OSOcean ScienceOSOcean Sci.1812-0792Copernicus GmbHGöttingen, Germany10.5194/os-11-965-2015Simulation of the mantle and crustal helium isotope signature in the Mediterranean Sea using a high-resolution regional circulation modelAyacheM.https://orcid.org/0000-0002-2965-3377DutayJ.-C.Jean-BaptisteP.FourréE.https://orcid.org/0000-0002-2554-9660Laboratoire des Sciences du Climat et de l'Environnement LSCE/IPSL,
CEA-CNRS-UVSQ, Université Paris-Saclay, 91191 Gif-sur-Yvette, FranceM Ayache (mohamed.ayache@lsce.ipsl.fr)21December201511696597829July201525August201520November
20159December2015This work is licensed under a Creative Commons Attribution 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by/3.0/This article is available from https://os.copernicus.org/articles/11/965/2015/os-11-965-2015.htmlThe full text article is available as a PDF file from https://os.copernicus.org/articles/11/965/2015/os-11-965-2015.pdf
Helium isotopes (3He, 4He) 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 mol3 He yr-1 and a lower
limit for the crustal flux at 1.6 ×10-74He 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.
Introduction
Helium isotopes are a powerful tool in Earth sciences. The ratio of 3He
to 4He varies by more than 3 orders of magnitude in terrestrial samples.
This results from the distinct origins of 3He (essentially primordial)
and 4He (produced by the radioactive decay of uranium and thorium
series) and their contrasting proportions in the Earth's reservoirs
(Fig. ). The atmospheric ratio, Rair=3He /4He = 1.384 × 10-6,
can be considered constant due to the long residence time of helium, which is
∼106 times longer than the mixing time of the atmosphere
based on the total helium content of the atmosphere and the global
helium degassing flux estimated by. Relative to this
atmospheric ratio, typical 3He /4He ratios vary from <0.1Rair in the Earth's crust to an average of
8 ±1Rair in the upper mantle, and up to some 40 to 50
Rair in products of plume-related ocean islands, such as Hawaii
and Iceland .
Schematic of helium components in the ocean. Note that the
tritiugenic component consists of 3He only. At the ocean surface, helium
is essentially in solubility equilibrium with atmospheric He.
At the ocean surface, helium is essentially in solubility equilibrium with
the atmosphere. However, at depth, several important processes alter the
isotopic ratio Fig. – seefor a review.
Firstly, 3He is produced by the radioactive decay of tritium
, and secondly, terrigenic helium is introduced not only
by the release of helium from submarine volcanic activity at mid-ocean ridges
and volcanic centres, with elevated 3He /4He ratios typical of
their mantle source
,
but also by the addition of helium with a low 3He /4He ratio
from the crust and sedimentary cover, mostly due to α-decay of uranium
and thorium minerals .
Oceanic 3He /4He variations are usually expressed as
δ3He, the percentage deviation from the atmospheric ratio,
defined as (Rsample/Rair-1) × 100.
Below the mixed layer, oceanic 3He /4He values are usually
significantly higher than the atmospheric ratio, with δ3He up to
40 % in the Pacific Ocean . However, there
are some exceptions. Intra-continental seas such as the Black Sea and the
Mediterranean display deep-water 3He /4He ratios indicative of
a preferential addition of 4He-rich crustal helium rather than
3He-rich mantle helium .
Early investigations in the eastern Mediterranean Meteor
cruise M5/1987, have indeed revealed that deep waters have a
crustal helium signature, with δ3He as low as -5 %
(Fig. ). Note that Fig. shows that this deep core of
crustal helium is being progressively erased by the addition of tritiugenic
3He produced by the bomb tritium transient and by the recent dramatic
changes in the thermohaline circulation of the eastern basin (EMed), known as
the Eastern Mediterranean Transient (EMT) , during which dense waters of Aegean origin replaced the
Adriatic source of the deep waters in the EMed.
δ3He sections of the Meteor cruises in 1987,
1995, 1999 and 2001. Numbers on top are station numbers, observations are
indicated by dots, and the actual sections are shown in the inset maps.
Isolines are by objective mapping reproduced from.
Deconvolution of the various helium components using neon indicates that the
mantle helium contribution is only ∼ 5 % . In
the Mediterranean Sea, terrigenic helium is therefore largely of crustal
origin due to the presence of a continental-type crust and a high sediment
load of continental origin, but also because mantle helium, which is produced
by the submarine volcanic activity in only a few places in the Mediterranean
Sea (Aeolian Arc, Aegean Arc, and Pantelleria Rift in particular), is
released at rather shallow depths and is therefore quickly
transferred to the atmosphere.
Mantle 3He was discovered in the deep ocean by . It is
injected at mid-ocean ridges as part of the processes generating new oceanic
crusts and advected by ocean currents. Since this discovery, helium isotopes
have been used extensively to trace the deep ocean circulation
and in conjunction with tritium have been used to study ocean circulation,
ventilation and mixing processes
.
Ventilation is defined as the process of moving a parcel of water from the
surface to a given subsurface location. It can occur through convection,
subduction, advection, and diffusion .
The helium isotope distribution in the deep oceans has also been simulated by
various ocean circulation models to constrain global helium degassing fluxes
and evaluate the degree to which models can correctly reproduce the main
features of the world's ocean circulation
.
In this study we build a source function for the release of terrigenic helium
components (crust and mantle) into the deep Mediterranean and apply it to a
high-resolution oceanic model of the Mediterranean Sea. The simulated
helium-isotope distribution is then compared with available data to constrain
terrigenic helium fluxes. In addition to providing constraints on the
degassing flux, our work is the first attempt to simulate natural helium-3 in
a high-resolution regional model of the Mediterranean Sea, and provides new
information on the model's capacity to represent the ventilation of deep
waters.
Description of the model
The model used in this work is the NEMO (Nucleus for European Modelling of
the Ocean) free surface ocean general circulation model in
a regional configuration called NEMO-MED12 .
This model of the Mediterranean Sea has been used previously to study
anthropogenic tritium and its decay product helium-3 , the
anthropogenic carbon uptake , the transport through the
Strait of Gibraltar , as well as the Western
Mediterranean Deep Water (WMDW) formation and the
mixed-layer response under high-resolution air–sea forcings
. This model satisfactorily simulates the main
structures of the thermohaline circulation of the Mediterranean Sea, with
mechanisms having a realistic timescale compared to observations. In
particular, tritium/helium-3 simulations have shown that
the EMT signal from the Aegean sub-basin is realistically simulated, with its
corresponding penetration of tracers into the deep water in early 1995. The
strong convection event of winter 2005 and the following years in the Gulf of
Lion was satisfactorily captured as well. However, some aspects of the model
still need to be improved: in the eastern basin, tritium/helium-3 simulations
have highlighted the too-weak formation of Adriatic Deep Water (AdDW),
followed by a weak contribution to the Eastern Mediterranean Deep Water
(EMDW) in the Ionian sub-basin. In the western basin, the production of WMDW
is correct, but the spreading of the recently ventilated deep water to the
south of the basin is too weak. The consequences of these weaknesses in the
model's skill in simulating some important aspects of the dynamics of the
deep ventilation of the Mediterranean will have to be kept in mind when
analysing these helium simulations.
