Seawater carbonate chemistry and survival, impairment of three phytoplankton species in a laboratory experiment

Sodium hypochlorite (NaOCl) is widely used to disinfect seawater in power plant cooling systems in order to reduce biofouling, and in ballast water treatment systems to prevent transport of exotic marine species. While the toxicity of NaOCl is expected to increase by ongoing ocean acidification, and many experimental studies have shown how algal calcification, photosynthesis and growth respond to ocean acidification, no studies have investigated the relationship between NaOCl toxicity and increased CO2. Therefore, we investigated whether the impacts of NaOCl on survival, chlorophyll a (Chl-a), and effective quantum yield in three marine phytoplankton belonging to different taxonomic classes are increased under high CO2 levels. Our results show that all biological parameters of the three species decreased under increasing NaOCl concentration, but increasing CO2 concentration alone (from 450 to 715 µatm) had no effect on any of these parameters in the organisms. However, due to the synergistic effects between NaOCl and CO2, the survival and Chl-a content in two of the species, Thalassiosira eccentrica and Heterosigma akashiwo, were significantly reduced under high CO2 when NaOCl was also elevated. The results show that combined exposure to high CO2 and NaOCl results in increasing toxicity of NaOCl in some marine phytoplankton. Consequently, greater caution with use of NaOCl will be required, as its use is widespread in coastal waters.

Seawater carbonate chemistry and combined mechanistic effects of CO2 and light on the N2-fixing cyanobacterium Trichodesmium IMS101, 2010

The marine diazotrophic cyanobacterium Trichodesmium responds to elevated atmospheric CO2 partial pressure (pCO2) with higher N2 fixation and growth rates. To unveil the underlying mechanisms, we examined the combined influence of pCO2(150 and 900 µatm) and light (50 and 200 µmol photons m-2 s-1) on TrichodesmiumIMS101. We expand on a complementary study that demonstrated that while elevated pCO2 enhanced N2 fixation and growth, oxygen evolution and carbon fixation increased mainly as a response to high light. Here, we investigated changes in the photosynthetic fluorescence parameters of photosystem II, in ratios of the photosynthetic units (photosystem I:photosystem II), and in the pool sizes of key proteins involved in the fixation of carbon and nitrogen as well as their subsequent assimilation. We show that the combined elevation in pCO2 and light controlled the operation of the CO2-concentrating mechanism and enhanced protein activity without increasing their pool size. Moreover, elevated pCO2 and high light decreased the amounts of several key proteins (NifH, PsbA, and PsaC), while amounts of AtpB and RbcL did not significantly change. Reduced investment in protein biosynthesis, without notably changing photosynthetic fluxes, could free up energy that can be reallocated to increase N2 fixation and growth at elevated pCO2 and light. We suggest that changes in the redox state of the photosynthetic electron transportchain and posttranslational regulation of key proteins mediate the high flexibility in resources and energy allocation in Trichodesmium. This strategy should enableTrichodesmium to flourish in future surface oceans characterized by elevated pCO2, higher temperatures, and high light.

Seawater carbonate chemistry, respiration, maximum photochemical efficiency and mortality of brooded larvae of Pocillopora//damicornis in a laboratory experiment

To evaluate the effects of temperature and pCO2 on coral larvae, brooded larvae of Pocillopora damicornis from Nanwan Bay, Taiwan (21°56.179' N, 120°44.85' E), were exposed to ambient (419-470 µatm) and high (604-742 µatm) pCO2 at ~25 and ~29 °C in two experiments conducted in March 2010 and March 2012. Larvae were sampled from four consecutive lunar days (LD) synchronized with spawning following the new moon, incubated in treatments for 24 h, and measured for respiration, maximum photochemical efficiency of PSII (F v/F m), and mortality. The most striking outcome was a strong effect of time (i.e., LD) on larvae performance: respiration was affected by an LD × temperature interaction in 2010 and 2012, as well as an LD × pCO2 × temperature interaction in 2012; F v/F m was affected by LD in 2010 (but not 2012); and mortality was affected by an LD × pCO2 interaction in 2010, and an LD × temperature interaction in 2012. There were no main effects of pCO2 in 2010, but in 2012, high pCO2 depressed metabolic rate and reduced mortality. Therefore, differences in larval performance depended on day of release and resulted in varying susceptibility to future predicted environmental conditions. These results underscore the importance of considering larval brood variation across days when designing experiments. Subtle differences in experimental outcomes between years suggest that transgenerational plasticity in combination with unique histories of exposure to physical conditions can modulate the response of brooded coral larvae to climate change and ocean acidification.

