Sub-orbital Timescales Research Articles

Late Pleistocene to modern precipitation changes at the Paranal clay pan, central Atacama Desert

The Atacama Desert in Chile is known to be one of the driest deserts on Earth, with dominating hyperaridity at least since the Miocene. During recent times, however, especially the southern part of the Atacama repeatedly experienced exceptional precipitation events, like in 2015 and 2017. Locally, these events with high rainfall rates caused catastrophic floods with significant destruction and human fatalities. Although the meteorological drivers of these heavy rains are widely understood, only little is known about the frequency and amplitude of similar events on geological timescales. Here we present the results of a study on an endorheic clay pan at the southern edge of the hyperarid core of the Atacama, an area with a mean precipitation of approx. 5 mm per year. A modern ground-truthing approach combining sediment data, remote-sensing and meteorological data as well as climate-modelling was applied. Our observations indicate that the clay pan reacted very sensitively to local precipitation during the past 30 years, with four events >20 mm total rain causing sufficient surface run-off in the catchment to partially flood the basin. Comparative analyses of the four events illustrate that the amount of run-off is dependent on the maximum rain rate during the events rather than the total rain sum. A 1.88-m long sediment core recovered from the centre of the clay pan records the local hydrological and -environmental history since the Late Pleistocene. Sedimentological, mineralogical, geochemical, and biological core analyses imply strong variations in the amplitude of the recorded rainfall, with a clear shift from enhanced alluvial activity caused by higher-amplitude rain events during the Late Pleistocene to lower-amplitude Holocene events. The Holocene background sedimentation is superimposed by seven severe “Millennial-scale rain events”, which imply precipitation maxima on sub-orbital timescales that are potentially driven by changes in the El Niño Southern Oscillation (ENSO). The results of the study shed new light on the glacial-interglacial but also the sub-orbital precipitation variability in the Coastal Cordillera of the Atacama Desert and its potential driving mechanisms, and provide perspectives of the future precipitation development in the region under progressive global warming.

Millennial and suborbital-scale El Niño/Southern Oscillation control of climate variability in southern China over the past 70 ka

Hydroclimatic changes in East Asia on suborbital and millennial time scales have been shown to be highly uncertain. The El Niño-Southern Oscillation (ENSO) activity plays a key role in precipitation in low-latitude East Asia on interannual and interdecadal time scales. However, there remained some ambiguity about their connection on millennial and suborbital time scales. This study comprehensively explored the multifaceted relationships between ENSO activities, suborbital and millennial-scale drought events, and hydroclimatic variations within the Huguangyan Maar Lake (HML) region during the past 70 ka. Four suborbital-scale dry and wet hydroclimatic phases interspersed with ten millennial-scale extreme dry intervals were revealed by the ratio of hematite and goethite (Hem/Goe). These stages and intervals unexpectedly coupled with the zonal sea surface temperature (ΔSST) of the tropical Pacific Ocean, underscored the complex spatial and temporal dynamics of ENSO impacts. We propose the “glacial-El Niño-arid” and “interglacial-La Niña-humid” hydroclimate patterns on the suborbital scale. While on the millennial-scale, La Niña-like fluctuations during the persistent cold period (16–40 ka) increased the frequency and intensity of droughts in low-latitude East Asia, which was in stark contrast to the wet climate in northern China. The dynamic relationship underpins a millennia-spanning La Niña-drought pattern, elucidating the intertwined nature of ENSO dynamics and hydroclimatic variability on both sub-orbital and millennial scales. The above findings can be attributed to changes in the location and intensity of the Western Pacific subtropical high (WPSH) over southern China induced by persistent mean ENSO-like states in the tropical Pacific. This also indicates that the hydroclimate in low-latitude East Asia is more sensitive to variations in tropical ENSO compared to northern China.