NEMO-MED12 covers the whole Mediterranean Sea, but also extends into the
Atlantic Ocean. Horizontal resolution is one-twelfth of a degree, thus
varying with latitude between 8 and 6.5 and 8 km from 30 to 46∘ N,
respectively, and between 5.5 and 7.5 km in longitude. Vertical resolution
varies with depth, from 1 m at the surface to 450 m at the bottom (50
levels in total). We use partial steps to adjust the last numerical level
with the bathymetry. The exchanges with the Atlantic Ocean are performed
through a buffer zone from 11 to 7.5∘ W, where 3-D temperature and
salinity model fields are relaxed to the observed climatology
.
NEMO-MED12 is forced at the surface by ARPERA
daily fields of the momentum, evaporation
and heat fluxes over the period 1958–2013. For the sea-surface temperature
(SST), a relaxation term is applied to the heat flux .
The total volume of water in the Mediterranean Sea is conserved by restoring
the sea-surface height (SSH) in the Atlantic buffer zone toward the GLORYS1
reanalysis .
The initial conditions (temperature, salinity) for the Mediterranean Sea are
prescribed from the MedAtlas-II climatology
weighted by a low-pass filter with a time window of 10 years using the
MedAtlas data covering the 1955–1965 period, following .
For the Atlantic buffer zone, the initial state is set from the 2005 World
Ocean Atlas for temperature and salinity
. River runoff is prescribed from the interannual data set
of and .
Full details of the model and its parameterizations are described by
, and .
The tracer model
Helium is implemented in the model as a passive conservative tracer which
does not affect ocean circulation. It is transported in the Mediterranean Sea
by NEMO-MED12 physical fields using an advection–diffusion equation (Eq. 1).
The rate of change of the concentration of each specific passive tracer C is
δCδt=S(C)-U⋅∇C+∇⋅(K∇C),
where S(C) is the tracer source (at the
seafloor) and sink (at the air–sea interface); U∇C is advection of
the tracer along the three perpendicular axes and ∇ (K∇C) is
the lateral and vertical diffusion, with the same parameterization as for the
hydrographic tracers.
Because 3He and 4He are passive tracers, simulations could be run
in a computationally efficient off-line mode. This method relies on
previously computed circulation fields (U, V, W) from the NEMO-MED12
dynamical model . Physical forcing fields are read daily
and interpolated to give values for each 20 min time step. The same approach
was used by to model the anthropogenic tritium invasion and
by to simulate CFCs and anthropogenic carbon. This choice
is justified by the fact that these tracers are passive. Their injection does
not alter the dynamics of the ocean, and they have no influence on the
physical properties of water, unlike hydrographic tracers such as temperature
or salinity.
The simulations were initialized with uniform 3He and 4He
concentrations corresponding to those at solubility equilibrium with the
partial pressures of these isotopes in the atmosphere, for seawater at
T=10∘C and S=34. Model simulations were
integrated for 500 years until they reached a quasi-steady state; that is,
the globally averaged drift was less than 10-2δ3He %
per 200 years of run.
Parameterization of the helium injection
Terrigenic helium in the Mediterranean Sea has two components: (1) crustal
helium, originating from the crust and overlying sediment cover, and (2)
mantle helium, injected by submarine volcanic activity. For the injection of
helium, we follow the protocol proposed by and
. Each component has a characteristic
3He /4He value. The anthropogenic 3He distribution due to
the decay of bomb tritium has already been addressed by .
For this study, we ran two separate simulations, one for each helium
component. Each simulation has two boundary conditions: a loss term at the
surface, due to the sea-to-air gas exchange, and a source term at the
seafloor, describing terrigenic tracer input. Each simulation thus represents
the sum of the specified terrigenic component and the atmospheric component,
with the distributions of 3He and 4He computed separately. We then
calculate the isotopic ratio using the δ3He notation.
Surface boundary condition
The only sink for oceanic helium is loss to the atmosphere. At the air–sea
interface, the model will exchange 3He and 4He with the atmosphere
using sea–air flux boundary conditions that are analogous to those developed
for helium during the second phase of OCMIP
http://ocmip5.ipsl.jussieu.fr/OCMIP/phase2/simulations/Helium/HOWTO-Helium.html. Using the standard flux-gradient formulation for a passive
gaseous tracer, the flux of helium FHe is given by
FHe=Kw(Ceq-Csurf),
where Kw is the gas transfer (piston) velocity (m s-1),
Csurf is the modelled surface ocean concentration of 3He or
4He as appropriate, and Ceq is the atmospheric solubility
equilibrium concentration at the local sea-surface
temperature (SST) and salinity (SSS).
Here, we neglect spatio-temporal variations in atmospheric pressure and
assume it remains at 1 atm. The gas transfer velocity is computed from
surface-level wind speeds, u (m s-1), from the ARPERA forcing
following the (Eq. 3)
formulation
Kw=au2(Sc/660)1/2,
where a=0.31 and Sc is the Schmidt number which is to be
computed from the modelled SST, using the formulation for 4He given by
, derived from . For 3He, we
reduce the Schmidt number (relative to 4He) by 15 %
(ScHe-3=ScHe-4/1.15) based
on the ratio of the reduced masses, which is consistent with helium isotopic
fractionation measurements by . Therefore, in the following,
the modelled atmospheric component is the helium distribution at equilibrium
with surface air–sea boundary conditions, without any helium flux from the
seafloor.
Crustal helium fluxes
Lake and groundwater studies have shown that radiogenic helium is
continuously released from the underlying crustal bedrock seefor a
review. Porewaters trapped in oceanic sediments are also
enriched in radiogenic 4He from the underlying oceanic crust and in situ
4He production by uranium- and thorium-rich minerals, releasing their
helium at the sea bottom . Deep
waters of intra-continental seas such as the Mediterranean are more prone to
exhibiting a radiogenic 4He signature than the open ocean because the
continental upper crust is about 40 times more enriched in uranium and
thorium than the oceanic crust .
In the deep eastern Mediterranean, southwest of Crete, extremely high
radiogenic 4He concentrations have indeed been measured in deep brine
pools created by the advection of deep buried fluids hosted by the
sedimentary matrix beneath the Messinian evaporites
. However, there are no data on the spatial
variability of the crustal helium injection into deep waters. Therefore, in
the model, crustal helium is injected as a uniform flux (in mol of helium per
square metre of seafloor >1000 m) with a 3He /4He ratio of
0.06 Rair. The initial value of
this flux is that estimated by Roether et al. (1998) (Table 2) using a
multi-box model in which the thermohaline circulation of the eastern
Mediterranean is represented by a deep reservoir (>1000 m depth) and two
intermediate water cells (see Table 2). Sensitivity tests
were made to determine the flux which produces the best agreement with
available data .
