METEOR (III) [1986-2026] M217/1

The research project “Boundary Circulation off Angola and Benguela Niños (BOCABENO)” focuses on improving our understanding of the physical and biogeochemical processes in tropical upwelling areas. Tropical upwelling regions play an active role in climate and oceanic biogeochemical cycles as well as supporting the most productive ocean food chains. They are home to the largest fishing grounds in the world and are characterised by a high level of marine biodiversity. Anthropogenic impacts in these regions will therefore have disproportionately large consequences for human society.
Climate change, fishing pressure and pollution will alter the tropical upwelling systems in the future. However, despite intense research activities in the past, process understanding in upwelling regions spanning the physical, biogeochemical, ecological and geological systems and their interactions remains poor.
BOCABENO aims to improve our understanding of tropical upwelling areas through:
• Investigating the variability of the eastern boundary circulation in the tropical Angolan upwelling region on timescales ranging from sub-seasonal to decadal;
• Investigating the influence of the changing mean state of the southeaster tropical Atlantic on the marine heat wave events Benguela Niño and Niña in terms of their frequency, strength, location and impact, as well as their predictability;
• Improving the ocean observation system off the coast of southwestern Africa.

As part of the MUSE CVOO buoy deployment (CVOO-BUOY) proposal, the aim of the cruise is to expand the long-term oceanographic observations at the Cabo Verde Ocean Observatory (CVOO). The primary goal is to install a new surface buoy next to the existing mooring. This will enable highly accurate measurements of carbon dioxid partial pressure in both the ocean and the atmosphere in order to more precisely determine the gas exchange between the air and the sea off West Africa. In addition, a weather station from the German Weather Service will be integrated into the buoy. The station will transmit real-time meteorological data via the Global Telecommunications System of the World Meteorological Organisation in order to increase the data basis for global weather forecast models and other assimilation products, as well as safety at sea in the region.

The work programme in the Cabo Verde region includes the deployment of the surface buoy in a water depth of approximately 3600 m. Additionally, full-depth conductivity-temperature-depth and oxygen (CTD/O2) profiles that includes biogeochemical sampling (dissolved oxygen and inorganic carbon, nutrients and total alkalinity (TA)) will be taken to extend the existing CVOO time-series data set.

The work program off Angola at 11°S consists of mooring work and a hydrographic section. The mooring work includes the recovery and redeployment of a mooring deployed at about 1200m depth and the recovery and redeployment of a bottom pressure - inverted echo sounder recorders. During the hydrographic section, CTD/O2 profiles will be taken along a section perpendicular to the continental slope at 11°S in Angolan territorial waters. The CTD/O2 unit will be attached to a rosette with 24 Niskin bottles and several additional sensors including turbidity, chlorophyll, nitrate, PAR and an underwater vision profiler. Water samples collected from the Niskin bottles will be analyzed for concentrations of oxygen, salinity, nutrients and greenhouse gas concentrations. Following each CTD/O2 station, microstructure measurements will be taken to collect data on turbulent mixing intensity.

An extensive chemical underway sampling program will be carried out that includes water sampling of fifty-six different persistent and other organic pollutants in surface waters and the atmosphere above including per- and polyfluoroalkyl substances and their precursors, herbicides, insecticides and fungicides.
Additionally, continuous underway measurements of
• trace gases (NOx, CO₂, CH₄, and N₂O),
• total alkalinity,
• dissolved inorganic carbon,
• velocity observations using acoustic Doppler current profilers,
• upper-ocean temperature and salinity by a thermosalinograph.
will be performed.