Abstract
Enhanced atmospheric input of dust-borne nutrients and minerals to the remote surface ocean can potentially increase carbon uptake and sequestration at depth. Nutrients can enhance primary productivity, and mineral particles act as ballast, increasing sinking rates of particulate organic matter. Here we present a two-year time series of sediment trap observations of particulate organic carbon flux to 3,000 m depth, measured directly in two locations: the dust-rich central North Atlantic gyre and the dust-poor South Atlantic gyre. We find that carbon fluxes are twice as high and a higher proportion of primary production is exported to depth in the dust-rich North Atlantic gyre. Low stable nitrogen isotope ratios suggest that high fluxes result from the stimulation of nitrogen fixation and productivity following the deposition of dust-borne nutrients. Sediment traps in the northern gyre also collected intact colonies of nitrogen-fixing Trichodesmium species. Whereas ballast in the southern gyre is predominantly biogenic, dust-derived mineral particles constitute the dominant ballast element during the enhanced carbon fluxes in the northern gyre. We conclude that dust deposition increases carbon sequestration in the North Atlantic gyre through the fertilization of the nitrogen-fixing community in surface waters and mineral ballasting of sinking particles.
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Acknowledgements
We thank the captains and crew of the RRS Discovery, RRS James Clark Ross and RRS James Cook during cruises D324, D334, JCR186, JCR215 and JC05 for deploying and recovering of the McLane sediment traps. We are grateful to M. Cooper, C. Marsay, P. Martin, A. Moje, P. Statham and M. Stinchcombe for their assistance with laboratory work and advice on analytical and sample-handling issues. We thank J. Prospero for providing the Barbados dust concentration data, and N. Mahowald for modelled dust deposition flux data. We thank the British Oceanographic Data Centre and NASA Ocean Colour, and Ocean Productivity website for providing ancillary data. We thank A. Poulton and R. Sanders for participation in results discussion and feedback on this manuscript. This work was funded by NERC Oceans 2025 project and EU FP7-ENV-2007-1 Collaborative Project 202955 EuroSITES, Integration and enhancement of key existing European deep-ocean observatories. This work is a part of doctoral dissertation of K.P. funded by National Oceanography Centre, Southampton and the University of Southampton. This study also contributes to the international IMBER project and was supported by the UK Natural Environment Research Council National Capability funding to Plymouth Marine Laboratory and the National Oceanography Centre, Southampton. This is contribution number 291 of the AMT programme.
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K.P. and R.S.L. designed and conducted the research; K.P. analysed the data and wrote the manuscript together with R.S.L.; J.B., C.C., R.M., P.P. and C.P. coordinated sediment trap operations; F.A.C.L.M. and C.M.M. contributed to the interpretation of the results; A.P.R., G.H.T. and E.M.S.W. provided the ancillary biogeochemical data.
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Pabortsava, K., Lampitt, R., Benson, J. et al. Carbon sequestration in the deep Atlantic enhanced by Saharan dust. Nature Geosci 10, 189–194 (2017). https://doi.org/10.1038/ngeo2899
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