Exploring Spatiotemporal Paleoenvironmental and Paleoceanographic Changes on the Continental Shelf Using Authigenic Greigite: A Case Study From the East China Sea

AbstractThe lack of suitable indicators of changes in such as sea‐level and circulation has been a major limit to paleoenvironmental and paleoceanographic investigations in continental shelf regions. This paper presents an environmental magnetic study by comparing two late‐Quaternary sediment cores (DH02 and DH03) from the outer shelf of the East China Sea (ECS). Late and early Marine Isotope Stage (MIS) 3 sediments were deposited in a prodelta under cold coastal currents and an open‐shelf with the Taiwan Warm Current and upwelling. The dominant iron‐bearing minerals of the late and early MIS 3 sediments are authigenic greigite (Fe3S4) and pyrite (FeS2), respectively, which were assumed to be formed nearly syndepositionally. The overlying sediments, however, are magnetically dominated by detrital magnetite. This pattern corresponds well to the temporal changes in sea‐level over this period. The widespread occurrence of greigite in the late MIS 3 sediments can also be used for future stratigraphic division and correlation in the ECS. Additionally, compared to microfossil assemblages, rock magnetic parameters based on greigite may be more sensitive to environmental changes on continental shelves. Furthermore, the inter‐borehole spatial comparisons imply not only a sedimentary hiatus/erosion of at least 30‐m thickness in core DH02, most probably during the Last Glacial Maximum, but also that core DH02 was in a more reductive environment than core DH03 during late MIS 3. The findings highlight the potential of authigenic greigite as an indicator of spatiotemporal changes in paleoenvironmental and paleoceanographic conditions on the continental shelf at orbital or even suborbital timescales.

Centennial-scale variability of the Indian Summer Monsoon during the middle to late Holocene and its links with ENSO activity

Relatively little is known about the relationship between the Indian summer monsoon (ISM) and the El Niño-Southern Oscillation (ENSO) on the centennial timescale during the Holocene. We present a well-dated high-resolution X-ray fluorescence (XRF) scanning record from a sediment core from Lake Qionghai on the southeastern Tibetan Plateau, which reveals the impact of ENSO activity on ISM variability. The results indicate a gradual drying of the regional climate on the sub-orbital timescale, which is in broad agreement with ISM changes controlled by Northern Hemisphere summer insolation. Additionally, centennial-scale drought events occurred at around 6230–5740, 4620–4250, 3820–3540, 3210–2440, 2180–1320, and 1000–615 cal yr B.P. and are consistent with enhanced ENSO activity, documenting the occurrence of ENSO-related drought events in the Holocene. Both ISM oscillations and ENSO variability show significant 350-yr, 500-yr, and 800-yr cyclicities, and there is a highly significant negative relationship between the ISM and ENSO at these cyclicities, indicating that a weak ISM was related to increased ENSO intensity, and vice versa. Our findings provide evidence for the modulation of ISM intensity by ENSO variability on the centennial timescale during the Holocene.

Spatial differences in East Asian climate transition at ∼260 ka and their links to ENSO

The East Asian summer precipitation exhibits significant spatial differences from inter-annual to sub-orbital timescales, which has been associated with El Niño-Southern Oscillation (ENSO). However, studies on spatial patterns of climate and their mechanisms on orbital and tectonic timescales are still scarce, impeding a better understanding of Asian monsoon dynamics on long timescales. Here, we present a loess section spanning the past 430 ka in the Menyuan (MY) basin from the Northeastern Tibetan Plateau (NETP), and compare it with records from other sites in East Asia in order to explore the spatial patterns of climate changes and their mechanisms. Our results reveal a distinct climate transition at ∼260 ka in various records, which is characterized a transition from a “wet–dry–wet” to a “dry–wet–dry” pattern in the north-south direction and a transition from a “dry–wet” to “wet–dry” pattern in the west-east direction. This climate transition coincides with a significant weakening of the equatorial Pacific zonal (east–west) thermal gradient which indicates a shift to a more El Niño-like state, suggesting that the climate transition in East Asia at ∼260 ka could be related to paleo-ENSO variation. A more El Niño-like state could force an intensification and southwestward extension of the Western Pacific Subtropical High (WPSH) which could in turn move the rainfall front westward with the maximum rainfall belt over central China, resulting in the persistence of the observed climate patterns in East Asia. Our model results suggest that the change of the paleo-ENSO condition at ∼260 ka could be related to the eccentricity-modulated insolation and the ice shelve changes in northern high latitudes. Our study highlights the important role of paleo-ENSO in regulating the long-term climate changes in different sub-regions in East Asia.

