  We explore a novel detection possibility for solar axions, which relies only
on their couplings to nucleons, via the axion-induced dissociation of deuterons
into their constituent neutrons and protons. An opportune target for this
process is the now-concluded Sudbury Neutrino Observatory (SNO) experiment,
which relied upon large quantities of heavy water to resolve the solar neutrino
problem. From the full SNO dataset we exclude in a model-independent fashion
isovector axion-nucleon couplings
$|g^3_{aN}|\equiv\frac{1}{2}|g_{an}-g_{ap}|>2\times10^{-5}$GeV${}^{-1}$ at 95 %
C.L. for sub-MeV axion masses, covering previously unexplored regions of the
axion parameter space. In the absence of a precise cancellation between
$g_{an}$ and $g_{ap}$ this result also exceeds comparable constraints from
other laboratory experiments, and excludes regions of the parameter space for
which astrophysical constraints from SN1987A and neutron star cooling are
inapplicable due to axion trapping.
