Week 08 Ice Sheets & Climate Change PDF

Physical Geography: Ice Sheets and Climate Change, Wisconsin Glacial History, and Periglacial Landscapes 10/21/2024-10/23/2024 PROFESSOR PETE PULEO 1 Ice Sheets and Climate Change 2 Learning Objectives Explain the timing of glacial-interglacial cycles...

Physical Geography: Ice Sheets and Climate Change, Wisconsin Glacial History, and Periglacial Landscapes 10/21/2024-10/23/2024 PROFESSOR PETE PULEO 1 Ice Sheets and Climate Change 2 Learning Objectives Explain the timing of glacial-interglacial cycles over the last ~2.6 million years. Explain the differences in CO2, temperature, sea level, and ice cover between glacial and interglacial periods. Explain the main forcings and feedbacks driving glacial-interglacial transitions Describe the archive and proxy records that reconstruct glacial- interglacial cycles 3  Pleistocene Epoch Pleistocene Epoch is just before our present Holocene Epoch Spans 2.6 million years ago (Ma/Myr) to 11.7 thousand years ago (Ka/Kyr). Earth’s Climate Past and Future by Ruddiman 3rd Ed 4  Pleistocene Epoch 41 kyr glacial - interglacial cycles between 2.7-0.8 ma 100 kyr glacial - interglacial cycles between 0.8- 0.0 ma. Earth’s Climate Past and Future by Ruddiman 3rd Ed 5  Glacial – Interglacial Cycles Glacial = Lower CO2, colder, lower sea level, more ice Interglacial = Higher CO2, warmer, higher sea level, less ice https://open.oregonstate.education/climatechange/chapter/paleoclimate/ 6  Milankovitch Cycles Primary driver or forcing of glacial – interglacial cycles Control amount of sunlight or insolation (W/m2) which causes initial temperature change https://open.oregonstate.education/climatechange/chapter/paleoclimate/ 7  Milankovitch Cycles Precession or wobble, Eccentricity, Obliquity or tilt https://open.oregonstate.education/climatechange/chapter/paleoclimate/ 8  Milankovitch Cycles Precession (Wobble) = 23 kyr Obliquity (Tilt) = 41 kyr Eccentricity = 100 kyr https://open.oregonstate.education/climatechange/chapter/paleoclimate/ 9 CO2 – Forcing or Feedback? Mostly a feedback because they often lag T changes 10 GHG Feedback: CO2 Solubility Decreasing Temperature -> Colder Water -> More CO2 drawdown from atmosphere -> Decreasing Temperature More CO2 Cooling Drawdown into Cooling Ocean Positive Feedback 11  GHG Feedbacks: Permafrost Positive Feedback https://www.thearcticinstitute.org/global-carbon-budget-permafrost-feedback- loops-arctic/ 12 GHG Feedback: Iron Fertilization Cold, Dry Conditions -> Increased Dust -> Increased Nutrient Delivery to Oceans -> Increased Phytoplankton -> Increased CO2 Drawdown -> Decreasing Temperatures Increased Dust More CO2 Cool/Dry and Nutrients to Drawdown via Cooling Ocean Photosynthesis Positive Feedback 13  Ice – Albedo Feedback Positive Feedback https://serc.carleton.edu/details/images/17956.html 14 Big Picture: Glacial-Interglacial Transitions Milankovitch Cycle driven changes in energy from the Sun are compounded on by several GHG positive feedback loops and albedo 15  Accumulation vs. Ablation https://www.antarcticglaciers.org/glaciers-and-climate/ice-cores/ice-core-basics/ Accumulation is the amount of snow and ice gained Ablation is the amount of ice lost during summer melt season Their meeting point is known as the equilibrium line Balance of the two controls overall growth/retreat of ice sheets and glaciers 16  Climate Factors for Ice Sheet Growth Summer Temperature Precipitation as snow (cold seasons) Importantly, seasonal temperature and precipitation trends are vital for understanding and predicting ice sheet change. Summer temperature drives snow and ice loss in the summer in the ablation zone. Increasing temperatures can also increase the size of the ablation zone. In the colder seasons, precipitation falls as snow over the ice sheets. If precipitation falls as rain, it will run off the ice sheet and not contribute to accumulation. 