Low Surface Pressure Research Articles

Electrochemistry of LB films of mixed MGDG:UQ on ITO

The electrochemical behaviour of biomimetic monolayers of monogalactosyldiacylglycerol (MGDG) incorporating ubiquinone-10 (UQ) has been investigated. MGDG is the principal component in the thylakoid membrane and UQ seems a good substitute for plastoquinone-9, involved in photosynthesis chain. The monolayers have been performed using the Langmuir and Langmuir–Blodgett (LB) techniques and the redox behaviour of the LB films, transferred at several surface pressures on a glass covered with indium–tin oxide (ITO), has been characterized by cyclic voltammetry. The cyclic voltammograms show that UQ molecules present two redox processes (I and II) at high UQ content and high surface pressures, and only one redox process (I) at low UQ content and low surface pressures. The apparent rate constants calculated for processes I and II indicate a different kinetic control for the reduction and the oxidation of UQ/UQH2 redox couple, being kRapp(I)=2.2·10−5s−1, kRapp(II)=5.1·10−14 kOapp(I)=3.3·10−3s−1 and kOapp(II)=6.1·10−6s−1, respectively. The correlation of the redox response with the physical states of the LB films allows determining the positions of the UQ molecules in the biomimetic monolayer, which change with the surface pressure and the UQ content. These positions are known as diving and swimming.

Morphological transition of a conductive molecular organization with non-covalent from nanonetwork to nanofiber

The formation of nanofiber morphology at a mesoscopic scale, and molecular level stacking of a tetrathiafulvalene (TTF) derivative with a chiral group were investigated by the one-dimensional growth method in interfacial molecular films. Monomolecular films of a TTF derivative with a chiral borneol group display a two-dimensional phase transition at the air/water interface. At high surface pressures, nanonetwork domains are formed, where the TTF molecular planes are densely packed with an interlayer distance of 4.1Å. The formation of this network is attributed to the organized aggregation of the TTF derivatives, which is a result of strong intermolecular interactions. Subsequently, the growth of morphology is encouraged by the application of the one-dimensional growth method at low surface pressure conditions, varying compression speeds, and subphase temperatures. At low surface pressure and a subphase temperature of 15°C, the TTF derivatives aggregated as nanofibers with close packing of molecules. Upon raising the subphase temperature, the thickness of the nanofibers was found to increase and hence, spontaneous morphogenesis at the air/water interface was achieved.

Effects of surface pressure on the properties of Langmuir monolayers and interfacial water at the air-water interface.

The effects of surface pressure on the physical properties of Langmuir monolayers of palmitic acid (PA) and dipalmitoylphosphatidic acid (DPPA) at the air/water interface are investigated through molecular dynamics simulations with atomistic force fields. The structure and dynamics of both monolayers and interfacial water are compared across the range of surface pressures at which stable monolayers can form. For PA monolayers at T = 300 K, the untilted condensed phase with a hexagonal lattice structure is found at high surface pressure, while the uniformly tilted condensed phase with a centered rectangular lattice structure is observed at low surface pressure, in agreement with the available experimental data. A state with uniform chain tilt but no periodic spatial ordering is observed for DPPA monolayers on a Na(+)/water subphase at both high and low surface pressures. The hydrophobic acyl chains of both monolayers pack efficiently at all surface pressures, resulting in a very small number of gauche defects. The analysis of the hydrogen-bonding structure/dynamics at the monolayer/water interface indicates that water molecules hydrogen-bonded to the DPPA head groups reorient more slowly than those hydrogen-bonded to the PA head groups, with the orientational dynamics becoming significantly slower at high surface pressure. Possible implications for physicochemical processes taking place on marine aerosols in the atmosphere are discussed.

