climate homeostasis

1. Palaeoecology
Bioenergy through time and
space

2. Structure of the Biosphere
genes
individuals/colonies
communities/
ecosystems
provinces
realms
Gaia??
Inputs Timescale
Radiation/mutagens
weather
climate/anthropogenic
longterm climate,
oceanic circulation
plate tectonics
solar output, style of tectonics
Instant-years
seasonal
Decades - 100 yrs
2 Kyr - 1 Myr
300 Myr
109 yr
ecologygeneticsbiogeography

3. Daisyworld - Gaia in theory!

4. Palaeoecology
 Ecology: from Greek “oikeia” and “logos” =
the study of housekeeping.
 Palaeoecology can be seen as two things:
 Ecology in the past - how past organisms lived
 Evolution of ecology - how ecological systems
have evolved

5. Example: a reef
 Several levels of analysis
possible:
 What do the organisms in it
do, and how do they
interact?
 How have those organisms
evolved or been replaced
through time?
 How have the functional
interactions themselves
evolved through time?

6. Then…

7. …and now

8. What has changed?
Atmospheric composition
Landscape dynamics (vegetation)
Weathering and runoff
Human activity
All biologically mediated!

9. What is ecology?
Fundamentally, can be seen as the
study of how energy is transferred from
initial sources through to biomass and
eventual burial or recycling

10. Ecosystem ecology: the study of natural systems from the standpoint of
the flow of energy, nutrients and matter.
 Organisms treated as “black boxes” and seldom studied directly.
 Ecosystems may be modeled as linked compartments among which elements
are cycled at various rates:
 photosynthesis moves carbon from an inorganic compartment (air or
water) to an organic compartment (plant)
 respiration moves carbon from an organic compartment (organism) to an
inorganic compartment (air or water)
Overview

11. Overview
Cycling of elements and energy flux:
 chemical elements are reused repeatedly
 energy flows through the system only once and some energy is lost
in all coupled redox reactions.
Energy transformations and element cycling are linked.
Organisms play important roles in cycling of elements when they carry out
chemical transformations:
Most biological energy transformations are associated with biochemical
oxidation and reduction of C, O, N and S

12. Assimilatory processes:
 incorporate inorganic forms of elements into organic forms,
requiring energy
 example: photosynthesis (reduction of carbon)
Dissimilatory processes:
 transform organic forms of elements into inorganic forms,
releasing energy
 example: respiration (oxidation of carbon)
Assimilatory and dissimilatory processes are often linked, one
providing energy for the other
Overview

13. Energy sources
Sunlight - by far the most important
(today)
Chemosynthesis - important in some
systems - more important in the past?
Thermal - but (probably) too low grade
to be of use to life

14. Energy availability
Sunlight - in the PHOTIC zone
Chemical energy - in the REDOX zone

17. Primary production
NEW REGENERATED
Food chain
Terrestrial input
Base of Photic Zone
Export
production
upwelling
Nutrient and organic matter cycling in the ocean
Organic matter
Nutrients

18. Carbon Cycle
Carbon is the “currency” of the global
biological energy budget. It is passed
from the atmosphere to organisms by
photosynthesis, and back by respiration.

19. Palaeoecology
Energy transfer through
organisms

20. Ricklefs Figure 7.3
Overview

21. The carbon cycle
• (1) Biotic carbon exchange
 Approximately 85 gigatons* (GT) of carbon enter into balanced
assimilatory / dissimilatory transformations each year.
 About 2,650 GT of global carbon is in organic matter (living
organisms plus organic detritus and sediments).
 Residence time for carbon in biological molecules = 2,650 GT / 85
GT / yr = 31 years
*1 gigaton = 109 metric tons = 1 billion metric tons

22. The carbon cycle
(2) Ocean-atmosphere exchange
 Exchange of carbon across the atmosphere-ocean interface links
carbon cycles of terrestrial and aquatic ecosystems.
 Dissolved carbon in the oceans is 30,000 GT, nearly 50 times more
than that of atmosphere (640 GT).
 Net atmospheric flux (assimilation/dissimilation and exchange with
oceans) is 119 GT/yr for mean atmospheric residence time (640 GT /
119 GT / yr) of about 5 years

23. The carbon cycle
(3) Precipitation and sedimentation of carbonates
Precipitation (and dissolution) of carbonates occurs in aquatic systems.
Precipitation (as calcium and magnesium carbonates) leads to formation
of limestone and dolomite rock.
Turnover of these sediments is far slower than those associated with
assimilation/dissimilation or ocean-atmosphere exchange.
Carbonate sediments represent the
single largest compartment of carbon
on planet (18,000,000 GT).

24. The carbon cycle
Precipitation of calcium and carbon
CO2 dissolves in water to form carbonic acid, which dissociates into
hydrogen, bicarbonate and carbonate ions:
CO2 + H2O  H2CO3
H2CO3  H+ + HCO3
-  2H+ + CO3
2-
Calcium ions combine with bicarbonate ions to form slightly insoluble
calcium carbonate, which precipitates:
Ca2+ + CO3
2-  CaCO3

25. The global energy budget
Humans at present use about 13.5
Terawatts of energy = 13.5 x1012 Js-1
 = 4.25 x 1020 Jy-1
What about the rest of the planet?

26. Planet energy cycle
 Total radiant energy from sun hitting top of
atmosphere:
 Total hitting surface (51%) = 88 000 TW
 From this, total of 104.9 x109 Gt of C are fixed
by plants every year
 = approx 130 TW fixed by plants, ie total
energy fixed by plants a year = 4.1 x 10 21 Jy-1

27. Humans: important energy players!
If say 10% of plant carbon is available
for energy input into ecosystems, then
human energy use is approximately
equal to total carbon energy fixation per
year!
Human energy usage may triple in the
next 50 years or so…

28. Earth as a living planet
Earth
Titan Venus
Mars

29. Planetary atmospheres
90-97% Nitrogen
0-6% Argon
2-5 % Methane
0.2% Hydrogen
95% Carbon
Dioxide
2.7% Nitrogen
1.6% Argon
1.3% Oxygen
77% Nitrogen
21% Oxygen
0.93% Argon
~ 1% water
(varies)
+ methane etc
96% Carbon
Dioxide
3.5% Nitrogen
Atmospheric
composition
-180 C-55 C15 C457 CAverage
surface
temperature
TitanMarsEarthVenus

30. Earth’s strange atmosphere
Note the large amount of oxygen…
…and the chemically unstable mix of
gases (e.g. Oxygen plus Methane)
Suggests thermodynamic disequilibrium

31. The oxygen cycle
All the oxygen in the atmosphere is
replaced every 2000 years.
Thus, if photosynthesis stopped, all the
oxygen in the atmosphere would
disappear within about 2000 years.

32. Summary
Life is a major player in shifting
chemicals around the Earth - and the
way in which it does it has changed
through time.
Earth is thus the living planet, first of all!