Radioactive and chemical tracers to evaluate sediment accumulation and biodiffusion in the southern Gulf of Mexico

In this paper, we present results that have important implications for understanding the sedimentation process and for evaluating the carbon cycle in deep-sea sediment of the southern Gulf of Mexico (sGM) in the current context of global climate change. Here we show results about short- and long-term biodiffusion rates obtained from natural (²³⁴Th, ²¹⁰Pb, ²¹⁴Pb, ²²⁶Ra) and anthropogenic (^239+240Pu) radionuclides in eleven sediment cores collected in the sGM: i) the outer continental shelf (2 cores), ii) the continental slope (5 cores), and iii) the abyssal plain (4 cores). The short- and long-term biodiffusion rates (D_b-Th and D_b-Pb) ranged from 95 to 4135 cm² kyr⁻¹ and 54 to 549 cm² kyr⁻¹, respectively. The D_b-Th (100 d time scale) values were less than one order of magnitude higher than the D_b-Pb (100 yrs time scale), possibly because of the oligotrophic condition of the surface ocean in the sGM to limit the biological activity in sediments. Changes in redox conditions were confirmed by the enrichment of Fe and Mn in the sediment profiles. These redox changes are likely responsible for increased Ra mobilization in the sediments and, consequently, for changes in the accumulation of unsupported ²¹⁰Pb. This process acts as an autochthonous source of ²¹⁰Pb_ex within the sediment layers and explains the disequilibrium observed between ²¹⁴Pb and ²¹⁰Pb in subsurface sections of some sediment cores. Numerical simulation of ^239+240Pu profiles using an advection-diffusion equation in non-steady-state conditions fit well (R² > 0.86) with measured ^239+240Pu profiles in four of six cores. The biodiffusion rates obtained from the Pu model were comparable to those obtained from ²¹⁰Pb, but different than the short-term biodiffusion rates elucidated with ²³⁴Th. The accumulation rates from Pu deconvolutions were similar to data reported previously by ¹⁴C dating.

Multi-tracer result aproch in sediment core F38: Radioactive (²¹⁰Pb, ²¹⁴Pb, ²²⁶Ra) and chemical (Mn, Fe, Al) tracers for assessing sediment accumulation and biodiffusion, and comparison of the 239+240Pu activity profile with the advection–diffusion model simulation in sediment core F38.

https://doi.org/10.1016/j.jenv...
M. Díaz-Asencio ^{a b}, J.A. Corcho-Alvarado ^c, O. Díaz-García ^d, J.C. Herguera ^b, M.A. Huerta-Diaz ^e, P.T. Schwing ^f, R. Larson ^f, G.R. Brook ^f, S. Röllin ^c, L.W. Daessle ^eaEscuela Nacional de Estudios Superiores Unidad Mérida, UNAM, Mérida, Yucatán, México^bDivision of Oceanology. CICESE, Ensenada Center for Scientific Research and Higher Education, Ensenada, Baja California, México^cNuclear Chemistry Division, Spiez Laboratory, Federal Office for Civil Protection, Spiez, Switzerland^dThe Water Institute of the Gulf. Center for Coastal and Deltaic Solutions, Baton Rouge, LA, United States of America^eInstituto de Investigaciones Oceanológicas, Universidad Autónoma de Baja California, Campus Sauzal, Carretera Transpeninsular Ensenada-Tijuana, No. 3917, Frac. Playitas, Ensenada, Baja California, CP 22860, México^fEckerd College, St. Petersburg, Florida, United States of America