Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
doi:10.5194/bg-2016-548
© Author(s) 2017. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
11 Jan 2017
Review status
This discussion paper is under review for the journal Biogeosciences (BG).
On the long-range offshore transport of organic carbon from the Canary Upwelling System to the open North Atlantic
Elisa Lovecchio1, Nicolas Gruber1, Matthias Münnich1, and Zouhair Lachkar2 1ETH-Zürich, Universitätstrasse 16, 8092 Zürich, Switzerland
2Center for Prototype Climate Modeling, New York University Abu Dhabi, Abu Dhabi, UAE
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 north-western 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 over the whole CanUS about 19 Tg C yr−1 away from the nearshore 100 km, amounting to more than a third of the NCP in this region. The offshore transport extends beyond 1500 km into the subtropical North Atlantic, along the way adding organic carbon 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 on the north-western 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 to the upper 100 m as much organic carbon as nearly 60 % of the local NCP, giving rise to a sharp peak of offshore respiration that extends to the middle of the gyre. 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.

Citation: Lovecchio, E., Gruber, N., Münnich, M., and Lachkar, Z.: On the long-range offshore transport of organic carbon from the Canary Upwelling System to the open North Atlantic, Biogeosciences Discuss., doi:10.5194/bg-2016-548, in review, 2017.
Elisa Lovecchio et al.
Elisa Lovecchio et al.
Elisa Lovecchio et al.

Viewed

Total article views: 170 (including HTML, PDF, and XML)

HTML PDF XML Total BibTeX EndNote
134 33 3 170 1 3

Views and downloads (calculated since 11 Jan 2017)

Cumulative views and downloads (calculated since 11 Jan 2017)

Viewed (geographical distribution)

Total article views: 170 (including HTML, PDF, and XML)

Thereof 170 with geography defined and 0 with unknown origin.

Country # Views %
  • 1

Saved

Discussed

Latest update: 27 Feb 2017
Publications Copernicus
Download
Short summary
We find that a big portion of the phytoplankton, zooplankton and detrital organic matter produced near the North African coast is laterally transported towards the open North Atlantic. This offshore flux sustains a relevant part of the biological activity in the open sea and reaches as far as the middle of the North Atlantic. Our results, obtained with a state of the art model, highlight the fundamental role of the narrow but productive coastal ocean in the sustainment of the global marine life.
We find that a big portion of the phytoplankton, zooplankton and detrital organic matter...
Share