Scientific Merit. This Arctic Observatory Network (AON) award produced information on how arctic soils are thawing and on how the elements carbon (C) and nitrogen (N) are transported from land to surface waters (lakes and streams). The elements C and N are important because nitrogen is a key limiting nutrient for plant growth, and carbon in soils and surface waters is a source of greenhouse gases that are warming our planet. Knowing the controls on how these elements behave will allow us to better predict how a warming arctic system will feedback and impact the climate on Earth. For example, as currently frozen soils thaw, more carbon deeper in soils can be converted to greenhouse gases, and these gases are released to the atmosphere and increase temperatures on Earth. This increase in temperature in turn drives more thaw of frozen soils, more greenhouse gas release, and creates a positive feedback loop known as Arctic Amplification.   

The first step in gauging the potential strength of an arctic amplification of global climate change is to measure how fast frozen soils are thawing. This project continued long-term data collection on the thawing of permafrost (permanently frozen) soils. Each summer in this part of the Alaskan tundra the surface soils thaw down to 50-100 cm depth, and then they refreeze in the fall. From 2003 to 2018 the average thaw depth in late summer increased almost 30% from 38 cm to 53 cm. In other measurements near this site, the temperature of the deeper permafrost has been rising, suggesting that this area is vulnerable and may be close to crossing a tipping point of even deeper and faster permafrost thaw.

The second step in understanding the global impacts of a warming Arctic is to determine what controls the delivery of C and N from land to surface waters. This delivery is a major component of the global C and N cycles, fuels large releases of greenhouse gases from lakes and streams to the atmosphere, and moves substantial amounts of dissolved organic carbon (DOC) and nitrogen (DON) to the world’s oceans. A critical nexus in this delivery is at the land-water interface, where small, headwater streams are dominant contributors of DOC and DON to larger watersheds. The unknowns in this debate on how and when the arctic C cycle will amplify global climate change are due in part to our limited understanding of how hydrology controls C and N transport. In this project we found that the delivery of DOC and DON from land to streams was controlled by how water moved in and out of surface soils. Specifically, we found that the humps and hollows created by tundra vegetation forced water at the soil surface flowing downslope back into the soil, causing a rapid exchange of C and N with deeper, more C and N-rich soil waters. In other words, the water porpoises from just above to just below the land surface and back again as it moves downslope. Discovery of this mechanism that controls how C and N are picked up and moved on land toward surface waters will help us make better predictions of how C and N movement in the Arctic could affect climate change in other parts of the world.

The final step in understanding carbon behavior in arctic systems combined results from our AON project partners that are measuring how carbon gases move directly from plants and soils into the atmosphere. We found that greater movement of C from land to streams, for example during large rain events, is often accompanied by greater release of C gases from land directly to the atmosphere. This suggests that future changes in storm frequency or intensity will strongly affect the loss of C from watersheds and the resulting impacts on the atmosphere or oceans.

Broader Impacts:  This project produced publicly-available datasets, helped produce 14 scientific publications, and helped train two young scientists who published PhD Dissertations and are continuing to study how ecosystems in the arctic can influence humans and the rest of the world.

Currently, humanity is struggling to understand and adapt to how climate change is redefining the relationship between humans and their environment in this century. Scientists in particular are struggling to understand how much “arctic amplification” will strengthen the impacts of changing climate, including rising temperatures and larger and more frequent storms and droughts, in the future. This project, as part of the Arctic Observing Network, has (1) monitored the status and rates of thawing in permafrost soils, which exposes previously frozen carbon now available to form greenhouse gases, and (2) discovered a new mechanism of how carbon moves from land to surface waters that will allow for better predictions of how a changing Arctic will impact climate on Earth at lower latitudes.

Last Modified: 05/02/2019
Modified by: George W Kling