Early cenozoic climate history Flashcards
What large scale geological events occurred in the Eocene?
Major volcanic activity with N Atlantic rifting
Alpine uplift
Drakes passage and Tasman gateway open (Antarctic circulation)
India - early collision with Asia
What are the 3 main types of proxy?
Biotic
Geochemical
Sedimentary
What are biotic proxies?
Based on environment-controlled distribution of species
What is an example of biotic proxies?
Tropical and sub-tropical distribution of palms
What are geochemical proxies?
Based on the environment-controlled chemistry of geological materials, including fossil shells, organic biomarkers, mineral deposits
What are sedimentary deposits?
Based on environment-controlled deposition of sediments
What are some examples of climate archives?
Marine sediments
Ice cores
Corals
Speleothems
Tree rings
What is the primary proxy for ocean temperature and planetary ice volume?
Oxygen isotopes in foraminifera
What is the abundance of O16 and O18 like?
O16 lighter and has higher abundance
O18 heavier and less abundant
What are foraminifera?
heterotrophic amoeboid protozoa
Where would you find foraminifera?
Free floating in the surface oceans (planktonic) and on/in sediment surface at the bottom of the seas / oceans (benthic)
What have some foraminifera be able to produce?
Calcareous shell (calcite)
What does a positive O18 value mean?
There is relatively more of isotope O18
What do foraminifera host?
symbiotic algae
What 2 factors can the variations of O18 recorded by foram CaCO3 be attributed to?
1) Temperature-dependent fractionation of isotopes between water (seawater) and calcite (foraminifera)
2) Changes in the oxygen isotopic composition of seawater
What can change the composition of O18 ration in sea water and freshwater?
Warmer temp will led to higher O18 in ocean as lighter O16 preferred
Lower O18 in water vapour as its heavier and condenses easier
WHat does a 1*c change do to the O18 value in foram shells?
increased by 0.25% per mil
What is the effect of ice sheets on O18?
Ice sheets lock up O18 depleted water for Ka to Ma thus making oceans O18 +
What has happened to O18 values over time?
Became more positive with a link to cooling deep oceans and glaciation around 30 Ma
Why is the cenozoic important?
Provides one of the best records for the effect of higher co2 ppm with a max of 1900 ppm
What is an indicator of how hot the Palaeogene greenhouse earth was?
Supported an boa 13m which would have needed mean temp of 35*c
How can Antarctica be evidence for how warm Palaeogene greenhouse earth was?
Palm pollen
Biomolecular data show ~20*c warmer (sub-tropical)
What is evidence of warmer Palaeogene in the Arctic?
Fern and duckweed linking to same as modern day black sea
How were levels of organic carbon seasonally controlled?
6 months of darkness experienced due to the tilt of the poles
What is the a balance between in the carbon cycle on a million year timescale?
CO2 input to atmosphere: volcanism related to rifting and spreading
CO2 removal from the atmosphere: chemical weathering of silicate rocks, organic carbon burial
What was one of the main volcanic sources of carbon dioxide in the eocene?
North Atlantic LIP (Icelandic hotspot)
What was a cause of a 200,000 year warming period in the Eocene?
Increased calcium carbonate in oceans as a result of it being eroded by carbonic acid
What was the effect of warming on terrestrial ecosystems cenozoic?
Forest habitats expanding into high latitude and opening up migration routes for early primates to move from Eurasia to the Americas
How far back is there evidence for ice rafted debris and thus glaciers?
Late Eocene
What occurred in Greenland which is evidence for early glaciation?
Sporadic expansion of valley glaciers and calving of icebergs into Greenland sea
What organic evidence is there for glaciation in the late Eocene?
Diatoms which are usually associated with sea ice
What was the main driver of a cooler climate?
The east Antarctic ice sheet
What was the development of the East Antarctic ice sheet driven by?
Ice sheets merge, buffer and ice-albedo feedbacks
Geologically rapid transition (10*5 years)
When was the first major expansion of Antarctic ice sheets?
Eocene-Oligocene boundary (shown by switch in O18 value becoming more positive)
How does deposition environment for limestone change as a result of glaciation?
Switch to deep marine as regression occurs
