Aeolian Dust Input Research Articles

Early Pleistocene Orbital‐Scale Variability in Australian Northwest Shelf Sediments

AbstractPaleoclimate proxy records from regions sensitive to humidity/aridity extremes provide crucial insights into the natural forcing mechanisms underlying long‐term climate variability in broader regions. One such area is Northwest Australia, where the Australian monsoon impacts its northernmost fringes, which are bordered by the Great Sandy Desert inland. Marine sediments from the Australian Northwest Shelf record fluvial run‐off and eolian dust input during the wet and dry seasons, respectively. The location is therefore ideal for investigating long‐term variability in the Australian monsoon and Northwest Australian dust flux over orbital timescales. However, there are few continuous, high‐resolution paleoclimate records from this region spanning the early Pleistocene, when strong ice‐climate feedbacks of the late Pleistocene did not yet dominate global climate. Here, we present geochemical and environmental magnetic proxy records that reveal %CaCO3 and dust‐flux variability between 2.9 and 1.6 million years (Myr) ago from International Ocean Discovery Program Expedition 356 Site U1464 on the Australian Northwest Shelf. We establish a new, orbitally‐tuned chronology for Site U1464, primarily based on ∼400 thousand year (kyr) eccentricity cyclicity in %CaCO3, and observe strong obliquity variability (41 and 54 kyr periodicities) but almost no precession signal in the dust‐flux records. We propose that the 41 kyr cycle in Northwest Australian dust flux could be a linear response to East Asian winter monsoon intensity and/or the summer inter‐tropical insolation gradient (SITIG), whereas the 54 kyr cyclicity might be a non‐linear response to obliquity amplitude modulation via the SITIG effect on the cross‐equatorial atmospheric circulations.

Deep-sea response to interglacial-glacial variability on the South Australian margin over the last 94 ka

The continuous record offered by deep-sea sediments has been extensively used to constrain shifting continental and oceanographic conditions. Yet, past fluctuations in deep-sea benthic conditions and bottom-currents are in numerous parts of the globe scarcely documented, one such example being the South Australian margin. Indeed, though variations in surface water masses and continental aeolian dust and river outflow are well documented in the area, little is known about benthic environments and their dynamics during the last interglacial-glacial cycle. We focus here on benthic foraminiferal assemblages sampled from a sediment core recovered at 2420 m depth from a small plateau south of Kangaroo Island within the underwater Murray Canyons Group (South Australian margin). Benthic foraminiferal assemblages show a distinct separation between interglacial and glacial periods over the last 94 ka, and indicate that the benthic environment was well-ventilated and oligotrophic during glacial periods, whilst being rather marked by reduced oxygenation associated to higher food input during the Holocene and Marine Isotope Stage 5a-c. We demonstrate that autochtonous deep-sea benthic foraminiferal communities neither respond to changes in the Murray River's discharges, nor do they follow variations in aeolian dust input from South Australia. Instead, the deep-sea and the terrestrial realm appear decoupled. Moreover, our observations suggest that bottom-water slope currents were stronger during the Holocene and Marine Isotope Stage 5a-c. We propose that this strengthening was triggered by an intensification of the poleward-circulating deep eastern boundary current transporting carbon-rich Indian Deep Water. In contrast, glacial seafloor conditions, especially during the Last Glacial Maximum, may reflect a greater influence and a shoaling of oxygen-rich Antarctic Bottom Water of South Australia. This bottom-water shift would follow the northward displacement of the Subtropical and Subantarctic Fronts and coincide with a withering influence of the Leeuwin Current within surface waters.

Environmental magnetic characterization for the Pialli Level and the Cretaceous Oceanic Red Bed 7 (late Albian, Poggio le Guaine core, central Italy)

