Water and Carbon cycles

Biogeochemical cycles:

• cycles involving biotic and abiotic components.

• eg = carbon is stored in forests but also in rocks

The water (hydrological) cycle:

• is the continuous transfer of water between the land, atmosphere and oceans

The carbon cycle:

• is the continuous movement of carbon between living organisms and the environment through processes like photosynthesis, respiration, decomposition and combustion.

A systems approach:

• A systems approach simplifies the complexity of life

• it organises and presents complex relationships between the different components of the physical environment

Systems are:

• bounded

• a generalisation of reality (eg used to produce global climate models to predict potential impacts of rising levels of CO2 in the atmosphere)

• have inputs, outputs, stores and flows (about movement of matter or energy)

• are studied at a range of scales - from the local to the global.

Boundary definition:

• the edge of the system

Flow/transfer definition:

• the links or relationships between stores/components that involves the movement of energy or mass

Input definition:

• material or energy that moves into the system

Store/component definition:

• a part of the system where energy/mass is stored or transformed

Output definition:

• material or energy that moves out of the system

Energy definition:

• power or driving force

• in lots of cases this will be from the sun.

Closed system:

Open system:

Dynamic equilibrium definition:

• the balance of inputs and outputs in a system

How dynamic equilibrium can change:

• if one of the inputs or outputs changes and therefore changes the amount in stores, this disrupts the equilibrium.

• in coasts = this could be the balance between erodion and deposition.

• in water cycle = it could be impacted by an increase in the melting of sea ice.

• timescale matters!

Positive feedback: definition

• where the effects of an action are amplified or multiplied by subsequent knock-on effects.

• the effects take us away from dynamic equilibrium

Positive feedback loop in the carbon cycle:

Human burning of fossil fuels:

• increasing atmospheric co2 and other greenhouse gases can raise global temps, melt tundra permafrost and release stored cyrospheric methane and co2.

• raises global temps can increase melting of sea ice and reduce polar albedo and increases solar absorption.

Negative feedback definition:

• where the effects of an action are nulified by its subsequent knock on effects

• the effects take us back towards dynamic equilibrium.

A negative feedback loop applied to the carbon cycle:

Human burning of fossil fuels:

• increasing atmospheric co2 and other greenhouse hases so raises global temps, more evaporation & precipitation so more co2 dissolved in rainwater and then stored, so carbon stores increase and climate cools.

• raises global temps, so encourages more plant growth so plants take in co2, carbon stores increase and climate cools.

The earth as a closed system:

• The Earth could be viewed as a closed system.

• Solar energy is the input into the system which is balanced by the energy radiation back from the Earth.

Sea ice near Kulusuk, Germany:

• inputs = include precipitation and radiation (heat) from the sun.

• stores = water stored in the form of liquid water, snow and ice

• flows = water transferred between the hydrosphere and atmosphere by processes such as evaporation and sublimation.

• positive feedback = warmer temps cause ice melt, which increases exposure of dark surfaces (rock, water) which further increases temps and so on.

• outputs = includes water and dissolved carbon.

What is the hydrosphere?

• Total amount of water on a planet.

• Can be liquid, vapour or ice/frozen.

Liquid hydrosphere:

• In the surface form of oceans, lakes and rivers.

• in the form of groundwater; in wells and aquifers.

Vapour hydrosphere:

• Is most visible as clouds and fog.

Frozen hydrosphere:

• Is made of ice - glaciers, ice caps and icebergs.

• Frozen part of the hydrosphere has its own name - cryosphere.

Water cycle:

• Water moves through the hydrosphere in a cycle.

• Water collects in clouds, then falls to earth in the form of rain or snow.

• This water collects in rivers, lakes and oceans.

• Then it evaporates into the atmosphere to start the cycle all over again.

What is the Lithosphere?

• The Lithosphere is the solid, outer part of Earth, including the brittle upper portion of the mantle and the crust.