Mantle helium fluxes
The subduction of the African plate below Europe is responsible for the
volcanic activity which takes place in the Mediterranean basin
(Fig. ). The main submarine activity is found in the Tyrrhenian and
Aegean seas, and in the Sicily Channel .
Depth (in metres) and localization of mantle helium injection in the
Mediterranean Sea.
Hydrothermal vents in the Tyrrhenian sub-basin are found all along the
Aeolian volcanic arc (Fig. ) from Palinuro in the north to Eolo and
Enarete in the southwest , as well as on the Marsili
seamount .
In the Aegean, hydrothermal systems occur along the southern Aegean volcanic
arc from Sousaka and Methana in the west to Kos, Yali and Nisiros in the east
.
Finally, a recent helium isotope survey across the Sicily Channel, which
separates the Sicilian platform from Africa, also suggests hydrothermal
helium input between 600 and 1000 m depth associated with the Pantelleria
Rift (Fourré and Jean-Baptiste, unpublished results).
Location and depth of the active zones are shown in Fig. . Table 1
summarizes the 3He fluxes used for our simulations. For the Aeolian and
Aegean volcanic arcs, 3He fluxes were determined by simple scaling to
the global 3He flux from arc volcanism, which can be estimated (to
within a factor of 2) to be ∼4×10-3 mol of 3He
per kilometre of arc based on the assumption that the magma production rate
of arcs is ∼ 20 % of that of mid-ocean ridges
and the total length of subduction zones.
For the Marsili seamount, the 3He flux was estimated from 3He
fluxes at nearby subaerial volcanoes .
3He /4He isotopic ratios were chosen according to available in
situ data (when available) or to 3He /4He data from nearby
subaerial volcanoes.
Release rates of mantle helium in the
Mediterranean Sea used in the model (see Sect. 3.1.3).
Release rate of crustal helium used in the
model and comparison with crustal helium fluxes in various geological
settings.
Region3He (mol m-2 yr-1)4He (mol m-2 yr-1)ReferencesMediterranean Sea1.32×10-141.6×10-7This workContinental crust4.7×10-141.4×10-6Continental crust–2.2×10-6Eastern Med.–1.6×10-6Black Sea5.8×10-130.7×10-6Global Ocean floor(1.5–4.6)×10-15(0.2–1.4)×10-7Pacific Ocean–(0.01–0.2)×10-7Pacific Ocean–0.75×10-7Observations used for the comparison with model results
The tracer data in the Mediterranean which are relevant for comparison with
model results are the Meteor cruises across the eastern
Mediterranean basin (; see Fig. 2) and the helium
isotope survey carried out by in the Tyrrhenian Sea.
Additional δ3He data (Fourré and Jean-Baptiste, unpublished
data) from the November 2013 Record cruise in the Sicily Channel
(Geotraces program) are also available. The 1987 Meteor section is
of particular interest since it is the less affected by tritiugenic 3He
(Fig. ) and therefore the deconvolution of the various helium
components using neon is the most accurate. This deconvolution is carried out
using the method proposed by , which allows
one to derive the atmospheric helium component from the neon distribution and
then to obtain the terrigenic 4He component by substracting this
atmospheric component from the total measured helium concentration. The
atmospheric and terrigenic 3He components are then obtained using the
3He /4He ratios of dissolved atmospheric and terrigenic
helium, respectively. For the Tyrrhenian Sea, the δ3He excess due
to hydrothermal activity along the Aeolian arc is obtained by substracting
the background vertical δ3He profile of vertical cast V01
see from the measured δ3He. The same method
was used for Sicily Channel data. Accuracy of the deconvoluted
δ3He is in the range 1–1.5 %.
ResultsCrustal helium distribution
We begin our analysis by providing an overview of the simulated
crustal + atmospheric helium component. Figure a displays a
section of modelled δ3Hecrust+atm along a W–E
transect across the EMed. As expected, the
δ3Hecrust+atm distribution exhibits negative
values, predominately in the deep waters, hinting at the presence of crustal
He highly enriched in radiogenic 4He. The model correctly simulates the
crustal-He distribution in the Levantine sub-basin (Fig. c), where
the simulated δ3Hecrust+atm values agree
reasonably well with observations from Meteor cruise M5. However,
modelled δ3Hecrust+atm values for the deep Ionian
sub-basin are too low, with a mean value below 3500 m around -7 %
compared to -4.5±0.7 % in the data (Fig. d). This too
large an accumulation of crustal 4He is the expected consequence of the
too low ventilation of the deep Ionian sub-basin in the model, as already
diagnosed in the anthropogenic tritium/3He simulations of
. The model generates too weak a formation of Adriatic Deep
Water (AdDW) that prevents the model from reproducing the observed signal
associated with injection at depth of surface water.
Crustal+atmospheric δ3He (in %) model–data
comparison along the Meteor M5 (September 1987) section:
(a) Colour-filled contours indicate simulated δ3He
(%), whereas colour-filled dots represent the crustal + atmospheric
δ3He deduced from in situ observations using the component
separation method of Roether et al. (1998) in the eastern basin (see Sect. 4
for details). (b): same as (a), but in the western basin
(WMed). There are no quantitative data for comparison in the WMed.
(c) and (d): comparison of average vertical profiles along
the Meteor M5/9-1987 section for the Levantine and Ionian
sub-basins, respectively; model results are in blue; red indicates the in
situ data.
The simulated δ3Hecrust+atm distribution in the
western basin (Fig. b) shows the same gradient as in the Levantine
basin, with negative values in the deep water (values around -5.5 %) as
a result of the homogenous crustal-He flux over the whole basin (see
Sect. 3). In the surface layer helium in solution is essentially in
equilibrium with atmospheric helium (δ3Hecrust+atm
values around -1.6 %) but decreasing steadily with depth down to a
layer of minimum δ3Hecrust+atm values in deep
waters. Although the terrigenic component cannot been estimated
quantitatively for the WMed because of the lack of a precise value for its
3He /4He ratio (Rter), the lower limit of
δ3Hecrust+atm (taking Rter equal to
zero) is in the range -3.5 to -4.5 % for deep waters. This is less
radiogenic than in the eastern basin, in agreement with the conclusions of
that the crustal component may be small in the WMed. Our
model results (-5.5 % on average) are somewhat lower, suggesting that,
as already observed in the eastern basin, the model probably underestimates
the ventilation rate of deep waters in the western basin too.
Mantle helium distribution
As discussed above, the main active submarine volcanic systems are located in
the Tyrrhenian and Aegean seas and in the Sicily Channel (Fig. ).
Pantelleria Rift
In the Pantelleria Rift, a clearly visible plume of mantle helium is
simulated between 500 and 1000 m depth (Fig. a). The modelled
δ3Hemantle+atm plume anomaly at 12.5∘ E
reaches a maximum value of 2.5 % above the atmospheric background of
-1.6 %. This value is in good agreement with in situ observations at
the same location (2.3 % above background at 800 m, Fig. d;
Fourré and Jean-Baptiste, unpublished data).
