Extended Data Fig. 1: Prognostic five-box ocean model.
From: Nitrogen isotopic constraints on nutrient transport to the upper ocean
Schematic of the meridional overturning circulation showing the reservoirs and processes included in the prognostic five-box ocean model (see Supplementary Material). This model is used to test the effects of the fixed N budget on the NO3− δ15N difference between the deep ocean and the pycnocline. The symbols in the diagram follow those in the main text and Fig. 1. Straight arrows represent water exchange terms, curved arrows show export production and remineralization, and dashed arrows indicate the addition and removal of nitrate by N2 fixation (N2 fix.) and denitrification (Deni.), respectively, occurring either in the pycnocline or in the deep ocean. The five boxes are the deep ocean, the pycnocline, the AZ mixed layer, the PFZ-SAZ ventilating area, and the low-latitude mixed layer. The values used for the model parameters are varied over the same sensitivity ranges as in the one-box model (Extended Data Table 1); except for mAZ and the degree of NO3− consumption in both the AZ mixed layer and PFZ-SAZ ventilating area, which are held constant (at 20 Sv, 0.12 and 0.16, respectively), and denitrification, which varies from 100 to 250 Tg N yr−1.
