Ocean 10Be/9Be as denudation rate proxy. Does 9Be deliver?

The ratio of meteoric cosmogenic 10Be to that of stable 9Be in seawater has been suggested to serve as a proxy for terrestrial weathering and denudation rates (D), in the modern ocean [1], and in the past when measured in chemical sediment of known age [2, 3]. The principle is remarkably simple. The only input of 10Be is atmospheric deposition into seawater. This flux is well-known at the scale of ocean basins. The trace metal9Be enters the oceans after continental weathering via two potential pathways: a) direct riverine input into the coastal ocean (both dissolved and mobilised from particles); b)  the release of “reactive” terrigenous Be from particles into seawater during early marine diagenesis, called “boundary exchange”. When the dissolved 9Be is mixed with seawater, the unknown weathering and denudation input flux of 9Be can be calculated from the 10Be/9Be ratio.However, because Be is an element that readily attaches to reactive particles, not all riverine 9Be escapes the coastal zone. We have estimated this delivery fraction (fdel) to be about 6% of the dissolved and adsorbed riverine Be [1]. For pathway a) we already suggested the possibility that with changing sediment delivery to the coastal ocean, fdel might potentially be a function of D itself [1]. However, global river data show that river particle concentration and D are not correlated. Yet, this erroneous assumption was made to suggest that 10Be/9Be fails to serve as a denudation rate proxy [4].In any case such dependence does not affect pathway b) “boundary exchange” [5]. This pore water input may even dominate the marine 9Be budget [6].Research is thus required to evaluate all of these potential input pathways of 9Be, how strongly sediment delivery onto the seafloor, also being a function of particulate riverine input flux, controls the release flux of 9Be, and whether its release is buffered in any way. Given the simple pathway of the known 10Be input, the 10Be(meteoric)/9Be ratio offers much potential to explore these fluxes, both in the terrestrial and the marine domain, and to evaluate their dependence on denudation and delivery – even three decades  after the first introduction of this system [7].von Blanckenburg, F. and J. Bouchez, Earth and Planetary Science Letters, 2014. 387 Willenbring, J.K. and F. von Blanckenburg, Nature, 2010. 4 von Blanckenburg, F., Bouchez, J., Ibarra, D.E., Maher, K., Nature Geoscience, 2015. 8 Li, S., S.L. Goldstein, and M.E. Raymo, Proc Natl Acad Sci USA, 2021. 118 von Blanckenburg, F., Bouchez, J., Willenbring, J.K., Ibarra, D.E., Rugenstein, J.K.C., Proc Natl Acad Sci USA, 2022. 119 Deng, K., Rickli, J., Suhrhoff, T.J., Du, J., Scholz, F., Severmann, S., Yang, S., McManus, J., Vance, D., Science Advances, 2023. 9 Kusakabe, M., Ku, T., Southon, J., Vogel, J., Nelson, D., Measures, C., Nozaki, Y., 1987. Earth and planetary science letters 82, 231-240