Mantle+atmospheric δ3He (%) model–data comparison in
(a) the Sicily Channel, (b) Tyrrhenian sub-basin, and
(c) Aegean sub-basin. (d) Vertical profiles of
δ3He (above the atmospheric background of -1.6 %) at
12.5∘E in the Sicily Channel; model results are in blue; red
indicates in situ data (Fourré and Jean-Baptiste, unpublished results).
(e): same as (d) for the Tyrrhenian sub-basin. The data are
from . The few stations located right above a plume in
have been discarded because they cannot be compared to
model results which are averaged over the volume of the model cell
(∼ 20 km3). There are no data for the Aegean basin.
Tyrrhenian Sea
The submarine volcanic activity in the Tyrrhenian is essentially confined to
depths less than 1200 m. The corresponding mantle helium input creates a
weak but well-defined δ3Hemantle+atm plume
(Fig. b) centred around 1000 m depth, which propagates into the
entire Tyrrhenian sub-basin (Fig. ). Average simulated
δ3Hemantle+atm values above the atmospheric
background (-1.6 %) are within δ3Hemantle+atm=-0.5 % of the corresponding above-background δ3He
measurements of in the same area (Fig. b and e).
Aegean Sea
Hydrothermal venting in the Aegean sub-basin occurs at shallow depths
(between 50 and 450 m depth) compared to the two other sites in the
Mediterranean Sea; in consequence the simulated
δ3Hemantle+atm anomaly is particularly weak in
this area due to the rapid helium degassing into the atmosphere
(Fig. c) and the signal does not propagate into the larger area
around the Aegean Sea (Fig. ). Note that no δ3He data
are available for comparison in the Aegean basin.
Horizontal distribution of δ3Hemantle
(%) (vertically averaged) across the Mediterranean Sea.
Figure provides a descriptive view of the global distribution of
the modelled δ3Hemantle+atm signal over the
Mediterranean Sea. The figure highlights the location of mantle-He sources,
and of their propagation through the interior of the Mediterranean Sea. The
δ3Hemantle+atm anomaly is clearly visible over the
three main areas of submarine volcanic activity. The mantle-He plume injected
by the Aeolian Arc spreads over the entire Tyrrhenian sub-basin, then leaves
through the Corsican Channel (1900 m) and extends into the Liguro-Provencal
sub-basin associated with the Levantine Intermediate Water (LIW) trajectory,
and into the Algerian sub-basin through the Sardinian Channel. The input from
the Pantelleria Rift is topographically trapped in the Sicilian Channel. The
Aegean sub-basin is also impacted by the mantle He: the He excess is
localized in the western part of this sub-basin between mainland Greece and
the island of Crete.
Total helium-3 distribution
The Mediterranean Sea is characterized by coexisting terrigenic and
tritiugenic helium throughout its subsurface waters. Figure
presents a model–data comparison of the simulated total δ3He
(sum of terrigenic, tritiugenic and atmospheric helium) in 1987, along the
W–E Emed transect corresponding to the Meteor 5 cruise (1987). The
tritiugenic component in 1987 is taken from .
Figure exhibits a δ3He maximum at a few hundred metres
depth, hinting at the presence of tritiugenic 3He produced by the
radioactive decay of anthropogenic bomb tritium. Further down
δ3He values decrease and, in the Levantine basin, even dropping
below the value for solubility equilibrium with the atmosphere
(∼-1.6 %). This represents the signature of crustal helium in
the deep Mediterranean waters.
Total δ3He (sum of terrigenic, tritiugenic and
atmospheric helium) model–data comparison along the Meteor M5
(September 1987) section. (a) Colour-filled contours indicate
simulated δ3He (%), whereas colour-filled dots represent in
situ observations. (b) and (c): comparison of average
vertical profiles for the Levantine and Ionian sub-basins, respectively;
model results are in blue; red indicates in situ data.
The model correctly reproduces the δ3He maximum of the
intermediate waters, with values similar to observations, except in the
eastern part of the section, where it tends to be overestimated. Deeper, we
have a realistic simulation of the helium signal in the Levantine sub-basin
(Fig. b) with δ3He around -5 %, which is in good
agreement with observations made during Meteor cruise M5, with only
10 % of difference between the simulated δ3He mean vertical
profile and in situ data below 2000 m depth (Fig. b). Again, one
can clearly see that the shortcoming associated with the too-weak EMDW
formation in the Adriatic sub-basin leads to excessively negative
δ3He values at depth: the model tends to underestimate the
δ3He levels in the deep water by more than 60 % compared to
observations below 2000 m depth (Fig. c).
Comparison of the tritiugenic and mantle δ3He signatures, which
occur at similar depths in the Mediterranean Sea, shows that tritiugenic
3He clearly dominates over mantle 3He. This finding agrees with
those of for the Tyrrhenean basin; they concluded that
most of the helium-3 excess is tritiugenic.
Helium inventory (in mole) in the
Mediterranean Sea.
We have presented the first simulation of the terrigenic helium isotope
distribution in the Mediterranean Sea, using a high-resolution model
(NEMO-MED12). For this simulation we built a source function for terrigenic
(crustal and mantle) helium isotopes obtained by simple scaling of published
flux estimates (Tables 1 and 2). For crustal helium, our helium flux equal to
1.6 ×10-74He mol m-2 yr-1 generates a satisfying
agreement with the data in the Levantine basin, where the tritium/3He
simulations of have shown that modelled ventilation of the
deep waters is correct. This flux represents only 10 % of the previous
estimate by for the eastern Mediterranean (1.6 ×10-64He mol m-2 yr-1), based on a box model where the
thermohaline circulation of the eastern Mediterranean is represented by a
deep-water reservoir (>1000 m depth) and two intermediate water cells.
The tritium/3He and CFC
simulations have shown that the model adequately represents ventilation of
near-surface and intermediate waters but globally underestimates the
ventilation rate of the Mediterranean deep waters, particularly in the Ionian
sub-basin, where the deep-water ventilation associated with the Adriatic Deep
Water (AdDW) is too shallow in the simulations compared to observations. This
mismatch is likely due to an overestimation of the freshwater flux
(precipitation–evaporation and runoff) into the Adriatic sub-basin. Taking
into account this model deficiency, our estimate must be considered as a
lower limit of the crustal helium flux into the Mediterranean basin.
For mantle helium, our simple parameterization produces realistic simulated
δ3He values that are in agreement with in situ measurements, thus
supporting our scaling approach. This study provides a useful constraint on
the magnitude of the hydrothermal helium-3 fluxes in the Mediterranean Sea
(Table 1) that is of interest because this flux can now be used to estimate
the hydrothermal flux of other chemical species. Hydrothermal venting
produces plumes in the ocean that are highly enriched in a variety of
chemical species. Hydrothermal activity impacts the global cycling of
elements in the ocean , including economically valuable
minerals such as rare-earth elements (REE) which are deposited in deep sea
sediments. These minerals are crucial in the manufacture of novel electronic
equipment and green-energy technologies . Hydrothermal
chemical elements such as iron also impact biological cycles and eventually
the carbon cycle and climate . Our simulations show that
high-resolution oceanic models coupled with measurements of conservative
hydrothermal tracers such as helium isotopes can be useful tools to study the
environmental impact of hydrothermal activity in a variety of marine
environments and at a variety of scales. Beyond the case of hydrothermal
activity, it also shows that high-resolution ocean circulation models such as
NEMO-MED 12 are well suited for the study of the evolution of quasi-enclosed
basins such as the Mediterranean Sea that are under increasing anthropogenic
pressure.
