Northward expansion of the westerlies over glacial southeastern Australia: evidence from semi-arid lunette dunes, temperate basalt plains, and wind modelling

It has long been hypothesized that the last glacial maximum (LGM) oversaw cold, arid, windy climates across southern Australia, and that these were driven by intensification and northward expansion of mid-latitude westerly circulation. Moreover, it was recently suggested that Australia experienced an extended LGM which began several millennia before the global peak. Aeolian sedimentary deposits provide key evidence for these hypotheses, and climate modelling an alternative means to test them. As yet, however, combined approaches to reconstructing glacial environments on the continent are scarce. Here we provide new evidence for westerly wind regimes across glacial southeastern Australia. We confirm active transverse lunette deposition at c. 29 ka and c. 23–19 ka in the semi-arid Willandra Lakes, and identify aeolian sand incursions to Spring Creek on the temperate Western Victorian Volcanic Plains from c. 29 ka. The Spring Creek deposits contain a surprising quantity of sand-sized quartz given the basalt setting, which we propose to be allochthonous and likely transported some distance. The site lies more than 50 km east and south of dunefields which were active at the same time and may have contributed sediment via long distance transport. We investigate the hypothesis for northward glacial expansion of westerly winds by combining our sediment records with aeolian particle transport simulations. We find that LGM near-surface winds were dominated by stronger, more focussed westerly air flow across southeastern Australia, compared with presently more diffuse wind regimes. Our results suggest stronger potential for LGM eastward distal sand transport onto the basalt plains, coeval with enhanced aeolian activity in the semi-arid Australian dunefields. Our combined reconstruction of aeolian deposition and trajectory modelling confirms the extended LGM hypothesis and indicates a northward migration of westerly winds over southeastern Australia during this period

COSMOGENIC 14CO FOR ASSESSING THE OH-BASED SELF-CLEANING CAPACITY OF THE TROPOSPHERE

An application of radiocarbon (14C) in atmospheric chemistry is reviewed. 14C produced by cosmic neutrons immediately forms 14CO, which reacts with hydroxyl radicals (OH) to 14CO2. By this the distribution and seasonality (the lifetime of 14CO is ∼1 month) of the pivotal atmospheric oxidant OH can be established. 14CO measurement is a complex but unique application which benefitted enormously from the realization of AMS, bearing in mind that 14CO abundance is of the order of merely 10 molecules per cm3 not only provides 14CO an independent measure for the OH based self-cleansing capacity of the troposphere, but also enabled detection of 14C production due to high energy solar protons in 1989. Although its production takes place throughout the atmosphere and does not have the character of a point source, transport processes in the atmosphere affect the distribution of 14CO. Vertical mixing in the troposphere renders gradients in its production rate less critical, but considerable meridional gradients exist. One question has remained open, namely confirmation of calculated 14C production by direct measurement. A new sampling method is proposed. The conclusions are a guide to future work on 14CO in relation to OH and atmospheric transport

Exceptional Operators in N=4 super Yang-Mills

We consider one particularly interesting class of composite gauge-invariant operators in N=4 super Yang-Mills theory. An exceptional feature of these operators is that in the Thermodynamic Bethe Ansatz approach the one-loop rapidities of the constituent magnons are shown to be exact in the 't Hooft coupling constant. This is used to propose the mirror TBA description for these operators. The proposal is shown to pass several non-trivial checks.Comment: 40 pages, 2 figures, 1 attached Mathematica noteboo

Comments on the Mirror TBA

We discuss various aspects of excited state TBA equations describing the energy spectrum of the AdS_5 \times S^5 strings and, via the AdS/CFT correspondence, the spectrum of scaling dimensions of N = 4 SYM local operators. We observe that auxiliary roots which are used to partially enumerate solutions of the Bethe-Yang equations do not play any role in engineering excited state TBA equations via the contour deformation trick. We further argue that the TBA equations are in fact written not for a particular string state but for the whole superconformal multiplet, and, therefore, the psu(2,2|4) invariance is built in into the TBA construction.Comment: 28 pages, 1 figure, v2: misprints are correcte

Exploring the mirror TBA

We apply the contour deformation trick to the Thermodynamic Bethe Ansatz equations for the AdS_5 \times S^5 mirror model, and obtain the integral equations determining the energy of two-particle excited states dual to N=4 SYM operators from the sl(2) sector. We show that each state/operator is described by its own set of TBA equations. Moreover, we provide evidence that for each state there are infinitely-many critical values of 't Hooft coupling constant \lambda, and the excited states integral equations have to be modified each time one crosses one of those. In particular, estimation based on the large L asymptotic solution gives \lambda \approx 774 for the first critical value corresponding to the Konishi operator. Our results indicate that the related calculations and conclusions of Gromov, Kazakov and Vieira should be interpreted with caution. The phenomenon we discuss might potentially explain the mismatch between their recent computation of the scaling dimension of the Konishi operator and the one done by Roiban and Tseytlin by using the string theory sigma model.Comment: 69 pages, v2: new "hybrid" equations for YQ-functions, figures and tables are added. Analyticity of Y-system is discussed, v3: published versio