17  Continental Configuration Land near poles facilitates ice sheet growth Google Earth Pro Plate tectonics also greatly influences ice sheet growth. The location of continental crust near the poles is essential for forming large ice sheets. This provides an anchor point for ice sheets above sea level and at the coldest places on the planet. 18  Last Interglacial – Eemian (130-115 ka) Dalton et al., 2022 19 Last Interglacial – Eemian (130-115 ka) CO2 at ~290 ppm, today is ~420 ppm 20  Last Interglacial – Eemian (130-115 ka) Eemian vs. Pre-Industrial (~1750 CE) https://link.springer.com/article/10.1007/s00382-016-3274-5 21  Last Glacial Maximum (LGM) Laurentide Ice Sheet extent ~24-20 ka ~6 degrees C cooler than present globally https://open.oregonstate.education/climatechange/chapter/paleoclimate/ 22  End of LGM Ice Sheet Margin Movement https://surroundingtownsgeologytour.weebly.com/background.html 23  How Do We Know about Past Climate? Paleoclimatology The study of past climate change https://www.usgs.gov/programs/climate-research-and-development- program/science/paleoclimate-archives 24  How Do We Know about Past Climate? Archives and Proxies Archives – Geological and biological materials that record evidence of climate change Proxies – Measurements made on materials stored in an archive https://www.usgs.gov/media/images/paleoclimate-archives-and-proxies 25  Oxygen Isotopes Isotope - Variations of an element with a different number of neutrons (mass) https://open.oregonstate.education/climatechange/chapter/paleoclimate/ 26  Oxygen Isotopes Fractionation – Partitioning of heavier and lighter isotopes during a process KE = 1/2mv2 https://open.oregonstate.education/climatechange/chapter/paleoclimate/ Because the mass of a water molecule with 18O is larger, its velocity must be smaller to have the same kinetic energy. Higher velocity molecules take less energy to transition from a liquid to a gas phase and are preferentially removed. Therefore, the heavier isotopes will remain in the liquid phase more often than the lighter isotopes during evaporation. This process is called fractionation, and it enables oxygen isotopes to be used as a tracer and a climate proxy. 27  Oxygen Isotopes In Action https://open.oregonstate.education/climatechange/chapter/paleoclimate/ Here is a simplified diagram showing fractionation in action. We see that oxygen isotope values of the atmosphere are depleted in heavy oxygen compared to the ocean that it evaporated from. Then, as the air mass moves and cools, rain forms and is enriched in 18O relative to the air mass due to heavy water molecules preferentially raining out. Eventually, air masses can move over ice sheets and rain out very 18O depleted water over the ice sheets. This means that when there is more land ice, the surface ocean water will become enriched in 18O. 28  Ice Core Records https://www.antarcticglaciers.org/ glaciers-and-climate/ice- cores/ice-core-basics/ Vostok, Antarctica ice core 29  Marine Foram Oxygen Isotopes Do higher or lower d18O values correspond to glacial periods? Ren et al., 2017 30  Marine Foram Oxygen Isotopes Do higher or lower d18O values correspond to glacial periods? Higher since ice removes 18O depleted water from the ocean Ren et al., 2017 31 Pros and Cons of δ18O Proxy Pros Cons Insight on T and P Complex to interpret given changes in temperature, moisture Tracer for moisture source/path source/path, and precipitation Available in several archives (trees, seasonality ice, lake and marine sediment, speleothems) Available from several materials (CaCO3, cellulose, chitin, etc.) 32 Activity 1 Description 1. Work Independently to draw and describe the timing of the Milankovitch Cycles (Hint: 3 total). Compare with a partner after you have made your best attempt. 