So, first let's imagine an earth-like planet (roughly the same size and axis tilt, presence of a moon, etc). The majority of the landmasses on this planet are in the southern hemisphere, and unlike earth, the plurality of the land is in the Hadley cell area. Now let's imagine a large freshwater sea straddling the equator (say, .5 the size of the Mediterranean) that flows into an ocean about 1/3 the width of the Atlantic, but with the same North to South distance. What might be the effects of such a sea on the surrounding climate zones?
Edit: There's a very large chain of mountains that's to the east of the freshwater sea. It seems that glacial melting would be one plausible cause for the formation of said sea, so let's go with that.
Edit: Swapped "biomes" for "climate zones."