The Lithosphere:

• It is bounded by the atmosphere above and the asthenosphere (another part of the upper mantle below).

• Rigid, solid outer layer consisting of the crust and the uppermost mantle. It forms the tectonic plates.

Asthenosphere:

• Semi-molten/viscous layer of the upper mantle directly below the lithosphere.

• It is ductile (capable of flowing slowly), allowing the rigid lithospheric plates to move over it.

Oceanic Lithosphere:

• Denser, thinner and constantly created/destroyed at plate boundaries.

Continental Lithosphere:

• Less dense, thicker, older and cannot be subducted.

Tectonic activity and boundaries:

• The lithosphere is broken into major plates that collide, pull apart, or slide past each other at plate boundaries.

Plate movement drivers:

• Driven by mantle heat (thermal energy), which powers mantle dynamics like convection currents.

Landforms and Hazards:

• Plate interactions form deep ocean trenches, fold mountains (orogeny), rift valleys and mid ocean ridges, while causing seismic and volcanic hazards ) earthquakes and volcanoes).

Crustal thinning in Lithosphere:

• The lithosphere is thinnest at divergent margins (rift valleys and ocean ridges).

Interconnected earth system:

• The lithosphere interacts with the atmosphere (air), hydrosphere (water), cryosphere (ice) and biosphere (life) to shape Earths physical landscape.

Pedogenesis (Soil Formation):

• The Pedosphere (soil) forms when weathered/eroded lithospheric rock mixes with biological organic matter.

Topography and Climate:

• High altitude lithospheric landforms (like mountain ranges) alter local atmospheric conditions, creating microclimates and influencing biological adaption.

Atmosphere Composition and Structure:

• Gas composition = composed primarily of 78% nitrogen and 21% oxygen.

• Trace gases make up the remaining 1%, including greenhouse gases like CO2 and water vapour, which drive atmospheric energy budgets and the water cycle.

Atmospheric Layers:

• Troposphere

• Stratosphere

• Upper layers (mesosphere, thermosphere, exosphere)

Troposphere:

• The lowest & densest layer (7 - 15km high, thickest at equator) containing 75%-80% of atmospheric mass and almost all water vapour.

• This is where all weather, cloud formation and hydrological cycle interactions occur.

• Temp decreases with altitude (environmental lapse rate)

Stratosphere:

• Extends up to 50km.

• Contains the ozone layer, which absorbs incoming solar UV radiation, shielding earth and causing temps to increase with altitude.

What is the biosphere?

• The biosphere encompasses all living organisms on earth and functions as an open system powered by solar energy.

• It overlaps with the lithosphere, atmosphere and hydrosphere.

Nutrient cycling and flow of energy:

• Photosynthesis acts as the primary input converting light energy into biomass.

• food webs and decomposers recycle nutrients through organic and inorganic stores (soil, ocean, atmosphere)

Human impacts and carbon/water cycle distributions:

• Anthropogenic disturbance = deforestation and fossil fuel combustion release stored carbon, increasing atmospheric CO2, reducing carbon sequestration, and driving global climate change.

Spatial inequity:

• Climate change and biodiversity loss disproportionately impact populations in the global south, despite higher per capita emissions, originating in the global north.

Ecosystem Management and sustainability strategies:

• UNESCO biosphere reserves = designed to balance biodiversity conservation with sustainable socio-economic development via local community involvement.

Indigenous and community led governance:

• Management strategies that actively involve local and indigenous populations show higher rates of success and biodiversity retention compared to top-down or exclusionary conservation schemes.

What is the cryosphere?

• The cryosphere is the frozen water part of the Earth system.

The cryosphere as a water store:

• definition = all portions of Earth’s surface where water is in solid form.

• terrestrial ice stores = includes continental ice sheets (Antarctica and greenland), ice caps, valley glaciers, permafrost and shelf ice.

