Aeolian Dust Input Research Articles

Aeolian dust deposition and the perturbation of phosphorus transformations during long-term ecosystem development in a cool, semi-arid environment

Abstract Aeolian dust deposition is an important phosphorus (P) input to terrestrial ecosystems, but its influence on P dynamics during long-term ecosystem development remains poorly understood. In this study, we characterized P speciation using P K-edge XANES spectroscopy in surface soils (0–15 cm, A horizon) and contemporary aeolian dust collected at each site of a 3000-ky volcanic soil chronosequence in a cool, semi-arid environment. Phosphorus speciation in dust was dominated by calcium-bound P (Ca-P; 54–74%), with 11–23% iron and aluminum-bound P [(Fe + Al)-P] and 7–25% organic P (Po). In soils, Po contributed 1–23% of total P, being greater in older soils; however, the proportions of Ca-P (16–39%) and (Fe + Al)-P (48–82%) fluctuated with increasing weathering over the soil chronosequence. These soil fluctuations resulted from the accumulation and preservation of alkaline aeolian dust during pedogenesis in the semi-arid climate, which significantly increased soil Ca-P while decreasing the total amounts and relative abundances of soil (Fe + Al)-P. We suggest that the effects of an aeolian dust input on soil P transformations are functions of the relative magnitude and chemical composition of the dust input and the soil weathering intensity. For a given source of dust, when the net dust flux is greater than the weathering rate, dust accumulates and thus alters the pattern of P transformations during pedogenesis; otherwise, the dust influence on soil P transformations is negligible. By accurately identifying the chemical nature of P pools, our work highlights the advantage of P K-edge XANES spectroscopy over chemical extractions in examining soil P dynamics, and demonstrates how dust inputs can modify the Walker and Syers model of pedogenic P transformations in semi-arid environments. Overall, this work provides a foundation for understanding how dust influences P cycling during soil and ecosystem development, and indicates that dust inputs and composition, and the soil weathering rate, all must be considered for developing integrated climate-biogeochemical models with predictive power in terrestrial ecosystems.

Role of dust fluxes in stimulating Ethmodiscus rex giant diatom blooms in the northwestern tropical Pacific during the Last Glacial Maximum

The strontium (Sr) and neodymium (Nd) isotope compositions and clay-mineral assemblages of the lithogenic fraction of sediments in the southern Mariana Trench together with major- and trace-elements concentrations of bulk sediments have been determined to trace the sediment provenance and investigate the relationship between Asian dust input and blooms of the giant diatom Ethmodiscus rex (E. rex). Enrichment of barium (Ba) in relative to upper continental crust (UCC) and low average Rb/K ratios in all study cores point to both hydrothermal and volcaniclastic inputs to the sediments. Both the Sr-Nd isotope compositions and the clay-mineral assemblages of the lithogenic fraction reflect a two-component mixing system consisting of Mariana arc volcaniclastics and Asian eolian dust. Decreases in smectite content and kaolinite/chlorite ratio and increases in illite content and illite/kaolinite ratio just preceding the formation of laminated diatom mats (LDMs) suggest changes in the source of the eolian dust from eastern Asian deserts (EADs) to central Asian deserts (CADs) at the onset of the Last Glacial Maximum (LGM) which stimulated the blooming of E. rex giant diatom. These observations suggest a potential causal linkage among atmospheric circulation patterns, the sources of Asian eolian dust, and marine productivity. We postulate that intensified eolian dust input sourced from CADs may have played a greater role in promoting biological productivity in the oligotrophic northwestern tropical Pacific Ocean during the LGM than previously realized.

An Integrated Study of the Eolian Dust in Pelagic Sediments From the North Pacific Ocean Based on Environmental Magnetism, Transmission Electron Microscopy, and Diffuse Reflectance Spectroscopy

