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

Question 1

what are the short term changes to the water cycle DIURNAL (daily) changes?

Answer 1

lower temps at night = decreases evaporation
- convectional rainfall is dependent on the heating of the land by the sun - a daytime phenomenon - therefore the rain is concentrated in the afternoon in the rainforest

Question 2

what are the short term changes to the carbon cycle DIURNAL (daily) changes?

Answer 2

in the daytime carbon flows from atmosphere to the vegetation (photosynthesis)
- at night, when there is no sun, the flow is reversed - photosynthesis switches off and respiration releases carbon into the atmosphere
- the phytoplankton in the oceans follows the same diurnal patterns

Question 3

what are the seasonal changes to the cycles (short term)?

Answer 3

• variations in the intensity of solar radiation during the year. In the UK the intensity peaks in mid june with 8002/m2 thus evaporation is highest in summer + lowest in winter
• in driest parts of lowland england up to 80% of precipitation in may is lost to evaporation. river flows are at their lowest in later summer

Question 4

what is the month to month variation in cycles?

Answer 4

month-to-month variation in NPP of vegetation in mid and high latitudes due to the changes in day length, and temperature during the year.

Question 5

Short term changes to the foliage?

Answer 5

NPP changes are linked to the amount of foilage, in the northern hemisphere summer there is a net flow of co2 from the atmosphere to the biosphere, causing atmospheric co2 levels to fail.
- in the autumn/winter this flow is reversed as the leaves fall - reducing photosynthesis and increasing decomposition which returns the co2 to the atmosphere
- global / temperate forests extract huge amounts of co2 having an important global impact

Question 6

how does phytoplankton affect marine life - yearly change

Answer 6

in the oceans, phytoplankton is stimulated by photosynthetic activity - rising water temperature and intense sunlight/longer day length. every year in the atlantic there is an explosion of microscopic plant life between march and mid-summer.

Question 7

what are the long-term changes (millions) in stores and flows?

Answer 7

over past million years earth climate = unstable –> large fluctuations in global temps. in the past 400,000 years there have been 4 major glacial cycles. 20,000 yrs ago, at the height of last glacial, avg temp in britian were 5 degrees lower than today.
- longer term, temps have reached 7-8 degrees higher than today
- climatic shifts have major impact on C + W cycles

Question 8

what are the long-term changes to the water cycle (millions)?

Answer 8

• glacial periods - net transfer of water from oceans into storage in the ice sheets, glaciers + permafrost
• as result, sea level falls 100-130 metres globally
• increase in ice sheets + glaciers to cover 1/3 of continental land mass
• as ice sheets grow + advance they destroy forests/grasslands –> area covered by vegetation + water shrinks
• meanwhile climate in tropics becomes dried and grasslands + desert displaces the tropical forests with decreased evaporation + decreased exchange of water between the atmosphere, biospheres + soils
• as so much water is stored as ice the water cycle slows down significantly

Question 9

what are the long-term changes to the carbon cycle? (millions years)

Answer 9

• glacials lead to a dramatic decrease in carbon dioxide in the atmosphere
• temp and co2 have close correlation (carbon –> deep ocean changes in ocean circulation brings nutrients to surface = stimulating photosynthesis - vegetation dies and sinks to bottom of ocean –> where carbon is stored)
• carbon stored in vegetation decreases as ice sheets advance
• deserts increase, tundra replaces temperate forests and grasslands replace rainforests
• so much is covered by ice that the carbon stored in soil is no longer exchanged with the atmosphere
• tundra sequesters huge amounts of carbon in the permafrost. less vegetation, lower temperatures, less precipitation, less NPP and carbon fixed in photosynthesis decreases = leading to overall slowing of carbon cycle