Friday, May 04, 2007

Quantification of the Biosphere, biomass forcing the hydrological cycle.

The biosphere is the area from the top of the trees, to several metres below the ground level on the terrestrial surface. Whilst life extends to the sea bottom inhabited by chemotropic organisms ,most life in the ocean is in the photic zone of the top 200m.

According to recent estimates the planetary biomass is 10*28 organisms ,most are unicellular micro-organisms. With the earths surface being ~500million km2 this means there is around 2x10*7 organisms per cm2.With the thickness of the biosphere being equal to the photic zone (200m) 10*3 organisms populate each centimeter of this layer, or 10*3 organisms for each cm3 of the geographical surface.

Quantification of the living biomass has increased vastly in recent times rising from 1000gt to 10,000gt..This means (if we scale) that each 1cm2 of the planetary surface contains 0.001g-0.01grams of living matter(biomass)On the terrestrial biosphere this is 1.-2 magnitudes higher in some areas. This thin film of living substance during photosynthesis produces around the same mass of matter each year. Over a period of 1000 years this equates to a layer of around 1m ,and over 1 million years a layer of more then 1 km. One gram of living matter requires the transpiration of 100-1000g of water, which is released into the atmosphere

The living biomass is distributed non uniformly being several magnitudes higher on land then in the ocean ,and several magnitudes higher in the forests. Taking into account the leaf area, we can assume the leaf biomass is 4 times that of other land areas Therefore land and forest is an important part of the hydrological cycle.

Buermann et al have an interesting paper entitled The changing carbon cycle at Mauna Loa Observatory .

The seasonal cycle of atmospheric CO2 at the MLO, with a maximum at the beginning of the growing season (May) and a minimum at the end of the growing season (September/October), records the "breathing" of the northern hemisphere (NH) biosphere, that is, the seasonal asynchrony between photosynthetic drawdown and respiratory release of CO2 by terrestrial ecosystems


The amplitude of the CO2 seasonal cycle at the Mauna Loa Observatory (MLO) increased from the early 1970s to the early 1990s but decreased thereafter despite continued warming over northern continents. Because of its location relative to the large-scale atmospheric circulation, the MLO receives mainly Eurasian air masses in the northern hemisphere (NH) winter but relatively more North American air masses in NH summer. Consistent with this seasonal footprint, our findings indicate that the MLO amplitude registers North American net carbon uptake during the warm season and Eurasian net carbon release as well as anomalies in atmospheric circulation during the cold season. From the early 1970s to the early 1990s, our analysis was consistent with that of Keeling et al. [Keeling CD, Chin JFS, Whorf TP (1996) Nature 382:146–149], suggesting that the increase in the MLO CO2 amplitude is dominated by enhanced photosynthetic drawdown in North America and enhanced respiration in Eurasia. In contrast, the recent decline in the CO2 amplitude is attributed to reductions in carbon sequestration over North America associated with severe droughts from 1998 to 2003 and changes in atmospheric circulation leading to decreased influence of Eurasian air masses. With the return of rains to the U.S. in 2004, both the normalized difference vegetation index and the MLO amplitude sharply increased, suggesting a return of the North American carbon sink to more normal levels.

They introduce an interesting lag phase of 2-3 years in the cyclical amplitude across the 11 years cycle.


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