The global inventory of helium isotopes in the Mediterranean Sea based on our
simulations indicates the relative contribution of each source of the tracer
(Table 3). Besides atmospheric helium, which is the main source of both
3He and 4He, it shows that tritiugenic 3He and crustal
4He are the main contributors to 3He and 4He excesses over
solubility equilibrium. Therefore, in contrast to the world's oceans, where
mantle helium dominates over other terrigenic and tritiugenic components, the
mantle helium component linked to the submarine volcanic/hydrothermal
activity is relatively small compared to the other sources of helium in the
Mediterranean Sea. This is due to the cumulated effects of (1) the relatively
shallow depths of hydrothermal injections in the Mediterranean (<1000 m)
compared to the mid-ocean ridges (MORs), mostly in the range 2000–4000 m
that favour a more rapid degassing through the air–sea interface; (2) lower
helium flux from arc volcanism (20 %) compared to MOR volcanism
; and (3) high crustal-He flux in the
Mediterranean basin due to its intra-continental nature (i.e. with a
continental-type crust and high sediment load of continental origin).
However, despite its minor contribution to the global helium-3 budget, the
hydrothermal component remains identifiable due to its elevated isotopic
signature.
Conclusions
The terrigenic helium isotope distribution was simulated for the first time
in the whole Mediterranean Sea, using a high-resolution model (NEMO-MED12) at
one-twelfth of a degree horizontal resolution (6–8 km). The
parameterization of the helium injection at the seafloor led to results of
sufficient quality to allow us to put valuable constraints on the crustal and
mantle helium fluxes. Helium simulations also confirmed some shortcomings of
the model dynamics in representing the deep ventilation of the Ionian basin,
already pinpointed by recent transient tracer studies. In spite of these
limitations and of the limited data set at our disposal for model–data
comparison, our work puts additional constraints on the origin of the helium
isotopic signature in the Mediterranean Sea. The simulation of this tracer
and its comparison with observations provide a new and additional technique
for assessing and improving the NEMO-MED12 dynamical regional model. This is
essential if we are to improve our ability to predict the future evolution of
the Mediterranean Sea under the increasing anthropogenic pressure that it is
suffering . It also offers new opportunities to study
chemical element cycling, particularly in the context of the increasing
amount of data that will result from the international GEOTRACES effort
.
Acknowledgements
We are grateful to M. Hecht (topical editor) for his careful reading of the
manuscript. We thank W. Roether and the anonymous referee for their
constructive comments and suggestions. We thank J. Palmieri for his help with
technical aspects, and Y. Donnadieu for computing support.
Edited by: M. Hecht
References
Allard, P.: Global emissions of helium-3 by subaerial volcanism,
Geophys.
Res. Lett., 19, 1479–1481, 1992a.
Allard, P.: Correction to “Global emissions of helium-3 by subaerial
volcanism”, Geophys. Res. Lett., 19, 2103–2103,
1992b.
Andrie, C. and Merlivat, L.: Tritium in the western Mediterranean Sea during
1981 Phycemed cruise, Deep-Sea Res. Pt. A, 35, 247–267, 1988.
Antonov, J. I., Locarnini, R. A., Boyer, T. P., Mishonov, A. V., and Garcia,
H. E.: World Ocean Atlas 2005, Salinity, edited by: Levitus, S., NOAA
Atlas NESDIS 62, US Government Printing Office, Washington, DC, 2, 182
pp., 2006.Ayache, M., Dutay, J.-C., Jean-Baptiste, P., Beranger, K., Arsouze, T.,
Beuvier, J., Palmieri, J., Le-vu, B., and Roether, W.: Modelling of the
anthropogenic tritium transient and its decay product helium-3 in the
Mediterranean Sea using a high-resolution regional model, Ocean Sci., 11,
323–342, 10.5194/os-11-323-2015,
2015.
Ballentine, C. J. and Burnard, P. G.: Production, Release and Transport of
Noble Gases in the Continental Crust, Rev. Mineral.
Geochem., 47, 481–538, 2002.Beuvier, J., Béranger, K., Lebeaupin Brossier, C., Somot, S.,
Sevault,
F., Drillet, Y., Bourdallé-Badie, R., Ferry, N., and Lyard, F.:
Spreading of the Western Mediterranean Deep Water after winter 2005: Time
scales and deep cyclone transport, J. Geophys. Res., 117,
C07022, 10.1029/2011JC007679,
2012a.
Beuvier, J., Lebeaupin Brossier, C., Béranger, K., Arsouze, T.,
Bourdallé-Badie, R., Deltel, C., Drillet, Y., Drobinski, P., Lyard, F.,
Ferry, N., Sevault, F., , and Somot, S.: MED12, Oceanic component for the
modelling of the regional Mediterranean Earth System, Merc. Oc.
Quart. Newslett., 46, 60–66, 2012b.
Bianchi, D., Sarmiento, J. L., Gnanadesikan, A., Key, R. M., Schlosser, P.,
and
Newton, R.: Low helium flux from the mantle inferred from simulations of
oceanic helium isotope data, Earth Planet. Sci. Lett., 297,
379–386, 2010.Capaccioni, B., Tassi, F., Vaselli, O., Tedesco, D., and Poreda, R.:
Submarine
gas burst at Panarea Island (southern Italy) on 3 November 2002: A magmatic
versus hydrothermal episode, J. Geophys. Res., 112, B05201,
10.1029/2006JB004359, 2007.
Capasso, G., Carapezza, M. L., Federico, C., Inguaggiato, S., and Rizzo, A.:
Geochemical monitoring of the 2002–2003 eruption at Stromboli volcano
(Italy): precursory changes in the carbon and helium isotopic composition of
fumarole gases and thermal waters, Bull. Volcanol., 68, 118–134, 2005.Chaduteau, C., Jean-Baptiste, P., Fourré, E., Charlou, J.-L., and
Donval,
J.-P.: Helium transport in sediment pore fluids of the Congo-Angola margin,
Geochem. Geophys. Geosyst., 10, 1–12,
10.1029/2007GC001897,
2009.
Charlou, J., Donval, J., Zitter, T., Roy, N., Jean-Baptiste, P., Foucher, J.,
and Woodside, J.: Evidence of methane venting and geochemistry of brines on
mud volcanoes of the eastern Mediterranean Sea, Deep-Sea Res. Pt. I, 50, 941–958,
2003.Clarke, W., Jenkins, W., and Top, Z.: Determination of tritium by mass
spectrometric measurement of 3He, Int. J. Appl.
Radiat. Isotopes, 27, 515–522, 1976.
