A TEX₈₆ lake record suggests simultaneous shifts in temperature in Central Europe and Greenland during the last deglaciation

High-resolution quantitative temperature records from continents covering glacial to interglacial transitions are scarce but important for understanding the climate system. We present the first decadal resolution record of continental temperatures in Central Europe during the last deglaciation (similar to 14,60010,600cal. yrB.P.) based on the organic geochemical palaeothermometer TEX86. The TEX86-inferred temperature record from Lake Lucerne (Vierwaldstattersee, Switzerland) reveals typical oscillations during the Late Glacial Interstadial, followed by an abrupt cooling of 2 degrees C at the onset of Younger Dryas and a rapid warming of 4 degrees C at the onset of the Holocene, within less than 350years. The remarkable resemblance with the Greenland and regional stable oxygen isotope records suggests that temperature changes in continental Europe were dominated by large-scale reorganizations in the northern hemispheric climate system

Efficient and accurate modeling of electron photoemission in nanostructures with TDDFT

We derive and extend the time-dependent surface-flux method introduced in [L. Tao, A. Scrinzi, New J. Phys. 14, 013021 (2012)] within a time-dependent density-functional theory (TDDFT) formalism and use it to calculate photoelectron spectra and angular distributions of atoms and molecules when excited by laser pulses. We present other, existing computational TDDFT methods that are suitable for the calculation of electron emission in compact spatial regions, and compare their results. We illustrate the performance of the new method by simulating strong-field ionization of C60 fullerene and discuss final state effects in the orbital reconstruction of planar organic molecules

Glycerol dialkyl glycerol tetraether membrane lipids in lacustrine environments and their application as proxies for palaeoclimate reconstructions. Geologica Ultraiectina (322)

Lacustrine sediments often contain relatively high amounts of organic matter because of limited bottom water oxygenation and relatively high sedimentation rates. The membrane lipids of Crenarchaeota, a major group of the domain Archaea, consist of isoprenoid glycerol dialkyl glycerol tetraether (GDGTs) containing cyclopentane moieties, a characteristic considered an adaptation mechanism to temperature of the membrane. Analyses of core top sediments showed that the distribution of isoprenoid GDGTs varies with sea surface temperature (SST), a relation expressed in the TetraEther indeX of lipids with 86 carbon atoms (TEX86). Branched GDGTs were detected in peat bogs, soils, and coastal marine and lacustrine sediments. Their abundance in marine sediments decreases relative to crenarchaeol (an isoprenoid GDGT) with increasing distance from river mouths, indicating transport of branched GDGTs from land to aquatic environments. This relation was expressed in the Branched versus Isoprenoid Tetraether (BIT) index. Branched GDGTs contain a different number of cyclopentane moieties and also a different degree of methylation, which were shown to be related to air temperature and soil pH via two newly developed proxies: CBT (Cyclisation ratio of Branched Tetraethers) and MBT (Methylation index of Branched Tetraethers). This thesis describes the distribution and biological sources of GDGT membrane lipids in lacustrine environments, their potential use as temperature proxies and their application in reconstructing past continental temperatures. Isoprenoid and branched GDGTs were detected in variable amounts in particulate matter and top 5 cm of the sediment from 47 European lakes. The results show that not only large lakes but also smaller size lakes with high in situ productivity of isoprenoid GDGTs are suited for the use of TEX86. Winter temperatures correlate better with TEX86 indicating that the isoprenoid GDGT producing organisms probably have their peak abundances during this season. In an extended set of lakes we observed that the distribution of branched GDGTs varied substantially among the lake sediments. The MBT/CBT-reconstructed temperatures were consistently below annual mean air temperature of the catchment of the lake. Still, a significant correlation exists between the reconstructed temperature and the temperature measured on site. The results of a seasonal study in Lake Lucerne show that fluxes of GDGTs and concentrations in the water column vary according to a seasonal pattern, with a similar trend in suspended particulate matter and sediment traps. Fluxes and concentrations of isoprenoid GDGTs increase with depth, indicating production of isoprenoid GDGTs by Group 1 Crenarchaeota in the deep, aphotic zone. To reconstruct temperature changes during the Late Glacial Interstadial, the Younger Dryas and the Early Holocene (~14,600 to 10,600 cal. yr BP) the relative distribution of GDGTs in a sediment core from the same Lake Lucerne was determined. Reconstructed lake temperatures indicate a step-wise pattern of climate change, with a warming at the onset of the late-glacial interstadial, followed by an abrupt cooling at the onset of Younger Dryas and a rapid warming from 5.5 to 9 C at the Younger Dryas/Holocene transition within less than 200 years

Seasonal changes in glycerol dialkyl glycerol tetraether concentrations and fluxes in a perialpine lake: Implications for the use of the TEX₈₆ and BIT proxies