Domain Morphologies of Complex Phosphoinositide/Lipid Langmuir Films in the Presence of Bivalent Cations

Although phosphatidylinositol (PI) and phosphoinositides (PIPs) only comprise a small percentage of the inner leaflet of the plasma membrane, they mediate a large variety of signaling events. In previous studies, we have observed the absence of macroscopically discernible domains in mixtures of PI/PC and PI(4,5)P2/PC. The addition of cholesterol to these mixtures results in condensation of the monolayer and hence domain formation. To better mimic the ionic conditions and hydrogen bonding properties of the inner leaflet plasma membrane, we investigated in this study the effect of common inner leaflet plasma membrane lipids like phosphatidylethanolamine (PE), phosphatidylserine (PS) and PI, on phosphoinositide domain behavior in the presence of cholesterol and/or bivalent cations. We find that the addition of varying concentrations of Ca2+ to PI(4,5)P2/cholesterol monolayer leads to a size reduction of the domains. We hypothesize that this is due to a penetration of the Ca2+ ions into the PI(4,5)P2 headgroup region, leading to a disruption of the hydrogen bond network formed by the PI(4,5)P2 headgroup and cholesterol. We find for PE/PI(4,5)P2 and PI/PI(4,5)P2 homogeneous mixing of the monolayer. The addition of cholesterol to PE/PI(4,5)P2 leads to the formation of small domains at low surface pressures that disappear at higher pressures. In addition to cholesterol, we also investigate in this study the effect of bivalent cations on these lipid mixtures.

Positional specificity of sardine digestive lipase in the hydrolysis of triacylglycerols and analogs

Using lipid emulsions as well as the monomolecular film technique, we studied some kinetic properties of sardine digestive lipase (SaDL). The pure lipase was able to hydrolyze a triolein emulsion in the absence of any additives and seems therefore to tolerate the accumulation of long free fatty acids at the interface. The kinetic behavior of SaDL can be explained by the high penetration capacity of this enzyme into a lipidic interface. SaDL hydrolyzes efficiently pure tributyrin, in the absence of additives. Subsequently, the sardine lipase is not denaturated at high interfacial energy. A kinetic study of the surface pressure dependency of the regioselectivity of SaDL was performed using an optically pure stereoisomer of diglyceride (1,2‐sn‐dicaprin) and a prochiral isomer (1,3‐sn‐dicaprin) that were spread as monomolecular films at the air‐water interface. At low surface pressure, SaDL acts preferentially on distal carboxylic ester groups of the diglyceride isomer (1,3‐sn‐dicaprin) but at high surface pressure, this enzyme prefers adjacent ester groups of the (1,2‐sn‐dicaprin) isomer. Interestingly, the SaDL was found to hydrolyze efficiently the secondary ester group of a triglyceride analog. This is in line with the fact that SaDL hydrolyzed triolein at the sn‐2 position, as shown using the thin‐layer chromatography technique. This property is sought for the synthesis of specific triacylglycerol‐based compounds, such as structured lipids.Practical applications: The sardine digestive lipase was found to efficiently hydrolyse the secondary ester group of a triglyceride analogue, a characteristic sought for the synthesis of structured lipids.The sardine digestive lipase (SaDL) showed an ability to hydrolyze the secondary ester group of a triglyceride analog (1,2‐DDG) with the R configuration (R3).

The Role of Membrane Context in the Interaction of Polyglutamine Peptides with Lipid Membranes

Huntington's disease is a dominant genetic neurodegenerative disorder associated with motor and cognitive decline, caused by a mutation in the poly-glutamine (polyQ) region near the N-terminus of the huntingtin (htt) protein. Expansion of the polyQ region above 35-40 repeats results in the disease that is characterized by inclusion body aggregates of mutated protein. The polyQ expansion in htt is flanked by a 17 amino acid N-terminal sequence (Nt17) and a proline-rich (polyP) region. To investigate the interaction between htt exon1 and lipid membranes, a combination of Langmuir trough techniques and vesicle permeability assays measuring calcein leakage were used to directly monitor the interaction of a variety of synthetic polyQ peptides with total brain lipid extract (TBLE) model membranes doped with specific membrane components. Our data suggests that the Nt17 domain plays a critical role in htt binding and aggregation on lipid membranes, and this lipid/htt interaction is enhanced by the presence of the polyP domain. The exogenous addition of cholesterol, a primary neuronal plasma membrane component reduced in many Huntington's disease models, to the TBLE monolayer caused a notable condensing effect in the membrane at low surface pressures. This resulted in reduced peptide insertion into lipid monolayers and decreased levels of induced vesicle permeability, though the effect does not scale linearly with cholesterol concentration. Results from parallel studies on htt-membrane interaction with sphingomyelin, a major component of membranes in the nervous system, will also be discussed.