Timing and climatic-driven mechanisms of glacier advances in Bhutanese Himalaya during the Little Ice Age

Abstract. Mountain glaciers provide us a window into past climate changes and landscape evolution, but the pattern of glacier evolution at centennial or suborbital timescale remains elusive, especially in monsoonal Himalayas. We simulated the glacier evolution in Bhutanese Himalaya (BH), a typical monsoon-influenced region, during the Little Ice Age (LIA) using the Open Global Glacier Model driven by six paleoclimate datasets and their average. Compared with geomorphologically mapped glacial landforms, the model can well capture the patterns of glacier length change. Simulation results revealed four glacial substages (the 1270s, 1470s, 1710s, and 1850s) during LIA in the study area. Statistically, a positive correlation between the number of glacial substages and glacier slope was found, indicating that the occurrence of glacial substages might be a result from heterogeneous responses of glaciers to climate change. Monthly climate change analysis and sensitivity experiments indicated that the summer temperature largely dominates the regional glacier evolution during the LIA in BH.

Holocene hydroclimatic change in the Altai Mountains and its impact on human migration

An historical perspective on Holocene hydroclimatic change and its driving mechanisms in arid central Asia (ACA) can provide insights into both the sustainable development of the natural ecosystems of the region and ancient human-environment interactions. Here, we characterize changes in the Holocene (11.3–0 cal ka BP) aquatic ecosystem and hydrologic environment of a glacier-fed lake (i.e., Kanas Lake) in the Altai Mountains, based mainly on sedimentary records of cladocerans and Pediastrum. The low total abundances of cladocerans and Pediastrum during the middle to late Holocene (6–0 cal ka BP) suggest that an oligotrophic environment like that of today had developed mainly due to the increased river runoff. The higher runoff during this period resulted mainly from the increased precipitation that is indicated by climatic records from the sediments of Kanas Lake and other environmental archives in ACA. We conclude that the changes in the Holocene hydrological environment of glacier-fed lakes in ACA on the sub-orbital timescale were mainly modulated by the regional precipitation, and that the increased precipitation and hence availability of water resources greatly intensified the trans-Eurasian dispersal of crops and livestock along the grassland routeway.

Peat development in the Napahai wetland and its response to variations in the intensity of the Indian summer monsoon, southwestern China, since the last deglaciation

Knowledge of peatland dynamics and its response to the intensity of the Indian summer monsoon (ISM) is crucial to predict the future fate of the peatlands in the southwestern China under climate warming scenarios. In this study, we obtained a sediment core from the Napahai wetland in southwestern China and analyzed geochemical indices, including loss on ignition at 550 °C, carbonate content, as well as magnetic susceptibility, and ash-free bulk density, to investigate the peatland development since the last deglaciation. Results show that peat formation at ca. 13.3 cal. kyr BP in the Napahai wetland was likely attributed to climate warming during the Bølling-Allerød period. The results clearly suggest the peat continuously accumulated from 13.3 to 7.2 cal. kyr BP and weakened from the Middle to Late Holocene (7.2–1.5 cal. kyr BP), indicating notably wet conditions during the Early to Middle Holocene (11.8–7.2 cal. kyr BP) and a clear long-term drying trend in the Middle to Late Holocene. A comparison of the Napahai records with other monsoon intensity and related hydroclimatic records in areas dominated by the ISM suggests that the development of the Napahai peatland at orbital–suborbital timescales corresponded to the variations in the ISM intensity and the summer insolation.

Rock magnetic properties as proxy indicators of characteristic periodicities in Holocene aeolian sediments (Arturo Dune, Tierra del Fuego, Argentina)

The objective of this contribution is to distinguish characteristic wind speed periodicities from a roughly 19 m-thick profile of Arturo Dune (Tierra del Fuego, Argentina), which contains eight interbedded paleosoils. The results include different magnetic properties and ratios measured in 29 aeolian sediment samples. These properties are coercive force (HC), saturation magnetization (MS), low-frequency (470 Hz) magnetic susceptibilities (kLF), anhysteretic remanent magnetization (ARM), among others.The statistical analysis of the variations in the magnetic properties of detrital minerals over time could indirectly indicate prevailing periodicities of the wind rate during the studied interval. The power spectral analysis was done using wavelets and multiple cross wavelets. The analysis by wavelets made it possible to distinguish periodicities in the variations of climatic parameters.A main periodicity of 2824 years was obtained in the different wavelet and multiple cross wavelet analyses of the magnetic parameters. By adding the δ18O series from the deep South Atlantic Ocean to the spectral power analysis, a periodicity of around 3000 years was also obtained.These periodicities could be related to a fundamental solar mode, with a periodicity of 2300 years (Hallstattzeit cycle). Still, they are not conclusive as solid empirical evidence to support sun-climate relationships on a series of millennial suborbital time scales.

