Description: Cruise M140 combined sampling of plankton, mineral dust and other particles in the water column with recovery of data and samples from long-term observational platforms (sediment traps and dust-collecting buoys). The aim of the cruise was to provide new observations to improve our understanding of the ecology of planktonic foraminifera as important carriers of paleoceanographic proxies and to investigate how mineral dust deposition and the production of marine snow and biogenic particle ballast vary in space and time and how they affect the marine biological pump. To this end, the cruise followed a transect in the central western Atlantic between oligotrophic waters of the subtropical gyre and the productive coastal waters off Mauretania affected by coastal upwelling. To characterise population dynamics, ecology and physiology of planktonic foraminifera, we obtained a series of fourteen vertically resolved plankton net profiles along the cruise track, together with profiles of physical and chemical properties of the ambient water masses. Live foraminifera extracted from these profiles were used to quantify photosynthetic activity of selected species and determine their photoadaptation. High-resolution spatial and temporal sampling of the upper 300 m over 24 hours was carried out at two locations (recovering 41 and 46 vertical profiles), allowing the characterisation of patchiness and daily vertical migration of planktonic foraminifera. Moorings with sediment traps monitoring the seasonal and short-term variability of particle fluxes and buoys monitoring atmospheric dust deposition in the region were successfully recovered in the central Atlantic (M3), south of Cabo Verde (M1) and off Mauretania (CB and CBi) and redeployed in the latter two regions to continue the monitoring. Short-term variability of sizes and types of sinking particles in the water column were characterised in each of the monitoring regions with drifting sediment traps and in the Cape Blanc region off Mauretania also with continuous vertical particle camera profile. All aims of the cruise have been met – the plankton sampling and particle characterization studies were carried out successfully and all moorings and buoys could be recovered and/or redeployed as planned.

Description: Cruise M160 is part of concerted MOSES/REEBUS Eddy Study featuring three major research expeditions (M156, M160, MSM104). It aims to develop both a qualitative and quantitative understanding of the role of physical-chemical-biological coupling in eddies for the biological pump. The study is part of the MOSES “Ocean Eddies” event chain, which follows three major hypotheses to be addressed by the MOSES/REEBUS field campaigns: (1) Mesoscale and sub-mesoscale eddies play an important role in transferring energy along the energy cascade from the large-scale circulation to dissipation at the molecular level. (2) Mesoscale and sub-mesoscale eddies are important drivers in determining onset, magnitude and characteristics of biological productivity in the ocean and contribute significantly to global primary production and particle export and transfer to the deep ocean. (3) Mesoscale and sub-mesoscale eddies are important for shaping extreme biogeochemical environments (e.g., pH, oxygen) in the oceans, thus acting as a source/sink function for greenhouse gases. In contrast to the other two legs, MOSES Eddy Study II during M160 did not include any benthic work but focused entirely on the pelagic dynamics within eddies. It accomplished a multi-disciplinary, multi-parameter and multi-platform study of two discrete cyclonic eddies in an unprecedented complexity. The pre-cruise search for discrete eddies suitable for detailed study during M160 had already started a few months prior to the cruise. Remote sensing data products (sea surface height, sea surface temperature, ocean color/chlorophyll a) were used in combination with eddy detection algorithms and numerical modelling to identify and track eddies in the entire eddy field off West Africa. In addition, 2 gliders and 1 waveglider had been set out from Mindelo/Cabo Verde for pre-cruise mapping of the potential working area north of the Cabo Verdean archipelago. At the start of M160, a few suitable eddies – mostly of cyclonic type – had been identified, some of which were outside the safe operation range of the motorglider plane. As technical problems delayed the flight operations, the first eddy (center at 14.5°N/25°W) for detailed study was chosen to the southwest of the island of Fogo. It was decided to carry out a first hydrographic survey there followed by the deployment of a suite of instruments (gliders, waveglider, floats, drifter short-term mooring). Such instrumented, we left this first eddy and transited – via a strong anticyclonic feature southwest of the island of Santiago – to the region northeast of the island of Sal, i.e. in the working range of the glider plane. During the transit, a full suite of underway measurements as well as CTD/RO section along 22°W (16°-18.5°N) were carried in search for sub-surface expressions of anticyclonic eddy features. In the northeast, we had identified the second strong cyclonic eddy (center at 18°N/22.5°W) which was chosen for detailed study starting with a complete hydrographic survey (ADCP, CTD/RO, other routine station work). After completion of the mesoscale work program, we identified a strong frontal region at the southwestern rim of the cyclonic eddy, which was chosen for the first sub-mesoscale study with aerial observation component. There, the first dye release experiment was carried out which consisted of the dye release itself followed by an intense multi-platforms study of the vertical and horizontal spreading of the initial dye streak. This work was METEOR-Berichte, Cruise M160, Mindelo – Mindelo, 23.11.2019 4 – 20.12.2019 supported and partly guided by aerial observation of the research motorglider Stemme, which was still somewhat compromised by technical issues and meteorological conditions (high cloud cover, Saharan dust event). Nevertheless, this first dye release experiment was successful and showed rapid movement of the dynamic meandering front. After completion of work on this second eddy and execution of a focused sampling program at the Cape Verde Ocean Observation, RV METEOR returned to the first eddy for continuation of the work started there in the beginning of the cruise. This was accompanied by a relocation of the airbase of Stemme from the international airport of Sal to the domestic airport of Fogo. The further execution of the eddy study at this first eddy, which again included a complete hydrographic survey followed by a mesoscale eddy study with dye release, was therefore possible with aerial observations providing important guidance for work on RV METEOR. Overall, M160 accomplished an extremely intense and complex work program with 212 instrument deployments during station work, 137 h of observation with towed instruments and a wide range of underway measurements throughout the cruise. Up to about 30 individually tracked platforms (Seadrones, glider, wavegliders, drifters, floats) were in the water at the same time providing unprecedented and orchestrated observation capabilities in an eddy. All planned work components were achieved and all working groups acquired the expected numbers of instrument deployments and sampling opportunities.

