Tracing the Impact of Coastal Water Geochemistry on the Re‐Os Systematics of Macroalgae: Insights From the Basaltic Terrain of Iceland

Abstract

This study presents rhenium (Re) and osmium (Os) elemental and isotope data for macroalgae, dissolved load, and bed load from Icelandic coastal and/or river waters, an environment adjacent to predominantly basaltic terrains, ranging in age from historic to~12 Ma. Both the Re (0.1 to 88.4 ppb) and Os (3.3 to 254.5 ppt) abundance in macroalgae are shown to be primarily controlled by uptake from the dissolved load of local seawater and are largely dependent on the relative influence of local freshwater inputs. Incorporation of Re and Os into macroalgae appears to be complicated by additional Re and Os uptake from the bed load. The 187 Os/ 188 Os (0.16 to 0.99) composition of macroalgae is highly variable and is explained in terms of an unradiogenic 187 Os/ 188 Os contribution from rivers draining younger basaltic catchments that have undergone congruent weathering (and/or hydrothermal input) and a radiogenic 187 Os/ 188 Os contribution from two distinct sources: rivers draining older catchments that have undergone incongruent weathering of radiogenic primary basaltic minerals and North Atlantic seawater. The 187 Re/ 188 Os composition (~65 to 40,320) of macroalgae traces that of water, with higher values associated with higher salinity waters, but far exceeds the 187 Re/ 188 Os of water due to the preferential uptake of Re over Os by macroalgae in areas of high dissolved and/or bed load Re abundances. This study substantiates the utility of macroalgae as a proxy for the long-term (months to years) average 187 Os/ 188 Os composition of seawater, which holds the potential to elucidate a range of Earth system and anthropogenic processes.Macroalgae are known to accumulate Re and Os from seawater (Mas et al., 2005;Prouty et al., 2014;Racionero-Gómez et al., 2016;Racionero-Gómez et al., 2017;Rooney et al., 2016;Scadden, 1969;Yang, 1991), and recent studies have shown that macroalgae can act as a proxy for the 187 Os/ 188 Os of the seawater in which it lived SPROSON ET AL. 2791

Tracing the natural and anthropogenic influence on the trace elemental chemistry of estuarine macroalgae and the implications for human consumption

“…Fv contains Re (20-95 ppb) and Os (5-25 ppt; Fig. 7a, b) abundances within the range of previously published data (Re = 0.1-313 ppb; Os = 3.3-254.5 ppt) (Racionero-Gómez et al, 2016Rooney et al, 2016;Sproson et al, 2018). The higher Re and Os values seaward (Fig.…”

“…Fv was selected for Re\ \Os analysis as it spans the length of the Forth estuary and reliably records Re\ \Os data in relation to the water mass in which it lives (Racionero-Gómez et al, 2016;Rooney et al, 2016;Racionero-Gómez et al, 2017;Sproson et al, 2018). Fv contains Re (20-95 ppb) and Os (5-25 ppt; Fig.…”

“…However, this is further complicated by competition between Re and Os due to similar uptake mechanisms into the macroalgae. This can cause lower macroalgal Os abundances in waters of higher Re concentrations, and vice versa (Racionero-Gómez et al, 2017;Sproson et al, 2018).…”

“…Macroalgae can reflect the chemistry of the waters in which it lives (Bryan, 1983;Davis et al, 2003;Racionero-Gómez et al, 2016, and thus can be analysed for a multitude of elements including: trace metals (Balls et al, 1994;Forsberg et al, 1988), rhenium and osmium (Racionero-Gómez et al, 2016, iodine (Fecher et al, 1998;Teas et al, 2004) and arsenic (Khan et al, 2015;Rose et al, 2007). As such, macroalgae has been shown to be a valuable environmental indicator for marine and estuarine environments (Almela et al, 2006;Bryan, 1983;Fuge and James, 1973;Sproson et al, 2018).…”

“…These different inputs carry various elements into the estuary. Analysis of macroalgae can help to understand these inputs, the abundance of the elements within the macroalgae, and the mixing processes (e.g., Bryan, 1983;Francesconi and Edmonds, 1998;Huang et al, 2013;Sproson et al, 2018).…”