3.b. pathways and processes which control the cycling of water and carbon vary over time

short term- diurnal changes

significant changes occur within 24h period. lower temps at night= reduced evaporation and transpiration. convectional precipitation, dependent on direct heating of the ground surface by sun= daytime phenomenon, often in afternoon= maximum temps. particularly significant in climatic regions in the tropics where the bulk of precipitation is from convectional storms, flows of carbon vary both diurnally and seasonally. daytime- co2 flows from atmosphere to vegetation. night- flux reversed, no sunlight no photosynthesis and vegetation loses co2 to atmosphere. same for phytoplankton in ocean

short term- seasonal changes

seasons controlled by variation in the intensity of solar radiation. uk- peak june, typical input 800w/m2, dec 150w/m2. evapotranspiration is highest in summer. drier parts= 80% precipitation lost to evapotranspiration. seasonal variation in carbon is month to month changes in net primary productivity of vegetation NPP. middle and high latitudes day length or photoperiod and temp drive seasonal changes in NPP. trees in full foliage= net global flow of co2 from atmosphere to biosphere. atmospheric co2 fall by 2ppm, flow reversed at the end of summer as photosynthesis slows. during growing seasons ecosystems such as the boreal and temperate forests extract huge amounts of co2 from the atmosphere= global impact. oceans phytoplankton are stimulated by photosynthetic activity by rising water temps more intense sunlight and lengthening photoperiod. every year in N Atlantic there is an explosion of microscopic oceanic plant life which starts in march and peaks in mid summer. resulting agal blooms are so extensive

climate record over last million years

highly unstable climate, large fluctuations in global temps at regular intervals. past 400,000= major glacial cycles- cold glacials then warmer inter glacials. cycle last 100,000 years. last glacial 20,000 years ago= temp 5 degrees lower, north and scotland covered by 1km thick ice. warm interglacials= similar to today. longer scale they have been more extreme= average temp 22 degrees 250 mil years ago. affect water and carbon cycles

long term changes- water cycle

glacial: net transfer of water from the ocean reservoir to storage in ice sheets, glaciers and permafrost. sea level falls by 100m, ice sheets and glacier expand= cover around ½ of continental land mass. forests and grasslands destroyed. area covered by vegetation and water stored in biosphere shrinks. tropics= drier and deserts displace large areas of rainforest. lower rates of evapotranspiration during glacial= reduced exchange of water between atmosphere and oceans, biosphere and soils.

long term changes- carbon cycle

glacial: dramatic reduction of co2 in atmosphere. close correlation between temp and atmospheric co2 over past 400,000 years. glacial- maximum co2 conc fall to around 200ppm while warmer inter glacials are 100ppm higher. no clear explanation- possible that excess co2 finds its way from atmosphere to deep ocean. changes in ocean circulation during glacials= nutrients to surface and stimulate phytoplankton growth. they fix large amount of co2 by photosynthesis before dying and sinking to deep ocean where carbon is stored. lower temp= co2 more soluble in surface water. terrestrial biosphere- carbon pool in vegetation sinks as ice sheets advance and occupy large areas. desert expand, tundra replaces forests and grasslands encroach on tropical rainforests. carbon stored in soils will no longer be exchanged with atmosphere. expanses of tundra beyond the ice limit sequester huge amounts of carbon in permafrost. less vegetation= fewer forests= lower temp and lower precipitation, NPP and total volume of carbon fixed in photosynthesis will decline. an overall flowing of the carbon flux and smaller amount of co2 returned to the atmosphere through decomposition

importance of monitoring

given the potentially damaging impact of climate change, accurate monitoring of changes in global air temps, sea surface temps, sea ice thickness and rates of deforestation is essential. relies heavily on satellite technology and remote sensing. continuous monitoring by satellite on a day to day month to month or year to year basis allows changes to be observed on various time scales. using geographical information systems techniques this data can be seen mapped and analysed to shoe areas of anomalies and trends and regions of greatest change