History of Earth s climate Content Background reading: D. Hartman Chapter 8 and 11 B. Saltzmann: Dynamical Paleoclimatology F. Ruddiman: Earth s Climate -History of Earth s Climate -Past Climate forcing mechanisms -Types of observational records Roderik van de Wal http://www.staff.science.uu.nl/~wal00105/climdyn/climdynuu.html r.s.w.vandewal@uu.nl (320.000 yr) Space and time scales 10 12 Rationale (3200 yr) (0.32 yr) Why study past climates? Provides clues on how the climate system works. Past is the key to the future Gives perspective on range of climate change possible. (variability of the system) height of the tropopause radius of the earth 1
Geological Hymalayan calendar Background Paleo-climatology Age of Mammals Alpine Rockies Age of Dinosaurs Sea-level Breakup Pangea climate proxy Final assembly Pangea Consolidation continents δ180 time? Earliest known life (~3500) dating Formation of Earth (~5000) Forcing Mechanisms for the Climate Example of different forcings *Variations in solar forcing: -Solar constant -Earth Orbit Eccentricity (~400 and 100 ka) Obliquity (~41 ka) Precession (~19, 23 ka) *Continental geography and topography Oceanic gateway location and bathymetry *Concentration of atmospheric greenhouse gases *Volcanic activity De Conto and Pollard 2003 2
Surface Ocean Circulation Surface Ocean Circulation 65 million years ago Today Cretaceous model runs Red:CT1250 Green:CT2500 Black data δ 18 O Dotted:seasons psu T 3
Proxies Instrumental records http://www.ipcc.ch/ Historical records Historical records Written or oral accounts of past events Problem: Likely biased to extreme events How to link these records to climate parameters; temperature, precipitation, wind. transfer functions? Type of data: Agricultural Weather diaries Ship logs Flooding information Ancient art and cultures etc Rock painting Tassili-N-Ajjer, Southern Algeria, ±5000 BP Sea ice occurrence in months per year on the northern tip of Iceland Vikings in Greenland 980-1350 AD 4
Proxy Records Surface biological and geomorphological: Tree rings Corals (Marine) Shorelines Subsurface, cores: Marine and lake sediment cores Ice cores Analyses: Non-isotopic stratigraphic analyses Non-isotopic geochemical methods Isotopic methods Surface proxi evidence: biological Biological entities that exhibit annual layering tree rings corals molluscan shells Corals Information on water temperature, salinity, sea level Shells Information on temperature, day length Tree rings Example: Tree rings Very well dated by counting rings and cross matching of records Information in width, structure and isotopic contents Growth rate proportional to temperature and moisture availability Information on temperature, precipitation and soil moisture 5
Surface proxi evidence: Geomorphological Information in the landscape itself Surface geomorphological evidence marine shorelines lake shorelines soils ice and glacier signatures Shorelines Marine shorelines Information in coastal features, reef growth Information on sea level, ice volume Lake shorelines Information in level and sediments Information on temperature, precipitation, evaporation, runoff 0 kyr Soils 6 kyr 400-kyr Eccentricity minimum Obliquity Ancient soils Information in type of soil on temperature, precipitation, drainage 100-kyr Eccentricity minimum Precession minimum Precession maximum Glaciers and ice sheets: Information in terminal position Information on extent of glaciers and area of ice sheets Hilgen, pers. Com. Sapropel-marl cycles of late Miocene age (Gibliscemi section, Sicily, Italy) 6
Marine Cores Marine and lake cores The Cenozoic Isotopic Record from Zachos et al., 2001 Fossil pollen (biological, terrestrial): Information in type and concentration Information on vegetation, temperature, precipitation, soil moisture Eocene-Oligocene Transition: δ18o shift of ~0.8 in ~50 kyr Mg/Ca record shows this is mostly due to ice volume, not deep-water temperature (Lear et al., 2000) Sediments (marine): Information in: Accumulation rates Fossil plankton and benthic types Mineralogical composition Information on wind direction, SST + salinity, sea ice extent, global ice volume, bottom water temperature, chemistry and water flux. Other dated evidence from circum-antarctic sediments: Ice-Rafted Debris Clay mineralogy Challenged recently Science 2009 A high latitude SST (composite) Bottom line E-O transition not just inception also cooling Ice cores Information in ice itself, air bubbles in the ice and empty borehole Oxygen isotope concentration Layer thickness Mechanical + electrical properties of the ice Dust, trace elements concentration Chemical composition of air bubbles Temperature and deformation borehole Information on temperature, accumulation, chemical composition atmosphere 10 m 120 m 550 m (from R. Mulvaney) 7
Example: Ice cores Type of analyses Non-isotopic stratigraphic analyses Non-isotopic geochemical methods Isotopic methods Nonisotopic stratigraphic analyses Deposition of sediments in oceans and lakes which consolidate into layered sedimentary rock Surface exposed layering Marine and lake cores Ice sheets Physical indicators Drainage from size material Glacial extent from ice rafted debris Wind and aridity from deposition of dust and ashes Paleobiological indicators Pollen and spores Imprints of plant fossils Bone material large animals Calcerious or siliceous shells of marine organisms Non-isotopic geochemical methods Cadmium concentration Indirect method which gives information on deep ocean circulation Greenhouse gasses in trapped air in ice cores Information on greenhouse gasses in the atmosphere over period of 100-800 kyr Dust layers in ice cores Chemical and biological constituents of these layers give information on wind, aridity, ocean currents 8
