²¹⁰Pb Atmospheric Flux and Growth Rates of a Microbial Mat from the Northwestern Mediterranean Sea (Ebro River Delta)

Abstract

Environmental archives are needed to study the variability of natural systems and the impact of man on them. Microbial mats, modern homologues of stromatolites, can be found in extreme environments such as the Ebro River Delta and were studied as potential environmental archives of atmospheric deposition. 210Pb, a radiotracer widely used in geochronology studies, was used both to determine the growth rates of a microbial mat from this environment and to estimate the 210Pb atmospheric flux in the northwestern Mediterranean Sea. The 210Pb profile showed the presence of three distinct peaks related to low growth-rate periods. This variability indicated the sensitivity of the system to external forcing. The annual atmospheric flux of 210Pb was 81.2 ± 1.4 Bq m-2 yr-1, which is similar to other values found in the literature. The age profile showed two layers of differing growth rates, being 0.99 ± 0.10 mm yr-1 from the surface down to 10 mm depth. The accumulated mass profile showed a change at about 9 mm depth, corresponding to year 1983 ± 1. It is noteworthy that this is coincident with a strong El Niño Southern Oscillation event during 1982−1983, which has been shown to affect other ecosystems, including some in the Mediterranean area.

Water Circulation, Sediment Transport, and Pollutant Dynamics in Southern Iberia Waters: A Review on Numerical Modelling Studies

“…us, in the lower layer, distributions are clearly different for both radionuclides due to the different efficiency of the removal process of dissolved radionuclides by settling suspended particles. [84]. A more detailed evaluation may be seen in [85]; however the use of a mean value (which also is in good agreement with the average calculated by these last authors) is enough for our modelling purposes.…”

Sedimentation rates and trace metal input history in intertidal sediments from San Simón Bay (Ría de Vigo, NW Spain) derived from 210Pb and 137Cs chronology

“…These are consistent with other values found in the scarce existing literature for the European continent from which 210 Pb xs inventory measured in peat bogs and estuarine sediments ranged between 2000 Bq m À2 and 9800 Bq m À2 and 210 Pb xs fluxes ranged between 60 Bq m À2 y À1 and 300 Bq m À2 y À1 (Carvalho, 1995;Cundy and Croudace, 1995b;Holynska et al, 1998;Gascó et al, 2006). Atmospheric 210 Pb xs fluxes have not been reported for the study area, although they have been established for other areas of the Iberian Peninsula, such as the West Mediterranean Sea where the flux is about 80 Bq m À2 y À1 (Sanchez-Cabeza et al, 1999), which is of the same order of that reported here.…”

Slime travelers: Early evidence of animal mobility and feeding in an organic mat world

“…We refer to these as “ecological” to represent intervals smaller than those of ontogenetic change, roughly equivalent to timescales of common biotic interactions. Modern microbial mats grow at variable rates, typically on the order of a few mm per year vertically (Buffan‐Dubau, Pringault, & de Wit, ; Sanchez‐Cabeza, Masqué, Martínez‐Alonso, Mir, & Esteve, ). Thus, footprints, commonly <0.5 mm in total relief, would have been obscured by mat regrowth over much shorter intervals.…”