Following publications have been announced. Fur further information please contact the marked authors.
Primo, C., Kelemen, F.D., Feldmann, H., Akhtar, N., & Ahrens, B. (2019): A regional atmosphere–ocean climate system model (CCLMv5.0clm7-NEMOv3.3-NEMOv3.6) over Europe including three marginal seas: on its stability and performance. Geosci. Model Dev., 12, 5077–5095, doi:10.5194/gmd-12-5077-2019
The frequency of extreme events has changed, having a direct impact on human lives. Regional climate models help us to predict these regional climate changes. This work presents an atmosphere–ocean coupled regional climate system model (RCSM; with the atmospheric component COSMO-CLM and the ocean component NEMO) over the European domain, including three marginal seas: the Mediterranean, North, and Baltic Sea. To test the model, we evaluate a simulation of more than 100 years (1900–2009) with a spatial grid resolution of about 25 km. The simulation was nested into a coupled global simulation with the model MPI-ESM in a low-resolution configuration, whose ocean temperature and salinity were nudged to the ocean–ice component of the MPI-ESM forced with the NOAA 20th Century Reanalysis (20CR). The evaluation shows the robustness of the RCSM and discusses the added value by the coupled marginal seas over an atmosphere-only simulation. The coupled system is stable for the complete 20th century and provides a better representation of extreme temperatures compared to the atmosphere-only model. The produced long-term dataset will help us to better understand the processes leading to meteorological and climate extremes.
Tim, N., Zorita, E., Emeis, K.-C., Schwarzkopf, F.U., Biastoch, A., & Hünicke, B. (2019): Analysis of the position and strength of westerlies and trades with implications for Agulhas leakage and South Benguela upwelling. Earth Syst. Dynam., 10, 847–858, doi:10.5194/esd-10-847-2019
The westerlies and trade winds over the South Atlantic and Indian Ocean are important drivers of the regional oceanography around southern Africa, including features such as the Agulhas Current, the Agulhas leakage, and the Benguela upwelling. Agulhas leakage constitutes a fraction of warm and saline water transport from the Indian Ocean into the South Atlantic. The leakage is stronger during intensified westerlies. Here, we analyze the wind stress of different observational and modeled atmospheric data sets (covering the last 2 millennia, the recent decades, and the 21st century) with regard to the intensity and position of the southeasterly trades and the westerlies. The analysis reveals that variations of both wind systems go hand in hand and that a poleward shift of the westerlies and trades and an intensification of westerlies took place during the recent decades. Furthermore, upwelling in South Benguela is slightly intensified when trades are shifted poleward. Projections for strength and position of the westerlies in the 21st century depend on assumed CO2 emissions and on their effect relative to the ozone forcing. In the strongest emission scenario (RCP8.5) the simulations show a further southward displacement, whereas in the weakest emission scenario (RCP2.6) a northward shift is modeled, possibly due to the effect of ozone recovery dominating the effect of anthropogenic greenhouse forcing. We conclude that the Agulhas leakage has intensified during the last decades and is projected to increase if greenhouse gas emissions are not reduced. This will have a small impact on Benguela upwelling strength and may also have consequences for water mass characteristics in the upwelling region. An increased contribution of Agulhas water to the upwelling water masses will import more preformed nutrients and oxygen into the upwelling region.
Liang, C., Xie, X., He, Y., Chen, H., Yu, X., Zhang, W., Mi, H., Lu, B., Tian, D., Zhang, H., Li, M., & Zhou, Z. (2019): Multiple sediment sources and topographic changes controlled the depositional architecture of a palaeoslope-parallel canyon in the Qiongdongnan Basin, South China Sea. Marine and Petroleum Geology, 2019, 104161, doi:10.1016/j.marpetgeo.2019.104161
Submarine canyon deposits have drawn attention due to their significance on source-to-sink analysis and hydrocarbon exploration. High-resolution 2-D and 3-D seismic and exploration well data recently collected in the Ledong-Lingshui segment of the Qiongdongnan Basin are used to investigate the depositional architecture of the palaeoslope-parallel Central Canyon, which is distinct from other slope-perpendicular canyons. This study indicates that the canyon developed along the thalweg of a multiple stepped palaeotopography with a slope-parallel descending trend eastwards. The location of the thalweg is controlled by regional tectonics and progradational slope clinoforms in the western Qiongdongnan basin. Geographic changes in an extending direction and slope gradient of the palaeotopography resulted in variations in the depth and width of the canyon. Analysis of the canyon infillings indicates multiple sediment sources including an axial sediment source from the Central Vietnam and the western Hainan Island and a canyon-side source from the northern slope of the Qiongdongnan basin. Provenance study shows that the former source supplied relatively coarse-grained turbidites and the later supplied fine-grained mass transport deposits (MTD). Most of such MTDs originated from the northern slope of the basin. Evolution of the Central Canyon can be classified into three stages. Stage 1 is characterised by significant incisions that are responsible for the formation of the canyon. Subsequently or contemporaneously, the sharp bend at the beginning of the middle segment of the canyon likely resulted in lateral erosion, which triggered large-scale and small-scale canyon margin failures in the middle and lower segments of the canyon, respectively. The subsequent early filling stage (Stage 2) refers to the deposition of turbidites supplied by the axial sediment source. However, the morphology of the stepped thalweg slope resulted in sediment bypass in the upper segment of the Central Canyon. During the late filling stage (Stage 3), MTDs supplied by the canyon-side sediment source were dominated, and interbedded with turbidite deposits. The deposition of the MTDs resulted in the sharp decreases in canyon accommodation space and the abrupt southeastwards stepping of the deepest part of the canyon. Moreover, complex interactions between debris-flows and turbidity-flows occurred during this stage. Such variations in architecture of the canyon were controlled by multiple sediment supplies and topographic changes. The proposed conceptual model of canyon infilling and the resulting stratigraphic architecture could be applied in other analogous canyons for hydrocarbon exploration.