Clarke, W. B., Beg, M. A., and Craig, H.: Excess helium 3 at the North
Pacific
Geosecs Station, J. Geophys. Res., 75, 7676–7678,
1970.
Craig, H. and Lupton, J. E.: Helium-3 and mantle volatiles in the ocean and
the oceanic crust, Oc. Lithos., 7, 391–428, 1981.
Craig, H. and Weiss, R. F.: Dissolved gas saturation anomalies and excess
helium in the ocean, Earth Planet. Sci. Lett., 10, 289–296,
1971.
D'Alessandro, W., De Gregorio, S., Dongarrà, G., Gurrieri, S.,
Parello,
F., and Parisi, B.: Chemical and isotopic characterization of the gases of
Mount Etna (Italy), J. Volcanol. Geotherm. Res., 78,
65–76, 1997.
Dando, P., Stüben, D., and Varnavas, S.: Hydrothermalism in the
Mediterranean Sea, Prog. Oceanogr., 44, 333–367,
1999.Drobinski, P., Anav, A., Lebeaupin Brossier, C., Samson, G.,
Stéfanon,
M., Bastin, S., Baklouti, M., Béranger, K., Beuvier, J.,
Bourdallé-Badie, R., Coquart, L., D'Andrea, F.,
de Noblet-Ducoudré, N., Diaz, F., Dutay, J.-C., Ethe, C., Foujols,
M.-A., Khvorostyanov, D., Madec, G., Mancip, M., Masson, S., Menut, L.,
Palmieri, J., Polcher, J., Turquety, S., Valcke, S., and Viovy, N.: Model of
the Regional Coupled Earth system (MORCE): Application to process and climate
studies in vulnerable regions, Env. Modell. Software, 35, 1–18, 10.1016/j.envsoft.2012.01.017,
2012.
Dutay, J.-C., Bullister, J., Doney, S., Orr, J., Najjar, R., Caldeira, K.,
Campin, J.-M., Drange, H., Follows, M., Gao, Y., Gruber, N., Hecht, M.,
Ishida, A., Joos, F., Lindsay, K., Madec, G., Maier-Reimer, E., Marshall, J.,
Matear, R., Monfray, P., Mouchet, A., Plattner, G.-K., Sarmiento, J.,
Schlitzer, R., Slater, R., Totterdell, I., Weirig, M.-F., Yamanaka, Y., and
Yool, A.: Evaluation of ocean model ventilation with CFC-11: comparison of
13 global ocean models, Ocean Modell., 4, 89–120,
2002.
Dutay, J.-C., Jean-Baptiste, P., Campin, J.-M., Ishida, A., Maier-Reimer, E.,
Matear, R., Mouchet, A., Totterdell, I., Yamanaka, Y., Rodgers, K., Madec,
G., and Orr, J.: Evaluation of OCMIP-2 ocean models' deep circulation with
mantle helium-3, J. Mar. Syst., 48, 15–36,
2004.
Dutay, J. C., Emile-Geay, J., Iudicone, D., Jean-Baptiste, P., Madec, G., and
Carouge, C.: Helium isotopic constraints on simulated ocean circulations:
Implications for abyssal theories, Environ. Fluid Mechan., 10,
257–273, 2010.
Elderfield, H. and Schultz, A.: Mid-Ocean Ridge Hydrothermal Fluxes and the
Chemical Composition of the Ocean, Ann. Rev. Earth Planet.
Sci., 24, 191–224, 1996.
England, M. H.: The age of water and ventilation timescales in a global
ocean
model, J. Phys. Oceanogr., 25, 2756–2777, 1995.Farley, K. A., Maier-Reimer, E., Schlosser, P., and Broecker, W. S.:
Constraints on mantle 3 He fluxes and deep-sea circulation from an oceanic
general circulation model, J. Geophys. Res., 100, 3829,
10.1029/94JB02913,
1995.
Ferry, N., Parent, L., Garric, G., Barnier, B., and Jourdain, N. C.:
Mercator
Global Eddy Permitting Ocean Reanalysis GLORYS1V1: Description and Results,
Mercat. Oc. Quart. Newslett., 36, 15–28, 2010.Fiebig, J., Chiodini, G., Caliro, S., Rizzo, A., Spangenberg, J., and
Hunziker,
J. C.: Chemical and isotopic equilibrium between CO2 and CH4 in fumarolic
gas discharges: Generation of CH4 in arc magmatic-hydrothermal systems,
Geochim. Cosmochim. Ac., 68, 2321–2334,
2004.
Fourré, E., Allard, P., Jean-Baptiste, P., Cellura, D., and Parello,
F.:
H3e/H4e Ratio in Olivines from Linosa, Ustica, and Pantelleria Islands
(Southern Italy), J. Geol. Res., 2012, 1–8,
2012.
GEOTRACE: GEOTRACES – An international study of the global marine
biogeochemical cycles of trace elements and their isotopes, Chemie der Erde
– Geochemistry, 67, 85–131, 2007.
Goodman, P. J.: The Role of North Atlantic Deep Water Formation in an OGCM's
Ventilation and Thermohaline Circulation, J. Phys. Oceanogr.,
28, 1759–1785, 1998.
Graham, D. W.: Noble Gas Isotope Geochemistry of Mid-Ocean Ridge and Ocean
Island Basalts: Characterization of Mantle Source Reservoirs, Rev.
Mineral. Geochem., 47, 247–317, 2002.Herrmann, M., Sevault, F., Beuvier, J., and Somot, S.: What induced the
exceptional 2005 convection event in the northwestern Mediterranean basin?
Answers from a modeling study, J. Geophys. Res., 115,
C12051, 10.1029/2010JC006162,
2010.Herrmann, M. J. and Somot, S.: Relevance of ERA40 dynamical downscaling for
modeling deep convection in the Mediterranean Sea, Geophys. Res.
Lett., 35, L04607, 10.1029/2007GL032442, 2008.Hilton, D. R., Fischer, T. P., and Marty, B.: Noble Gases and Volatile
Recycling at Subduction Zones, Rev. Mineral. Geochem., 47,
319–370, 10.2138/rmg.2002.47.9, 2002.Jähne, B., Heinz, G., and Dietrich, W.: Measurement of the diffusion
coefficients of sparingly soluble gases in water, J. Geophys.
Res., 92, 10767, 10.1029/JC092iC10p10767,
1987a.Jähne, B., Münnich, K. O., Bösinger, R., Dutzi, A., Huber,
W., and Libner, P.: On the parameters influencing air-water gas exchange,
J. Geophys. Res., 92, 1937, 10.1029/JC092iC02p01937,
1987b.Jamous, D., Mémery, L., Andrié, C., Jean-Baptiste, P., and
Merlivat, L.: The distribution of helium 3 in the deep western and southern
Indian Ocean, J. Geophys. Res., 97, 2243,
10.1029/91JC02062, 1992.Jean-Baptiste, P., Charlou, J., Stievenard, M., Donval, J., Bougault, H., and
Mevel, C.: Helium and methane measurements in hydrothermal fluids from the
mid-Atlantic ridge: The Snake Pit site at 23∘ N, Earth Planet.
