942 / 2024-09-19 21:31:53

Spatial and temporal variability in the Kuroshio Extension nutrient stream from BGC-Argo and repeat hydrography

Kuroshio Extension,BGC-Argo,Nutrient stream,Productivity,Nitrate

The depth of the nutricline and the magnitude of vertical nutrient fluxes have a direct influence on primary productivity and the strength of the biological carbon pump. Western boundary currents have been shown to be hotspots for carbon cycling, largely due to their high levels of eddy kinetic energy superimposed over large latitudinal gradients in physical and biogeochemical properties. The presence of mesoscale eddies and submesoscale filaments drives variability in the mixed layer and the nutricline depth over a wide range of space and time scales, and contributes to the maintenance of a subsurface “nutrient stream”. The Kuroshio Extension nutrient stream supports large lateral transports of nutrients within the upper thermocline, and is characterized by a persistent along-isopycnal positive nitrate anomaly. However the extent of spatial and temporal variability in the along-stream nutrient anomaly and nutricline depth in the north western Pacific is not well known, partly due to the relatively sparse number of nutrient profiles over the broader region. In this study, data from a large number of continuous nitrate profiles from BGC-Argo floats deployed in the western Pacific as well as repeat hydrography data, spanning multiple years and seasons, are used to determine temporal and spatial variability in the nutricline depth and nitrate anomaly, and how they relate to physical dynamics and primary productivity estimated from remote sensing.