11:30 AM - 11:45 AM
[ACG45-10] An observational constraint on global ocean net community production by dissolved oxygen mass balance
Keywords:Net Community Production, Dissolved oxygen, BGC Argo
The ocean has a carbon storage capacity fifty times greater than that of the atmosphere. Once absorbed by the oceans, carbons can be sequestered from the atmosphere. The oceans therefore play an important role in regulating the climate.
Some of the CO2 that passes through the ocean surface is fixed as organic matter by photosynthesis and transported to the deeper oceans, while some of the organic matter formed is respired back into inorganic form. This oceanic carbon uptake by biological activity is known as the biological pump. How much carbon is fixed and exported to the deep ocean by the biological pump is still uncertain because it is difficult to observe, in contrast to the air-sea CO2 fluxes determined from observations of CO2 partial pressure at the sea surface, which are relatively well observed over the global ocean.
This study quantifies global ocean CO2 uptake by the biological pump (Annual Net Community Production, ANCP) using dissolved oxygen observations, the number of which has increased in the last decade due to the expansion of the Biogeochemical Argo observing array. Dissolved oxygen in the upper ocean is balanced between (1) physical supply/removal by air-sea exchange, advection and diffusion and (2) biological production/consumption by photosynthesis and respiration, that is, (time changes in oxygen) = (air-sea exchange) + (advection) + (diffusion) + (biological production). The physical fluxes are calculated from ship and profiling float-based temperature, salinity and dissolved oxygen data, and sea surface wind data from satellites and atmospheric reanalysis. And then the biological oxygen production is obtained as the residual. The resulting net biological oxygen production is converted to net carbon fixed by biological activity (ANCP) using the molar ratio of oxygen to carbon during photosynthesis/respiration (ΔO2/ΔC = 1.45). Our results show that the net biological oxygen production in the global upper ocean is 773.4 ± 108.2 Tmol O2 yr-1, i.e. the global ANCP is estimated to be 6.4 ± 0.9 Pg C yr-1. Given that the most recent estimate of global ocean net primary production (NPP) is 53 ± 7 Pg C yr-1, the global ocean carbon export rate is about 12%. In the presentation we will further discuss the spatial pattern and seasonal cycle of NCP and its driving factors.
Some of the CO2 that passes through the ocean surface is fixed as organic matter by photosynthesis and transported to the deeper oceans, while some of the organic matter formed is respired back into inorganic form. This oceanic carbon uptake by biological activity is known as the biological pump. How much carbon is fixed and exported to the deep ocean by the biological pump is still uncertain because it is difficult to observe, in contrast to the air-sea CO2 fluxes determined from observations of CO2 partial pressure at the sea surface, which are relatively well observed over the global ocean.
This study quantifies global ocean CO2 uptake by the biological pump (Annual Net Community Production, ANCP) using dissolved oxygen observations, the number of which has increased in the last decade due to the expansion of the Biogeochemical Argo observing array. Dissolved oxygen in the upper ocean is balanced between (1) physical supply/removal by air-sea exchange, advection and diffusion and (2) biological production/consumption by photosynthesis and respiration, that is, (time changes in oxygen) = (air-sea exchange) + (advection) + (diffusion) + (biological production). The physical fluxes are calculated from ship and profiling float-based temperature, salinity and dissolved oxygen data, and sea surface wind data from satellites and atmospheric reanalysis. And then the biological oxygen production is obtained as the residual. The resulting net biological oxygen production is converted to net carbon fixed by biological activity (ANCP) using the molar ratio of oxygen to carbon during photosynthesis/respiration (ΔO2/ΔC = 1.45). Our results show that the net biological oxygen production in the global upper ocean is 773.4 ± 108.2 Tmol O2 yr-1, i.e. the global ANCP is estimated to be 6.4 ± 0.9 Pg C yr-1. Given that the most recent estimate of global ocean net primary production (NPP) is 53 ± 7 Pg C yr-1, the global ocean carbon export rate is about 12%. In the presentation we will further discuss the spatial pattern and seasonal cycle of NCP and its driving factors.