2. Work with a partner to define and distinguish paleoclimate archives and proxies while providing at least two examples for each. 3. Work with a partner to describe the major factors that influence where/why an ice sheet forms. 33 Activity 1 Solution 1. Work Independently to draw and describe the timing of the Milankovitch Cycles (Hint: 3 total). Compare with a partner after you have made your best attempt. Precession (Wobble) = 23 kyr Obliquity (Tilt) = 41 kyr Eccentricity = 100 kyr 34 Activity 1 Solution 2. Work with a partner to define and distinguish paleoclimate archives and proxies while providing at least two examples for each. Archives – Geological and biological materials that record evidence of climate change (tree rings, ice cores, sediment cores, speleothems, etc.) Proxies – Measurements made on materials stored in an archive (oxygen isotopes, pollen species assemblages, sediment chemistry, etc. ) 35 Activity 1 Solution 3. Work with a partner to describe the major factors that influence where/why an ice sheet forms. Continental configuration (where land is located due to plate tectonics and sea level) Summer temperatures (ablation) Snowfall amount (accumulation) 36 Wisconsin Glacial History 37 Learning Objectives Summarize the history of continental glaciation in North America and how our understanding of that history has changed over time Describe the development of the Great Lakes 38 Thomas C. Chamberlain (1843-1928) Geologist that grew up in WI and taught at UW Studied glacial geological history of WI Named the most recent glacial stage the Wisconsinan, due to evidence on the WI landscape 39  How Do We Know Past Ice Sheet Positions? Glacial features like moraines can indicate extent of past glaciers https://testbook.com/ias-preparation/moraines 40 https://www.facebook.com/wisconsinhistoricalsociety/posts/did-you-know- wisconsin-is-right-about-in-the-middle-when-it-comes-to-land-area- a/802194828621038/ 41 Laurentide Ice Sheet Movement https://youtu.be/rq90Qv0-tbo 42 https://www.wisconsinwetlands.org/updates/wisconsin-wetlands-the-ice-age- connection/ 43  Glacial Depressions -> Wetlands Green = Wetland areas Corresponds to ice sheet movement https://www.wisconsinwetlands.org/updates/wisconsin-wetlands-the-ice-age- connection/ 44 Glacial Extent 45 https://www.britannica.com/science/Wisconsin-Glacial-Stage 46  Ecological Development http://sciencebitz.com/?page_id=41 47  Ice Age Animals of the Midwest Woolly mammoths, muskox, and caribou fed on tundra vegetation Sabertoothed cats were apex predators https://home. https://iceage.museum.state.il.us/mammals/sabertoothed- catswgnhs.wisc.edu/wisconsin-geology/ice-age/ 48 49  The Great Lakes: Volume 21% of world’s surface freshwater https://bobby-c-blog.com/2013/09/06/great-lakes-volume-math/ 50  The Great Lakes: Average Depth https://en.wikipedia.org/wiki/Great_Lakes 51  The Great Lakes: Elevation + Flow https://vividmaps.com/great-lakes-profile/ 52  The Great Lakes: Bathymetry https://commons.wikimedia.org/wiki/File:Great_Lakes_bathymetry_map.png 53  Prerequisites for The Great Lakes Lake Superior was a failed rift valley (Midcontinental Rift) Led to basin development https://en.wikipedia.org/wiki/Midcontinent_Rift_System 54 Prerequisites for The Great Lakes Lake Michigan and Huron were covered with soft rock that was easily eroded by the Laurentide Ice Sheet 55  Forming the Great Lakes The Laurentide Ice Sheet excavated the lowlands, leaving behind deep basins that filled with meltwater https://www.seagrant.wisc.edu/resources/the-formation-of-the-great- lakes/how-they-were-made/ 56 The Great Lakes: Water Level and Flow Path Change 57  The Great Lakes: Isostatic Rebound https://www.usgs.gov/media/images/glacial-isostatic-adjustment 58  The Great Lakes: Isostatic Rebound https://en.wikipedia.org/wiki/Post-glacial_rebound 59 Activity 2 Description Independently visit the following website (https://wgnhs.wisc.edu/pubshare/ES056.pdf) that describes the glacial history of Wisconsin and answer the following questions. 