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

Abstract

While 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.

Carbon cycling in the North American coastal ocean: a synthesis

“…Carbon export flux from coastal waters to the deep ocean cannot be quantified easily or accurately through direct observation, especially considering the three-dimensional nature of exchanges between the coastal and open ocean (Frischknecht et al, 2018). Thus, the only available estimates of such export are indirect, using mass balances of POC and dissolved oxygen (Hales et al, 2006), mass balances of DOC (Barrón and Duarte, 2015;Vlahos et al, 2002), mass balances of TOC and DIC (Najjar et al, 2018), or model estimates (Izett and Fennel, 2018a, b;Bourgeois et al, 2016;Fennel and Wilkin, 2009;Mannino et al, 2016;Xue et al, 2013;Frischknecht et al, 2018). If the total carbon inventory in a coastal system can be considered constant over a sufficiently long timescale (i.e., of the order of years), inferring carbon export is possible using the sum of all other exchange fluxes across the system's interfaces over that same period.…”

Dynamics of inorganic carbon and pH in a large subtropical continental shelf system: Interaction between eutrophication, hypoxia, and ocean acidification

“…However, a mechanistic understanding and quantitative diagnosis of DIC and pH dynamics in complex coastal environments is challenging. In contrast to coastal upwelling systems (e.g., Gruber et al ; Lachkar and Gruber ; Capone and Hutchins ; Frischknecht et al ), the physical transport and biological transformation of carbon and nutrients in coastal regions affected by large riverine discharges are more dynamic and complicated due to substantial anthropogenic disturbances (Doney ; Regnier et al ; Wallace et al ) and their spatial decoupling (Cai et al ; Rabalais et al ; Zhang et al ). A sufficient quantity of freshwater input facilitates the stabilization of the water column and strengthens vertical stratification (MacCready et al ; Lu and Gan ), leading to a proliferation in phytoplankton biomass in the thin, fast‐flowing buoyant plume flowing over onshore‐entrained seawater (e.g., Yin et al ; Dai et al ; Zhou et al ; Wong et al ) but inhibiting the ventilation of subsurface water.…”

A Lagrangian study of the contribution of the Canary coastal upwelling to the open North Atlantic nitrogen budget

“…Bay area (22 • S-24 • S) were linearly extrapolated to the whole BenCS Frischknecht et al (2018). also found high offshore export of both organic and inorganic nitrogen from the productive central region of the California current system (CalCS) to the open ocean as far as 500 km from the coast(Table 4, SI).…”

“…For instance, it has been estimated that continental margins contribute nearly half of the globally integrated oceanic primary production, although they only occupy about 10% of the world ocean surface (Walsh, 1991;Smith and Hollibaugh, 1993;Muller-Karger et al, 2005;Liu et al, 2010;Jahnke, 1990). The coastal ocean is not only highly productive, but is also a major source of nutrients and organic matter to the open ocean (Liu et al, 2000(Liu et al, , 2010Lovecchio et al, 2017;Frischknecht et al, 2018). For example, Wollast (1998) and Ducklow and McCallister (2004) estimated that about half of the total production in the coastal ocean is exported laterally, leading to substantial modifications of the biogeochemical cycles there.…”