Panthalassa was a hemisphere-sized ocean, much larger than the modern Pacific. It could be expected that the large size would result in relatively simple ocean current circulation patterns, such as a single gyre in each hemisphere, and a mostly stagnant and stratified ocean. Modelling studies, however, suggest that an east-west sea surface temperature (SST) gradient was present in which the coldest water was brought to the surface by upwelling in the east while the warmest water extended west into the Tethys Ocean.