%0 Journal Article
%T Does terrestrial drought explain global CO2 flux anomalies induced by El Ni o?
%A C. R. Schwalm
%A C. A. Williams
%A K. Schaefer
%A I. Baker
%A G. J. Collatz
%A C. R denbeck
%J Biogeosciences (BG) & Discussions (BGD)
%D 2011
%I Copernicus Publications
%X The El Ni o Southern Oscillation is the dominant year-to-year mode of global climate variability. El Ni o effects on terrestrial carbon cycling are mediated by associated climate anomalies, primarily drought, influencing fire emissions and biotic net ecosystem exchange (NEE). Here we evaluate whether El Ni o produces a consistent response from the global carbon cycle. We apply a novel bottom-up approach to estimating global NEE anomalies based on FLUXNET data using land cover maps and weather reanalysis. We analyze 13 years (1997¨C2009) of globally gridded observational NEE anomalies derived from eddy covariance flux data, remotely-sensed fire emissions at the monthly time step, and NEE estimated from an atmospheric transport inversion. We evaluate the overall consistency of biospheric response to El Ni o and, more generally, the link between global CO2 flux anomalies and El Ni o-induced drought. Our findings, which are robust relative to uncertainty in both methods and time-lags in response, indicate that each event has a different spatial signature with only limited spatial coherence in Amaz nia, Australia and southern Africa. For most regions, the sign of response changed across El Ni o events. Biotic NEE anomalies, across 5 El Ni o events, ranged from ¨C1.34 to +0.98 Pg C yr 1, whereas fire emissions anomalies were generally smaller in magnitude (ranging from ¨C0.49 to +0.53 Pg C yr 1). Overall drought does not appear to impose consistent terrestrial CO2 flux anomalies during El Ni os, finding large variation in globally integrated responses from ¨C1.15 to +0.49 Pg C yr 1. Despite the significant correlation between the CO2 flux and El Ni o indices, we find that El Ni o events have, when globally integrated, both enhanced and weakened terrestrial sink strength, with no consistent response across events.
%U http://www.biogeosciences.net/8/2493/2011/bg-8-2493-2011.html