放射性(Pu、210Pb、234Th和226Ra)和化学(Mn、Fe、Al)追踪器,以评估墨西哥湾南部的沉积物积累和生物分化.

Radioactive (Pu, 210Pb, 234Th and 226Ra) and chemical (Mn, Fe, Al) 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 (Db-Th and Db-Pb) ranged from 95 to 4135 cm2 kyr-1 and 54 to 549 cm2 kyr-1, respectively. The Db-Th (100 d time scale) values were less than one order of magnitude higher than the Db-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 210Pbex 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.