1) When did glacial Lake Scuppernong exist on the SE WI landscape? 2) When did glacial Lake Wisconsin exist in the central WI landscape? 3) When did glacial Lake Oshkosh form in NE WI (Hint: several times)? 4) How do we know where glacial lakes existed? 60 Activity 2 Solution 1) When did glacial Lake Scuppernong exist on the SE WI landscape? 26,500 – 24,500 years ago and 18,500 – 16,000 years ago 61 Activity 2 Solution 2) When did glacial Lake Wisconsin exist in the central WI landscape? 28,500 – 27,500 years ago and 24,000 – 19,000 years ago 62 Activity 2 Solution 3) When did glacial Lake Oshkosh form in NE WI (Hint: several times)? 31,500, 26,000, 18,000, and 13,000 years ago 63 Activity 2 Solution 4) How do we know where glacial lakes existed? The geologic evidence for these former lakes is the distribution of lake sediment on the landscape. A few places also have beach deposits associated with past lake shorelines. 64 Periglacial Landscapes 65 Learning Objectives Discuss the nature and distribution of permafrost Explain the processes that shape periglacial landscapes Describe the major landforms of periglacial regions Briefly review the broader importance of periglacial environments 66 Periglacial Environments near glaciers or in very cold climates 67  Periglacial Extent https://learningglaciers.blogspot.com/2012/09/an-introduction-to- periglacial.html 68 Permafrost Permanently frozen ground 69 Permafrost Permafrost Table – Upper surface of permafrost 70 Permafrost Active Layer – Soil subject to freezing and thawing annually 71 Permafrost Talik – Unfrozen zone under lake and above permafrost 72 Permafrost Types Continuous – Largely unbroken, thick permafrost 73 Permafrost Types Discontinuous – Generally thin with many unfrozen areas 74 Permafrost Types Alpine – High elevation permafrost at lower latitudes 75 Permafrost and Water Frozen water is impermeable meaning water doesn’t flow through it Why would that matter? 76 Permafrost and Water Frozen water is impermeable meaning water doesn’t flow through it Why would that matter? Causes water to pool on surface 77 Permafrost and Water Typically, water can percolate through soil in the active layer but doesn’t go through the impermeable permafrost 78 Frost Action or Wedging A type of mechanical weathering involving the freezing and expansion of water 79  Frost Heaving When soils freeze and expand, overlying material gets forced upward https://www.researchgate.net/figure/Schematic-of-evolution-of-frost-heave- from-unsaturated-through-saturated-state-at-the_fig1_327559981 80  Frost Creep Mass movement of particles in the active layer downslope from gravity http://www.physicalgeography.net/fundamentals/10ag.html 81 Solifluction Slow flow of water saturated soil over permafrost 82 Solifluction Less likely with porous soils with a lot of space between particles (sand/gravel) 83 Periglacial Landforms: Ice Wedges Ground contracts/cracks in winter and is filled in by water in the summer which eventually freezes Leads to polygons on surface (requires permafrost) 84 Periglacial Landforms: Patterned Ground Rock and soil debris sorted in a manner that resembles rings, polygons, lines, or other patterns 85 Periglacial Landforms: Patterned Ground Thought to be from freeze-thaw cycles (frost heaving and gravity) 86 Periglacial Landforms: Pingos Mounds on landscape up to 600 m in diameter and 60 m high 87  Periglacial Landforms: Pingos Form from water lenses in the soil freezing and lifting soil above https://www.britannica.com/science/pingo 88 Periglacial Landforms: Blockfields Large areas covered in blocky boulders from frost action/wedging and mass movement 89 Activity 3 Description Work with a partner to answer the following questions. Prepare to share your answers. 