Three hundred eighty thousand year long stable isotope and faunal records from the Red Sea : influence of global sea level change on hydrography

Stable isotope and faunal records from the central Red Sea show high-amplitude oscillations for the past 380,000 years. Positive δ18O anomalies indicate periods of significant salt buildup during periods of lowered sea level when water mass exchange with the Arabian Sea was reduced due to a reduced geometry of the Bab el Mandeb Strait. Salinities as high as 53‰ and 55‰ are inferred from pteropod and benthic foraminifera δ18O, respectively, for the last glacial maximum. During this period all planktonic foraminifera vanished from this part of the Red Sea. Environmental conditions improved rapidly after 13 ka as salinities decreased due to rising sea level. The foraminiferal fauna started to reappear and was fully reestablished between 9 ka and 8 ka. Spectral analysis of the planktonic δ18O record documents highest variance in the orbital eccentricity, obliquity, and precession bands, indicating a dominant influence of climatically - driven sea level change on environmental conditions in the Red Sea. Variance in the precession band is enhanced compared to the global mean marine climate record (SPECMAP), suggesting an additional influence of the Indian monsoon system on Red Sea climates

The potential of dust detection by means of µXRF scanning in Eifel maar lake sediments

Mittels kontinuierlicher und hochauflösender μXRF-Geochemieanalysen wird die Variabilität äolischer Sedimente der letzten 60.000 Jahre rekonstruiert. Dazu werden zwei Sedimentbohrkerne jeweils aus einem Maarsee und einem Trockenenmaar (Eifel, Deutschland) untersucht. Beide Kerne umfassen das letzte Glazial, einschließlich des MIS-3, des LGM und MIS-2, Transition I als auch das Holozän. Die energiedispersive RFA-Messungen der Eagle III μXRF wird direkt an Harz imprägnierten Proben angewendet. Diese sogenannten Tränklinge bilden die Grundlage für die Herstellung von petrographischen Dünnschliffen und somit können die Messergebnisse direkt mit einer Mikrofaziesanalyse verglichen werden. Anhand eines Sedimentkerns wird gezeigt, dass eine Quantifizierung der μXRF-Ergebnisse mittels der undamentalparametermethode geeignete ist. Eine Überprüfung der Ergebnisse findet dabei mit wellenlängen-dispersiven RFA-Messungen an diskreten Proben statt. Die Ergebnisse zeigen, dass sich jedes einzelne Maar in der lithologischen Zusammensetzung und damit auch geochemisch unterscheidet. Deshalb wird auf die grundlegenden Prozesse der Elementdeposition in die Seen eingegangen, die mit der Ablagerung von Sedimenten, der Variabilität der chemischen Verwitterung oder der Wasserzirkulation in Zusammenhang stehen. Mittels Hauptkomponentenanalysen standardisierter Variablen ist darüber hinaus die objektive Ableitung eines äolischen Sedimentsignals möglich. Es wird gezeigt, dass dieser Ansatz verlässliche Ergebnisse für alle untersuchten Zeitabschnitte liefert, solange für die Interpretation weitere Kenntnisse über die Lithologie und Paläoökologie zur Verfügung stehen. Das auffälligste Element zur Charakterisierung von Staub ist in beiden untersuchten Kernen Kalzium. Die höchsten Werte (>5 Gew.-%) werden während vollglazialer Bedingungen erreicht. Kalzium hat einen wesentlichen Einfluss auf den Staubfaktor der Hauptkomponentenanalyse. Eine zusätzliche Kombination der Kalziumgehalte mit dem Staubfaktor der Hauptkomponentenanalyse sowie Grauwertmessungen verbessert den Nachweis äolischen Staubs in laminierten Seesedimenten zusätzlich. In beiden Kernen konnten Sedimente mit erhöhten Staubkonzentrationen geochemisch nachgewiesen werden: Während des MIS-3 sind das vor allem das größte Heinrich-Ereignis H4 sowie der Anstieg des atmosphärischen Staubgehalts während der Wiedervereisung der Inlandsgletscher. Weiterhin ist das gesamte MIS-2 einschließlich LGM und der Jüngeren Dryas von starker Staubdeposition charakterisiert. Eine erhöhte Staubkonzentration ist ebenfalls ab dem Subboreal nachgewiesen und wird als anthropogene Aktivität gedeutet.researc

Terrigenous plant wax inputs to the Arabian Sea : implications for the reconstruction of winds associated with the Indian Monsoon

