Download Glossary, acronyms and abbreviations 137Cs: Cesium

Glossary, acronyms and abbreviations
137Cs:
Cesium-137, a short-lived radioisotope (half-life: 30.1 years) of anthropogenic origin that
provides useful dating horizons through correlation to the history of thermonuclear weapons
testing, including a major peak at 1963.
210Pb: Lead-210,
a natural isotope (half-life: 22.3 years) formed in the atmosphere from Radon222 decay and widely used for dating sediments spanning the last ca. 150 years.
239+240Pu:
Isotopes of plutonium associated with thermonuclear weapons testing and thus
having stratigraphic distributions much like Cesium-137.
α, β and γ particles: Energized subatomic particles emitted during radionuclide decay.
AMS: Accelerator mass spectrometry.
accelerator mass spectrometry: The use of a tandem particle accelerator that enables highprecision measurements of radiocarbon (and other isotopes) on small targets by direct ion
counting.
alanine blanks: Commonly used standard for assessing the sensitivity of AMS 14 C to trace
levels of radiocarbon contamination.
amino acid racemization: The time- and temperature-dependent conversion of amino acids
from their L to D isomeric configurations, which can potentially be used to date chemicallyclosed systems including certain protein-rich organic matrices.
allochthonous: Materials that are derived from outside a body of water and transported to lake
sediments by wind, erosion, or fluvial transport.
atmospheric fallout: Transfer of chemical compounds and particulate matter from the
atmosphere to land and water surfaces. Includes both dry and wet deposition, the latter
being more important in most instances.
autochthonous: The collection of materials formed within a given body of water and eventually
accumulating in sediments. Includes both mineral precipitates and vestiges of aquatic
organisms.
benthos: The biological community living in or on aquatic sediments.
bioturbation: Disturbance of bottom sediments by the feeding and burrowing of benthic
organisms.
brine exsolution: Ejection of salts from solution following the freezing of water.
bottom-freezing: Influence of ice on the integrity of sediments, either in the littoral zones of
deep lakes where ice is seasonally anchored, or more widely in shallow lakes (ponds) less
than ca. 2 m deep.
colluvial: Sediments derived from hillslope processes.
DIC: Dissolved inorganic carbon.
dissolved inorganic carbon: The fraction of soluble carbon in natural waters that derives from
remineralized organic matter, respiration, and weathering of carbonate minerals. Dissolved
inorganic carbon typically includes CO2(aq.) , HCO 3 -, and CO3 2+ .
DOC: Dissolved organic carbon.
dissolved organic carbon: The fraction of soluble carbon that is derived from decomposed but
non-remineralized plant, algal and bacterial biomass. Dissolved organic carbon frequently
stains natural waters brown, and plays an important role in attenuating ultraviolet radiation.
dose rate: Estimated natural radioactivity of a geological sample, required to normalize the
sample’s equivalent dose in order to generate luminescence ages.
ED: Equivalent dose.
equivalent dose: The approximation of a geological sample’s total radiation dose accumulated
over time, based on TL or OSL measurements of electron trap eviction.
Fm: Fraction modern.
fraction modern: Ratio between the radiocarbon activities of the sample being dated and a
recognized modern standard such as National Bureau of Standards oxalic acid. In determining
conventional radiocarbon ages, the modern standard reflects atmospheric radiocarbon content
in 1950. Thus, samples with a fraction modern >1.0 are enriched by anthropogenic
radiocarbon associated with thermonuclear weapons testing.
fulvic acids: A class of dissolved organic matter that remains soluble in both acid and base.
geological luminescence: Light emission from silicate minerals resulting the time-dependent
storage of electrons in lattice charge defects. The release and subsequent quantification of
geological luminescence is accomplished by heating or exposure to light.
geomagnetic poles: The points of emergence at the Earth’s surface of the axis of the magnetic
dipole that most closely approximates the Earth’s magnetic field.
geomagnetic shielding: Influence of Earth’s magnetic field on the cosmic ray flux reaching the
upper atmosphere, and hence influencing radiocarbon production by the bombardment of
nitrogen. Geomagnetic shielding and radiocarbon production have covaried significantly over
the past 50 ka.
