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 & Glacial period. The organization has 14563 authors who have published 37279 publications receiving 970381 citations. The organization is also known as: Universität Bremen.

Reassessing foraminiferal stable isotope geochemistry: Impact of the oceanic carbonate system (experimental results)

Abstract: Laboratory experiments with living planktic foraminifers show that the δ13C and δ18O values of shell calcite decrease with increasing sea water pH and/or carbonate ion concentration The effect has been quantified in symbiotic (Orbulina universa) and non-symbiotic (Globigerina bulloides) species and is independent of symbiont activity and temperature It is concluded that a kinetic fractionation process affects both the carbon and oxygen isotopic composition of the shell simultaneously At present it cannot be determined definitively whether the relationship is controlled by the pH dependent balance between hydration and hydroxylation of CO2 or by [CO3 2-] related variations in the calcification rate However, independent of which factor ultimately controls the relationship between the carbonate chemistry and isotopic fractionation, in the real ocean [CO3 2-] and pH covary linearly across the relevant pH range The true relationship between shell isotopic composition and the bulk carbonate chemistry is masked by the fact that host respiration and symbiont activity locally modify the carbonate system Respiration lowers and photosynthesis increases ambient pH and [CO3 2-] This translates into modified absolute shell values but leaves the slope between the shell isotopic composition and the bulk carbonate chemistry unaffected A second level of shell isotopic modification is introduced by the incorporation of respired carbon, enriched in 12C, which depletes the shell δ13C value In symbiont bearing species this depletion is partially negated by a shell δ13C enrichment in the light As an alternative to the RUBISCO hypothesis (enrichment via preferential removal of 12CO2), we propose that scavenging of respired CO2 during photosynthesis, raises the shell δ13C value Our results have partly been documented before (Spero et al 1997) and demonstrate that the carbonate chemistry is undoubtedly a major control on temporal geochemical variability in the fossil record For instance, the sea water carbonate system of the pre-Phanerozoic world (Berner 1994; Grotzinger and Kasting 1993) or during glacials (Sanyal et al 1995) was significantly different from today confounding direct interpretation of foraminiferal stable isotope data using existing relationships (see companion paper in this volume by Lea et al)

The detection of large HNO3-containing particles in the winter Arctic stratosphere.

Abstract: Large particles containing nitric acid (HNO3) were observed in the 1999/2000 Arctic winter stratosphere. These in situ observations were made over a large altitude range (16 to 21 kilometers) and horizontal extent (1800 kilometers) on several airborne sampling flights during a period of several weeks. With diameters of 10 to 20 micrometers, these sedimenting particles have significant potential to denitrify the lower stratosphere. A microphysical model of nitric acid trihydrate particles is able to simulate the growth and sedimentation of these large sizes in the lower stratosphere, but the nucleation process is not yet known. Accurate modeling of the formation of these large particles is essential for understanding Arctic denitrification and predicting future Arctic ozone abundances.

Context for interpreting equilibrium climate sensitivity and transient climate response from the CMIP6 Earth system models.

Abstract: For the current generation of earth system models participating in the Coupled Model Intercomparison Project Phase 6 (CMIP6), the range of equilibrium climate sensitivity (ECS, a hypothetical value of global warming at equilibrium for a doubling of CO2) is 18°C to 56°C, the largest of any generation of models dating to the 1990s Meanwhile, the range of transient climate response (TCR, the surface temperature warming around the time of CO2 doubling in a 1% per year CO2 increase simulation) for the CMIP6 models of 17°C (13°C to 30°C) is only slightly larger than for the CMIP3 and CMIP5 models Here we review and synthesize the latest developments in ECS and TCR values in CMIP, compile possible reasons for the current values as supplied by the modeling groups, and highlight future directions Cloud feedbacks and cloud-aerosol interactions are the most likely contributors to the high values and increased range of ECS in CMIP6