Author Posting. © The Authors, 2005. This is the author's version of the work. It is posted here by permission of Elsevier B. V. for personal use, not for redistribution. The definitive version was published in Geochimica et Cosmochimica Acta 69 (2005): 2547-2558, doi:10.1016/j.gca.2005.01.001.We have determined the accumulation rates and carbon isotopic compositions (δ13C) of long-chain (C24–C32) terrigenous plant wax fatty acids in 19 surface sediment samples geographically distributed throughout the Arabian Sea in order to assess the relationship between plant wax inputs and the surrounding monsoon wind systems. Both the accumulation rate data and the δ13C data show that there are three primary eolian sources of plant waxes to the Arabian Sea: Africa, Asia, and the Arabian Peninsula. These sources correspond to the three major wind systems in this region: the summer (Southwest) monsoon, the winter (Northeast) monsoon, and the summer northwesterlies that blow over the Arabian Peninsula. In addition, plant waxes are fluvially supplied to the Gulf of Oman and the Eastern African margin by nearby rivers. Plant wax δ13C values reflect the vegetation types of the continental source regions. Greater than 75% of the waxes from Africa and Asia are derived from C4 plants. Waxes delivered by northwesterly winds reflect a greater influence (25–40%) of C3 vegetation, likely derived from the Mesopotamian region. These data agree well with previously published studies of eolian dust deposition, particularly of dolomite derived from the Arabian Peninsula and the Mesopotamian region, in surface sediments of the Arabian Sea. The west-to-east gradient of plant wax δ13C and dolomite accumulation rates are separately useful indicators of the relationship between the northwesterly winds and the winds of the Southwest monsoon. Combined, however, these two proxies could provide a powerful tool for the reconstruction of both southwest monsoon strength as well as Mesopotamian aridity.This work was supported by a SGER grant from the National Science Foundation to D.O. and a Schlanger Ocean Drilling Fellowship to K.D

Faecal Steroids and n-Alkanes in Lake Sediments

Lake sediments are used as archives for climate and environmental reconstructions. This study investigated if biomarker analyses in lake sediments can be used to reconstruct anthropogenic landscape modifications during Holocene. In contrast to the mineral matrix of sediments and e.g. pollen, plant macro remains and charcoal particles, biomarkers can be more easily translocated within soil profiles before erosion and deposition. Furthermore, a translocation can also occur in lake sediments. Therefore, we tested if biomarker concentrations and patterns correlated with pollen patterns and further paleo environmental proxies in sediments of two maar lakes in the Eifel region. Five core sections of Lake Holzmaar and two core sections of Lake Ulmener Maar were sampled. The analysed core sections contain ca. 10 000 years and a number of data existed from previous analyses (ELSA project). As example for biomarkers for the reconstruction of vegetation changes, n-alkanes were analysed. Steroids incl. bile acids were used as proxies for the deposition of faeces of animals (animal husbandry). Patterns of n-alkanes correlated with pollen data. Parts of the core that show characteristics of dense forest in the catchment area had relatively low amounts of faecal steroids and the steroid patterns indicated the presence of several different animals. In parts of the core that show characteristics for grassland and agricultural fields, faecal steroids showed the presence of animal husbandry. The correlation of biomarker concentrations with pollen data and other data showed that it possible to detect changes in vegetation and land use with biomarker analyses within the catchment area of the two maar lakes

Multidecadal variations in the early Holocene outflow of Red Sea Water into the Arabian Sea

We present Holocene stable oxygen isotope data from the deep Arabian Sea off Somalia at a decadal time resolution as a proxy for the history of intermediate/upper deep water. These data show an overall δ18O reduction by 0.5‰ between 10 and ~6.5 kyr B.P. superimposed upon short-term δ18O variations at a decadal-centennial timescale. The amplitude of the decadal variations is 0.3‰ prior, and up to 0.6‰ subsequent, to ~8.1 kyr B.P. We conclude from modeling experiments that the short-term δ18O variations between 10 and ~6.5 kyr B.P. most likely document changes in the evaporation-precipitation balance in the central Red Sea. Changes in water temperature and salinity cause the outflowing Red Sea Water to settle roughly 800 m deeper than today

Sea surface temperature pattern reconstructions in the Arabian Sea

Author Posting. © American Geophysical Union, 2006. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 21 (2006): PA1014, doi:10.1029/2005PA001162.Sea surface temperature (SST) and seawater δ18O (δ18Ow) were reconstructed in a suite of sediment cores from throughout the Arabian Sea for four distinct time intervals (0 ka, 8 ka, 15 ka, and 20 ka) with the aim of understanding the history of the Indian Monsoon and the climate of the Arabian Sea region. This was accomplished through the use of paired Mg/Ca and δ18O measurements of the planktonic foraminifer Globigerinoides ruber. By analyzing basin-wide changes and changes in cross-basinal gradients, we assess both monsoonal and regional-scale climate changes. SST was colder than present for the majority of sites within all three paleotime slices. Furthermore, both the Indian Monsoon and the regional Arabian Sea mean climate have varied substantially over the past 20 kyr. The 20 ka and 15 ka time slices exhibit average negative temperature anomalies of 2.5°–3.5°C attributable, in part, to the influences of glacial atmospheric CO2 concentrations and large continental ice sheets. The elimination of the cross-basinal SST gradient during these two time slices likely reflects a decrease in summer monsoon and an increase in winter monsoon strength. Changes in δ18Ow that are smaller than the δ18O signal due to global ice volume reflect decreased evaporation and increased winter monsoon mixing. SSTs throughout the Arabian Sea were still cooler than present by an average of 1.4°C in the 8 ka time slice. These cool SSTs, along with lower δ18Ow throughout the basin, are attributed to stronger than modern summer and winter monsoons and increased runoff and precipitation. The results of this study underscore the importance of taking a spatial approach to the reconstruction of processes such as monsoon upwelling.Analyses were funded by a SGER grant from the NSF (OCE03–34598). Funding was also provided by a Schlanger Ocean Drilling Program Fellowship (to K.A.D.) and NSF Grant OCE02–20776 (to D.W.O.). 1

