The Proxy Observation Ontology
Assemblage
Chemical
Composition
Diffraction
Fluorescence
Atoms can be simply described as consisting of protons, electrons, and neutrons. Isotopes of the same element differ by the number of neutrons in the nucleus, resulting in different mass.
Isotope
Major element
Paleoceanographers use the term biomarker to describe organic molecules found in marine sediments, initially produced by a variety of organisms either on land or in the marine environment [1]. A key characteristic of biomarkers is their ability to survive deposition in the archive in terms of their original structure and steroidal configuration (i.e., spatial distribution of the atoms) [1]. Their usefulness for paleoceanographic reconstructions largely depends on their degradation within the archive [1]. ? 1.0 1.1 1.2 Rosell-Melé, A., & McClymont, E. L. (2007). Biomarkers as Paleoceanographic proxies. Developments in Marine Geology, 1, 441-490. doi:10.1016/S1572-5480(07)01016-0
Organic index
Physical observation
Proxy observation
Radioisotope
Reflectance
Spectral observation
Carbon in nature exists in oxidized (i.e., CO2 and carbonates), elemental (i.e., graphite and diamond), and reduced (i.e., methane and organic matter]) forms. Carbon has two stable isotopes: the light isotope 12C (abundance: 98.9%, mass: 12.000000 amu) and the heavy isotope 13C (abundance: 1.1%, mass: 13.003355 amu). Since the mass of 13C is higher than the mass of 12C, the carbon isotopes are fractionated by chemical and biological processes. In general, 12C is strongly partitioned into organic matter (reduced form) while the heavy isotope is concentrated in the oxidized forms of carbon.
Stable Carbon isotope
Stable Hydrogen isotope
Stable isotope
Stable Nitrogen isotope
Stable Oxygen isotope
Stable sulfur isotope
Trace element
Ar-Ar
Clay fraction
Color
Density
Diffuse spectral reflectance
Faunal
Floral
Grain size
Historic
Layer thickness
Lead Isotope
Lithics
Luminescence
Magnetic susceptibility
Mineral matter
Moisture Content
Neodymium
Organic matter
Permeability
Porosity
Radiocarbon
Resistivity
Sand fraction
Silt fraction
The use of TEX86 (TetraEther indeX of 86 carbons) as a tool to reconstruct past sea surface temperature variability is based on the relative cyclization of isoprenoidal glycerol dialkyl glycerol tetra ethers (GDGTs) produced by marine archaea. TEX86 is defined as [1]: TEX_{86}=\frac{GDGT-2+GDGT-3+Cren'}{GDGT-1+GDGT-2+GDGT-3+Cren'} where GDGTs 1-3 indicate compounds containing 1-3 cyclopentyl moieties, respectively, and Cren' denotes the regioisomer of crenarchaeol, a diagnostic biomarker for the Thaumarchaeota, the primary producers of GDGTs in the marine realm. By definition, values of the TEX86 index are comprised between 0 and 1. Experimental evidence suggests that archaea produce GDGTs with more rings warmer waters, a response observed in cultures of hyperthermophile archaea [2] [3] and mesocosm experiments with natural seawater containing heterogenous archaeal population [4] [5]. References [1] Schouten, S., Hopmans, E. C., Schefuß, E., & Sinninghe Damsté, J. S. (2002). Distributional variations in marine crenarchaeotal membrane lipids: a new organic proxy for reconstructing ancient sea water temperatures? . Earth and Planetary Science Letters, 204, 265-274. [2] de Rosa, M., Esposito, E., Gambacorta, A., Nicolaus, B., & Bu'Lock, J. (1980). Effects of temperature on ether lipid composition of Caldariella acidophilia. Phytochemistry, 19, 827-831. [3] Uda, I., Sugai, A., Itoh, Y., & Itoh, T. (2001). Variation in molecular species of polar liipds from Thermoplasma acidophilum depends on growth temperature. Lipids, 36, 103-105. [4] Wuchter, C., Schouten, S., Coolen, M. J. L., & Sinninghe Damsté, J. S. (2004). Temperature-dependent variation in the distribution of tetraether membrane lipids of marine Crenarchaeota: implications for TEX86 paleothermometry. Paleoceanography, 19, PA4028. doi:10.1029/2004PA001041 [5]Schouten, S., Forster, A., Panato, E., & Sinninghe Damsté, J. S. (2007). Towards the calibration of the TEX86 paleothermometer on ancient greenhouse worlds. Organic Geochemistry. doi:10.1016/j.orggeochem.2007.05.014
