The Impacts of Maritime Continent Topography in the Preindustrial and the Pliocene Warm Period Using HadCM3

The Maritime Continent (MC) plays a critical role in regulating global atmospheric and oceanic circulation. This study explores the impact of MC topography on both regional and remote climate under preindustrial (PI) and mid-Pliocene warm period (mPWP) conditions using a lately tuned version of the HadCM3 climate model. Simulations are conducted by varying the topography of the northern MC (MCn) and southern MC (MCs), following the Pliocene Model Intercomparison Project (PlioMIP) Phase 2 experimental framework.

Results indicate that changes in the MCn topography during the mPWP, compared to PI conditions, lead to cooling in the northwestern Pacific, while variations of the MCs results in cooling over the eastern Indian Ocean. The MC topography variation has a large impact on the net hydrological flux (precipitation minus evaporation) over the MC and Indian Ocean, with both MCn and MCs leading to a decrease near the Timor passage region and an increase over the northern Indian Ocean. Compared to the PI, there is a westward movement of the Walker Circulation in the mPWP, and the MCs topography contributes to this westward movement. Although MC topographical changes have a limited effect on the total volume transport of the Indonesian Throughflow (ITF), variations in MCs topography substantially affect the ITF structure above 200 meters, and variations in MCn topography affect the ITF structure at depths around 1000 meters.

While the overall contribution of MC topography to global temperature changes is relatively small compared to the combination of other mPWP boundary conditions (CO₂, ice sheets, soil, vegetation, lakes, and changes in topography of other regions), it plays a critical role in shaping the ITF and influencing both local and remote climate systems.