Extended Data Fig. 4: Emergent constraint on growing season (October to March) Southern Ocean (SO) net community production (NCP) using the seasonal net outgassing of the non-thermal O2 flux cycle (SNObio).
From: Atmospheric oxygen constraints on Southern Ocean productivity and drivers of carbon uptake
We use the variable ‘fbddtdic’ as a proxy for NCP, defined as the rate of change of DIC due to biological activity, which is available in only 8 of the 22 models and experiments analyzed here. The emergent constraint method is identical to that reported in Fig. 3. The red point with error bars denotes the mean and standard deviation of constrained NCP (1.5 ± 0.20 PgC yr−1) and SNObio derived using HEC (Methods). We focus specifically on growing season (October to March) NCP because SNObio measures growing season net O2 outgassing that directly relates to biological activities. During winter, negative NCP from respiration and limited photosynthesis does not correlate with SNObio. We note that previous studies suggest that the model variable ‘epc100’ (Extended Data Fig. 5e), which represents the export production at 100-m, can serve as a proxy for NCP, but significant uncertainty arises from temporal variations in organic carbon storage across models (refs. 14,20). Therefore, we do not use ‘epc100’ here.
