GEOG Feb 4 (L9) The Younger Dryas PDF

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Summary

Some Announcements: - The midterm will cover material up until today - Best way to study is to cover the questions associated with each topic - Don’t study the lecture slides, not everything is on the slides - Read the entire book Ice Ages - From the assignment, you need to know general ideas for th...

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Some Announcements: - The midterm will cover material up until today - Best way to study is to cover the questions associated with each topic - Don’t study the lecture slides, not everything is on the slides - Read the entire book Ice Ages - From the assignment, you need to know general ideas for the exam, not specifics of where everything is Reading Questions: ● What was the Younger Dryas and when did it occur? ○ A short duration cold event ○ 12,800 to 11,500 calendar years ago ● What types of evidence are there for the Younger Dryas? ○ Soil cores with dryad flowers that only exist in tundra conditions. The flowers are now found in a temperate deciduous forest indicating a significant temperature change ● How quickly did the climate change to Younger Dryas conditions? ○ Within 20 years ● What theories have been proposed to explain the cooling during the Younger Dryas? ○ Most popular: icebergs broke off from the Greenland ice sheet as the earth warmed and floated towards the landmasses bordering the Atlantic. ○ This theory was eventually proved incorrect because it didn’t explain why areas like New Jersey would have dryas flowers. Icebergs in New Jersey were unlikely because the ice would have melted by the time it reached this area. ● How did a change in evidence of this event result in different theories for the cooling? ○ The change in evidence was due to the use of carbon-14 dating which exposed the precise time period and palynology- reconstruction of past vegetation. RESULTED IN WHAT DIFFERENT THEORIES? ■ comets? ● How can palynology help us to detect past climate change? ○ Pollen and spores are incredibly resistant to organic decomposition. Every species can only exist in certain climates-- phenomena called ecological affinities. Therefore, finding a tundra flower in what today is a temperate delicious climate suggested strongly that the area was once a tundra. ● What are some of the limitations of palynology and how do scientists deal with these? ○ The wide dispersal of pollen does not mean that seeds of its parent species or the adult plants necessarily will also be widely dispersed. This means that the estimates of where areas began and ended were not completely precise. ● Can you work your way through the pollen diagrams presented and detect changes associated with the Younger Dryas? ○ In the pollen diagrams, you can draw a line horizontally across a specific time period. If boreal trees and their spores are found during that time then it was a boreal climate. If temperature delicious trees were found, then temperature delicious climate. Same for Tundra climate. ● What is a stadial and what is an interstadial?

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○ Stadial- a cold period occurring within a glacial or interglacial time ○ Interstadial- the warmer time between stadials How did an advance in dating techniques enable the new finding of the Younger Dryas at Alpine Swamp, New Jersey? ○ Carbon 14 dating allowed for extremely precise measurements of when pollen and spores were deposited in the soil. Previously, the measurements were inaccurate for a few hundred years. Because the younger dryas was so short, this error amount was too significant for previous scientists to conclude anything. How would a comet collision (or its fragments) trigger Younger Dryas cooling? ○ A comet collision could have sparked many wildfires. The wildfires would have released smoke into the atmosphere. The amount of smoke would have blocked the sun resulting in a large cooling of the earth. Evidence for this has been found in the dust of Greenland’s ice cores. What evidence is proposed for the comet and its impacts? ○ Evidence has been found in the dust of Greenland’s ice cores. IMPACTS?

Feb 4 Notes: The Younger Dryads Time Context: 1. Previous Ice Ages - What causes Ice Ages 2. Present Ice Age with Glacials/Interglacials - Currently in an interglacial, lasts 10,000 years 3. Last Glacial Maximum 4. Younger Dryas 5. Hypsitherma 6. Medieval Warm Period 7. Little Ice Age 8. Anthropocene Younger Dryas - First noticed form evidence in northwest Europe - A short cold event - Within an interglacial, a short cold event is a stadial - In the UK called “Loch Lomond stadial” - Discovered evidence at Loch Lomond - Evidence: pollen cores from lakes and bogs (moss-filled wetlands) - Note: during the cold period, there was almost no dark-colored organic matter (lack of plant production and peat development) - It was so cold that most plants were unable to grow so the soil was lighter in

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color because it didn’t have the organic matter in it After warming had begun and ecosystems shifted to those representing something warmer than tundra climate suddenly cooled confirmed - POLLEN FROM ARCTIC WILDFLOWER (DRYAS)

Dryas Wildflower - Appeared 12,870 years ago - The pollen grains are how we identified the temperature! - These flowers only exist in tundras→ its a tundra plant -

Therefore, the presence of Dryad pollen indicated tundra climate

Evidence - In Nova Scotia and New Brunswick where small glaciers remained those small glaciers re advanced and deposited more glacial till and then receded and solid deposited and then re advanced with a layer of glacial till and then retreated and soil fell etc.

