This is the blog of expedition M159 of the German research vessel METEOR. The team onboard investigates the western boundary current system off South America. These currents are important for regional and global ocean and climate variability. On shorter time scales they modulate the tropical Atlantic climate and associate rain fall variability over Brasil, the Caribbean and West Africa. The deep flows are part of the Atlantic wide meridional overturning circulation (AMOC). This circulation involved deep water formation in the Labrador, Irminger and Nordic Seas, passes along the East coast of the United States, the Bahamans and flows along the South American continent. Our project maintains a long term ocean observatory of this the western boundary of the coast of Brasil at 11°S.
One particular focus of the observations at the western boundary off Brazil is the transport variability of the relatively shallow North Brazil Undercurrent (NBUC) – reaching from the surface to 300m depths as part of the northward flowing upper branch of the AMOC. The NBUC is also part of the subtropical cells (STCs) – which regulate the tropical Atlantic surface temperatures on time-scales from intraseasonal to decadal. These observations will be complemented with the observations obtained on the meridional section across the equator at 35°W especially with respect to the signal propagation and changes of water masses.
The other focus is on the southward flowing the deep western boundary current (DBWC) which transports cold water south in depths below 1500m. This lower branch of the AMOC is part of the global thermo-haline circulation – under climate change this current is predicted to slow down. The measurements, when maintained over a long time, will be able to document this important consequence of climate change on the ocean.
The main operations during M159 will be the recovery and redeployment of the ocean observatory, which consists of several deep sea moorings. In addition data will be acoustically read out from two moored pressure inverted echo sounders (PIES). Once the observatory has been replaced a large number of stations will be done using a combination of CTD and Lowered ADCP with many sensors. In addition, underway measurements of upper ocean currents with the two shipboard ADCPs, swath bathymetry measurements and with the thermosalino-graph probe will be performed.
The expedition will end at the Cape Verde Island, where another ocean observatory will be recovered and redeployed.
The scientific crew comes largely from GEOMAR, but in addition we have researchers from Brasil, Portugal, Argentina, Columbia and Nigeria on board. Some of them are supported by POGO and have the opportunity to share practical experience of the work at sea.
The research program of cruise M159 contributes to the BMBF collaborative research project RACE – Nordatlantik Synthesis, the Programme-Oriented Funding (POF) of GEOMAR and observations for the BMBF joint project REEBUS.
Dr. Rebecca Hummels (project leader)
Prof. Dr. Martin Visbeck (chief scientist)
GEOMAR Helmholtz Centre for Ocean Research Kiel
Düsternbrooker Weg 20
Website of the Research Unit Physical Oceanography at GEOMAR