MISSRHODIA2

Name: MISSRHODIA2
Start: 2018-05-20
End: 2018-06-03
Location: Mediterranean Sea, Western Basin

Type	Oceanographic cruise
Ship	Téthys II
Ship owner	CNRS until 2019 - IFREMER since 2020
Dates	20/05/2018 - 03/06/2018
Chief scientist(s)	RABOUILLE Christophe
	LABORATOIRE DES SCIENCES DU CLIMAT ET DE L'ENVIRONNEMENT - UMR 8212 Orme des Merisiers Bâtiment 714 Chemin de Saint Aubin - RD 128 91191 Gif sur Yvette Cedex +33(0)1 69 08 77 11 contact@lsce.ipsl.fr https://www.lsce.ipsl.fr/
DOI	10.17600/18000473
Objective	Estuarine and deltaic regions are crucial in our understanding and quantification of the ocean carbon cycle. These regions are characterized by large spatial gradients linked to the river input. Indeed, in deltaic systems, the particulate matter is exported in the river plume and quickly settles to the seafloor where it accumulates in sediment, giving rise to a large transfer of particulate organic carbon and nutrients. The recycling of organic and inorganic material in surficial sediments participates to the regulation of carbon and nutrient fluxes in the coastal zone. Due to human activity in river basins, environmental conditions in deltaic regions are often degraded by hypoxia or acidification, therefore increasing the vulnerability of these land-ocean interfaces and the ecosystem services they provide. In the Rhône River delta, biogeochemical recycling in sediment anoxic zones generates an alkalinity flux which influences carbon exchange with the atmosphere. During the MissRhoDia2 cruise, we studied particulate organic matter recycling either from terrestrial or marine origin. We placed a particular focus on anoxic sediments and the interaction between organic matter recycling and calcium carbonate dissolution/precipitation during early diagenesis. The cruise took place at the end of the spring 2018 with the objective to continue the work of the DICASE cruise in june 2014. The principal objectives were: - Study anoxic and oxic sediments in the Rhône prodelta and nearby continental shelf and measure exchange fluxes using core incubations. - Study the organic and inorganic carbon recycling after deposition in the sediment with a focus on the regulation of acidification by organic-inorganic carbon interaction, and the alkalinity fluxes generated by oxic and anoxic processes. The series of results collected during the cruises DICASE, AMOR-BFlux and MissRhoDia2 will be combined in order to provide information on the pelagic-benthic coupling, dissolved inorganic carbon and alkalinity transfer from the deltaic sediments to the coastal zone and their potential influence on CO₂ fluxes. These series are being published in a current thesis at LSCE (L. Brethous) and will be used to calibrate an early diagenetic model specially designed for this purpose. In situ and ex situ techniques were used during the cruise at 9 different stations: LSCE autonomous profiler, core incubations, LSCE benthic station. These measurements were completed by classical techniques: porewater extraction from cores under inert atmosphere (N2), water column sampling using Niskin bottles.

Sea/Ocean

Mediterranean Sea, Western Basin

(Gulf of Lion, Rhône River mouth)

Ports

Port of departure : Port-Saint-Louis-du-Rhône (France)

Port of return : Port-Saint-Louis-du-Rhône (France)

Limits

North	South	West	East
43.3	43.1	4.8	4.9

Scientific Authority

LABORATOIRE DES SCIENCES DU CLIMAT ET DE L'ENVIRONNEMENT - UMR 8212

Orme des Merisiers

Bâtiment 714

91191 Gif sur Yvette Cedex

+33(0)1 69 08 77 11

contact@lsce.ipsl.fr

https://www.lsce.ipsl.fr/

Participating bodie(s)

CNRS, CEA, UVSQ

Discipline(s)

CHEMICAL OCEANOGRAPHY

Code	Label	Quantity	PI
G046	Surface corer Unitube corer UWITECH	9 stations	RABOUILLE Christophe
H09	Water bottle stations	-	RABOUILLE Christophe
H21	Oxygen Bottom water and in situ sediment microprofiles by amperometric microeletrodes on LSCE autonomous profiler	9 stations	RABOUILLE Christophe
H22	Phosphate Bottom water and interstitial waters. Colrimetric method	9 stations	RABOUILLE Christophe
H27	Alkalinity Bottom water and interstitial waters - HCl titration	9 stations	RABOUILLE Christophe
H28	pH Bottom water: colorimetric méthod sediment: micro-profiles by potentiometric micro-electrodes calibrated by NBS buffers	9 stations	RABOUILLE Christophe
H76	Ammonia Bottom water and interstitial waters - colorimetric method	9 stations	RABOUILLE Christophe
H90	Other chemical oceanographic meas. Dissolved inorganic carbon - bottom water and interstitial waters. Measured by acidification, gas extraction and LICOR IR quantification (Appollo)	9 stations	RABOUILLE Christophe

Scientific context

This project aimed at a better understanding of the role of exchanges at the water-sediment interface in controlling coastal disturbances such as hypoxia and acidification in regions influenced by the inflows of rivers and their impact on carbonated meiofauna. The main hypothesis to test was: does hypoxia in the water column promote anoxic diagenetic pathways and amplify the oxygen flux to the sediment and the alkalinity transfers to the water column?

