..1 T-Mobile 00:25 100%- HW3 Paleoclimate.docX Background to the SPECMAP dataset
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..1 T-Mobile 00:25 100%- HW3 Paleoclimate.docX Background to the SPECMAP dataset We will be working with the SPECMAP dataset, which contains information about the volume of ice on land at various times in earth's history. These data are calculated from planktonic records collected from multiple sediment cores in the Atlantic Ocean. Background to the insolation dataset We will compare the SPECMAP dataset to insolation curves at 65°N latitude on the northern hemisphere summer solstice. Analytical Concepts In this homework, you will explore the relationship between the two above datasets. You will work with normalized versions of each dataset, and you will analyze correlations between the normalized variables as they change in time. Normalization A normalized dataset varies from roughly -1 to+ over time, and has no units. To calculate the normalized version of a specific dataset, one must use both the anomaly and the standard deviation. You are already familiar with anomaly: Anomaly-variable at a specific time-Reference quantity For the reference quantity, we have been using averages over a specific time interval (remember Homework 1, where the reference quantity was the average global temperature over 1951-1980). In this homework, we will use the average of each variable over the entire time series as our reference quantity Anomalies have units (e.g., °C, W/m, etc.) and often have specific and recognizable magnitudes (e.g., roughly 10-30°C for temperatures of the earth, roughly 200-500 W/m for radiation on earth). Normalized datasets do not have units, and their magnitudes vary from roughly -1 to . To generate a normalized dataset, we divide the anomaly by the standard deviation. The standard deviation is a statistical measure of how much a quantity varies. (In the above examples, the quantities vary by 20°C and by-300 W/m.) Normalized variable = Anomaly . Standard deviation In this homework, the time series of each variable will be provided to you in the spreadsheet. The time series of each normalized variable will also be calculated for you and provided Open With PrintExplanation / Answer
A1) The chemical compound is calcium carbonate or limestone (CaCO3) of planktonic foraminifera from which this 18O value is obtained .Limestone is deposited from the calcite shells of microorganisms. Calcite, or calcium carbonate, is formed from water, H2O, and carbon dioxide, CO2, dissolved in the water. The carbon dioxide provides two of the oxygen atoms in the calcite. The calcium must rob the third from the water. The isotope ratio in the calcite is therefore the same as the ratio in the water from which the microorganisms of a given layer extracted the material of the shell. simce the istope ratio of (CaCO3) is same as the water from which its componets has been extracted .
Hence the 18O value of calcium carbonate from which the shells of planktonic foraminifera are formed reflect the isotopic compositon of ocean water and its variation can be intrepreted by analysing different factors on which fractionation of oxygen isotope depends.
A2) During Evaporation lighter oxygen isotope which is 16O is incorporated in vapor whereas heavier one is incorporated in the liquid ( since 18O is more stable and prefers more stable phase and liquid is relatively more stable than vapor phase), hence ocean water gets richer in18O isotope wheraas vapor depleted in 16O and these vapor contributes the isotopic composition of ice sheets during precipiation.
Glacial ice is therefore made up primarily of water with the light 16O isotope. This leaves the oceans enriched in the heavier 18O, or “more positive. That means that ocean water will have higher percentage of water molecules rich in heavier 18O isotope than the Laurentide ice sheets.
A3) From the above answer we know , Glacial ice is therefore made up primarily of water with the light 16O isotope. This leaves the oceans enriched in the heavier 18O. During ice ages, cooler temperatures extend toward the equator, so the water vapor containing heavy oxygen rains out of the atmosphere at even lower latitudes than it does under milder conditions.
Hence during glacial periods, more 16O is trapped in glacial ice and the oceans become even more enriched in 18O.
Conversely as temperatures rise, ice sheets melt, and freshwater runs into the ocean.So, interglacial periods, 16O melts out of ice and the oceans become less 18O rich, or “more negative” in 18O.
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