Evidence for early warming and cooling in North Atlantic surface waters during the last interglacial

In-depth analysis of planktic foraminiferal census data paired with δ18O records of specific indicator species provides new insight into the surface ocean evolution of the northeast Atlantic during the previous interglacial warm period (oxygen isotope stage (OIS) 5e). Full interglacial conditions existed at the study site for a maximum of only 8 kyr, between 125 and 117 ka. Highest sea surface temperatures (SSTs) occurred during early OIS 5e concomitant with high summer insolation but after the main phase of ice sheet melting of the preceding glaciation (Saalian). This early peak SST interval is marked by the appearance of tropical-subtropical species and lasted for 4 kyr until 121 ka, as corroborated by a major change in planktic δ18O. Relative stability in global ice volume continued for another 3–4 kyr before SSTs dropped further toward the next stadial. During early OIS 5e the situation of the surface water vertical structure appears to have been different from the early Holocene. For OIS 5e it is therefore suggested that the particular melting history of late Saalian ice had a long-lasting and profound effect on both postdeglacial surface water mass configuration in the North Atlantic and heat-moisture transfer into Europe

Local radon flux maxima in the quaternary sediments of Schleswig–Holstein (Germany)

This paper presents radon flux profiles from four regions in Schleswig–Holstein (Northern Germany). Three of these regions are located over deep-rooted tectonic faults or salt diapirs and one is in an area without any tectonic or halokinetic activity, but with steep topography. Contrary to recently published studies on spatial patterns of soil radon gas concentration we measured flux of radon from soil into the atmosphere. All radon devices of each profile were deployed simultaneously to avoid inconsistencies due to strong diurnal variations of radon exhalation. To compare data from different seasons, values had to be normalized. Observed radon flux patterns are apparently related to the mineralogical composition of the Quaternary strata (particularly to the abundance of reddish granite and porphyry), and its grain size (with a flux maximum in well-sorted sand/silt). Minimum radon flux occurs above non-permeable, clay-rich soil layers. Small amounts of water content in the pore space increase radon flux, whereas excessive water content lessens it. Peak flux values, however, are observed over a deep-rooted fault system on the eastern side of Lake Plön, i.e., at the boundary of the Eastholstein Platform and the Eastholstein Trough. Furthermore, high radon flux values are observed in two regions associated with salt diapirism and near-surface halokinetic faults. These regions show frequent local radon flux maxima, which indicate that the uppermost strata above salt diapirs are very inhomogeneous. Deep-rooted increased permeability (effective radon flux depth) or just the boundaries between permeable and impermeable strata appear to concentrate radon flux. In summary, our radon flux profiles are in accordance with the published evidence of low radon concentrations in the “normal” soils of Schleswig–Holstein. However, very high values of radon flux are likely to occur at distinct locations near salt diapirism at depth, boundaries between permeable and impermeable strata, and finally at the tectonically active flanks of the North German Basin

Sea surface temperatures of the western Arabian Sea during the last deglaciation.

In this study we present a sea surface temperature (SST) record from the western Arabian Sea for the last\ud 20,000 years. We produced centennial-scale d18O and Mg/Ca SST time series of core NIOP929 with focus on\ud the glacial-interglacial transition. The western Arabian Sea is influenced by the seasonal NE and SW monsoon\ud wind systems. Lowest SSTs occur during the SW monsoon season because of upwelling of cold water, and\ud highest SSTs can be found in the low-productivity intermonsoon season. The Mg/Ca-based temperature record\ud reflects the integrated SST of the SW and NE monsoon seasons. The results show a glacial-interglacial SST\ud difference of 2C, which is corroborated by findings from other Arabian Sea cores. At 19 ka B.P. a yet\ud undescribed warm event of several hundred years duration is found, which is also reflected in the d18O record. A\ud second centennial-scale high SST/low d18O event is observed at 17 ka B.P. This event forms the onset of the\ud stepwise yet persistent trend toward Holocene temperatures. Highest Mg/Ca-derived SSTs in the NIOP929\ud record occurred between 13 and 10 ka B.P. Interglacial SST is 24C, indicating influence of upwelling. The\ud onset of Arabian Sea warming occurs when the North Atlantic is experiencing minimum temperatures. The rapid\ud temperature variations at 19, 17, and 13 ka B.P. are difficult to explain with monsoon changes alone and are\ud most likely also linked to regional hydrographic changes, such as trade wind induced variations in warm water\ud advection