AbstractEolian dust is a major terrigenous component in North Pacific Ocean pelagic sediments and is an important recorder of Asian terrestrial environmental evolution and Northern Hemisphere atmospheric circulation. In order to extract and quantify wind‐borne mineral signals and develop a reliable eolian dust proxy for pelagic sediments, we investigated sediments from Ocean Drilling Program Hole 885A, North Pacific Ocean, by integrating results from environmental magnetism, transmission electron microscopy, and diffuse reflectance spectroscopy (DRS). Our results indicate that ferrimagnetic and antiferromagnetic minerals coexist in the sediments. The former includes biogenic magnetite, nano‐sized single domain (titano) magnetite inclusions embedded in silicate hosts, submicron vortex state magnetite, and ultrafine superparamagnetic maghemite. The latter includes hematite and goethite. Our results indicate that magnetic properties can be used to determine an overall trend of increased eolian dust inputs, with additional significant influence from biogenic and volcanogenic components. In contrast, a newly proposed parameter RelHm+Gt (combined hematite and goethite concentration) obtained from DRS measurements extracts precisely the eolian signal and precludes other components. Our DRS results indicate that hematite/goethite and siliceous fractions deposited at Hole 885A were jointly delivered to the North Pacific Ocean from Asian dust sources. Therefore, we suggest that RelHm+Gt is a reliable eolian dust proxy for pelagic sediments in this region.

Abnormal Rb/Sr ratio in lacustrine sediments of Qaidam Basin, NE Qinghai–Tibetan Plateau: A significant role of aeolian dust input

The Rb/Sr ratio is an important indicator of weathering intensity in both lacustrine and loess sediments because of the inertness of the Rb element and the activity of the Sr element during the weathering process. Generally, the environmental interpretation of Rb/Sr ratio proxy in lacustrine sediments is contrary to that in the loess-paleosol sequence: it shows a negative correlation between the Rb/Sr ratio and chemical weathering intensity in lacustrine sediments, but shows a positive pattern in the loess-paleosol sequence. However, in this study, we investigated the Rb/Sr ratio of a lacustrine core (ISL1A) from Qarhan Salt Lake (QSL) in eastern Qaidam Basin (QB), and found the Rb/Sr ratio indicated a positive correlation with regional precipitation. This pattern is similar to that of the loess-paleosol sequence rather than the lacustrine sediments. According to grain size statistics and the comparison of Rb/Sr ratio with other proxies (halite and calcite contents, grain size, and F values of grain size discriminant function), we preliminarily proposed that the abundant input of aeolian materials, transported by the strong northwest wind, cause these unexpected Rb/Sr ratio fluctuations in the ISL1A core. The comparison between background Rb and Sr elemental data of relevant regions and these of the core indicated the aeolian origin of Rb/Sr ratio in the lacustrine sediments, and the Rb and Sr elemental composition probably represents the geochemical characteristics of the dust source area. The Sr-Nd isotopic composition indicates that the erosive paleo-lake strata in western QB could be the origin of aeolian materials in lacustrine sediments in the QSL, as well as the loess deposits in Dulan County, Qinghai Lake Basin, and Xining Basin. The regional correlation between proxies of the ISL1A core and other aeolian records also supports the aeolian origin of detrital input in the core. Finally, we propose that the origin of the detrital input must be distinguished before the Rb/Sr ratio is applied as a weathering intensity proxy in lacustrine sediments, especially in arid basins.

Central Tibetan Plateau atmospheric trace metals contamination: A 500-year record from the Puruogangri ice core

A ~500-year section of ice core (1497–1992) from the Puruogangri ice cap has been analyzed at high resolution for 28 trace elements (TEs: Ag, Al, As, Ba, Bi, Cd, Co, Cr, Cs, Cu, Fe, Ga, Li, Mg, Mn, Na, Nb, Ni, Pb, Rb, Sb, Sn, Sr, Ti, Tl, U, V and Zn) to assess different atmospheric contributions to the ice and provide a temporal perspective on the diverse atmospheric influences over the central Tibetan Plateau (TP). At least two volcanic depositions have significantly impacted the central TP over the past 500years, possibly originating from the Billy Mitchell (1580, Papua New Guinea) and the Parker Peak (1641, Philippines) eruptions. A decreasing aeolian dust input to the ice cap allowed the detection of an atmospheric pollution signal. The anthropogenic pollution contribution emerges in the record since the early 1900s (for Sb and Cd) and increases substantially after 1935 (for Ag, Zn, Pb, Cd and Sb). The metallurgy (Zn, Pb and steel smelting) emission products (Cd, Zn, Pb and Ag) from the former Soviet Union and especially from central Asia (e.g., Kyrgyzstan, Kazakhstan) likely enhanced the anthropogenic deposition to the Puruogangri ice cap between 1935 and 1980, suggesting that the westerlies served as a conveyor of atmospheric pollution to central Tibet. The impact of this industrial pollution cumulated with that of the hemispheric coal and gasoline combustion which are respectively traced by Sb and Pb enrichment in the ice. The Chinese steel production accompanying the Great Leap Forward (1958–1961) and the Chinese Cultural Revolution (1966–1976) is proposed as a secondary but proximal source of Pb pollution affecting the ice cap between 1958 and 1976. The most recent decade (1980–1992) of the enrichment time series suggests that Puruogangri ice cap recorded the early Sb, Cd, Zn, Pb and Ag pollution originating from developing countries of South (i.e., India) and East (i.e., China) Asia and transported by the summer monsoonal circulation.

