All depends on your definitions of "North", "South" and "total exports".
Deep South cotton was undoubtedly 50% of the total, including specie.
But everything else classified "Southern" could be and was produced in the Upper South, Union South, Northern Border and Western states.
This was proved conclusively in 1861 when all Confederate exports were deleted from Union totals and yet "Southern exports" excluding cotton fell net-net only $3 million.
Finally, 1860 Northern "exports" to the South totaled about $200 million, which explains the source of funds for Northern imports from Europe, and puts the lie to claims that "Northeast power brokers" were ripping off the pooooor Southern plantation owners.
I used to think it did, but I eventually realized that it didn't matter. We don't know exactly how Kettle characterized what was "southern" and what was "northern", but we don't really need to know.
Those producers who would benefit from direct Trade with Europe would have eventually done what was in their economic best interest, so even if his "Southern origin" included the slave states that remained in the Union, once they saw others reaping far greater profits than they, they would have been of a mind to join that other coalition.
The threat to New York's money stream was the same, the only question was one of timing. It may have happened sooner, or it may have taken a little longer, but New York's (and Washington's) money stream was going to get interrupted absent a war to stop it.
This was proved conclusively in 1861
Nothing can be proven by 1861 and subsequent years, because everything was in upheaval and the natural market had been destroyed. With Federal gunboats steering trade back to New York, and prohibiting Southern trade that would otherwise have occurred, it became a "captured market" in a very different meaning from the usual economic term.
Without the interference with Trade, the Union numbers would be much worse, and the Confederate numbers would be much better. It is dishonest to pretend they represented what would have happened absent the conflict.