Observation: Cooling is present on both sides of the northern Atlantic - Occam’s Razor → applies the simplest explanation -

Resulted in theory→ as the ice sheet retreated, icebergs broke off and cooled off the lands surrounding the northern Atlantic

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HOWEVER, at the Alpine Swamp, New Jersey - The first study showed no evidence of Younger Dryas - But- new developments in carbon-14 dating allowed us to date very small amounts of carbon, such as single seeds or spruce needles

What is paleoecology? - the study of interactions between organisms and/or interactions between organisms and their environments across geologic timescales What is palynology? (a technique used in NJ to identify evidence) - Palynology- reconstructing past vegetation through which we can interpret climate, the study of pollen and spores - Pollen- the powdery stuff on the anthers - The male gamete produced by a flowering plant - Size from 10 to 100 microns (a micron is 0.001 mm)

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- Only visible under a microscope - Transported by insects or by wind Pollen dispersal should not be confused with plant dispersal - Wide dispersal of pollen does not mean that the species of its parent will also be widely dispersed Spores - Produced by “lower” or more primitive plants without flowers - Asexual reproduction - no fertilization is required - An example of a spore-producing plant is a fern - Those little circles hold spores beneath them

Taxonomy- the classification of living things - Can be applied to plants → called taxonomic classification Taxonomic resolution - Fossils can be identified to a specific level of taxonomic resolution - Pollen form (or morphology) may be unique to the species or may be representative of a genus or even a family - The level of taxonomic resolution is variable, but usually good enough to allow a palynologist to get a good idea of the nature of past plant community form a collection of the pollen and spores produced by the plants in the community. The fossil assemblage group is not biased by contamination or differential preservation - Few paleoecological studies can meet this but we deal wit hit by understanding bias - For instance,→ palynologists have conducted research to determine which types are not preserved -

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To minimize contamination we select appropriate types of deposits for the study of pollen assemblages. The most appropriate deposits are those with a little mixing and low rates of decomposition - e.g. lake and ocean bottoms, bogs We apply the Law of Superposition applied to geography- the older material is at the bottom and younger at the top

The ecological affinities → environmental conditions in which they are most commonly found -

The ecological affinities of the organisms which produced the fossils were not different from the same or close related species today I.e. organisms should not have evolved new adaptations Something most appropriate to assume in the Quaternary, but the likelihood of evolution increase as we go back in time

Valid Exam Question: Which of the following relies on the assumption that “ecological affinities have not changed through time”? → The appearance of pollen of the Dryas flower indicated cooling - Dryas only found in cooler climates Pollen Diagram

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Pollen diagram from Alpine Swamp demonstrates the beginning of the Younger Dryas paradigm shift - Time is shown on the y-axis- shown as depth in the core What does it show us? Taxonomic resolution is not to the species level, but it is still useful Each graph represents the abundance of a pollen type over the same period Thus, if we read across we can compare the abundance of pollen extracted from a sample Each sequential plot represents the abundance of each pollen type On the right, Peteet grouped the various levels into pollen zones

Valid Exam Question: What do we find in pollen zone A-2? Which of the two most abundant taxa in this zone? → Pinus and Cyperaceae What does this tell us? - About 12,000 years ago oak was present → TEMPERATE DECIDUOUS -

Remember these are not calibrated dates

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Around 11,000 years ago oak disappeared and spruce increated and birch increased→ BOREAL -

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The shift from delicious to Boral indicates cooling This new evidence indicated the spatial extent of the Younger Dryas was much larger - Because icebergs can’t explain cooling in NJ! A search began for evidence in other locations and it was found

Evidence of the reason for the Younger Dryads - Found in the Greenland ice cores - The layers in the ice cores are like tree rings - We see an increase in dust - Indicates the cooling took 20 years

Valid Exam Question: Oak is indicative of which biome/vegetation type? → Temperature broadleaf delicious forest -

Recall: oak has wide leaves and is not part of boreal

New Theory for Younger Dryas: - The second theory is linked to thermohaline circulation and pro-glacial lakes Thermohaline circulation

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Thermohaline circulation- creates flows of ocean water and air associated with the formation of North Atlantic Deep Water (NADW) Flows as a current around the globe NADW is a mechanism for transferring heat around the northern hemisphere Europe has a warmer climate than us at the same latitude due to these warm winds

How the NADW distributes heat: - Cold + salty = dense - Dense water dinks - It is an indicator of climate change - Flows down into the southern hemisphere - Why does the water come up? - Ocean winds create upwelling zones and push surface water away to allow deep water to be on top which in turn warms the water - Upwelling zones are by INDIA and in the PACIFIC - Surface warm-water currents return to the North Atlantic where more NADW is formed. What happens if the Greenland ice sheet melts? - The ocean will be less salty - Less dense water - No formation of DADW → a showing or a stop in thermal circulation -

It would take thousands of years for the land to recover

Could something of the Arctic Sea ice or the Greenland Ice Sheet affect thermohaline circulation in the future? - Yes...