Quiz #4
Beetles as a proxy!
- 150000 inspect species in North America -Beetles are the best preserved -30000 species of Coleoptera - Wash and sieve a peat core to concentrate beetle parts, and have to identify the beetle from its parts - Advantage: they are preserved well and they move into a region quicker than vegetation -Different beetles have different temperature ranges where you can find them
North American Ice Sheet Retreat
- 20000 years ago was max extent of ice - Laurentide ice sheet, extended up into Canadian arctic -was as thick as the Rockies are tall -Innuitian Ice sheet, Cordilleran ice sheet, Mountain ice caps - In Laurentide, there was a dome in the center and streams flowed outward from the glacier in al direction, stones dropping into find sedimentation as ice sheet is retreating
Fourier Spectrum of squigglyO18 data
- 3 periods - Shows oxygen isotope data summarized - 100,000 year period is dominant
Ocean Cores
- 9 billion tons of sediment accumulate on ocean floor each year (oceanic ooze) - Rate is very slow (50 cm/1000 yrs to <1cm/1000 yrs - Composed of biologic and terrigenous material ---plankton skeletons
Africa and Australia
- Africa and Australia were pretty dry during the last ice age, 18 KBP - Lake levels at 6 KBP, Africa was full of lakes - Modern lake levels : a lot more dry
Ice Core Locations
- Antarctic (Vostok) -Greenland Ice Cores - see slides 2 and 3 in Ppt 10
Glacial Erosion
- At Yosemite and Central Park there are striations in rock -Striations due to moving ice (glaciation), flowing by and scratching bedrock - Erets in Alaska/Yukan area are pointy mountain like formations
Model with only 20,000 yr insolation period
- Because it takes a long time for ice sheet to grow, it actually matches up with the 100,000 period - Ice sheet cross- section: the hotter it gets, the more ice melts, which makes it warmer (less albedo)
Problems with Dating Ocean Cores
- Bioturbation (mixes core-top samples) - Plankton takes 2000-4000 years to drift to ocean floor - Modern SST (sea surface temp) not really well known especially where temp. and salinity gradients are high - thin-walled forms dissolve more easily, so preserved assemblages not exactly all original assemblages
Beetle Results forTwo Creeks Forest Bed
- Buried spruce trees -Climate like southern Boreal Forest - July avg. temp was 15 C Present July temp is 21 C - Dry environment (no aquatic beetles) -Mosses present, but no open water -Spruce forest not dense with dry gravelly sands on local highs
Volcanic Eruptions on Climate Change
- Can cause cold weather in subsequent years -ash goes up to troposphere and then spreads out and falls into the stratosphere all over
A sample of possible ages for 220 yr C14 age
- Can mean between 150-210 yrs, 280-320 yrs, or 410-420 yrs - due to variation - but getting something to + or - 75 years is pretty good
Changes in Atmospheric Concentration of C14
- Cosmic ray production (sunspots, interstellar sources change) (increased sunspots --> decreased C14 - Geomagnetic field of earth changes reducing (increasing) cosmic ray shielding (decrease of geomagnetic field can cause increases in C14 - Nuclear testing (since 1945 AD) - CO2 in atmosphere from volcanoes varies - Fossil fuel contribution (old CO2 from coal and oil of great age)
Lake Bonneville
- Covered 1/3 of Utah, fresh water lake -Can see the shorelines in Salt Lake City - Salt Lake because it has been evaporating, but leaving the salt behind (higher salt to water ratio)
Using Magnetic Inclination and Declination as a time scale
- Declination = direction - Inclination = angle - If you can match them up (match up the graphs) then you can determine a chronological template in which undated sediments can be placed
Argon correlation with Deuterium
- Deuterium giving us temperatures in ice cores is correlated with Argon and CO2 gas bubbles -Argon gas is correlated with Deuterium in ice, which is related to Temperature --> Argon is related to temperature - Based on CO2 and Ar --> temp. changes first, 800 years before CO2 - so temp. changed first according to this
Europe glacial history
- Didn't cover all, partway down across Denmark - Thick ice sheets around Alaska but most of Alaska and Siberia wee not covered by ice. Why? ---Because even though it was cold, there was no precipitation
Micro-particles (aerosols)
- Dust - Light - Cl - NO3 - SO4
Milankovitch Orbital Perturbations (concerning earth's orbit around the sun)
- Eccentricity: orbit more circular v. more elliptical (it changes) - Obliquity (tilt) - Now at 23.5 degrees relative ecliptic, but varies from 21-25. The more tilt, the more seasonality - Precession - referring to tilt spinning like a top, the orientation of the rotating axis --- this gives you different Milankovitch cycles
What to look for in glaciers
- Erosional features - Depositional features
Mechanism of Climate Change
- Extraterrestrial --Galactic dust clouds --Solar variability (solar constant not actually constant) --Orbital perturbations (milankovitch hypothesis) - Terrestrial --Diastrophism (higher elevations or sea level change) --Plate tectonics moving continents northward --Volcanism --Atmospheric CO2 --Random extra cold summer (albedo stays high)
Packrat Middens
