Past Environmental Change Notes

Past Environmental Change

Recommended Reading

  • Holden, J., 2005. "An Introduction to Physical Geography and the Environment." Pearson. Chapter 20 – Quaternary Environmental Change
  • Lowe, J.J. and Walker, M.J.C., 2014. "Reconstructing Quaternary Environments." Longman
  • Anderson, D.E., Goudie, A.S., Parker, A.G., 2007. "Global environments through the Quaternary: exploring environmental change." Oxford: Oxford University Press.
  • Bell, M. & Walker, M.J.C., 2004. "Late Quaternary Environmental Change: Physical + Human perspectives." Pearson - Prentice Hall.
  • Williams, M., Dunkerley, D., Deckker, P.D., Kershaw, P., Chappell, J., 1998. "Quaternary Environments." Routledge.
  • Encyclopedia of Quaternary Science (ScienceDirect website) and Web of Science are recommended resources.

Environmental Systems & Change

  • Global Circulation Systems
  • Earth Surface Materials: Part of the rock cycle.
  • The Rock Cycle:
    • Weathering.
    • Transportation.
    • Deposition.
    • Lithification (Compaction and Consolidation).
    • Sedimentary Rocks.
    • Metamorphism.
    • Metamorphic Rocks.
    • Melting.
    • Magma (Intrusive).
    • Crystallisation (Extrusive).
    • Igneous Rocks.
    • Uplift & Exposure.
    • Sediments.
  • Plant Photosynthesis: Inputs include radiation, carbon dioxide, and water. Outputs include sugars, oxygen, water and heat.
  • Plant Respiration: Inputs include sugars, minerals, water, and other nutrients. Outputs include carbon dioxide, water, and other nutrients.
  • The Ocean System:
    • Covers 71% of Earth's surface.
    • Contains >93% of water.
    • Produces oxygen (phytoplankton).
    • Absorbs CO_2.
    • Transfers energy (ocean circulations).
    • Controls climate and weather.
  • Earth System: Interaction of the Atmosphere, Geosphere, and Biosphere.

Today’s Session

  1. Why Study Past Environmental Change?
  2. The Quaternary Period:
    • What is it?
    • Why is it important?
    • What are its characteristics?
  3. Theory of the Ice Ages
    • Orbital Forcing
    • Land vs terrestrial sediment records

Why Study Past Environmental Change?

  • Climate change is a critical issue.
  • Key questions include:
    • How will climates change in the future?
    • How will these changes affect biomes and ecosystems?
    • How will geomorphic systems respond to these changes?
  • Observed monthly global mean surface temperature trends:
    • Includes human-induced temperature change, total externally-forced temperature change and CMIP5 model average. It also includes IPCC-AR5 near-term projection.
  • Understanding long-term environmental change is crucial for answering these questions.
  • Climate change affects trees, woodlands, and forestry.
  • Phenological records (e.g., oak budburst) provide valuable information about seasonal changes.
  • Trend of wine grape harvesting dates:
    • Harvesting dates in various vineyards (Alsace, Champagne, Châteauneuf-du-Pape) are trending earlier.
  • Future UK temperatures:
    • Projections indicate temperature changes under different RCP scenarios (RCP2.6 and RCP8.5).
    • RCP2.6: fastest rate of change in near future
    • RCP8.5: fastest rate of change at end of century
    • Similarity between scenarios over the next couple of decades.
  • Predicted changes in European climates (IPCC 2007):
    • Temperature and precipitation responses vary across different latitudes.
  • Climate models can estimate changes in temperature or rainfall.
  • Need to consider how Geosphere or Biosphere responds to those changes (IPCC 2007).
  • Studying past environments helps to understand how the Earth System responds to different climate change events.
  • Allows investigation of how biomes and ecosystems respond to rapid cooling/warming.
  • Enables understanding of how river catchments, soils, glaciers, and slopes respond to rapid change.
  • Understanding past environmental change is essential for understanding how climates change and how those changes affect the Geosphere and Biosphere.
  • Some concerns about future climate change include:
    • Global warming leading to rapid climate cooling in the North Atlantic.
      • Due to Glacial Meltwater switching off thermohaline conveyer
    • Identify periods when rapid cooling/warming occurred.
    • Studying the past can allow us to establish rates of change and response of Biosphere and Geosphere.
    • Increasing global temperatures, major changes in biomes, and rising sea level.
    • Palaeo-record helps:
      • Identify periods of known enhanced global warming.
      • Reconstruct the degree of warming.
      • Understand the magnitude of sea level change.
  • Reconstructing past environments involves studying:
    • Sea-level change
    • Ocean circulation
    • Collapse of past civilizations
    • Shifts in vegetation zones
    • Geochronology
    • Global ice volume
    • Climate change

