In the oligotrophic Southeastern Mediterranean Sea (SEMS), it has been shown that dissolved inorganic nutrient (DIN) from fresh submarine groundwater discharge (FSGD) enhance primary production in ...coastal waters. In this study pH, Total Alkalinity (TA) and DIN of seawater and fresh water in a sea‐cave in the northern part of the Israeli Mediterranean coast and a nearby contact spring, respectively, were measured during October 2018–March 2020. The results show gradients of measured salinity, TA, pH and DIN along the cave axis year‐round, suggesting that they are influenced by FSGD. The seawater near the back of the cave was supersaturated with respect to atmospheric CO2 nearly year‐round and there is a strong positive divergence from its regional open‐water thermal dependence, which suggests that FSGD is also a source of atmospheric CO2 in this region. Comparison of TA, salinity and pCO2 from the back of the sea cave to their corresponding values from an abrasion platform monitoring site, ca. 3 km south of the cave, suggests that FSGD is occurring along the entire shoreline in this region. Thus, despite the increased productivity due to FSGD mediated nutrient enrichment of adjacent coastal waters of the oligotrophic SEMS, they are still a source of atmospheric CO2 nearly year‐round. Finally, the apparent trends of seawater acidification (ΔpH/Δt = −0.006 yrs−1) and pCO2 increase (+8 ppmV yr−1) observed at the nearby monitoring site since 2013 are explained by increased groundwater recharge and resulting FSGD total alkalinity compared to dissolved inorganic carbon inputs (ΔTA/ΔDIC = 1:1.2).
Plain Language Summary
Submarine groundwater discharge is an important source of dissolved inorganic nutrients that support organic matter production in the Mediterranean Sea. Furthermore, the contribution of fresh groundwater discharge to the alkalinity budget of the Mediterranean Sea compared to riverine inputs is also significant. Approximately half of the groundwater discharged into the Mediterranean originates from karst lithologies. In this study we followed the annual variations in seawater chemical properties in the Rosh‐Hanikra sea‐cave, located along the northern Mediterranean coast of Israel. The results suggest that fresh groundwater discharge supports the observed gradients of measured seawater chemistry along the cave axis year‐round with a stronger influence during the wintertime compared to summertime and that it helps maintain coastal waters as a source of atmospheric CO2 year‐round. Furthermore, the data suggest that submarine groundwater discharge, which is enriched in dissolved inorganic carbon increases the rate of ocean acidification associated with increasing atmospheric CO2 in the coastal waters of this region.
Key Points
Fresh submarine groundwater discharge (FSGD) is apparent in seawater properties of the Rosh‐Hanikra Mediterranean Sea sea‐cave year‐round
FSGD into coastal waters in the Rosh‐Hanikra region causes them to be a source of atmospheric CO2 year‐round
FSGD augments seawater acidification along the northern Mediterranean coast of Israel despite nutrient enrichment and increased productivity
Double-pion photo-production represents one of the strongest contributions to the photonucleon total cross-section at high energies, and thus it plays an important role in probing the nucleon ...resonance spectrum. The polarization observables are useful because of the additional sensitivity they provide in unraveling the reaction dynamics, and so the goal of this study is to extract the specific polarization observables
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reaction. The data were taken as a part of the CLAS g9b (FROST) experiment at Jefferson Laboratory, which used a transversely-polarized target and a circularly-polarized photon beam with energies up to 3 GeV. The data will help deepen the current knowledge of resonance photocouplings and hadronic decays and possibly assist in identifying new baryon resonances via partial-wave analyses and in this way will contribute to a more comprehensive understanding of the strong interaction.
The structure dependent radiative K+→e+νγ (Ke2γSD+) decay was investigated with stopped positive kaons. The e+ momentum spectra containing 574±30Ke2γSD+ events with a K+→μ+ν (Kμ2) background of 28±19 ...events were measured with and without a photon in coincidence and analyzed with Monte Carlo simulations for acceptance and detector response to extract the ratio of the branching ratio of the Ke2γSD+ decay and the K+→e+ν decay including the internal bremsstrahlung process (Ke2(γ)). A value of Br(Ke2γSD+)/Br(Ke2(γ))=1.12±0.07stat±0.04syst was obtained. This indicates a partial branching ratio, Br(Ke2γSD+,pe>200MeV/c,Eγ>10MeV)/Br(Kμ2)=(1.85±0.11stat±0.07syst)×10−5, which is 25% (∼2.5σ) higher than the previous experimental result.