- Furry little desert animals - Gather "treasures from countryside and store in middens (i.e. garbage dumps) - to preserve, packrats urinate over the middens -Middens contain remains of desert vegetation common at the time (use radiocarbon dating and can determine the trees and other plants of the region) - All over the west (Nevada, Utah)
Land evidence of climate change
- Glacial ---Glaciers ---Rivers ---Proglacial lakes -Periglacial -Pluvial Lakes -Speleothems -Biological ---Pollen ---Beetles
U234/Th230 Dating
- Half life is 250000 yrs (so can be used for much earlier times) - Dates from 0 to 350000 years - Corals, mollusks, and speleothems make skeletons out of calcite, aragonite, and U - U decays to Th at a known rate, so can use the ratio of U/Th to determine the age - Th is the daughter (product) of U decay, and Th is not soluble or found in ocean water - High precision possible (+/- 1000 years at 125000 BP - Corals are best because mollusks and bone can absorb more U even after death (so date is too young)
Kettle holes, moraines, and fiords
- Kettle holes are holes that form due to melting ice sheets and glacier retreating. When the ice sheet melts, some ice can remain and then sediment can cover this ice. Eventually the climate warms enough that this ice melts, leaving a shallow sediment-filled body of water. - Moraines are sediment deposits formed from water flow in a glacier, the water flow deposits the sediment at the foot of the glacier. They are located where ice was more stagnant - Fiords are long, narrow deep inlets of the sea between high cliffs, it's the submergence of a glaciated valley. Found in Norway and Iceland
Continental Glaciation
- Large ice sheet slowly advanced from the north -Once ice retreats, land is left with glaciation effects - Lakes dam up at the edge of the ice, forming deltas and river channels - Glacial meltwater --> glacial fluvial sediment (sediment deposited by glacial rivers)
Marine cores and periodicity
- Marine cores indicate that there is a consistent periodicity -Any mechanism should be able to explain this periodicity - shows that there are interglacial periods every 100,000 years that last 10,000 years
O16 and O18, Stable Oxygen Isotope Defn
- O16 is normal - O18 is a stable isotope - For Defn See PPT 10 slide 5 - The standard is often SMOW (standard mean ocean water) - PDB for carbonate fossil analysis
RadioCarbon Dating (C14)
- Only useful from 250-25000 BP - Wood, peat, bone, shell, old seawater, marine sediments, and CO2 trapped in glacier ice - Normal stable Carbon is C12 - N14 + cosmic ray neutron --> C14 + H - Neutrons are a max at 15 km in atmosphere = C14 +O2 --> C14O2 is in plants --> animals - Decay half life 5730 years - C14--> N14 + electron + neutrino
Modern Extent of Periglacial Conditions
- Periglacial: relating to or denoting an area adjacent to a glacier or ice sheet or otherwise subject to repeated freezing and thawing. -Sub-sea permafrost (permafrost in ocean, always frozen) - Patterned ground in Spitsbergen, due to freezing and thawing, cryoturbation, pushes rocks to the side to form patterned ground - when permafrost melts, very swampy
Climate thresholds for periglacial features
- Permafrost --discontinuous <-2 C --continuous <-8 C - Ice-wedge polygons <-15 C or 5 F - Pingos <-1 C - Thermo-karst <-1 C -Rock glaciers <+2 C -Stone polygons <-4 C - Stone stripes <-4 C
Vegetation where packrat middens are found
- Ponderosa Pines - Piñon pines - Cactus (prickly pear) -- This is also the same area where there are pluvial lakes
Time Series Component Cycles
- Red blue and green are sin curves with different amplitudes over a 60,000, 20000, and 8000 year period - So you go to a given year, add all the sin curves together to get the real (total date) line on the graph
Delayed Ice sheet response due to external forcing
- Takes a long time for the ice sheet to grow when it's cold and a long time to melt (maybe why the insolation data doesn't match up with ice sheet change)
Ice Core Climate Indicators (proxies)
- Temperature --> Oxygen Isotope squigglyO18 - Humidity --> Deuterium excess - Snow accumulation --> Seasonal signals - Volcanic activity --> Conductivity & SO4 - Wind speed --> Particle size & amount - Atmospheric gases --> CO2, CH4, N2O - Solar activity --> Be10
Pluvial Lakes
- They occur with high precipitation/less evaporation ratio, lakes during ice age period - Occur in interglacial period, connection with salt deposits due to Pleistocene glacial period - they were wetter than present, large lakes are present where now desert - Indicates precipitation changes - Pluvial lakes in SW US would survive if: --Change in temp is 5 C or less --Evap is 30% less, Precipiation is 80% greater - These basins filled with water
Use of plankton for dating
- Use plankton to determine how the oceans have varied up and down over time - Controversial because oxygen isotopes are related to temp. AND volume of water - When you have an ice age, a lot of this is stored in ice sheets - Water molecules evaporated tend to be lighter with less squigglyO18, so oceans during an ice age have greater squigglyO18 - When ice melted, all the squigglyO18 came up again and planktons used it - NOW squigglyO18 is going down... IS IT BECAUSE OF TEMP OR VOLUME??? - found that it was 2/3 because of volume, 1/3 because of temp.
