Earth

1
Earths Biosphere

• Interaction of physical processes in Earths
  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
• 10-100s 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 (lt10-7)
  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
UK37 Varies with Temperature

• Alkenone unsaturation global calibration
• UK37 determined in core top sediment samples
• SST from from Levitus ocean atlas
• Figure from Muller et al. (1998)

28
Global UK37 SST Correlation