But exactly how much of the plastic ends up accumulating within the centre of the gyres is not known. Between 2016 to 2017, the Algalita Marine Research Foundation explored the South Pacific, where it collected samples from the South Pacific Subtropical Gyre, and found what they thought were high concentrations of plastic fragments, but whose quantities were not disclosed. But they couldn"t be sure these concentrations were above normal levels; they have called for more data to address what could be large errors in estimates of the amount of global plastic now found in the ocean. Before that study, and in 2014, it was believed that the gyres only had between 200 to 600g (7 to 21 oz) worth of plastic litter per square kilometre.