US Periglacial features
- We know this area is really really cold - all the symbols on PPT 15 slide 18 are periglacial features
Dust Flux at Vostok
- When temp is cold (25000 years ago), there was lots of dust (possibly due to high winds) - colder, more dust - warmer, less dust
Drumlin
- a low oval mound or hill, formed by compacted boulder clay from past glacial action
Johnson Mound
- a mound that was formed by over deposited sediment - you can tell this is the case because it's well-sorted
Sunspots
- appears to be cyclical - there is a correlation with climate - fewer sunspots = cold weather
Pingos
- arctic pimples - lake starts to form, causes land above to rise, pore water expelled in front of rising permafrost, pressures cause frozen ground to rise - like a hill, last for 100 years or so, Takes 20-30 years to grow
Distribution of Planktonic Forams
- assemblages indicate ocean temp. and salinity - tropical, warm subtropical, cool subtropical, sub polar, and polar are some categories - different plankton live in different types of water at the surface - can be used to determine temp. of ocean water surface over time - Foram assemblages v. ocean temp can be used to study species distribution v. temperature
Vostok Ice Core
- at the last interglacial time, had high levels of squigglyO18 like now - 16000 BP climate warming, ice sheets melting until a little cold snap called the dryas (younger dryas - glacial time) - Glacial to Holocene transition -- cooling trend starting 16000 years BP (16 ka BP) - 400,000 record shows that about every 100,000 years we have an ice age, and our 10,000 yrs is about up
Ice wedges
- bands of ice that grow larger and larger -expands, cracks, ice melts, and water goes down to form new holes in the ground - ice wedge polygons (weird patterned ground), can form concentric polygons which is interested
Speleothems
- cave formations (like stalagmites and stalactites) - they are secondary mineral deposits formed in a cave - typically form in limestone or dolostone solution caves - Stalactites: contain oxygen isotopes that can be used to calculate the history of the land (squigglyO18)
Summer sunshine and Ice sheet volume
- don't match up to the periodicity over Milankovtich orbital perturbations, not as simple as Milankovtich makes it out to be - The good news: periods of insolation spectra are identical to observed periods - Bad news: the 100,000 year period, when we would expect the biggest change for ice sheets, the summer sunshine does not correlate (insolation)
Solifluction lobes
- gradually flowing downhill, tundra turf on top - active layer is on top
Baltic Sea History
- ice retreated more and more, changing from fresh water to salt water - then land uplifted, then all of ocean changed back to fresh - ocean rose about 120 m as glaciers melted so salt water again -Switching back and forth from fresh to salt
Annual banding of corals
- if you core down and take an x-ray, you can see bands on corals to help analyze ocean temp. - can go back around 1000 years - there is an annual cycle of SST and coral chemistry
British periglacial features
- line on ppt 15 slide 17 shows limit of ice age glacial advance - by the time the ice retreated up north, the temp. must have increased dramatically because DID NOT CAUSE PERIGLACIAL FEATURES in Northern UK - Europe temperatures were colder than present (from periglacial features) by 17 C or 31 F
Great Lakes History
- numbers are radio carbon dating of trees in moraines (left by glacial retreats) - moraines indicate the extent of an ice sheet - Two Creeks Buried Forest Bed - spruce trees buried underneath hill - Max extent of world glaciers at 15 kbp - All of the great lakes melting was going out of Chicago, found some whale bones in Lake Huron - By about 5000 BP, pretty much all retreated
Ocean cores can indicate:
- rate of sedimentation - rate of erosion on land -temperature of surface ocean water - temperature of water on ocean floor -extent of sea ice - volume of glacier ice - rate of iceberg production -ocean salinity -paleomagnetic stratigraphy
Glacial erratics
- rocks transported by glaciers, know they are not from the area because they have a completely different lethology - sometimes you can trace back thousands of km to the source
Deep Ocean Sediments
- some skeletons are made of calcium carbonate (CaCo3), some from other material (coccolith, dinoflagellate) foraminifera (type of fossil), diatoms make up their skeleton from silica - chalk is made from foraminifera
Ice flow cause problems
- the higher you go on an ice sheet, the colder it gets - the best location to core is at an ice divide (see ppt. 10 slide 11) - an ice core that is further down will have a record of ice originating upstream, hence the dating won't be as accurate. - The higher you core on an ice sheet, the less problems you'll have dating the ice because ice flows affect it less
Rock glaciers
- they look like glaciers, but their rocks -They still move!!
