Assessing impacts of coastal warming, acidification, and deoxygenation on Pacific oyster (Crassostrea gigas) farming: a case study in the Hinase area, Okayama Prefecture, and Shizugawa Bay, Miyagi Prefecture, Japan

Coastal warming, acidification, and deoxygenation are progressing primarily due to the increase in anthropogenic CO2. Coastal acidification has been reported to have effects that are anticipated to become more severe as acidification progresses, including inhibiting the formation of shells of calcifying organisms such as shellfish, which include Pacific oysters (Crassostrea gigas), one of the most important aquaculture resources in Japan. Moreover, there is concern regarding the combined impacts of coastal warming, acidification, and deoxygenation on Pacific oysters. However, spatiotemporal variations in acidification and deoxygenation indicators such as pH, the aragonite saturation state (Ωarag), and dissolved oxygen have not been observed and projected in oceanic Pacific oyster farms in Japan. To assess the present impacts and project future impacts of coastal warming, acidification, and deoxygenation on Pacific oysters, we performed continuous in situ monitoring, numerical modeling, and microscopic examination of Pacific oyster larvae in the Hinase area of Okayama Prefecture and Shizugawa Bay in Miyagi Prefecture, Japan, both of which are famous for their Pacific oyster farms. Our monitoring results first found Ωarag values lower than the critical level of acidification for Pacific oyster larvae in Hinase, although no impact of acidification on larvae was identified by microscopic examination. Our modeling results suggest that Pacific oyster larvae are anticipated to be affected more seriously by the combined impacts of coastal warming and acidification, with lower pH and Ωarag values and a prolonged spawning period, which may shorten the oyster shipping period and lower the quality of oysters.</p

Electronic structure of self-doped layered Eu 3 F 4 Bi 2 S 4 material revealed by x-ray absorption spectroscopy and photoelectron spectromicroscopy

International audienceWe have studied the electronic structure of Eu 3 F 4 Bi 2 S 4 using a combination of Eu L 3-edge x-ray absorption spectroscopy (XAS) and space-resolved angle-resolved photoemission spectroscopy (ARPES). From the Eu L 3-edge XAS, we have found that the Eu in this system is in mixed valence state with coexistence of Eu 2+ /Eu 3+. The bulk charge doping was estimated to be ∼0.3 per Bi site in Eu 3 F 4 Bi 2 S 4 , which corresponds to the nominal x in a typical REO 1−x F x BiS 2 system (RE: rare-earth elements). From the space-resolved ARPES, we have ruled out the possibility of any microscale phase separation of Eu valence in the system. Using a microfocused beam we have observed the band structure as well as the Fermi surface that appeared similar to other compounds of this family with disconnected rectangular electronlike pockets around the X point. The Luttinger volume analysis gives the effective carrier to be 0.23 electrons per Bi site in Eu 3 F 4 Bi 2 S 4 , indicating that the system is likely to be in the underdoped region of its superconducting phase diagram. The BiS 2-based superconductors are composed of a layered structure with active BiS 2 bilayers intercalated by insulating spacer layers [1]. The typical BiS 2-based system REOBiS 2 (RE: rare-earth elements) is usually a band insulator, and the band filling can be controlled by electron doping; by substituting O by F [2] or tetravalent ions by trivalent La at RE site [3]. As the doping level increases, superconductivity develops within the BiS 2 layers with the maximum T c of 10.5 K found in LaO 0.5 F 0.5 BiS 2 [4]. The conduction bands are composed of Bi 6p x/y orbitals giving rise to rectangular electron pockets around the X point of the Brillouin zone [5,6]. With the same crystal structure, EuFBiS 2 shows super-conductivity without any doping. It is thought to be caused by the self-doped electrons coming from Eu that is in a mixed valence state with coexisting Eu 2+ and Eu 3+ [7]. A similar situation seems to occur in a new class of the BiS 2-based family Eu 3 F 4 Bi 2 S 4 system that is found to show bulk superconductivity with T c = 1.5 K induced by self-doping [8]. The structure is rather complex with an additional EuF 2 layer intercalated into the EuFBiS 2 structure as shown in Fig. 1(a). In this work we have studied the electronic structure of Eu 3 F 4 Bi 2 S 4 by means of Eu L 3-edge x-ray absorption spectroscopy (XAS) and space-resolved angle-resolved pho-toemission spectroscopy (ARPES); the Eu L 3-edge XAS is a bulk sensitive probe on the valence state while the space-resolved ARPES can reveal the space-dependent electronic structure, which is especially important on the present system with a mixed valence of Eu and highly disordered local symmetry [9-11]. High-quality single crystals of Eu 3 F 4 Bi 2 S 4 were grown by the CsCl-flux method with powders of EuS, Bi 2 S 3 , and BiF 3. The excess CsCl flux was removed using H 2 O. The crystals were well characterized for their crystal structures and transport properties prior to the spectroscopy measurements [12]. The Eu L 3-edge XAS measurements have been performed at BM30B beamline of the European Synchrotron Radiation Facility. At the BM30B, the synchrotron radiation was monochromatized by a double crystal Si(220) monochromator, and the energy resolution is close to the intrinsic resolution of the Si crystals, i.e., around 0.35 eV at the Eu L 3 edge [13]. Two Si mirrors covered by a Rh layer allow us to avoid high energy photons (harmonics). The Eu 3 F 4 Bi 2 S 4 crystals were mounted in a continuous flow He cryostat and XAS measurements were carried out in a partial fluorescence yield mode at a temperature of 21 K. The experimental geometry in sketched in the inset of Fig. 1(b) with the linearly polarized light falling at an angle of 33 • with respect to the normal direction of the sample. This angle avoids the polarization effects and provides the angle-independent bulk spectrum. The Eu L 3-edge absorption spectrum was collected by detecting the Eu L α1 fluorescence photons over a large solid angle using a multielement Ge detector. The obtained XAS spectrum was corrected for the self-absorption using the FLUO algorithm embedded in Athena software [14]. Space-resolved ARPES measurements have been performed at the Spectromicroscopy beamline, Elettra synchrotron facility, Trieste [15]. Incident photons of 74 eV were focused using a Schwarzschild optics down to a 500 × 500 nm 2 beam spot. For the present measurements the total energy resolution is about ∼100 meV while the angular resolution is 0.5 •. The single crystals of Eu 3 F 4 Bi 2 S 4 were cleaved and oriented in situ at 40 K under ultrahigh vacuum condition (<10 −10 mbar). All the measurements were carried 2469-9950/2017/95(3)/035152(5) 035152-