  Results are reported from a joint analysis of Phase I and Phase II data from
the Sudbury Neutrino Observatory. The effective electron kinetic energy
threshold used is T_eff=3.5 MeV, the lowest analysis threshold yet achieved
with water Cherenkov detector data. In units of 10^6 cm^{-2} s^{-1}, the total
flux of active-flavor neutrinos from 8B decay in the Sun measured using the
neutral current (NC) reaction of neutrinos on deuterons, with no constraint on
the 8B neutrino energy spectrum, is found to be Phi_NC = 5.140
^{+0.160}_{-0.158} (stat) ^{+0.132}_{-0.117} (syst). These uncertainties are
more than a factor of two smaller than previously published results. Also
presented are the spectra of recoil electrons from the charged current reaction
of neutrinos on deuterons and the elastic scattering of electrons. A fit to the
SNO data in which the free parameters directly describe the total 8B neutrino
flux and the energy-dependent nu_e survival probability provides a measure of
the total 8B neutrino flux Phi_8B = 5.046 ^{+0.159}_{-0.152} (stat)
^{+0.107}_{-0.123} (syst). Combining these new results with results of all
other solar experiments and the KamLAND reactor experiment yields best-fit
values of the mixing parameters of theta_{12}=34.06 ^{+1.16}_{-0.84} degrees
and Delta m^2_{21}=7.59 ^{+0.20}_{-0.21} x 10^{-5} eV^2. The global value of
Phi_8B is extracted to a precision of ^{+2.38}_{-2.95} %. In a three-flavor
analysis the best fit value of sin^2\theta_{13} is 2.00 ^{+2.09}_{-1.63} x
10^{-2}. Interpreting this as a limit implies an upper bound of
sin^2\theta_{13} < 0.057 (95% C. L.).
