Blog entry by Felipe Vilela-Silva, Natalia Vazques Riveiros & Bruno Ferron
The crew and scientists on board L’Atalante have obtained 10 short-core samples with sediment and water containing a rich logbook of the last few millennia with valuable information of the past physico-chemical and dynamical conditions at the surface and deep ocean. These observations are timely to compare the current health status of the Earth before and after the human-induced changes after the Industrial Revolution. We are sampling immediately downstream of the region where the sinking of dense water masses in winter essentially drives the circulation of the overturning cell. These deep-sea treasures around the Flemish Cap reveal the relatively slow changes throughout AMOC’s timeline. This signal from the past captures the low-frequency and natural variability of the AMOC which is fundamental to understand the present time and provide hints about the future.
Above: Scientists (N. Vazques Riveiros, S. Toucanne, and J. Gouriou) having prelimary discussions about the signals captured by the short-core samples after (below) casting the carotte to the bottom of the ocean with the help of the crew aboard L’Atalante. Photos by Stephane Lesbats.
We also have other stopwatches in hand oscillating at higher frequencies to observe the fast changes at the Deep Western Boundary Current (DWBC). The high-frequency signal comes from the successfully recovered moorings sampling temperature, salinity, velocity, and microstructures within the DWBC. The microstructure within the DWBC will be diagnosed from the vertical changes in temperature and velocity sampled by the microstructure mooring together with the new 10 casts of the vertical mixing profiler that complete the 39 casts made in 2024. The recovery of the microstructure mooring prototype is a big advance for process studies in observing deep ocean turbulence. In fine, such a mooring should improve our understanding of ocean mixing and kinetic energy dissipation by providing microstructure measurements from the surface to the seafloor. This improves the estimates of the ocean’s mixing efficiency and parameterizations as current model simulations do not resolve transport of climate-related tracers at the infinitesimal scales of space and time.
Above: Successful recovery of the microstructure mooring after combined efforts between the scientists, engineers and crew (B. Ferron, S. Leizour and P. Le Cann). Photos by Stephane Lesbats.