• oceanic/surface water ice stores = includes sea ice (arctic/antarctic/ and frozen lakes/ rivers)

Cryosphere role in Earth systems & climate regulation:

• Albedo Effect = high reflectively (albedo) of snow and ice reflects incoming solar radiation back into space, helping regulate global temps.

Cryosphere as a climate indicator:

• Highly sensitive to global temp changes, making cryospheric melt a key early indicator of climate change.

Positive feedback:

• Warmer temperatures cause ice melt, which increases exposure of dark surfaces (rock, water) which further increases temperature and so on.

Inputs in an environment:

• Include precipitation and radiation (heat) from the sun.

Flows in an environment:

• Water transferred between the hydrosphere and atmosphere

Stores in an environment:

• Water stored in the form of liquid water, snow and ice

Outputs in an environment:

• Includes water and dissolved carbon

Flow/ Transfer:

• A form of linkage between one store/component and another that involves movement of energy or mass.

Input:

• The addition of matter and/or energy into a system

Store/Component:

• A par of the system where energy/mass is stored or transformed

Positive feedback:

• Where the effects of an action are amplified or multiplied by subsequent knock-on or secondary effects

Negative feedback:

• Where the effects of an action are nullified by its subsequent knock-on effects

Closed system:

• These have transfers of energy both into and beyond the system boundary but not transfer of matter.

Open system:

• These are where matter and energy can be transferred from the system across the boundary into the surrounding environment.

Equilibrium:

• A balance between input and outputs.

The Water Cycle and Water Stores:

1) The heat from the sun heats the warmer.

2) Evaporation occurs and water vapour increases.

3) Condensation occurs to form clouds.

4) Precipitation occurs as clouds get bigger = causes rain, hail, snow, sleet.

5) Interception of rainfall by vegetation

6a) Evapotranspiration occurs (the total way water moves from the ground and plants up into the sky as invisible water vapor)

6b) Stemflow downwards.

7) Surface run off

8) Infiltration - water enters the soil

9) throughflow - the movement of water through/inside soil.

10) percolation - the downward movement of water through soil and porous rock layers driven by gravity.

11) Groundwater flow

Oceanic Water:

• contains dissolved salts - salts allow it to stay as liquid water below 0*c.

• the change in pH in oceanic water is linked to the increase in atmospheric carbon and has impact on marine ecosystem.

Cryospheric Water:

• Ice Sheets = 2 major ice sheets mostly in greenland and antarctica.

• Last ice advance - ice sheets in NA, NE and Argentina.

• Sea Ice = Arctic ocean frozen and waters surrounding Antarctica. Forms when water in oceans is cooled to temps below freezing.

• Ice sheets over 1000s yrs, layers of snow pile up into thick masses of ice, growing thicker and denser as weight of new snow compresses old snow - are in constant movement.

Ice Shelves:

• Platforms of ice that form where ice sheets and glaciers move out into the oceans.

Ice caps:

• Thick layers of ice on land <50,000 km², usually in mountainous area, dome-shaped and centred over highest point of upland area and flows outwards.

Alpine glaciers:

• Thick masses of ice found in deep valleys or in upland hollows.

• Most valley glaciers are fed ice to form ice caps/smaller corrie glaciers

Permafrost:

• As ground (soil or rock and included ice or organic material) that remains below or at 0*c for at least 2 consecutive years.

• Most permafrost existing today formed during cold glacial periods - Holocene (last 10000 years), 2nd part of Holocene (last 6000 yrs) and some during Little Ice Age (400 - 150 yrs ago)

Climate Change:

• Permafrost has begun to melt as climate warms.

• This melting is releasing large amounts of carbon dioxide and methane, affecting global climates

Types of Terrestrial Water:

• Not that important to know = Rivers, Lakes

• Important = Wetlands, Groundwater, soil water, biological water

Rivers and lakes:

• Rivers = store and transfer water. they transfer water from the ground, from soils and from the atmosphere to a store.