Planktonic Lipidome Responses to Aeolian Dust Input in Low-Biomass Oligotrophic Marine Mesocosms

The effect and fate of dry atmospheric deposition on nutrient-starved plankton in the Eastern Mediterranean Sea (EMS; Crete, 2012) by spiking oligotrophic surface seawater mesocosms (3 m3) with Saharan dust (SD; 1.6 g L-1; 23 nmol NOx mg-1; 2.4 nmol PO4 mg-1) or mixed aerosols (A; 1.0 g L-1; 54 nmol NOx mg-1; 3.0 nmol PO4 mg-1) collected from natural and anthropogenic sources. Using high resolution liquid chromatography-mass spectrometry, the concentrations of over 350 individual lipids were measured in suspended particles to track variations in the lipidome associated with dust fertilization. Bacterial and eukaryotic intact polar lipid (IPL) biomarkers were categorized into 15 lipid classes based on headgroup identity, including four novel IPL headgroups. Bulk IPL concentrations and archaeal tetraether lipids were uncoupled with the doubling of chlorophyll concentrations that defined the stimulation response of oligotrophic plankton to SD or A amendment. However, molecular level analysis revealed the dynamics of the IPL pool, with significant additions or losses of specific IPLs following dust spikes that were consistent among treatment mesocosms. Multivariate redundancy analysis further demonstrated that distribution of IPL headgroups and molecular modifications within their alkyl chains were strongly correlated with the temporal evolution of the plankton community and cycling of phosphate. IPLs with phosphatidylcholine, betaine, and an alkylamine-like headgroup increased in the post-stimulated period, when phosphate turnover time had decreased by an order of magnitude and phosphorus uptake was dominated by plankton > 2 µm. For most IPL classes, spiking with SD or A yielded significant increases in the length and unsaturation of alkyl chains. A lack of corresponding shifts in the plankton community suggests that the biosynthesis of nitrogenous and phosphatidyl lipids may respond to physiological controls during episodic additions of dust to the EMS. Furthermore, alkyl chain distributions of IPLs containing N, P, and S invoked a bacterial source, suggesting that bacterioplankton are able to modulate these lipids in response to nutrient stress.

Provenance of late Quaternary sediments on the southwestern slope of the Ulleung Basin, East/Japan Sea

The provenance of fine-grained sediments deposited since the late Quaternary was recovered from drill site UBGH2-1_1 on the southwestern slope of the Ulleung Basin, East/Japan Sea. Based on geochemical analyses, including rare earth elements (REEs), the fine-grained sediments could be interpreted as mixtures of sediments from China via various pathways and sediments discharged from the Nakdong River (NRS). A comparison of variations in REE fractionation factor with Marine Isotope Stages (MISs) indicated that the provenance of the fine-grained sediments on the southwestern slope of the Ulleung Basin was controlled by global eustatic sea-level change. During glacial periods, most of the fine-grained sediments were supplied via the atmospheric pathway by an intensified East Asian Winter Monsoon, and sediments from Chinese rivers (CRS) transported into the Ulleung Basin through the Korea Strait were limited due to the morphological characteristics of the Korea Strait and low sea-level. During interglacial periods, The CRS transported into the Ulleung Basin through the Korea Strait increased with sea-level rise and eolian dust inputs decreased due to attenuated East Asian Winter Monsoon. Simultaneously, NRS also should have been deposited when sea-level was higher than −40 m relative to present sea-level during MIS 1 and MIS 5. In particular, during MIS 1, signals of NRS were revealed since 11 ka; thus, it can be suggested that the present coastal current system around the southeastern coast of Korea became established by around 11 ka.