Wall Interference Effect on the Aerodynamics of a High-speed Train

Wall interference effect has been researched numerically on a simplified 1/8 scale high-speed train model with three carriages in several elaborately designed closed wind tunnels. With the yaw angle and blockage increasing, the deviation of aerodynamic forces in the closed wind tunnel compared with the free stream is growing larger. Guidelines regarding acceptable blockage limits are suggested. Further, the mechanism of wall interference on a high-speed train in large yaw angle is explored. The streamlines around the train in large yaw angle are constrained by side and top walls then the flow velocity increases, giving rise to lower surface pressure on the train. Constrained streamlines also leads to the change of vortex structures on the leeward side and the wake of the train. The knowledge gained in this work can be a guide for the test on slender high-speed trains in a closed wind tunnel.

Crystallization behavior of single isotactic poly(methyl methacrylate) chains visualized by atomic force microscopy.

We have, for the first time, successfully visualized the crystallization behavior of a single isolated polymer chain at the molecular level by atomic force microscopy (AFM). Previously, we found that isotactic poly(methyl methacrylate) (it-PMMA) formed two-dimensional folded chain crystals composed of double-stranded helices upon compression of its Langmuir monolayer on a water surface, and the molecular images of the crystals deposited on mica were clearly visualized by AFM (Kumaki, J.; et al. J. Am. Chem. Soc. 2005, 127, 5788). In the present study, a high-molecular-weight it-PMMA was diluted in a monolayer of an it-PMMA oligomer which cannot crystallize at the experimental temperature due to its low molecular weight. At a low surface pressure, isolated amorphous chains of the high-molecular-weight it-PMMA solubilized in the oligomer monolayer were observed. On compression, the isolated chains converted to crystals composed of a single chain, typically some small crystallites linked by an amorphous chain like a necklace. Detailed AFM observations of the crystals indicated that the crystalline nuclei preferentially formed at the ends of the chains, and the size of the nuclei was almost independent of the molecular weight of it-PMMA over a wide range. At an extremely slow compression, crystallization was promoted, resulting in crystallization of the whole chain. The crystallization behavior of a single isolated chain provides new insights in understanding the polymer crystallization process.

Self-Assembly Behaviors of a Well-Defined Amphiphilic Brush Polymer at the Air-Water Interface

Self-assembly characteristics of a well-defined brush polymer, poly(oxy(n-dodecyl-thiomethyl)ethylene) were in detail investigated at the air-water interface with surface–area isotherm, X-ray reflectivity, and infrared spectroscopy analyses. The brush polymer self-assembled at the air-water interface as a fully-extended chain via favorable lateral packing of the bristles in a fully extended conformation, forming highly ordered, oriented Langmuir monolayer. This well-ordered monolayer was produced via a five-regime structure formation with varying surface pressure. A Langmuir monolayer film with ≤1.92 nm thick was formed in the low surface pressure regime ≤18 mN/m and then converted to a highly dense, ordered monolayer with 3.65 nm thick in the high surface pressure regime ≥35 mN/m through monolayer-to-bilayer transition and bilayer-to-monolayer inversion. These Langmuir film formations and their ordering and orientation might be driven by the well-defined chemical architecture and the lateral orderings of the polymer backbones and the bristles in fully extended conformations.

