Atmospheric Composition during the Last Glacial maximum:

Atmospheric Composition during the Last Glacial maximum:

Image 1: Last Glacial Maximum Ice cover. 

The last Glacial Maximum has been studied in great detail but there does exist areas where greater research must be done and one of these areas is the composition of the atmosphere during this period compared to the current atmosphere pre-industrialization.

Most of the effort when it comes to studying the atmosphere of the last glacial maximum has been focused on atmospheric carbon dioxide and its sequestration, with little attention being paid to methane and dust and the effects they have on the global climate during this glacial period.

Carbon Dioxide vs Methane:
One of the main reasons as to why CO2 is so extensively studied is the fact that during the Devonian the drop in CO2 levels caused a major Glaciation at the end of the Devonian. However, as a Greenhouse gas CO2 is not the strongest naturally occurring greenhouse gas as methane per ton is four times more potent that CO2 however it does have a shorter life span than CO2 with a lifespan of CH4 in the order of a decade as Kaplan indicated. Kaplan found that Methane as a natural gas is not produced as rapidly as CO2 with the main producers of Methane being wetlands and boreal wetlands in the northern hemisphere.

Image 2: Natural Methane Production

Methane Importance:
Dust is an important component in the atmosphere as it plays a number of roles which range from absorbing and scattering incoming solar and outgoing infrared radiation and indirectly by acting as ice nuclei as well as providing micronutrients for organisms in the ocean affecting the biochemical cycles within the ocean which are responsible for the reduction and increase in atmospheric CO2. The priority nutrient within dust is Iron as it the main nutrient needed for phytoplankton to grow and remove CO2 from the atmosphere and store it in deep ocean sinks.

The atmosphere of the Last Glacial Maximum is known to be very different in terms of composition with studies conducted by Lambert showing that during the last glacial maximum dust deposition was 2-3 times higher in the tropics and South Pacific, 5 times higher in the South Atlantic and 20-30 times higher in polar regions than present. Lamberts study also crucially found out that the Last Glacial Maximum contained 3-4 times more dust than the Holocene. The increase in dust partial concentrations during the last glacial maximum is partially due to the increase in erosion caused by advancing glaciers which mechanically abraded underlying rock turning it into dust.

The concentration of Methane during the Last Glacial Maximum is thought to have been around 385ppb, with an increase to 450ppb from the last glacial maximum to pre-industrialization, with this figure coming from a study conducted by Kaplan. Kaplan’s study also gave the reasons as to why there was a great decrease in the concentration of methane, the biggest contributor to the low methane concentrations was the reduction in the production of methane as wetlands reduced in total land coverage so did that of plants and the number of animals.

As common knowledge the concentration of atmospheric Carbon dioxide was lower during the last Glacial maximum than pre-industrialization and present, with atmospheric CO2 concentration during the last glacial maximum being 40% lower than the Holocene which sat at 280ppm and 368ppm post-industrialization. The most intriguing aspect about the concentration of atmospheric CO2 and methane is that they have a synchronous increase and decrease pattern as Monnin found in his study, with it also being noticed today that as ice caps melt trapped methane gas is being released which adds more greenhouses gases into the atmosphere increasing temperature as it would have at the termination of the Last Glacial Maximum.

The different greenhouse gases and other atmospheric components vary depending on the climatic reign at the time, with an interconnected relation existing between dust, methane and carbon dioxide. Dust increase in atmosphere increase phytoplankton production and therefore atmospheric carbon sequestration which decreases global temperatures reducing the production of methane and shortening its lifespan as more OH is available to react with the remaining methane. All these factors contribute to the continuation of a glaciation and the termination of one and subsequent warming of the Earth.

Reference List:

 Monnin, E., Indermühle, A., Dällenbach, A., Flückiger, J., Stauffer, B., Stocker, T.F., Raynaud, D. and Barnola, J.M., 2001. Atmospheric CO2 concentrations over the last glacial termination. Science, 291(5501), pp.112-114.

 Lambert, F., Tagliabue, A., Shaffer, G., Lamy, F., Winckler, G., Farias, L., Gallardo, L. and De Pol‐Holz, R., 2015. Dust fluxes and iron fertilization in Holocene and Last Glacial Maximum climates. Geophysical Research 

 Kaplan, J.O., Folberth, G. and Hauglustaine, D.A., 2006. Role of methane and biogenic volatile organic compound sources in late glacial and Holocene fluctuations of atmospheric methane concentrations. Global Biogeochemical Cycles, 20(2).