Thaw lakes and vegetated thaw lake basins (VTLBs) are common features in permafrost zones and can comprise a large proportion of the land surface [1-7] (Figure 1). Thaw lakes on the Arctic Coastal Plain (ACP) of Alaska are estimated to have begun forming approximately 10,000 years ago in the Holocene when the climate was warmer and wetter than today [8, 9]. Initiation of drainage is thought to have begun about 5,000 years ago during the cooler, drier part of the Holocene [6, 10, 11]. Since that time the land surface of the ACP has undergone a slow, continuous, and overlapping cycle of lake drainage, vegetation succession, and lake re-formation, resulting in a collage of lakes and variously-aged VTLBs classified as young (< 50 yr), medium (50-300 yr), old (300-2000 yr), and ancient (2000-5500 yr) (Figure 2) [5, 6, 11-13].
Recent changes in thaw lake extent have been attributed to current global warming, but the net direction of change for continuous permafrost zones such as the ACP is still unclear [1, 2, 14-18]. While some studies have identified increasing numbers and extents of thaw lakes and ponds due to warming-induced thermokarst (thawing and subsidence of the ground surface) [2, 14, 19], others have documented decreases in lake extent due to increased evapotranspiration or sudden lake drainage via accelerated thermal erosion of outlet channels [16, 20]. Still others have found no long-term trend [15, 18, 21].
The future presence of thaw lakes and VTLBs is quite pertinent today under our current scenario of increasing global temperatures caused by rising atmospheric greenhouse gas concentrations. Northern permafrost regions contain vast stores of historically undecomposed organic material. Thus, there is great concern that accelerated decomposition and associated release of greenhouse gases (CO2 and CH4) under a warmer climate may result in one of the largest feedbacks to climate change . As indicated by recent studies, continued warming in this region will likely result in significant changes to thaw lakes, be it in the form of greater lake extent or drainage accompanied by edaphic and vegetation change through time. Either of these trajectories will likely affect the characteristics of primary productivity and organic matter decomposition for a large part of the Arctic Coastal Plain. The current collage of lakes and differently aged VTLBs on the ACP provides the opportunity to understand how millennial-scale ecosystem change alters the carbon balance of this system, which may aid in forecasting the response to future change. We plan to examine the CO2 and CH4 fluxes along this chronosequence for the Barrow Peninsula with low-flying flux aircraft, portable eddy covariance towers, and remote sensing measurements.
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