ALBERT

Description: Dust deposition in the Southern Ocean constitutes a critical modulator of past global climate variability, but how it has varied temporally and geographically is underdetermined. Here, we present data sets of glacial-interglacial dust-supply cycles from the largest Southern Ocean sector, the polar South Pacific, indicating three times higher dust deposition during glacial periods than during interglacials for the past million years. Although the most likely dust source for the South Pacific is Australia and New Zealand, the glacial-interglacial pattern and timing of lithogenic sediment deposition is similar to dust records from Antarctica and the South Atlantic dominated by Patagonian sources. These similarities imply large-scale common climate forcings, such as latitudinal shifts of the southern westerlies and regionally enhanced glaciogenic dust mobilization in New Zealand and Patagonia.

Description: The combined use of plant wax n-alkane δD and branched glycerol dialkyl glycerol tetraether lipids (brGDGT) provide a novel approach for paleoaltitude reconstructions. Previous studies from East Africa, however, revealed inconsistent results between the proxy estimates and altitudinal parameters. Here, we explore these proxies in soils of different land use (forest, cropland and pasture) along an altitudinal transect in the Jimma zone of the southwest Ethiopian highlands to better understand environmental and plant-specific factors controlling the isotopic composition and distribution of n-alkanes and brGDGTs. The hydrogen isotope composition of individual n-alkanes does not unambiguously reflect the altitude effect on precipitation δD, but seems largely influenced by the specific land use. Only forest soil-derived n-C27 and n-C29 alkane δD values exhibit a significant linear relation with altitude (r = -0.87, p 〈 0.05), likely reflecting the most stable ecosystem. The resulting lapse rate of -17‰/1000 m is comparable with that of local precipitation in the southwest Ethiopian highlands. In addition, the linear correlation of the average chain length (ACL) and δ13C values of forest soil n-alkanes suggests a physiological adaptation of the specific plant type waxes to altitude-induced environmental changes in the study area. The distribution of brGDGTs also reveals a significant linear correlation with altitude (r = -0.97, p 〈 0.01), reflecting the decrease in temperature with higher elevation independent of land use. In addition, brGDGT-based mean annual air temperature estimates (MAT) of 19.5°C to 14.0°C and temperature lapse rate of -6°C/1000 m are in good agreement with direct measurements in the Jimma zone. In contrast to previous studies from East Africa, our results show that both soil n-alkane δD values and brGDGT-based MAT distributions track present day altitude effects on local environmental gradients in the southwest Ethiopian highlands.

Description: Northern Africa's past hydroclimate is characterized by a prolonged humid period known as the African Humid Period (AHP), giving origin to the "Green Sahara" and supporting human settlements into areas that are now desert. The spatial and temporal extent of climate change associated with the AHP is, however, subject to ongoing debate. Uncertainties arise from the complex nature of the African climate, which is controlled by the strength and interactions of different monsoonal systems, resulting in meridional shifts in rainfall belts and zonal movements of the Congo Air Boundary (CAB), associated with changes in dominant moisture sources. Here, we examine a ~12,500-year record of hydroclimate variability from Lake Dendi, East Africa, based on a combination of plant-wax-specific hydrogen (δD) and carbon (δ13C) isotopes. In addition, pollen data from the same sediment core are used to investigate the response of the local vegetation to changing climate conditions. Our δD record indicates high precipitation during the peak AHP (from ca. 10 to 8 ka BP) followed by a gradual transition towards a drier late Holocene climate. Likewise, vegetation cover changed from predominant grassland towards an arid montane forest dominated by Juniperus and Podocarpus trees accompanied by a general reduction of understory grasses. This trend is corroborated by δ13C values pointing to an increased contribution of C3 plants during the mid- to late Holocene. Peak aridity occurred around 2 ka BP, followed by a return to a generally wetter climate (indicated by higher Podocarpus and lower Juniperus pollen values) possibly linked to enhanced Indian Ocean Monsoon strength. Starting at around 1 ka BP, increased anthropogenic activity, i.e. deforestation and agriculture is indicated by the pollen data, in agreement with intensified human impact recorded for the region. The magnitude of δD change (ca. 40‰) between peak wet conditions and late Holocene aridity is in line with other regional δD records of East Africa. The timing and pace of aridification parallels those of African and Indian monsoon records indicating a gradual response to local insolation change. Our new record combining plant-wax δD and δ13C values with pollen highlights the sensitive responses of the local vegetation to precipitation changes in the Ethiopian highlands. Our results also stress that information on local vegetation structure is important when interpreting hydroclimate change.

