Penn State, ABIOL 574

Excerpt: ... Lecture 16 Oxygen isotope s/Keplers laws Abiol 574 How do we know how warm it was millions of years ago? Ice cores: bubbles contain samples of the atmosphere that existed when the ice formed. (ancient pCO2) Marine isotopes: oxygen isotope s in carbonate sediments from the deep ocean preserve a record of temperature. The records indicate that glaciations advanced and retreated and that they did so frequently and in regular cycles. Oxygen isotope s and paleoclimate Oxygen has three stable isotopes: 16O, 17O, and only care about 16O and 18O.) 18O 18O. (We is heavier than 16O. The amount of 18O compared to 16O is expressed using delta notation: 18O = 18O/16O of sample -18O/16O of standard 1000 18O/16O of standard Fractionation: Natural processes tend to preferentially take up the lighter isotope, and preferentially leave behind the heavier isotope. Oxygen isotope s and paleoclimate Oxygen isotope s are fractionated during evaporation and precipitation of H2O H ...

Penn State, GEOSC 5

Excerpt: ... 5.3.2 -15.3.2 Conversion Between Oxygen Isotope Reference Scales Print this Section Save Zoom When isotope fractionation occurs in the sample preparation procedure, the conversion of the measured isotopic compositions to a reporting scale needs to take this into account. As an example we consider the case of oxygen isotopic composition measurements, where several fractionation factors can be involved. To report oxygen isotope s one has used frequently the PDB, VPDB, SMOW and VSMOW scales. For geochemical discussions all results need to be referred to one scale and thus conversions may be necessary. The need to convert between oxygen isotopic composition scales arises, for example, when one would like to compare results from different researchers, or one wishes to use one measurement reference gas for the analyses of waters, silicates, and carbonates. When only water isotopic compositions are investigated, the analyst might choose a water sample as measuring reference and calibrate it directly using VSMOW. The ...

Colorado, GEOL 1020

Excerpt: ... Homework #4, Geol 1020, Spring 2008 1. Which of the following is NOT geologic evidence for glaciation and/or climate change in the Pleistocene? A. oxygen isotope s in marine shells B. unsorted and unlayerd conglomerates (tills) C. pollen in lake sediments D. abundance of gasses in ice cores E. all of the above are evidence for glaciation and/or climate change solar 2. Fill in the blank with one word - The earth's climate is an engine driven by _ energy. 3. Why does the oxygen isotopic ratio of seawater change in a glacial period relative to a non-glacial period? A. the 16O isotope of oxygen selectively concentrates in the oceans when glacial ice sheets are growing B. the 18O isotope of oxygen selectively concentrates in the oceans when glacial ice sheets are growing C. the 18O isotope of oxygen selectively concentrates in ice when glacial ice sheets are growing C. the 18O isotope of oxygen selectively concentrates in ice when glacial ice sheets are melting 4. When geologists work with the is ...

University of Hawaii - Hilo, FEB 08

Excerpt: ... Compositional Balancing Before Moon Formation A striking feature of the Earth and Moon is that they have identical oxygen isotopic compositions, in spite of considerable variation throughout the solar system. PSRD presents www.psrd.hawaii.edu/Feb08/EarthMoonFormation.html Compositional Balancing Before Moon Formation Painting by James Garry Planet formation involved substantial mixing throughout inner solar system as planetary embryos accreted. Considering the variability in Oisotopes throughout the solar system, why do Earth and Moon have the same oxygen isotopic composition? PSRD presents Planetary embryo accretion simulation by John Chambers. Note how much mixing there is as accretion proceeds. www.psrd.hawaii.edu/Feb08/EarthMoonFormation.html Compositional Balancing Before Moon Formation Oxygen isotope s might have equilibrated between Earth and Moon via the hot silicate atmosphere surrounding the proto-Earth and proto-lunar disk. PSRD presents www.psrd.hawaii.edu/Feb08/EarthMoonFormation.html ...

Penn State, GEOSC 4

Excerpt: ... 4.5-14.5 Preparation of Samples for Oxygen Isotopic Analysis Print this Section Save Zoom Oxygen is surpassed only by iron in its abundance in the Earth and constitutes close to 29 % of its total weight. In the Earth's crust it is by far the most ab ...

Oregon State, OC 560

Excerpt: ... Jed Roberts Article Review 5/14/2009 Lamy, F., Kaisser, J., Ninnemann, U., Hebbeln, D., Arz, H. W., and Stoner, J. 2004. Antarctic Timing of Surface Water Changes off Chile and Patagonian Ice Sheet Response. Science. 304: 1959-62. Summary Lamy et al. explore complex paleo-climatic relationships between various proxies during the most recent glacial period and subsequent deglaciation (8 to 50 thousand years before present). The authors introduce a new paleo-climate record of alkenone-based sea surface temperature (SST) derived from sediment cores drilled off the southern coast of Chile (Ocean Drilling Program Site 1233). This SST record is then compared against five other principle paleo-climate records from around the world: (1) diatom-based sea ice reconstruction from the South Atlantic, (2) Mg/Ca SST record from the Southwest Pacific, (3) oxygen isotope record reflecting SST, derived from Globigerina bulloides in the South Atlantic, (4) oxygen isotope record derived from ice cores in Antarctica, and (5) ...