Sci.
Lett., 106, 17–28, 10.1016/0012-821X(91)90060-U,
1991a.Jean-Baptiste, P., Charlou, J. L., Stievenard, M., Donval, J., Bougault, H.,
and Mevel, C.: Helium and methane measurements in hydrothermal fluids from
the Mid Atlantic Ridge: the SNAKE PIT site at 23∘ N, Earth Planet. Sci.
Lett., 106, 17–28, 1991b.
Jean-Baptiste, P., Mantisi, F., Memery, L., and Jamous, D.: Helium-3 and CFC
in the Southern Ocean: tracers of water masses, Mar. Chem., 35,
137–150, 1992.Jean-Baptiste, P., Dapoigny, A., Stievenard, M., Charlou, J. L., Fouquet, Y.,
Donval, J. P., and Auzende, J. M.: Helium and oxygen isotope analyses of
hydrothermal fluids from the East Pacific Rise between 17∘ S and 19∘ S,
Geo-Mar. Lett., 17, 213–219, 1997.
Jean-Baptiste, P., Fourré, E., Metzl, N., Ternon, J., and Poisson, A.:
Red Sea deep water circulation and ventilation rate deduced from the 3He and
14C tracer fields, J. Mar. Syst., 48, 37–50, 2004.Jenkins, D. J., Wolever, T. M., Leeds, A. R., Gassull, M. A., Haisman, P.,
Dilawari, J., Goff, D. V., Metz, G. L., and Alberti, K. G.: Dietary fibres,
fibre analogues, and glucose tolerance: importance of viscosity., Tech.
Rep.,
6124, 10.1136/bmj.1.6124.1392,
1978.
Jenkins, W. and Clarke, W.: The distribution of 3He in the western Atlantic
ocean, Deep-Sea Res. Oceanogr. Abstr., 23, 481–494, 1976.
Jenkins, W. J.: Tritium-helium dating in the sargasso sea: a measurement of
oxygen utilization rates., Science (New York, NY), 196, 291–2,
1977.
Jenkins, W. J.: The use of Anthropogenic Tritium and He-3 to Study
Sub-Tropical Gyre Ventilation and Circulation, Philos. T. R. Soc. A, 325, 43 – 61, 1988.
Kato, Y., Fujinaga, K., Nakamura, K., Takaya, Y., Kitamura, K., Ohta, J.,
Toda,
R., Nakashima, T., and Iwamori, H.: Deep-sea mud in the Pacific Ocean as a
potential resource for rare-earth elements, Nature Geosci., 4, 535–539,
2011.
Kipfer, R., Aeschbach-Hertig, W., Peeters, F., and Stute, M.: Noble Gases in
Lakes and Ground Waters, Rev. Mineral. Geochem., 47,
615–700,
2002.
Lebeaupin Brossier, C., Béranger, K., Deltel, C., and Drobinski, P.:
The Mediterranean response to different space-time resolution atmospheric
forcings using perpetual mode sensitivity simulations, Oc. Modell., 36,
1–25, 2011.
Locarnini, R. A., Mishonov, A. V., Antonov, J. I., Boyer, T. P., and Garcia,
H. E.: World Ocean Atlas 2005, Volume 1: Temperature, edited by: Levitus, S., NOAA
Atlas NESDIS 61, US Government Printing Office, Washington, DC, 182 pp.,
2006.
Ludwig, W., Dumont, E., Meybeck, M., and Heussner, S.: River discharges of
water and nutrients to the Mediterranean and Black Sea: Major drivers for
ecosystem changes during past and future decades?, Prog. Oceanogr.,
80, 199–217,
2009.Lupton, J.: Hydrothermal helium plumes in the Pacific Ocean, J.
Geophys. Res., 103, 15853, 10.1029/98JC00146,
1998.Lupton, J., de Ronde, C., Sprovieri, M., Baker, E. T., Bruno, P. P.,
Italiano,
F., Walker, S., Faure, K., Leybourne, M., Britten, K., and Greene, R.:
Active hydrothermal discharge on the submarine Aeolian Arc, J.
Geophys. Res., 116, B02102, 10.1029/2010JB007738,
2011.Lupton, J. E.: Helium-3 in the Guaymas Basin: Evidence for injection of
mantle
volatiles in the Gulf of California, J. Geophys. Res., 84,
7446, 10.1029/JB084iB13p07446,
1979.
Lupton, J. E.: A Far-Field Hydrothermal Plume from Loihi Seamount, Science,
272, 976–979, 1996.
Lupton, J. E., Weiss, R. F., and Craig, H.: Mantle helium in the Red Sea
brines, Nature, 266, 244–246,
1977a.
Lupton, J. E., Weiss, R. F., and Craig, H.: Mantle helium in hydrothermal
plumes in the Galapagos Rift, Nature, 267, 603–604,
1977b.
Madec, G. and NEMO-Team.: Note du Pôle de modélisation, Institut
Pierre-Simon Laplace (IPSL), France, NEMO Ocean Engine, 27, ISSN
N1288-1619, 2008.Martelli, M., Caracausi, A., Paonita, A., and Rizzo, A.: Geochemical
variations of air-free crater fumaroles at Mt Etna: New inferences for
forecasting shallow volcanic activity, Geophys. Res. Lett., 35,
L21302, 10.1029/2008GL035118,
2008.
MEDAR-MedAtlas-group: Medar-Medatlas Protocol (Version 3) Part I: Exchange
Format and Quality Checks for Observed Profiles, P. Rap. Int.
IFREMER/TMSI/IDM/SIS002-006, 50, 2002.Palmiéri, J., Orr, J. C., Dutay, J.-C., Béranger, K., Schneider,
A., Beuvier, J., and Somot, S.: Simulated anthropogenic CO2
storage and acidification of the Mediterranean Sea, Biogeosciences, 12,
781–802, 10.5194/bg-12-781-2015, 2015.
Parello, F., Allard, P., D'Alessandro, W., Federico, C., Jean-Baptiste, P.,
and Catani, O.: Isotope geochemistry of Pantelleria volcanic fluids, Sicily
Channel rift: a mantle volatile end-member for volcanism in southern Europe,
Earth Planet. Sci. Lett., 180, 325–339,
2000.
Rhein, M., Send, U., Klein, B., and Krahmann, G.: Interbasin deep water exchange in the western Mediterranean. J. Geophys. Res., 104, 23495–23508,
1999.
Rixen, M., Beckers, J. M., Levitus, S., Antonov, J., Boyer, T., Maillard, C.,
Fichaut, M., Balopoulos, E., Iona, S., Dooley, H., Garcia, M. J., Manca, B.,
Giorgetti, A., Manzella, G., Mikhailov, N., Pinardi, N., and Zavatarelli, M.:
The Western Mediterranean Deep Water: A proxy for climate change,
Geophys. Res. Lett., 32, 1–4, 2005.Roether, W. and Lupton, J. E.: Tracers confirm downward mixing of Tyrrhenian
Sea upper waters associated with the Eastern Mediterranean Transient, Ocean
Sci., 7, 91–99, 10.5194/os-7-91-2011,
2011.