Rotation-Induced Breakdown of Torsional Quantum Control

Control of the torsional angles of nonrigid molecules is key for the development of emerging areas like molecular electronics and nanotechnology. Based on a rigorous calculation of the rotation-torsion-Stark energy levels of nonrigid biphenyl-like molecules, we show that, unlike previously believed, instantaneous rotation-torsion-Stark eigenstates of such molecules, interacting with a strong laser field, present a large degree of delocalization in the torsional coordinate even for the lowest energy states. This is due to a strong coupling between overall rotation and torsion leading to a breakdown of the torsional alignment. Thus, adiabatic control of changes on the planarity of this kind of molecule is essentially impossible unless the temperature is on the order of a few Kelvin.

Comparing the Luttinger–Kohn–Pikus–Bir and the Empiric K·P Hamiltonians in quantum dot intermediate band solar cells manufactured in zincblende semiconductors

The calculation of the energy spectrum and absorption coefficients of quantum dot nanostructured intermediate band solar cells using the Empiric K·P Hamiltonian method and its agreement with experimental data are summarized. The well established Luttinger Kohn Hamiltonian modified by Pikus and Bir for strained material, such as quantum dot arrays, is presented using a simplified strain field that allows for square band offsets. The energy spectrum and absorption coefficients are calculated with this new Hamiltonian. With the approximations made the energy spectrum results to be exactly the same but the absorption coefficient fits experiments less accurately. The computer time using the latter Hamiltonian is much longer than the former one.

Ab initio calculation of electronic coupling in the photosynthetic reaction center

We have carried out an ab initio electronic structure calculations of electron transfer couplings between chromophores in the bacterial photosynthetic reaction center. The couplings agree remarkably well with parameters obtained from recent quantum dynamical modeling of experimental data assuming an explicit intermediate mechanism. We also have computed couplings on the M-side of the reaction center and have found that the interaction of the primary donor to the M-side intermediate bacteriochlorophyll is quite small because of destructive interference of the two localized coupling matrix elements. This may explain the slow rate of electron transfer down the M-side of the reaction center.

Symmetry in chemistry from the hydrogen atom to proteins

The last 2 decades have seen discoveries in highly excited states of atoms and molecules of phenomena that are qualitatively different from the “planetary” model of the atom, and the near-rigid model of molecules, characteristic of these systems in their low-energy states. A unified view is emerging in terms of approximate dynamical symmetry principles. Highly excited states of two-electron atoms display “molecular” behavior of a nonrigid linear structure undergoing collective rotation and vibration. Highly excited states of molecules described in the “standard molecular model” display normal mode couplings, which induce bifurcations on the route to molecular chaos. New approaches such as rigid–nonrigid correlation, vibrons, and quantum groups suggest a unified view of collective electronic motion in atoms and nuclear motion in molecules.

Quantum Dot-Sensitized Solar Cells Based on Directly Adsorbed Zinc Copper Indium Sulfide Colloids

Heavy metal-based quantum dots (QDs) have demonstrated to behave as efficient sensitizers in QD-sensitized solar cells (QDSSCs), as attested by the countless works and encouraging efficiencies reported so far. However, their intrinsic toxicity has arisen as a major issue for the prospects of commercialization. Here, we examine the potential of environmentally friendly zinc copper indium sulfide (ZCIS) QDs for the fabrication of liquid-junction QDSSCs by means of photoelectrochemical measurements. A straightforward approach to directly adsorb ZCIS QDs on TiO2 from a colloidal dispersion is presented. Incident photon-to-current efficiency (IPCE) spectra of sensitized photoanodes show a marked dependence on the adsorption time, with longer times leading to poorer performances. Cyclic voltammograms point to a blockage of the channels of the mesoporous TiO2 film by the agglomeration of QDs as the main reason for the decrease in efficiency. Photoanodes were also submitted to the ZnS treatment. Its effects on electron recombination with the electrolyte are analyzed through electrochemical impedance spectroscopy and photopotential measurements. The corresponding results bring out the role of the ZnS coating as a barrier layer preventing electron leakage toward the electrolyte, as argued in other QD-sensitized systems. The beneficial effect of the ZnS coating is ultimately reflected on the power conversion efficiency of complete devices, reaching values of 2 %. In a more general vein, through these findings, we aim to call the attention to the potentiality of this quaternary alloy, virtually unexplored as a light harvester for sensitized devices.

