Discharge data derived from five water level gauges and discharge measurements in the Aguima and Niaou catchment, Benin, West Africa

This paper analyzes the hydrological processes and the impact of soil properties and land use on these processes in tropical headwater catchment in the sub-humid part of Benin (West-Africa), the Aguima catchment. The presented study is integrated in the GLOWA IMPETUS project, which investigates the effects of global change on the water cycle and water availability on a regional scale in Morocco and Benin. The lack of field investigations concerning soil and surface hydrology in the Benin research area necessitates detailed field measurements including measurements of discharge, soil water dynamics, soil physical properties etc. on the local scale in order to understand the dominant runoff generation processes and its influencing factors. This is a pre-requisite to be able to forecast the effects which global change has on hydrological processes and water availability in the region. The paper gives an overview over the hydrologic measuring concept of the IMPETUS-Benin project focusing on measurements concerning the soil saturated conductivity ksat and discharge behaviour of two different sub-catchment of the Aguima catchment. The results of ksat measurements revealed that interflow is the dominant runoff process on the hillslopes of the investigated catchment. Concerning the impact of land use on the hydrological processes infiltration experiments showed that infiltration rates were reduced on cultivated land compared to natural land cover. This results in significant differences in runoff behaviour and runoff ratios while comparing natural and agricultural used catchments.

Sedimentological and paleomagnetic investigations on two gravity cores and ODP sites 113-690 and 693 off Kapp Norvegia, Antarctic continental margin

Oligocene to Quaternary sediments were recovered from the Antarctic continental margin in the eastern Weddell Sea during ODP Leg 113 and Polarstern expedition ANT-VI. Clay mineral composition and grain size distribution patterns are useful for distinguishing sediments that have been transported by ocean currents from those that were ice-rafted. This, in turn, has assisted in providing insights about the changing late Paleogene to Neogene sedimentary environment as the cryosphere developed in Antarctica. During the middle Oligocene, increasing glacial conditions on the continent are indicated by the presence of glauconite sands, that are interpreted to have formed on the shelf and then transported down the continental slope by advancing glaciers or as a result of sea-level lowering. The dominance of illite and a relatively high content of chlorite suggest predominantly physical weathering conditions on the continent. The high content of biogenic opal from the late Miocene to the late Pliocene resulted from increased upwelling processes at the continental margin due to increased wind strength related to global cooling. Partial melting of the ice-sheet occurred during an early Pliocene climate optimum as is shown by an increasing supply of predominantly current-derived sediment with a low mean grain size and peak values of smectite. Primary productivity decreased at ~ 3 Ma due to the development of a permanent sea-ice cover close to the continent. Late Pleistocene sediments are characterized by planktonic foraminifers and biogenic opal, concentrated in distinct horizons reflecting climatic cycles. Isotopic analysis of AT. pachyderma produced a stratigraphy which resulted in a calculated sedimentation rate of 1 cm/k.y. during the Pleistocene. Primary productivity was highest during the last three interglacial maxima and decreased during glacial episodes as a result of increasing sea-ice coverage.

Calculated sea level records and deep ocean temperatures from DSDP and ODP sites

During the mid-Pleistocene transition the dominant 41 ka periodicity of glacial cycles transitioned to a quasi-100 ka periodicity for reasons not yet known. This study investigates the potential role of deep ocean hydrography by examining oxygen isotope ratios in benthic foraminifera. Oxygen isotope records from the Atlantic, Pacific and Indian Ocean basins are separated into their ice volume and local temperature/hydrography components using a piece-wise linear transfer function and a temperature calibration. Although our method has certain limitations, the deep ocean hydrography reconstructions show that glacial deep ocean temperatures approached freezing point as the mid-Pleistocene transition progressed. Further analysis suggests that water mass reorganisation could have been responsible for these temperature changes, leading to such stable conditions in the deep ocean that some obliquity cycles were skipped until precessional forcing triggered deglaciation, creating the apparent quasi-100 ka pattern. This study supports previous work that suggests multiples of obliquity cycles dominate the quasi-100 ka glacial cycles with precession components driving deglaciations.