Combined Use of Short-Lived Radionuclides (Th and Po) as Tracers of Sinking Particles in the Ocean.

Radionuclides can provide key information on the temporal dimension of environmental processes, given their well-known rates of radioactive decay and production. Naturally occurring radionuclides, such as Th and Po, have been used as powerful particle tracers in the marine environment to study particle cycling and vertical export. Since their application to quantify the magnitude of particulate organic carbon (POC) export in the 1990s, Th and, to a lesser extent, Po have been widely used to characterize the magnitude of the biological carbon pump (BCP).

Impact of particle flux on the vertical distribution and diversity of size-fractionated prokaryotic communities in two East Antarctic polynyas.

Antarctic polynyas are highly productive open water areas surrounded by ice where extensive phytoplankton blooms occur, but little is known about how these surface blooms influence carbon fluxes and prokaryotic communities from deeper waters. By sequencing the 16S rRNA gene, we explored the vertical connectivity of the prokaryotic assemblages associated with particles of three different sizes in two polynyas with different surface productivity, and we linked it to the magnitude of the particle export fluxes measured using thorium-234 (Th) as particle tracer. Between the sunlit and the mesopelagic layers (700 m depth), we observed compositional changes in the prokaryotic communities associated with the three size-fractions, which were mostly dominated by , , and .

Review of the analysis of Th in small volume (2-4 L) seawater samples: improvements and recommendations.

The short-lived radionuclide Th is widely used to study particle scavenging and transport from the upper ocean to deeper waters. This manuscript optimizes, reviews and validates the collection, processing and analyses of total Th in seawater and suggests areas of further improvements. The standard Th protocol method consists of scavenging Th from seawater via a MnO precipitate, beta counting, and using chemical recoveries determined by adding Th.

Sampling Device-Dependence of Prokaryotic Community Structure on Marine Particles: Higher Diversity Recovered by Pumps Than by Oceanographic Bottles.

Microbes associated with sinking marine particles play key roles in carbon sequestration in the ocean. The sampling of particle-attached microorganisms is often done with sediment traps or by filtration of water collected with oceanographic bottles, both involving a certain time lapse between collection and processing of samples that may result in changes in particle-attached microbial communities. Conversely, water filtration through submersible pumps allows a faster storage of sampled particles, but it has rarely been used to study the associated microbial communities and has never been compared to other particle-sampling methods in terms of the recovery of particle microbial diversity.

Analysis of Po, Bi, and Pb in atmospheric and oceanic samples by simultaneously auto-plating Po and Bi onto a nickel disc.

Po and Pb are commonly measured to study particle cycling and particulate organic carbon export (POC) flux from the upper ocean. Bi is a potential oceanographic tracer. However, no convenient and rapid analytical method for Bi has been developed in the marine environment due to its short half-life (5 days).

Accumulation of natural and anthropogenic radionuclides in body profiles of Bryidae, a subgroup of mosses.

Mosses can be used as biomonitors to monitor radionuclide deposition and heavy metal pollution in cities, forests, and grasslands. The aims of this work were to determine the activity concentrations of natural (Po, Pb or Pb (excess Pb is defined as the activity of Pb minus the activity of Ra), Be, K, Ra, U, and Th) and anthropogenic radionuclides (Cs) in moss body profiles and in situ underlying soils of moss samples and to assess/determine the distribution features and accumulation of these radionuclides. Activity concentrations of radionuclides in the samples were measured using a low-background gamma spectrometer and a low-background alpha spectrometer.