Gallium: A New Tracer of Pacific Water in the Arctic Ocean

Abstract

Determining the proportions of Atlantic and Pacific Ocean seawater entering the Arctic Ocean is important both for understanding the mass balance of this basin as well as its contribution to formation of North Atlantic deep water. To quantify the distribution and amount of Pacific and Atlantic origin seawater in the western Arctic Ocean, we used dissolved Ga in a four‐component linear endmember mixing model. Previously, nutrients, combined in their Redfield ratios, have been used to separate Pacific‐ and Atlantic‐derived waters. These nutrient tracers are not conservative in practice, and there is a need to find quantities that are conserved. Dissolved Ga concentrations show measurable contrast between Atlantic and Pacific source waters, shelf‐influenced waters show little impact of shelf processes on the dissolved Ga distribution, and dissolved Ga in the Arctic basins is conserved along isopycnal surfaces. Thus, we explored the potential of Ga as a new parameter in Arctic source water deconvolution. The Ga‐informed deconvolution was compared to that generated with the NO3:PO4 relationship. While distributions of the water masses were qualitatively similar, the Ga‐based deconvolution predicted higher amounts of Pacific water at depths between 150 and 300 m. The Ga‐based decomposition yields a smoother transition between the halocline and Atlantic layers, while nutrient‐based solutions have sharper transitions. A 1‐D advection‐diffusion model was used to constrain estimates of vertical diffusivity (Kz). The Ga‐based Kz estimates agreed better with those from salinity and temperature than the nutrient method. The Ga‐based approach implies greater vertical mixing between the Pacific and Atlantic waters.

Separating individual contributions of major Siberian rivers in the Transpolar Drift of the Arctic Ocean

“…These estimates are based on transects in the Canadian Basin, therefore no information is available for the Eurasian side of the Arctic Ocean. Based on the following discussion we suggest that the radiogenic signal is rather caused by Yenisei/Ob water than Pacific water: even though Pacific water may have been present around the North Pole in 2015 23 , 60 , it is very unlikely that Pacific water is advected as far as station 69 in the Eurasian Basin in high amounts . Contributions of Pacific water calculated based on salinity, δ 18 O and N/P are highest at the surface at st. 96 and 101.…”

“…Previous studies have suggested that Pacific water is restricted to the Canadian Basin with the Pacific front ranging from the Mendeleev Ridge to the Lomonosov Ridge and correlated with changes in atmospheric circulation 19 , 23 , 55 – 59 . Studies based on samples from 2015 show the front of Pacific water in the halocline at the Mendeleev Ridge 23 or dominance of Pacific water up to the Lomonosov Ridge 60 depending on the method. These estimates are based on transects in the Canadian Basin, therefore no information is available for the Eurasian side of the Arctic Ocean.…”

New Constraints on the Physical and Biological Controls on the Silicon Isotopic Composition of the Arctic Ocean

“…This pattern could be explained by mixing between the LHL and underlying AAW as both the Si isotope signature and silicic acid concentration of LHL lies between those of the UHL and AAW (+1.82 ± 0.01 , 6.6 ± 0.2 µmol kg −1 , Figure 3). Such mixing is evident when using Ga as a tracer of Pacific water in the Canada Basin (Whitmore et al, 2020) and has been invoked to explain the distribution of both dissolved Zn (Jensen et al, 2019) and DIC (Brown et al, 2016) in the halocline of the Canada Basin.…”

A Review on the Elemental and Isotopic Geochemistry of Gallium

“…Similarly, the dissolved Ga flux from rivers to oceans is about 1.1 × 10 3 t yr −1 (Gaillardet et al, 2003(Gaillardet et al, , 2014Viers et al, 2009). However, this dissolved Ga flux may be overestimated, as the recent studies report much lower Ga contents in riverwaters (Colombo et al, 2019;Gaillardet et al, 2014;Shiller & Frilot, 1996;Whitmore, et al, 2020), and the riverine dissolved Ga may be further partially scavenged and removed by complex processes at Bruland (1983); Evans (2012); Gale et al (2013); Hu and Gao (2008); Huang et al (2014); Hunt (1972); Koljonen (1992); Løvik et al (2015); Li (1985); Lodders and Fegley (1998); Maring and Duce (1987); Matschullat (2000); Metz and Trefry (2000); Nielsen et al (2006); Niu et al (2012); O'Neill and Palme (1998); Prospero (1981); Rudnick and Gao (2003); Trenberth et al (2007); Viers et al (2009). estuary (Ho et al, 2019;Mcalister & Orians, 2012;Schier et al, 2021).…”

“…Similarly, the dissolved Ga flux from rivers to oceans is about 1.1 × 10 3 t yr −1 (Gaillardet et al, 2003(Gaillardet et al, , 2014Viers et al, 2009). However, this dissolved Ga flux may be overestimated, as the recent studies report much lower Ga contents in riverwaters (Colombo et al, 2019;Gaillardet et al, 2014;Shiller & Frilot, 1996;Whitmore, et al, 2020), and the riverine dissolved Ga may be further partially scavenged and removed by complex processes at estuary (Ho et al, 2019;Mcalister & Orians, 2012;Schier et al, 2021). To be mentioned, the delivery of sediments to oceans most likely increases with time, implying a change in the continental Ga flux over geological history (Vanlaningham et al, 2009), although the historical Ga-ocean flux is beyond the scope of this study.…”