11 results on '"Henrich, Rüdiger"'
Search Results
2. The significance of high-boreal to subarctic maerl deposits in northern Norway to reconstruct holocene climatic changes and sea level oscillations
- Author
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Freiwald, André, Henrich, Rüdiger, Schäfer, Priska, and Willkomm, Horst
- Published
- 1991
- Full Text
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3. Geochemical composition of Tanzanian shelf sediments indicates Holocene climatic and sea-level changes.
- Author
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Xiting Liu, Rendle-Bühring, Rebecca, and Henrich, Rüdiger
- Subjects
GEOCHEMISTRY ,MARINE sediments ,HOLOCENE Epoch ,CLIMATE change ,SEA level ,GRAIN size - Abstract
We present a high-resolution geochemical and grain-size record from a Holocene sediment core off the Pangani River mouth, Tanzania. Elemental ratios between biogenic elements and Al (i.e., Ca/Al, Mg/Al, and Sr/Al) are mainly influenced by terrigenous dilution on carbonate concentration and/or limitation of carbonate production as a result of variations in the supply of fine-grained terrigenous sediments of the Pangani River. Such elemental ratios increased significantly at the end of the mid-Holocene between 5 and 3.5 ka, demonstrating a gradual transition from the humid early and mid-Holocene to the arid late Holocene in East Africa. Among the elemental ratios between terrigenous elements and Al, Si/Al and K/Al ratios correlate to grain-size variation, indicating a change in sedimentation regime. Fe/Al and Ti/Al ratios show that the sediment source area has shifted from the terrestrial volcanic region of Tanzania (Fe, Ti rich) to the coastal and inner-shelf regions (Fe, Ti poor) around 7.5 ka, in response to arid climate and high sea level. Our geochemical results correspond with a sea-surface temperature record derived from the same sediment core, indicating that the end of the East African Humid Period could have been gradual and related to the cooling water in the western Indian Ocean. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
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4. Carbonate dissolution revealed by silt grain-size distribution: comparison of Holocene and Last Glacial Maximum sediments from the pelagic South Atlantic.
- Author
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FRENZ, MICHAEL and HENRICH, RÜDIGER
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GLOBAL warming , *OCEAN , *CARBONATES , *SILT , *FORAMINIFERA , *BOTTOM water (Oceanography) - Abstract
The current issue of global warming and the role of the ocean in global exchange of CO2 increases the interest in solid budgets of marine carbonate production and dissolution. The present study utilizes grain-size composition of pelagic sediments in order to trace spatial and temporal variability of carbonate sedimentation in the South Atlantic for the Holocene and Last Glacial Maximum (LGM, 19–23 cal kyr BP). A decrease in grain size (e.g. sand content, mean grain size of coarse carbonate silt) indicates increased carbonate dissolution as a result of increased fragmentation of calcareous microfossils. The spatial grain-size pattern suggests a threshold water depth below which a gradual grain-size decrease becomes increasingly rapid. This water depth is considered as the sedimentary lysocline. For the Holocene time slice, a constant, gradual decrease of foraminifer carbonate of about 5–10% per 1000 m water depth above the lysocline gives evidence for supra-lysoclinal dissolution. The water depth of the lysocline for the Holocene is tied to the interface of North Atlantic Deep Water and Antarctic Bottom Water (AABW) ( ca 4100 m). Submarine ridges which restrict intrusion of AABW into the Angola Basin cause an asymmetry in carbonate preservation across the Mid-Atlantic Ridge. The lysocline was reconstructed at ca 3100 m for the LGM. These data suggest that the ca 1000 m rise of the lysocline eradicated the Holocene east–west asymmetry. [ABSTRACT FROM AUTHOR]
- Published
- 2007
- Full Text
- View/download PDF
5. Climate and sea-level controls on turbidity current activity on the Tanzanian upper slope during the last deglaciation and the Holocene.