Konishi operator at intermediate coupling

TBA equations for two-particle states from the sl(2) sector proposed by Arutyunov, Suzuki and the author are solved numerically for the Konishi operator descendent up to 't Hooft's coupling lambda ~ 2046. The data obtained is used to analyze the properties of Y-functions and address the issue of the existence of the critical values of the coupling. In addition we find a new integral representation for the BES dressing phase which substantially reduces the computational time.Comment: lots of figures, v2: improved numerics, c1=2, c2=0, c4 does not vanis

Foundations of the AdS_5 x S^5 Superstring. Part I

We review the recent advances towards finding the spectrum of the AdS_5 x S^5 superstring. We thoroughly explain the theoretical techniques which should be useful for the ultimate solution of the spectral problem. In certain cases our exposition is original and cannot be found in the existing literature. The present Part I deals with foundations of classical string theory in AdS_5 x S^5, light-cone perturbative quantization and derivation of the exact light-cone world-sheet scattering matrix.Comment: 161 page

Global 3-D Simulations of the Triple Oxygen Isotope Signature Δ17O in Atmospheric CO2

The triple oxygen isotope signature Δ¹⁷O in atmospheric CO₂, also known as its “¹⁷O excess,” has been proposed as a tracer for gross primary production (the gross uptake of CO₂ by vegetation through photosynthesis). We present the first global 3-D model simulations for Δ¹⁷O in atmospheric CO₂ together with a detailed model description and sensitivity analyses. In our 3-D model framework we include the stratospheric source of Δ¹⁷O in CO₂ and the surface sinks from vegetation, soils, ocean, biomass burning, and fossil fuel combustion. The effect of oxidation of atmospheric CO on Δ¹⁷O in CO2 is also included in our model. We estimate that the global mean Δ¹⁷O (defined as Δ¹⁷O = ln( ¹⁷O + 1) − RL · ln( ¹⁸O + 1) with RL = 0.5229) of CO₂ in the lowest 500 m of the atmosphere is 39.6 per meg, which is ∼20 per meg lower than estimates from existing box models. We compare our model results with a measured stratospheric Δ¹⁷O in CO₂ profile from Sodankylä (Finland), which shows good agreement. In addition, we compare our model results with tropospheric measurements of Δ¹⁷O in CO₂ from Göttingen (Germany) and Taipei (Taiwan), which shows some agreement but we also find substantial discrepancies that are subsequently discussed. Finally, we show model results for Zotino (Russia), Mauna Loa (United States), Manaus (Brazil), and South Pole, which we propose as possible locations for future measurements of Δ¹⁷O in tropospheric CO₂ that can help to further increase our understanding of the global budget of Δ¹⁷O in atmospheric CO₂

String hypothesis for the AdS_5 x S^5 mirror

We discuss the states which contribute in the thermodynamic limit of the mirror theory, the latter is obtained from the light-cone gauge-fixed string theory in the AdS_5 x S^5 background by the double-Wick rotation. We analyze the Bethe-Yang equations for the mirror theory and formulate the string hypothesis. We show that in the thermodynamic limit solutions of the Bethe-Yang equations arrange themselves into Bethe string configurations similar to the ones appearing in the Hubbard model. We also derive a set of equations describing the bound states and the Bethe string configurations of the mirror theory.Comment: LaTex, 18 pages, typos are correcte

The population history of northeastern Siberia since the Pleistocene.

Northeastern Siberia has been inhabited by humans for more than 40,000 years but its deep population history remains poorly understood. Here we investigate the late Pleistocene population history of northeastern Siberia through analyses of 34 newly recovered ancient genomes that date to between 31,000 and 600 years ago. We document complex population dynamics during this period, including at least three major migration events: an initial peopling by a previously unknown Palaeolithic population of 'Ancient North Siberians' who are distantly related to early West Eurasian hunter-gatherers; the arrival of East Asian-related peoples, which gave rise to 'Ancient Palaeo-Siberians' who are closely related to contemporary communities from far-northeastern Siberia (such as the Koryaks), as well as Native Americans; and a Holocene migration of other East Asian-related peoples, who we name 'Neo-Siberians', and from whom many contemporary Siberians are descended. Each of these population expansions largely replaced the earlier inhabitants, and ultimately generated the mosaic genetic make-up of contemporary peoples who inhabit a vast area across northern Eurasia and the Americas