University of Bremen

About: University of Bremen is a education organization based out in Bremen, Germany. It is known for research contribution in the topics: Population & Context (language use). The organization has 14563 authors who have published 37279 publications receiving 970381 citations. The organization is also known as: Universität Bremen.

Stable water isotopes in the ECHAM5 general circulation model: Toward high‐resolution isotope modeling on a global scale

Abstract: [1] In this study, a first set of four present-day global experiments with the ECHAM5 atmospheric general circulation model enhanced by stable water isotope diagnostics (ECHAM5-wiso) is presented. Model resolution varies from a typical coarse horizontal grid of 3.8° × 3.8° (T31) to a fine grid of 0.75° × 0.75° (T159). Vertical resolution varies from 19 to 31 model levels. On a global scale, the ECHAM5-wiso simulation results are in good agreement with available observations of the isotopic composition of precipitation from the Global Network of Isotopes in Precipitation (GNIP), on an annual as well as a seasonal time scale. In many instances, the isotope simulation results clearly benefit from an increased horizontal and vertical model resolution. The exemplary relevance of this model resolution dependence is demonstrated for the simulation of the isotopic composition of Antarctic precipitation. Here, the simulation with the fine T159L31 model resolution not only yields a better agreement with observational data sets but also allows for a more realistic retuning of the supersaturation function leading to improved deuterium excess performance over the Antarctic continent, which is important for the interpretation of polar ice cores. Finally, the ECHAM5-wiso simulation results are compared to newly available measurements of the isotopic composition of atmospheric water vapor. Model and data agree well, with differences in the range of ±10‰ for near-surface atmospheric values at several GNIP stations. A comparison of the ECHAM5-wiso simulations with total column averaged HDO data from the Scanning Imaging Absorption Spectrometer for Atmospheric Cartography (SCIAMACHY) instrument on board the environmental satellite Envisat shows the same latitudinal gradients but an offset between 20‰ and 50‰ of unknown origin.

Frost flowers on sea ice as a source of sea salt and their influence on tropospheric halogen chemistry

Abstract: [1] Frost flowers grow on newly-formed sea ice from a saturated water vapour layer. They provide a large effective surface area and a reservoir of sea salt ions in the liquid phase with triple the ion concentration of sea water. Recently, frost flowers have been recognised as the dominant source of sea salt aerosol in the Antarctic, and it has been speculated that they could be involved in processes causing severe tropospheric ozone depletion events during the polar sunrise. These events can be explained by heterogeneous autocatalytic reactions taking place on salt-laden ice surfaces which exponentially increase the reactive gas phase bromine (‘‘bromine explosion’’). We analyzed tropospheric bromine monoxide (BrO) and the sea ice coverage both measured from satellite sensors. Our model based interpretation shows that young ice regions potentially covered with frost flowers seem to be the source of bromine found in bromine explosion events. INDEX TERMS: 0322 Atmospheric Composition and Structure: Constituent sources and sinks; 1640 Global Change: Remote sensing; 3309 Meteorology and Atmospheric Dynamics: Climatology (1620); 3339 Meteorology and Atmospheric Dynamics: Ocean/atmosphere interactions (0312, 4504); 3360 Meteorology and Atmospheric Dynamics: Remote sensing. Citation: Kaleschke, L., et al. (2004), Frost flowers on sea ice as a source of sea salt and their influence on tropospheric halogen chemistry, Geophys. Res. Lett., 31, L16114, doi:10.1029/ 2004GL020655.

Isotope composition of air moisture over the Mediterranean Sea: an index of the air–sea interaction pattern

Abstract: The isotope composition of atmospheric moisture over the Mediterranean Sea, collected during the cruise of the research vessel meteor in January 1995, confirmed that the intensive air–sea interaction near the coast under conditions of a large humidity deficit labels the resultant atmospheric waters with a large deuterium-excess parameter. The present data set shows this effect to result both when cold air from the European continent moves over the sea as well as when warm and dry air from North Africa is involved. The situation in the eastern and western Mediterranean differ in the vertical structure of the isotope composition further away from the coast, as expressed by the gradients of the d excess values with altitude over the sea surface, i.e. increasing with altitude in the eastern Mediterranean, whereas the opposite effect is noted in the western section and near the coast. A comparison of the isotopic composition of the samples with the expected buildup of moisture over the sea, based on the Craig–Gordon model, suggests that up to one half of the added moisture may have resulted at times from the evaporation of sea-spray droplets, without any significant isotope fractionation, in addition to the vapour-mediated transport from the sea surface, which favors the lighter isotopic species. DOI: 10.1034/j.1600-0889.2003.00081.x

Hydrothermal recharge and discharge across 50 km guided by seamounts on a young ridge flank.

Abstract: Hydrothermal circulation within the sea floor, through lithosphere older than one million years (Myr), is responsible for 30% of the energy released from plate cooling, and for 70% of the global heat flow anomaly (the difference between observed thermal output and that predicted by conductive cooling models)1,2. Hydrothermal fluids remove significant amounts of heat from the oceanic lithosphere for plates typically up to about 65 Myr old3,4. But in view of the relatively impermeable sediments that cover most ridge flanks5, it has been difficult to explain how these fluids transport heat from the crust to the ocean. Here we present results of swath mapping, heat flow, geochemistry and seismic surveys from the young eastern flank of the Juan de Fuca ridge, which show that isolated basement outcrops penetrating through thick sediments guide hydrothermal discharge and recharge between sites separated by more than 50 km. Our analyses reveal distinct thermal patterns at the sea floor adjacent to recharging and discharging outcrops. We find that such a circulation through basement outcrops can be sustained in a setting of pressure differences and crustal properties as reported in independent observations and modelling studies.

High-resolution absorption cross-section of glyoxal in the UV–vis and IR spectral ranges

Abstract: High-resolution absorption cross-sections of glyoxal have been recorded at 296 K in the ultraviolet and visible (UV–vis: 19000–40000 cm−1, 250–526 nm) and infrared (IR: 1200–8000 cm−1) spectral ranges by means of a Fourier transform spectrometer (FTS). The UV–vis spectra were measured at 1 atm of N2 bath gas. The spectral resolution of the FTS was selected to be 0.06 cm−1 for the richly structured A ˜ 1Au – X ˜ 1Ag and a ˜ 3Au – X ˜ 1Ag band systems, and 1 cm−1 for the diffuse B ˜ − X ˜ transition, which was sufficient to resolve most spectral structures. In addition, low and high-resolution IR spectra (1 and 0.009 cm−1 spectral resolution) of glyoxal/N2 mixtures were recorded around 2835 cm−1 at 0.2 mbar, 100 mbar, 300 mbar and 1 atm total pressure. UV–vis and IR spectra were recorded quasi-simultaneously by making sequential measurements of identical glyoxal mixtures in the cell, enabling the direct comparison of UV–vis and IR spectral parameters for the first time. The high-resolution spectra have been used to simulate deviations from Lambert–Beer's law, which occur at lower resolution when spectra are not fully resolved. Special attention has been paid to reduce the uncertainty of the UV–vis spectrum, allowing for an improved determination of the atmospheric photolysis of glyoxal. Finally, the new UV–vis spectrum has been used to redetermine our previous DOAS measurements of glyoxal yields from the reactions of OH radicals with benzene, toluene and p-xylene. The high-resolution spectral data can be obtained from http://iup.physik.uni-bremen.de/gruppen/molspec/index.html or email request to the authors.