Characterization of Langmuir Films Prepared from Copolyesterurethanes Based on Oligo(ω‐pentadecalactone) and Oligo(ε‐caprolactone) Segments

A series of multiblock copolymers (PDLCL) synthesized from oligo(ω‐pentadecalactone)diol (OPDL) and oligo(ε‐caprolactone)diol (OCL), which are linked by 2,2(4),4‐trimethyl‐hexa­methylene diisocyanate (TMDI), is investigated by the Langmuir monolayer technique at the air–water interface. Brewster angle microscopy (BAM) and spectroscopic ellipsometry are employed to characterize the polymer film morphologies in situ. PDLCL containing ≥40 wt% OCL segments form homogeneous Langmuir monofilms after spreading. The film elasticity modulus decreases with increasing amounts of OPDL segments in the copolymer. In contrast, the OCL‐free polyesterurethane OPDL‐TMDI cannot be spread to monomolecular films on the water surface properly, and movable slabs are observed by BAM even at low surface pressures. The results of the in situ morphological characterization clearly show that essential information concerning the reliability of Langmuir monolayer degradation (LMD) experiments cannot be obtained from the evaluation of the π–A isotherms only. Consequently, in situ morphological characterization turns out to be indispensable for characterization of Langmuir layers before LMD experiments. image

Dwelling on the adsorption of surfactant at the air/water interface in relation to its states in the bulk: A comprehensive analysis

The self-aggregation (micellization) of surfactants in the bulk in relation to their adsorption at the air/water interface has been analyzed and discussed. In this respect, the thermodynamic rationales of Traube, and Rosen and Aronson have been considered and analyzed at length. The first deals with adsorption at low surface pressure, the second hypothetically deals with concentration close to the critical micelle concentration having a constant surface excess and zero surface pressure. The question of possible micelle formation prior to completion of the process of adsorption has been also addressed. The standard Gibbs free energy of adsorption by Traube's method, and the method of Rosen and Aronson for ionic, non-ionic, zwitterionic, and bolaform surfactants have been evaluated: their differences have been attempted to account for and discussed. Considering a Born–Haber type cycle, the free energies of adsorption and micelle formation have been coupled together to describe the thermodynamic manifestation of the interrelated systems with a justification.Although the standard free energy of adsorption is lower than the standard free energy of micellization, and hence it is relatively more favored, but it has been perceived that with increasing surfactant concentration (i.e., with the progress of the process), the apparent (non standard) free energy of adsorption of amphiphiles may become relatively more positive, resulting in micelle formation even before the surface saturation.

Molecular arrangement of symmetric and non-symmetric triblock copolymers of poly(ethylene oxide) and poly(isobutylene) at the air/water interface

The behavior of a series of amphiphilic triblock copolymers of poly(ethylene oxide) (PEO) and poly(isobutylene) (PIB); including both symmetric (same degree of polymerization (DP) of the terminal PEO blocks) PEOm-b-PIBn-b-PEOm and non-symmetric (different DP of the terminal PEO blocks) PEOm-b-PIBn-b-PEOz, is investigated at the air/water interface by measuring surface pressure vs mean molecular area isotherms (π vs mmA), Langmuir–Blodgett (LB) technique, and infrared reflection–absorption spectroscopy (IRRAS). The block copolymer (PEO32-b-PIB160-b-PEO32) with longer PEO segments forms a stable monolayer and the isotherm reveals a pseudo-plateau starting at π∼5.7mN/m, also observed in the IRRAS, which is assigned to the pancake-to-brush transition related to the PEO dissolution into the subphase and subsequent PEO brush dehydration. Another plateau is observed at π∼40mN/m, which is attributed to the film collapse due to multilayer formation. The pancake-to-brush transition could not be observed for samples with smaller PEO chains. The isotherms for block copolymers, with short PEO chains, both symmetric (PEO3-b-PIBn-b-PEO3) and non-symmetric (PEO12-b-PIBn-b-PEO3), reveal another transition at π∼20–25mN/m. This is interpreted to be due to the conformational transition from a folded state where the middle PIB block is anchored to the water surface at both ends by the terminal hydrophilic segments to an unfolded state with PIB anchored to the water surface at one end. It is assumed that this transition involves the removal of PEO3 chains from the water surface in case of non-symmetric PEO12-b-PIB85-b-PEO3 and in case of symmetric, probably one PEO3 of each PEO3-b-PIB85-b-PEO3 chain. Because of the weaker interaction of the short PEO3 chains with the water surface as compared with the relatively longer PEO12 chains, the film of PEO3-b-PIB85-b-PEO3 collapses at much lower surface pressure after the transition as compared with the PEO12-b-PIB85-b-PEO3. The AFM images reveal the formation of microdomains of almost uniform height (6–7nm) in LB films of PEO3-b-PIB85-b-PEO3 and PEO12-b-PIB85-b-PEO3 after transferring onto silicon surfaces. These domains are assumed to be the mesomorphic domains of ordered and folded PIB chains.

