Detecting regional patterns of changing CO ₂ flux in Alaska

Abstract

With rapid changes in climate and the seasonal amplitude of carbon dioxide (CO 2 ) in the Arctic, it is critical that we detect and quantify the underlying processes controlling the changing amplitude of CO 2 to better predict carbon cycle feedbacks in the Arctic climate system. We use satellite and airborne observations of atmospheric CO 2 with climatically forced CO 2 flux simulations to assess the detectability of Alaskan carbon cycle signals as future warming evolves. We find that current satellite remote sensing technologies can detect changing uptake accurately during the growing season but lack sufficient cold season coverage and near-surface sensitivity to constrain annual carbon balance changes at regional scale. Airborne strategies that target regular vertical profile measurements within continental interiors are more sensitive to regional flux deeper into the cold season but currently lack sufficient spatial coverage throughout the entire cold season. Thus, the current CO 2 observing network is unlikely to detect potentially large CO 2 sources associated with deep permafrost thaw and cold season respiration expected over the next 50 y. Although continuity of current observations is vital, strategies and technologies focused on cold season measurements (active remote sensing, aircraft, and tall towers) and systematic sampling of vertical profiles across continental interiors over the full annual cycle are required to detect the onset of carbon release from thawing permafrost.carbon cycle | permafrost thaw | climate | Earth system models | remote sensing T he future trajectory of carbon balance in the Arctic-Boreal Zone (ABZ) is of global importance because of the vast quantities of carbon sequestered in permafrost soils (1). Climate warming threatens to increase permafrost thaw and release soil carbon back to the atmosphere as a positive feedback promoting additional warming (2). It is unclear whether the observed intensification of the northern high-latitude carbon cycle is dominated by plant productivity or microbial decomposition, both of which seem to be increasing (3-6). Although warming temperatures and C/N fertilization promote greening and higher summer productivity during the short, intense growing season, these same factors also drive increased emissions during the long cold season (3-5).Detecting changes in ABZ carbon balance requires sustained observations over the full annual cycle. In the last decade, researchers have recognized the importance of year-round landatmosphere CO 2 flux observations (3-5). Synthesis studies of these data show that increasing growing season uptake has been offset by stronger winter respiration. Measurements of atmospheric CO 2 collected from in situ and remote sensing instruments provide spatially and temporally integrated constraints of net CO 2 exchange on regional to pan-Arctic scales. In situ observations have been limited primarily to a small network of surface towers and infrequent, short duration airborne campaigns designed primarily to detect the pan-Ar...

Isentropic transport and the seasonal cycle amplitude of CO2

“…Simulations are spun up from 2000 to 2008 to establish hemispheric gradients. The experiments based on GEOS‐Chem and CLM are described in more detail in Parazoo et al []. As we will demonstrate, the modeled CO 2 seasonal cycle from our GEOS‐Chem/CLM setup compares well with that from the NOAA Marine Boundary Layer Reference data set.…”

Spring photosynthetic onset and net CO2 uptake in Alaska triggered by landscape thawing

“…Future efforts to reduce these errors and interpret patterns of thaw vs. C flux onset requires at a minimum nonlinear interpolation methods for monthly SIF and ideally more spatiotemporal explicit application of satellite SIF data in light use efficiency models. More sustained early season, spatially intensive sampling of airborne CO 2 (Parazoo et al., ) and longer term eddy covariance fluxes and from additional sites in high northern boreal forests is also needed.…”

Detecting the permafrost carbon feedback: talik formation and increased cold-season respiration as precursors to sink-to-source transitions

“…We use the coupled permafrost and biogeochemistry Community Land Model version 4.5 (CLM4.5) to investigate in detail the subsurface thermal processes driving C emissions from shallow (0-3 m) and deep (> 3 m) permafrost C stocks and to project the rate of NHL permafrost C feedbacks (> 55 • N) over the 21st century. Using CLM4.5 in the framework of an observing system simulation experiment (Parazoo et al, 2016), we ask how we might be able to (1) identify potential thresholds in soil thaw, (2) detect the specific changes in soil thermal regimes that lead to changes in ecosystem C balance, and (3) project future C sources following talik onset. We hypothesize that talik formation in permafrost triggers accelerated respiration of deep soil C and, ultimately, NHL ecosystem transition to long-term C sources.…”