  We perform experiments to study the inverse cascade regime of gravity wave
turbulence on the surface of a fluid. Surface waves are forced at an
intermediate scale corresponding to the gravity-capillary wavelength. In
response to this forcing, waves at larger scales are observed. The spectrum of
their amplitudes exhibits a frequency-power law at high enough forcing. Both
observations are ascribed to the upscale wave action transfers of gravity wave
turbulence. The spectrum exponent is close to the value predicted by the weak
turbulence theory. The spectrum amplitude is found to scale linearly with the
mean injected power. We measure also the distributions of the injected power
fluctuations in the presence of upscale (inverse) transfers or in the presence
of a downscale (direct) cascade in gravity wave turbulence.