Response of the North African summer monsoon to precession and obliquity forcings in the EC-Earth GCM

We investigate, for the first time, the response of the North African summer monsoon to separate precession and obliquity forcings using a high-resolution state-of-the-art coupled general circulation model, EC-Earth. Our aim is to better understand the mechanisms underlying the astronomical forcing of this low-latitude climate system in detail. The North African monsoon is strengthened when northern hemisphere summer insolation is higher, as is the case in the minimum precession and maximum obliquity experiments. In these experiments, the low surface pressure areas over the Sahara are intensified and located farther north, and the meridional pressure gradient is further enhanced by a stronger South Atlantic high pressure area. As a result, the southwesterly monsoon winds are stronger and bring more moisture into the monsoon region from both the northern and southern tropical Atlantic. The monsoon winds, precipitation and convection also extend farther north into North Africa. The precession-induced changes are much larger than those induced by obliquity, but the latter are remarkable because obliquity-induced changes in summer insolation over the tropics are nearly zero. Our results provide a different explanation than previously proposed for mechanisms underlying the precession- and, especially, obliquity-related signals in paleoclimate proxy records of the North African monsoon. The EC-Earth experiments reveal that, instead of higher latitude mechanisms, increased moisture transport from both the northern and southern tropical Atlantic is responsible for the precession and obliquity signals in the North African monsoon. This increased moisture transport results from both increased insolation and an increased tropical insolation gradient.

Supramolecular assembly of single-walled carbon nanotubes at air-solid interface

We formed a stable and reversible Langmuir film (LF) of bundles of unfunctionalized single-walled carbon nanotubes (SWCNTs) at the air–water interface. The film exhibits gas-like and liquid-like phases. The Raman spectrograph of Langmuir–Blodgett (LB) film of single layer of SWCNTs on Si/SiO2 substrate shows the characteristic G, D, and radial breathing mode frequencies of the single-walled carbon nanotubes. Using atomic force microscope (AFM) in spreading resistance imaging mode, we obtained a dependence of target surface pressure on the assembly of SWCNTs in the LB films. The film deposited at very low surface pressure (0.5 mN/m) exhibited an assembly wherein the long axis of the nanotube bundles aligned in the direction of deposition. The LB films deposited in the liquid-like phase of the SWCNTs exhibited supramolecular donut structure. The average width of the SWCNTs was around 30 nm. The current–voltage characterization of the local structures of the LB films using the conducting AFM probe indicates semi-metallic and metallic nature of the donut and the hole in the donut (nanopore), respectively. Such supramolecular assembly of the SWCNTs can find application in the fabrication of the devices like sensors, photochemical cells, batteries, etc.

