The Permian-Triassic transition witnessed the largest mass extinction event in Earth's history, multiple mechanisms have been proposed to explain the cause of this catastrophe, however, relatively less attention has been paid to the paleogeography and major element chemistry of seawater and its possible link to mass extinction during this interval. Syndepositional massive marine dolostones could record the Mg isotope signature of contemporaneous seawater that hold clues of ancient Mg cycling. In this study, we investigated Mg isotopes of dolomite from three widely spaced carbonate sections in the Paleotethys to trace oceanic Mg cycling during this critical period. The latest Permian dolostones from all studied sections have similar delta Mg-26 values around -2.1 +/- 0.1 parts per thousand. However, a remarkable and consistent increase in delta Mg-26(dolomite) across the extinction interval occurred in both eastern and western margins of the Paleotethys. The results suggest that delta Mg-26 of seawater in Paleotethys fluctuated by 0.4 parts per thousand within similar to 750 kyr across the Permian-Triassic transition. Modeling reveals that the high rate of change in delta 26Mg(seawater)required an extremely short residence time for seawater Mg. This is attributed to dramatically intensified dolomitization in a restricted oceanic environment, with Mg isotope evidence revealing that the Paleotethys Ocean experienced transient restriction events, in association with radical changes in the major cation composition of seawater, around the end-Permian mass extinction event (EPME). (C) 2020 Elsevier B.V. All rights reserved.