The mid-Cretaceous is known as the most extreme greenhouse period in the last 150 Myr and was punctuated by repeated environmental perturbations. The mid-Cretaceous was also characterized by the emplacement of major Large Igneous Provinces and the deposition of organic-rich layers known as Oceanic Anoxic Events. Here, we present a high-resolution environmental magnetic and stable isotopic records of the western Tethyan pelagic interval in the Poggio le Guaine (PLG, Italy) core, deposited during the late Albian. Environmental magnetic data are here applied to detect redox and paleoproductivity variations across the OAE 1d and CORB 7 events. Combing the magnetic data and geochemical data from carbon (δ13C) and oxygen (δ18O) isotopic records, we document changes in the paleoenvironmental conditions across the Pialli Level and CORB 7 events in the Tethyan realm. The magnetic properties of the 10-m-thick pelagic marine sediments of the PLG core record the onset between upper part of Cretaceous Oceanic Red Bed 7 (CORB 7) and the Pialli Level that is a part of the Oceanic Anoxic Event (OAE) 1d. An increase in the magnetic mineral concentrations with hematite and goethite as the main magnetic carrier characterizes the upper CORB 7 sediments. Variations in “hard” isothermal remanent magnetization and the S-ratio during the upper CORB 7 are interpreted as changes in aeolian dust input into the Umbria-Marche Basin. During the interval between the upper part of CORB 7 and OAE 1d (Pialli Level), the magnetic mineral concentration decreases, and the magnetic mineralogy changes from hematite to magnetite, suggesting a change in the oceanic system. This change might be associated to an increase in orbital forcing capable of modulating the monsoon activity at the onset of the Pialli Level. First-order reversal curves for all samples from the PLG core are similar and indicate a dominance of detrital magnetite. The absence of magnetically non-interacting single domain biogenic particles suggests that an increase in primary productivity was not significant or variation of the anoxic-oxic boundary could have also occurred. Finally, our records show cyclic alterations that reflect changes in the terrigenous input that was triggered by a period of enhanced orbital forcing paced by monsoonal systems.

Lake eutrophication in northeast China induced by the recession of the East Asian summer monsoon

Lakes are one of the most important freshwater resources on Earth and they provide a wide range of ecosystem services. However, due to rapid economic development and the intensification of human activities, many lakes have become eutrophic, which may threaten their status as water resources. Human activities have played a significant role in lake eutrophication, but whether this role is independent of, or coupled with, natural climate change requires further study. We selected Dali Lake, a large lake affected by human activity within the ancient warfare borders, to clarify the ecological response of a lake to climate change and human activity. We used analyses of sedimentary n-alkanes and AMS 14C dating to reconstruct the paleolimnological evolution of Dali Lake since 15 cal kyr BP, and specifically to assess the timing and causes of eutrophication. The results show that the short-chain n-alkanes (C17–19-alkanes) in Dali Lake are mainly produced by bacteria and algae within the lake, and that the sedimentary absolute abundance of short-chain n-alkanes (A17–19-alkanes) can be used as a proxy for assessing the ecological status of the lake. The ecological status of Dali Lake was the most stable during the early to middle Holocene, when the East Asian summer monsoon was strong, but bacterial and algal outbreaks occurred during three episodes of a weakened summer monsoon—the Older Dryas, Younger Dryas, and the Common Era—when the lake experienced different degrees of eutrophication. During the recession of the East Asian summer monsoon, the weakening of precipitation recharge of the lake led to a reduction in lake area and an increase in nutrient concentrations in the lake water, while aeolian dust input was an additional nutrient source, leading to bacterial and algal outbreaks. During the Common Era, lake eutrophication occurred in the context of both summer monsoon recession and enhanced human activities, but their combined effects did not lead to more intense lake eutrophication than was caused by monsoon recession during the Younger Dryas. We conclude that, although human activities have enhanced the eutrophication of Dali Lake, the reduction in lake size due to monsoon recession and the resulting increase in the salinity and nutrient concentration of the lake water, combined with increased aeolian inputs, were a more important trigger of lake eutrophication.

Climate, vegetation and fire history during the past 18,000\xa0years, recorded in high altitude lacustrine sediments on the Sanetti Plateau, Bale Mountains (Ethiopia)

