Presented at the 2018 Ocean Salinity Science Team and Salinity Continuity Processing MeetingOcean surface carbon dioxide partial pressure governs major variability of the ocean uptake of atmospheric carbon dioxide. The up-take mitigates greenhouse warming and increases ocean acidification; acidification is harmful to marine life. We have produced daily maps of the partial pressure and pH. pH is a logarithm scale of the concentration of hydrogen ion in a solution; more acidic solutions have lower value and neutral is 7. Our data reveal that water freshens up the ocean (lower surface salinity), dilutes the carbon in the ocean, causes lower partial pressure and higher pH (lower acidity). The relation was observed in region of major water input, under the intertropical convergence zones (ITCZ), at major river discharges, and near arctic ice melt. At the mouth of the Amazon River, surface salinity measured by Aquarius gives a good indication of river discharge; lower salinity corresponds to lower partial pressure and higher pH all year round. For the fresh water carried by the North Brazilian Current Retroflection along 8°N from July to October, such relation also holds. Such relation is also observed under the ITCZ in the Pacific. There is a sharp boundary between the region influenced by rainfall under the ITCZ and the region where ocean chemistry is driven by ocean upwelling along the equator to the south. If the carbon dioxide partial pressure in the atmosphere and the prevailing wind do not change over temporal and spatial scales of partial pressure in the ocean, a reduction of ocean partial pressure implies potential increase in uptake of atmospheric carbon dioxide and potential for increase in ocean acidification. The increase in carbon dioxide flux into the ocean counters the rainfall effect in reducing acidification, and should bring the ocean back towards an equilibrium state. The time scales and locations of such processes remains to be characterize and understand. This study opens up a new perspective on the impact of salinity measurements in global climate change, not only on its impact through hydrological cycle, but through greenhouse warming by carbon dioxide and ocean primary production and carbon sequestration.