Please enable JavaScript.
Coggle requires JavaScript to display documents.
Eocene-Oligocene Transition (E/OT) (Causes (Declining atmospheric…
Eocene-Oligocene Transition (E/OT)
Causes
Declining atmospheric greenhouse gases forcing (CO2 is the only one with known proxy)
Lowering annual snowline elevations until extensive regions of high Antarctic topography (De Conto & Pollard, 2003)
Formation of small, highly dynamic ice caps on high Antarctica plateaux (De Conto & Pollard, 2003)
Preconditioning of the system (Pearson et al., 2009)
Atmospheric CO2 levels fell bellow a critical threshold of 750 ppmv (De Conto & Pollard, 2003; Pagani et al., 2005; De Conto et al., 2008)
Feedbacks related to snow/ice-albedo and ice-sheet height/mass-balance (De Conto & Pollard, 2003)
The bright surface of the ice cap reflects more sunlight (Pearson et al., 2009)
Once an ice cap has formed, melting at its margin is compensated by flow from the cold, high latitude interior (Pearson et al., 2009)
1 more item...
Timing and magnitude of pCO2 atm relative to the evolution of the ice sheet is still unclear
Orbital Forcing
A minimum in Earth’s long-term cycles = low eccentricity and low-amplitude change in obliquity (Coxall et al., 2005)
Affected the distribution of solar radiation received by the Earth (DeConto & Pollard, 2003; Coxall et al., 2005)
Dampened seasonality (DeConto & Pollard, 2003; Coxall et al., 2005)
Prolonged absence of warm summers (DeConto & Pollard, 2003; Coxall et al., 2005)
Inhibition of summer snow melt (DeConto & Pollard, 2003; Coxall et al., 2005)
Establishment of the first major Cenozoic ice sheets on Antarctica
(DeConto & Pollard, 2003; Coxall et al., 2005; Pälike et al., 2006)
Not the occurrence of cool winters favouring accumulation (DeConto & Pollard, 2003; Coxall et al., 2005)
Opening of southern hemisphere oceanic gateways (Tasmania and Drake Passages)
Tectonic opening of Southern Ocean gateways (Kennett, 1977; Exon et al., 2000)
Tasmanian Passage (Antarctica-Australia) and Drake Passage (Antarctica-South America)
Formation of the Antarctic Circumpolar Current - ACC (Kennett, 1977)
Cooling Southern Ocean sea surface temperatures by ~3ºC (Toggweiler & Bjornsson, 2000; Nong et al., 2000)
Creation of a thermal isolation of the Antarctic continent (Kennett, 1977)
Perhaps making Antarctica a continent with a less arid maritime climate (Lear et al., 2000)
Glaciation in Antarctica (Kennett, 1977)
1 more item...
Not significant deep-water passage until several million years later (Lawver & Gahagan, 1998; Barker & Burrell, 1977)
Meteor impacts
No microtektites or other evidences for extra-terrestrial impact were found in TDP 11, 12 or 17 in Tanzania, African margin of the Indian Ocean (Pearson et al., 2008)
Consequences
Cooling
Evidences
Low latitudes (Lear et al., 2008; Katz et al., 2008; Liu et al., 2009)
Oceans
Deep waters (Zachos et al., 1996; Coxall et al., 2005)
Long-term
Shallow waters (Lear et al., 2008; Katz et al., 2008)
3-6ºC cooling in sea-surface temperatures (Wade et al., 2012)
Continents (Eldrett et al., 2009; Bo et al., 2009)
Terrestrial cooling = Tropospheric temperatures decreased by ~8°C (Dupont-Nivet et al., 2007; Zanazzi et al., 2007)
Progressive cooling and drying on land between the late Eocene into the early Oligocene (Frederiksen, 1988; Oboh et al., 1996)
Counter-arguments
No change in temperature (Zachos et al., 1994)
No temperature changes in Tanzania
Tanzanian δ18Opf record may be influenced by local sea-surface hydrographic changes adjacent to the continent
Temperature did not notably change (e.g. Ivany et al., 2000; Kobashi et al., 2001; Kohn et al., 2004; Grimes et al., 2005; Sheldon, 2009)
High latitudes (Eldrett et al., 2009; Liu et al., 2009; Bo et al., 2009)
Hypothesis
Cooling began only later in the early Oligocene (Seisser, 1984)
