Earth’s Biosphere Interaction of physical processes in Earth’s climate system with biosphere Results from the movement of carbon Carbon Cycle Carbon moves freely between reservoirs Flux inversely related to reservoir size Photosynthesis photosynthesis 6CO2 6 H 2O C6 H12O6 6O2 oxidation Sunlight, nutrients, H2O Transpiration in vascular plants Efficient transfer of H2O(v) to atmosphere Oxidation of Corg Burning Decomposition 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 Local Influence on Precipitation Orographic precipitation influences distribution of biomass and biomes Influences the distribution of precipitation 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) 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 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 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 HNLC Growth in regions limited by micronutrients (Fe) High nutrient low chlorophyll (N. Pacific, SO) Higher production linked with removal of CO2 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 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 Climate Archives Four major archives of climate records Sediments Ice Corals Trees Each archive has different time span, resolution and ease of dating 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 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 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 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 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 climatedependent phenomena Such phenomena provide a proxy record of the climate 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 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 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 Steps in Reconstructing Climate Paleoclimate reconstruction proceeds through a number of stages st stage is proxy data collection, followed The 1 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 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 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 Alkenones as biomarkers • Long-chain (C37-C39) di-, tri- and tetraunsaturated methyl and ethyl ketones (alkenones) found in oceanic sediments 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 Emiliania huxleyi Makes Alkenones 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) Global UK’37 SST Correlation