Continental bedrock and riverine fluxes of strontium and neodymium isotopes to the oceans
Miller, Mark W.
MetadataShow full item record
Realistic models of past climate and ocean chemistry depend on reconstructions of the Earth's surface environments in the geologic past. Among the critical parameters is the geologic makeup of continental drainage. Here we show, for the present, that the isotope composition of dissolved strontium in rivers increases linearly with the age of bedrock in drainage basins, with the notable exception of the drainage area of Arabia, India, and Southeast Asia that is affected by unusually radiogenic dissolved Sr from the Himalaya. We also demonstrate that the neodymium isotope compositions of suspended matter in rivers as well as clastic sediments deposited along the ocean margins decrease linearly with the bedrock ages of river drainage basins and large-scale continental drainage regions, as determined from digital geologic maps. These correlations are used to calculate the present-day input of dissolved Sr (4.7 × 1010 mol yr−1, 87Sr/86Sr of ∼0.7111) and particulate Nd isotopes (ɛNd of approximately −7.3 ± 2.2) to the oceans. The fact that the regionally averaged ɛNd of the global detrital input to the global coastal ocean is identical to globally averaged seawater (ɛNd of −7.2 ± 0.5) lends credence to the importance of “boundary exchange” for the Nd isotope composition of water masses. Regional biases in source areas of detrital matter and runoff are reflected by the observation that the average age of global bedrock, weighted according to the riverine suspended sediment flux, is significantly younger (∼336 Myr) than the age of global bedrock weighted according to water discharge (394 Myr), which is younger than the average bedrock age of the nonglaciated, exorheic portions of the continents (453 Myr). The observation that the bedrock age weighted according to Sr flux is younger (339 Myr) than that weighted according to water flux reflects the disproportionate contribution from young sedimentary and volcanic rocks to the dissolved Sr load. Neither the isotope composition of the dissolved nor the particulate continental inputs to the ocean provide unbiased perspectives of the lithologic makeup of the Earth's surface. Temporal changes in bedrock geology as well as the shifting focal points of physical erosion and water discharge will undoubtedly have exerted strong controls on temporal and spatial changes in the isotope chemistry of past global runoff and thus seawater.
Author Posting. © American Geophysical Union, 2010. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 11 (2010): Q03016, doi:10.1029/2009GC002869.
Suggested CitationGeochemistry Geophysics Geosystems 11 (2010): Q03016
Showing items related by title, author, creator and subject.
Fiege, Katherina; Miller, Christian A.; Robinson, Laura F.; Figueroa, Ricardo; Peucker-Ehrenbrink, Bernhard (2009-08-26)Analyses of Chilean river waters indicate that the average yield of unradiogenic Sr (~ 517 mol Sr km− 2 yr− 1, 87Sr/86Sr ~ 0.7057) from western South America (1,220,853 km2) into the southeastern Pacific Ocean is ~ 2–4 ...
Dissolved strontium in the subterranean estuary- implications for the marine strontium isotope budget Beck, Aaron J.; Charette, Matthew A.; Cochran, J. Kirk; Gonneea, Meagan E.; Peucker-Ehrenbrink, Bernhard (2013-01-13)Submarine groundwater discharge (SGD) to the ocean supplies Sr with less radiogenic 87Sr/86Sr than seawater, and thus constitutes an important term in the Sr isotope budget in the modern ocean. However, few data exist for ...
Casso, Susan A.; Clarke, William R.; Livingston, Hugh D.; Palmieri, Julianne M.; Surprenant, Lolita D. (Woods Hole Oceanographic Institution, 1988-04)This report is a follow-up to Woods Hole Oceanographic Institution Technical Report WHOI-84-40. It contains 137cs and 90sr data from seawater samples collected on four cruises in the northwestern North Atlantic, Arctic ...