Origin, Transformation, and Fate: The Three‐Dimensional Biological Pump in the California Current System

Abstract

AbstractWhile the Ekman drift as the cause for the high productivity of the California Current System was unraveled more than a century ago, it is less clear where the nutrients within the upwelling waters are coming from, and what the fate of the produced organic matter is. Here we address these questions using a high‐resolution simulation with a regional coupled physical/biogeochemical/ecological model within a Pacific Ocean setup. Our results, emerging from both Eulerian and Lagrangian analyses, reveal that prior to coastal production, inorganic nutrients get transported laterally over thousands of kilometers toward central California. More than 80% of the nutrients originate from central offshore or southern alongshore locations. About half of it is supplied by the California Undercurrent alone, underscoring its importance in sustaining the high coastal productivity. Even though most of the inorganic nutrients get quickly transformed into organic matter once upwelled to the euphotic layer along the coast, a substantial fraction remains unused. Together with these unused nutrients, about 36% of the organic matter produced within the nearshore 100 km gets laterally exported toward the open ocean, mostly in southwestward direction. This leakage of inorganic nutrients from the coastal zone and the continuous recycling of organic matter along the way support up to 24% of the overall observed production at a distance of 500 km from the coast. This set of processes linking the origin, biological transformation, and fate of nutrients support the growing view of the biological pump being an inherently three‐dimensional process.