  We present maps of Neptune in and near the CO (2-1) rotation line at 230.538
GHz. These data, taken with the Combined Array for Research in Millimeter-wave
Astronomy (CARMA) represent the first published spatially-resolved maps in the
millimeter. At large (~5 GHz) offsets from the CO line center, the majority of
the emission originates from depths of 1.1-4.7 bar. We observe a latitudinal
gradient in the brightness temperature at these frequencies, increasing by 2-3
K from 40 degrees N to the south pole. This corresponds to a decrease in the
gas opacity of about 30% near the south pole at altitudes below 1 bar, or a
decrease of order a factor of 50 in the gas opacity at pressures greater than 4
bar. We look at three potential causes of the observed gradient: variations in
the tropospheric methane abundance, variations in the H2S abundance, and
deviations from equilibrium in the ortho/para ratio of hydrogen. At smaller
offsets (0-213 MHz) from the center of the CO line, lower atmospheric pressures
are probed, with contributions from mbar levels down to several bars. We find
evidence of latitudinal variations at the 2-3% level in the CO line, which are
consistent with the variations in zonal-mean temperature near the tropopause
found by Conrath et al. (1998) and Orton et al. (2007).