East-west asymmetry in the distribution of rainfall in the Chinese Loess Plateau during the Holocene

As the cradle of Chinese civilization the Chinese Loess Plateau (CLP) and its climatic and environmental history have attracted much research attention; however, the spatial characteristics of Holocene climatic conditions across the CLP remains unclear. We investigated five loess sections from the Ganjia Basin in the western CLP, and used paleoclimatic indexes from one well-dated loess-paleosol sequence to reconstruct precipitation variation during the past ~15,000 years. The chronology of the loess section is well established, based on 12 AMS 14C dates from bulk organic matter. Loess deposited before 8 ka (1 ka = 1000 years before 1950 CE) indicates that precipitation was low from ~15 to 8 ka. Subsequently, a paleosol, characterized by higher magnetic susceptibility and more negative organic carbon isotopic values, developed under the moist conditions of the middle to late Holocene. Comparison with paleoclimatic records from the CLP revealed that precipitation across the CLP was low during the early Holocene and reached its highest level during 8–3 ka, against the background of an enhanced East Asian summer monsoon (EASM). In the eastern CLP (the region east of the Liupan Mountains), the climate became dry after 3 ka because of a weakening of the EASM; however, precipitation in the western CLP was relatively high at this time. This observation of an east–west asymmetry in precipitation in the CLP during the Holocene based on geological data is supported by numerical modeling results from PMIP3, which indicate that it could have been caused by the westward extension of the western Pacific subtropical high. Our findings provide an analog for the study of interglacials on a longer time-scale and they demonstrate that the pattern of moisture conditions between the eastern and western CLP may differ on sub-orbital timescales.

Control Mechanisms of Primary Productivity Revealed by Calcareous Nannoplankton From Marine Isotope Stages 12 to 9 at the Shackleton Site (IODP Site U1385)

AbstractNowadays, primary productivity variations at the SW Iberian Margin (IbM) are primarily controlled by wind‐driven upwelling. Thus, major changes in atmospheric circulation and wind regimes between the Marine Isotope Stages (MIS) 12 and 9 could have driven substantial changes in phytoplankton productivity which remains poorly understood. We present a high‐resolution calcareous nannofossil record from the Shackleton Site Integrated Ocean Discovery Program Site U1385 that allow the assessment of primary productivity and changing surface conditions on orbital and suborbital timescales over the SW IbM. These records are directly compared and integrated with terrestrial – Mediterranean forest pollen – and marine – benthic and planktic oxygen stable isotopes (δ18O), alkenone concentration [C37], Uk´37‐Sea Surface Temperature and % C37:4 – proxy records from Site U1385. Our results indicate intra‐interglacial increase in primary productivity together with intensification of the Azores anticyclonic high‐pressure cell beyond the summer that suggests a two‐phase upwelling behavior during the full interglacial MIS 11c (∼420–397 ka), potentially drived by atmospheric NAO‐like variability. Primary productivity is largely enhanced during the inception of glacial MIS 10 and the early MIS 10 (∼392–356 ka), linked to intensified upwelling and associated processes during a period of strengthened atmospheric circulation. In agreement with the conditions observed during Heinrich events of the last glacial cycle, primary productivity reductions during abrupt cold episodes, including the Heinrich‐type (Ht) events 4 to 1 (∼436, 392, 384 and 339 ka) and the Terminations V and IV, seems to be the result of halocline formation induced by meltwater arrival, reducing the regional upward nutrient transference.