1) Why are wet, saturated soils common in periglacial environments even though precipitation there is relatively low? 2) What is the distinction between continuous and discontinuous permafrost? Where are they located relative to one another on Earth? 3) What is a pingo? How do pingos form? Provide a drawing and a written description. 90 Activity 3 Solution 1) Why are wet, saturated soils common in periglacial environments even though precipitation there is relatively low? Permafrost prevents adequate drainage, trapping water in the active layer and keeping soils saturated 91 Activity 3 Solution 2) What is the distinction between continuous and discontinuous permafrost? Where are they located relative to one another on Earth? Continuous permafrost has frozen soil everywhere in the area whereas discontinuous permafrost has frozen soil in some areas. Continuous permafrost occurs at higher latitudes or higher elevations compared to discontinuous permafrost since it requires a colder climate. 92 Activity 3 Solution 3) What is a pingo? How do pingos form? Provide a drawing and a written description. A pingo is a mound in a periglacial landscape. Water drains into the soil after the active layer thaws. Then, that water lens freezes and lifts the soil above. 93  Multiple Choice Practice Qs Take ~ 1 minute to independently think about and write down an answer to the question on the board. Then, turn to a partner and discuss your reasoning for choosing that answer. Write a second answer after you have discussed your thoughts with a partner (its okay to write the same answer twice or change your answer, just be sure to have two answers per question). Finally, we will discuss the correct answer as a class. Be sure to have your name and date on top and hand in before you leave. 94 Question 1 What primarily drives the glacial-interglacial cycles? A) Greenhouse gases B) Milankovitch cycles C) Ice-albedo feedback D) Sun’s brightness 95 Solution 1 What primarily drives the glacial-interglacial cycles? A) Greenhouse gases B) Milankovitch cycles C) Ice-albedo feedback D) Sun’s brightness 96 Question 2 What primarily causes ice sheet ablation? A) Warm summers B) Dry winters C) Dry summers D) Warm winters 97 Solution 2 What primarily causes ice sheet ablation? A) Warm summers B) Dry winters C) Dry summers D) Warm winters 98 Question 3 What former glacial lake existed in present day Whitewater? A) Glacial Lake Wisconsin B) Glacial Lake Oshkosh C) Glacial Lake Whitewater D) Glacial Lake Scuppernong 99 Solution 3 What former glacial lake existed in present day Whitewater? A) Glacial Lake Wisconsin B) Glacial Lake Oshkosh C) Glacial Lake Whitewater D) Glacial Lake Scuppernong 100 Question 4 Permafrost: A) Is more common in the Southern Hemisphere that the Northern Hemisphere B) is primarily discontinuous north of the Arctic Circle C) is not currently present in Alaska D) extends further south during periods of extensive glaciation 101 Solution 4 Permafrost: A) Is more common in the Southern Hemisphere that the Northern Hemisphere B) is primarily discontinuous north of the Arctic Circle C) is not currently present in Alaska D) extends further south during periods of extensive glaciation 102 Question 5 In what permafrost layer would you expect to find the most rocks broken down by frost wedging? A) Active layer B) The permafrost table C) Where permafrost meets bedrock D) Permanently frozen ground at moderate depths 103 Solution 5 In what permafrost layer would you expect to find the most rocks broken down by frost wedging? A) Active layer B) The permafrost table C) Where permafrost meets bedrock D) Permanently frozen ground at moderate depths 104 Question 6 Which term describes the movement of water-saturated soil downslope above permafrost? A) Glacial plucking B) Solifluction C) Frost wedging D) Frost heaving 105 Solution 6 Which term describes the movement of water-saturated soil downslope above permafrost? A) Glacial plucking B) Solifluction C) Frost wedging D) Frost heaving 106