Eolian dust forcing of river chemistry on the northeastern Tibetan Plateau since 8 Ma

Eolian dust is one of the most important factors controlling fluvial hydrological evolution in modern arid and semi-arid central Asia. Here, we present the bulk carbonate Ca–Mg–Sr concentrations and Sr isotopic compositions recorded in water soluble salts, carbonate and silicate fractions, as well as the Nd isotopic compositions in the silicate fraction of a Late Miocene (12.2–5.1 Ma) fluvial sequence exhibiting paleosol development, in the Linxia Basin on the northeastern Tibetan Plateau (TP). Bulk carbonate Mg–Sr systematics show a distinct pattern in log–log plots of Mg/Ca versus log Sr/Ca ratios, and clearly higher 87Sr/86Sr ratios since ∼8 Ma. These findings cannot be adequately explained by the mechanism of prior calcite precipitation (PCP) – this latter process results in a positive correlation between the Mg/Ca and Sr/Ca ratios in authigenic calcite, evident in the fixed gradient in their log–log plots and has been isolated as being the major factor controlling carbonate Mg–Sr systematics before 8 Ma. Nor can these findings be explained by other mechanisms related to the catchment's provenance/sedimentation. The dramatic changes in carbonate Sr contents, Sr isotopes, and Sr/Mg ratios since ∼8 Ma may therefore be inferred to have been triggered by significant inputs of eolian dust via the dissolution of dust carbonates and evaporites in the paleowaters where fluvial and paleosol carbonates precipitated. This process of eolian dust input can be reliably illustrated using a binary mixing model corresponding to a series of varying PCP fluxes (identical to processes affecting the area before 8 Ma) combined with a constant eolian influx calculated from the co-variations between Mg/Ca, Sr/Ca and Sr isotopic ratios. Eolian dust also leaves a fingerprint in the carbonate and silicate minerals of bulk sediments, as revealed respectively by their Sr and Nd isotopic compositions. Eolian dust compositions for the ∼8–5 Ma on the northeastern TP can thus be taken to be characterized by a εNd value ≤−10.5 for the silicate fraction, and by a 87Sr/86Sr value ≥0.7115 for the labile faction (carbonates and evaporites). Eolian dust is now recognized to have made a significant impact on the hydrological evolution of arid and semi-arid northern China as far back as ∼8 Ma, suggesting an enhanced regime of dust activity and regional aridification in central Asia at that time.

High‐latitude forcing of diatom productivity in the southern Agulhas Plateau during the past 350 kyr

AbstractThe hydrography of the Indian‐Atlantic Ocean gateway has been connected to high‐latitude climate dynamics by oceanic and atmospheric teleconnections on orbital and suborbital timescales. A wealth of sedimentary records aiming at reconstructing the late Pleistocene paleoceanography around the southern African continent has been devoted to understanding these linkages. Most of the records are, however, clustered close to the southern South African tip, with comparatively less attention devoted to areas under the direct influence of frontal zones of the Southern Ocean/South Atlantic. Here we present data of the composition and concentration of the diatom assemblage together with bulk biogenic content and the alkenone‐based sea surface temperature (SST) variations for the past 350 kyr in the marine sediment core MD02‐2588 (approximately 41°S, 26°E) recovered from the southern Agulhas Plateau. Variations in biosiliceous productivity show a varying degree of coupling with Southern Hemisphere paleoclimate records following a glacial‐interglacial cyclicity. Ecologically well‐constrained groups of diatoms record the glacial‐interglacial changes in water masses dynamics, nutrient availability, and stratification of the upper ocean. The good match between the glacial maxima of total diatoms concentration, Chaetoceros spores abundance, and opal content with the maximum seasonal cover of Antarctic ice and the atmospheric dust records points to a dominant Southern Hemisphere forcing of diatom production. Suborbital variability of SST suggests rapid latitudinal migrations of the Subtropical Front and associated water masses over the southern Agulhas Plateau, following millennial contractions and expansions of the subtropical gyres. Warmings of the upper ocean over site MD02‐2588 during terminations IV to I occurred earlier than that in the Antarctic Vostok, which is indicative of a Northern Hemisphere lead. Our multiparameter reconstruction highlights how high‐latitude atmospheric and hydrographic processes modulated orbital highs and lows in primary production and SST as triggered by northward transport of Si, eolian dust input, and latitudinal migrations of frontal zones.