Cooling was far more extreme at high latitudes than at low (Zachos et al., 1994)
Relative consistency in temperature through time in the Gulf Coast (Zachos et al., 1994)
Increased seasonality
(Ivany et al., 2000; Eldrett et al., 2009)
Winters became about 4ºC colder (Ivany et al., 2000)
Temperature variability, rather than change in mean annual temperature, helped to cause faunal turnovers (Ivany et al., 2000)
Late Eocene summers ~15-20ºC and winters <13.5ºC (Ivany et al., 2000)
Oligocene summers 20ºC and winters ~11ºC and possibly even colder (Ivany et al., 2000)
Sudden growth/establishment of the EAIS - East Antarctica Ice Sheet
Evidences
(Kennett & Schackleton, 1976; Miller et al., 1991; Miller et al., 2005; Coxall et al., 2005; Lear et al., 2008; Zachos et al., 2008; Barrett, 2009)
Marine records (Zachos et al., 1996; Zachos et al., 2001; Lear et al., 2000)
Remnants found in Early Oligocene strata
Glaciomarine sequences on the continental shelves (Cooper & O'Brien, 2004)
Coarse grains of ice-rafted debris (IRD) in pelagic sediments (Zachos et al., 1992)
A shift from smectite- to illite-dominated clay mineral assemblages signals the transition from a chemical to a mechanical weathering regime (Ehrmann & Mackensen, 1992)
Process
Started in the East Antarctic interior (~33.9Ma) (Barrett, 1996)
Erosion followed by weathering products carried to depocentres around the circum-Antarctic (Barrett, 1996)
Discharging mainly via the Lambert Graben to Prydz Bay (Barrett, 1996)
Transantarctic Mountains restricting ice flow towards the Ross Sea (Barrett, 1996)
Ice sheets did not reach sea level
Glaciation persisted (until ~33.7Ma)
1 more item...
Paced by Milankovitch orbital parameters (Zachos et al., 1996; Naish et al., 2001)
Sea-level Fall and Widespread Regression
Estimates
55-70m eustatic change (Pekar et al., 2002)
Isostatic response of the oceanic lithosphere to the change in weight of the overlying water (hydroisostasy)
The actual water-volume change from transferring ocean water to glacial ice is ~33% higher than the eustatic change, and this difference accounts for part of the δw change
The 55-70m eustatic change corresponds to a change in the volume of ocean water of ~82-105m - correcting for isostatic loading and assuming full compensation
~105m relative sea-level and ~67m eustatic fall (Coxall et al., 2005)
Assuming that there were small (~10-m-sea-level-equivalent) northern-hemisphere ice sheets (Shackleton et al., 1984), this requires growth of an Antarctic sheet that was 20% larger than it is today
~70m (Pekar et al., 2002; Coxall et al., 2005; Miller et al., 2008)
Evidences
Coeval erosional event in the Priabonian type section (Brinkhuis & Visscher, 1995) in facies more sensitive to small sea-level changes
CCD (calcite compensation depth) deepening
(van Andel and Moore, 1974; Coxall et al., 2005)
CCD = the ocean depth at which the rate of calcium carbonate input from surface waters equals the rate of dissolution (= ~4500m today)
Growth of large Antarctic ice sheets
Glacio-eustatic sea-level fall
Decrease in the size of shelf carbonate reservoir + exposing widespread Upper Cret Late Paleogene limestones to erosion (increasing global river inputs and δ13C of dissolved inorg. carbon and alkalinity)
Higher deep-ocean CO3
Deeper CCD
1 more item...
Increase in global siliceous (at the expense of calcareous) plankton export production
It was not a single event, but two steps (~40kyr each) separated by an intermediate plateau (~200kyr) (Coxall et al., 2005)
Bipolar Glaciation
Contemporaneous Northern Hemisphere glaciation
Yes (Davies et al., 2001; Coxall et al., 2005)
No (Barrett, 2008; DeConto et al., 2008; Eldrett et al., 2009; Pearson et al., 2009)
Contemporaneous West Antarctica Ice Sheet
No (Barrett, 2008; DeConto et al., 2008; Eldrett et al., 2009)