GEOL101-Lab 12–Paleoclimate Fall 2023 (2)

1 GEOL101 Dynamics of the Earth – Fall 2023 Name: Laboratory 12-Paleoclimatology (learning from the past) Section: Learning Outcomes: ● Investigate and evaluate climate data on various time scales ● Understand how isotopes of oxygen can help infer past temperatures ● Relate cyclic patterns of global change to Earth’s orbit (tilt, wobble, stretch) ● Utilize tree rings to determine past temperature and rainfall patterns ● Compare past rates of change to modern rates of change Introduction The planet has warmed and cooled in the geological past. Paleoclimate on Earth can be deduced by investigation of fossils, sediment, ice cores, tree rings, coral, sea level, and more. Anything used to infer past climate is referred to as a paleoclimate proxy. Compared to the overall geologic history, we are currently living in an ice age (graph B). The last time the Earth was this cold was in the Paleozoic (Pennsylvanian and Permian Periods). The planet has cooled since the Early Cenozoic (Eocene) and continental ice sheets advanced (built up) and retreated (melted away) cyclically starting about 2.65 million years ago. We call this epoch of ice the Pleistocene. We are now in the Holocene which is the epoch since the last ice age ended (11,700 ybp). In this lab we will utilize and analyze data to reconstruct paleoclimate patterns and be able to compare rates of change. We will also relate global temperatures to rainfall amounts as indicated by tree rings (The diagram below shows the ice pattern for the last 1 million years-A, and the last 500 million years-B). 2

Cycles of Global Climate (Wobble, Tilt, Stretch) Realization of relatively recent continental ice sheets was proposed by Louis Agassiz in the middle 1800’s to explain observations in the northern hemisphere like large transported boulders, scoured bedrock, glacial deposits (till or drift) as well as sea level changes. With more and more data the idea of multiple ice-ages was developed. This data emerged from the northern hemisphere. Because this is where the continental masses largely reside and it is here that the effects of heat changes and ice sheets are most apparent, though they still had a global impact. (Image to the right shows deposits of glacial sediment distributed across the state of Indiana) In the 1930’s Serbian astrophysicist Milutin Milankovich developed a theory to explain how the solar energy received by Earth (insolation) varies cyclically. These temporal patterns of surface temperature are caused by Earth’s orbital interaction with other planets. One aspect of his theory helped explain an ancient observation called “precession of the equinoxes”, which we now know relates to the “wobble” of Earth’s axis of rotation every 23-26K years. This variation determines when in Earth’s orbit the northern hemisphere summer will occur. It turns out that summer time temperatures in the northern mid-latitudes cause ice sheets to either build up or melt away . Another way that northern hemisphere summer temperatures can vary is by changes in the tilt of Earth’s axis (obliquity) currently at 23.5°. This tilt is why we have seasons on Earth. With no tilt at all (0°) there would be no seasons as the sun would always be over the equator. Greater tilt results in colder winters and hotter summers. Less tilt means warmer winters and colder summers. Less tilt can play a role in initiation of an ice age because if summers are cold the snow that fell the previous winter will not melt completely away and a glacier can start to build up. If the tilt is greater then warm summers will cause the snow to melt away. The tilt changes over a 41,000 year cycle. By far the greatest orbital change and the one that correlates nicely with the last 10 ice ages is called eccentricity or the “stretch” of Earth’s path of revolution around the sun. This has 100,000 and 400,000 year cycles. In a more eccentric orbit (stretched) Earth is carried farther away from the sun and it will obviously be cooler. All of these cycles work together to change the climate on Earth. 3 COLD NORTHERN HEMISPHERE SUMMERS would happen with LESS TILT, MORE

Ocean waters rich in light oxygen: Conversely, as temperatures rise, ice sheets melt, and freshwater runs into the ocean. Melting returns light oxygen to the water, and reduces the salinity of the oceans worldwide. Higher concentrations of light oxygen in ocean water indicate that global temperatures have warmed, resulting in less global ice cover and less saline waters. Also water vapor containing heavy oxygen condenses and falls as rain before water vapor containing light oxygen so higher local concentrations of light oxygen indicate that the watersheds draining into the sea in that region experienced heavy rains, producing more diluted waters. Thus, scientists associate lower levels of heavy oxygen with fresher water, which on a global scale indicates warmer temperatures and melting, and on a local scale indicates heavier rainfall. Warmer ocean waters (interglacial) contain lower concentrations of heavy oxygen (O18 ) (Colder rain has less O18, so there is less O18 in the polar ice. The heavy O18 has been left behind in the ocean waters, during ice ages, ocean creatures like foraminiferans build their shells with oxygen that is slightly enriched in the heavy O isotope, O18) Questions: 1) How are oxygen isotopes helpful in assessing past temperatures? How does the ratio of O16 to heavy O18 in the oceans vary according to temperature? In coral, Oxygen isotopes can be determined as well as calcium-strontium ratios to infer past temperatures. Scientists can compare the ratio of O16 (light isotopes) and O18 (heavy isotopes) found in certain ice cores, sediments, or fossils to determine past climates. Warmer tropical temperatures evaporate more heavy Oxygen (18) lowering the relative amount that is in the ocean resulting that fossils have lower amounts of O18. When climate is cold-ocean fossils have higher levels of O18