TEX86
U-Th
The C37 alkenone unsaturation index ( U_{37}^{k'} ) is a firmly established tool for past sea surface temperatures reconstruction and is based on the relative abundance of di- (C37:2) and tri- (C37:3) unsaturated ketones with 37 carbon atoms. The index varies between 0 and 1, thus it may saturate in the temperature extremes as it becomes more challenging to determine since C37:3 and C37:2 alkenones approach their detection limits. Since alkenones come exclusively from a few species of haptophyte algae which require sunlight, alkenone thermometry offers the advantage of direct estimate of near-surface ocean temperatures. The ubiquitous presence of alkenone-synthesizing organisms (most commonly the coccolithophorids Emiliania huxleyi and Gephyrocapsa oceanic through the world's ocean and the rapidity and high-precision of the alkenone analyses had made U_{37}^{k'} a valuable proxy for paleoceanographic reconstructions. However, the U_{37}^{k'} proxy is subject to non-temperature effects, such as lateral transport through oceanic currents (Ohkouchi et al. (2002)) and preferential post-depositional oxidation of C37:3 compared to C37:2 [1] [2]. Furthermore, changes in the seasonality of the proxy (i.e., which part of the seasonal cycle the proxy is recording) may bias the inferred temperatures toward winter or summer conditions [3]. Finally in oceanic regions where the photic zone extends below the surface mixed layer, the sedimentary signal may not strictly represent sea surface temperatures but rather a composite temperature of the mixed layer and the thermocline [4][5]. References [1] Hoefs, M. J. L., Versteegh, G. J. M., Rijpstra, W. I. C., de Leeuw, J. W., & Damsté, J. S. S. (1998). Postdepositional oxic degradation of alkenones: Implications for the measurement of palaeo sea surface temperatures. Paleoceanography, 13(1), 42-49. doi:10.1029/97pa02893 [2] Ohkouchi, N., Eglinton, T. I., Keigwin, L. D., & Hayes, J. M. (2002). Spatial and temporal offsets between proxy records in a sediment drift. Science, 298(5596), 1224-1227. doi:10.1126/science.1075287 [3] Herfort, L., Schouten, S., Boon, J. P., & Sinninghe Damsté, J. S. (2006). Application of the TEX86 temperature proxy in the southern North Sea. Organic Geochemistry, 37, 1715-1726. [4] Müller, P. J., Kirst, G., Ruhland, G., von Storch, I., & Rosell-Melé, A. (1998). Calibration of the alkenone paleotemperature index U_{37}^{k'} based on core-tops from the eastern South Atlantic and the global ocean (60°N-60°S). Geochimica et cosmochimica acta, 62, 1757-1772. [5] Prahl, F. G., Mix, A. C., & Sparrow, M. A. (2006). Alkenone paleothermometry: biological lessons from amrine sediment records off Western South America. Geochimica and Cosmochimica Acta, 70, 101-117.
Uk37
The currently accepted U37kprime (Prahl and Wakeman, 1987) varies positively with temperature, and is defines as C(37:2)/(C(37:2)+C(37:3), where C(37:2) represents the quantity of the di-unsaturated ketone and C(37:3) the quantity of the tri-unsaturated form. Herbet, T.D., 2003, Alkenone paleotemperature determinations in Treatise on Geochemistry, Volume 6, pp 391-432
Uk 37'
X-Ray diffraction
X-ray fluorescence
d13C
d15N
Oxygen has three naturally-occuring stable isotopes: 16O, 17O, 18O, with 16O being the most abundant (99.762%). Two international reference standards are used to report variations in oxygen isotope standards: PDB and SMOW. The use of the PDB standard in reporting oxygen isotope composition is restricted to carbonates of low-temperature origins (e.g., oceanic, lacustrine ). The conversion between SMOW and PDB scales is given by: \delta^{18}O_{SMOW} = 1.03091 (\delta^{18}O_{PDB}) +30.91 δ18O may be measured on the shells of foraminifera
d34S
Al/Ca
B/Ca
Ba/Ca
Fe/Ca
Li/Ca
Mg/Ca
Mn/Ca
Sr/Ca
Zn/Ca