Past methane from lakes in Alaska: integrating proxy records and models

Increasing concentrations of greenhouse gases in the atmosphere trap heat and cause global warming. Methane is key, as it is 28 times more potent than carbon dioxide in trapping heat. Unfortunately, there is great uncertainty in how the amount of methane in the atmosphere will change under future conditions, so we urgently need more accurate numbers for future methane emissions as the Earth continues to warm. This proposal will make a radical new contribution by providing much better constrained estimates of methane contributions from lakes in Alaska, as an example of a high-latitude region susceptible to global warming. The high northern latitudes are particularly important to climate change effects because climatic warming is accentuated toward the poles, which will accelerate biological processing of carbon, including the production of methane.
The uncertainty in future atmospheric methane content reflects the fact that emissions are caused by human actions and natural processes that are themselves affected by climate change. Lakes form one of the largest natural sources of methane. Lake methane production strongly increases in warmer and wetter conditions, leading to more methane entering the atmosphere, where it contributes to further warming. This is an important positive feedback mechanism that could have large impacts on future global climate. This climate-methane feedback is strongest at high latitudes, where lakes are very abundant and recent warming is most severe. However, because temperature is only one of several factors that are likely to affect methane release from lakes and wetlands, the extent of the methane feedback can only be understood through careful numerical modelling.
In the past, warmer-than-present climatic conditions prevailed in interior Alaska between 11,000-6,000 years ago. If we can understand how methane behaved under these conditions, we will be in a better position to anticipate future change. We can do this by deriving data directly from lake sediment records coupled with a model to simulate the processes of methane generation and emission. Comparison of model output and observed data forms a powerful hypothesis-testing system that we can use to ascertain how much methane emissions have changed in the past, and why they changed.
This study's observed record comes from dated lake sediments. Lake sediments accumulate continuously and preserve records of chemical and biological processes plus information about past climate. Studying these records will allow us to reconstruct information on past methane emissions. Key factors for methane emissions (temperature, water level, organic matter availability, oxygen regime) will also be reconstructed and modelled, which allows us to understand the processes behind lake methane emissions.
Our study focuses on lakes in Alaska because this region is well-studied compared with other high-latitude areas, with extensive background information about past climate and carbon cycling. We will reconstruct methane emissions from lakes that were 2-5 degrees warmer 11,000-6,000 years ago, compared with today. We will use a new, quantitative tool for estimating past methane emissions from lakes based on the chemical composition of fossils in sediment records. We will also adapt an existing numerical model that simulates present-day methane emissions to estimate past and future methane emissions. Our integrated approach, combining geochemical measurements and modelling, will allow us to: (1) assess the magnitude of methane emissions through time, (2) identify the key factors driving methane emissions, (3) find critical values for these factors that lead to change, and (4) understand how factors interact to produce observed methane emissions. Our numerical methane model, refined through comparison with empirical observations, will then allow us to make robust estimates for how much greater a contribution lakes may have to atmospheric methane in the future.

We have identified three main impact themes:
1) Disseminating scientific knowledge to policy makers and national agencies. Fundamental research is of interest to governments of countries in the Arctic and their scientific organizations. UK Partners in this project are the All-Party Parliamentary Group on Polar Regions (APPG) consisting of government departments with an interest in Arctic Science under the coordination of the Foreign and Commonwealth Office (FCO) as well as the NERC Arctic Office (AO). The AO has indicated a clear need for better knowledge exchange between the arctic scientific community and policy makers. We will address this issue by (a) compiling a state-of-the-art policy brief on the impact of arctic environmental change aimed to answer key questions of policy makers. These questions will be identified in a workshop with APPG, AO, and key UK arctic scientists at the onset of the project.
In Alaska, we work with the National Park Service (NPS), the United States Geological Survey (USGS), and the University of Alaska, which are very active in research on the functioning/management of the arctic carbon cycle. We will (b) contribute to the NPS Inventory and Monitoring Program and (c) the USGS Alaska Lake Dynamics Studies and their National Assessment of Ecosystem Carbon Sequestration and Greenhouse Gas Fluxes. Contacts of PI and Co-I Edwards and PDRA will ensure that main dataset and findings are deposited and assessed at NPS and USGS. In turn, PDRA will review recent reports by NPS and USGS relevant for the policy brief (activity a).
In the UK we will (d) organise an international symposium on carbon cycling in high latitude lake systems from a palaeoenvironmental perspective, which will be aimed at academics as well as our impact stakeholders, including the APPG in the UK, and international partners like the USGS.

2) Knowledge exchange with indigenous communities. A number of our sites in Alaska are located in remote regions that are the traditional lands of indigenous people and/or managed as public conservations lands. It is our experience that meetings with local communities to enable a sharing of knowledge about the local environment are greatly appreciated and advance the regard with which science is held in these communities. We will build on established contacts with local communities and schools. Activities include (e) a field visit to a nearby lake with school groups of the Effie Kokrine Early College in Fairbanks and the Nunamiut School in Anaktuvuk Pass (12-17 year olds with native and non-native backgrounds). This will provide students with field experience and initiate them to academic research, stimulating them to continue to college/university. Together with local communities we will produce a photo book with native Alaskans on locations that highlight their concern of climate/environmental change, which will be distributed in Alaska and the UK; and (f) in collaboration with the NPS and Denakkanaaga (native elders organization) we will work with the native elders in Fairbanks to get insights into their key concerns and predictions of local impact of environmental change.

3) Public education and awareness. Science research concerning global warming, carbon cycling, and environmental issues is of general interest to the public at large. In Alaska we will work with the NPS using established pathways in public outreach for science. Activities include (g) development of materials for a NPS newsletter, and NPS school program, communication to Subsistence Boards, and educational programmes for the general public (via Park information centres and NPS website). Also, (h) project members will work with local partners to give public lectures at the Morris Thompson Cultural Center and the Museum of the North as part of an existing lecture series. The PDRA will also take part in (i) outreach activities organised with schools in Newcastle and at the Hancock Museum, and interviews for local radio.