Climate-correlated variations in seawater 187Os/188Os over the past 200,000 yr: Evidence from the Cariaco Basin, Venezuela

Dissolved osmium in Bengal plain groundwater: Implications for the marine Os budget

“…Such an increase would lead to a greater supply of radiogenic Os to the oceans during glacial periods. However, exactly the opposite is observed -glacial periods are strongly correlated with lower 187 Os/ 188 Os ratios in seawater (Oxburgh et al, 2007). This suggests that groundwater Os fluxes do not greatly increase during glacial intervals, or that such fluxes are compensated by even greater non-radiogenic fluxes from other sources.…”

“…Levasseur et al, 1999 used this mass balance equation, and their estimates of the total Os river flux (295 kg/g) and Os input from non-radiogenic sources (126 kg/yr), to estimate a s Os of 25-54 kyr, with a mean value of $35 kyr. As emphasized by Oxburgh, 2001, even considering the large uncertainties, this relatively long Os residence time is inconsistent with the very rapid changes in the marine Os isotopic composition recorded by hydrogenous sediments deposited during glacial-interglacial cycling (Oxburgh, 1998;Dalai et al, 2005;Williams and Turekian, 2004;Oxburgh et al, 2007).…”

“…The analysis of the Os content and isotopic composition of river waters and seawater Levasseur et al, 1998Levasseur et al, , 1999 allows an Os residence time of $ 35-50 kyr to be calculated from mass balance. However, rapid variations in 187 Os/ 188 Os linked to glacial-interglacial variations, recorded by hydrogenous sediments of different oceans (Oxburgh, 1998;Williams and Turekian, 2004;Dalai et al, 2005;Oxburgh et al, 2007), indicate a much lower Os marine residence time of $8 Kyr (Oxburgh, 2001). This disagreement underscores the current gaps in our understanding of the Os marine budget.…”

“…This value, second only to the global river Os flux, is greater than the total non-radiogenic Os input resulting from seafloor alteration and cosmic dust dissolution. A groundwater contribution of this magnitude would reduce the Os residence time in the ocean from 35000 yrs to $25000 yrs, and partially reconcile s Os estimates by mass balance (Levasseur et al, 1999) and 187 Os/ 188 Os glacial-interglacial variations (Oxburgh, 1998;Oxburgh et al, 2007) in marine hydrogenous sediments. Furthermore, as global groundwater is likely to have a radiogenic Os composition similar to that of global river water, an increase in the groundwater flow would likely increase the 187 Os/ 188 Os ratio of the ocean, and perhaps contribute to the change in the marine Os isotopic ratio over the Cenozoic.…”

Investigation of an early Pleistocene marine osmium isotope record from the eastern equatorial Pacific

“…The Os isotope composition of the integrated continental weathering flux to the oceans is radiogenic and distinctly different from the Os flux from the mantle and extraterrestrial sources. Late Quaternary records show that marine 187 Os/ 188 Os fluctuated during the glacial-interglacial cycles (Oxburgh, 1998;Peucker-Ehrenbrink and Ravizza, 2000a;Williams and Turekian, 2004;Dalai et al, 2005;Oxburgh et al, 2007) supporting the idea that 187 Os/ 188 Os can indeed be used as a proxy of changes in continental weathering fluxes induced by climate change.…”