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

Abstract

Abstract. The Canary Current System (CanCS) is a major eastern boundary upwelling system (EBUS), known for its high nearshore productivity and for sustaining a large fishery. It is also an important but not well quantified source of nitrogen to the adjacent oligotrophic subtropical gyre of the North Atlantic. Here, we use a Lagrangian modeling approach to quantify this offshore transport and investigate its timescales, reach and contribution to the fueling of productivity in the offshore regions. In our Lagrangian model, we release nearly 10 million particles off the northwestern African coast and then track all those that enter the nearshore region and upwell along the coast between 14 and 35∘ N. We then follow them as they are transported offshore, also tracking the biogeochemical transformations, permitting us to construct biogeochemical budgets along the offshore moving particles. The three-dimensional velocity field as well as the biogeochemical tracers and fluxes are taken from an eddy-resolving configuration of the Regional Ocean Modeling System (ROMS). Our Lagrangian model analysis reveals a very intense offshore transport of nitrogen, with about 20 %–40 % in the form of organic nitrogen. The transport varies greatly along the coast. Even though the central CanCS (21–28∘ N) transports the largest amount of water offshore, its offshore transport of nitrogen is somewhat smaller than that in the southern CanCS (14–21∘ N), primarily because of the higher nitrogen content of the upwelling waters there. Around one-third of the total offshore transport of water occurs around major capes along the CanCS. The persistent filaments associated with these capes are responsible for an up to 4-fold enhancement of the offshore transport of water and nitrogen in the first 400 km. Much of this water and nitrogen stems from upwelling at quite some distance from the capes, confirming the capes' role in collecting water from along the coast. North of Cape Blanc and within the first 500 km from the coast, water recirculation is a dominant feature of offshore transport. This process, likely associated with mesoscale eddies, tends to reduce the efficiency of offshore transport. The Canary upwelling is modeled to supply around 44 and 7 mmol N m−2 yr−1 to the North Atlantic Tropical Gyral (NATR) and the North Atlantic Subtropical Gyral East (NASE) Longhurst provinces, respectively. In the NATR, this represents nearly half (53 ± 26 %) of the estimated total new production, while in the NASE, this fraction is small (4 ± 2 %). Our results highlight the importance of the CanCS upwelling as a key source of nitrogen to the open North Atlantic and stress the need for improving the representation of EBUS in global coarse-resolution models.

Seasonal and Interannual Salish Sea Inflow Origins Using Lagrangian Tracking

“…Lagrangian simulations were done using Ariane, an offline Lagrangian tool capable of 3D parcel trajectory and volume transport calculations in its quantitative mode (e.g., Hailegeorgis et al., 2021; Schmidt et al., 2021; Vecchioni et al., 2023). Ariane integrates water parcel paths either forward or backwards in time (forwards for the study of pathways, backwards for source water analysis) based on velocity fields from an ocean model by calculating 3D streamlines (assuming local non‐divergence) within the cell in which a parcel is located at each time‐step (Blanke & Raynaud, 1997).…”

Climate change in the Canary/Iberia upwelling region: the role of ocean stratification and wind

“…Regional climate system models are able to account for mesoscale processes, which are not resolved by the global climate models [28,29]. This ability to reproduce the mesoscale processes allows to assess the impact of climate change on CCUS in a more realistic way, given the importance of the eddies and coastal filaments that enrich the oligotrophic open waters [30][31][32].…”

Atmospherically Driven Seasonal and Interannual Variability in the Lagrangian Transport Time Scales of a Multiple‐Inlet Coastal System

“…Transport time scales (TTS), such as the residence, exposure, transit, age, and flushing times (Monsen et al., 2002; Zimmerman, 1976), are measures for the efficiency of transport and exchange of water or freshwater content within a water body system and with its surroundings (Cucco et al., 2009; Duran‐Matute et al., 2014; Rayson et al., 2016; Xiong et al., 2021). They also serve to estimate the time that a substance, like dissolved nitrogen, takes to be transported off‐shore from high‐productivity coastal regions (Hailegeorgis et al., 2021); to understand the variability of the mineralization rates of organic matter in sediments (den Heyer & Kalff, 1998); to explain regional differences of nutrient and eutrophication levels (González et al., 2008; Schwichtenberg et al., 2017); and as a first‐order estimation of the exposure of a region (e.g., a protected area) to pollutants (Patgaonkar et al., 2012; Pawlowicz et al., 2019; Soomere et al., 2011).…”