Pattern formation in Langmuir–Blodgett films of tricycloquinazoline based discotic liquid crystal molecules

The assembly of molecules on the surface has drawn considerable attention because of its potential to tailor the physicochemical, electronic, and magnetic properties of materials. The structure of aggregates of molecules can be influenced by the molecular interactions and the external parameters like temperature, pressure and ion contents. We have found a stable Langmuir monolayer of amphiphilic tricycloquinazoline based discotic liquid crystal (AmTCQ) molecules at air–water (A–W) interface. The monolayer exhibits gas phase, low density liquid phase and high density liquid phase. The structural evolution in Langmuir–Blodgett (LB) films of the AmTCQ molecules as a function of target surface pressure is studied using an atomic force microscope. We found aggregation of the discotic molecules leading to nucleation sites at a lower surface pressure. With the increasing surface pressure, each nucleation site grows to form a stable triangular structure. The shape and size of the triangular structure remain stable till the target surface pressure for LB films deposition exceeds the equilibrium surface pressure of the AmTCQ molecules. The number of triangles in the film increases with increasing target surface pressure of LB deposition. The target surface pressure of LB deposition acts as a controlling parameter for obtaining desired number of triangular domains in the film.

BEHAVIOR OF METHYLENE BLUE WITH ARACHIDIC ACID IN THE RESTRICTED GEOMETRY OF LANGMUIR–BLODGETT FILM

Anti-malarial methylene blue (MB) doped in arachidic acid (AA) have been incorporated in the Langmuir monolayer at the air–water interface and also in the Langmuir–Blodgett films deposited on quartz substrate. The pressure–area (π–A) isotherm studies at different concentrations of MB pointed out that pure MB could not form stable monolayer at the air–water interface and collapse readily at very low surface pressures. However, mixture of MB with AA formed stable monolayers and they could be transferred into solid quartz substrate to form mono/multi layered films of MB. The area per molecule of floating mixed monolayers was systematically decreased with the increasing concentrations of MB in the mixture. The pressure–time (π - t) isotherm study indicated the interaction kinetics between MB and AA. Higher the concentration of MB, higher is the increase in pressure. The spectroscopic characteristics of the mixed LB films have been compared with that of pure MB solution, microcrystal and layer-by-layer self assembled film with UV-Vis absorption spectroscopy. Surface morphology of the mixed LB and LbL film of MB was measured with atomic force microscopy (AFM).

Formation and structure of fine multi-particle layered organo-modified zirconium dioxides fabricated by Langmuir–Blodgett technique

Formation and structure of multilayered organization of organo-modified zirconium dioxide are investigated by surface pressure–area (π–A) isotherms, out-of-plane and in-plane X-ray diffraction (XRD) analysis, and atomic force microscopy (AFM). In this study, solubilization technology of inorganic fine particles into general solvent has proposed and formation technology of highly ordered single-particle layer has also established by using that inorganic solution as “spreading solution” of the interfacial film. The surface modification of zirconia particles is performed using several long-chain carboxylic acids of different lengths. Accordingly, it is easily achieve a regular arrangement of ZrO2 particles to overcome the relatively weak van der Waals interactions between the inorganic materials. A Langmuir monolayer of these particles is extremely condensed. A multi-particle layered structure is constructed by the Langmuir–Blodgett (LB) technique. The out-of-plane XRD measurement of multilayered organization of stearate-modified ZrO2 particles confirms sharp peaks at 59Å. AFM images on a mesoscopic scale of this single-particle layer of stearate-modified ZrO2 show the aggregate of particles with 50nm diameters. However, fine particles with ∼5nm diameter are confirmed from high-resolution AFM observations in the case of single-particle layers transferred at low surface pressure. That is to say, a regular periodic structure along the c-axis and a hierarchical aggregated particle form are fabricated by Langmuir and LB techniques.

