Palaeoecology

Bioenergy through time andspace

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

ecologygenetics

biogeography

Daisyworld - Gaia in theory!

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

Example: a reef

Several levels of analysispossible: What do the organisms in it

do, and how do theyinteract?

How have those organismsevolved or been replacedthrough time?

How have the functionalinteractions themselvesevolved through time?

Then…

…and now

What has changed?

Atmospheric compositionLandscape dynamics (vegetation)Weathering and runoffHuman activityAll biologically mediated!

What is ecology?

Fundamentally, can be seen as thestudy of how energy is transferred frominitial sources through to biomass andeventual burial or recycling

Ecosystem ecology: the study of natural systems from the standpoint ofthe flow of energy, nutrients and matter.

Organisms treated as “black boxes” and seldom studied directly.

Ecosystems may be modeled as linked compartments among which elementsare cycled at various rates:

photosynthesis moves carbon from an inorganic compartment (air orwater) to an organic compartment (plant)

respiration moves carbon from an organic compartment (organism) to aninorganic compartment (air or water)

Overview

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 outchemical transformations:

Most biological energy transformations are associated with biochemicaloxidation and reduction of C, O, N and S

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, oneproviding energy for the other

Overview

Energy sources

Sunlight - by far the most important(today)

Chemosynthesis - important in somesystems - more important in the past?

Thermal - but (probably) too low gradeto be of use to life

Energy availability

Sunlight - in the PHOTIC zoneChemical energy - in the REDOX zone

Primary productionNEW REGENERATED

Food chain

Terrestrial input

Base of Photic Zone

Exportproduction

upwelling

Nutrient and organic matter cycling in the ocean

Organic matter

Nutrients

Carbon Cycle

Carbon is the “currency” of the globalbiological energy budget. It is passedfrom the atmosphere to organisms byphotosynthesis, and back by respiration.

Palaeoecology

Energy transfer throughorganisms

Ricklefs Figure 7.3

Overview

The carbon cycle

• (1) Biotic carbon exchange

Approximately 85 gigatons* (GT) of carbon enter into balancedassimilatory / dissimilatory transformations each year.

About 2,650 GT of global carbon is in organic matter (livingorganisms plus organic detritus and sediments).

Residence time for carbon in biological molecules = 2,650 GT / 85GT / yr = 31 years

*1 gigaton = 109 metric tons = 1 billion metric tons

The carbon cycle

(2) Ocean-atmosphere exchange

Exchange of carbon across the atmosphere-ocean interface linkscarbon cycles of terrestrial and aquatic ecosystems.

Dissolved carbon in the oceans is 30,000 GT, nearly 50 times morethan that of atmosphere (640 GT).

Net atmospheric flux (assimilation/dissimilation and exchange withoceans) is 119 GT/yr for mean atmospheric residence time (640 GT /119 GT / yr) of about 5 years

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 formationof limestone and dolomite rock.

Turnover of these sediments is far slower than those associated withassimilation/dissimilation or ocean-atmosphere exchange.

Carbonate sediments represent thesingle largest compartment of carbonon planet (18,000,000 GT).

The carbon cycle

Precipitation of calcium and carbon

CO2 dissolves in water to form carbonic acid, which dissociates intohydrogen, bicarbonate and carbonate ions:

CO2 + H2O H2CO3

H2CO3 H+ + HCO3- 2H+ + CO3

2-

Calcium ions combine with bicarbonate ions to form slightly insolublecalcium carbonate, which precipitates:

Ca2+ + CO32- CaCO3

The global energy budget

Humans at present use about 13.5Terawatts of energy = 13.5 x1012 Js-1

= 4.25 x 1020 Jy-1

What about the rest of the planet?

Planet energy cycle

Total radiant energy from sun hitting top ofatmosphere:

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

Humans: important energy players!

If say 10% of plant carbon is availablefor energy input into ecosystems, thenhuman energy use is approximatelyequal to total carbon energy fixation peryear!

Human energy usage may triple in thenext 50 years or so…

Earth as a living planet

Earth

Titan Venus

Mars

Planetary atmospheres

90-97% Nitrogen 0-6% Argon 2-5 % Methane 0.2% Hydrogen

95% CarbonDioxide 2.7% Nitrogen 1.6% Argon 1.3% Oxygen

77% Nitrogen 21% Oxygen 0.93% Argon ~ 1% water(varies)+ methane etc

96% CarbonDioxide 3.5% Nitrogen

Atmosphericcomposition

-180 C-55 C15 C457 CAveragesurfacetemperature

TitanMarsEarthVenus

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

The oxygen cycle

All the oxygen in the atmosphere isreplaced every 2000 years.

Thus, if photosynthesis stopped, all theoxygen in the atmosphere woulddisappear within about 2000 years.

Summary

Life is a major player in shiftingchemicals around the Earth - and theway in which it does it has changedthrough time.

Earth is thus the living planet, first of all!