Authigenic Iron Sulfides Indicate Sea‐Level Change on the Continental Shelf: An Illustration From the East China Sea

AbstractAlthough sea‐level is the primary control over sedimentary architectures on continental shelves, deciphering such changes is still challenging, except for the easily recognized transgression‐regression cycles. This problem becomes more prominent in sedimentary units with relatively homogenous and fine‐grained lithologies that have been deposited over short periods. Here, we focus on a dominantly clayey silt section of a sediment core from the outer shelf of the East China Sea. Detailed rock magnetic and electron microscopy analyses indicate that authigenic greigite (Fe3S4) is the major magnetic component in an almost 4‐m‐thick interval that was deposited during the late Marine Isotope Stage (MIS) 3, while pyrite (FeS2) is enriched in the underlying middle MIS 3 sediments. According to microfossil analyses, the identified greigite formed in a prodelta setting that was affected by cold coastal currents after the middle MIS 3, when the Taiwan Warm Current and its associated upwelling were prevailing within a middle‐outer shelf setting favorable for pyrite formation. Large‐amplitude regression occurred subsequently during the MIS 2, limiting sulfate supply and favoring the greigite preservation. Our results, along with the previous studies, demonstrate that both the material and environmental conditions that are crucial to iron sulfide survival have been largely controlled by sea‐level change. Moreover, we make a preliminary proposition that a water depth range of 30–60 m is more likely to lead to the enrichment of greigite on continental shelves. We, therefore, provide a promising avenue for the assessment of sea‐level change on continental shelves over orbital and even suborbital timescales.

Correlation and anti-correlation of the Asian summer monsoon and westerlies during the Holocene

The relationship between the Asian summer monsoon (ASM) and westerlies at different timescales is still under discussion. In this paper, we present Holocene precipitation records derived from loess and lake sediment in the northeastern Tibetan Plateau and reconstruct changes in the strength of the ASM during the Holocene. Compared with other Eurasian paleohydroclimatic records, we find that precipitation variations between ASM- and westerlies-dominant regions are positively correlated (anti-correlated) at millennial (sub-orbital) timescales. Based on the analysis of the TraCE-21 results, we suggest that Atlantic meridional overturning circulation may be the primary reason for this in-phase pattern at millennial timescales whereas this anti-phased pattern at sub-orbital timescales is attributed to precessional changes. Due to different response mechanisms, the relationship between the ASM and westerlies may differ significantly at different timescales, which highlights the complex dynamic characteristics of atmospheric systems in the Northern Hemisphere and the challenges for future predictions.

Monsoon variations inferred from high-resolution geochemical records of the Linxia loess/paleosol sequence, western Chinese Loess Plateau

Chinese eolian deposits have been investigated intensively to reconstruct East Asian monsoon changes at tectonic to millennial timescales. However, high-resolution elemental proxies sensitive to rapid monsoon changes remains sparse. Here we present multiple elemental ratios of the Linxia loess sequence generated by scanning and conventional X-ray fluorescence (XRF) to assess East Asian monsoon variability at glacial-interglacial to sub-orbital timescales. The results show that 11 elements (Al, Si, K, Ca, Ti, Mn, Fe, Rb, Sr, Zr and Ba) can be reliably measured by XRF scanning of loess cores, albeit with relatively lower precision and increased noise levels (due to variable water content and matrix effects) when compared to XRF scanning of dry and homogenized powder samples. Seven elements (Ca, Fe, Ti, Mn, Zr, Rb and Sr), measured by XRF scanning of the core face and powder samples show high correlation (R2 > 0.7, n = 100) with those measured by conventional XRF methods, and thus can be considered as robust indicators for chemical weathering and grain-size sorting. We employ element ratios of Ca/Ti and Rb/Sr to reflect precipitation-induced weathering intensity, and the Zr/Rb ratio and mean grain size to infer the sorting effects related to winter-monsoon winds. These element ratios exhibit significant glacial-interglacial fluctuations, similar to records of magnetic susceptibility and mean grain size. Precessional- to millennial-scale monsoon changes are also persistent in our high-resolution elemental proxies, consistent with those in Gulang loess elemental ratios and Hulu/Sanbao speleothem δ18O records. Our results suggest that high resolution XRF scanning elemental ratios of Chinese loess have great potential for evaluating co-evolution of orbital- and millennial-scale monsoon variations.

