6 research outputs found
The release of dissolved actinium to the ocean : A global comparison of different end-members
Author Posting. © Elsevier B.V., 2007. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Marine Chemistry 109 (2008): 409-420, doi:10.1016/j.marchem.2007.07.005.The measurement of short-lived 223Ra often involves a second measurement for supported
activities, which represents 227Ac in the sample. Here we exploit this fact, presenting a set of
284 values on the oceanic distribution of 227Ac, which was collected when analyzing water
samples for short-lived radium isotopes by the radium delayed coincidence counting system.
The present work compiles 227Ac data from coastal regions all over the northern hemisphere,
including values from ground water, from estuaries and lagoons, and from marine endmembers.
Deep-sea samples from a continental slope off Puerto Rico and from an active
vent site near Hawaii complete the overview of 227Ac near its potential sources.
The average 227Ac activities of nearshore marine end-members range from 0.4 dpm * m-3 at
the Gulf of Mexico to 3.0 dpm *m-3 in the coastal waters of the Korean Strait. In analogy to
228Ra, we find the extension of adjacent shelf regions to play a substantial role for 227Ac
activities, although less pronounced than for radium, due to its weaker shelf source. Based
on previously published values, we calculate an open ocean 227Ac inventory of 1.35 *
1018 dpm 227Acex in the ocean, which corresponds to 37 moles, or 8.4 kg. This implies a flux
of 127 dpm*m-2*y-1 from the deep-sea floor. For the shelf regions, we obtain a global
inventory of 227Ac of 4.5 * 1015 dpm, which cannot be converted directly into a flux value, as
the regional loss term of 227Ac to the open ocean would have to be included.
Ac has so far been considered to behave similarly to Ra in the marine environment, with the
exception of a strong Ac source in the deep-sea due to 231Paex. Here, we present evidence of
geochemical differences between Ac, which is retained in a warm vent system, and Ra,
which is readily released (Moore et al., submitted). Another potential mechanism of
producing deviations in 227Ac/228Ra and daughter isotope ratios from the expected production
value of lithogenic material is observed at reducing environments, where enrichment in
uranium may occur. The presented data here may serve as a reference for including 227Ac in
circulation models, and the overview provides values for some end-members that contribute
to the global Ac distribution
Shipbuilding Supply Chain Framework and Digital Transformation: A Project Portfolios Risk Evaluation
A review of present techniques and methodological advances in analyzing 234Th in aquatic systems
The short-lived thorium isotope 234Th (half-life 24.1 days) has been used as a tracer for a variety of transport processes in aquatic systems. Its use as a tracer of oceanic export via sinking particles has stimulated a rapidly increasing number of studies that require analyses of 234Th in both marine and freshwater systems. The original 234Th method is labor intensive. Thus, there has been a quest for simpler techniques that require smaller sample volumes. Here, we review current methodologies in the collection and analysis of 234Th from the water column, discuss their individual strengths and weaknesses, and provide an outlook on possible further improvements and future challenges. Also included in this review are recommendations on calibration procedures and the production of standard reference materials as well as a flow chart designed to help researchers find the most appropriate 234Th analytical technique for a specific aquatic regime and known sampling constraints. <br/
Global coastal groundwater and subterranean estuary nutrients
These data were compiled from original and published datasets of coastal groundwater / subterranean estuary research efforts along global coastline (sites within 1km of shoreline). The dataset includes sampling site names, locations, original sample information, sample depth, temperature, salinity, dissolved nitrogen concentrations, and dissolved phosphorus concentrations. The data source or curator is also included in the dataset