Modeling the time-dependent response of the Asian summer monsoon to obliquity forcing in a coupled GCM: a PHASEMAP sensitivity experiment

To study the time-dependent response of the Asian summer monsoon to obliquity forcing, we analyze a 284,000-year long transient simulation produced by a fully coupled global climate model (GCM) using a new phase mapping (PHASEMAP) approach. Here we focus on understanding the phase response of monsoonal circulation to insolation forcing at the Earth-orbital obliquity band (41 Kyr). Our results show that the East Asian summer monsoon (EASM) can be divided into two geographic regions: the North East Asian summer monsoon (NEASM) and the South East Asian summer monsoon (SEASM). The Indian summer monsoon (ISM) and the SEASM are in phase at the obliquity band, strengthened with an increase in obliquity from Obliquity minima (Omin) to Obliquity maxima (Omax). The NEASM is out of phase with the ISM and SEASM, weakened with an increase in obliquity from Omin to Omax. We hypothesize that the inverse phase between the NEASM and the ISM at the obliquity band results from an ISM–NEASM teleconnection linked to the formation mechanism of the Bonin High.     

The monsoon imprint during the ‘atypical’ MIS 13 as seen through north and equatorial Indian Ocean records

Previous studies have suggested that Marine Isotope Stage (MIS) 13, recognized as atypical in many paleoclimate records, is marked by the development of anomalously strong summer monsoons in the northern tropical areas. To test this hypothesis, we performed a multi-proxy study on three marine records from the tropical Indian Ocean in order to reconstruct and analyse changes in the summer Indian monsoon winds and precipitations during MIS 13. Our data confirm the existence of a low-salinity event during MIS 13 in the equatorial Indian Ocean but we argue that this event should not be considered as “atypical”. Taking only into account a smaller precession does not make it possible to explain such precipitation episode. However, when considering also the larger obliquity in a more complete orbitally driven monsoon “model,” one can successfully explain this event. In addition, our data suggest that intense summer monsoon winds, although not atypical in strength, prevailed during MIS 13 in the western Arabian Sea. These strong monsoon winds, transporting important moisture, together with the effect of insolation and Eurasian ice sheet, are likely one of the factors responsible for the intense monsoon precipitation signal recorded in China loess, as suggested by model simulations.     

Lead and stable Pb-isotope characteristics of tropical soils in north-eastern Brazil

Stable Pb-isotope ratios are widely used as tracers for Pb-sources in the environment. Recently, a few publications have challenged the predominating view of environmental applications of Pb-isotopes. Present applications of Pb-isotopic tracers in soils largely represent the northern hemisphere. This study focuses on tropical soils from Paraíba, north-eastern Brazil. Lead concentrations and Pb-isotopic signatures (both 7N HNO₃) were determined at 30 sites along a 327 km E–W-transect, from the Atlantic coast at João Pessoa to some kilometers west of Patos, to identify possible processes for the observed (and anticipated) distribution pattern. Thirty samples each of litter (ORG) and top mineral soil (TOP) were taken on pasture land at suitable distance from roads or other potential contamination sources. Lead-content was determined by inductively-coupled plasma atomic emission spectrometry (ICP-AES) and the ratios of ²⁰⁶Pb/²⁰⁷Pb, ²⁰⁶Pb/²⁰⁸Pb, and ²⁰⁸Pb/²⁰⁷Pb by ICP-sector field mass spectrometry (ICP-SFMS). Both sample materials show similarly low Pb-concentrations with a lower median in the ORG samples (ORG 3.4 mg kg⁻¹ versus TOP 6.9 mg kg⁻¹). The ²⁰⁶Pb/²⁰⁷Pb ratios revealed a large spread along the transect with median ²⁰⁶Pb/²⁰⁷Pb ratios of 1.160 (ORG) and 1.175 (TOP). The ²⁰⁶Pb/²⁰⁷Pb ratios differ noticeably between sample sites located in the Atlantic Forest biome along the coast and sample sites in the inland Caatinga biome. The “forest” sites were characterised by a significant lower median and a lower spread in the ²⁰⁶Pb/²⁰⁷Pb and ²⁰⁶Pb/²⁰⁸Pb ratios compared to the Caatinga sites. Results indicate a very restricted influence of anthropogenic activities (individual sites only). The main process influencing the spatial variability of Pb-isotope ratios is supposed to be precipitation-dependent bioproductivity and weathering.     

