Kiminori Sugino

and 1 more

Zinc (Zn) is biogeochemically significant due to its crucial role in biological processes. In the global ocean, there is an apparent coupling between the concentrations of zinc and silicon (Si), and there is a consistent ratio between the two. However, this coupling is observed to be disrupted in the North Pacific Ocean. It has been suggested that this disruption is due to Zn that originates on the continental shelf. However, this explanation relied on the particular circulation field used in the model described in the relevant study. The aim of the current study was to use more realistic circulation fields as the basis of a more accurate evaluation of deep circulation and export production in the North Pacific. We also aimed to analyze the impact of uptake parameters, continental-shelf supply, and regeneration of Zn on the observed Zn–Si decoupling in the North Pacific. Sensitivity experiments employing two distinct circulation fields were performed. It was found that the two circulation fields yielded different decoupling influences: continental-shelf supply or regeneration. A comparison between the two circulation fields also revealed discrepancies in the concentration of regenerated Zn. The main factors causing these differences were found to be the age of the water masses in the North Pacific and the magnitude of export production. Greater export production and a more stagnant circulation field in the North Pacific led to more regenerated Zn and a higher probability of decoupling without the need for an input of Zn from the continental shelf.

Fanny Lhardy

and 15 more

Model intercomparison studies of coupled carbon-climate simulations have the potential to improve our understanding of the processes explaining the pCO2 drawdown at the Last Glacial Maximum (LGM) and to identify related model biases. Models participating in the Paleoclimate Modelling Intercomparison Project (PMIP) now frequently include the carbon cycle. The ongoing PMIP-carbon project provides the first opportunity to conduct multimodel comparisons of simulated carbon content for the LGM time window. However, such a study remains challenging due to differing implementation of ocean boundary conditions (e.g. bathymetry and coastlines reflecting the low sea level) and to various associated adjustments of biogeochemical variables (i.e. alkalinity, nutrients, dissolved inorganic carbon). After assessing the ocean volume of PMIP models at the pre-industrial and LGM, we investigate the impact of these modelling choices on the simulated carbon at the global scale, using both PMIP-carbon model outputs and sensitivity tests with the iLOVECLIM model. We show that the carbon distribution in reservoirs is significantly affected by the choice of ocean boundary conditions in iLOVECLIM. In particular, our simulations demonstrate a ~250 GtC effect of an alkalinity adjustment on carbon sequestration in the ocean. Finally, we observe that PMIP-carbon models with a freely evolving CO2 and no additional glacial mechanisms do not simulate the pCO2 drawdown at the LGM (with concentrations as high as 313, 331 and 315 ppm), especially if they use a low ocean volume. Our findings suggest that great care should be taken on accounting for large bathymetry changes in models including the carbon cycle.