Simulation of the mantle and crustal helium isotope signature in the Mediterranean Sea using a high-resolution regional circulation model

Abstract

Abstract. Helium isotopes ( 3 He, 4 He) are useful tracers for investigating the deep ocean circulation and for evaluating ocean general circulation models, because helium is a stable and conservative nuclide that does not take part in any chemical or biological process. Helium in the ocean originates from three different sources, namely, (i) gas dissolution in equilibrium with atmospheric helium, (ii) helium-3 addition by radioactive decay of tritium (called tritiugenic helium), and (iii) injection of terrigenic helium-3 and helium-4 by the submarine volcanic activity which occurs mainly at plate boundaries, and also addition of (mainly) helium-4 from the crust and sedimentary cover by α-decay of uranium and thorium contained in various minerals.We present the first simulation of the terrigenic helium isotope distribution in the whole Mediterranean Sea using a high-resolution model (NEMO-MED12). For this simulation we build a simple source function for terrigenic helium isotopes based on published estimates of terrestrial helium fluxes. We estimate a hydrothermal flux of 3.5 mol 3 He yr −1 and a lower limit for the crustal flux at 1.6 × 10 −7 4 He mol m −2 yr −1 .In addition to providing constraints on helium isotope degassing fluxes in the Mediterranean, our simulations provide information on the ventilation of the deep Mediterranean waters which is useful for assessing NEMO-MED12 performance. This study is part of the work carried out to assess the robustness of the NEMO-MED12 model, which will be used to study the evolution of the climate and its effect on the biogeochemical cycles in the Mediterranean Sea, and to improve our ability to predict the future evolution of the Mediterranean Sea under the increasing anthropogenic pressure.

High resolution regional modeling of natural and anthropogenic radiocarbon in the Mediterranean Sea

“…This model correctly simulates the main structures of the thermohaline circulation of the Mediterranean Sea, with mechanisms having a realistic timescale compared to observations (Ayache et al, 2015a). In particular, tritium (Ayache et al, 2015a) and helium isotope simulations (Ayache et al, 2015b) have shown that the EMT signal from the Aegean sub-basin is realistically simulated during early 1995. However, some aspects of the model still need to be improved: for instance the too-weak formation of Adriatic Deep Water (AdDW), followed by a low contribution to the EMDW in the Ionian sub-basin.…”

“…A time-step of 20 minutes is applied. The same approach was used to simulate the εNd (neodymium) distribution in the Mediterranean Sea (Ayache et al, 2016), and the mantle and crustal helium isotope signature (Ayache et al, 2015b), as well as to model the anthropogenic tritium invasion (Ayache et al, 2015a), and CFC and anthropogenic carbon storage (Palmiéri et al, 2015).…”

“…Here, we used a high-resolution regional model (NEMO-MED12, horizontal resolution 1/12 • , ∼ 7 km) of the entire Mediterranean Sea (Beuvier et al, 2010(Beuvier et al, , 2012a. This model has been used previously for biogeochemical studies (Ayache et al, 2015b;Guyennon et al, 2015;Ayache et al, 2015a;Palmiéri et al, 2015;Ayache et al, 2016) and dynamical application (Soto-Navarro et al, 2014;Beuvier et al, 2012a;Lebeaupin Brossier et al, 2011). Here, we use the model to provide the first simulation of radiocarbon distribution and the related reservoir age.…”

High-resolution neodymium characterization along the Mediterranean margins and modelling of <i>ε</i><sub>Nd</sub> distribution in the Mediterranean basins

“…Lacan and Jeandel, 2005;Jeandel, 1993;Jeandel et al, 1998;Frank, 2002;Goldstein and Hemming, 2003;Piotrowski et al, 2004Piotrowski et al, , 2012Stichel et al, 2012;Martin et al, 2012;Pena et al, 2013;Molina-Kescher et al, 2014;Arsouze et al, 2008). However, because Nd is particle reactive, Nd parameters are also successfully used to study Nd exchange between dissolved and particulate phases (Bertram and Elderfield, 1993;Henry et al, 1994;Jeandel et al, 1995;Tachikawa et al, 1999Tachikawa et al, , 2003Garcia-Solsona et al, 2014;Rousseau et al, 2015;Haley et al, 2014).…”