The role of climate and aeolian dust input in calcrete formation in volcanic islands (Lanzarote and Fuerteventura, Spain)

Calcretes are widely described in non-marine settings with carbonates in their catchment, or vicinity areas, but in volcanic islands without carbonates in their substrate, calcretes are not very common. In Lanzarote and Fuerteventura Canary Islands, characterized by impressive volcanic landscapes, the sedimentary carbonate rocks are rare except for some recent marine and aeolian deposits. In these settings very well-developed calcretes cover large areas of the present landscape. The source of calcium required for the formation of these calcretes has not been discussed in much detail till now, although its role is critical to an understanding of the climatic conditions in which calcium was transported and fixed and of the calcrete formation processes. The petrological and geochemical studies (87Sr/86Sr ratios, δ13C, δ18O, major, trace and REE) carried out in this paper do confirm the important role of aeolian dust input in the formation of these calcretes. Canarian calcretes were mainly generated by pedogenic processes and are composed of various irregular carbonate lamina interbedded with fine clastic deposits. Our study indicates that these interbeddings were the result of several stages in which, during dry periods, aeolian dust deposition alternated with leaching and calcite precipitation during wetter periods when plants, insects and bacteria played an important role in carbonate precipitation. The δ18O (−2.70 to +2.22‰ VPDB) and δ13C (−8.21 to +0.24‰ VPDB) values indicate that calcretes were formed by pedogenic processes. Comparison of calculated ∆18O values for the Canary calcretes with continental mid-latitude calcrete values reflects the more homogeneous temperature regimes of calcrete formation in island (oceanic) settings. Calcrete87Sr/86Sr ratios (0.706357 to 0.709208) show strong affinity with those obtained in aeolian carbonate dust and marine deposits, and are relatively different from those obtained in basalts. REE, major and trace element concentrations show that Ca-bearing minerals from volcanic host rock contributed little to calcrete formation and most of the calcium was supplied by aeolian deposits such as the aeolian dust coming from the Sahara and Sahel or sand dunes.

Assemblage characteristics of clay minerals and its implications to evolution of eolian dust input to the Parece Vela Basin since 1.95 Ma

To understand the provenance and evolution of eolian input in the last 1.95 Ma in the Parece Vela Basin in the eastern Philippine Sea, the clay mineral assemblage of a gravity core PV090510 from the basin was investigated using paleogeomagnetic dating and X-ray diffraction. The assemblage of the core mainly consisted of smectite (46%) and illite (40%), with some chlorite (10%) and kaolinite (4%). Analysis of the provenance of these minerals suggested that smectite was mainly derived from volcanic rocks of the Mariana Arc, while illite, chlorite, and kaolinite were mainly transported as eolian dust by the East Asian monsoon from central Asia. We used the ratio of (illite+chlorite+kaolinite)/smectite as a proxy for Asian eolian input to the Parece Vela Basin since 1.95 Ma. This ratio followed glacial and interglacial cycles and was consistent with the intensity of the East Asian monsoon and aridity of central Asia since 1.95 Ma. The changes of the ratio reflected three different stages of the East Asian monsoon and provenance climate.

Eolian dust input to the Subarctic North Pacific

Eolian dust is a significant source of iron and other nutrients that are essential for the health of marine ecosystems and potentially a controlling factor of the high nutrient-low chlorophyll status of the Subarctic North Pacific. We map the spatial distribution of dust input using three different geochemical tracers of eolian dust, 4He, 232Th and rare earth elements, in combination with grain size distribution data, from a set of core-top sediments covering the entire Subarctic North Pacific. Using the suite of geochemical proxies to fingerprint different lithogenic components, we deconvolve eolian dust input from other lithogenic inputs such as volcanic ash, ice-rafted debris, riverine and hemipelagic input. While the open ocean sites far away from the volcanic arcs are dominantly composed of pure eolian dust, lithogenic components other than eolian dust play a more crucial role along the arcs. In sites dominated by dust, eolian dust input appears to be characterized by a nearly uniform grain size mode at ∼4 μm.Applying the 230Th-normalization technique, our proxies yield a consistent pattern of uniform dust fluxes of 1–2 g/m2/yr across the Subarctic North Pacific. Elevated eolian dust fluxes of 2–4 g/m2/yr characterize the westernmost region off Japan and the southern Kurile Islands south of 45° N and west of 165° E along the main pathway of the westerly winds. The core-top based dust flux reconstruction is consistent with recent estimates based on dissolved thorium isotope concentrations in seawater from the Subarctic North Pacific. The dust flux pattern compares well with state-of-the-art dust model predictions in the western and central Subarctic North Pacific, but we find that dust fluxes are higher than modeled fluxes by 0.5–1 g/m2/yr in the northwest, northeast and eastern Subarctic North Pacific. Our results provide an important benchmark for biogeochemical models and a robust approach for downcore studies testing dust-induced iron fertilization of past changes in biological productivity in the Subarctic North Pacific.

