OVIDE 2018 Cruise Report 11/06/2018 to 14/07/2018 - On board R/V Thalassa Brest (France) - Brest (France)

Abstract

OVIDE 2018 cruise focused on the 9th repetition of the OVIDE section. OVIDE cruises have been run biennially since 2002, always in June-July, and the section is labelled as a high-resolution reference section in the international program GO-SHIP. OVIDE 2018 started in Brest on June 11 and ended in Brest on July 14 on the N/O Thalassa. The 98 stations of the OVIDE section, from Portugal to the tip of Greenland, were cast within 3 weeks, and 6 stations were added afterwards in the Bight Fracture Zone. The core of the work consisted in acquiring surface-to-bottom hydrographic profiles of pressure, temperature, salinity and dissolved oxygen, and analyzing 20 physical and biogeochemical tracers from 17500 samples drawn from the Niskin bottles of the CTD frame. Data of the CTDO2 probe are indeed complemented with measurements of pH, alkalinity and nutrients to determine the concentration in dissolved inorganic carbon and anthropogenic carbon. Independent measurements of the isotopic fractions of carbon and seawater oxygen also help to follow the anthropogenic signal and the sources of fresh water respectively. In order to determine the age and the origin of the water masses, four anthropic tracers are measured from the sampled sea water: chlorofluorocarbon (CFC), Sulfur hexafluoride (SF6), iodine (129I) and uranium (236U) isotopes. Currents are determined by Acoustic Doppler Current Profilers (mounted on the ship and on the rosette), that are combined to the currents deduced from density gradients to obtained absolute geostrophic velocities and transports across the section. The deployment of deep-Argo floats in specific circulation features identified in real time brings additional information on the deep circulation that suffers from a lack of observations, as revealed by our previous studies. The oceanic currents around the Reykjanes Ridge is studied with the renewal of 2 ASFAR moorings (Autonomous System for Argo floats Release) that release an ARGO float at pre-determined dates. Finally, 26 samples were taken for phytoplankton identification. The data analysis of the survey is performed in synergy with the Argo and OSNAP programs, the satellite altimetry, the oceanic re-analysis (ISAS, EN4, ORAS4, GLORYS) and the output of physical-biogeochemical coupled models

OVIDE 2018 cruise focused on the 9th repetition of the OVIDE section. OVIDE cruises have been run biennially since 2002, always in June-July, and the section is labelled as a high-resolution reference section in the international program GO-SHIP. OVIDE 2018 started in Brest on June 11 and ended in Brest on July 14 on the N/O Thalassa. The 98 stations of the OVIDE section, from Portugal to the tip of Greenland, were cast within 3 weeks, and 6 stations were added afterwards in the Bight Fracture Zone. The core of the work consisted in acquiring surface-to-bottom hydrographic profiles of pressure, temperature, salinity and dissolved oxygen, and analyzing 20 physical and biogeochemical tracers from 17500 samples drawn from the Niskin bottles of the CTD frame. Data of the CTDO2 probe are indeed complemented with measurements of pH, alkalinity and nutrients to determine the concentration in dissolved inorganic carbon and anthropogenic carbon. Independent measurements of the isotopic fractions of carbon and seawater oxygen also help to follow the anthropogenic signal and the sources of fresh water respectively. In order to determine the age and the origin of the water masses, four anthropic tracers are measured from the sampled sea water: chlorofluorocarbon (CFC), Sulfur hexafluoride (SF6), iodine (129I) and uranium (236U) isotopes. Currents are determined by Acoustic Doppler Current Profilers (mounted on the ship and on the rosette), that are combined to the currents deduced from density gradients to obtained absolute geostrophic velocities and transports across the section. The deployment of deep-Argo floats in specific circulation features identified in real time brings additional information on the deep circulation that suffers from a lack of observations, as revealed by our previous studies. The oceanic currents around the Reykjanes Ridge is studied with the renewal of 2 ASFAR moorings (Autonomous System for Argo floats Release) that release an ARGO float at pre-determined dates. Finally, 26 samples were taken for phytoplankton identification. The data analysis of the survey is performed in synergy with the Argo and OSNAP programs, the satellite altimetry, the oceanic re-analysis (ISAS, EN4, ORAS4, GLORYS) and the output of physical-biogeochemical coupled models