Proxies 2 Flashcards
What does a more negative value of 18O Benthic forams indicate?
Less ice and/or warmer DEEP water
What does a more positive value of 18O Benthic forams indicate?
More ice and/or colder DEEP water
What isotope is measured when investigating the forams for sea level and water temperature variables and what part of the chemical composition of the foram?
Delta (change) 18O in the calcite carbonate CaCO3, here the oxygen in the forams chemical composition is measured.
What isotope is measured when investigating the forams for carbon cycling/levels and what part of the chemical composition of the foram?
Delta (change) 13C in CaCO3, where the carbon in the composition is measured.
What variables are investigated when measuring 13C?
The carbon isotopic ratios of 13C and 12C of marine calcite and organic matter give an insight into the climate system of local and global carbon cycling.
What isotope of carbon is most abundant and at what percentage?
12C with 98.9%
What isotopes of carbon is stable and unstable?
Stable: 12C and 13C. Unstable: 14C.
What is the fundamental principle for carbon? (favouritism) And this makes organic matter rich in??
12C is favoured during photosynthesis, therefore the organic matter is rich in 12C.
What part of the foram is organic and what part is inorganic?
The SHELL in the forams is inorganic since it uses the carbon (inorganic) dissolved in water (CO2 from the atmosphere) to make up its shell. But the forams BODY is made up of organic carbon. (LOOK AT THE SLIDE)
What do more positive 13C forams indicate?
More marine organic carbon burial. Photosynthesizing organisms, such as algae and plankton, preferentially uptake C12 during photosynthesis, which leaves more C13 in the water column with which marine organisms build their shells.
What do more negative 13C forams indicate?
Less marine organic carbon burial. Have a think about the difference between organic and inorganic carbon and how it relates to plant uptake and therefore marine burial…
What does the 13C in foram calcite reflect?
13C is the carbon (dissolved CO2) content dissolved in seawater from the atmosphere.
What variability explains the changes of BENTHIC 13C on long time scales in the oceans?
It can be explained by the amount of carbon 12C burial or release. Which is 1 out of 3 factors.
What should be considered when comparing 13C between different ocean basins? As factor 2 for changes in benthic 13C on long time scales.
Consider the process of deep water ageing, they have different pathways when it comes to deep overturning ocean circulation.
For shorter time scales (give years) what factors can be considered when looking at 13C in benthic forams?
1,000-10,000 years (during Ice ages) consider variability in ocean CO2 storage…
Name the four ocean circulation proxies and briefly what they are?
Benthic foram 13C (stable isotope), radiocarbon 14C giving the water mass age (50-60 000 years only = last 7 glacial cycles), measuring Neodymium (metalloid element) isotopes in ichthyolites (fish teeth), contourites being drift sediments.
Name the five atmospheric carbon dioxide proxies and briefly describe what they are?
Marine algal (alkenone) 13C, non-marine are first paleosol carbonate 13C and leaf stomatal (CO2 concentrations) proxy.
Explain the process of fractionation and formation of Alkanenoes…
Alkenones (produced by coccolithophores), during photosynthesis and the formation of Alkenones the carbon isotopes (13C/12C) in the CO2 that are dissolved in seawater, are fractionated. The fractionation is lower at times with relatively low CO2 (less carbon dissolved in water, therefore less fractionation?) The fractionation signal is locked into the alkenones cell and preserved for ma years.
What is the Boron isotope linked to?
Boron isotopes in planktonic foraminifera is a pH to CO2 proxy…
What are some proxies for ocean paleoproductivity and carbon cycling?
The marine vertical carbon pump (difference in 13C between planktic and benthic forams, CCD (calcite compensation depth) variability
What are some limitations and uncertainties associated with ALL these proxy methods?
The distribution of different types of marine sediments and the availability of signal carrying materials, preservation quality, plankton depth and seasonality (how deep in the water column were the plankton originally living? To understand SST proxies, sea surface temperatures)
What’s the most convincing proxy?
Multi-proxy approach.
