Spatial Coherence of NEE Response of Different Ecosystems to the Same Climate Anomaly Martha Butler 1, Ken Davis 1, Peter Bakwin 2, David Hollinger 3, Steven Wofsy 4 1 The Pennsylvania State University, 2 NOAA CMDL, 3 USDA Forest Service, 4 Harvard University

Premise Different ecosystems, separated in space, exposed to the same climate anomaly, may have similar responses. If the climate anomaly includes a large area, this regional ecosystem response may be large enough to be detected globally.

Spring 1998 as a Test Case Spring 1998 was one of the warmest (earliest) on record for a large part of North America. There are several FLUXNET sites within the anomaly area with data for both 1997 and Look for common responses: –March, April, May mean temperature –March, April, May cumulative NEE –Spring onset, phenological changes –Local CO 2 signals

The size of the dots indicate how much warmer (red) or cooler (blue) Jan-Jul 1998 was compared to the same period in Source:

Sites Included in This Study Data sources: FLUXNET gap-filled data (//daac.ornl.gov/FLUXNET), Black et al. (2000), and the PI-maintained data access sites for flux towers at Harvard Forest, Howland Forest, Northern Old Black Spruce, and WLEF

Spring 1998 vs. Spring 1997 SiteVegetation Type MAM Mean Temperature [°C] Delta TMAM Cumulative NEE [gC/m 2 ] Delta NEE Northern Old Black Spruce Boreal Coniferous Old AspenBoreal Deciduous >-150 WLEFTemperate Mixed Howland Forest Temperate Coniferous Harvard Forest Temperate Deciduous BondvilleAgriculture Walker Branch Temperate Deciduous Little Washita Grassland increase in carbon uptake: ~50 g C m -2 spring -1 (managed) (outside of anomaly)

Timing of Spring Onset The “cross-over” of latent and sensible heat fluxes occurred earlier in 1998 than in Data are 15-day bin averages of mean daily fluxes from FLUXNET gap-filled daily data.

Local CO 2 Mixing Ratio Measurements Data courtesy of the flux tower PIs and GLOBALVIEW-CO 2

Evidence in the Local CO 2 Record Earlier spring decrease in mean daytime CO 2 mixing ratios in However, an early spring is not a guarantee of a productive growing season. Difference of 1998 and day bin averages for midday (10-14 LST), with bin averages as deviations from the site annual mean data are normalized to 1997 by subtracting the global trend.

From Local to Global … If such a large part of North America is affected, can this signal be seen in the global CO 2 measurement network? Or... –What does the global measurement network show? –What is the magnitude of the land response that could account for the global observations?

A Simple Box Model Approach Consider two sites in the global measurement network, at roughly 53N. Assume a mean westerly wind, U = 10 ms -1. Assume that any change in CO 2 between the two sites is due to land interaction in North America (land traverse of d = 5 x 10 6 m). Assume any change in CO 2 is mixed through the depth of the troposphere, h = 10 4 m.

A Simple Box Model Approach Using dC/dt = F c /h, where –dC is the mean difference in CO 2 mixing ratio between SHM and MHD for Spring months –dt is the time of transverse of North America –h is the mixing depth Find the net North American land flux, F c, that can account for the SHM-MHD CO 2 difference dC = ppm; 1998 dC = ppm This requires ~40 g C m -2 more uptake in Spring 1998, which is comparable to the ~50 g C m -2 more uptake indicated by the flux tower NEE.

Conclusions In this case of an extreme climate anomaly, there is spatial coherence in the responses of different forest ecosystems. There is information of global significance in the continental CO 2 measurement data from these flux tower sites. Thanks to: the PIs, DOE/TCP, NIGEC, and NSF FLUXNET and its data archives NOAA CMDL GLOBALVIEW-CO 2