AIMS OF DUSTCO
DUSTCO project as a gap-filler!
Most of the existing dust-fertilization studies are based on models, bioassays and satellite data that only cover the surface of the ocean, whereas there are very few studies that are based in actual field observations and taking into account phytoplankton productivity along the entire photic zone. This happens because implementing long-term sampling to constrain the spatial and temporal variability of these processes in the vast and remote open ocean is rather costly and logistically complicated. DUSTCO aims to contribute to fill this gap, by investigating the biological and biogeochemical effects of Saharan dust across the tropical North Atlantic, based on in situ observations of the atmosphere and of the entire photic layer, and using a multidisciplinary and spatio-temporal approach.
where and how are we going to do it?
DUSTCO is based on biological, sedimentological and hydrological data that were collected and measured along a transatlantic array between the NW Africa and the Caribbean, lying right underneath the largest dust plume originating from Africa (12º N), during the DUSTTRAFFIC JC134 expedition (19 March – 16 April 2016).
The first step was to monitor the hydrological and biological characteristics of the photic layer, for which we have used a CTD. A CTD is an oceanographic instrument that is used to measure the conductivity, temperature and pressure of the seawater, that often comes incorporated within a "rosette" of NISKIN bottles that are closed remotely from the ship to collect seawater samples at predefined depths. In addition to the CTD, we can also attach other sensors to measure relevant parameters.
At every station during the expedition, we used a CTD-rosette to measure how temperature, salinity, oxygen, fluorescence, light, nutrients and Chl-a varied from the surface of the ocean down to underneath the photic zone.
Once the CTD was recovered back to the ship, we collected plankton samples from the NISKIN-bottles for the coccolithophore analysis, which had been sampled at 10 m, 20 m, 40 m, 60 m, 80 m, 100 m, 125 m, 150 m, 200 m and 250 m. For most of the cases, 5 L of these water samples were filtered through cellulose nitrate filters (25 mm diameter, 0,45 μm pore size) by means of a water jet pump immediately on board.
In addition to the water sampling and CTD profiling, we also collected daily aerosol samples which will provide the basis to quantify the amount and composition of dust deposited in the ocean and investigate their link to changes in biomass and species composition. We are especially curious about the events of 29-31 March and 9-10 April which was when the dust-collector filters clearly indicated high levels of atmospheric dust in the study area.
Finally, the material and data collected from the photic layer will be further compared with 1-year of dust- and coccolith flux data from 5 long-term sediment trap moorings which were deployed along the same transatlantic array: sites M1, M2, M4 and M5 located at ~12ºN, collecting particles synchronously between Oct. 2012 and Nov. 2013; and site CB located at ~21º N offshore the Cape Blanc upwelling region (Mauritania), collecting particles from Oct. 2012 to Feb. 2014. Each mooring was equipped with ADCPs, current meters and temperature-salinity sensors, and the sediment traps were sampling at 1200 m water depth.