Week 10: How to Build a Planet: The Cenozoic Earth

Question 1

What are the general trends in the global temperature and sea level through the Cenozoic?

Answer 1

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

Question 2

What were the climatic conditions during the Early Eocene climatic optimum? What caused this warming trend?

Answer 2

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))

Question 3

What ocean circulation patterns existed in the Palaeocene/Eocence and why?

Answer 3

-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)

Question 4

What are hypothermals (see also Class 10)?

Answer 4

short periods of relatively warmer global temperatures that occur within an overall cooler climate period

Question 5

What is PETM and what is thought to have triggered it?

Answer 5

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)

Question 6

How did deep water ocean circulation patterns change in the mid Eocene? Why?

Answer 6

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

Question 7

What is the circum-Antarctic ocean current? When did it initiate? What effect did it have on global temperature? How?

Answer 7

(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

Question 8

What ocean closed as India moved northwards?

Answer 8

The Tethys ocean

Question 9

When did ice sheets start to develop on Antarctica, and what plate tectonic occurrence (s) triggered this?

Answer 9

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)

Question 10

How did uplift of the Tibetan Plateau contribute to global cooling?

Answer 10

lead to enhanced weathering and cooling

Question 11

When did ice sheets start to develop in the Northern Hemipshere, and what plate tectonic occurrence (s)
triggered this?

Answer 11

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

Question 12

What is the Atlantic Meridonal Overturning Circulation, and what plate tectonic occurrence (s) triggered this and when?

Answer 12

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

Question 13

What is the age of the start of the Quaternary and what defines the start?

Answer 13

Quaternary (2.6ma-present) is defined by the pleistocene glaciations

Question 14

What are the names of the two epochs of the Quaternary (and their ages)?

Answer 14

Pleistocene= 2.58 Ma- 11,700yra
Holocene=around 12,000yra- today

Question 15

What records are used to create a high-resolution climatic record for the Quaternary?

Answer 15

-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

Question 16

What events established the conditions for an abrupt shift into a state of widespread continental glaciation in the Quaternary?

Answer 16

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)

Question 17

What is the basis for inferring palaeoclimate from oxygen isotopes?

Answer 17

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.

Question 18

Are cooling phases associated with increases or decreases in 180 levels in sea water? How does sea level vary with oxygen isotopes?

Answer 18

Cooling phases are associated with higher levels of ^18O in seawater. During colder periods, more of the lighter ^16O is trapped in ice sheets

Question 19

What two records is oxygen isotope data measured from?

Answer 19

1. ice cores
2. marine records (sediments or microfossils)

Question 20

Be familiar with the Marine Isotope Stage labelling system, e.g., is MIS17 a glacial or an interglacial?

Answer 20

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)

Question 21

What drives Milankovic cycles? Over what periodicities do they occur?

Answer 21

1. Eccentricity - changing the shape of the earths orbit around the sun (100,000 years)
2. Obliquity - changes in the titlt of earths axis (41,000 years)
3. Precession - wobbling motion of earths axis (23,000 years)

Question 22

How do these relate to changes in the periodicity and amplitude of glacial-interglacial cycles before and after the EMPT?

Answer 22

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

Question 23

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?

Answer 23

41ka increased to 100ka, ampltidue increased, turned to rapid heating followed by longer more gradual cooling

Question 24

After the Early – Middle Pleistocene Transition were warming phases of the glacial-interglacial cycle shorter or longer than cooling phases?

Answer 24

longer more gradual cooling

Question 25

When was the Last Glacial Maximum?

Answer 25

20,000 years ago

Question 26

What effect did it have on global sea level? What geomorphological features provide evidence of widespread glaciers?

Answer 26

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

Question 27

What is the age of the start of the Holocene? How abruptly did global temperatures rise and by how much?

Answer 27

11.7Ka
general warming trend after Pleistocene and Last glacial maximum

Question 28

When in the Holocene did eustatic sea levels approximately reach present day values?

Answer 28

6000years ago

Question 29

Why has eustatic sea level rise resulted in a relative sea level rise in some places and a relative sea level fall in others?

Answer 29

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

Question 30

What defines the Anthropocene?

Answer 30

proposed geological epoch
dating from the commencement of human impact on Earth’s geology and ecosystems

Question 31

(Anthropocene) What evidence for it might there be in deposits? When did it begin

Answer 31

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