Climate mediated size variability of diatom Fragilariopsis kerguelensis in the Southern Ocean

Fragilariopsis kerguelensis (O'Meara) Hustedt is the most abundant open ocean diatom species in Southern Ocean sediments and its average valve area has recently been used to infer glacial–interglacial paleoceanographic conditions. Studies from the Atlantic sector of the Southern Ocean demonstrated how larger average valve area of F. kerguelensis during the Last Glacial compared to the interglacial possibly relate to greater availability of iron (through wider sea ice coverage and higher eolian dust input). We present here data on average valve area of F. kerguelensis from three sediment cores covering the last ∼42 cal ka BP from different zones of the Southern Ocean. Our records confirm previous results from the Atlantic sector, but highlight a different pattern from the Indian sector where the largest valves of F. kerguelensis are encountered during the Holocene. Fragilariopsis kerguelensis average valve area variations in the Antarctic Polar Front (APF) of the Atlantic sector and Subantarctic Front of the Indian sector are in phase with records of opal burial while this correlation does not hold for the APF of the Indian sector. Variations in circum-polar upwelling were suggested as the main controlling factor of opal production during the last 20,000 years. We here hypothesize that high nutrient input from the Antarctic Peninsula during the last deglaciation may have exerted a stronger control on F. kerguelensis average valve area and opal export in the Atlantic sector of the Southern Ocean than inferred changes in circum-polar upwelling.

High- and low-latitude forcing of the Nile River regime during the Holocene inferred from laminated sediments of the Nile deep-sea fan

Sediments deposited on deep-sea fans are an excellent geological archive to reconstruct past changes in fluvial discharge. Here we present a reconstruction of changes in the regime of the Nile River during the Holocene obtained using bulk elemental composition, grain-size analyses and radiogenic strontium (Sr) and neodymium (Nd) isotopes from a sediment core collected on the Nile deep-sea fan. This 6-m long core was retrieved at ∼700m water-depth and is characterized by the presence of a 5-m thick section of finely laminated sediments, which were deposited between 9.5 and 7.3ka BP and correspond to the African Humid Period (AHP). The data show distinct changes in eolian dust inputs as well as variations in discharge of the Blue Nile and White Nile. Sedimentation was mainly controlled by changes in fluvial discharge during the Holocene, which was predominantly forced by low-latitude summer insolation and by the location of the eastern African Rain Belt. The changes in relative contribution from the Blue Nile and White Nile followed changes in low-latitude spring/autumn insolation, which highlights the role of changes in seasonality of the precipitation on the Nile River regime. The relative intensity of the Blue Nile discharge was enhanced during the early and late Holocene at times of higher spring insolation (with massive erosion and runoff during the AHP at times of high summer insolation), while it was reduced between 8 and 4ka at times of high autumn insolation. The gradual insolation-paced changes in fluvial regime were interrupted by a short-term arid event at 8.5–7.3ka BP (also associated with rejuvenation of bottom-water ventilation above the Nile fan), which was likely related to northern hemisphere cooling events. Another arid event at 4.5–3.7ka BP occurred as the apex of a gradually drier phase in NE Africa and marks the end of the AHP.

Paleoenvironments during the Rhaetian transgression and the colonization history of marine biota in the Fatric Unit (Western Carpathians)

Abstract Terminal Triassic environmental changes are characterized by an integrated study of lithology, litho- and cyclostratigraphy, paleontology, mineralogy, geochemistry and rock magnetism in the Tatra Mts. The Carpathian Keuper sequence was deposited in an arid environment with only seasonal rivers, temporal lakes and swamps with scarce vegetation. Combination of a wide range of δ18O values (-0.7 to + 2.7) with negative δ13C values documents dolomite precipitation either from brackish or hypersaline lake water, or its derivation from pore water comparably to the Recent Coorong B-dolostone. Negative δ13C values indicate microbial C productivity. Rhaetian transgressive deposits with restricted Rhaetavicula fauna accumulated in nearshore swamps and lagoons. Associations of foraminifers, bivalves and sharks in the Zliechov Basin were controlled by physical factors. Bivalve mollusc biostromes were repetitively destroyed by storms, and temporary firm bottoms were colonized by oysters and burrowers. Subsequent black shale deposition recorded input of eolian dust. Bottom colonization by pachyodont bivalves, brachiopod and corals started much later, during highstand conditions. Facies evolution also revealed by geochemical data, C and O isotope curves reflect eustatic and climatic changes and help reconstruct the evolution of Rhaetian marine carbonate ramp. The Fatra Formation consists of 100 kyr eccentricity and 40 kyr obliquity cycles; much finer rhythmicity may record monsoonlike climatic fluctuations. Fluvial and eolian events were indicated by analysis of grain size and content of clastic quartz, concentrations of foraminiferal (Agathammina) tests in thin laminae indicates marine ingression events. Magnetic susceptibility (MS) variations reflect the distribution of authigenic and detrital constituents in the sequence. Increasing trend of MS correlates with the regressive Carpathian Keuper sequence and culminates within the bottom part of the Fatra Formation. Decreasing trend of MS is observed upwards the transgressive deposits of the Fatra Formation.

