Influence of glacial meltwater on global seawater δ234U. (15th March 2018)

• Record Type: Journal Article
• Authors: Arendt, Carli A.; Aciego, Sarah M.; Sims, Kenneth W.W.; Das, Sarah B.; Sheik, Cody; Stevenson, Emily I.
• Is Part Of: Geochimica et cosmochimica acta. Volume 225(2018)
• Page Start: 102
• Page End: 115
• Publication Date: 2018-03-15
• Subjects: Greenland ice sheet -- Meltwater -- Seawater chemistry -- Subglacial processes -- Uranium -- Radiogenic isotopes -- Glacial-interglacial -- Glaciology -- Paleoclimatology; Geochemistry -- Periodicals; Meteorites -- Periodicals; Géochimie -- Périodiques; Météorites -- Périodiques; Geochemie; Astrochemie; Electronic journals; 551.905
• DOI: 10.1016/j.gca.2018.01.007
• Languages: English
• ISSNs: 0016-7037

Abstract

Abstract: We present the first published uranium-series measurements from modern Greenland Ice Sheet (GrIS) runoff and proximal seawater, and investigate the influence of glacial melt on global seawater δ 234 U over glacial-interglacial (g-ig) timescales. Climate reconstructions based on closed-system uranium-thorium (U/Th) dating of fossil corals assume U chemistry of seawater has remained stable over time despite notable fluctuations in major elemental compositions, concentrations, and isotopic compositions of global seawater on g-ig timescales. Deglacial processes increase weathering, significantly increasing U-series concentrations and changing the δ 234 U of glacial meltwater. Analyses of glacial discharge from GrIS outlet glaciers indicate that meltwater runoff has elevated U concentrations and differing 222 Rn concentrations and δ 234 U compositions, likely due to variations in subglacial residence time. Locations with high δ 234 U have the potential to increase proximal seawater δ 234 U. To better understand the impact of bulk glacial melt on global seawater δ 234 U over time, we use a simple box model to scale these processes to periods of extreme deglaciation. We account for U fluxes from the GrIS, Antarctica, and large Northern Hemisphere Continental Ice Sheets, and assess sensitivity by varying melt volumes, duration and U flux input rates based on modern subglacial water U concentrations and compositions. All scenarios support the hypothesis that global seawater δ 234 U has varied by more than 1‰ through time as a function of predictable perturbations in continental U fluxes during g-ig periods.