Recycling of the elements

Importance of Carbon All life is based on carbon CO2 important greenhouse gas Regulates ocean acidity Transfer to sedimentary rocks keeps atmosphere oxygen-rich

GLOBAL CARBON CYCLE Terrestrial and marine processes Biologic and non-biologic Tens of years to millions of years

TERRESTRIAL ORGANIC CARBON CYCLE

TIME SCALES Years to decades Millions In atmosphere Photosynthesis Decomposition Millions Burial and lithification in marine sediments

SHORT TIME SCALES CO2 removed from atmosphere via photosynthesis Returned via respiration & decomposition Methane released from soils Some terrestrial organic carbon buried in sedimentary basins or brought to sea Decomposition in ocean releases carbon Some organic matter is buried in marine sediments

LONGER TIME SCALES Organic matter lithified (mostly shales) If organic matter high enough, fossil fuels may form Tectonic uplift exposes rocks to weathering, organic matter oxidizes, CO2 produced and reenters the atmosphere

RESERVOIR DYNAMICS HOW DOES THIS SYSTEM OF RESERVOIRS RESPOND TO PERTURBATIONS?

SYSTEMS APPROACH Atmosphere is a reservoir of carbon Reservoirs are temporary repositories Size changes in response to inflow/outflow If atmospheric concentration remains the same (that is - inflow=outflow) system is at steady state

SYSTEMS APPROACH System not at steady state – anthropogenic disturbances have caused a steady rise in CO2 For steady state to be achieved, couplings that link reservoir size to inflow/outflow must exist A negative feedback loop exists – CO2 fertilization As CO2 increases, photosynthesis increases, which causes CO2 to decrease

CO2 FERTILIZAITON TERRESTRIAL BIOTA TEND TO STABILIZE ATMOSPHERIC CO2 LEVELS

SHORT-TERM TERRESTRIAL ORGANIC CARBON CYCLE

SHORT-TERM MARINE ORGANIC CARBON CYCLE Producers – phytoplankton Top 100 meters – sufficient light for photosynthesis Gas exchange with atmosphere Consumers – zooplankton Organic matter settles to bottom Only 1% makes it to the bottom Decomposers recycle nutrients 0.1% of organic matter that settles ends up in the sediment Decomposition releases CO2 & nutrients (needed at surface)

THE MARINE BIOLOGICAL PUMP

RESULT – BIOLOGIC PUMP & THERMOHALINE CIRCULATION DO concentrations minimum due to aerobic decomposers DO increases with depth due to thermohaline circulation Surface waters depleted of C & nutrients due to photosynthesis and sinking Decomposers release nutrients, but use up oxygen

LONG-TERM ORGANIC CARBON CYCLE Geologic processes the important controls on atmospheric CO2 on longer time scales

CARBON LEAKS & OXYGEN REPLENISHMENT Buried organic carbon is a leak from the short-term organic carbon cycle Maintains atmospheric O2 For every carbon atom that enters the sedimentary rock reservoir, one oxygen molecule is left behind

INORGANIC CARBON CYCLE

REMOVAL OF CO2 The net effect of CaCO3 weathering on land and CaCO3 precipitation in the ocean is zero Combining silicate weathering on land and carbonate precipitation in the sea leads to a net conversion of atmospheric CO2 to solid CaCO3 Net outflow of CO2 from the atmosphere A reduction in atmospheric CO2 creates a concentration gradient and CO2 will diffuse from the oceans to the atmosphere There must be a return flux of CO2 to offset this outflow There is …

THE CARBONATE-SILICATE GEOCHEMICAL CYCLE Plate tectonics provides return flux of CO2 via metamorphic and volcanic CO2 inputs to the atmosphere

SHAL WE BECOME MARS? Without this balance between inflow and outflow of CO2, it would be quickly depleted and Earth would soon freeze But, how is this balance maintained?

LONG-TERM FEEDBACKS IN THE CARBONATE-SILICATE CYCLE THE FEEDBACK TENDS TO STABILIZE EARTH’S CLIMATE AGAINST PERTURBATIONS

THE PHOSPHORUS CYCLE

THE PHOSPHORUS FEEDBACK LOOP

THE NITROGEN CYCLE