Week 10: How to Build a Planet: The Cenozoic Earth Flashcards
What are the general trends in the global temperature and sea level through the Cenozoic?
Early paleocene to mid Eocene= warming trend=the EECO/Early Eocene Climatic Optimum (tropical waters 5-10degrees warmer, deep oceans 9-12 derees warmer)= changes in configuration of continents
Subsequently from mid Eocene to present day= long term cooling phase= formation of polar ice sheets and ice age
What were the climatic conditions during the Early Eocene climatic optimum? What caused this warming trend?
tropical waters 5-10 degrees warmer
deep oceans 9-12 degrees warmer
(Paleocene-Eocene Thermal Maximum thought to have been caused by large increases in greenhouse gases from the main phase of the north atlantic province (LIP))
What ocean circulation patterns existed in the Palaeocene/Eocence and why?
-SA seperates from antartica forming the drake passage
-australia seperates from antartica forming the tasman passages
-ocean circulation changed from equatorial to circumpolar by 35.5ma
-appearance of atlantic meriodional overturning circulation (AMOC)
What are hypothermals (see also Class 10)?
short periods of relatively warmer global temperatures that occur within an overall cooler climate period
What is PETM and what is thought to have triggered it?
Palaeocene-Eocene thermal maximum
55.5Ma
implies sudden, large increase in greenhouse gas concentrations Volcanic CO2 insufficient source
Triggers:
linked with main phase (56Ma) of North Atlantic Igneous Province (NAIP)
How did deep water ocean circulation patterns change in the mid Eocene? Why?
ocean circulation changed from equatorial to circumpolar
Why?:
-South America separated from Antartica= Drake passage
-Australia separated from Antartica (thermal isolation of Antartica from warm equatorial currents) = Tasman passage
What is the circum-Antarctic ocean current? When did it initiate? What effect did it have on global temperature? How?
(Southern Ocean circulation and circumpolar ocean fronts)
Initiated by 35.5Ma
Effects:
-thermal isolation of Antarctica from warm equatorial currents
-Antarctic convergence zone= upwelling of nutrient rich waters
-cooling effect in middle Eocene enabled Antarctica ice sheets to form
What ocean closed as India moved northwards?
The Tethys ocean
When did ice sheets start to develop on Antarctica, and what plate tectonic occurrence (s) triggered this?
position of continents allowing ice sheet build up at poles, Antartic case = continent at pole, artic case = continents form a ring around the north pole, these prevent sea ice dispersal
-polar regions allowed to cool via circum-polar oceanic currents which extract heat (opening of tasman and drake passages in 35ma)
How did uplift of the Tibetan Plateau contribute to global cooling?
lead to enhanced weathering and cooling
When did ice sheets start to develop in the Northern Hemipshere, and what plate tectonic occurrence (s)
triggered this?
ice sheets developed in the northern hemisphere during pleistocene around 2.6ma, caused by:
-milankovitch cycles
-tectonic changes, e.g. closure of panama isthmus lead to effects on ocean circulation
What is the Atlantic Meridonal Overturning Circulation, and what plate tectonic occurrence (s) triggered this and when?
AMOC is a major system of ocean currents in the atlantic that transports warm surface waters from the tropical wtowards higher latitudes and returns colder waters back towards the equator
-created when the Isthmus of Panama was closed, leading to the restrictoin of flow between the atlantic and pacific oceans
-the opening of the atlantic ocean
What is the age of the start of the Quaternary and what defines the start?
Quaternary (2.6ma-present) is defined by the pleistocene glaciations
What are the names of the two epochs of the Quaternary (and their ages)?
Pleistocene= 2.58 Ma- 11,700yra
Holocene=around 12,000yra- today
What records are used to create a high-resolution climatic record for the Quaternary?
-annual alternations of darker (summer) and lighter (winter) ice
-ice core cut plan
-silver of Antarctic ice showing trapped bubbles
-ice core drilling sites on Antarctica
What events established the conditions for an abrupt shift into a state of widespread continental glaciation in the Quaternary?
major shift in position of North Atlantic Ocean current= large scale climate reorganisation (first major influx of ice rafted debris into mid-latitudes of Atlantic)
What is the basis for inferring palaeoclimate from oxygen isotopes?
Oxygen isotopes, particularly oxygen-16 (^16O) and oxygen-18 (^18O), are used as proxies in paleoclimatology. The ratio of these isotopes in various substances like ice cores, marine sediments, and shells of marine organisms reflects past climatic conditions.
Are cooling phases associated with increases or decreases in 180 levels in sea water? How does sea level vary with oxygen isotopes?
Cooling phases are associated with higher levels of ^18O in seawater. During colder periods, more of the lighter ^16O is trapped in ice sheets
What two records is oxygen isotope data measured from?
- ice cores
- marine records (sediments or microfossils)
Be familiar with the Marine Isotope Stage labelling system, e.g., is MIS17 a glacial or an interglacial?
The Marine Isotope Stage (MIS) labeling system is used to categorize different climatic periods based on variations in oxygen isotope records found in marine sediment cores.
MIS 17=interglacial
(odd numbers are generally interglacial)
What drives Milankovic cycles? Over what periodicities do they occur?
- Eccentricity - changing the shape of the earths orbit around the sun (100,000 years)
- Obliquity - changes in the titlt of earths axis (41,000 years)
- Precession - wobbling motion of earths axis (23,000 years)
How do these relate to changes in the periodicity and amplitude of glacial-interglacial cycles before and after the EMPT?
Early to Middle Pleistocene Transition (EMPT) glacial-interglacial cycles shifted from
-primarily dominated by the 41,000-year obliquity cycle
-to the 100,000-year eccentricity cycle as the main driver
What was the average length of glacial-interglacial cycles before the Early – Middle Pleistocene Transition and what has been the average length of glacial-interglacial cycles after it? Higher or lower amplitude?
41ka increased to 100ka, ampltidue increased, turned to rapid heating followed by longer more gradual cooling
After the Early – Middle Pleistocene Transition were warming phases of the glacial-interglacial cycle shorter or longer than cooling phases?
longer more gradual cooling
When was the Last Glacial Maximum?
20,000 years ago
What effect did it have on global sea level? What geomorphological features provide evidence of widespread glaciers?
decreased global sea level, however after the last glacial maximum, there has been eustatic sea level rise
features:
1.Glacial striations on rock shows direction of ice flow
2.U-shaped valeys
3.glacial erosion causing hills and mountains
4.glacial deposits
What is the age of the start of the Holocene? How abruptly did global temperatures rise and by how much?
11.7Ka
general warming trend after Pleistocene and Last glacial maximum
When in the Holocene did eustatic sea levels approximately reach present day values?
6000years ago
Why has eustatic sea level rise resulted in a relative sea level rise in some places and a relative sea level fall in others?
eustatic sea level rise since the LGM caused by the melting of glaciers
However isostatic rebound changes in some areas due TO
-removal of glaciers=removal of weight=land uplifts, other factors
-local tectonic factors
-tidal regime changes
What defines the Anthropocene?
proposed geological epoch
dating from the commencement of human impact on Earth’s geology and ecosystems
(Anthropocene) What evidence for it might there be in deposits? When did it begin
Evidence:
-microplastics have moved into every crevice on Earth
-plastiglomerates from Hawaii
Begin date undecided between:
1. Mid-Holocene= when agricultural practices started to influence atmospheric composition
2. AD 1750= when the industrial Revolution gathered momentum
3.AD 1950= when population growth, industrialization and the use of atomic fission accelerated
