Abstract
Abstract. Measurements of atmospheric O2
have been used to quantify large-scale
fluxes of carbon between the oceans, atmosphere and land
since 1992 (Keeling and Shertz, 1992). With time,
datasets have grown
and estimates of fluxes have become more precise, but
a key uncertainty in these calculations is the exchange ratio
of O2
and CO2 associated with the net land carbon sink
(αB). We present measurements of atmospheric
O2 and CO2 collected over
a 6-year period from a mixed deciduous forest in central
Massachusetts, USA (42.537∘ N, 72.171∘ W).
Using a differential fuel-cell-based
instrument for O2 and a nondispersive infrared analyzer for
CO2, we analyzed airstreams collected within and ∼5 m above the forest canopy. Averaged over the entire
period of record, we find these two species covary with a slope of -1.081±0.007 mol of O2 per mole of
CO2 (the
mean and standard error of 6 h periods).
If we limit the data to values collected on summer days within the
canopy, the slope is -1.03±0.01. These are the conditions in which
biotic influences are most likely to dominate.
This result is significantly
different from the value of −1.1 widely used in O2-based
calculations of the global carbon budget, suggesting the need for a deeper understanding of the exchange ratios of the various fluxes and pools comprising the net sink.
Funder
National Science Foundation
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