Partitioning the Export of Distinct Biogenic Carbon Pools in the Northeast Pacific Ocean Using a Biogeochemical Profiling Float

Abstract

We leverage observations from chemical and bio‐optical sensors mounted on a biogeochemical profiling float in the Northeast Pacific Ocean to quantify the cycling and export potential of distinct biogenic carbon pools, including particulate inorganic carbon (PIC), particulate organic carbon (POC), and dissolved organic carbon (DOC). Year‐round observations reveal complex carbon cycle dynamics among these carbon pools. Net DOC production peaked during bloom initiation, about 3 months prior to the summer peak in POC production. We validate the float estimates of DOC cycling with seasonal accumulation and removal rates derived from ship‐board DOC observations over the same period. By combining chemical and bio‐optical tracers of POC cycling, we estimate the instantaneous POC sinking flux (FPOCsinking ${\mathrm{F}}_{{\text{POC}}_{\text{sinking}}}$). The cooccurrence of DOC consumption and POC production and sinking during fall and winter resolves the regional conundrum of a persistent particle sinking flux observed by sediment traps during a season that is known to be heterotrophic. PIC production is small, and uncertainties are large. By combining float‐based estimates of instantaneous net primary production (NPP) and FPOCsinking ${\mathrm{F}}_{{\text{POC}}_{\text{sinking}}}$, we quantify a real‐time carbon export ratio ([FPOCsinking ${\mathrm{F}}_{{\text{POC}}_{\text{sinking}}}$/NPP] × 100%) for the euphotic zone. Elevated export ratios during summer are associated with an increase in the fraction of particles larger than 100 μm in size. Elevated export ratios during winter are associated with the physical redistribution of particles through seasonal deep mixing. Our study demonstrates how the combined use of multiple sensors on biogeochemical profiling floats can provide more nuanced information about upper ocean carbon cycle dynamics.

Relationship between surface dissolved iron inventories and net community production during a marine heatwave in the subarctic northeast Pacific

“…25 Using ΔNO 3 − alone to estimate NCP in this manner assumes that all variation in dissolved NO 3 − is due to phytoplankton uptake and that biases introduced by evaporation/precipitation, diapycnal diffusion and horizontal advection are negligible. 14,25,26 Average depth integrated trace metal concentrations were calculated over the same depth range, along with winter to summer dissolved iron : nitrate (ΔFe : ΔNO 3 − ), silicate : nitrate (ΔSi : ΔNO 3 − ), and cadmium : phosphate (ΔCd : ΔPO 4 ) uptake ratios.…”

Controlling factors of the climatological annual cycle of the surface mixed layer oxygen content: A global view

“…F p may be estimated using (Liang et al, 2013;Yang et al, 2017;Emerson et al, 2019;Huang et al, 2022):…”

A new, global optical sediment trap calibration

“…A growing network of autonomous ocean-observing platforms now provides estimates of total BCP fluxes through geochemical budgets of DIC, nitrate, and oxygen, but these estimates do not distinguish the contribution of the GCP (Nicholson et al 2008;Johnson et al 2017;Huang et al 2022). Profiling platforms that measure optical backscattering (bbp) provide POC flux estimates by measuring change in the depth-integrated POC inventory vs. time (Dall'Olmo and Mork 2014), and are calibrated using a broad global dataset of POC:bbp measurements (e.g., Cetinić et al 2012).…”