Earth’s Biosphere

1. Earth’s Biosphere • Interaction of physical processes in Earth’s climate system with biosphere • Results from the movement of carbon

2. Carbon Cycle • Carbon moves freely between reservoirs • Flux inversely related to reservoir size

3. Photosynthesis • Sunlight, nutrients, H2O • Transpiration in vascular plants • Efficient transfer of H2O(v) to atmosphere • Oxidation of Corg • Burning • Decomposition

4. Terrestrial Photosynthesis • CO2 and sunlight plentiful • H20 and correct temperature for specific plants not always sufficient • Biomass and biome distribution controlled by rainfall and temperature

5. Local Influence on Precipitation • Orographic precipitation influences distribution of biomass and biomes • Influences the distribution of precipitation

6. Marine Photosynthesis • H2O, CO2 and sunlight plentiful • Nutrients low (N, P) • Nutrients extracted from surface water by phytoplankton • Nutrients returned by recycling • Upper ocean (small) • Upwelling (high) • External inputs (rivers, winds)

7. Ocean Productivity • Related to supply of nutrients • Nutrient supply high in upwelling regions • Equatorial upwelling • Coastal upwelling • Southern Ocean • Wind-driven mixing • Short growing season • Light limitation

8. Productivity – Climate Link • “Biological Pump” – photosynthesis takes up CO2 and nutrients, plants eaten by zooplankton, dead zooplankton or excreted matter sinks carrying carbon to sediments

9. Export – Removal of Carbon • For every 1000 carbon atoms taken up by phytoplankton • 50-100 sink below 100 m • 10 are exported to depths below 1 km • Stored for millennia • 1 carbon atom is buried in deep sea sediments • Sequestered for eons

10. HNLC • Growth in regions limited by micronutrients (Fe) • High nutrient low chlorophyll (N. Pacific, SO) • Higher production linked with removal of CO2

11. Effect of Biosphere on Climate • Changes in greenhouse gases (CO2, CH4) • Slow transfer of CO2 from rock reservoir • Does not directly involve biosphere • 10-100’s millions of years • CO2 exchange between shallow and deep ocean • 10,000-100,000 year • Rapid exchange between ocean, vegetation and atmosphere • Hundreds to few thousand years

12. Increases in Greenhouse Gases • CO2 increase anthropogenic and seasonal • Anthropogenic – burning fossil fuels and deforestation • Seasonal – uptake of CO2 in N. hemisphere terrestrial vegetation • Methane increase anthropogenic • Rice patties, cows, swamps, termites, biomass burning, fossil fuels, domestic sewage

13. Climate Archives • Four major archives of climate records • Sediments • Ice • Corals • Trees • Each archive has different time span, resolution and ease of dating

14. Understanding Climate Change • Understanding present climate and predicting future climate change requires • Theory • Empirical observations • Study of climate change involves construction (or reconstruction) of time series of climate data • How these climate data vary across time provides a measure (quantitative or qualitative) of climate change • Types of climate data include temperature, precipitation (rainfall), wind, humidity, evapotranspiration, pressure and solar irradiance

15. Contemporary & Past Climate • Contemporary climate studies use empirically observed instrumental data • Temperature records available from central England beginning in the 17th century • Period traditionally associated with instrumental records extends back to middle of the 19th century • Climate change from periods prior to the recording of instrumental data • Must be reconstructed from indirect or proxy sources of information

16. Climate Construction from Instrumental Data • Contemporary climate change studied by constructing records (daily, monthly and annual) which have been obtained with standard equipment • Temperature • Rainfall • Humidity • Wind

17. Paleoclimate Reconstructions • Climate varies over different time scales and each periodicity is a manifestation of separate forcing mechanisms • Different components of the climate system change and respond to forcing factors at different rates • To understand the role each component plays in the evolution of climate we must have a record longer than the time it takes for the component to undergo significant change

18. Paleoclimatology • Study of climate change prior to the period of instrumental measurements • Instrumental records span only a fraction (<10-7) of Earth's climatic history • Provide a inadequate perspective on climatic variation and the evolution of the climate today and in the future • A longer perspective on climate variability can be obtained by the study of natural climate-dependent phenomena • Such phenomena provide a proxy record of the climate

19. Paleoclimate Proxy Records • Many natural systems are dependent on climate • It may be possible to derive paleoclimatic information from them • By definition, such proxy records of climate all contain a climatic signal • The signal may be weak and embedded in a great deal of (climatic) background noise • Proxy material acts as a filter, transforming climate conditions in the past into a relatively permanent record • Deciphering that record can often be complex

20. Proxy Data • Proxy material can differ according to • Its spatial coverage • The period to which it pertains • Its ability to resolve events accurately in time • For example • Ocean floor sediments, reveal information about long periods of climatic change and evolution (107 years), with low-frequency resolution (103 years) • Tree rings useful only during the last 10,000 years, but offer high frequency (annual) resolution • The choice of proxy record (as with the choice of instrumental record) depends on physical mechanism under review

21. Factors to Consider • When using proxy records to reconstruct paleoclimates one must consider • The continuity of the record • The accuracy to which it can be dated • Ocean sediments may be continuous for over 1 million years but are hard to date • Ice cores may be easier to date but can miss layers due to melting and wind erosion • Glacial deposits are highly episodic, providing evidence only of discrete events in the past • Different proxy systems have different levels of inertia with respect to climate • Some systems vary in phase with climate forcing • Some systems lag behind by as much as several centuries

22. Steps in Reconstructing Climate • Paleoclimate reconstruction proceeds through a number of stages • The 1st stage is proxy data collection, followed by initial analysis and measurement • This results in primary data • The 2nd stage involves calibration of the data with modern climate records • The secondary data provide a record of past climatic variation • The 3rd stage is the statistical analysis of this secondary data • The paleoclimatic record is statistically described and interpreted

23. Proxy Calibration • The uniformitarian principle is typically assumed • Contemporary climatic variations form a modern analog for paleoclimatic changes • However the possibility always exists that paleo-environmental conditions may not have modern analogs • The calibration may be only qualitative, involving subjective assessment, or it may be highly quantitative

24. Proxy Calibration: An Example • Emiliania huxleyi is one of 5000 or so species of phytoplankton • Most abundant coccolithophore on a global basis, and is extremely widespread • Occurs in all except the polar oceans • Produces unique compounds • C37-C39 di-, tri- and tetraunsaturated methyl and ethyl ketones

25. Emiliania huxleyi Blooms • E. huxleyi can occur in massive blooms • 100,000 km2 • During blooms E. huxleyi cell numbers usually outnumber those of all other species combined • Frequently they account for 80 or 90% of the total number of phytoplankton SeaWiFS satellite image of bloom off Newfoundland in the western Atlantic on 21 July 1999

26. Emiliania huxleyi Makes Alkenones

27. UK’37 Varies with Temperature • Alkenone unsaturation global calibration • UK’37 determined in core top sediment samples • SST from from Levitus ocean atlas • Figure from Muller et al. (1998)

28. Global UK’37 SST Correlation