Penn State, GEOSC 4

Excerpt: ... However, since that time the determination of the oxygen isotopic composition of phosphates has become of interest in other respects. For example, Longinelli and Nuti (1968) argued, on the basis of the oxygen isotopic composition of marine phosphorites, that the oxygen isotopic composition of the ocean water changed during geologic time, alternatively, changes in the ocean temperature could be proposed to explain the firmly established *18Ophosphate - time trend (e.g., Shemesh et al. 1983, 1988, Karhu and Epstein 1986). While the isotope exchange between phosphates and water is slow, even on a geologic time scale, in enzyme-catalyzed reactions the exchange between water and the phosphate ion takes place in minutes. Hence one may suppose that in biogenically formed phosphates (bones, teeth) the oxygen isotope record reflects that of the fluid present in their formation (blood), whose *18O, in turn, is governed by that of the environmental water. Because the resistance of phosphates to isotopic exchange after ...

University of Texas, GEO 302C

Excerpt: ... GEO302C 03/31/08 Lecture 28: Millennial Changes: Delta 18O in Ice Sheets Homework Definitions Dates Important People 1. Climate change at different time scales a. Tectonic: longest scale- hundreds of millions of years b. Orbital: tens to hundreds of thousands of years- cycles c. Millennial: thousands of years- oscillations 2. Oscillations recorded in Greenland Ice Cores a. Delta18O and dust help to date ice b. Early studies in 1970 c. Lots of dust mean climate was windier and more polluted d. Underlying trend of graduate glacial- interglacial changes 3. Millennial Oscillations a. Younger Dryas- during the last deglaciation i. 1500 yrs long ii. Abrupt beginnings and endings (about 10 yrs) b. Millennial Oscillations during glacial period vs. interglacial i. Very wide spacing and amplitude ii. Average spacing: 1500 yrs iii. Called Dansgaard-Oeschger cycles 4. Oxygen isotope ratios in Ice and Ocean Cores a. Ocean Cores i. D18O signals 2 influences: Temp. Change and Ice volume b. Ice cores i. D18O signals refl ...

Pittsburgh, GEO 0060

Excerpt: ... eir sources. Handout/overhead: Fig. 30 (Flint, 1947) 3. Handout/overhead: Glacial maps of North America (Fig. 470, Chamberlin and Salisbury, 1907) and the World (Fig. 1.12, Wilson e t a l ., 2000). 4. 1 4 C dating indicates maximum extent of most recent glaciation (Last Glacial Maximum (LGM) = ~18,000 years. (Pieces of wood and other organic matter buried in sediment can be dated this way.) -Examination of patterns of end moraines and buried soil horizons on land suggests 4 or at most 5 major glaciations. - 1 4 C method becomes difficult for samples older than about 30,000 years and impossible for samples older than 75,000 years. Using 14C dating alone, all we can say is that older glacial maxima are more than 75,000 years old. B. Oxygen isotope s: A key to paleoclimate research 1. Background. a. Element: atoms that share identical chemical properties. This is a function of the number of electrons in the electron orbitals, which in turn is a direct function of the number of protons in the nucleus. Number of p ...

Penn State, GEOSC 4

Excerpt: ... 4.5.2-14.5.2 Carbonates Print this Section Save Zoom Carbonates are an important part of the sedimentary record of the Earth's history, and their oxygen isotopic composition has attracted interest, since it can bear information about the geologic co ...

Caltech, GE 112

Excerpt: ... Lecture 18 Sea-level record of the past m illion years This record of d18O is fromplanktonic foram froma core in the subs tropical Atlantic ocean. It is a record of tem perature and ice volum for the past 130,000 years or e so. A longer record froma core in the Equatorial Pacific ocean. These are divided into tim e-rock (chronostratigraphic) units, the Marine Oxygen Isotope stages A tabulation of the Marine Oxygen Isotope ages The cyclic filling and draw ing dow of the w oceans n orld has a profound effect on processes and history along coastlines. Let's revisit the littoral clastic record, and then w turn to e'll the record of fringing coral reefs An exam fromHalf Moon Bay, central California ple Mahia peninsula, North Island, NewZealand Pasadena Palos Verdes peninsula Fringing reef terraces Ages by alpha-particle counting, ~ 1968, at Colum University bia Ages by therm ionization al m spectrom ass etry, ~ 1988, here at Caltech ...