• Lakes = collections of fresh water found in hollows on the land surface. Only a lake if greater than 2 hectares.

Wetlands:

• Areas of marsh, peatland or water. Doesn’t matter if its natural/artificial/permanent/temporary. With water that is static or flowing where there is lots of vegetation.

• Fosters unique soils and adapted biodiversity.

• Provides vital functions like flood control, water purification and carbon storage.

Groundwater:

• Fills underground rock and soil pore spaces below water table.

• Cycles naturally through surface recharge and spring decharge, but stores rapidly shrinking due to agri over extraction

Soil Water:

• Help with air in earth’s unsaturated upper layer, driving key biological and hydrological processes.

• it regulates heat and moistue exchange (evaporation/transpiration), directly influencing runoff, slope stability and weather.

Biological Water:

• Stored in biomass (vegetation/trees, minimal in animals), varying globally from high in rainforests to low in deserts.

• trees absorb water via roots and release it through transpiration, regulating local climates - vegetation loss can lead to deforestation.

Atmospheric Water:

• Exists mainly as invisible vapour that regulates temps, holding more moisture in warm tropical air than cold polar air and creating a positive feedback loop that drives further global warming

• clouds form when cooling or adding vapour saturates lower atmospheric air, producing visible water droplets or ice crystals that fall as rain when large enough.

Phase changes and latent heat:

• 3 states of matter = water vapour (gas), liquid water, solid water (ice)

• energy transfers = phase changes involve the transfer of latent heat.

• Evaporation, melting and sublimation absorb latent heat, cooling surrounding environment.

• Condensation, freezing and deposition release latent heat, warming atmosphere.

• Latent heat transfers drive major atmospheric processes, including cloud formation and precipitation.

Evaporation:

• Evaporation = solar radiation heats liquid water on surfaces/land, causing a state change to water vapour

• evaporation rates increase with high solar energy, high water availability, high air temperatures (Warmer air holds more vapour) and low air humidity.

Transpiration:

• Plants draw up groundwater and release vapour through leaf pores (stomata).

• Plant canopies also intercept rainfall, allowing direct evaporation before water reaches the soil.

Condensation and cloud formation:

• Dew point = As air cools, its capacity to hold water vapour decreases until it becomes saturated at its dew point temp → triggering condensation.

• Condensation Nuclei = Vapour requires micro-particles (dust, salt, smoke) or cool surfaces to condense onto

• Cooling mechanisms

Cooling mechanisms:

• Constant volume cooling = Occurs when warm, moist air moves over cold ground (advection) or via terrestrial radiation loss on clear winter nights

• Adiabatic cooling = Occurs as rising air expands under lower atmospheric pressure. Driven by orographic relief uplift (forced over hills), frontal systems (Warm air forced over denser cold air) or convectional heating (surface heating causes air to rise).

Accumulation vs Ablation:

• Water storage in the cryosphere depends on the mass balance between ice addition (accumulation) and loss via melting/sublimation (ablation)

Quaternary Glaciation:

• During glacial periods over the last 2.58 million years, expanded cryospheric stores caused global sea levels to drop by approximately 120m, disrupting standard hydrological transfers.

Interglacials & Permafrost:

• Interglacial periods feature ablation exceeding accumulation, restoring water to oceanic stores.

• Permafrost develops where low air temperatures freeze sub-surface soil and groundwater.

Total Global Water:

• Oceans 96.6%

• Fresh Water 2.5%

• Other Saline 0.9%

Total Freshwater:

• Glaciers, Ice caps, Ice sheets 68.7%

• Groundwater 30.1%

• Surface/other 1.2%

Surface water and other fresh water:

• Ground ice and permafrost 69%

• Lakes 20.9%

• soil water 3.8%

• swamps and marshes 2.6%

• rivers 0.44%

• living things 0.26%

• atmosphere 3%