Description: Anaerobic ammonium oxidation (anammox) has been recognized as an important process converting fixed nitrogen to N2 in many marine environments, thereby having a major impact on the present-day marine nitrogen cycle. However, essentially nothing is known about the importance of anammox in past marine nitrogen cycles. In this study, we analyzed the distribution of fossil ladderane lipids, derived from bacteria performing anammox, in a sediment core from the northern Arabian Sea. Concentrations of ladderane lipids varied between 0.3 and 5.3 ng/g sediment during the past 140 ka, with high values observed during the Holocene, intervals during the last glacial, and during the penultimate interglacial. Maxima in ladderane lipid abundances correlate with high total organic carbon (4-6%) and elevated d15N (〉8 per mil) values. Anammox activity, therefore, seems enhanced during periods characterized by an intense oxygen minimum zone (OMZ). Low concentrations of ladderanes (〈0.5 ng/g sediment), indicating low-anammox activity, coincide with periods during which the OMZ was severely diminished. Since anammox activity covaried with OMZ intensity, it may play an important role in the loss of fixed inorganic nitrogen from the global ocean on glacial-interglacial timescales, which was so far attributed only to heterotrophic denitrification.

Description: In this study, we present a new multiproxy data set of terrigenous input, marine productivity and sea surface temperature (SST) from 52 surface sediment samples collected along E-W transects in the Pacific sector of the Southern Ocean. Allochtonous terrigenous input was characterized by the distribution of plant wax n-alkanes and soil-derived branched glycerol dialkyl glycerol tetraethers (brGDGTs). 230Th-normalized burial rates of both compound groups were highest close to the potential sources in Australia and New Zealand and are strongly related to lithogenic contents, indicating common sources and transport. Detection of both long-chain n-alkanes and brGDGTs at the most remote sites in the open ocean strongly suggests a primarily eolian transport mechanism to at least 110°W, i.e. by prevailing westerly winds. Two independent organic SST proxies were used, the UK'37 based on long-chain alkenones, and the TEX86 based on isoprenoid GDGTs. Both, UK'37 and TEX86 indices show robust relationships with temperature over a temperature range between 0.5 and 20°C, likely implying different seasonal and regional imprints on the temperature signal. While alkenone-based temperature estimates reliably reflect modern SST even at the low temperature end, large temperature residuals are observed for the polar ocean using the TEX86 index. 230Th-normalized burial rates of alkenones are highest close to the Subtropical Front and are positively related to lithogenic fluxes throughout the study area. In contrast, highest isoGDGT burial south of the Antarctic Polar Front is not related with dust flux but may be largely controlled by diatom blooms, and thus high opal fluxes during austral summer.

Description: We report on the EPICA Dronning Maud Land (East Antarctica) deep drilling operation. Starting with the scientific questions that led to the outline of the EPICA project, we introduce the setting of sister drillings at NorthGRIP and EPICA Dome C within the European ice-coring community. The progress of the drilling operation is described within the context of three parallel, deep-drilling operations, the problems that occurred and the solutions we developed. Modified procedures are described, such as the monitoring of penetration rate via cable weight rather than motor torque, and modifications to the system (e.g. closing the openings at the lower end of the outer barrel to reduce the risk of immersing the drill in highly concentrated chip suspension). Parameters of the drilling (e.g. core-break force, cutter pitch, chips balance, liquid level, core production rate and piece number) are discussed. We also review the operational mode, particularly in the context of achieved core length and piece length, which have to be optimized for drilling efficiency and core quality respectively. We conclude with recommendations addressing the design of the chip-collection openings and strictly limiting the cable-load drop with respect to the load at the start of the run.