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Tracing the Impact of Coastal Water Geochemistry on the Re‐Os Systematics of Macroalgae: Insights From the Basaltic Terrain of Iceland
Author(s) -
Sproson Adam D.,
Selby David,
Gannoun Abdelmouchine,
Burton Kevin W.,
Dellinger Mathieu,
Lloyd Jeremy M.
Publication year - 2018
Publication title -
journal of geophysical research: biogeosciences
Language(s) - English
Resource type - Journals
eISSN - 2169-8961
pISSN - 2169-8953
DOI - 10.1029/2018jg004492
Subject(s) - radiogenic nuclide , weathering , basalt , geochemistry , seawater , geology , groundwater , salinity , sediment , environmental science , environmental chemistry , oceanography , chemistry , mantle (geology) , geomorphology , geotechnical engineering
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.