Polarization transfer to a bound proton in polarized electron knock-out reactions, A(e→,e′p→), is a powerful tool to look for an in-medium modification of the bound proton. It requires comparison to ...calculations that consider the many-body effects accompanying the quasi-free process. We report here measured components Px′, Pz′, and their ratio Px′/Pz′, of polarization transfer to protons bound in Ca40, which is described well by the shell model and for which reliable calculations are available. While the calculations capture the essence of the data, our statistical precision allows us to observe deviations that cannot be explained by simple scaling, including by varying the proton electromagnetic form factor ratio GE/GM. We further explore the deviations of the ratio of the polarization transfer components from that of a free proton, (Px′/Pz′)A/(Px′/Pz′)H, and its dependence on the bound-proton virtuality.
We present the first measurements of the double ratio of the polarization-transfer components (Px′/Pz′)p/(Px′/Pz′)s for knock-out protons from the s and p shells in C12 measured by the C12(e→,e′p→) ...reaction in quasi-elastic kinematics. The data are compared to theoretical predictions in the relativistic distorted-wave impulse approximation. Our results show that the differences between s- and p-shell protons, observed when compared at the same initial momentum (missing momentum), largely disappear when the comparison is done at the same proton virtuality. We observe no difference in medium modifications between protons from the s and p shells with the same virtuality in spite of the large differences in the respective nuclear densities.
We measured the ratio Px/Pz of the transverse to longitudinal components of polarization transferred from electrons to bound protons in C12 by the C12(e→,e′p→) process at the Mainz Microtron (MAMI). ...We observed consistent deviations from unity of this ratio normalized to the free-proton ratio, (Px/Pz)C12/(Px/Pz)H1, for both s- and p-shell knocked out protons, even though they are embedded in averaged local densities that differ by about a factor of two. The dependence of the double ratio on proton virtuality is similar to the one for knocked out protons from H2 and He4, suggesting a universal behavior. It further implies no dependence on average local nuclear density.
We present measurements of the electron helicity asymmetry in quasi-elastic proton knockout from 2H and 12C nuclei by polarized electrons. This asymmetry depends on the fifth structure function, is ...antisymmetric with respect to the scattering plane, and vanishes in the absence of final-state interactions, and thus it provides a sensitive tool for their study. Our kinematics cover the full range in off-coplanarity angle ϕpq, with a polar angle θpq coverage up to about 8°. The missing energy resolution enabled us to determine the asymmetries for knock-out resulting in different states of the residual 11B system. We find that the helicity asymmetry for p-shell knockout from 12C depends on the final state of the residual system and is relatively large (up to ≈0.16), especially at low missing momentum. It is considerably smaller (up to ≈0.01) for s-shell knockout from both 12C and 2H. The data for 2H are in very good agreement with theoretical calculations, while the predictions for 12C exhibit differences with respect to the data.
We report the measurement of the ratio of polarization-transfer components, Px/Pz, in the H2(e→,e′p→)n reaction at low and high missing momenta, in search of differences between free and bound ...protons. The observed deviation of Px/Pz from that of a free proton, which is similar to that observed in 4He, indicates that the effect in nuclei is a function of the virtuality of the knock-out proton and the missing momentum direction, but not
the average nuclear density. There is a general agreement between the data and calculations, which assume free proton form factors, however, the measurements are consistently about 10% higher.
We report the first measurements of the transverse (Px and Py) and longitudinal (Pz) components of the polarization transfer to a bound proton in the deuteron via the H2(e→,e′p→) reaction, over a ...wide range of missing momentum. A precise determination of the electron beam polarization reduces the systematic uncertainties on the individual components to a level that enables a detailed comparison to a state-of-the-art calculation of the deuteron using free-proton electromagnetic form factors. We observe very good agreement between the measured and the calculated Px/Pz ratios, but deviations of the individual components. Our results cannot be explained by medium modified electromagnetic form factors. They point to an incomplete description of the nuclear reaction mechanism in the calculation.
A comparison between polarization-transfer to a bound proton in quasi-free kinematics by the A(e→,e′p→) knockout reaction and that in elastic scattering off a free proton can provide information on ...the characteristics of the bound proton. In the past the reported measurements have been compared to those of a free proton with zero initial momentum. We introduce, for the first time, expressions for the polarization-transfer components when the proton is initially in motion and compare them to the 2H data measured at the Mainz Microtron (MAMI). We show the ratios of the transverse (Px) and longitudinal (Pz) components of the polarization transfer in H2(e→,e′p→)n, to those of elastic scattering off a “moving proton”, assuming the proton's initial (Fermi-motion) momentum equals the negative missing momentum in the measured reaction. We found that the correction due to the proton motion is up to 20% at high missing momentum. However the effect on the double ratio (Px/Pz)A(Px/Pz)H1 is largely canceled out, as shown for both 2H and 12C data. This implies that the difference between the resting- and the moving-proton kinematics is not the primary cause for the deviations between quasi-elastic and elastic scattering reported previously.
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