Sediment provenance and evolution of the East Asian winter monsoon since 700 ka recorded by major elements in the West Philippine Sea

To synthetically realize the character of major-element compositions as well as its significance for provenance and paleoenvironment recorded in core sediments of the West Philippine Sea over the last 700 ka, grain size and major elements of 221 bulk sediments, together with major-element compositions in the detrital phase of 16 typical samples, in core MD06-3047 collected from the Benham Rise were analyzed. Both discrimination plot and R-mode factor analysis indicate that vertical changes of major elements are mainly controlled by the sedimentation of nearby volcanic matter and the eolian dust input, whereas influences from marine biologic deposition and hydrothermal activity are minor. In particular, Al2O3 and K2O are representative of an eolian dust factor. The variation in the eolian dust factor score is characterized by the obviously glacial-interglacial periodicity and can be well compared with the paleotemperature record of the Antarctic ice core and the evolution of the East Asian winter monsoon (EAWM) recorded in the Chinese loess sequence, and then offers a new proxy for the evolution history of eolian dust input into the study area that is controlled by the EAWM intensity and aridity in the continental source regions of atmospheric dust.

The role of Volcanic vs Seismic actions in ground deformations recorded in Oceanic Volcanic Islands: Examples from the Eastern Canary Islands (Spain)

Calcretes are widely described in non-marine settings with carbonates in their catchment, or vicinity areas, but in volcanic islands without carbonates in their substrate, calcretes are not very common. In Lanzarote and Fuerteventura Canary Islands, characterized by impressive volcanic landscapes, the sedimentary carbonate rocks are rare except for some recent marine and aeolian deposits. In these settings very well-developed calcretes cover large areas of the present landscape. The source of calcium required for the formation of these calcretes has not been discussed in much detail till now, although its role is critical to an understanding of the climatic conditions in which calcium was transported and fixed and of the calcrete formation processes. The petrological and geochemical studies (87Sr/86Sr ratios, δ13C, δ18O, major, trace and REE) carried out in this paper do confirm the important role of aeolian dust input in the formation of these calcretes. Canarian calcretes were mainly generated by pedogenic processes and are composed of various irregular carbonate lamina interbedded with fine clastic deposits. Our study indicates that these interbeddings were the result of several stages in which, during dry periods, aeolian dust deposition alternated with leaching and calcite precipitation during wetter periods when plants, insects and bacteria played an important role in carbonate precipitation. The δ18O (− 2.70 to + 2.22‰ VPDB) and δ13C (− 8.21 to + 0.24‰ VPDB) values indicate that calcretes were formed by pedogenic processes. Comparison of calculated ∆18O values for the Canary calcretes with continental mid-latitude calcrete values reflects the more homogeneous temperature regimes of calcrete formation in island (oceanic) settings. Calcrete87Sr/86Sr ratios (0.706357 to 0.709208) show strong affinity with those obtained in aeolian carbonate dust and marine deposits, and are relatively different from those obtained in basalts. REE, major and trace element concentrations show that Ca-bearing minerals from volcanic host rock contributed little to calcrete formation and most of the calcium was supplied by aeolian deposits such as the aeolian dust coming from the Sahara and Sahel or sand dunes.

