, these approaches require a full accounting of radium sources to the coastal ocean including rivers. Here, we aim to quantify river radium inputs into the Arctic Ocean for the first time for 226Ra and to refine the estimates for 228Ra. Using new and existing data, we find that the estimated combined (dissolved plus desorbed) annual 226Ra and 228Ra fluxes to the Arctic Ocean are [7.0–9.4] × 1014 dpm y−1 and [15–18] × 1014 dpm y−1, respectively. Of these totals, 44% and 60% of the river 226Ra and 228Ra, respectively are from suspended sediment desorption, which were estimated from laboratory incubation experiments. Using Ra isotope data from 20 major rivers around the world, we derived global annual 226Ra and 228Ra fluxes of [7.4–17] × 1015 and [15–27] × 1015 dpm y−1, respectively. As climate change spurs rapid Arctic warming, hydrological cycles are intensifying and coastal ice cover and permafrost are diminishing. These river radium inputs to the Arctic Ocean will serve as a valuable baseline as we attempt to understand the changes that warming temperatures are having on fluxes of biogeochemically important elements to the Arctic coastal zone.

Seasonality of submarine groundwater discharge to an Arctic coastal lagoon

“…The dissolved Ra activities in the Kuparuk River and Putuligayuk River were similar, with No Point Creek (reported as runoff) having slightly higher values (Table 1). Most Arctic rivers have not been sampled for short‐lived isotopes; however, 226 Ra activities measured in this study ranged between 1.4 and 3.9 dpm 100 L −1 , which are lower than those seen in large Arctic rivers such as the Yenisey and Lena Rivers in Siberia (Rutgers van der Loeff et al 2003), or the Mackenzie and Yukon Rivers in North America (Kipp et al 2020), but are comparable to activities seen in similarly sized Arctic rivers such as the Ellice River, rivers near Anchorage, AK (Bullock et al 2022), and rivers in Greenland (Linhoff et al 2020).…”

“…Lagoon surface, river, and ocean Ra activities across seasons for (a) 224 Ra, (b) 223 Ra, (c) 228 Ra, and (d) 226 Ra. (Rutgers van der Loeff et al 2003), or the Mackenzie and Yukon Rivers in North America (Kipp et al 2020), but are comparable to activities seen in similarly sized Arctic rivers such as the Ellice River, rivers near Anchorage, AK (Bullock et al 2022), and rivers in Greenland (Linhoff et al 2020).…”

Radium Isotopes as Tracers of Shelf‐Basin Exchange Processes in the Eastern Arctic Ocean

“…Although rivers account for a much smaller percentage of Ra inputs to Arctic surface waters than continental shelves (∼5% compared to 92% for 228 Ra; Bullock et al., 2022; Kipp et al., 2018), river discharge can nonetheless act as a significant source of Ra to Arctic seas. In 2021, elevated 228 Ra (21–25 dpm/100L) and 226 Ra (11–13 dpm/100L) activities were observed in the top 40 m along the East Siberian Slope near the 200 m isobath (stations 79–83; Figures 3, 5).…”

“…This is likely Lena River‐influenced water that has been transported from the Laptev Sea. Although the Kolyma River empties directly into the ESS, its discharge and Ra activities are much lower than that of the Lena River, resulting in lower Ra fluxes (6 × 10 12 vs. 52 × 10 12 dpm 226 Ra/y and 6 × 10 12 vs. 108 × 10 12 dpm 228 Ra/y from the Kolyma and Lena, respectively; Bullock et al., 2022). The modeled water parcel back trajectories indicate water transport from the Laptev to the ESS along the slope, supporting this hypothesis (Figure 6).…”

“…However, the 2018 stations only have surface measurements, and both studies are located on the outer edge of the ESS; our average 228 Ra concentration may therefore be an underestimate because it is biased toward surface values (while we expect highest activities near the seafloor) and excludes the shallowest regions of the East Siberian and Laptev Seas. The 228 Ra source via river discharge into the Laptev and ESS is a total of 2.01 × 10 18 atoms/d (Bullock et al., 2022). The average water residence time was estimated to be 13.4 ± 1.8 months, based on the modeled mean time water parcels spent over both shelves in 2018–2021 (see Section 4.2).…”