Abstract
To assess the impacts of Amazon River discharge, Saharan dust deposition, N2-fixation and mixed-layer deepening on the biological carbon pump, sediment traps were moored from October 2012 to November 2013 at two sites in the western tropical North Atlantic (49°W,12°N/57°W,12°N). Particle exports interpreted along with satellite- and Argo-float data show peak fluxes in biogenic silica (31 mg m−2 d−1) and organic carbon (25 mg m−2 d−1) during the fall of 2013 that were ten to five times higher than any time earlier during the year. These high export fluxes occurred in tandem with high surface chlorophyll a concentrations associated with the dispersal of the Amazon River plume, following retroflection into the North-Atlantic-Counter-Current. High fucoxanthin fluxes (' 80 μg m−2 d−1) and low δ15N-values (−0.6‰) suggest a large contribution by marine diatom-diazotrophic-associations, possibly enhanced by wet Saharan dust deposition. During summer, the Amazon River plume resulted in high mass fluxes at 57°W that were enriched in biogenic silica but weakly influenced by diazotrophic-associations compared to the fall event at 49°W. High carbonate-carbon fluxes (17 mg m−2 d−1) dominated a second single event at 49°W during spring that was likely triggered by mixed-layer deepening. Rain-ratios of BSi/Ccarb amounted to 1.7 when associated with high export fluxes linked to the Amazon River plume. Compared to an annual average of 0.3, this indicates a more efficient uptake of CO2 via the biological pump compared to when the plume was absent, hence supporting earlier observations that the Amazon River plume is important for ocean CO2 sequestration.
Original language | English |
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Pages (from-to) | 2108-2124 |
Number of pages | 17 |
Journal | Limnology and Oceanography |
Volume | 65 |
Issue number | 9 |
Early online date | 2 Apr 2020 |
DOIs | |
Publication status | Published - Sept 2020 |
Funding
This project is funded by the ERC (project no. 311152) and NWO (project no. 822.01.008). In addition, this study had the support of the European Union, through a Marie Sklodowska‐Curie European Fellowship supported by the European Union H2020‐MSCA‐IF‐2017 under grant agreement no. 796802, awarded to Catarina V. Guerreiro ( www.dustco-online.pt ). The authors acknowledge NIOZ technicians, captains and their crews for their assistance during cruises Meteor M89 and Pelagia 64PE378. The authors thank Jort Ossebaar for helping with the EA‐IRMS analysis, Sharyn Ossebaar for assisting with biogenic silica measurements and Evaline van Weerlee for UPLC‐measurements. Carolina Sá (MARE, University of Lisbon, Portugal) is thanked for downloading and processing of the satellite data and Jon Lewis (Loughborough University, UK) for diatom identification. The authors would like to thank two anonymous reviewers for their time, comments and helpful suggestions that contributed to improving the manuscript.
Funders | Funder number |
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European Union H2020-MSCA-IF-2017 | 64PE378 |
European Union H2020‐MSCA‐IF‐2017 | |
Horizon 2020 Framework Programme | 796802, 311152 |
European Commission | |
European Research Council | |
Loughborough University | |
Nederlandse Organisatie voor Wetenschappelijk Onderzoek | 822.01.008 |
Universidade de Lisboa |