The Xiamen Symposium on Marine Environmental Sciences (XMAS 2025)

Both the Indonesian Throughflow (ITF) and the Leeuwin Current (LC) play pivotal roles in climatic and oceanic settings of the northwest shelf of Australia. However, the development of the LC as well as the potential climatic and environmental impacts of the ITF and the LC to the northwest shelf of Australia through the Pliocene-Pleistocene period remain elusive. In order to disentangle these issues, we applied molecular biomarkers to reconstruct variations of surface and subsurface sea temperatures, production and composition of phytoplankton, and terrestrial material input on the northwest shelf of Australia through the Pliocene-Pleistocene period. Firstly, our sea surface temperature record indicates progressive warming since ~1.2 Ma, with temperature values comparable to those in the Indo-Pacific Warm Pool, in contrast with the long-term global cooling trend, indicating a stronger LC since the Mid-Pleistocene Transition. The stronger LC after ~1.2 Ma was more likely triggered by enhanced atmospheric circulation. Secondly, the stronger ITF during ~6.0–3.8 Ma and stronger LC during ~1.2–0 Ma both induced lower production of phytoplankton and higher contributions of diatoms to total phytoplankton, while increased terrestrial soil input in the mid-Pleistocene might be the potential reason for increasing contribution of diatoms at ~1.7 Ma. Thirdly, records of the terrestrial material input to the northwest shelf of Australia indicate a general wet climate in northwestern Australia during the early Pliocene, a continuously drying trend to the mid-Pleistocene, and a drier phase with less vegetation coverage and expanded desert during the late Pleistocene, which is modulated by ongoing ITF constriction and global atmospheric circulations instead of the increased LC strength. Therefore, the climatic and oceanic settings of the northwest shelf of Australia through the Pliocene-Pleistocene period were largely impacted by oceanic currents and atmospheric circulations in both regional and global scales.

Northwest shelf of Australia,Leeuwin Current,Pliocene-Pleistocene,temperatures,phytoplankton productivity,terrestrial material input