- Author
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Liu, Xiting, Rendle-Bühring, Rebecca, and Henrich, Rüdiger
- Subjects
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CLIMATE change , *SEA level , *TURBIDITY currents , *SLOPES (Physical geography) , *GLACIAL melting , *HOLOCENE Epoch - Abstract
Turbidity current is one of the most important mechanisms for rapid transportation of terrigenous sediments from the continental margin to the deep sea. Although extensive work on turbidite systems has been carried out globally, the Tanzanian margin, off East Africa, is poorly understood. This paper will therefore use a well-dated high-resolution marine core (GeoB12624-1), obtained during RV Meteor Cruise M75/2, from the upper Tanzanian continental slope, offshore the Rufiji River delta, to demonstrate which environmental parameters, e.g., climate versus sea level, control the temporal distribution of the turbidite deposits during the last deglaciation and the Holocene. Results show that the turbidite deposits are composed of coarser-grained sediments with normally graded bedding. The thickness, mean grain size and frequency of the turbidite beds were estimated to detect turbidity current activity since the Last Glacial Maximum (LGM). A total of 12 turbidite beds (TI-T12) was recognized and divided into three intervals, based on the presence and intensity of the turbidite deposits. (I) a glacial sea-level lowstand (LGM and Heinrich Stadial 1; 19.3–14.6 ka): suppressed turbidity current activity due to arid conditions in the hinterland and sea-level lowstand. (II) A deglacial sea-level rise period (Bølling-Allerød interval to the early Holocene; 14.6–8 ka): turbidity current activity started to be strengthened during the Bølling-Allerød warming interval (T1), followed by a first increase in turbidite frequency, thickness and mean grain-size during the Younger Dryas (T2–T4) and a second increase during the early Holocene (T5–T10). (III) An interglacial sea-level highstand period (mid-to late Holocene; 8–2.5 ka): turbidity current activity diminished from the mid- (T11, T12) to late Holocene. This temporal distribution of turbidite deposits indicates that turbidity currents were most active during the last sea-level rise, synchronous with more humid climate in the hinterland, than during a sea-level lowstand (e.g., LGM) when climate was more arid. Thus, we propose that it is the climate conditions in the hinterland that form the primary controlling factor for turbidity current activity of Tanzanian slope. The remobilization of lowstand sediments on the Tanzanian continental margin during a sea-level rise, combined with shedding sediments towards the study area from the main canyon/channel, also plays a role in supplying new sediments to the turbidite system. These new data demonstrate that, in specific continental margin, high fluvial discharge will promote sediment transfer along the shelf and slope even during sea-level rise and highstand. [ABSTRACT FROM AUTHOR]
- Published
- 2016
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6. Variability in terrigenous sedimentation processes off northwest Africa and its relation to climate changes: Inferences from grain-size distributions of a Holocene marine sediment record
- Author
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Holz, Christine, Stuut, Jan-Berend W., Henrich, Rüdiger, and Meggers, Helge
- Subjects
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SEDIMENTATION & deposition , *MARINE sediments , *SEDIMENTS - Abstract
Abstract: Variations in deposition of terrigenous fine sediments and their grain-size distributions from a high-resolution marine sediment record offshore northwest Africa (30°51.0′N; 10°16.1′W) document climate changes on the African continent during the Holocene. End-member grain-size distributions of the terrigenous silt fraction, which are related to fluvial and aeolian dust transport, indicate millennial-scale variability in the dominant transport processes at the investigation site off northwest Africa as well as recurring periods of dry conditions in northwest Africa during the Holocene. The terrigenous record from the subtropical North Atlantic reflects generally humid conditions before the Younger Dryas, during the early to mid-Holocene, as well as after 1.3 kyr BP. By contrast, continental runoff was reduced and arid conditions were prevalent at the beginning of the Younger Dryas and during the mid- and late Holocene. A comparison with high- and low-latitude Holocene climate records reveals a strong link between northwest African climate and Northern Hemisphere atmospheric circulation throughout the Holocene. Due to its proximal position, close to an ephemeral river system draining the Atlas Mountains as well as the adjacent Saharan desert, this detailed marine sediment record, which has a temporal resolution between 15 and 120 years, is ideally suited to enhance our understanding of ocean–continent–atmosphere interactions in African climates and the hydrological cycle of northern Africa after the last deglaciation. [Copyright &y& Elsevier]
- Published
- 2007
- Full Text
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7. Holocene changes in Antarctic Intermediate Water flow strength in the Southwest Atlantic.
