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Expanded of tundra beyond the ice-limit sequester (locking in - absorbing) HUGE amounts of carbon in permafrost.
With LESS vegetation cover:

Fewer forests

Lower temperatures

Lower precipitation

NPP (Net primary productivity) and the total volume of carbon fixed in photosynthesis = will decline.

Implications = overall slowing Of he carbon flux and smaller amounts of CO2 returned to the atmosphere through decomposition.

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This picture shows Europe during the last glacial maximum 20,000 years. Ago

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At all sites, there is an accelerating upward trend in CO₂ levels driven mostly by fossil fuel burning. The main difference between the sites is the amount of seasonal fluctuation in CO₂ levels observed each year. In general, researchers found strong seasonal CO2 fluctuations throughout the Northern Hemisphere and weaker fluctuations near the equator and in the Southern Hemisphere.

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Other changes - occur in terrestrial biosphere.

The carbon pool (in vegetation) shrinks during glacials as the ice sheets advance, then occupy large areas of the continents.

In the process of movement to occupy continents:

Desert expand

Tundra replaces temperate forests

Grasslands encroach on tropical rainforests.

With much of the land surface being buried by ice - carbon stored in soils = will no longer be exchanged with the atmosphere.

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This graph shows temperature and CO2 changes in the past 400,000 years.

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Lower  of evaporation during glacial phases reduce exchanges of water between the atmosphere and the oceans, biosphere and soils.
This together width so much fresh water stored as snow and ice slows the water cycle appreciably

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No clear explanation - drop in atmospheric CO2 during the glacial periods. However, it is possible that excess CO2 finds its way from the atmosphere to the deep ocean. ONE MECHANISM = change in ocean circulation during glacial that bring nutrients to the surface and stimulate phytoplankton growth. PHYTOPLANKTON = fix large amounts of CO2 by photosynthesis during dying and sinking to the deep ocean - where carbon is stored. Lower ocean temperatures = make CO2 more soluble in surface waters.

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The process of photosynthesis causes a reduction in the CO₂ concentration together with the reduction due to the cooling of the southern oceans and this change is opposed by the increase due to the warming of the northern oceans. The annual amplitude - the change observed between May and September of each year - does vary but is not connected to the annual increases.

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However on a longer time scale...global temperatures have been much more extreme.
An example being 250 million years ago, average global temperatures reached 22 C which is at least 7 C to 8 C higher then today.
These climate shifts had a major impact on the water and carbon cycle.

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During warm inter-glacial periods temperatures were similar to those we experience today.

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At times of glacial maxima CO2 concentration levels fall to around 180ppm - while in warmer inter-glacial periods they are 100ppm higher.

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long term -CO2 concentration and temperature relationship

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long term -CO2 concentration and temperature relationship

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During Glacial periods CO2 concentration in the atmosphere decrease dramatically. At times of glacial maxima, CO2 concentrations fall below 180ppm, while in inter-glacial periods the concentration of CO2  are 100ppm higher.

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Maximum CO2 levels were observed in May and minimum CO2 levels were observed in September

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During our recent glacial cycle Scotland, Wales and most of northern England were submerged by ice up to 1km thick.

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Striking feature of carbon Dudley during glacial periods - the dramatic reduction in CO2 (in the atmosphere).

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Flows vary both diurnally and seasonally. In the daytime CO2 flows from the atmosphere to vegetation, but in the night it is reversed. Without sunlight, there is no photosynthesis, causing vegetation to lose CO2 to the atmosphere.

This is the same with phytoplankton in the oceans.

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Long term: In last 400,000 years, there has been 4 major glacials- these consist of a cold glacial followed by an inter glacial and then another cold glacial. 

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Long term: In last 400,000 years, there has been 4 major glacials- these consist of a cold glacial followed by an inter glacial and then another cold glacial. 

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Each glacial cycle lasted around 100,000 years. Our most recent cycle was around 20,000 years ago where annual temperatures in the British isles were 5 C lower then today.

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Seasonal changes with high levels of precipitation lead to increased surface runoff and channel flow. In mountainous regions increased channel flow and run off due to the melting of ice. With large losses of precipitation to evapotranspiration and the exhaustion of soil moisture, river flows in England are normally at their lowest in late summer.

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Long term - water cycle changes in glacial periods.

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Long term - water cycle changes in glacial periods.

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-During glacial and interglacial phases, evapotranspiration rates change. exchange of water between the biosphere, atmosphere, oceans and soils. In glacial periods, temperatures are sub-zero, this causes low flows of water, as water is frozen. this slows the water cycle appreciably

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Lower temperatures at night reduce evaporation and transpiration. Conventional precipitation, dependent on direct heating of the ground surface by the sun, is a daytime phenomenon often falling in the afternoon when temperatures reach a maximum. This is particularly significant in climatic regions where the bulk of precipitation is from conventional storms.