Climate‐Induced Variability in Mediterranean Outflow to the North Atlantic Ocean During the Late Pleistocene

AbstractMediterranean Outflow Water (MOW) adds salt and density to open ocean intermediate waters and is therefore an important motor of Atlantic meridional overturning circulation (AMOC) and climate variability. However, the variability in strength and depth of MOW on geological timescales is poorly documented. Here we present new detailed records, with excellent age control, of MOW variability from 416 ka to present from rapidly accumulated marine sediments recovered from the West Iberian Margin during Integrated Ocean Drilling Program (IODP) Expedition 339. Our records of X‐ray fluorescence (XRF), physical grain size, and paleocurrent information from the anisotropy of magnetic susceptibility (AMS) indicate (i) a close relationship between the orientation of principle AMS axes and glacial‐interglacial cycles and (ii) two distinct regimes of MOW behavior over the last ~416 kyr in grain‐size and AMS variability at orbital (mainly precessional) and suborbital timescales. Between marine isotope stage (MIS) 10 and MIS 4, MOW was focused at a generally shallow depth on the West Iberian Margin, and changes in MOW strength were strongly paced by precession. A transition interval occurred during MISs 5 and 4, when MOW deepened and millennial‐scale variability in flow strength was superimposed on orbitally paced change. During MIS 11 and from MIS 3 to present, MOW was deeply focused and millennial‐scale variability dominated. We infer that late Pleistocene variability in MOW strength and depth were strongly climate influenced and that changes in circum‐Mediterranean rainfall climate were likely a primary control.

East Asian Precipitation δ18O Relationship With Various Monsoon Indices

AbstractChinese speleothem oxygen isotope (δ18O) variations have been widely interpreted as recording the evolution of the Asian Monsoon. However, calibration of δ18O to monsoon intensity has not yet been carried out in a quantitative way. To understand the climatic significance of δ18O, we measured monthly precipitation δ18O data at Heshang Cave, China, where speleothem δ18O records were previously obtained. We examined the influence of local climate and large‐scale atmospheric circulation on the δ18O by correlating to local meteorological data and various monsoon indices. We find neither a significant amount effect nor temperature effect, and therefore suggest that local climate is not the primary driver of δ18O variability. On seasonal timescales, monthly δ18O is significantly correlated to all monsoon indices, especially the Indian Monsoon (IM) and Western North Pacific Monsoon (WNPM) indices, proving δ18O responds dominantly to the tropical monsoon circulation. On interannual timescales, there are significant negative correlations between annual δ18O and the WNPM and IM monsoon indices defined by zonal winds, reflecting the impact of the El Niño‐Southern Oscillation on δ18O. Similar correlations between δ18O and precipitation amount in these monsoon regions lend further support to this finding. As the driving force of seasonal and interannual monsoon changes can be compared to variations on orbital and suborbital scales, respectively, we argue that speleothem δ18O in southern China is influenced by both external forcing and internal variability. Solar radiation plays an indispensable role on the orbital and seasonal scale δ18O variations, whereas ocean–atmosphere interactions are dominant on suborbital timescales.

Grain‐size Age Model in Reconstructing Orbital‐ and Suborbital‐scale Climate Changes on the Northeastern Tibetan Plateau Since the Late Glacial

AbstractReconstructions of past climatic changes on the northeastern Tibetan Plateau (NETP) can provide insights into the Asian summer monsoon (ASM) variability. However, the regional climate changes on both orbital and suborbital time scales since the late Glacial remain controversial. Here we present the results of high‐resolution geochemical and grain‐size analyses of a sediment core from Genggahai Lake, a small, shallow lake in this area. Changes of the accumulation rate of the core sediments show a similar trend with variations of the coarse fraction. Accordingly, the chronological framework is constructed using a grain‐size age model. In addition, the histories of chemical weathering and aeolian activity since the late Glacial are reconstructed based on the Al/Ti ratios and coarse fractions, respectively. The results suggest that an enhanced chemical weathering and a weakened aeolian activity occurred on the NETP under a warmer, wetter climate during the early to mid‐Holocene (11.3–6.3 ka cal BP), compared with the late Glacial (17.1–11.3 ka cal BP) and the late Holocene (6.3 ka cal BP to present), which responded mainly to the strengthened ASM on orbital time scale. In addition, the synchronous occurrences of weakened chemical weathering, low lake level and intense aeolian activity on suborbital time scale reflect several episodes of weakened ASM. Furthermore, these episodes largely coincide with the centennial‐ to millennial‐scale cold events in the North Atlantic, which demonstrates the close connection between the ASM and the cooling at high latitudes.