Description: The 22 participating scientists from Germany, Norway, the Netherlands, Denmark, Sweden, Finland and the United States covered scientific expertise in (micro-) biology, chemistry, and oceanography. Apart from aerosol and rainwater collection, which was applied to assess atmospheric deposition, sampling was restricted to the water column. Phyto and zooplankton were sampled by vertical net hauls using a plankton net, multinet and a pump system for the filtration of large water volumes to collect different size classes of phytoplankton, followed by DNA and RNA extraction. Phytoplankton was also characterized and quantified onboard by microscopy and flow cytometry. Primary productivity was assessed in incubations in the isotope container using radiocarbon labels. Clonal cultures were established to identify selected key species. Bacterial abundance, community composition and production were also determined onboard. Chemical sampling and analytical parameters, most of which taken from the CTD water sampler, will be measured back in the home labs. The final dataset will cover inorganic nutrients, oxygen concentration, dissolved inorganic carbon, total alkalinity, He/Ne ratios for the estimation of basal melt water, δ18O for the contribution of meteoric water, particulate and dissolved organic carbon and nitrogen, optical properties (fluorescence), molecular characterization and radiocarbon age of organic matter. A FerryBox system continuously recorded surface water information on turbidity, chlorophyll fluorescence, temperature, salinity, colored dissolved organic matter and salinity. At each station, salinity and temperature profiles were recorded by the CTD system and by profiler deployments, which also recorded the spectral light profile in the water column. The vertical material flux was investigated by the deployment of drifting sediment traps, a camera system and a marine snow catcher.

Description: Over the past decades, two key grazers in the Southern Ocean (SO), krill and salps, have experienced drastic changes in their distribution and abundance, leading to increasing overlap of their habitats. Both species occupy different ecological niches and long-term shifts in their distributions are expected to have cascading effects on the SO ecosystem. However, studies directly comparing krill and salps are lacking. Here, we provide a direct comparison of the diet and fecal pellet composition of krill and salps using 18S metabarcoding and fatty acid markers. Neither species’ diet reflected the composition of the plankton community, suggesting that in contrast to the accepted paradigm, not only krill but also salps are selective feeders. Moreover, we found that krill and salps had broadly similar diets, potentially enhancing the competition between both species. This could be augmented by salps’ ability to rapidly reproduce in favorable conditions, posing further risks to krill populations.

Description: In the version of this article initially published, author Cora Hörstmann was wrongly listed with a second affiliation with the Department of Ecoscience–Applied Marine Ecology and Modelling, Aarhus University rather than the Mediterranean Institute of Oceanography (MIO), Marseille, France. Furthermore, references 83–97, now found in the Supplementary Tables caption, were wrongly cited in the Data Availability section. The errors have been corrected in the HTML and PDF versions of the article.

Description: Large amounts of atmospheric carbon can be exported and retained in the deep sea on millennial time scales, buffering global warming. However, while the Barents Sea is one of the most biologically productive areas of the Arctic Ocean, carbon retention times were thought to be short. Here we present observations, complemented by numerical model simulations, that revealed a deep and widespread lateral injection of approximately 2.33 kt C d−1 from the Barents Sea shelf to some 1,200 m of the Nansen Basin, driven by Barents Sea Bottom Water transport. With increasing distance from the outflow region, the plume expanded and penetrated into even deeper waters and the sediment. The seasonally fluctuating but continuous injection increases the carbon sequestration of the Barents Sea by 1/3 and feeds the deep sea community of the Nansen Basin. Our findings combined with those from other outflow regions of carbon-rich polar dense waters highlight the importance of lateral injection as a global carbon sink. Resolving uncertainties around negative feedbacks of global warming due to sea ice decline will necessitate observation of changes in bottom water formation and biological productivity at a resolution high enough to quantify future deep carbon injection.

Description: Krill and salps are important for carbon flux in the Southern Ocean, but the extent of their contribution and the consequences of shifts in dominance from krill to salps remain unclear. We present a direct comparison of the contribution of krill and salp faecal pellets (FP) to vertical carbon flux at the Antarctic Peninsula using a combination of sediment traps, FP production, carbon content, microbial degradation, and krill and salp abundances. Salps produce 4-fold more FP carbon than krill, but the FP from both species contribute equally to the carbon flux at 300 m, accounting for 75% of total carbon. Krill FP are exported to 72% to 300 m, while 80% of salp FP are retained in the mixed layer due to fragmentation. Thus, declining krill abundances could lead to decreased carbon flux, indicating that the Antarctic Peninsula could become a less efficient carbon sink for anthropogenic CO2 in future.