The Dusty Team - including researchers from MARE, NIOZ and MARUM-Bremen - is finally preparing everything to get on board of Research Vessel Pelagia, to be part of an expedition led by dust-expert and CHASE partner Jan-Berend Stuut (NIOZ) for investigating the biogeochemical effects of Saharan dust deposition in the tropical Atlantic. This is especially exciting for those of us who haven’t sailed since before the Covid pandemics!
The RV Pelagia is a 66 m versatile vessel fully equipped for multidisciplinary research, and is the Netherland’s largest sea-going research vessel. Our pre-expedition on-line meeting was on the 17 January to discuss the scientific goals of each member of the team, and outline the best sampling/monitoring strategy towards maximising the expedition outcomes in the context of ongoing collaborations between MARE-UL, NIOZ and MARUM-Bremen.
Printscreen from the presentation given by the chief-scientist Jan-Berend Stuut during our pre-cruise online meeting. Jan-Berend is senior researcher at the NIOZ, with expertise in mineral dust dynamics (from source to sink) and long-time scientific partner during our investigations across the tropical North Atlantic in the context of former projects ERC-DustTraffic and H2020-DUSCTO, and of our ongoing projects FCT-CHASE and NWO-Med-Trap.
At MARE, all the equipment and laboratory material needed for collecting marine phytoplankton (including the beautiful coccolithophores!) have been dully packed and shipped to the NIOZ.
Chasing the effects of dust in the ocean: why do we care?
Of all the continental deserts, the Sahara is the world’s largest source of atmospheric soil dust. Up to ca. 180 Million Tons of dust are blown out from the Saharan and Sahel desert regions and transported across the Atlantic by the Trade Winds. This is recurrently seen from satellite remote sensing images of massive dust plumes extending from Africa to the Americas, as illustrated from the European Space Agency (ESA) image shown below. The image shows the spread of aerosols from the Saharan dust plume (nicknamed “Godzilla”) moving westward across the Atlantic Ocean in June 2020, measured by Copernicus Sentinel-5P.
African dust plumes can also travel north, reaching latitudes as high as the Netherlands or the UK, affecting the quality of the air and turning skies orange all over Europe. This was precisely the case nearly one year ago, when a massive dust plume travelled far north in March 2022, affecting the atmosphere and landscapes of all countries in its path. Spain, France, and Portugal were the regions more affected in terms of decreased air quality due to the high volumes from this extreme dust event. A strikingly orange sky over the 25 April bridge, linking Lisbon to Almada (Portugal) nicely captures this event in the image below (Photo credits: Gomes et al., 2022).
As if these aspects of atmospheric dust dynamics weren’t already fascinating enough, it turns out that a huge amount of African dust ends up being deposited across the Atlantic and on the Amazon rainforest, acting as a long-range vehicle of transport of nutrients (such as phosphorus and iron) that are essential for fuelling marine phytoplankton. This crucially matters because phytoplankton contributes up to half of the oxygen that we breathe while also contributing to sequester up to 50% of atmospheric CO2 through photosynthesis. This means that atmospheric dust deposition has the potential of changing the earth’s climate through fertilising the ocean (nutrient source) and by accelerating the export and sequestration of carbon via the biological carbon pump (ballasting effect). All these processes are likely to become increasingly important under the current scenario of climate-driven ocean warming and its subsequent nutrient-depletion.
It is precisely with the aim of investigating these issues that we are leaving the harbour of Mindelo (Cape Verde) on the 5 March to sail across a meridional transect off the coast of Mauritania, collecting in situ data from the atmosphere and from the underlaying ocean. Being adjacent to NW Africa, the tropical NE Atlantic provides a natural laboratory to explore the effects of Saharan-driven land-atmosphere-ocean extreme compound events on marine productivity and biogeochemistry.
This is also the region where our partner institutes NIOZ and MARUM-Bremen have deployed multi-parametric buoys with dust collectors (powered by solar panels, which suck air through filters), and oceanographic moorings with sediment traps to collect material settling through the ocean. Combined, these oceanographic instruments provide time-series of fluxes of dust, as well as of biogenic particles (both organic and inorganic) that are mostly produced by plankton, which are further compared with satellite and meteorological data.
Jan-Berend Stuut (left) and Bob Koster (right) from the NIOZ, looking at sediment trap mooring M1 being recovered after collecting 1 year of particles fluxes in the NE tropical North Atlantic during the DustTraffic expedition on board RRV James Cook, in March-April 2016 (Photo Credits: Catarina V. Guerreiro).
Our goal is to combine insights from the biological, hydrological, and sedimentological data collected during the expedition with data from these buoys and sediment traps for investigating the link of Saharan dust deposition to shifts in phytoplankton communities living in the underling photic zone. Our interest will be especially focused on studying the response of coccolithophore communities because of their biogeochemical importance, as the major group of calcifying primary producers in the modern ocean, and thereby key players in modulating the biological carbon pump (Guerreiro et al., 2021).
View of the multiparametric buoy with the dust collector on top, being recovered at mooting site CB located offshore Cape Blanc (Mauritania), during the DustTraffic expedition on board RRV James Cook, in March-April 2016. You can see how highly productive are ocean conditions at site CB, as illustrated by the surface of the buoy completely covered with barnacles after being deployed for only 6 months (Photo Credids: Catarina V. Guerreiro).
Since our study region is part of the Canary Current Eastern Boundary Upwelling System (EBUS), outcomes from the expedition will also contribute to the aims of CHASE-affiliated ESA-funded project PRIMUS (PRIMary-productivity in Upwelling Systems) where we lead an Earth Science Case using particle flux data from sediment trap mooring sites CB and M1.