- Author
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Voigt, Ines, Chiessi, Cristiano M., Piola, Alberto R., and Henrich, Rüdiger
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HOLOCENE Epoch , *HYDRAULICS , *MERIDIONAL overturning circulation , *CLIMATE change , *PALEOCURRENTS - Abstract
Antarctic Intermediate Water (AAIW) is an essential component of the Atlantic meridional overturning circulation (AMOC) contributing to balance the southward flow of North Atlantic Deep Water (NADW). However, the role of AAIW in Holocene abrupt climate changes remains poorly understood. Here we reconstruct changes in the flow strength of AAIW based on a high temporal resolution paleocurrent record from the Southwest Atlantic. Superimposed on a slight increase in AAIW strength at ~ 7 ka BP, a succession of millennial-scale AAIW variations is recognized in our paleocurrent records indicating a highly variable intermediate water circulation throughout the Holocene. Although variations in the strength and position of the Southern Westerlies Winds (SWW) are proposed to greatly influence the formation and circulation of AAIW, we cannot confirm such a potential SWW-AAIW linkage since our records of AAIW flow strength do not correlate to Holocene shifts of the SWW across the Atlantic. However, our data shows a good correspondence with abrupt variations in the AMOC with enhanced (reduced) northward advection of AAIW during periods of reduced (enhanced) NADW circulation. These results provide evidence for a Holocene AAIW-NADW see-saw. Thus, although the exact forcing mechanism remains unresolved, we suggest that Holocene perturbations in AAIW exerted a significant impact on the AMOC. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
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8. Holocene shelf sedimentation patterns off equatorial East Africa constrained by climatic and sea-level changes.
- Author
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Liu, Xiting, Rendle-Bühring, Rebecca, Meyer, Inka, and Henrich, Rüdiger
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HOLOCENE paleontology , *SEDIMENTATION & deposition , *SEA level , *PALEOCLIMATOLOGY , *PALEOCEANOGRAPHY , *CONTINENTAL shelf - Abstract
Equatorial East Africa experienced significant variations in paleoclimatic and paleoceanographic conditions during the Holocene. These environmental changes influenced sedimentation patterns on the continental shelf. To date, however, little is known about the sediment source, its transport to, and deposition on, the Tanzanian shelf. This paper presents a new high-resolution Holocene sedimentary record off northeast Tanzania (equatorial East Africa) and provides insights into how sedimentation patterns responded to climatic and oceanographic changes during the Holocene. Based on grain-size distribution patterns and mineral assemblages, three types of shelf sediments were identified: Type I (fine-grained terrigenous sediment) is dominated by clay minerals that originated from continental weathering; Type II (coarse-grained terrigenous sediment) is mainly composed of feldspar and quartz, derived from reworking of pre-existing deposits; and Type III (biogenic marine sediment), with low- and high-magnesium calcite, was produced by marine carbonate-secreting organisms. The high input of Type I sediment during the early Holocene (10–8 cal kyr BP) was caused by river mouth bypassing. This supply-dominated regime was controlled by intense river discharge and subsequent resuspension of mud in shelf settings, responding to the humid climate in the hinterland and sea-level rise with low rate off Tanzania. The first occurrence of Type II sediments was around 8 cal kyr BP and dominated when sedimentation rates lowered. This accommodation-dominated regime was caused by shoreface bypassing due to an arid climate and sea-level highstand. Type III sediments increased significantly from the early to late Holocene, resulting from the weakening dilution effect of the terrigenous component. The sedimentation pattern on the Tanzanian shelf shifted from allochthonous to autochthonous sedimentation constrained by climatic changes and relative sea-level fluctuations at the end of the early Holocene. Our results also suggest that, with respect to sea-level rise, high sedimentation rate on the continental shelf could be caused by high terrigenous sediment input as a result of a dynamic interplay between the shelf topography and humid climatic conditions inland. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