HA: Humic acids.
half-life: The length of time required for decay of half the initial inventory of radioactivity
associated with an individual radionuclide. As a guideline, the dating utility of a given
radioisotope can be approximated by 8-10 times its half-life.
humic acids: The base soluble, acid insoluble humic fraction of decomposed organic matter.
Humic acids include a range of recalcitrant high molecular mass biomolecules associated with
algal, bacterial, and terrestrial precursors.
humin: The humic fraction of decomposed organic matter that is insoluble in both acid and base.
hypolimnion: Lowest water column in thermally stratified lakes, where light penetration and
biological activity are minimal, and turbulence is reduced.
hypopycnal flow: A sediment-laden plume of water of lower density than the water body it
enters, resulting in widespread dispersal of suspended sediment across the basin. Most
common where glacial meltwater enters saline water bodies.
ICP-MS: Inductively-coupled plasma mass spectrometry.
inductively-coupled plasma mass spectrometry: Analytical technique for the detection and
quantification of multiple elements at trace concentrations by combining ionization with
mass spectrometry. Parts per million to parts per trillion concentrations are attainable. The
analytical process includes sample nebulization into an aerosol stream, ionization by an
argon plasma source, mass to charge ratio discrimination, and quantification.
ka: Kilo annum, 1000 years.
lattice charge defects: Loci of electron capture over geological time formed during mineral
crystallization or by exposure to natural radiation. Electrons accumulated over time in lattice
charge defects are the source of luminescence used in geochronology.
Libby half-life: The half-life of radiocarbon accepted for calculation of conventional radiocarbon
ages, given as 5568 years, and named in recognition of Willard F. Libby who pioneered
radiocarbon dating (1946-49). The known half-life of radiocarbon is ca. 5730 years.
MAAD: Multiple aliquot additive dose.
multiple aliquot additive dose: Method of determining sample equivalent dose in luminescence
dating, applied principally to fine-grained polymineral or quartz fractions such as those in
waterlain sediments. The method applies incremental additive doses (β or γ) to natural
luminescence in separate sample aliquots to construct a dose response curve that both
simulates future doses and can be extrapolated to an equivalent dose at the solar reset level.
Although MAAD was developed for TL dating, it can also be used with OSL.
OSL: Optically stimulated luminescence.
optically stimulated luminescence: The fraction of time-dependent luminescence accumulated
in silicate minerals that is liberated by exposure to light at specific wavelength ranges,
typically between 400 and 900 nm.
palynomorph: Broadly defined group of ornamented microfossils composed of sporopollenin
and related polymers, highly resistant to decay, and including pollen grains, spores,
dinoflagellate cysts, and acritarchs.
POC: Particulate organic carbon.
particulate organic carbon: Undecomposed organic matter in natural waters, including algal
cells, zooplankton, palynomorphs and fragments of detrital plant tissues (leaves, roots,
stems, seeds).
periglaciation: Cold climate geomorphic processes associated with the presence of permafrost.
photosynthate: Pigmented organic matter associated with photosynthesis, including
chlorophylls, carotenoids, and their degradation products.
proglacial lake: Lake that is hydrologically and sedimentologically influenced by the presence
of one or more glaciers within its catchment.
SAR: Single aliquot regeneration.
single aliquot regeneration: Method of determining sample equivalent dose in luminescence
dating, applicable to either fine or coarse fractions. In SAR, an age is determined for each
aliquot by matching a regenerated signal from the light reset level to the original natural
level.The method is particularly useful for young sediments (< 50 ka) and shows potential
for decadal resolution in sediments eolian younger than 1000 years.
single-grain OSL: The application of optically stimulated luminescence to date individual
mineral grains, typically sand-size quartz.
SCUBA: Self-contained underwater breathing apparatus.
TL: Thermoluminescence.
thermoluminescence: The fraction of time-dependent luminescence accumulated in silicate
minerals that is liberated by heating the sample.
turbidite: Graded sedimentary deposit associated with a discrete event of upslope sediment
destabilization. The base of turbidites are frequently erosional.
varve: Cycles of sedimentation that can be definitively attributed to annual periodicities, thus
enabling the development of annually-resolved sediment chronologies. Varves are most often
composed of recognizable summer and winter couplets.