Late Quaternary loess accumulation at the Rudak section in Uzbekistan, central Asia: Chronology and palaeoclimate implications

Many studies have been carried out to understand the nature of the loess formation and its palaeoenvironmental significance in different parts of Eurasia, especially Europe and China. However, in spite of its key position, our knowledge about the loess deposits at the core of the Eurasian loess belt in central Asia is still limited, particularly in terms of absolute dating. This study presents a new luminescence chronology of a loess-palaeosol sequence (Rudak section) in the vicinity of the Gissar Range, Uzbekistan, using both quartz optically stimulated luminescence dating and polymineral post-IR IRSL dating techniques. The dating results suggested a loess accumulation history over the past 180 kyr at Rudak section, characterized by a great depositional hiatus during the entire last glacial period, likely owing to too harsh climate conditions for favouring dust accretion and loess preservation in the piedmont areas of central Asia. Hence, contrasting with the traditional concept of continuous (quasi-continuous) deposition of loess, the direct stratigraphical correlation might be problematic for climatic interpretation of loess-palaeosol sequence in this area. Furthermore, magnetic susceptibility of Rudak section demonstrated the moisture peaks in phase with ice-volume minima over the glacial and interglacial cycles, indicating moisture variation in the Westerlies-dominated central Asia was broadly consistent with that in monsoonal Asia on orbital timescales, but nearly contrasting picture with each other on the suborbital timescales, at least through the Holocene epoch. The Westerlies-dominated central Asia has generally experienced a dry first half and a wet second half of the Holocene, which has likely been driven by solar insolation gradients between mid-latitudes and high-latitudes as well as the melt-water flux.

Reconstructing Saharan dust transport to the Eastern Mediterranean Sea during the last 180 ka using endmember modelling of grain size data

AbstractEndmember modelling on the terrigenous silt fraction of nine marine sediment cores spanning up to 180,000 years reveals the influx of North African dust into the Eastern Mediterranean Sea. The dust grain size modes decrease with transport distance, from >50 µm off the African coast to ca. 30 µm in the Aegean Sea. The dust signal is strongly influenced by hydrological changes in northern Africa. Changes from arid to humid periods are documented in the grain size data of all cores. The climatic signal gets weaker with growing distance from the source and close to large fluvial sediment sources such as the Nile. Frequency and wavelet analyses show a strong orbital precession signal that is known to trigger the migration of the monsoonal rain belt in northern Africa. The influence of climate changes on suborbital time scales on dust influx is less distinct, but Dansgaard-Oeschger interstadials and Heinrich-like events are documented in some cores. In the sediment core closest to the source, three endmembers represent one or more dust sources in northern Africa. With growing distance from the source, the three modes cannot be separated anymore and appear as one multimodal dust endmember.

High-and low-latitude forcing of the East African climate since the LGM: Inferred from the elemental composition of marine sediments off Tanzania

We present X-Ray Fluorescence (XRF) Scanner measurements from a 6 m long sediment core (GeoB12624-1) on the upper slope of Tanzania to reconstruct the climatic evolution in East Africa since the Last Glacial Maximum (LGM). Log-ratios of Fe/Ca and Ti/Ca are indicative for sediment discharge of the Rufiji River, which is controlled by climatic conditions in the Rufiji catchment area. The most significant changes in major elemental composition occurred at 15.1 and 7.4 ka highlighted by the regime shift index values. The data set records distinct precipitation peaks during the early Holocene. This corresponds a maximum in the Northern Hemisphere (NH) summer insolation and results in a transition from the arid LGM to the humid early Holocene. Our geochemical record also indicates that this climatic transition was interrupted by two severe droughts that occurred during NH cold intervals: the Heinrich stadial 1 (HS1) and the Younger Dryas (YD). Through a comparison with other nearby paleoclimatic records, we suggest that arid climatic conditions only occurred in East Africa north of 8–10°S, whereas in southern East Africa around 15–20°S increased humidity during the HS1 and YD prevailed. We thus conclude that these two drought events were caused by a southward migration of the Intertropical Convergence Zone (ITCZ) which was fostered by the NH cooling during the HS1 and YD. Hence, our new geochemical record clearly documents that the East African climate not only responded to low-latitude insolation forcing on sub-orbital time scales, but also, was strongly influenced by high-latitude cooling during the HS1 and YD periods.