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i truely wonder how anyone would measure or even guess the water temperatures are various depths 55 million years ago, though.
Average global temperatures increased by ~6 °C in the space of 20,000 years. This is based on Mg/Ca and δ18O values of forams. δ18O is a more useful proxy for palæotemperature during the Eocene, as the lack of ice makes it safe to assume that the oceans' δ18O signature is constant. Due to the positive feedback effect of melting ice reducing albedo, temperature increases would have been greatest at the poles, which reached an average annual temperature of 10-20 °C; the surface waters of the northernmost Arctic ocean warmed, seasonally at least, enough to support tropical lifeforms requiring surface temperatures of over 22°C.
Originally posted by TheRedneck
reply to post by Shere Khaan
Hmmm, all I did was mention that evaporation increases with temperature (much more so than thermal expansion, btw) and made mention of the methods being used to extrapolate temperature estimates from pre-historic times using ice core samples. Exactly which of those was incorrect?
Until you explain the errors behind my posts, I will assume the error was that I disagreed with you.
Foraminifera shells of calcium carbonate (CaCO3), having oxygen in them, and being found in many common geological features, are most commonly used to do tests on. The ratio of 18O to 16O is used to tell the temperature of the surrounding water of the time solidified, indirectly. The ratio varies slightly depending on the temperature of the surrounding water, as well as other factors such as the water's salinity, and the volume of water locked up in ice sheets.
δ18O also reflects local evaporation and freshwater input, as rainwater is 16O enriched - a result of 16O's preferential evaporation from seawater. Consequently, the surface ocean contains greater amounts of 18O around the subtropics and tropics where there is more evaporation, and lesser amounts of 18O in the mid-latitudes where it rains more.