The Ice Age sequence in the Quaternary Subdivisions of the Quaternary Period System Series Stage Age (Ma) Holocene 0 0.0117 Tarantian (Upper) 0.0117 0.126 Quaternary Ionian (Middle) 0.126 0.781 Pleistocene Calabrian (Lower) 0.781 1.806 Gelasian (Lower) 1.806 2.588 Milankovitch Cycle Ice sheet changes Interglacial oscillations http://www.gerhardriessbeck.de
Record is based on the analysis of ice layers by 18 O, 13 C, isotope fractionation, long-lived radioactive isotopes, aerosol and dust composition, and other physical and chemical properties of annual, centennial, and millennial ice layers
Vostok ice core in Antarctica 3740 m Russian, France, US collaboration Comparison of the 18 O, 2 D fractionation based temperature data and CO 2 abundance data in the Vostok ice core material shows a strong correlation between the temperature and CO 2.
Milankovitch cycle or astronomical forcing The Milankovitch cycles are periodic oscillations associated with the eccentricity of the Earth orbit, the precession of Earth around its axis and the obliquity cycle in the axial tilt of Earth that influence the insolation F 0 : Annual orbit causes summer winter effect, eccentricity of ellipsoid orbit changes from near spherical (now) to elliptic orbit with a periodicity of t 95,000 years. Earth axis has a tilt with respect to the orbital plane, which varies by 2.4 o with a period of t 41,000 years changing the extend of seasonal insolation. Earth rotates around its axis (day night period). The direction of the spin vector precesses in a gyroscopic motion with a period of t 25,000 years due to the tidal forces of the sun that give Earth an oblate shape.
Three periodic motions impact the distance of earth or earth s hemispheres from the sun Flux=Solar Constant=Insolation): F 0 =1.37 10 3 W/m 2, R earth = 6371 km Solar power incident on earth: S 0 = R earth2 F 0 =1.75 10 17 W Increase in eccentricity causes colder winters because of insolation reduction Obliquity or change of axis tilt modifies summer-winter differences by bringing northern hemisphere closer to sun Precession introduces variation in distance between northern and southern hemisphere from sun Overall impact: F ~1/r 2
All three distance fluctuations have a different period determining the periodicity of the solar flux constant or insolation F(t)! Orbital eccentricity The change in orbital eccentricity changes the flux as a function of sun-earth distance Axis Precession The spin precession around the axis introduces a regular periodicity for the amplitude of temperature for both the northern and southern seasons Axis Obliquity The obliquity or change of spin axis tilt modifies the distance and inflow angle for the solar flux, changing the summer winter temperature difference Fourier Analysis Model predictions for Earth temperature variations by coupling various oscillation shows sequence of hot and cold periods.
Milankovitch Cycle Demonstrator
Milankovitch theory seems to predict the long-term temperature oscillation pattern reflected in the observational data of the Vostok ice core.
The last four ice-ages Ice-age 360ka BP 260 ka BP 160 ka BP 40 ka BP Warm- Period 420ka BP 320 ka BP 240 ka BP 120 ka BP now
Ice sheets and thermohaline circulation The change in insolation changes the extension and volume of the sea ice coverage. Extended ice sheet areas cause higher reflection of incoming flux, reducing insolation and further enhancing the cooling effect. The extension/shrinkage of the ice sheet is a balance between snow accumulation (snow fall) and ablation (melting, slipping, calving) and operates on a delayed timescale compared to Milankovitch forcing. The thermohaline circulation down-wells further south for extended ice sheet conditions, reducing heat transfer north and the associated ablation process..
Accumulation and ablation of ice shelves Accumulation and ablation of ice depends on the overall temperature conditions the net balance is called ice mass balance. At very cold temperatures the ice mass balance is positive but small, because of the lack of snow fall. Ice sheet can only develop when temperatures are not too low, humidity and wind effects sufficient during winter to generate the necessary precipitation, and the summer are not too warm to reduce melting process. This needs to be included in model! http://www.gerhardriessbeck.de
growth rate: 10 5 m 2 /yr Model predictions for ice sheet development in the Pleistocene considering the impact of mid latitude atmospheric circulation (westerlies) on growth rate, thickness, and shape depending on wind direction, precipitation and melting.
The growth and equilibrium conditions depend critically on the insolation as well as the associated local climate factors such as temperature and wind directions! Growth rate (height, area, volume) for different feedbacks (SL precipitation, SW wind effects). Roe & Lindzen J. Climate 14 (2000) 1450 Initial growth rate of ice sheet slows down with increasing cooling through extended ice sheet, decreasing temperature, humidity and precipitation!
Glacial-Interglacial Oscillations viewed from north Appears in ice coverage, sea-level, atmospheric conditions, and ocean currents!
Glacial-interglacial oscillations The earth as a box model. Included are: Heat exchange between atmosphere and ocean atm 0 Cpw Dw QT T fow fsi D si Gildor & Tziperman, Paleocanography 15(2000) 605 C pw heat capacity, D w thickness of mixed layer, D si thickness of sea ice, potential temperature, time constant for exchange, insulating factor, f ow and f si fractions of open water and sea ice Salinity exchange by precipitation P (fresh water inflow) and evaporation E Q atm S P E S0 Temperature exchange and heat flux associated with sea ice melting and freezing processes Q si T 0 C pw si V w T si T Salinity exchange due to sea ice melting and freezing processes with L as latent heat Q si S si QT L si S 0
temperature o C THC in polar box temperature o C box fraction box fraction Salinity THC in polar box temperature o C box fraction Salinity 100ka glacial oscillation pattern without Milankovitch forcing Glacial oscillation pattern with Milankovitch forcing The 100 ka glacial oscillations rely on the feedback coupling of sea ice albedo and precipitation, temperature. Milankovitch forcing, overlaying the oscillator system, yielding temperature, salinity, and THC variations close to observations..
From Past to Future What causes the predictions of rapidly increasing global temperature on such a short time scale? Greenhouse again