Low-altitude lakes in eastern Africa have long been investigated and have provided valuable information about the Late Quaternary paleohydrological evolution, such as the African Humid Period. However, records often suffer from poor age control, resolution, and/or ambiguous proxy interpretation, and only little focus has been put on high-altitude regions despite their sensitivity to global, regional, and local climate change phenomena. Here we report on Last Glacial environmental fluctuations at about 4000 m asl on the Sanetti Plateau in the Bale Mountains (SE Ethiopia), based on biogeochemical and palynological analyses of laminated lacustrine sediments. After deglaciation at about 18 cal kyr BP, a steppe-like herb-rich grassland with maximum Chenopodiaceae/Amaranthaceae and Plantago existed. Between 16.6 and 15.7 cal kyr BP, conditions were dry with a desiccation layer at ~ 16.3 cal kyr BP, documenting a temporary phase of maximum aridity on the plateau. While that local event lasted for only a few decades, concentrations of various elements (e.g. Zr, HF, Nb, Nd, and Na) started to increase and reached a maximum at ~ 15.8–15.7 cal kyr BP. We interpret those elements to reflect allochthonous, aeolian dust input via dry northerly winds and increasingly arid conditions in the lowlands. We suggest an abrupt versus delayed response at high and low altitudes, respectively, in response to Northern Hemispheric cooling events (the Heinrich Event 1). The delayed response at low altitudes might be caused by slow negative vegetation and monsoon feedbacks that make the ecosystem somewhat resilient. At ~ 15.7 cal kyr BP, our record shows an abrupt onset of the African Humid Period, almost 1000 years before the onset of the Bølling–Allerød warming in the North-Atlantic region, and about 300 years earlier than in the Lake Tana region. Erica pollen increased significantly between 14.4 and 13.6 cal kyr BP in agreement with periodically wet and regionally warm conditions. Similarly, intense fire events, documented by increased black carbon, correlate with wet and warm environmental conditions that promote the growth of Erica shrubs. This allows to conclude that biomass and thus fuel availability is one important factor controlling fire events in the Bale Mountains.

Abyssal Manganese Nodule Recording of Global Cooling and Tibetan Plateau Uplift Impacts on Asian Aridification

AbstractThe impact of central Asian aridification on the low latitude North Pacific Ocean since the late Miocene remains unclear. To address this question, we systematically studied an abyssal manganese nodule from the northwestern Pacific Ocean, which is expected to be sensitive to eolian dust sourced from central Asia. Geochemical variations and the fossilized remains of magnetotactic bacteria within the studied nodule manifest two prominent Asian aridification events at ∼8–7 Ma and 3.6–0 Ma. These results suggest that central Asian aridification impacted both primary productivity and abyssal microbial activity in the NW Pacific Ocean via eolian dust inputs. In contrast to the Pliocene aridification event, the late Miocene event was associated with a primary productivity bloom that is not evident in coeval global primary productivity records, which indicates that the ∼8–7 Asian aridification event was likely due to NE Tibetan Plateau uplift rather than to global cooling.

Magnetic properties of the surface sediments from the Huguangyan Maar Lake in tropical Southern China and the sediment source identification

ABSTRACTDeciphering the source(s) of sediment deposited in Hugunagyan Lake in South China using magnetic properties will advance our understanding of the evolution of East Asian monsoon systems. However, the source of magnetic minerals in the surface sediments of this lake is unknown, still needing further exploration. Due to simple hydrological systems, the Hugunagyan Lake provides a unique record for investigating the magnetic property of sediments and surface processes. In this study, based on the magnetic properties of 43 surface sediment, 12 surface soil, and 7 volcanic rock samples from the catchment, we demonstrate that the magnetic minerals in sediments were dominated by fine super paramagnetic magnetic particles, with coexistence of pseudo‐single‐domain states minerals. There are no signatures showing the presence of biogenic and authigenic magnetite. The magnetic properties of surface sediments display significant differences between the potential sources of aeolian dust from the loess in North China and modern surface soils in Central Asia, suggesting that the magnetic minerals mainly originate from the weathered materials in the catchment, and there are no further signals of winter monsoon‐driven aeolian dust input.

Sedimentology of a Late Quaternary lacustrine record from the south‐eastern Carpathian Basin

ABSTRACTThe Upper Pleistocene geoarchives in the south‐eastern Carpathian Basin are represented predominantly by loess–palaeosol records. In 2015, a 10 m sediment core composed of clay‐rich lacustrine sediments was recovered by vibracoring a dry lake basin located between the Vršac Mountains (Serbia) and the Banat Sands in the south‐eastern Carpathian Basin; a location relevant for placing regional archaeological results in a palaeoenvironmental context. Here, we present results from geoelectrical prospection and a lithostratigraphic interpretation of this sequence supported by a detailed granulometric study supplemented by ostracod analysis. An age model based on luminescence dating is discussed against sedimentological proxy data and its implication for palaeoenvironmental change. The cores show a stratigraphy of lighter ochre‐coloured and darker greyish sediment, related to the deposition of clay and silt trapped in an aquatic environment. Geophysical measurements show ~20 m thick lacustrine sediments. The grain‐size distributions including the variability in fine clay are indicative of a lacustrine environment. Fine particles were brought into the depositional environments by aquatic input and settled from suspension; also, direct dust input is constrained by grain‐size results. Riverine input and aeolian dust input interplayed at the locality.

