Exchange of carbon by an upwelling filament off Cape Ghir (NW Africa)

García-Muñoz, Mercedes; Arı́stegui, Javier; Pelegrí, Josep Lluís; Antoranz, Ana; Ojeda, Antonio A. Ramón; Torres, M. A. Lopez

doi:10.1016/j.jmarsys.2004.07.005

Cited by 63 publications

(58 citation statements)

References 31 publications

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“…The portion of CanUS located north of the Cabo Verde front can be regarded as the very eastern edge of the North Atlantic Gyre . Several studies highlight the way in which the abundant coastal filaments of this northern CanUS sector substantially enhance the offshore transport and the downwelling of organic carbon in the first hundreds of kilometers from the coast (Álvarez-Salgado et al, 2007;Gabric et al, 1993;García-Muñoz et al, 2005;Ohde et al, 2015). These structures together with a strong mean offshore flow explain the intense zonal transport and the vertical downwelling in the shelf region of the northern CanUS and the sharp decline of these two fluxes in the open waters.…”

Section: Implications and Comparison With Previous Workmentioning

confidence: 99%

“…On top of the mean Ekman transport, persistent filaments originating on the CanUS shelf have been reported to be able to export up to 50 % of the coastally produced organic matter as far as several hundreds of kilometers offshore (Gabric et al, 1993;Ohde et al, 2015). Due to these fluxes, a substantial amount of coastally produced organic carbon in the CanUS escapes remineralization in the nearshore region and is advected offshore towards the center of the North Atlantic Gyre García-Muñoz et al, 2005;Álvarez-Salgado and Arístegui, 2015). Estimates from multiple local surveys indicate that on average about 16 % of the coastal production from phytoplankton is laterally exported to the open sea (Duarte and Cebrián, 1996).…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

On the long-range offshore transport of organic carbon from the Canary Upwelling System to the open North Atlantic

Lovecchio¹,

Gruber²,

Münnich³

et al. 2017

Biogeosciences

106

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Abstract. A compilation of measurements of net community production (NCP) in the upper waters of the eastern subtropical North Atlantic had suggested net heterotrophic conditions, purportedly supported by the lateral export of organic carbon from the adjacent, highly productive Canary Upwelling System (CanUS). Here, we quantify and assess this lateral export using the Regional Ocean Modeling System (ROMS) coupled to a nutrient, phytoplankton, zooplankton, and detritus (NPZD) ecosystem model. We employ a new Atlantic telescopic grid with a strong refinement towards the northwestern African shelf to combine an eddy-resolving resolution in the CanUS with a full Atlantic basin perspective. Our climatologically forced simulation reveals an intense offshore flux of organic carbon that transports about 19 Tg C yr −1 away from the nearshore 100 km over the whole CanUS, amounting to more than a third of the NCP in this region. The offshore transport extends beyond 1500 km into the subtropical North Atlantic, adding organic carbon along the way to the upper 100 m at rates of between 8 and 34 % of the alongshore average NCP as a function of offshore distance. Although the divergence of this lateral export of organic carbon enhances local respiration, the upper 100 m layer in our model remains net autotrophic in the entire eastern subtropical North Atlantic. However, the vertical export of this organic carbon and its subsequent remineralization at depth makes the vertically integrated NCP strongly negative throughout this region, with the exception of a narrow band along the northwestern African shelf. The magnitude and efficiency of the lateral export varies substantially between the different subregions. In particular, the central coast near Cape Blanc is particularly efficient in collecting organic carbon on the shelf and subsequently transporting it offshore. In this central subregion, the offshore transport adds as much organic carbon as nearly 60 % of the local NCP to the upper 100 m, giving rise to a sharp peak of offshore respiration that extends to the middle of the gyre. Our modeled offshore transport of organic carbon is likely a lower-bound estimate due to our lack of full consideration of the contribution of dissolved organic carbon and that of particulate organic carbon stemming from the resuspension of sediments. But even in the absence of these contributions, our results emphasize the fundamental role of the lateral redistribution of the organic carbon for the maintenance of the heterotrophic activity in the open sea.

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Section: Implications and Comparison With Previous Workmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

On the long-range offshore transport of organic carbon from the Canary Upwelling System to the open North Atlantic

Lovecchio¹,

Gruber²,

Münnich³

et al. 2017

Biogeosciences

106

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“…Mesoscale structures and especially filaments are known to export large quantities of DOC, which can represent up to 70 % 10 of the total C org transported offshore (Santana-Falcón et al, 2016;García-Muñoz et al, 2005). However, only a small part of this exported DOC is biologically available for the offshore biological activity (Hansell et al, 2009).…”