Precambrian Why stable isotopes? * * Natural concentrations are constant Differences between reservoirs and phases as a result they can be used as tracers Physical and chemical processes influence the isotope ratio (fractionation) Examples oxygen: 16O, 18O hydrogen: H, 2H = D Oxygen: 18O/16O, Hydrogen: D/H Carbon: 13C/12C Archean 4.5-2.5 Ga Development atmosphere, ocean, continents Primary atmosphere Solar nebula removed by solar winds (less noble gases) Secondary atmosphere Outgassing (volcanic eruptions) H2O, CO2, N O2 from life (3.5 Ga) Ocean forms 0.57 Ga Earliest known life (~3500) 4.5 Ga Info lost due to erosion Archean 4.5-2.5 Ga Continents Crust formation 4.3-3.8 Ga (cooling) Micro continent scale landmasses, small plates 3.8-2.5 Ga Large continents, large plates 2.5 Ga (changes in interior thermal regime) Climate 20-30% lower solar luminosity CO2 concentration 30-300 times present value Water on continents Evidence of life in combination with CO2 concentrations constrain temperature to <60 C at 4.2 Ga (present 15 C). First evidence of glacial conditions 2.7 Ga 9
Proterozoic 2.5-0.57 Ga Evidence for low latitude glaciation 2.7-2.3 Ga 0.9-0.6 Ga Questions: Why glaciation? Snul low, CO2 Low? Why moderate climate between 2.3 0.9 Ga? Major tectonic events: Super continent Rodinia breaks up to form Gondwanaland and Laurasia North America South America Afrika Eurasia Australia Paleozoic Climates on super continents Formation Pangaea 0.2 Ga North America South America Afrika Eurasia Australia 0.57 Ga General climate knowledge: Life Water Paleozoic 0.57-0.23 Ga Generally mild with 2 major glaciation events 0.44-0.41 0.33-0.23 Sea level variations NOT glacio-eustatic Variations in tectonic activity (ocean ridges) Cambrian 0.57-0.46 Ga North America South America Afrika Eurasia Australia Knowledge still limited (no plant life yet) Relatively warm period Sea levels high (enhanced volcanic activity after break up of Rodinia) CO2 estimates 10 times present value 10
Late Ordovician 0.44-0.41 Ga North America South America Afrika Eurasia Australia Mid paleozoic 0.41-0.33 Ga North America South America Afrika Eurasia Australia First period with glacial evidence: Sahara desert, located at south Pole. CO 2 levels still high (10 times), in contrast to pleistocene glaciation indicating low CO 2 values in glacial times. Location pole Transition No evidence for glaciation Drop in sea level restricts ocean circulation Increase in seasonal cycle of temperature over land Expansion of plant life affects climate decrease surface albedo decrease in CO 2 change in hydrological cycle Paleozoic glaciation 0.33-0.23 Ga Glaciation triggered by uplifting of Australia and South America, extend similar to Pleistocene North America South America Afrika Eurasia Australia Paleozoic glaciation 0.33-0.23 Ga Sea level variations now linked to glacial extend Removal of ice sheet could have happened very quick Characteristic time scale of variations is ~400 000 yrs, suggesting orbital insolation changes Massive coal deposition Final formation of Pangea North America South America Afrika Eurasia Australia 11
0.065 Ga 0.2 Ga Mesozoic Break up of Pangea Age of the Dinosaurs Mesozoic 0.33-0.065 Ga Extremely continental climates, large seasonal variations Temperature same range as present, but warmer Salt deposits indicate very arid conditions CO 2 4-6 times higher Break up of Pangea starts 140 Ma Regional seas enhance precipitation regionally Some evidence in orbital induced variations in monsoon intensity North America South America Afrika Eurasia Australia Cretaceous 136-65 Ma Late Cretaceous Evidence for mid- and high latitude warmth, Antarctica still ice free? Poles 20 degrees warmer than P-D? Explained by Changes in land-sea distribution Changes in ocean heat transport Higher levels of CO 2 Ends with a big bang! North America South America Afrika Eurasia Australia End Cretaceous/Mesozoic 65 Ma K-T Boundary clay deposits marked by anomalously high iridium content ~75% of all living species became extinct Evidence suggests some species earlier than 65 Ma Cycles of extinction? 12
The end of the Cretaceous / Mesozoic 65 Ma Evidence (high iridium content) suggests an asteroid impact Diameter of ~ 10 km Likely impact site near Yucatan Peninsula in Gulf of Mexico The end of the Cretaceous / Mesozoic 65 Ma Nitric acid production Water pollution Reduction ozone Burning vegetation Shock waves Tsunami s Dust in stratosphere Summary Not much knowledge on the early climate history of the Earth Large climate variations Increasing knowledge towards the present Decrease in temperature, CO 2, sea level Interesting questions arise Faint Young Sun paradox (S 0 and CO 2 ) Mild conditions 2.3-0.6 Ga (??) High CO 2 during Ordovician glaciation 0.44-0.41 Ga (Location pole) Small meridional gradient in warm climates Pleistocene glacial variability forcing (Orbital) Summary 3 types of records: Instrumental Historical Paleoclimatological Different types of records have their own specific problems Continuity Length, period open to study Accuracy Sampling interval Dating of records is crucial Correct transfer functions necessary 13
What did we learn? *Background concept of paleoclimatology transfer function/dating problem *Geological calendar *Forcing mechanisms *Concept of proxies biological,tree rings, shore lines, marine sediments, ice cores 14