The climatic wind energy potential — present and future: GIS-analysis in the region of Freiburg im Breisgau based on observed data and Regional Climate Models

The current and future wind energy potentials for two square areas (SA) in the region of Freiburg were assessed and analyzed, with the aim of mitigating climate change by increasing the use of wind energy. For future conditions the regional climate models REMO and CLM were taken into account for the IPCC Emission Scenarios (SRES) A1B and B1. One aim was to provide information of the applicability of data from regional climate models in terms of wind energy. As a reference dataset, the wind energy potentials of the two measurement stations of the German Weather Service (DWD) (1961–1990) in Freiburg (SA I) and on the Feldberg (SA II) were assessed. Calculations were carried out by the Wind Analysis and Application Program (WAsP). Results were in terms of visual analysis displayed with maps. While the annual electricity performances of the reference data in SA I and SA II reach up to 7.2 GWh and 10.1 GWh respectively, the calculations for REMO and CLM show an underestimation of the real conditions for every period and Emission Scenario. Hence the applicability of the models in consideration seems to be limited. Nevertheless, with regard to different socio-economic developments (SRES A1B and B1), the results provide an overview of the wind energy potentials’ development in the different periods.     

The unusual distribution of molecular gas and star formation in Arp 140

We investigate the atomic and molecular interstellar medium and star formation of NGC 275, the late-type spiral galaxy in Arp 140, which is interacting with NGC 274, an early-type system. The atomic gas (H  i ) observations reveal a tidal tail from NGC 275 which extends many optical radii beyond the interacting pair. The H  i morphology implies a prograde encounter between the galaxy pair approximately ∼1.5 × 10⁸ yr ago. The Hα emission from NGC 275 indicates clumpy irregular star formation, clumpiness which is mirrored by the underlying mass distribution as traced by the K _s-band emission. The molecular gas distribution is striking in its anticorrelation with the H  ii regions. Despite the evolved nature of NGC 275's interaction and its barred potential, neither the molecular gas nor the star formation is centrally concentrated. We suggest that this structure results from stochastic star formation leading to preferential consumption of the gas in certain regions of the galaxy. In contrast to the often-assumed picture of interacting galaxies, NGC 275, which appears to be close to merger, does not display enhanced or centrally concentrated star formation. If the eventual merger is to lead to a significant burst of star formation it must be preceded by a significant conversion of atomic to molecular gas as at the current rate of star formation all the molecular gas will be exhausted by the time the merger is complete.     

Gas in early-type galaxies: cross-fuelling in late-type–early-type pairs?

We present  ¹²CO ( J = 1–0)  and  ¹²CO ( J = 2–1)  observations of eight early-type galaxies, forming part of a sample of interacting galaxies, each consisting of one late- and one early-type system. All of the early-type galaxies observed are undetected in CO to low levels, allowing us to place tight constraints on their molecular gas content. Additionally, we present H  i absorption data for one system. The implications for possible gas transfer from the late- to the early-type galaxy during the interaction are discussed.     

RAM-Pressure Stripping of a Galaxy's ISM

NGC 4485 is a late-type galaxy moving through the very extended HI envelope of its companion, NGC 4490. NGC 4485 is undetected in HI,CO and IRAS wavebands, but a peak at all of these frequencies is seen displaced from the optical disk. HI data show a prominent bow-shock ahead of this displaced gas. It is argued that almost the entire ISM, including molecular clouds, has been stripped from this galaxy byram-pressure, and that it will emerge from the encounter with very little star forming potential. This revised version was published online in July 2006 with corrections to the Cover Date.     

Quaternary palaeoceanographic changes in the northern South China Sea (ODP Site 1146): radiolarian evidence

The abundance and accumulation rates of siliceous microfossils in the northern South China Sea, including radiolarians, diatoms and sponge spicules, increased during most glacial intervals within the past 1100 kyr. Similar trends are observed in the index of thermocline surface radiolarians (TSR), diatom accumulation rates (DAR), charcoal accumulation rates (CAR) and the abundance of radiolarian species Cycladophora davisiana davisiana. Decreasing sea‐surface temperature accompanied by increased seasonality since 900 ka is indicated by a decline in the tropical radiolarian assemblage, including Tetrapyle octacantha and Octopyle stenozona, and by an increase in the subtropical assemblage, including Pterocorys zancleus, Peromelissa phalacra and Ommatartuts tetrathalamus tetrathalamus. Rapid increases at about 800 to 700 ka of siliceous microfossils, charcoal, subsurface and intermediate radiolarians, as well as the TSR index and the DAR, imply a fundamental shift in climate and a shoaling thermocline. Although these fundamental changes in the silicious fauna and flora of the South China Sea take place within the context of a developing 100‐kyr cycle, they do not change in step with changing sea‐level as indicated by marine δ¹⁸O. This is most clearly illustrated by the step‐like increase in silica accumulation (radiolaria, diatoms and sponge spicules) at 680 ka. Rather, these fundamental changes probably reflect intensified surface productivity associated with enhanced East Asian winter‐monsoon circulation. Copyright © 2003 John Wiley & Sons, Ltd.