231Pa and 230Th in the ocean model of the Community Earth System Model (CESM1.3)
Sifan Gu and Zhengyu Liu
Department of Atmospheric and Oceanic Sciences and Center for Climate Research, University of Wisconsin-Madison, Madison, WI, USA
Received: 22 Mar 2017 – Accepted for review: 10 Apr 2017 – Discussion started: 20 Apr 2017
Abstract. Sediment 231Pa/230Th activity ratio is emerging as an important proxy for deep ocean circulation in the past. In order to allow for a direct model-data comparison and to improve our understanding of sediment 231Pa/230Th activity ratio, we implement 231Pa and 230Th in the ocean component of the Community Earth System Model (CESM). In addition to the biotic 231Pa and 230Th that is fully coupled with the active marine ecosystem module, another form of abiotic 231Pa and 230Th have also been implemented with prescribed particle flux fields of the present climate. The comparison of the two forms of 231Pa and 230Th helps to isolate the influence of the particle fluxes from that of circulation. Under present day climate forcing, our model is able to simulate water column 231Pa and 230Th activity and sediment 231Pa/230Th activity ratio in good agreement with available observations. For past climate, our model is able to simulate a comparable magnitude of the change of sediment 231Pa/230Th activity ratio between the state with and without active AMOC in reconstruction. In addition, in hosing experiments, the biotic and abiotic sediment 231Pa/230Th activity ratios behave similarly over large areas of low productivity, but can differ substantially in some regions of high productivity, indicating the importance of biological productivity in addition to physical circulation. Therefore, our model provides a potentially powerful tool to help our interpretation of sediment 231Pa/230Th reconstructions and to improve our understanding of past ocean circulation and climate changes.
Gu, S. and Liu, Z.: 231Pa and 230Th in the ocean model of the Community Earth System Model (CESM1.3), Geosci. Model Dev. Discuss., doi:10.5194/gmd-2017-82, in review, 2017.