Just to add something, we can make some guesses about the circulation of the ocean and wind currents during Roman times because we know that the Roman Warm Period approximated the climate we enjoy today, for several reasons. For example the locations where date palms are grown and dates harvested. We have at least one account which mentions that date palms can be planted in e.g. Greece but that dates will not fruit there (which is the case today), but that dates can be grown and harvested in Judea, which was not the case between the time of the Roman Empire and today because of the colder climate. Medieval scholars weren't sure what to think of that.