Friday, September 28, 2012

Permafrost Thawing: An Exclusive Interview with with Ecologist, Dr. Edward Schuur, University. of Florida

(Originally posted in 2006)

In the July 16, 2006 edition of SCIENCE a research team in which Dr. Edward A. Schuur of the University of Florida participated, reported new findings about the reservoir of carbon stored in the permafrost in Siberia. The researchers specifically addressed loess soil, known as ”yedoma” in Siberia, a wind and water born dust frozen in permafrost in depths down to 50 m (~164’). The concentration of carbon in the deep yedoma deposits was much higher than expected compared to deep soils elsewhere.

SMO: Dr. Schuur, your paper estimates the varying reservoirs of carbon in gigatons (Gt)
  • oceans 40,000 Gt
  • soils 1,500 Gt (all soils globally, including tundra to a depth of 1 m (3.3’)
  • vegetation 650 Gt

Could you please explain how the mass of carbon is measured and estimated in the atmosphere and in the other pools?

DR. SCHUUR: Mass of carbon is the concentration times the volume. In the case of yedoma, we need to know the thickness of the yedoma (av = 25m), the bulk density (weight of dry soil per volume of soil, in other words kg of soil per cubic meter) and then the carbon concentration, which we can measure on an elemental analyzer. The elemental analyzer combusts the soil sample and measures the amount of carbon dioxide that is released upon combustion. We take soil samples from a range of geographic locations and vertically throughout the yedoma to describe a large area. A similar approach is used for ocean, atmosphere too.

SMO: Please describe the carbon reservoirs in the Arctic and how your team’s discovery fits in.

DR. SCHUUR: There are two comparisons in our paper: the first comparison is between deep permafrost yedoma (~500gt) and the surface values that are typically used for northern ecosystems ~450gt. The latter value is focused on 1m depth. So, we are saying that there is another, more or less equivalent (large) amount stored deeper below.

The second comparison is an estimate of carbon pools for >10,000 years ago when there were ice sheets at the last glacial maximum. The first comparison is the most relevant for current and future changes.

SMO: Most scientists believed that the organic material locked beneath the permafrost in Siberia, Canada and Alaska was in the form of partially decomposed peat, Sphagnum moss. But your study seems to indicate that the yedoma is also  a carbon repository.

a) How was this overlooked before?
b) Where did the yedoma come from? What plants or animals? When?
c) How was it sequestered in permafrost?

DR. SCHUUR: We are studying soils that are deeper than the traditional 1m depth that many soil studies focus on. Because carbon enters soil as plants and animals die and decompose, it is reasonable in most places to focus on the surface because that is where the biological activity is.

The reason that yedoma is different is that the surface of the soil was rising because, in the glacial/interglacial periods, dust was falling and accumulating on the surface. Even though it was only mm to cm falling per year, over decades, this adds up to a lot of material, up to 53m (174’) thick in some places.

As the surface of the soil rose, carbon that was in the soil became trapped in permafrost (permanently frozen) before it had time to decompose fully. As a result you can see intact plant roots preserved deep in the frozen soil. This happened at a time where the ecosystem was steppe-tundra with lots of grasses and herbivores (think mammoth, bison, etc., other Pleistocene mega fauna)

This process resulted in carbon trapped much deeper than is expected in many places, and cut off from decomposition by microbes because it was frozen.

SMO: In regions at the southern extreme of continuous permafrost, how fast is it melting and what CO2 contributions to the atmosphere is this making today?

DR. SCHUUR: This is the $64,000 question. There is permafrost thawing (that is the word that permafrost scientists prefer rather than melting) occurring, and we are trying to estimate how fast it might be coming out. This paper is mostly about the size of the pool, and given how large it is, it is something that we should be worried about if it decomposes. Our lab experiments show that this old frozen carbon can be decomposed when thawed, now it is a matter of making projections into the future with the use of models.

SMO: If the melting is an accelerating positive feedback loop, can you make any estimates of how much faster the out gassing might be with a given temperature or atmospheric CO2 level increase?

DR. SCHUUR: Again this is the current and future research figuring out how much of a climate impact this pool will have using g/c/ms and future scenarios.

SMO: What are the most important actions that you believe should be taken to halt or retard the thawing of the permafrost layer?

DR. SCHUUR: Permafrost stability (and preservation of carbon therein) is affected by climate change. Currently, human-caused changes in atmospheric greenhouse gases are likely to affect global climate, thus anything that we can do to reduce emissions to the atmosphere will help mitigate this problem.

SMO: There is a school of thought which believes that permafrost thawing will result in the tundra becoming a carbon sink rather than a carbon source. The theory is that as the polar climate warms, plant communities currently limited by the cold temperatures will expand their range northward. And since plants are carbon sinks, the net effect of carbon and methane release from the melting permafrost in the tundra will be cancelled.

DR. SCHUUR: This is an important point and cannot be ignored. It depends on the rate of plant response and soil microbe response. In the yedoma soils there is far more total carbon than can be offset by plant growth, but then that depends on how extensively/fast the soil thaws. In general though there is so much carbon in yedoma down deep (~500gt), that if you consider the total land plant biomass (~650gt) worldwide that you can see that if all the yedoma thawed that there is no way to grow enough plants to offset.

SMO: Wildcard. Here you can ask your own question and answer it if you wish.

DR. SCHUUR: Here's a comment regarding surprises in climate change research. One aspect about this yedoma pool is that we are saying that this is 500 billion tons of carbon that was not really considered before. One extension of this is to think that if this surprise is out there, might there not be other surprises in the earth carbon cycle/climate system that can have a significant impact on our climate trajectory? This research makes me think that there are more surprises out there, and some we might only discover as they change in response to changing climate.

Ted Schuur, Ph.D.
Asst. Professor of Ecosystem Ecology
Department of Botany
University of Florida
Gainesville, FL, 32611-8526

Ron S. Nolan, Ph.D.
Solar Metro Online
Aptos, CA 95003

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