Simulating atmospheric CO2, 13C and the marine carbon cycle during the Last Glacial–Interglacial cycle: possible role for a deepening of the mean remineralization depth and an increase in the oceanic nutrient inventory

Using the Earth system model of intermediate complexity Bern3D, we transiently simulate changes in atmospheric CO2 and climate over the Last Glacial–Interglacial cycle. A third of the glacial–interglacial atmospheric CO2 change can be explained by relatively well-established forcings such as temperature, salinity, a shallowing and weakening of the Atlantic Meridional Overturning Circulation, iron fertilization of the marine biosphere by aeolian dust input and land carbon inventory changes. A 10% increase in the oceanic phosphate inventory decreases atmospheric CO2 by 50 ppmv during the glaciation, however due to the long residence time of phosphorus in the ocean and the long time scales of ocean–sediment interactions it only contributes to a 5 ppmv increase between 20 and 0 ka B.P. The enhanced surface nutrient utilisation simulated as a result of a greater oceanic phosphate inventory leads to a good representation of glacial export production and δ13CO2 changes, lending support to this hypothesis. A deepening of particulate organic matter remineralization can effectively lower pCO2 during the glaciation, however it leads to a significant increase in deep [CO32−] and to changes in export production in poor agreement with paleo-proxies. Finally the parametrization of brine rejection around Antarctica could lead to 10–20 ppmv change in pCO2, but its timing casts doubt onto its effectiveness in forcing CO2 variations over the Last Glacial–Interglacial cycle. The results highlight the importance of a transient, 3-dimensional setting for the interpretation of proxy records.

Glacial‐interglacial size variability in the diatom Fragilariopsis kerguelensis: Possible iron/dust controls?

The valve area of Fragilariopsis kerguelensis, the most abundant diatom species in the Southern Ocean, strongly changes in size in response to varying conditions in the surface ocean. We examined the link, both in two iron fertilization experiments and in sediment samples covering several glacial Terminations, between size variability in this species and environmental conditions across the Antarctic Polar Front, including sea ice extent, sea surface temperature, and the input of eolian dust. The iron fertilization experiments show valve area to be positively correlated with iron concentrations in ambient waters, which suggests the possibility of a causal relation between valve size of Fragilariopsis kerguelensis and ambient surface water iron concentration. Larger valves are usually found during glacial times and thus seem to be related to lower sea surface temperature and wider sea ice coverage. Moreover, our results indicate that there usually is a strong correlation between larger valve size and increased input of eolian dust to the Southern Ocean. However, this correlation, obvious for the fertilization experiments and for glacial Terminations I, II, III, and V, does not seem to be valid for Termination VI, where size appears to be inversely correlated to dust input.

Impact of climate variability in the western Mediterranean during the last 20,000 years: oceanic and atmospheric responses

Eolian input fluctuations and paleoceanographic conditions in the western Mediterranean have been reconstructed by using a multi-proxy approach to infer climate variability for the last 20,000 yr. A sediment core from the East Alboran Sea basin provides high-resolution geochemical, mineralogical and grain size distribution records from the Last Glacial Maximum onward. The accurate chronology obtained, closely related with the North Greenland Ice core Project, has provided a detailed paleoclimate reconstruction at the centennial–millennial time scale. Mineral and chemical compositions as well as sediment grain size distribution have been used to establish both fluvial and eolian input variations, deep-water current intensity, and ventilation and productivity conditions at the time of deposition. During the cold period Greenland Stadial-2a, the analyzed proxies evidence significant climate oscillations. Redox proxies, showing marked Mn/Al and Fe/Al peaks, as well as granulometric parameters, support major changes in thermohaline circulation, with active circulation triggered by the Western Mediterranean Deep Water formation. Ba/Al ratios and the presence of authigenic barite point to high productivity during the Last Heinrich event. At this time, Zr/Al, Si/Al and Ti/Al ratios as well as quartz and palygorskite contents also corroborate dryer conditions in the Alboran borderlands, with a major reorganization of atmospheric circulation at the beginning of the deglaciation and during the Last Heinrich event. In contrast, a decreasing trend in the Zr/Al ratio and increasing Mg/Al, K/Al and illite + chlorite/kaolinite ratios would indicate enhanced river runoff and supporting lower eolian dust input and wetter periods during the Bölling–Alleröd. Short-term and abrupt climate oscillations such as the Intra-Alleröd Cold Period are likewise reflected by minor yet conspicuous changes in eolian proxies. During the Younger Dryas, we distinguish an initial cold and dry phase, with major westerlies intensity, thermohaline reactivation, and high productivity levels, and a second wetter phase characterized by sporadic rainfalls over poorly vegetated surrounding continental areas. Then, during the Holocene, alternating phases of major humidity and aridity were recorded by major fluctuations in detrital input. These are also correlated with recurrent forest cover declines reported from pollen records, with a noteworthy early decline in the African Humid Period. During the Holocene, an initial demise of the Last Organic-Rich Layer is also evidenced, tentatively associated with aspiration forces promoted by intense thermohaline circulation through the Gibraltar Strait.