Roether, W., Roussenov, V. M., and Well, R.: A tracer study of the
thermohaline circulation of the eastern Mediterranean, Oc. Proc.
Clim. Dynam., 371–394, 1994.
Roether, W., Manca, B. B., Klein, B., Bregant, D., Georgopoulos, D., Beitzel,
V., Kovacevic, V., and Luchetta, A.: Recent Changes in Eastern Mediterranean
Deep Waters, Science, 271, 333–335, 1996.Roether, W., Well, R., Putzka, A., and Rüth, C.: Component separation
of
oceanic helium, J. Geophys. Res., 103, 27931–27946, 10.1029/98JC02234,
1998.
Roether, W., Well, R., Putzka, A., and Rüth, C.: Correction to
“Component separation of oceanic helium” by Wolfgang Roether, Roland
Well, Alfred Putzka, and Christine Rüth, J. Geophys.
Res., 106, 4679–4679,
2001.
Roether, W., Klein, B., Manca, B. B., Theocharis, A., and Kioroglou, S.:
Transient Eastern Mediterranean deep waters in response to the massive
dense-water output of the Aegean Sea in the 1990s, Prog. Oceanogr.,
74, 540–571, 2007.Roether, W., Jean-Baptiste, P., Fourré, E., and Sültenfuß,
J.:
The transient distributions of nuclear weapon-generated tritium and its
decay product 3He in the Mediterranean Sea, 1952–2011, and
their oceanographic potential, Ocean Sci., 9, 837–854,
10.5194/os-9-837-2013, 2013.
Roether, W., Klein, B., and Hainbucher, D.: The Eastern Mediterranean
Transient: Evidence for Similar, Am. Geophys. Union, 12, 75–83,
2014.
Rüth, C., Well, R., and Roether, W.: Primordial in South Atlantic deep
waters from sources on the Mid-Atlantic Ridge, Deep-Sea Res. Pt. I, 47, 1059–1075, 2000.
Sano, T., Hataya, T., Terai, Y., and Shikata, E.: Hop stunt viroid strains
from dapple fruit disease of plum and peach in Japan, J.
Gen. Virol., 70, 1311–9,
1989.Sano, Y. and Wakita, H.: Geographical distribution of 3He /4He ratios in
Japan: Implications for arc tectonics and incipient magmatism, J.
Geophys. Res., 90, 8729, 10.1029/JB090iB10p08729, 1985.
Sano, Y., Wakita, H., Ohsumi, T., and Kusakabe, M.: Helium isotope evidence
for magmatic gases in Lake Nyos, Cameroon, Geophys. Res. Lett., 14,
1039–1041, 1987.
Schlosser, P. and Winckler, G.: Noble Gases in Ocean Waters and Sediments,
Rev. Mineral. Geochem., 47, 701–730,
2002.
Schlosser, P., Bullister, J. L., and Bayer, R.: Studies of deep water
formation and circulation in the Weddell Sea using natural and anthropogenic
tracers, Mar. Chem., 35, 97–122, 1991.
Shimizu, A., Sumino, H., Nagao, K., Notsu, K., and Mitropoulos, P.:
Variation
in noble gas isotopic composition of gas samples from the Aegean arc,
Greece, J. Volcanol. Geotherm. Res., 140, 321–339, 2005.Soto-Navarro, J., Somot, S., Sevault, F., Beuvier, J., Béranger, K.,
Criado-Aldeanueva, F., and García-Lafuente, J.: Evaluation of
regional ocean circulation models for the Mediterranean Sea at the Strait of
Gibraltar : volume transport and thermohaline properties of the outflow,
Clim. Dynam., 44, 1277–1292, 10.1007/s00382-014-2179-4,
2014.Srinivasan, A., Top, Z., Schlosser, P., Hohmann, R., Iskandarani, M., Olson,
D. B., Lupton, J. E., and Jenkins, W. J.: Mantle 3He distribution and deep
circulation in the Indian Ocean,
https://darchive.mblwhoilibrary.org/handle/1912/3711, 2004.
Tagliabue, A., Bopp, L., Dutay, J.-C., Bowie, A. R., Chever, F.,
Jean-Baptiste,
P., Bucciarelli, E., Lannuzel, D., Remenyi, T., Sarthou, G., Aumont, O.,
Gehlen, M., and Jeandel, C.: Hydrothermal contribution to the oceanic
dissolved iron inventory, Nat. Geosci., 3, 252–256,
2010.
Taylor, S. and McLennan, S.: The Continental Crust, Its composition and
evolution, an examination of the geochemical record preserved in sedimentary
rocks, Blackwell, Oxford, 312 pp., 1985.Tedesco, D. and Scarsi, P.: Intensive gas sampling of noble gases and carbon
at Vulcano Island (southern Italy), J. Geophys. Res., 104,
10499, 10.1029/1998JB900066,
1999.
Tedesco, D., Miele, G., Sano, Y., and Toutain, J. P.: Helium isotopic ratio
in
Vulcano island fumaroles: temporal variations in shallow level mixing and
deep magmatic supply, J. Volcanol. Geotherm. Res., 64,
117–128, 1995.
Top, Z. and Clarke, W. B.: Helium, neon, and tritium in the Black Sea,
J. Mar. Res., 41, 1–17, 1983.
Top, Z., Östlund, G., Pope, L., and Grall, C.: Helium isotopes, neon
and
tritium in the Black Sea: A comparison with the 1975 observations, Deep-Sea
Res. Pt. A, 38, S747–S759,
1991.
Torgersen, T.: Terrestrial helium degassing fluxes and the atmospheric
helium
budget: Implications with respect to the degassing processes of continental
crust, Chem. Geol., 79, 1–14,
1989.Torgersen, T.: Continental degassing flux of 4 He and its variability,
Geochem. Geophys. Geosyst., 11, Q06002,
10.1029/2009GC002930,
2010.
Vörösmarty, C. J., Fekete, B. M., and Tucker, B. A.: Global
River
Discharge Database (RivDIS V1.0), International Hydrological Program, Global
Hydrological Archive and Analysis Systems, UNESCO, Paris, 1996.Wanninkhof, R.: Relationship between wind speed and gas exchange over the
ocean, J. Geophys. Res., 97, 7373, 10.1029/92JC00188,
1992.
Weiss, R. F.: Solubility of helium and neon in water and seawater, J.
Chem. Engin. Data, 16, 235–241, 1971.Well, R., Lupton, J., and Roether, W.: Crustal helium in deep Pacific
waters,
J. Geophys. Res., 106, 14165, 10.1029/1999JC000279,
2001.
Winckler, G., Suess, E., Wallmann, K., de Lange, G. J., Westbrook, G. K., and
Bayer, R.: Excess helium and argon of radiogenic origin in Mediterranean
brine basins, Earth Planet. Sci. Lett., 151, 225–231,
1997.