Using A Time-Dependent Dynamical Box Model to Understand Intermediate Water Records of Radiocarbon and Temperature

The circulation of Intermediate Waters influences global oceanic heat and carbon transport and changes in their distributions are also tied to glacial-interglacial climate transitions. In the modern ocean, temperature dominates interior density gradients and thus, to a large extent controls the deep circulation. Our chief tool for understanding the rate of this deep circulation comes from radiocarbon. Coupled radiocarbon and U/Th dates on deep-sea Desmophyllum dianthus corals allows for the reconstruction of past Intermediate Water circulation rates. Additionally, clumped isotope-based temperature estimates yield insight into the physical mechanisms contributing to circulation variability. We present deep-sea coral radiocarbon and clumped isotope temperature records from the North Atlantic and Southern Ocean, which show a high amount of variability during Heinrich Stadial 2 and the Antarctic Cold Reversal. Radiocarbon data from the north and south are very consistent with each other, and other datasets from similar depths broadly agree. We further explore the ocean dynamics behind our observations using a time-dependent dynamical box model. This model consists of an ACC channel, an Atlantic basin, and a Pacific basin. There are multiple layers representing different density classes and the volume of the boxes responds to realistic residual-mean Southern Ocean dynamics. Our model has a surface buoyancy flux, wind forcing and transfer of mass between the basins in the ACC region, diffusive upwelling in the basins, and North Atlantic Deep Water formation. The model solves for the circulation and stratification in addition to the volumes of the boxes. We use this model with added biogeochemistry to explore the mechanisms driving Intermediate Water signals observed during Marine Isotope Stage 2 and the deglaciation. Our box model is able to offer an independent and dynamical perspective to help understand these paleo records.