Climate variability in the Eastern Indian Ocean during Marine Isotope Stage 3: high-resolution proxy studies from the Timor Sea

Paleoclimate reconstructions based on marine sediment proxy data are important to understand the mechanisms of past climates and to test the predictability of climate models with regard to future climate predictions. Marine Isotope Stage 3 (MIS 3), a time period of high climate variability on millennial timescales with different shapes of temperature increases in the Northern and Southern Hemispheres as firstly detected in Greenland and Antarctica ice core records, is therefore subject of this thesis. During MIS 3 high-latitude Northern Hemisphere temperatures abruptly shifted to interstadial conditions (Dansgaard-Oeschger events) followed by gradual decreases to stadial conditions (Heinrich events), whereas the high-latitude Southern Hemisphere experienced gradual temperature in- and decreases. In contrast to the wealth of information concerning the regional climate impacts in the Northern Hemisphere high latitudes, relatively little is known about the low-latitude responses to these climate fluctuations and about the role of the tropics. To elucidate high- and low-latitude interactions in the tropics and to gain insights into the regional climate changes during MIS 3 high-resolution marine sediment multi-proxy records from the tropical eastern Indian Ocean (Timor Sea) were analyzed. Today, this area is influenced by the Intertropical Convergence Zone, which drives monsoonal winds, and by the Indonesian Throughflow (ITF), which represents a key component of the global thermohaline circulation system connecting the Pacific with the Indian Ocean. Thus, cores from the Timor Sea are ideally situated to monitor the linkages between tropical and high-latitude climate as well as regional paleoceanography and climate settings. Benthic d18O data (P. wuellerstorfi) clearly covary with Antarctic warm events as recorded in Southern Hemisphere ice cores. This southern high-latitude signal is transferred by Antarctic Intermediate Water flowing northward from the Southern Ocean into the Indian Ocean. Planktonic d18O (G. ruber) records show close affinity to northern high-latitude records and covary with Greenland temperature signals. These northern high-latitude signals in the tropical surface water are probably transmitted through atmospheric teleconnections and a tight coupling of the Asian-Australian monsoon system. Regional monsoon variability in the Timor Sea during D-O interstadials are estimated with respect to modern temperature and salinity conditions. Planktonic foraminiferal stable isotope values, Mg/Ca temperature and d18O-seawater estimates (G. ruber and P. obliquiloculata) reveal a weaker ITF intensity with a reduced transport of less saline water from the Pacific into the Indian Ocean during Heinrich events. During these stadials, when sealevel was extensively lowered, the regional paleoceanography in the outflow area of the ITF was influenced by a northward moving hydrological front between the West Australian Current and the Leeuwin Current. This front is probably associated with a change in food export to the seafloor as indicated by changing benthic foraminiferal accumulation rates of globocassidulinids. In contrast carbon-flux sensitive buliminids reveal increased abundances during Southern Hemisphere stadials due to higher paleoproductivity modulated by changes in the Asian-Australian monsoon system

Electronic Properties of Carbon Nanotubes studied in Field-Effect Transistor Geometries

Due to their outstanding properties carbon nanotubes have attracted considerable research effort during the last decade. While they serve as an example of a 1-dimensional electron system allowing one to study fundamental quantum effects nanotubes-especially semiconducting nanotubes-are an interesting candidate for next-generation transistor application with the potential to replace silicon-based devices. I have fabricated nanotubes using chemical vapor deposition techniques with various catalysts and gas mixtures. The nanotubes produced with these techniques vary in length from 100 nm to several hundreds of micrometers. While data taken on shorter metallic and semiconducting devices show Coulomb blockade effects, the main part of this work is concerned with measurements that shed light on the intrinsic properties of semiconducting nanotubes. On devices with lengths of more than 300 um I have carried out measurements of the intrinsic hole mobility as well as the device-specific field-effect mobility. The mobility measured on these nanotube devices at room temperature exceeds that of any semiconductor known previously. Another important consideration in nanotube transistor applications are hysteresis effects. I present measurements on the time scales involved in some of these hysteresis effects and a possible application of the hysteresis for memory devices

Evidence for Indonesian Throughflow slowdown during Heinrich events 3-5

We present sea surface and upper thermocline temperature records (60-100 year temporal resolution) spanning marine isotope stage 3 (similar to 24-62 ka B. P.) from International Marine Global Change Study core MD01-2378 (121 degrees 47.27'E and 13 degrees 04.95'S; 1783 m water depth) located in the outflow area of the Indonesian Throughflow within the Timor Sea. Stable isotopes and Mg/Ca of the near-surface-dwelling planktonic foraminifer Globigerinoides ruber (white) and the upper thermocline-dwelling Pulleniatina obliquiloculata reveal rapid changes in the thermal structure of the upper ocean during Heinrich events. Thermocline warming and increased delta O-18(seawater) (P. obliquiloculata record) during Heinrich events 3, 4, and 5 reflect weakening of the relatively cool and fresh thermocline flow and reduced export of less saline water from the North Pacific and Indonesian Seas to the tropical Indian Ocean. Three main factors influenced Indonesian Throughflow variability during marine isotope stage 3: (1) global slowdown in thermohaline circulation during Heinrich events triggered by Northern Hemisphere cooling, (2) increased freshwater export from the Java Sea into the Indonesian Throughflow controlled by rising sea level from similar to 60 to 47 ka, and (3) insolation-related changes in the Australasian monsoon with associated migration of hydrological fronts between Indian Ocean- and Indonesian Throughflow-derived water masses at similar to 46-40 ka

Superior SARS-CoV-2 RBD antigen designs for highly specific, quantitative serotests

Quantitative high-quality SARS-CoV-2 serotests that are easy-to-implement have been gaining great importance as means to characterize and monitor the magnitude of infection- or vaccine-induced immunity over time and are of particular interest for academic laboratories doing COVID-19 research or small diagnostic laboratories with basic equipment Please click Download on the upper right corner to see the full abstract

On Sub-ENSO Variability

Multichannel singular spectrum analysis (MSSA) of surface zonal wind, sea surface temperature (SST), 20° isotherm depth, and surface zonal current observations (between 1990 and 2004) identifies three coupled ocean–atmosphere modes of variability in the tropical Pacific: the El Niño–Southern Oscillation (ENSO), the annual cycle, and a mode with a 14–18-month period, which is referred to as sub-ENSO in this study. The sub-ENSO mode accounts for the near 18-month (near annual) variability prior to (following) the 1997/98 El Niño event. It was strongest during this El Niño event, with SST anomalies exceeding 1°C. Sub-ENSO peak SST anomalies are ENSO-like in structure and are associated with eastward propagating heat content variations. However, the SST anomalies are preceded by and in near quadrature with relatively strong remotely forced westward propagating zonal current variations, suggesting the sub-ENSO mode arises from the zonal-advective feedback. The sub-ENSO mode is found to exist also in an intermediate complexity model (ICM) of the tropical Pacific. A heat budget analysis of the model’s sub-ENSO mode shows it indeed arises from the zonal-advective feedback. In the model, both ENSO and sub-ENSO modes coexist, but there is a weak nonlinear interaction between them. Experiments also show that the observed changes in sub-ENSO’s characteristics may be explained by changes in the relative importance of zonal and vertical advection SST tendencies