9. Änderung der Ozeanzirkulation im westlichen Südatlantik während des Holozäns
- Author
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Voigt, Ines, Henrich, Rüdiger, and Wefer, Gerold
- Subjects
Mar del Plata Canyon ,western South Atlantic ,Holocene ,Antarctic Intermediate Water (AAIW) ,ddc:540 ,Brazil-Malvinas Confluence (BMC) ,540 Chemistry - Abstract
The western South Atlantic forms a key location in the global ocean conveyor belt. Different water masses formed in remote areas of the world extend into that area and generate a highly complex vertical stratification structure. In the upper ocean, this structure is dominated by the encounter of southward flowing Brazil Current and northward-flowing Malvinas-(Falkland) Current generating one of the most energetic regions of the world ocean; the Brazil-Malvinas Confluence (BMC). In the deep ocean, the vertical stratification structure is dominated by contributions from intermediate- and deep water masses, including the Antarctic Intermediate Water (AAIW) which represents an active player in the Atlantic meridional overturning circulation (AMOC). The western South Atlantic is thus critical in understanding global ocean-climate changes. However, a detailed insight into the past remains a significant challenge in climate research due to the lack of high temporal resolution climate archives. The presented research of this thesis focuses on the surface- and intermediate water circulation in the western South Atlantic during the Holocene with special emphasize on sedimentation processes in the Mar del Plata Canyon. Results of this research highlight the extraordinary potential of a submarine canyon for reconstructing paleoceanographic and paleoclimatic changes with high temporal resolution, and clearly demonstrate that a good knowledge of sediment transport phenomena is an indispensable precondition for understanding paleoceanographic/paleoclimatic changes, particularly in such highly energetic current regimes as the western South Atlantic.
- Published
- 2013
10. Variabilität der Meereisverbreitung in der Framstraße während des letzten Glazials und im Holozän: Ein neuartiger Biomarkeransatz
- Author
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Müller, Juliane, Stein, Ruediger, and Henrich, Rüdiger
- Subjects
550 Earth sciences and geology ,Holocene ,Last Glacial ,ddc:550 ,Arctic sea ice ,IP25 ,Fram Strait - Abstract
The concern about the future development of Arctic sea ice also prompts a gaining interest in past variations of the ice extent in the Arctic Ocean. The important question as to whether the palaeo variability in sea ice coverage in this climate-sensitive area can be firstly identified, and secondly, linked to climatic fluctuations thus motivates to look for tools that permit the reliable reconstruction of palaeo sea ice conditions. The recently established sea ice proxy IP25 is considered to be such a tool though a proper evaluation of the applicability of this biomarker hitherto has not been available. Within this thesis the occurrence of IP25 and its capability to display a previous sea ice coverage has been investigated by means of sediment cores from the Fram Strait - the only deep-water passage between the Arctic and Atlantic Ocean. Analyses of the biomarker composition of surface sediments revealed that the abundance of IP25 in these samples mirrors the recent, as derived from satellite and model data, sea ice distribution considerably well. It is found that the ice cover does not necessarily hamper but instead even may promote the phytoplankton productivity. This finding led to the establishment of a phytoplankton-IP25 (PIP25) index that facilitates the identification of different sea surface conditions (no ice, less/variable ice, marginal ice, perennial ice cover). Correlation analyses of these PIP25-based sea ice estimates with observed (and modelled) sea ice concentrations substantiate that this combinatory biomarker approach permits a more precise assessment of sea ice coverage than IP25 alone and could be used for quantitative (palaeo) sea ice reconstructions. Further, the