Pre-industrial cyanobacterial dominance in Lake Moon (NE China) revealed by sedimentary ancient DNA

Cyanobacterial blooms in water bodies have occurred on a worldwide basis in the last few decades, and knowledge of their occurrence under natural conditions, and of the mechanisms responsible, is important for understanding their origin. However, little is known about the long-term trends in cyanobacterial abundance in the pre-industrial era, and its causes. Traditional microscope analysis of microfossil plankton is widely applied in paleoecology, yet the majority of phytoplankton (e.g., cyanobacteria) are not preserved as microfossils in sediments, although they can leave a fingerprint in the form of sedimentary ancient DNA (sedaDNA). Here, sedaDNA is used for the first time to reconstruct the history of phytoplankton communities in a crater lake in northern China over the past two millennia. Our data show that changes in phytoplankton community structure and diversity were linked to temperature and precipitation variations during ∼0–1400 Common Era (CE). However, after ∼1400 CE the cyanobacterial abundance increased to an unprecedented degree, and cyanobacteria (mainly composed of Synechococcus) became disproportionately dominant relative to other phytoplankton. This rise was concomitant with increased aeolian dust input by winds driven by an intensified Siberian High, which resulted in increased dust transport across the entire mid-latitude region of the Northern Hemisphere. This suggests that dust input can exceed natural climatic variability as the dominant control on lake ecosystems in regions subject to dust deposition. We suggest that future lake ecological management strategies in areas of dust deposition should consider not only the influence of climatic warming but also the impact of nutrient inputs delivered by dust storms.

Monitoring Australian Monsoon variability over the past four glacial cycles

We analyse changes in terrigenous sedimentation along the northwestern Australian margin to monitor the latitudinal migration of the Intertropical Convergence Zone (ITCZ) and the shifting boundaries of climatic belts during the last four glacial cycles. We integrate high-resolution X-ray fluorescence (XRF) scanning elemental records from Core SO257–18548 and International Ocean Discovery Program Site U1482, situated southwest of the Scott Plateau at the southern edge of the present-day monsoonal belt, and from Core SO257–18571, located within the dust-cyclone belt offshore Northwest Cape south of the Exmouth Plateau. The chronology of these sediment successions is based on 14C dating over the last glacial termination and on correlation of the benthic oxygen isotope record to the LR04 stack (Lisiecki and Raymo, 200) and Antarctic ice core chronology. Our XRF derived records of riverine terrigenous run-off and aeolian dust input reveal rapid intensification of monsoonal precipitation and reduction of atmospheric dust during the Younger Dryas and early Holocene as well as during the terminal phase of other major deglaciations. Short-lived monsoonal maxima in the early Holocene (~10 ka), MIS 5e (~130 ka), MIS 7 (~200, ~220 and ~ 240 ka), and MIS 9 (~280, ~305 and ~ 330 ka) coincide with maxima in atmospheric carbon dioxide and methane concentrations. Monsoon intensification occurs during maxima in Southern Hemisphere spring (September) insolation, when intense heat low pressure cells over the Pilbara region trigger the southward shift of the ITCZ. Within the dust-cyclone belt, riverine sediment discharge was restricted to intervals of high atmospheric CO2 concentrations, when sea surface temperature thresholds promoted cyclone formation in the tropical Indian Ocean. Northwestern Australia remained dry and arid during MIS 5a-d, when the ITCZ was locked in a more northerly position and temperature thresholds were not attained.

Revisiting clay‐sized mineral and elemental records of the silicate weathering history in the northern Tibetan Plateau during the late Cenozoic: The role of aeolian dust

AbstractExceedingly strong aeolian dust activity has occurred in inland Asia. Comparisons of the late Cenozoic sedimentation rates between aeolian and fluvial‐lacustrine sequences around the northern Tibetan Plateau suggest that aeolian process has played an important role in the erosion, weathering and deposition of sediment. However, recognizing dust as an important source in fluvial‐lacustrine sequences is a vital but difficult task. Here, clay‐sized mineral and elemental records of regional silicate weathering histories are revisited during the period of Asian dust expansion at ~9–8 Ma. The aeolian dust input from the Tianshan‐Altay Orogens into the Jiuquan Basin is identified using the Th/Sc ratio while that from the Qilian Shan into the Xining Basin is identified based on inconsistent fine‐grained silicate weathering proxies. Our study suggests that the use of appropriate dust provenance tracers and recognition of wind transport‐induced changes in dust grain size and chemistry can provide useful aeolian dust discrimination approaches.

