That question can be answered by asking "Who had the money to buy imports?"
With the Southern export value being 73% of the total, and the Northern export value being 27% of the total, it would be reasonable to assume that the Southerners were somehow paying for 73% of the imports.
Of course that's not how it actually worked. In reality the Northern congressional representation had gamed the laws to favor Northern interests at the expense of Southern interests, so New York and Washington DC were actually grabbing most of that export value.
New York was getting profits on the front end of the horse with shipping, banking, insurance, warehousing, packet shipping, etc. New York was also getting a lot of profit off of the back end of the Horse, through the same methods.
Washington DC was getting all their percentage of the Southern production off of the back end of the Horse, when European products arrived in payment for the mostly Southern produced trade.
I've read many accounts that assert New York made off with about 40% of all Southern export value, and Washington DC of course made off with whatever the tariff costs were, which were at least 15% in your example, but likely much more.
“With the Southern export value being 73% of the total, and the Northern export value being 27% of the total, it would be reasonable to assume that the Southerners were somehow paying for 73% of the imports”
You seem to assume that only exports paid for imports.
This is not the case. The South was not the only section of the nation to create wealth.
As an example: from the 1860 census, the value of manufactured goods from the State of New York $378,800,000.
Little of these manufactured items found their way to Europe. These manufactured items were sold all over North America. Maybe the manufacturers in New York had enough money to buy imports in the quantities represented by your Tariff graphic.