Improving the Photoelectrochemical Response of TiO2 Nanotubes upon Decoration with Quantum-Sized Anatase Nanowires

TiO2 nanotubes (NTs) have been widely used for a number of applications including solar cells, photo(electro)chromic devices, and photocatalysis. Their quasi-one-dimensional morphology has the advantage of a fast electron transport although they have a relatively reduced interfacial area compared with nanoparticulate films. In this study, vertically oriented, smooth TiO2 NT arrays fabricated by anodization are decorated with ultrathin anatase nanowires (NWs). This facile modification, performed by chemical bath deposition, allows to create an advantageous self-organized structure that exhibits remarkable properties. On one hand, the huge increase in the electroactive interfacial area induces an improvement by 1 order of magnitude in the charge accumulation capacity. On the other hand, the modified NT arrays display larger photocurrents for water and oxalic acid oxidation than bare NTs. Their particular morphology enables a fast transfer of photogenerated holes but also efficient mass and electron transport. The importance of a proper band energy alignment for electron transfer from the NWs to the NTs is evidenced by comparing the behavior of these electrodes with that of NTs modified with rutile NWs. The NT-NW self-organized architecture allows for a precise design and control of the interfacial surface area, providing a material with particularly attractive properties for the applications mentioned above.

Calculation of paleoproductivity during the Eocene-Oligocene transition of ODP Site 113-689

High-resolution records of carbon and oxygen isotopes and benthic foraminiferal accumulation rates for the Eocene-Oligocene section at Ocean Drilling Program Site 689 (Maud Rise, Weddell Sea; paleodepth about 1500 m) were used to infer variations in paleoproductivity in relation to changes in climate and ventilation of the deeper-water column. The benthic foraminiferal abundance and isotope records show short-term fluctuations at periodicities of 100 and 400 ka, implying orbitally driven climatic variations. Both records suggest that intermediate-depth water chemistry and primary productivity changed in response to climate. During the Eocene, productivity increased during cold periods and during cold-to-warm transitions, possibly as a result of increased upwelling of nutrient-rich waters. In the Oligocene, in contrast, productivity maxima occurred during intervals of low delta18O values (presumably warmer periods), when a proto-polar front moved to the south of the location of Site 689. This profound transition in climate-productivity patterns occurred around 37 Ma, coeval with rapid changes toward increasing variability of the oxygen and carbon isotope and benthic abundance records and toward larger-amplitude delta18O fluctuations. Therefore, we infer that, at this time, temperature fluctuations increased and a proto-polar front formed in conjunction with the first distinct pulsations in size of the Antarctic ice sheet. We speculate that this major change might have resulted from an initial opening of the Drake Passage at 37 Ma, at least for surface- and intermediate-water circulation.

Seawater carbonate chemistry and photosynthetic response of Emiliania huxleyi (CS-369) to UV radiation and elevated temperature duirng experiments, 2011

Changes in calcification of coccolithophores may affect their photosynthetic responses to both, ultraviolet radiation (UVR, 280-400 nm) and temperature. We operated semi-continuous cultures of Emiliania huxleyi (strain CS-369) at reduced (0.1 mM, LCa) and ambient (10 mM, HCa) Ca2+ concentrations and, after 148 generations, we exposed cells to six radiation treatments (>280, >295, >305, >320, >350 and >395 nm by using Schott filters) and two temperatures (20 and 25 °C) to examine photosynthesis and calcification responses. Overall, our study demonstrated that: (1) decreased calcification resulted in a down regulation of photoprotective mechanisms (i.e., as estimated via non-photochemical quenching, NPQ), pigments contents and photosynthetic carbon fixation; (2) calcification (C) and photosynthesis (P) (as well as their ratio) have different responses related to UVR with cells grown under the high Ca2+ concentration being more resistant to UVR than those grown under the low Ca2+ level; (3) elevated temperature increased photosynthesis and calcification of E. huxleyi grown at high Ca2+concentrations whereas decreased both processes in low Ca2+ grown cells. Therefore, a decrease in calcification rates in E. huxleyi is expected to decrease photosynthesis rates, resulting in a negative feedback that further reduces calcification.