Increasing seasonal land-atmosphere CO2 exchange as a result of unidentified large-scale changes in arctic and boreal ecosystems

Lisa R Welp, Scripps Institution of Oceanography, UCSD, lwelp@ucsd.edu (Presenter)
Heather Graven, Scripps Inst. Oceanography, hgraven@ucsd.edu
Stephen Charles Piper, UCSD Scripps Institution of Oceanography, scpiper@ucsd.edu
Prabir Patra, JAMSTEC, prabir@jamstec.go.jp
Ramakrishna R. Nemani, NASA ARC, rama.nemani@nasa.gov
Ralph Keeling, UCSD Scripps Institution of Oceanography, rkeeling@ucsd.edu

High northern latitude Normalized Difference Vegetation Index (NDVI) trends have varied spatially over the satellite record. Recent work by Myneni et al. (2013) shows far more areas have greened than browned in the arctic and boreal regions from 1982 through 2010. We attempt to link these changes in NDVI to associated changes in ecosystem-atmosphere CO₂ fluxes.

We examined monthly land surface fluxes from two time-dependent atmospheric CO₂ inversion models (RIGC and Jena) from 1986 through 2006 to see how the seasonality of CO₂ exchange in the north has changed. Both models show a CO₂ flux amplitude increase of nearly 1% yr^-1 north of 60°N, and ~ 0.2 to 0.4% yr^-1 between 50°N and 60°N driven primarily by increased summer CO₂ uptake.

In a separate study comparing recent aircraft observations from the HIPPO campaign (2009-11) with earlier flights (1958-61), we find a widespread increase in CO₂ amplitude of magnitude ~50% in the mid troposphere north of 45°N (Graven et al., submitted). The boundary at 45°N implicates the boreal forests a major driver of this change. We show that increasing CO₂ uptake during the summer months of order 1% per year is also required to explain this longer-term increase.

These results suggest that despite areas of vegetation browning, increasing fire frequency, insect disturbance and land use, that the arctic and boreal regions are maintaining and likely increasing in CO₂ sink strength. Current coupled carbon-climate models incorporating temperature and CO₂ fertilization fail to reproduce the large CO₂ amplitude increase. We suggest there are as yet unidentified large-scale composition and structural changes in boreal and arctic ecosystems driven by climate change that are increasing the seasonal CO₂ exchange. The last few years, 2009-12, show the largest CO₂ amplitude on record at Barrow (71°N), indicating that the underlying ecosystem shifts are ongoing.

Presentation Type:  Poster

Session:  Poster Session 2-A   (Wed 11:00 AM)

Associated Project(s): 

• Recent trends and physiological constraints on northern extra-tropical ecosystems from atmospheric and satellite data

Poster Location ID: 85