Eskers, Moraines, Glacial till, Terminal moraines
- underground rivers when ice was stagnant on the bedrock - Bloomington moraine: extent of last ice age - Glacial till - material deposited on terrain due to past glacial action - Terminal moraines are located in the eastern US, between Hudson river and cape cod for example
Dead Sea
- wasn't always as low or salty, water has evaporated away - salt deposits on the side -water going down 1 ft/yr
Loess (wind-blown dust) and Ocean Inorganics
- we've had more loess during the last interglacial time -during interglacial times, loess levels dip (less loess)
Paleomagnetic Time Scale
- what was once magnetic north is now magnetic south - has reversed over the course of earth's existence - It can be seen in sediments, in ice cores, and in ocean cores to an extent, but they can be hard to verify - It can be seen in lava, as when a volcano erupts the lava cools and solidifies in the magnetic field of earth - This happens with rocks all over, and it can be seen on the ocean floor (normal and reverse magnetization)
When ice changed
About 2 million yrs ago, things really started to change --effects of ice ages getting more dramatic --N. America an European continents began to drift apart and northward -Our interglacial "peaked 5000 years ago and we are gradually going into the next ice age -->what Dr. Clark though in grad school -But Dr. Broecker predicted warming due to CO2 and was right
Infinite viscosity and ice sheets
An ice sheet on earth with infinite viscosity (doesn't change) --> ice would be constant - Earth's viscosity controls climate periodicity - the cycle of ice sheets --Earth's interior flows very, very slowly
Time required for air isolation at Volstok Vostok CO2 and CH4
Anywhere from 3000-6000 years - CO2 varies with temperature and so does CH4 - Did CO2 cause temp. change? Or vice versa? -there's a clear correlation, which came first? You can't tell
Radiocarbon Decay Rate
C14 = Co14 2^-(t/ro) - ro is constant half life, t is time, Co14 here is the amount of carbon at time = 0 (initial amount of carbon), t is the amount of time
C14 age departure from True Age determined by tree ring data
C14 age determined by radiocarbon dating can allow for a more continuous dating of tree rings, but the further back in time, the more off the dating is. - Once you get around 8000 BC, the C14 age might be too young by 1000 years.
Calcium carbonate composition
Calcium + carbon + oxygen --> CaCo3 - some of this oxygen is squigglyO18 so can be used to date - composite squigglyO18 for Ocean Cores mainly gives ocean volume - 3 million yr ocean core record of squigglyO18 shows record from snow and ice in Antarctica, shows ice ages and interglacial periods - continents were drifting farther northward, started to be able to hold large ice sheets
Ice tunnels
Formed by river flowing through the glacier
What data do you get from ice cores?
Ice core results: -- temperatures -- accumulation rates of snow -- atmospheric composition --dust
Spitsbergen
Located in the arctic - Question for research: was this whole area in arctic ocean covered by ice? - Misery mountain: only thing on desolate Bear Island, determined there were glaciers there but couldn't date it due to lack or organic matter - It was on the edge of sea ice - they found a giant whalebone in land, showed uplift
Spectral Signatures - Observed and Earth Orbital
Periodicity in ocean core data --100,000 year --40,000 to 43,000 year 1--9,500 to 24,000 year Periodicity of Orbital Variations (Milankovitch) --100,000 year Eccentricity --41,000 year Obliquity (tilt) --19,000 to 23,000 year Precession - *What does this mean? It means that the periodicity data from both match up! --But it's not that simple
Orbital perturbations and other mechanisms can account for some of the change, but not all.
Positive feedback effects
Volcanic signatures
help confirm what the ages are, trace elements can help determine which volcano it erupted from
squigglyO18 of Snow is Temp. Dependent or Independent?
squigglyO18 of snow is temp. dependent - as temp. gets cooler, amount of squigglyO18 is significantly less (than what you'd expect) - see graph on ppt. 10 slide 6 - because water vapor in atmosphere, water molecules with slightly heavier oxygen tend to precipitate first - water vapor gets progressively lighter the colder the environment is - evident in seasonal variation of squigglyO18 in Greenland - similar relationship for Deuterium - summary: the colder it is, the less squigglyO18 and deuterium
Isostasy
state of gravitational equilibrium between earth's crust and mantle, crust "floating" on mantle can rise and sink
