Paleoclimate and Sea Level Changes

Paleoclimate and Sea Level Changes

Global climate changes

• Glaciers and permafrost• Desertification• Evidence for change

– Long and short time scales

Graphical Representation of Climate in Geologic Time

Earth HistoryPrecambrian ???? – 540 Mio a

Paleozoic 540 – 250 Mio a

Mesozoic 250 – 65 Mio a

CenozoicTertiary 65 – 1.8 Mio aQuaternary 1.8 Mio a - today

Proxies

Measurements

Billions of years agoMajor continental shifts – earth extremely hot

Underwent cycles of glaciations

ice sheets existed at lower latitudes

Paleozoic EraInterglacial period

plants invade land

PermianMajor Glaciation

PaleoceneElevated greenhouse gases warmed up planetPalm trees in AlaskaCrocodiles in the Arctic

610 – 575 Ma

438 – 408 Ma

292 - 250 Ma

55 – 52 Ma

Antarctic ice sheets

formed

34 Ma

Pleistocene Ice Age

1 Ma

1.8 Ma –10 Kya

Holocene – cycle of glaciation and

melting of ice caps – rising sea levels

18 Kya

Last glacial period

Precambrian

beginning – 540 Mio a

Evidence of two major glaciations

„Faint Sun Paradox“

„Snowball Earth“

Paleozoic: CambrianN hemisphere (north of 30°) ocean

Increased tectonic activity

CO2 high, up to 10x of today

Warm and wet globally

Paleozoic:Ord: Ice formations 490 – 440 Mio a

Sil Dev: no glaciation 440 – 350 Mio a

Car Per: Ice ages 350 – 250 Mio a

Reason for this variation?

Carboniferous Ice age settings:


Continent near south pole

Maritime influence

Subfreezing T during most of year

Marine transgression – continental flooding

Reduced seasonality


CC driven by land – sea distribution

Reason for this variation?

CC driven by tectonics

Mesozoic Climate Variability:Trias 250 – 205 Mio a: Pangaea

Jurassic 205 – 145 Mio a: Pangaea break up

Cretaceous 145 – 65 Mio a: Continents as we know them today

Generally warm and arid periodNo evidence of glaciation

Why?

Mesozoic Climate Variability:Trias 250 – 205 Mio a: Pangaea

Pangaea characteristics:Large land mass at equator

Lower sea levels

Reduced rate of tectonics

Extreme continental climate

Extreme dry

Pangaea break - up:

Tethys seaway / transglobal equatorialseaway formed

Heating of water at equator

Heat transport to low latitudes

Mesozoic Climate Variability:Pangaea: No continent in pole position

Pangaea – too dry

Transequatorial seaway –heat redistribution

However – Model problem

Cenozoic Climate Variability:Tertiary (65 – 2 Mio a)

Quaternary (2 Mio a – today)

Relatively warm in early Cenozoic

Early Eocene (55-50 Mio a) tropicalconditions 10 – 15° further polewards

Cenozoic Climate Deterioration:

Oligocene: 25 Mio aInitiation of AntarcticIce Shield

Miocene: 15 – 10 Mio aGrowth of AntarcticIce shield


Hypothesis 1:

1) Transequatorial waterway blocked

2) Transpolar waterway opened throughDrake Passage – reduced heat transfer

3) Growth of ice – increase in albedo

4) Cooling



Hypothesis 2:

1) Change in continental topography

2) Colorado / Tibetian Plateau uplift

3) Winter cooling of N-hemisphere

4) Ice formation


Hypothesis 3:

1) Orogenic uplift (as in Hyp 2)

2) Alpine / Himalayas (20-30 Mio a ago)

3) Increase in silicate weathering

4) Removes CO2 from atmosphere


Hypothesis 3:

5) Silicate + CO2 = Bicarbonate

6) Bicarbonate is soluble

7) Transport to oceans and deposition

Indirect effect by reduced greenhouseforcing


Summary: Combination of processes isnecessary. Land – sea distribution,

ocean heat transfer, orography changeand CO2 are all likely to cause cooling

of earth.

Right now, since 10 Mio a we are in an Ice age (both poles ice capped) with

glacial and interglacial periods

Quaternary period:

Pleistocene 1.8 Mio a – 10Ta

Changes in former examples in Mio a

Drivers needed withcyclicity of 10-100Ta

e.g. Earth orbitvariations aroundsun

Quaternary period:2 model approaches forglacial / interglacial

A) Ice volume changes are driven byorbital forcing. Linear responses at 23/41 Ta, non-linear at 100 Ta.

