Handout flashcards
(30 cards)
What are biomarkers in geochemistry?
biomarkers are molecular fossils derived from the lipids of once-living organisms, preserved in sediments and petroleum
what are the characteristics of terrestrial biomarkers
derived from land plants; common examples include long-chain n-alkanes, lignin phenols and resin acids
what are the characteristics of marine biomarkers?
derived from algae and marine organisms; examples include steranes, hopanes and specific alkenones.
what compound indicates higher plant input in sediments?
long-chain n-alkanes (e.g. C27-C33) with a strong off over even C number preference
what is a common marine biomarker used to estimate past sea surface temperatures?
Alkenones, particularly unsaturates ketones produced by haptophyte algae
what does the pristane/phytane ratio indicate in sediments?
it reflects redox conditions during deposition
high ratio = oxic conditions
low ratio = anoxic
what are biomarkers used for in paleoenvironmental studies
biomarkers are molecular fossils that preserve environmental signals, including temperature, salinity and biological productivity
what is the UK’37 index used to estimate
past seas surface temperatures (SSTs) based on the degree of unsaturation in alkenones
which organisms produce alkenones used in UK’37 SST reconstruction
alkenones are primarily produced by haptophyte algae
how does the number of double bonds in alkenones relate to temp
more double bonds are associated with colder temps
what is the TEX86 index based on
the distribution of glycerol diakyl glycerol tetraethers (GDGTs) from marine Thaumarchaeota
what environmentals are suitable for TEX86 reconstructions
open marine settings with stable water column conditions are ideal for reliable TEX86 based temp reconstructions
what are some limitations of TEX86 as a temperature proxy
TEX86 can be influenced by non-thermal factors like archaeal community changes, depth habitat shifts and lateral transport
what is the MBT/CBT index used for?
to reconstruct terrestrial temperature and soil pH based on branched GDGTs in soil
what does MBT stand for and what does it represent
Methylation of Branched Tetraethers
reflects the degree of methylation in branched GHGTs correlating with temp
what does CBT stand for and measure
Cyclisation of branched tetraethers
influenced primarily by soil pH
why is calibration important in biomarker-based temperature reconstructions
calibration links biomarker indices to instrumental temp data, allowing quantitative paleotemperature estimates
what factor can affect the reliability of biomarker proxies in sediments
degradation
lateral transport
sediment mixing
non-climatic controls on biomarker production
what does a low dinosterol Vs sitosterol ratio indicate
a relatively high terrestrial input or origin of the organic matter present
what does a high composterol Vs campostanol ratio indicate?
a higher level of molecular functionality and thus better preservation or freshness of OM
what is UCM and what does it indicate
Unresolved complex mixture
the presence / influx of mature OM
what does a large delta 13C shift in higher plant HMW n-alkanes around the PETM show?
reflects a massive release of 13C depleted methane that impacted global CO2 levels and was recorded in plant-derived biomass
what does a shift in Paq from 0.6 to 0.3 indicate
a decrease in Sphagnum type material, suggesting drier conditions
what does a similar shift in Pwax to lower values indicate
increased presence of sphagnum type material - suggests wetter conditions