Holocene variability in IP25 and phytoplankton biomarker contents of sediment cores from the continental margin of West Spitsbergen and East Greenland was studied. Throughout the Middle to Late Holocene, the sea ice cover increased in eastern Fram Strait, whilst the sea ice export along the East Greenland coast continued and remained relatively unaffected by short-term variations in the oceanic circulation. Such fluctuations led to rapid sea ice oscillations along the West Spitsbergen margin during the Neoglacial that can be linked to abrupt changes in the advection of Atlantic water (possibly also due to shifts in the atmospheric NAO-like forcing). In a third study, which also represents the first long-term application of IP25, extreme variations in the sea ice cover during the last glacial-interglacial transition were reconstructed for northern Fram Strait. Permanent ice coverage is assumed for the Last Glacial Maximum such that the productivity of ice algae and phytoplankton at the sea surface was inhibited. Abrupt short-term cooling and warming events (e.g. the Intra-Allerød cold period and the Bølling warm phase) were correlated convincingly with sea ice advances and retreats, respectively. Within this thesis it is demonstrated that the approach to combine IP25 with phytoplankton-derived biomarkers occurs to be a promising and reliable method for palaeoceanographic sea ice reconstructions and which increases the significance of IP25. The studies provide information about the usage and interpretation of IP25 and they give new insight into the evolution of the sea ice conditions in Fram Strait over the past 30,000 years. Future studies on the spatial and temporal distribution of IP25 will likely extend the approach to use this proxy for quantitative sea ice reconstructions and also to elucidate sea ice (and climate) conditions of ancient times.
- Published
- 2011
11. Klimainduzierte Variabilität des fluviatilen und äolischen Sedimenteintrags und des gravitativen Sedimenttransports vor Nordwest-Afrika
- Author
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Holz, Christine, Henrich, Rüdiger, and Bohrmann, Gerhard
- Subjects
climate variability ,grain size ,end-member modelling ,Northwest Africa ,Holocene ,submarine canyon ,ddc:31 ,turbidity current - Abstract
This study focuses on climate-induced variability in terrigenous sediment supply and gravity-driven sediment transport off NW-Africa during the past 13 kyr. Sediment texture, mainly based on detailed grain-size analysis of the terrigenous silt and fine fraction and modelled end members for aeolian and fluvial supply, was studied on seabed samples recovered from the NW-African continental margin between 17° and 33°N as well as on a high-resolution Holocene sediment record off Morocco to display spatial and temporal variations in dominant sediment transport processes to the Atlantic Ocean and to obtain an overview of the evolution in continental aridity since the last deglaciation. Additional information on the evolution in Holocene NW-African climate and its implications for sediment transport processes is obtained from a high-resolution record of a submarine meandering channel system, the Cap Timiris Canyon, off presently hyperarid Mauritania.Under modern conditions terrigenous sediment supply along the NW-African continental margin north of 29°-30°N is characterized by fluvial discharge to the Atlantic Ocean, whereas further south, sediments are dominantly transported offshore by large dust plumes. During the Early to Mid Holocene relatively humid conditions were prevalent, although (sub-)millennial recurring dry phases are superimposed on this aridity record throughout the Holocene. Further south, off the Sahara desert, gravity-driven sediment transport is also controlled by climate variability during the past 13 kyr. We distinguish two phases of turbidity current activity and relate them to deglacial sea-level rise and Holocene climate variability, respectively. A climate-related coupling to be active for this depositional system during the Holocene is inferred by a (quasi-)periodic turbidity flow pattern and by excluding usually resorted triggers for turbidity current activity within this submarine channel system.
- Published
- 2005
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