Banse Early Career Scientist Seminar, 11 Oct 2023

Wednesday, October 11, 03:30 PM to 04:30 PM PDT

Banse Early Career Scientist Seminar
Contrasting Productivity and Carbon Export Regimes from Autonomous Observations in the EXPORTS Field Campaigns 

Shawnee Traylor
MIT/WHOI Joint Program

3:30 to 4:30 P.M., 425 Ocean Sciences Bldg 
with reception to follow

ABSTRACT:
The expansion of autonomous observation platforms offers vast opportunities for analyzing ocean ecosystems and their role in carbon export. As part of the EXport Processes in the Ocean from RemoTe Sensing (EXPORTS) field campaigns, we autonomously measured the productivity regimes in two contrasting endmember sites. The first campaign occurred in a high nutrient, low chlorophyll site in the subpolar North Pacific (NPac) near Ocean Station Papa, characterized by iron limitation and a highly regenerative regime, while the second captured a springtime bloom in the North Atlantic (NAtl), which typically drives efficient export of productivity. Using a combination of floats and gliders equipped with biogeochemical sensors, gross primary productivity (GPP), net community production (NCP), and an organic carbon flux (fCorg) were quantified and compared to ship-based measurements. The NAtl site demonstrated higher cruise-period productivity, with roughly 5x the GPP and 14x the euphotic zone NCP seen in the NPac. Greater export efficiency in the NAtl was reflected in numerous indices, such as the ratio of new production to NPP (ef-ratio; NPac: 0.23; NAtl: 0.74), the ratio of sinking particulate organic carbon (POC) to NPP (ez-ratio; NPac: 0.35; NAtl: 0.70), and total cruise-integrated 100m fCorg (NPac: 87; NAtl: 514 mmol C m-2). Together with POC flux derived from thorium-234 measurements, we infer that observed low NCP was almost entirely routed to sinking POC in the NPac, while the much higher NCP in the NAtl resulted in near equal proportions routed to dissolved organic carbon production and sinking POC flux.

The expansion of autonomous observation platforms offers vast opportunities for analyzing ocean ecosystems and their role in carbon export. As part of the EXport Processes in the Ocean from RemoTe Sensing (EXPORTS) field campaigns, we autonomously measured the productivity regimes in two contrasting endmember sites. The first campaign occurred in a high nutrient, low chlorophyll site in the subpolar North Pacific (NPac) near Ocean Station Papa, characterized by iron limitation and a highly regenerative regime, while the second captured a springtime bloom in the North Atlantic (NAtl), which typically drives efficient export of productivity. Using a combination of floats and gliders equipped with biogeochemical sensors, gross primary productivity (GPP), net community production (NCP), and an organic carbon flux (fCorg) were quantified and compared to ship-based measurements. The NAtl site demonstrated higher cruise-period productivity, with roughly 5x the GPP and 14x the euphotic zone NCP seen in the NPac. Greater export efficiency in the NAtl was reflected in numerous indices, such as the ratio of new production to NPP (ef-ratio; NPac: 0.23; NAtl: 0.74), the ratio of sinking particulate organic carbon (POC) to NPP (ez-ratio; NPac: 0.35; NAtl: 0.70), and total cruise-integrated 100m fCorg (NPac: 87; NAtl: 514 mmol C m-2). Together with POC flux derived from thorium-234 measurements, we infer that observed low NCP was almost entirely routed to sinking POC in the NPac, while the much higher NCP in the NAtl resulted in near equal proportions routed to dissolved organic carbon production and sinking POC flux.