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Alkalinity generation from rock weathering modulates Earth's climate at geological time scales. Although lithology is thought to dominantly control alkalinity generation globally, the role of other first-order controls appears elusive. Particularly challenging remains the discrimination of climatic and erosional influences. Based on global observations, here we uncover the role of erosion rate in governing riverine alkalinity, accompanied by areal proportion of carbonate, mean annual temperature, catchment area, and soil regolith thickness. We show that the weathering flux to the ocean will be significantly altered by climate warming as early as 2100, by up to 68% depending on the environmental conditions, constituting a sudden feedback of ocean CO2 sequestration to climate. Interestingly, warming under a low-emissions scenario will reduce terrestrial alkalinity flux from mid-latitudes (–1.6 t(bicarbonate) a−1 km−2) until the end of the century, resulting in a reduction in CO2 sequestration, but an increase (+0.5 t(bicarbonate) a−1 km−2) from mid-latitudes is likely under a high-emissions scenario, yielding an additional CO2 sink. The weathering alkalinity flux from mid-latitudes to the ocean will be strongly altered by climate warming by 2100. Under different emissions scenarios either a strengthening or a weakening of the flux and thus of the oceanic CO2 buffer is predicted. [ABSTRACT FROM AUTHOR]

Early studies revealed relationships between barium (Ba), particulate organic carbon and silicate, suggesting applications for Ba as a paleoproductivity tracer and as a tracer of modern ocean circulation. But, what controls the distribution of barium (Ba) in the oceans? Here, we investigated the Arctic Ocean Ba cycle through a one‐of‐a‐kind data set containing dissolved (dBa), particulate (pBa), and stable isotope Ba ratio (δ138Ba) data from four Arctic GEOTRACES expeditions conducted in 2015. We hypothesized that margins would be a substantial source of Ba to the Arctic Ocean water column. The dBa, pBa, and δ138Ba distributions all suggest significant modification of inflowing Pacific seawater over the shelves, and the dBa mass balance implies that ∼50% of the dBa inventory (upper 500 m of the Arctic water column) was supplied by nonconservative inputs. Calculated areal dBa fluxes are up to 10 μmol m−2 day−1 on the margin, which is comparable to fluxes described in other regions. Applying this approach to dBa data from the 1994 Arctic Ocean Survey yields similar results. The Canadian Arctic Archipelago did not appear to have a similar margin source; rather, the dBa distribution in this section is consistent with mixing of Arctic Ocean‐derived waters and Baffin Bay‐derived waters. Although we lack enough information to identify the specifics of the shelf sediment Ba source, we suspect that a sedimentary remineralization and terrigenous sources (e.g., submarine groundwater discharge or fluvial particles) are contributors. Plain Language Summary: We investigated the barium (Ba) cycle in the Arctic Ocean. The oceanic Ba cycle is supported by the interplay of seawater mixing, river inputs, sediment inputs, and particle formation and export from the water column. We determined that the distribution of dissolved Ba in the upper 500 m of the Arctic Ocean is largely set by a shelf sediment source; this is newly described, as previous literature assumed rivers and seawater mixing were the predominant contributors to the distribution. This discovery fits in with recent findings that the shelf sediments are a major source of radium and other trace metals to the surface Arctic Ocean. This is important to consider as the warming climate continues to erode Arctic ice cover (sea ice or glacial). Monitoring the relative sources of Ba to the water column can help define how warming impacts Arctic Ocean biogeochemistry. Key Points: A mass balance approach indicates margin sources of barium (Ba) account for ∼50% of the budgetAmerasian Arctic Ocean samples exhibit inverted Ba isotope profiles, though still fall on the global arrayParticle supply from the shelves and dissolution in the deep Amerasian Arctic Ocean is a likely source of dissolved Ba [ABSTRACT FROM AUTHOR]

As a shelf dominated basin, the Arctic Ocean and its biogeochemistry are heavily influenced by continental and riverine sources. Radium isotopes (226Ra, 228Ra, 224Ra, 223Ra), are transferred from the sediments to seawater, making them ideal tracers of sediment-water exchange processes and ocean mixing. 226Ra and 228Ra are the two longer-lived isotopes of the Radium Quartet (226Ra, t1/2 = 1600 y and 228Ra, t1/2 = 5.8 y). Because of their long half-lives they can provide insight into the water mass compositions, distribution patterns, as well as mixing processes and the associated timescales throughout the Canadian Arctic Archipelago (CAA). The wide range of 226Ra, 228Ra, and of the 228Ra / 226Ra ratio, 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 the 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, as well as distinctly differentiate surface waters in the eastern and western CAA. Furthermore, we identify water exchange across 80° W, inferring a draw of Atlantic water, originating from Baffin Bay, into the CAA. In other words, this implies 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 south-easternmost 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 radioactive isotopes can provide valuable information on the potential effects of climate change within vulnerable areas such as the CAA. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]