JULIO - Judicious Location for Intrusions Observations

[Lien vers la fiche source] ABSTRACT : JULIO (Judicious Location for Intrusions Observations) mooring is located close to the 100 m-deep isobath (around 5.25°E and 43.13°N), offshore Marseille. With its bottom-moored (300kHz) ADCP, it enables measuring horizontal currents (every 4 m and every ½ h) through the water column, and among others, identifying periods of exchange between the Northern Current and the continental shelf. It is one crucial component in the study of the coastal-offshore gradient from Marseille to the MOOSE 42°N5°E station, and potential covariances with the MIO radar and other MIO or international observing systems, as well as with the SOMLIT site (including also an ADCP) in the bay of Marseille. Moreover, with a bottom CTD, it can detect environmental anomalies in classical hydrographic data, useful for oceanographers. As one of the rare station at the interface between the continental shelf and offshore, it will allow to observe the long-term evolution of the Northern Current in the context of climate change and anthropogenic pressure, and its potential varying impact on the Gulf of Lion. The data are of course also crucial for modellers. Moreover they show a great potential when supplementing other MOOSE data (glider and radar). DETAILS : On the eastern side of the gulf, during specific conditions, a vein of the Northern Current can intrude on the shelf . Both in situ measurements and numerical modelling show that intrusions develop either as a part of the NC itself encroaching on the shelf or as a separated branch of the main vein of the NC (Gatti, 2008 ; Petrenko et al., 2013). These two types of intrusions can change from one type to the other, both in time and in space. Three kinds of wind events are likely to generate intrusions: the Mistral cessations, episodes of inhomogeneous Mistral or periods of East winds. In the first two cases, intrusions are due to the inhomogeneity of the wind event. The intrusions during East wind could be due to two processes: the Ekman drift and the shift of the current’s core towards the coast. Otherwise, intrusions cannot develop during homogeneous Mistral. Other factors, such as the vertical and horizontal extents of the NC as well as its degree of mesoscale instability, can also influence the development of intrusions. However, neither the NC seasonal variability nor the variation of the GoL’s water budget have an impact on the occurrence of intrusions. METHODS : Situated on the 100 m-deep isobath, the JULIO bottom-moored ADCP measures horizontal currents through the water column, to detect intrusions occurring upstream and on the eastern side of the Gulf of Lion. The ADCP (RDI Ocean Sentinel 300 kHz) provides a current time series every ½ hour and every 5m depth (4 m until 2016) throughout the water column. Last launching on June 24, 2022 from Research Vessel Antedon II. First localization of JULIO from 2012 to 2016: 5° 15,28' E – 43° 8,15' N or 5,255°E – 43,135°N with three time series: - from Feb. 12 to Oct 23, 2012; time series #1 - from Sep. 26, 2013 to March 28, 2014; time series #2 - from July 17, 2014 to April 10, 2015; time series #3 In September 2016, it was launched on the 23, but dragged probably 3 days after, and stayed at the bottom. ADCP was found during april 2017 by fishermen. If the ADCP looked good, but the cage was not responding to acoustic communication tests. A new location for the following time series: - from Sept 1st, 2021 to June 23, 2022 ; time series #4 - from Dec 7, 2020 to August 31, 2021; time series #5 - from June 23, 2022 to June 22, 2023; time series #6 - from July 12, 2023 to May 22, 2024; time series #7