Sea-level fluctuations across geological epochs have drastically reshaped coastlines and then significantly impacted ocean circulation and marine systems. In this study, we use the Regional Ocean Model (ROMS) to simulate the response of its thermohaline pattern and major ocean currents under the low sea level scenarios of (SLdrop120) the last glacial maximum (LGM) and the high sea level scenarios of (SLrise65) of the global ice sheet melting.
Our findings reveal a nonlinear effect on ocean circulation, with marginal seas experiencing pronounced thermohaline changes due to altered ocean connectivity. Low sea-levels exposed shelves, blocked straits, reducing Kuroshio flow in East China Sea, contrasting LGM studies, suggesting a complex interplay with glacial forcing. High sea-levels expanded shorelines, widened straits, enhancing western currents' westward expansion and diverting Kuroshio. The ITF's western branch is highly sensitive to sea-level changes. In an extreme low sea-level scenario, the closure of the Karimata Strait cuts off the western branch, eliminating the “freshwater blocking” effect and increasing the Makassar Strait flow by 2.31 Sv (1e6 m³/s). Conversely, in an extreme high sea-level scenario, the widening of both the Karimata and Makassar Straits increases water transport into the Indian Ocean.
Our discoveries underscore the nonlinear Kuroshio and ITF responses to coastline changes, emphasizing sea-level's pivotal role in shaping ocean currents.

extreme sea-level changes, regional ocean modeling system (ROMS), Kuroshio Current, Indonesian Throughflow (ITF), thermohaline structure, oceanic circulation system