The general objectives of this research project were twofold:

- the quantification of the exchange fluxes of oxygen, DIC and Alkalinity between the sediments and the water and the understanding of the processes in the sediments which underlie these exchanges in two contrasted zones of river deltas: the Gulf of Mexico and the coastal zone influenced by the Mississippi on the one hand and the Gulf of Lion and its continental shelf under the influence of the Rhone on the other hand.

- the impact of these drastic conditions of hypoxia and induced acidification on the fossilized carbonated meiofauna (benthic foraminifera)

The comparison of the two systems (Rhône and Mississippi) whose deltas have similar morphologies (microtidal systems dominated by waves) and similar nutrient intakes in concentration (Rabouille et al., 2008), but with very different effects in terms hypoxia and acidification presented an important element in the understanding of sedimentary processes as well as the impacts on meiofauna. Indeed, these two contrasting environments offer a fairly wide range of forcing to better understand the diagenetic mechanisms.

In addition, the diversity of expected biogeochemical conditions which are habitats for the meiofauna, and in particular foraminifera, should make it possible to better understand the questions of speciation and endemism and their link with the habitat for this branching in the zones affected by hypoxia. A phylogenetic study of foraminifera in the Mississippi prodelta should allow us to compare in detail the faunal adaptations to hypoxia in the Gulf of Mexico in contrast to the Gulf of Lion, and thus, to better predict the response mechanisms to environmental conditions (hypoxia, acidification).

The research questions therefore aimed to better constrain:

- the magnitude of the O2, DIC and alkalinity fluxes between sediment and bottom water in and out of hypoxic zones in the Gulf of Mexico and in the Rhône prodelta

- the relative importance of anoxic processes (reduction of iron oxides, sulfato-reduction, precipitation of iron sulfides, methanogenesis, anaerobic oxidation of methane, ...) in the recycling of organic matter and the consumption of oxygen

- the role of anaerobic processes and the precipitation / dissolution of calcium carbonate in the genesis of alkalinity and DIC in the sedimentary column and the relationship with exchange flows at the water-sediment interface.

- the distribution of populations of foraminifera living in the two deltas and their link with sedimentary habitats and biogeochemistry (hypoxia, acidification) using morphological description and molecular identification (individual and environmental DNA or DNA).

Main results

Data acquired and analyses carried out at sea and on shore

Published data

Ait Ballagh Fatima Ezzahra, Rabouille Christophe, Andrieux Francoise, Soetaert Karline, Lansard Bruno, Bombled Bruno, Monvoisin Gaël, Elkalay Khalid, Khalil Karima, Brethous Laurie, Villedieu Anouk (2020). Spatial variability of organic matter and phosphorus cycling in Rhône River prodelta sediments (NW Mediterranean Sea, France): a data-model approach. https://doi.org/10.17882/73204

Bibliography

Publications

Dumoulin J-P, Rabouille C, Pourtout S, Bombled B, Lansard B, Caffy I, Hain S, Perron M, Sieudat M, Thellier B, Delqué-Količ E, Moreau C, Beck L (2022). Identification in Pore Waters of Recycled Sediment Organic Matter Using the Dual Isotopic Composition of Carbon (δ13C and Δ14C): New Data From the Continental Shelf Influenced by the Rhône River. Radiocarbon, 64(6), 1617-1627. Publisher's official version : https://doi.org/10.1017/RDC.2022.71 , Open Access version : https://archimer.ifremer.fr/doc/00808/92046/

Ait Ballagh Fatima Ezzahra, Rabouille Christophe, Andrieux-Loyer Francoise , Soetaert Karline, Lansard Bruno, Bombled Bruno, Monvoisin Gael, Elkalay Khalid, Khalil Karima (2021). Spatial Variability of Organic Matter and Phosphorus Cycling in Rhône River Prodelta Sediments (NW Mediterranean Sea, France): a Model-Data Approach. Estuaries And Coasts, 44(7), 1765-1789. Publisher's official version : https://doi.org/10.1007/s12237-020-00889-9 , Open Access version : https://archimer.ifremer.fr/doc/00683/79493/