Abstract
The ratio between net community production (NCP) and net primary production (NPP) is a useful index of carbon export efficiency (e‐ratio). Seasonal variations of e‐ratio are poorly documented due to the lack of field measurements. In this study, the satellite‐based NPP and Argo‐Oxygen (O2) based NCP were used to determine e‐ratio in the subtropical gyres. Comparisons with long‐term field measurements at the Hawaii Ocean Time‐Series showed good agreement in annual mean and spring‐summer (April–July) e‐ratio. With the short‐term tracer (O2) the satellite‐Argo approach revealed significant seasonal variations in NCP and e‐ratio in the subtropical gyres of the North Pacific, North Atlantic, and South Pacific. The satellite‐Argo‐derived annual mean e‐ratio in all three Northern Hemisphere sites were close to those from the temperature‐based empirical model, but significantly lower in the South Pacific subtropical gyre where the sub‐annual NCP variations were stronger.
Plain Language Summary
e‐ratio is the ratio between organic carbon produced by the producers net primary production (NPP) and the organic carbon that is exported into the deeper ocean after the consumption of the consumers in the upper ocean net community production (NCP). It is a useful index of carbon export efficiency. Seasonal variations of e‐ratio are poorly documented due to the lack of field measurements. This study used satellite‐based NPP and Argo float‐based NCP to determine the e‐ratio in the subtropical gyres. Comparison with long‐term field measurements at Hawaii Ocean Time Series showed good agreement in annual mean and spring‐summer e‐ratio. The satellite‐Argo approach revealed significant seasonal variations in NCP and e‐ratio in the subtropical gyres of the North Pacific, North Atlantic, and South Pacific. The annual mean e‐ratio in all three North Hemisphere subtropical gyres were close to the e‐ratio calculated from the temperature‐based empirical model, but significantly lower in the South Pacific subtropical gyre where the seasonal NCP variations were stronger.
Key Points
Seasonal relationship between primary and net community production in the subtropical gyres was determined using satellite and Argo data
Strong seasonal variation in net community production to net primary production ratio (e‐ratio) was observed
In the northern hemisphere subtropical gyres the annual mean e‐ratio from empirical model was consistent with the satellite‐Argo method