The Quaternary Period

  • Focus on the last 2.6 million years.
  • Earlier periods are interesting but not as useful.
  • Quaternary is the most appropriate period for understanding implications of future climate change.
  • Over the last 2.6 million years, background factors controlling climate operate in the same ways as the present.
    • Greenhouse gases, ocean currents, and modern mountain ranges are comparable to the present.
    • This is not true prior to 2.6 million years.
  • Different geographies produce different climates; position of continents and mountain ranges dictate the movement of currents and air masses.
  • The Quaternary is characterized by "Ice Ages."
    • Regular oscillations between major glaciations and climates similar to the present day.
    • Glaciations occurred approx. once every 100,000 years.
  • Benthic Oxygen Isotopes are used to determine warm stages vs Glacials.
  • Understanding past climate change is fundamental to understanding future climate forcing.
  • Allows understanding of the sensitivity of the Earth System to climate change.
  • The Quaternary period is the best time period to look and investigate climate.
  • Quaternary – “The Ice Ages”

Theory of the Ice Ages

  • Occurrence of Ice Ages has been suggested since the 1830s, based on landforms and sediments.
  • By the 19th century, researchers suggested up to 4 separate Ice Ages.
  • Physical evidence
    • Footprints
    • Glacial erratic (Humber Stone)
    • Cloghvorra Stone, Ireland
    • Scandinavian Erratics in Germany.
    • Depositional landforms - Moraines
    • Depositional landforms - Drumlins
      • Orientations of drumlins can be used to reconstruct former ice flows
    • Cheshire-Shropshire lowlands moraine
    • Lowland Britain during the last ice age
    • Fluvioglacial processes: Outwash plains
    • Periglacial landforms - Pingos
      • Open system Pingo formation
    • Periglacial landforms- ice-wedges
    • Periglacial landforms
      • Frost shattering processes.
      • Ice-wedge polygons.
  • Ice wedges, ice wedge polygons, and Pingos are evidence of processes associated with permafrost conditions.
  • Understanding the extent and dynamics of former glaciers and ice sheets can help understand changes in paleoclimate.
  • Orbital forcing proposed by James Croll (1875).
  • Earth’s orbit changes over time due to gravitational pull of other planets.
  • As Jupiter, Saturn and Moon are also revolving around the Earth, this change will be cyclic.
  • Orbital theory developed by Milutin Milankovitch (1924-1927).
  • Identified three main ways that orbit, tilt, and orientation of Earth varied over time, known as Milankovitch Theory:
    • Eccentricity: Change in the shape of Earth’s orbit.
    • Obliquity: Change in the tilt of Earth’s axis.
    • Precession: Change in the wobble of Earth’s axis.
  • Combined effect of Milankovitch cycles results in major lows and highs every 100 kyrs.
  • Combined effect of Milankovitch forcing on incoming radiation over the past 800,000 years (July insolation 65oN).
  • Problems with Milankovitch Theory:
    • Terrestrial record didn’t contain evidence for the number of glaciations predicted.
    • British Record – only really evidence for three main glaciations.
  • Sequences in the terrestrial record are rarely complete.
    • Later erosion and removal of sediment.
  • Glaciations are major erosional events.
  • Terrestrial sequences frequently record:
    1. Most recent glaciation
    2. Most extensive glaciation
  • One of the few places on Earth where detailed continuous records exist is in the deep oceans where sediments produced in the water body can accumulate.
  • Few erosional processes to remove them.
  • Marine sediments are made up of Foraminifera.
  • They grow in the water body and precipitate shells made of calcium carbonate.
  • Foram shells are constructed from surrounding sea water, therefore, changes in sea water chemistry are preserved in forma shells.
  • As the water that is needed to construct ice sheet comes from the ocean, glacial/Interglacial cycles have huge impacts on ocean chemistry.
  • Sediment cores provide long records (>3 million years) of changing ocean chemistry.
  • Atoms consist of electrons (-ve) orbiting around nuclei, nuclei contain protons (+ve) and neutrons (no charge)
  • Isotopes of an element contain same no. of protons and electron but different numbers of neutrons
  • Oxygen isotopes in Forams:
    • All oxygen atoms contain 8 protons
    • Some oxygen atoms contain 8 neutrons (^{16}O)
    • Some oxygen atoms contain 10 neutrons (^{18}O).
  • Chemically isotopes will react in the same way, but………..
  • …………$16O$ will be lighter than $18O$..
  • Water = H_2O. Some water molecules will contain light $16O$ some will contain heavy $18O$
  • Foram shells made of CaCO_3
  • O in CaCO3 comes from O in H2O
  • Light vs Heavy water
  • What the Marine Isotope Record Tells us:
    • Peaks and troughs in the combined insolation record match those in the marine record of global ice volume
  • Oscillations in global ice volume as recorded oxygen isotope chemistry of marine forams supports the timing of major glacial/interglacial events as proposed by Milankovitch
  • It is now widely agreed that orbital forcing is what drives glacial/interglacial cycles
  • Orbital Forcing (Milankovitch) is the “pacemaker” of the ice ages
  • Any climate change that operates on 20, 40, 100 kyrs timescales is known as Milankovitch forcing
  • Many indicators of environmental change show climate variations on much shorter timescales as well
  • These are known as sub-Milankovitch forcing