How do we measure the earth’s temperature from the past? • Instruments record the past 140 years. • Historic records go back thousands of years. • Prehistoric climate data must be collected by something called proxies. Proxies can overlap instrument data and historic records to verify their accuracy.
What are Proxies? • 1. Tree rings • 2. Seafloor & lakebed sediments • 3. Ice cores • 4. Coral Reefs • 5. Packrats & Middens • 6. Speleothems from caves
Reading Tree Rings • A yearly tree ring consists of a light layer which grows in the spring and a dark layer formed in late summer. • Trees produce wide rings during wet, cool years and narrow rings during drought or severe winters. • The oldest living trees are 4,000 years but tree ring proxies go back 12,000 years.
Foraminifera Microorganisms • Some foraminifera respond to ocean temperature changes. • One group changes their shell coiling direction in response to temperature. • Studying the shells from foraminifera in the sea floor sediment give us an indicator of past climate.
Antarctica & Greenland • http://www.windows2universe.org/olpa/videos/videos_menu.html • Most of the ice core temperature data comes from either Antarctica or Greenland. • Antarctica Vostoc data goes back 425,000 yrs. • Greenland’s GISP data goes back 100,000 yrs.
Information in the Ice Core • The thickness of an ice core layer is like a tree ring telling us the precipitation that year. • Air pockets trap the gas in the air. • Beryllium-10 is linked to solar activity • *The ratio of O-16 to O-18 indicates global temperatures.
The O-18 Temperature Link • The ratio of concentrations of two isotopes of oxygen in the water molecules in ice serves as an indicator of global temperatures. Oxygen has two commonly occurring natural isotopes, the usual 16O and the less common 18O, which has two extra neutrons. Water molecules that contain 18O are heavier than usual, so they do not evaporate from the ocean as readily as the regular water molecules. When the temperature of the ocean is warmer, however, more of the heavier water molecules is able to evaporate. Thus, ice formed in glaciers during warmer times has a higher concentration of 18O than ice formed during cooler times.
February 2012 • After 20 years of drilling the Russian team reached lake Vostok. • The lake water has been isolated from the outside world for 15 to 20 million years.
Cave Records & Paleoclimate • Speleothem formations in caves are like ice core records in that they give a record of temperature and precipitation variations for the cave.
What are Middens? • Packrats, as their name implies, constantly collect all kinds of materials from their surroundings. Their collections, called "middens", provide clues to the past climates of the region. Packrat middens are clumps of vegetation, insects, remains of vertebrates, and other materials cemented together by crystallized packrat urine (referred to as amberat). These rock-hard deposits can be more than 20,000 years old.
Clues to past climate • Materials encased in middens are often remarkably well-preserved. Scientists are often able to sequence DNA from vegetation in middens, providing them with extraordinarily detailed insights to the evolution of plant communities, which in turn are good indicators of climatic conditions. Other astonishing artifacts have been discovered in middens. A midden from Utah contained a bone from a camel that, though once widespread in North America, had gone extinct more than 12,000 years ago.