Section: Model Limitationsmentioning

confidence: 99%

“…Locally, this transport can exceed the mean Ekman transport in the nearshore several times (Rossi et al, 2013;Álvarez-Salgado, 2007). The laterally exported C org , part of it in the form of particulate organic carbon (POC) and part of it in the form of dissolved organic carbon (DOC) (García-Muñoz et al, 2005), may accumulate then in the 20 oligotrophic open ocean regions (Álvarez-Salgado, 2007), eventually fueling heterotrophic activity there. In addition to C org , filaments are also responsible for the lateral export of chlorophyll, nutrients (Cravo et al, 2010) and living organisms (Brochier et al, 2014) to the open sea.…”

Section: Introductionmentioning

confidence: 99%

Mesoscale contribution to the long-range offshore transport of organic carbon from the Canary Upwelling System to the open North Atlantic

Lovecchio¹,

Gruber²,

Münnich³

2018

Preprint

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Abstract. Several studies in upwelling regions have suggested that mesoscale structures, such as eddies and filaments, contribute substantially to the long-range transport of the organic carbon from the nearshore region of production to the offshore region of remineralization. Yet this has not been demonstrated in a quantitative manner for the entire Canary Upwelling System (CanUS). Here, we fill this gap using the Regional Oceanic Modeling System (ROMS) coupled to a Nutrient, Phytoplankton, Zooplankton, and Detritus (NPZD) ecosystem model. We run climatological simulations on an Atlantic telescopic grid with 5 an eddy-resolving resolution in the CanUS. Using both a Reynolds flux decomposition and structure-identification algorithms, we quantify and characterize the organic carbon fluxes driven by filaments and eddies within the upper 100 m and put them in relationship to the total offshore transport. Our analyses reveal that both coastal filaments and eddies enhance the offshore flux of organic carbon, but that their contribution is very different. Upwelling filaments, with their high speeds and high organic carbon concentrations, transport this carbon offshore in a very intense, but coastally-confined, manner, contributing nearly 10 80% to the total flux at 100 km offshore distance. The filament contribution tapers off quickly to near zero values at 1000 km distance, leading to a strong offshore flux divergence that is the main lateral source of organic carbon in the first 500 km offshore. Some of this divergence is also due to the filaments inducing a substantial vertical subduction of the organic carbon below 100 m. Owing to the temporal persistence and spatial recurrence of filaments, the filament transport largely constitutes a time-mean flux and only to a limited degree represents a turbulent flux. At distances beyond 500 km from the coast, eddies 15 dominate the mesoscale offshore transport. Although their contribution represents only 20 % of the total offshore flux and of its divergence, eddies, especially cyclones, transport organic carbon offshore to distances as great as 2000 km from the coast.The eddy transport largely represents a turbulent flux, but striations in this transport highlight the existence of typical formation spots and recurrent offshore propagation pathways. While they propagate slowly, eddies are an important organic carbon reservoir for the open waters, since they contain on average a third of the offshore organic carbon, two third of which is found 20 in cyclones. Our analysis confirms the importance of mesoscale processes for the offshore organic carbon transport and the fueling of the heterotrophic activity in the eastern subtropical North Atlantic, and highlights the need to consider the mesoscale flux in order to fully account for the three-dimensionality of the marine biological pump.

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“…In the lifetime of CANIGO, permanent moorings, scientific and opportunity cruises, and remote sensing data provided an improved view of the spatio-temporal variability of the NW Africa system (e.g. Van Camp et al, 1991;Nykjaer and van Camp, 1994;Hernández-Guerra and Nykjaer, 1997;Pacheco and Hernández-Guerra, 1999;Hernández-Guerra et al, 2001;Knoll et al, 2002;Tejera et al, 2002;Hernández-Guerra et al, 2003;Pelegrí et al, 2005a;Pelegrí et al, 2005b;García-Muñoz et al, 2005;Machín et al, 2006a). One main outcome of the CANIGO program was to realize that a major fraction of the eastern boundary recirculation of central waters, or Canary Current (CC), occurs in the CTZ, a relatively narrow region where intense transfer takes place between subsurface and surface waters.…”

Section: Introductionmentioning

confidence: 99%

Three-dimensional circulation in the NW Africa coastal transition zone

Benítez-Barrios

Pelegrí

Hernández‐Guerra

et al. 2011

Progress in Oceanography

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High-resolution data collected southeast of the Canary Islands during late winter 2006 are analyzed to describe the hydrography and three-dimensional circulation in the coastal transition zone off NW Africa. The data are optimally interpolated over a regular grid, the geostrophic velocity field is calculated and the Q-vector formulation of the omega equation is used to compute the quasi-geostrophic (QG) mesoscale vertical velocity. The coastal transition zone is divided into upwelling, frontal and offshore regions with distinct physical and dynamic characteristics.

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Exchange of carbon by an upwelling filament off Cape Ghir (NW Africa)

Cited by 63 publications

References 31 publications

On the long-range offshore transport of organic carbon from the Canary Upwelling System to the open North Atlantic

On the long-range offshore transport of organic carbon from the Canary Upwelling System to the open North Atlantic

Mesoscale contribution to the long-range offshore transport of organic carbon from the Canary Upwelling System to the open North Atlantic

Three-dimensional circulation in the NW Africa coastal transition zone

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