2) How does evaporation play a role in differentiating O-isotopes? Because when o isotopes evaporate into the air, it decreases the amount in the ocean. O16 molecules evaporate easier than O18 molecules. 3) How does condensation play a role in concentrating light oxygen in the polar ice? Colder ocean waters contain higher concentrations of heavy oxygen and that is because The water vapor containing light oxygen moves toward the poles, causing condensation, which then falls onto the ice sheets. The water remaining in the ocean develops an increasingly higher concentration of heavy oxygen and the ice develops a higher concentration of light oxygen. 4) During an ice age when glaciers several kilometers thick amass on the northern continents what happens to sea level? How much does it fall (see first graph) During ice ages the global sea levels drop drastically during glaciation. From the graph it looks like it is dropping around -90 - -100 5

DATA SET—Fill in approximate temperatures for the O18 values below using the scatter plot data on the previous page, then create a plot of the temperature data on the graph. 35 years of O18 values in reference to standard (Fill in the approximate temperature) Year O18 ref Temp 1988 -0.54 _14__ 1989 -1.01 _5___ 1990 -1.75 _-13___ 1991 -0.43 __25__ 1992 -1.29 __-5__ 1993 -2.12. __-16__ 1994 -2.42 _-18___ 1995 -1.81 _-15___ 1996 -0.75 _0___ 1997 -1.11 _2___ 1998 -2.18 _-17___ 1999 -2.85 _-29___ 2000 -0.50 _20___ 2001 -0.82 __-3__ 2002 -0.65 _10___

2003 -1.92 _-15___ 2004 -2.82 _-28___ 2005 -1.95 __-13__ 2006 -0.61 _13___ 2007 -0.56 _14___ 2008 -1.00 _6___ 2009 -1.22 _-5___ 2010 -1.35 __-4__ 2011 -0.95 _7___ 2012 -0.65 __8__ 2013 -0.91 __7__ 2014 -0.40 __22__ 2015 -2.81 _-27___ 2016 -2.65 _-25___ 2017 -2.91 __-30__ 2018 -0.75 __0__ 2019 -2.62 __-19__ 2020 -0.95 _6___ 2021 -1.13 _-_5__ 2022 -1.54 _-14___ 7 Ocean Sediment; A long Paleoclimate Record Foraminiferans (forams) are the “gold standard” for marine paleoclimatology. Planktonic forams are tiny single cell animals ( amoeboid protists ) that make Calcium Carbonate (CaCO3) shells and are widespread in ocean sediments. The O18 analysis of the shells allows us to infer the sea surface temperature in which they formed. A longer term paleoclimate record of many millions of years can be inferred from oxygen isotope data on planktonic forams. This ocean sediment data shows the transition from the Pliocene to the Pleistocene about 2.65 million years ago when temperatures on Earth began swinging into colder periods. Beginning about 1 mya the ice age cycle changed. Keep in mind that on the scale of the data plot below anthropogenic warming (last 150 yrs) can not be plotted (The graph of paleotemperatures below was developed using O-isotope analysis of the carbonate shells of planktonic foraminifera collected from ocean sediment drill cores)

Antarctica. Unlike the Arctic where the majority of the ice floats on the sea, most of the ice in Antarctica is over land, making it ideal for deep ice coring. In the mid-1990s, cores drilled at Russia’s famous Vostok station reached depths of over 3 km and provided data for the past 425,000 years. In 2004, the European Union sponsored the European Project for Ice Coring in Antarctica (EPICA) which completed drilling a core several hundred miles from the Vostok Station. The data set used for the time-series graph below is from EPICA’s ice core analyses. These cores were collected at the Concordia Research Station, a facility built in 2005 near Dome C, Antarctica. This core contains climate data as far back as 800,000 years . Data can be viewed as an “active graph” at this link https://www.ces.fau.edu/nasa/module-3/temperature-changes/exploration-1.php 9 ) Describe the pattern that you see in the graph above? The pattern indicates very dramatic changed from high highs to low lows every few thousand years. 10 ) Approximately how many glacial periods do you observe in the past 800k yrs About 8 11) Describe the difference between the first 400k years and the second 400?

In the first half the temperature changes were spread out dramatically and the line weight is much lighter. In the second half the temperature changes are more condensed so they, and the line weight on the graph is much bolder. 9 12) In the second graph, over the last 420k years how many ice ages have occurred? About 9 13) What is the average range of temperature from minimum of the ice ages to maximum of the interglacials? Make 4-5 measurements and average the values. -8.9

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Last for this part, let’s compare temperature change for the last 100 years, and for the https://climate.nasa.gov/vital-signs/global-temperature/ Global Temperature | Vital Signs – Climate Change 16) Please enter your calculations below based on the 4 graphs presented …. Interval Interval Years Temperature Rate of Change Rate of Change Change Per year per 100 yrs 342,000 to 334,000 8000 11 degrees, 0.001375, 0.01375 139,000 to 129,000 10000 12 degrees, 0.0012, 0.012 18,000 to 12,000 6000 11 degrees, 0.00183, 0.0183 1920-2020 100 1.5 degrees, 0.15, 1.5 1965-2015 50 1 degree, 0.02, 2 17) What is the average rate of change per century for the 3 glacial to interglacial Pleistocene warming events and how does that compare to the warming rate indicated for the recent 100 year stretch? Rate of change is 0.0147 degrees. The last 100 year stretch was 1.5, 2 degrees showing rate of change is increasing a lot more than normal.

14 SCOTCH TAPE RECONSTRUCTED TREE RINGS HERE