climatic rhythems

climatic rhythems

1. climate through geological time

   • significant variation based on chemical physical and biological ''paleoclimatic'' data and computer simulations
   • late Proterozoic and Phanerozoic climte ossclated between 2 stable states ''green house'' ad ''ice house''
   • seven greenhouse-icehouse oscilations ca be recognised on broader scale from geological record ( lots of fluctuations within these too )
   • ice house world later Proterozoic severe and extensive glaciation very widespread glacial deposits led scientists to believe earth was completely frozen ''snowball earth'' still controvercial

2. early cambraian to late Ordovician Greenhouse world earth warmed during early Cambrian low lats reaching temps of 40 degrees C , plus climate a little wetter than at present

3. late Ordovician early Silurian ice house world glaciation in continents near to south pole increased aridity else where

4. GH - early siluriun to early carboniferous warm but arid

5. early carb - late Permian IHW formation of glaciers in gondwana increased humidity beyond glaciated areas

6. gh - late Permian to early cenozoic distinct global warmth ( although some cool modes) culminating in cretaceous greenhouse average global temp. 6 degrees c higher than today

7. iH Early cenozoic to present genral picture of cooling throughout cenozoic to glaciation/interglacial fluctuations in last 2 million years

8. radiation variations : variation in the amount of solar radiations received in the upper part of the atmosphere long term : passing of solar systems through dust clouds , reduced solar flux

   • shorter term : Milankovitch radiation variations : Minor variations in the earths Rotation and Orbit causes changes in solar flux between seasons and lattitudes
     • Precession : precession of earths axis : 19-23 Ka cycle
     • obliquity : tilt of earth axis 41 KA
     • eccentricity : orbit changes shap : 100ka-400ka cycles
   • timescale aggress well with those of glacial expansion and contraction particularly during quaternary and carboniferous driving force could be radiation variation although variation caused by cycles very small its the positive feedback or amplification to trigger large scale climate change

9. CAUSES : E.T causes : large meteorite generate global cooling through shielding effect of ejecta or ocean impact could vapourise water and incree cloud cover insulating the earth and causing warming controvercal and generally untested

10. variations in atmospheric co2 via greenhouse effect - govered by volcanic activity including sea floor spreading dds o2 and chemical weathering or formation of carbonaceous rocks removs co2

    • strng link between co2 conc and global temperature increased co2 = global warming decreaed co2 glbal cooling

11. changes in the distrubutionof land and sea

    • concentration. of continental land masses trigger ice house conditons via: accumulation of snow and ice : increasereflectivitty of earths surface : high lattitud land block polewrd penetration of warm ocean currents : most greenhouse phases associated with large well connected oceans allowed effective poleward heat transfer

12. single cause mechanism unlikely to be responsible between ery shift grom IH-GH codiions different combinations of forcing factors lkely a differen times e.g cnozoic coolin and the quaternary ice house

    • cenozoic cooling and the uaternary ice house
      • beginning of tertiary : deep sea temps 10-15 degrees warmer than today / sea surface temps around antartic warmer /tropical conditions extended 10-15 degrees latitude polwards than today / tropical assemblages of forams and coccoliths found in N.Atlantic sed .
      • causes : variations in ocean circulation and ocean heat transport continental position during early tertary , Tethys spanned whole earth .equatorial currents flowed unimpeded around earth several tims ten diverted north and south > pumping of warm equatral waters into high lats > cont. movement = closure of Tethys seaway > redced latitudinal heat transport
      • tertiary period also saw major escalation in orogenic uplift = building of alpine and Himalayan mountain chains , atmospheric circulations and monsoon rains increase rate of weatherin of silicate rocks = removal of co2 from atmosphere = reduce greenhouse-forcing= coolin
      • by quaternary . continental positions similar to those of today = any changes in climate not a result of diferent continental positions , or changes in co2 ou gassing . in QUAT , oxygen isotops analysis in nano fossils in deep sea cores , 2 basic climate states , glacial and interglacial , '' switches between two '' amay be very rapid
    • Late Eocene and Oligocene cooling
      • before 34 MA ice rafted debris in southern ocean > d^18O > considerable and rapid continental ice formation/ climatic deterioration continues> Miocine cooling event (10-15 Ma ) d^18 O record strongly increases due to rapid growth of antartic ice sheet and dee ater coling / ice rafted debris I norwigean sea and variations inplanktoni abundances due to changing sea surface tmp indicates : Northern henispher Mid-latitude glaciation by ca. 2MA (Pliocene)
    • Glacial/interglacial cycles thought to be caused by small variations in the Earth’s orbit around the sun (i.e. Milankovitch cycles), which are then amplified by changes in the Earth’s climate system and atmospheric composition (“greenhouse forcing”) i.e. CO2 variations over past 160ka correlate very well with temperature changes. Amplification due to rapid switches in ocean circulation, changes in ocean productivity, release of methane hydrates from the deep ocean……….???