Unit 9

The more unbalanced O18 and O16 are, the ______ the climate

Colder

Isotopes involved in paleoclimate reconstruction

016 vs 018, C14

Information available from speleotherms

1. Growth intervals: dating layers by measuring uranium and thorium (greater growth rates) or dry climate (periods of drought exhibit little to no growth) 2. Oxygen isotope analysis: variations in cave temperature, ocean temp, and property of rainfall (ie. evaporation from land or ocean surface) 3. Carbon (C13:C14 isotope ratio: changes in overlaying vegetation and vegetation density

Cross-dating

Comparing living trees to dead trees, or prehistoric trees or even timber used in primitive structures. careful matching of tree growth ring records from living trees with those from timbers in prehistoric dwellings, detailed tree ring chronologies are extended back in time thousands of years.

How do we extract ocean sediment information?

1. Marine organisms build their shells using calcium carbonate dissolved in sea water storing oxygen isotope information in their shells 2. when the organisms die, they settle on the ocean floor and overtime, build up a layering of information about global ocean sea surface temperatures 3. variations in oxygen isotope ratio document changes in the planet's glacial ice volume, a measure of past changes in temperature

How do ice cores work?

1. a glacier develops where a climate is such that a snowfall exceeds snowmelt over a succession of many years 2. accumulating snow compacts under its own weight and gradually transforms into solid ice 3. Antarctic ice caps are up to two miles thick 4.During compaction, air within original snow is trapped as bubbles 5. chemicals in original snowflakes are preserved (oxygen isotopes, aerosols, dust) *provide the only direct measurement of gas concentrations from the ancient atmosphere dating back to 800,00 yrs

Evidence for snowball earth

1. glacial rocks from the same geologic periods were deposited across the planter, including across paleo-equator 2. study of geomagnetism shows these deposits on the pale-equator existed for hundreds of thousands of years, possibly up to millions of years 3. iron formations from marine strata suggest an anoxic (oxygen free) enviroment, consistent with an ice covered ocean

Limitations of paleoclimate reconstructions from speleotherms

1. limited understanding of true sensitivity of isotopes with climate fluctuations 2. little long term cave monitoring that overlaps the instrument record

How does earth recover from ice earth?

1. plate tectonics 2. geothermal vents 3. these two things help create more greenhouse effect and it is solved within 2000 years

The three periods the earth was primarily covered in ice

2.2 bya, 710 bya, 640 mya. Earth would have to be -50 degrees celcius

Proxy Climate Records

Climate info prior to instrument era. Developed from climate sensitive sources (bedrock, sea/lake sediment, glacial ice cores, fossil pollen, coral, cave sediments, tree rings, historical documents)

Oxygen isotope analysis of ocean sediments

Because evaporation of oxygen isotopes is easier for )16, a global average temperature can be inferred by studying the ratio of these isotopes

Isotopes

Consist of atoms that are chemically identical, with same # of protons but diff # of neutrons in the nucleus. Can be either stable or unstable (decay to lower isotopes over time)

Silicate weather

Draws CO2 out of the atmosphere

2/3 how a tree grows

During the summer, wood cells have thicker walls that gives the wood a darker appearance

strengths of paleoclimate reconstructions from speleotherms

High temporal resolution with information dating back to 10,000 yrs ago with some specific locations such as the shanboa cave in china providing info 240,000 yrs ago

Paleosols

Layer of ancient soil, buried under other recent soil or sediment, thta can provide clues to past climate conditions. Layer upon layer of sediments provide chronological record of this deposition and may conserve elements from past conditions within layers

It takes____ time to evaporate O16 than O18

Less time, creating more O18 in the atmosphere

016 vs 018

Most common tool in paleoclimatology because of oxygen's association with the water cycle and the biosphere

Ice Cores

Nowhere on earth is there such an extensive and voluminous record of past climates as in the polar ice sheets. They provide the only direct measurements of gas concentrations fro the ancient atmosphere dating back to 800,000 years

Isotope Analysis

One of the most common ways to extract information about past climates is by looking at changes to various elements isotope ratio

Not much about the climate is known prior to the______

Phanerozoic (540 mya-present) when the makeup of the atmosphere was greatly different

Dendroclimatology

The study of past climates using information gathered from the growth of tree rings. Provide yearly and seasonal info about temp and precipitation, cloud cover, and wild fires. Trees must be exposed to a seasonal climate to provide this info.

C14

Used to date samples of climate proxies

Lake Sediments

Work in a similar fashion as ocean sediments but with several key differences. - can infer the amount of productivity of the surrounding biosphere

speleothem

a calacite or aragonite (CaCO3=calcium carbonate) deposit in a limestone cave or cavern that can yield high-resolution records of past climate states (stalactites/stalagmites)

Varve

a thin layer, or lamina, of sediment deposited annually in a body of still water, usually a lake fed by a stream

1/3 how a tree grows

beginning of growing season, plant tissue directly underneath the bath produces large thin-walled wood cells, which has a light appearance

Plate tectonics

complicates climate reconstruction because site locations change and the subduction of zones of ocean basins recycle sediment records at most every 200 million years

Corals

constructed by organisms that secrete CaCO3 (calcium carbonate) featuring growth rings that can offer extremely high-resolution information that in some cases can be dated at weekly scales

How are speleotherms formed?

forms when calcite precipitates from groundwater that seeped into a cave, and can either build downward from the roof of the cave creating a stalactite, or grow upward from the floor of the cave to form a stalagmite.

Wet periods=________ growth rate for speleotherms

greater

corals

just like marine organisms relying on calcium carbonate to create their shells store information about climate through isotopes, they do too. Many have growth rings. Their records are only really from the past 400 years but they can get weekly or monthly records. records of el nino/nina events.

drought= ______ growth for speleotherms

little to no

What caused ice earth?

maybe 1- a big enough reduction in earths greenhouse effect could trigger an ice-albedo positive feedback maybe 2- the first snowball earth coincides w the great oxygenation, which saw a substantial increase in free oxygen in the atmosphere. free oxygen breaks apart methane into CO2 which drastically reduces the greenhouse effect maybe 3- second 2 snowball events caused by silicate weather

Geologic Strata

provides the logest paleoclimate reconstruction evidence out of all proxies but with coarse temporal resolution. Bedrock, particularly sedimentary strata, is a widespread source of generalized information on past climates

Paleoclimatology

reconstruction of past climates.

Paleoclimate

study of earth's climate before direct observations were available

Geomorphology

study of landforms on earth's surface and the processes responsible for their formation. climate can play a role in these processes so generalized info can be inferred from landforms about past climates

palynology

the study of strewn particles, including dust and other microscopic objects like spores. Type of vegetation that grows in a location is sensitive to climate. Pollen build up. q1`

3/3 how a tree grows

tree growth ceases during the cold season