DATE2022-05-05 12:38:37
TITLEModelling of the the isotopic compositions of neodymium and oxygene in the Mediterranean Sea using a high-resolution regional model
AUTHORSMohamed Ayache (1) ,Jean-claude Dutay (1) ,Gilles Ramstein (1) ,Thomas Arsouze (2) ,Anne Mouchet (3) ,Kazuyo Tachikawa (4) ,Catherine Jeandel (5)
  1. 1) Laboratoire Des Sciences Du Climat Et De L’environnement, Université Paris Saclay, Gif-sur-yvette (France) ,2) Barcelona Supercomputing Center Barcelona, Barcelona (Spain) ,3) Freshwater And Oceanic Science Unit Of Research, Liège (Belgium) ,4) Aix Marseille Univ, Cerege, Aix-en-provence (France) ,5) Legos, University Of Toulouse, Toulouse (France)
ABSTRACTOur present knowledge of ocean ventilation relies on the distributions of hydrographic tracers such as oxygen and neodymium; (i) the oxygen isotopic composition (δ18O) of ocean water varies as a function of the evaporation–precipitation balance and water mass mixing. There is thus a direct relationship between salinity and δ18O values, which follow in a similar way the modifications of the water budget. (ii) the Nd isotopic composition (εNd) is one of the most useful tracers to fingerprint water mass provenance, εNd values of the water masses are conserved up to long distances from the source of lithogenic inputs when the local inputs are negligible. In such a context, it could be used to tag water masses with distinct isotopic compositions in order to constrain water mass mixing and pathways, as well as the thermohaline circulation in modern and past oceans. We have implemented these proxies in the high-resolution regional modeling platform NEMO/MED12/PISCES, and here, we present the calibration and evaluation with observations for the modern climate simulations. We have performed the first simulation of dissolved Nd concentration ([Nd]) and (εNd) in the Mediterranean Sea with an explicit representation of all Nd inputs, and the internal cycle, i.e. the interactions between the particulate and dissolved phases. The high resolution of the oceanic model (at 1/12°), essential to the simulation of a realistic Mediterranean circulation in present-day conditions, gives a unique opportunity to better apprehend the processes governing the Nd distribution in the marine environment. This work highlights that the exchange with the margins is the main source of Nd, and that the impact of river discharge on [Nd] is localized near the mouths of the main rivers. In contrast with the global ocean, the atmospheric dust input has a basin-wide influence, and improves the agreement of simulated [Nd] with field data in the Mediterranean Sea. This work also suggests that the parametrisation of the vertical cycling (scavenging/remineralisation) considerably constrains the ability of the model to simulate the vertical profile of εNd. We use the same high-resolution model to simulate the δ18O distribution for the first time in this basin. Atmospheric hydrologic fluxes (evaporation and precipitation, and their isotopic content) are provided by the isotope-enabled atmospheric LMDZ model. A reasonable east–west gradients of δ18O is simulated by the model, which separates the less-evaporated and more-productive western basin from the more-evaporated and less-productive eastern basin. The intermediate waters constitute a homogeneous layer in good agreement with the in situ observations. The knowledge of the present-day variability of the isotopic composition of the Mediterranean waters should help further studies dedicated to Mediterranean paleoceanography.