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Met­eor: 3. Weekly Re­port

3. Weekly Re­port (July 9, 2018 - July 15, 2018)

Go-Flo deployment on station
Figure 1: Go-Flo deployment on station (© Thomas Wilkop, MPIMM)

Un­der the rain-heavy skies of the In­ter­trop­ical Con­ver­gence Zone (ITCZ) theR/​V Met­eor­skirts the coast of West­ern Africa on the transit north to Las Pal­mas. Cruis­ing through the eco­nomicex­clus­ive zones of coun­tries such as Liberia and Si­erra Le­one sincelate Thursday morn­ing, the un­der­way data gath­er­ing sys­tems andwa­ter sampling sys­tem­shave been shut down, and the last sta­tion of this ex­ped­i­tion also lies over two days be­hind us.

Dur­ing our transit from the oxy­gen-min­imum zone off Nam­i­bia into the open wa­ters sampling began for the much more oli­go­trophic wa­ters of the East­ern South and Equat­orial At­lantic. These wa­ters not only have low con­cen­tra­tions of nu­tri­ents such as ni­trate, but are also low in trace ele­ments. Stand­ard sampling equip­ment of­ten poses a source of con­tam­in­a­tion for trace ele­ments, and spe­cial Te­flon-coated Go-Flo bottles were used on the shelf as well the open wa­ters to ob­tain very clean wa­ter samples for the ana­lysis of dis­solved and par­tic­u­late trace ele­ments, par­tic­u­larly iron (Fe)(Fig­ure 1).

Fe can limit primary pro­ductiv­ityin sev­eral oceanic re­gions, and the chem­ical phase and fluxes of Fe are not very well known in this so far un­der-sampled re­gion. The samples ob­tained on this cruise will later be ana­lyzed in the home labor­at­or­ies of the In­sti­tute for Chem­istry and Bio­logy of the Mar­ine En­vir­on­ment (ICBM) at the Uni­versity of Olden­burg, where not only the chem­ical phase of the trace ele­ments will be de­term­ined but also ana­lysis will be car­ried out to dis­tin­guish sed­i­ment­ary versus at­mo­spheric sources of trace ele­ments. Fig­ure 1: Oxy­gen con­cen­tra­tions across the Kunene up­welling cell (18°S) (pre­lim­in­ary CTD data; left­panel, V. Mohrholz) and Go-Flo de­ploy­ment on sta­tion (right panel).

 
Deployment of CTD
Deployment of CTD (© Thomas Wilkop, MPIMM)
CTD
CTD (© Ferdelman, MPIMM)
On-deck incubators on the aft deck to simulate in-situ light conditions
Figure 2: On-deck incubators on the aft deck to simulate in-situ light conditions (© Thomas Wilkop, MPIMM)
Primary production is not the only process that can be limited by Fe in the oligotrophic oceans. The fixation of dinitrogen (N2) gas, yet the largest external source of nitrogen (N) to the ocean, can also be limited by the availability of Fe. Scientists from the Max Planck Institute for Marine Microbiology in Bremen (MPI Bremen) carried out on-board experiments to determine both the rate of primary production and N2 fixation using stable isotopes. Water samples are kept at close-to-in-situconditions for a period of 24 h (Figure 2) and subsamples will later be analyzed at the MPI Bremen. While N2 fixation is usually highest in the oligotrophic waters, not much is known about this process in the Eastern South and Equatorial Atlantic. This is partially due to the assumption that the coastal and equato rial upwelling would inhibit this process rather than on direct sampling and experiments. The data from this cruise will add to our knowledge on the occurrence of N2 fixation and its driving forces in this region. 
Go-Flo (© T.Ferdelman, MPIMM)
Go-Flo (© T.Ferdelman, MPIMM)
N2 Fixation
N2 Fixation (© Thomas Wilkop, MPIMM)
Primary production is at the base of the food web in the ocean, and phytoplankton is grazed upon by larger organisms. To determine the composition of the zooplankton community and to study protists such as Foraminifera, a scientist from the Center for Marine Environmental sciences (MARUM) at the University of Bremen deployed a so-called multinet. The multinet collects plankton samples throughout the water columnat several intervals so that the depth distribution of the organisms can be studied. While the water column closer to the coastal upwelling off Namibia contained larger amounts of zooplankton, the oligotrophic waters were less densely populated, reflecting the oligotrophic conditions and the lower productivity in these waters. The samples from the multinet will be taken back home and will later be analyzed at the MARUM.
 
Back here on the ship, we are looking forward with anticipation to a nice Grill Evening on deck and the World Cup match.
 
Greetings from 12° 46’ N 17° 43’ E from Tim Ferdelman, Chief Scientist, on behalf of the scientists and crew
Deployment of multi-net.
Figure 3: Deployment of multi-net. (© MPIMM)
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