To determine where and when glycerol dialkyl glycerol tetraether (GDGT) membrane lipids in lakes are produced, we collected descending particles in Lake Lucerne (Switzerland) using two sediment traps (at 42 and 72 m water depth) with a monthly resolution from January 2008 to late March 2009. Suspended particulate matter (SPM) was monthly filtered from the water column at three different depths. The potential application of GDGTs in palaeoenvironmental and palaeoclimatic reconstructions was investigated by comparing core lipids and their relative GDGT distribution, with lake water temperatures throughout the year. Fluxes of GDGTs and their concentrations in the water column vary according to a seasonal pattern, showing a similar trend in the SPM and sediment traps. Fluxes and concentrations of isoprenoid GDGTs increase with depth, maximum values being observed in the deeper part of the water column, indicating production of isoprenoid GDGTs by Thaumarchaeota in the deep (similar to 50 m), aphotic zone of Lake Lucerne. The flux-weighted averages of the proxies TEX86 (0.27) and BIT (0.03) based on the total extracted GDGTs are similar at both trap depths. A sediment core from the same location showed that in the first few centimetres of the core TEX86 and BIT values of 0.29 and 0.07, respectively, are similar to those recorded for descending particles and SPM, indicating that the sedimentary TEX86 records the annual mean temperature of deeper waters in Lake Lucerne. TEX86 values are slightly higher below 20 cm in the core. This offset is interpreted to be caused by the present-day trophic state of the lake, which probably resulted in a deeper niche of the Thaumarchaeota. Branched GDGTs represent only a minor fraction of the total GDGTs in the lake and their origin remains unclear. Our data reveal that GDGTs in lakes have a large potential for palaeoclimatic studies but indicate that knowledge of the system is important for accurate interpretation

Seasonal and vertical distribution of putative ammonia-oxidizing thaumarchaeotal communities in an oligotrophic lake

The discovery of Archaea carrying an amoA gene coding for the A-subunit of ammonia monooxygenase gave a boost to studies aimed at detecting this gene under diverse conditions. Despite numerous studies describing the archaeal amoA gene abundance and richness in different habitats, the understanding of the freshwater ecology of potentially archaeal ammonia oxidizers, recently positioned in the phylum Thaumarchaeota, is still lacking. In a seasonal and vertical study of deep oligotrophic Lake Lucerne, Switzerland, with high Thaumarchaeota-specific crenarchaeol concentrations, we showed that all archaeal 16S rRNA genes found belong to the thaumarchaeotal phylum. The abundances of archaeal 16S rRNA and amoA genes remained in the same order of magnitude (average 6 × mL−1) and displayed matching seasonal dynamics within 16 monthly collected samples at three different water depths (r2 = 0.80, slope of 1.06). The Thaumarchaeota in this lake form a distinct cluster in both the 16S rRNA and amoA gene phylogenies, are affiliated to other thaumarchaeotal freshwater sequences within group 1.1a Archaea, and fall in the low saline cluster of the amoA phylogeny. In accordance with temperature and conductivity, the Thaumarchaeota in the surface water showed a significantly different seasonality and lower abundance than their counterparts in the deeper waters. This study indicates that the ecology of Thaumarchaeota, with their potential in nitrogen cycling, may differ per water depth in deep freshwater ecosystems.

Branched glycerol dialkyl glycerol tetraethers in lake sediments: Can they be used as temperature and pH proxies?

A series of surface sediments from 82 lakes of variable water depth and size was analyzed for glycerol dialkyl glycerol tetraethers (GDGTs) in order to investigate the potential of the MBT/CBT (methylation ratio/cyclization ratio of branched tetraethers) as a continental palaeothermometer in lacustrine environments. Branched GDGTs dominated in most sediments, as indicated by the high branched vs. isoprenoid tetraether (BIT) values. We observed that CBT and MBT varied substantially. Mean annual air temperature (MAAT reconstructed) and pH values were calculated using the CBT and MBT values and the calibration from the global soil data set. The MBT/CBT inferred temperatures were considerably lower than measured values. Nevertheless, there was a significant correlation between MAAT reconstructed and MAAT observed on site, although there was still considerable scatter (r(2) 0.47). Lacustrine sediments integrate organic remains of organisms in a lake and its drainage basin, thereby offering a unique opportunity for calibrating MBT and CBT, as small scale variability is averaged out. Since the source of the branched GDGTs in the lake sediments is ambiguous, it is not clear whether only temperature and pH in the catchment area are the driving factors. Therefore, even in lake sediments with high concentrations of branched GDGTs the straightforward application of MBT/CBT as palaeoproxies may be difficult given the uncertainties regarding their source and origin

Attosecond science

Attosecond technology builds on, and contributes to, important historic directions in science. For this reason, the science has the depth to yield important discoveries for a long time. Unfortunately the title "attosecond" science biases us to think mostly about dynamics but many of the most important applications of "attosecond technology" may not be related to dynamics at all. This broad set of applications point to the future impact of the technology.Peer reviewed: YesNRC publication: Ye