B) Ice volume changes happen, quasi period fluctuations which then aremodulated by orbital forcing

Quaternary period:

Important: Orbital forcing alone is notenough. Orbital forcing must interact

with internal climate variations

Quaternary period:

C02 feedbacks: C-cycle impacts on matching time-scales

e.g. Oceans: millenium time scale

However, existing ice core records do not allow resolution of the phaserelationship between CO2 and T

Cause – effect still unclear

Quaternary period:Pleistocene – Holocene boundary10-11 Ta

Glacial maximum at 18 Ta

Holocene thermal maximum at 6 Ta

Rapid climate changes

• When were the Ice Ages?– Periodicity

• Extent of glaciation• Climate characteristics• Possible forcing for climate change

– Astronomical– Tectonic– Climate dynamics

History of Ice Ages• Indications from geologic record

– First glaciation occurred in the Pre-Cambrian Era– Periods of glaciation occur about every 200 million

years

• Pleistocene ice ages are the most well known– Height of Ice Age between 150,000 and 10,000 years

BP– Although, episodes of advance/retreat have occurred

every 100,000 years since 900,000 years BP

Closer Look at Pleistocene Glaciation

• Several periods of warm interglacials and cold glacials– 130 ky BP – Emian interglacial

• Climate similar to what we have today• However, very unstable (Will we see this?)

– 110 ky BP – Rapid cooling, leading to glacial advances

• Much drier climate due to increase in continental ice at expense of marine ice and moisture

Pleistocene Glaciation (cont…)– 60 ky BP – large amplitude oscillations

between warm and cold– 30 ky BP – More rapid cooling ends with Last

Glacial Maximum (18 ky BP)• Very arid climate globally• Expansive desertification and reduction in forest

land– Interstadials – frequent and brief warm

periods– Heinrich events – very cold periods

Extent of Last Glacial Maximum

Transition to the Holocene– 14 ky BP – Major climate swings ending with the

Younger Dryas (Glacial surge)• Forests begin to rebound and ice begins to recede

– 10 ky BP – warming and beginning of the Holocene Epoch

• Rapid warming (actually warmer, wetter than today)– Especially Sahara (very little desertification)

• 1500-year oscillation of warm-cold cycles, outburst floods (stochastic resonance?)

• Lesson learned – LARGE CLIMATE SWINGS ARE NORMAL!!!!

Theories for the Onset of Glaciation

• Astronomical– Milankovitch cycles– Changes in solar parameter

• Tectonic– Continental drift– Orogenesis

• Climate dynamics– Increased planetary albedo– Interruption of Gulf Stream by termination of sinking of

hypersaline water in North Atlantic– Water vapor fluxes

Milankovitch Cycles

• Eccentricity – changes in shape of earth’s revolution about the sun (100 ky cycle)– Significant effect on insolation

• Obliquity – changes in axial tilt (41 kycycle)– Most significant effect on albedo

• Precessionary – reversal of equinoxes (19 and 23 ky)

Changes in Insolation

Implications of Milankovitch Cycles

• High correlation with solar and climate cycles

• Work of Saltzman and other show large oscillations in climate every 100 ky(Eccentricity)

• Climate oscillations to lesser extent on 20 ky (Precession) and 40 ky (Obliquity) cycles

Causes of glaciation/climate change

• Atmospheric gases and dust– Greenhouse gases->warming– Dust (volcanoes)->cooling

• Positions of the continents– Ice sheet nucleation with continents in polar

positions– Changes in ocean circulation

• Orbital factors

Milankovich cycles are cycles in the Earth's orbit that influence the amount of solar radiation striking different parts of the Earth at different times of year. They are named after a Serbian mathematician, Milutin Milankovitch, who explained how these orbital cycles cause the advance and retreat of the polar ice caps.

http://deschutes.gso.uri.edu/~rutherfo/milankovitch.html

The phase difference between two paleoclimatic time series is used to interpret processes that link Milankovitch-cycle-driven insolation changes with Earth's climate.

What is phase?

The figure shows three examples of the phase between two time series. In the top figure, two time series have different amplitudes but are exactly in phase (Phase=0). In the middle diagram, two time series are exactly out of phase (Phase=180). The bottom diagram shows the general case where one time series leads or lags a second time series. The magnitude of the lead or lag is the phase angle and can be positive or negative. http://deschutes.gso.uri.edu/~rutherfo/milankovitch.html

The influence of these cycles on insolation (INcident SOLar radiATION) at different latitudes is shown for 65 degrees north latitude from the present to 1 million years ago. In the Northern Hemisphere, peak summer insolation occurred about 9,000 years ago when the last of the large ice sheets melted. Since that time Northern Hemisphere summers have seen less solar radiation. http://deschutes.gso.uri.edu/~rutherfo/milankovitch.html

Annual energy flow to earth from sun

The Greenhouse effect

Greenhouse gases such as CO2 absorb energy and stop it from radiating away (Keller, 2002)

Concentration of

Atmospheric CO2 over time (Keller, 2002)

Global temperature changes

Maximum extent of glacial ice sheets during the Pleistocene glaciation (Keller, 2002)

Global temperature changes

Arid lands and desertification

National Geographic map of the world

Terrestrial Ecosystems are an…• Integral part of global carbon system• Plants take in and store carbon dioxide from the atmosphere through photosynthesis• Below ground microbes decompose organic matter and release organic carbon back into the

atmosphere

Cycle shows how nature’s sources of CO2 are self regulating – that which is released will be used again – Anthropogenic carbon not part of natures cycle – is in excess

www.bom.gov.au/.../ change/gallery/9.shtml

http://www.bom.gov.au/info/climate/change/gallery/9.shtml

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Paleoclimate and Sea Level Changes