Cholesterol favors the anchorage of human dystrophin repeats 16 to 21 in membrane at physiological surface pressure

Dystrophin (DYS) is a filamentous protein that connects the cytoskeleton and the extracellular matrix via the sarcolemma, conferring resistance to muscular cells. In this study, interactions between the DYS R16–21 fragment and lipids were examined using Langmuir films made of anionic and zwitterionic lipids. The film fluidity was modified by the addition of 15% cholesterol. Whatever the lipid mixture examined, at low surface pressure (20mN/m) few differences appeared on the protein insertion and the presence of cholesterol did not affect the protein/lipid interactions. At high surface pressure (30mN/m), the protein insertion was very low and occurred only in zwitterionic films in the liquid-expanded phase. In anionic films, electrostatic interactions prevented the protein insertion outright, and caused accumulation of the protein on the hydrophilic part of the monolayer. Addition of cholesterol to both lipid mixtures drastically modified the protein–lipid interactions: the DYS R16–21 insertion increased and its organization in the monolayer appeared to be more homogeneous. The presence of accessible cholesterol recognition amino-acid consensus sequences in this fragment may enhance the protein/membrane binding at physiological lateral pressure. These results suggest that the anchorage of dystrophin to the membrane in vivo may be stabilized by cholesterol-rich nano-domains in the inner leaflet of sarcolemma.

Properties of β-carotene and retinoic acid in mixed monolayers with dipalmitoylphosphatidylcholine (DPPC) and Solutol

The liposoluble vitamins and carotenoids are sensitive molecules and their antioxidant properties can be dramatically affected when included in membrane environment or in encapsulated carriers as liposomes or lipid nanocapsules (LNCs). The formation and state of mixed monolayers at air–water interface of β-carotene (βC) or retinoic acid (RA) with dipalmitoylphosphatidylcholine (DPPC) as simplest membrane model or with Solutol (Sol) which forms the soft layer covering the LNCs were studied by means of surface pressure (π) and surface potential (ΔV) measurements. The mutual miscibility and interfacial organization of components in studied mixed monolayers was found to strongly depend on their composition. It was suggested a better inclusion of βC small quantities in pure DPPC monolayer at low surface pressure than for films with more βC at higher surface pressure. The measurements of surface properties were complemented by Atomic Force Microscopy (AFM) as a suitable technique for direct visualization at nanoscale level of the monolayer microheterogeneity and the presence of interfacial structures. It was also found that the addition of bigger amounts of βC led to the appearance of stripe like phase which is more deeply formed at higher surface pressure.

Asian–Pacific Oscillation signal from a Qomolangma (Mount Everest) ice-core chemical record

AbstractThe Asian–Pacific Oscillation (APO) is a climate pattern related to the thermal differences between the Asian continent and the north Pacific. We present a 1000 year record of the major ions in a 108.83 m ice core from east Rongbuk glacier (28°01′ N, 86°58′ E; 6518ma.s.l.) on the northeast slope of Qomolangma (Mount Everest), and discuss its relationship with a 993 year time series of the summer APO index that has been reconstructed from Beijing’s summer temperature (recorded by a stalagmite) and the Pacific Decadal Oscillation (PDO) index. Empirical orthogonal function (EOF) analysis shows that crustal major ions (Mg2+, Ca2+, SO42–and NO3–) are highly loaded on EOF1, whereas marine major ions (Cl–and Na+) are highly loaded on EOF2. Higher EOF1 is associated with lower upper-troposphere temperature (UTT) over Mongolia, corresponding to a lower APO index and higher surface pressure. Higher EOF2 is associated with higher UTT over Mongolia, corresponding to a higher APO index and lower surface pressure. The higher burden of major ions and higher summer APO index during the period AD 1000–1323 may be due to drought and warm climate of the major-ion source regions. From AD1323 to 1900, EOF1 and EOF2 do not show a consistent correlation with summer APO index, indicating the complex mechanisms of ion transport over the southern Tibetan Plateau (TP) during this period. After AD 1900, the summer APO index is correlated negatively with EOF1 and positively with EOF2, indicating that ion transport over the southern TP during this period is influenced significantly by the APO. Our examinations of the PDO index and major-ion record show that higher PDO corresponds to higher EOF1 and lower EOF2. This suggests that the correlation between the recorded major-ion concentration and the APO index originates in the seesaw relationship in temperature between the Asian continent and the north Pacific.