As now you must be aware of what is an ice core by now, I decided in this post to talk about black carbon, a major constituent of ice cores which can tell us a lot about past and current climates.
Black carbon is a dirty black soot
Black carbon is soot produced by the incomplete combustion of biomass and fuel according to a talk given by Neil Rose on November 30, 2018, at the University College of London.
How is Black Carbon trapped in ice cores?
Since the main component of black carbon is Co2 , this gas presents in the atmosphere at a certain time can be trapped within the ice as bubbles (when the compacted snow turns to ice) as shown in Figure 1.
Black carbon shows human activity and pollution
A study run in the Himalayas glaciers (Tibetan Plateau) revealed a rapid increase in black carbon absorbed by glaciers since 1950.
Ice cores have been extracted at 5 different locations in the Tibetan Plateau. Figure 2 represents the results of one of these cores extracted at the Zuoqiupu Glacier. A global shift in black carbon (BC) content over a period of 60 years can be seen. Also, a major shift in black carbon has been observed since 1990. This is evidence that human activity and pollution have hincreased starting from the industrial revolution.
Black Carbon contributes to ice melting
Sunlight absorption by glaciers is directly linked to the colour of the ice according to Bond et al 2013.
Figure 3 shows how the amount of light absorbed increases when there are more impurities within the ice.
Black carbon particles darken the ice, increasing absorption of sunlight and melting of glaciers as stated in a study correlating radiations and black carbon emissions.
Figure 4 shows how black carbon forces ice-albedo (amount of light absorbed in ice) changes.
The impact of black carbon on ice is similar to the proliferation of the microbe on ice as stated in one of my last post: "Microbes accelerate ice melting".
The Little Ice Age may have been ended by the sudden and continuous inputs of black carbon on ice and atmosphere
Both graphs on Figure 5 obtained from a study by Painter et al 2013 shows a correlation between glacier retreat and emission of black carbon: the emission of black carbon has remarkably increased since the 1850s, and glaciers have been proportionally reduced in their size as the black carbon accumulated in them.
Black carbon within ice cores gives information about its sources of emission
Black soot can be produced either by the combustion of biomass or fossil fuels.
Figure 6 took from a study on ice cores black carbon records in the Himalaya shows the contribution of biomass to black carbon deposition in ice.
Figure 3a: different types of sources found for black carbon deposition in ice cores using satellite and meteorological tools.
Figure 3c: a molecular indicator is used to calculate the amount of black carbon generated by biomass burning.
We can see a large increase in black carbon concentrations starting the 1980s, then it strongly dropped down during the early 1990s, which could be associated with the USSR breakup.
What to remember
Analysis of black carbon found in ice cores is of extreme importance to better understand what triggers the current Climate Change, and what influences the ice to melt. Ice cores not only tells you about old past climates but also how human activities have influenced climate in the past centuries.
This black soot is trapped in ice regarding different factors: their production, transport by the wind and precipitations. Then their amount present in ice allows us to better understand and track their pathway and the nature of their source.
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