Development of a Correlated Fe‐Mn Crust Stratigraphy Using Pb and Nd Isotopes and Its Application to Paleoceanographic Reconstruction in the Atlantic

AbstractEight ferromanganese crust samples spanning the complete depth range of Tropic Seamount in the northeast Atlantic were analyzed for Pb and Nd isotopes to reconstruct water mass origin and mixing over the last 75 Ma. Pb isotopes were determined by laser ablation multicollector inductively coupled plasma mass spectrometer (LA‐MC‐ICP‐MS), which enables the rapid production of large, high spatial resolution data sets. This makes it possible to precisely correlate stratigraphy between different samples, compare contemporaneous layers, and create a composite record given the abundance of hiatuses in crusts. Pb and Nd isotope data show the influence of various oceanic and continental end‐members in the northeast Atlantic Ocean. This reflects its evolution from a restricted, isolated basins in the Late Cretaceous with influxes from the Tethys Ocean, to an increasingly well‐mixed, large‐scale basin, with a dominant Southern Ocean signature until the Miocene. Less radiogenic Nd isotope signatures suggest Labrador Sea Water influenced the northeast Atlantic basin as early as 17–15 Ma, flowing through a northern route such as the Charlie‐Gibbs Fracture Zone. Pb and Nd isotopes highlight the increasing influence of Saharan eolian dust input about 7 Ma, imparting a less radiogenic excursion to the binary mixing between North Atlantic water masses and riverine discharge from West and Central Africa. This highlights the influence of eolian dust input on the open ocean Pb and Nd budget and supports an early stage of North African aridification in the Late Miocene. This signature is overprinted about 3 Ma to the present by a strong North Atlantic Deep Water signature following the onset of Northern Hemisphere glaciation.

Effects of volcanic parent materials on the acid buffering capacity of forest soils on Yakushima Island, Japan

ABSTRACT Soil acidification is a natural pedogenetic process in forest ecosystems, but is accelerated by acidic deposition. Soils on Yakushima Island, in southwestern Japan, are derived from granitic bedrock and volcanic parent materials influenced by eolian dust inputs. Acid deposition and low acid-neutralizing capacity (ANC) of granite-derived soils are hypothesized to be the cause of acidic stream water that has been widely observed on Yakushima. It remains unclear, however, whether ANCs are also limited in volcanic soils, which contain weatherable minerals and have high buffering capacities. To compare acidification rates between granite-derived soils and volcanic soils, we estimated changes in ANCs between granite and volcanic parent materials and the resulting soils at a pedogenetic timescale, using the mass balance of titanium. After 7300 years of soil development following the eruption of the Kikai caldera, decreased ANCs and total base reserves were observed in both granite-derived and volcanic soils, compared to their respective parent materials. No difference in soil ANC was observed between granite and volcanic parent materials. Different cations contribute to acid neutralization in soils: decreasing ANC results primarily from the loss of Al in granite-derived soils, while acidity is neutralized by the loss of base cations from volcanic soils. In granite-derived soils, resistance to weathering and K retention in 2:1 type silicate clays limit the loss of bases while increasing the accumulation of exchangeable Al. In volcanic soil profiles, base leaching and the sorption of organic acids onto short-range order minerals can neutralize acidity, although erosion and admixing of granite or eolian dust-derived materials lead to a reduction of ANC in surface soil horizons.

Unmixing biogenic and terrigenous magnetic mineral components in red clay of the Pacific Ocean using principal component analyses of first-order reversal curve diagrams and paleoenvironmental implications

Red clay widely occupies the seafloor of pelagic environments in middle latitudes, and potentially preserves long paleoceanographic records. We conducted a rock-magnetic study of Pacific Ocean red clay to elucidate paleoenvironmental changes. Three piston cores from the western North Pacific Ocean and IODP Hole U1365A cores in the South Pacific Ocean were studied here. Principal component analyses applied to first-order reversal curve diagrams (FORC-PCA) reveals three magnetic components (endmembers EM1 through EM3) in a core of the western North Pacific. EM1, which represents the features of interacting single-domain (SD) and vortex states, is interpreted to be of terrigenous origin. EM2 and EM3 are carried by non-interacting SD grains with different coercivity distributions, which are interpreted to be of biogenic origin. The EM1 contribution suddenly increases upcore at a depth of ~ 2.7 m, which indicates increased eolian dust input. The age of this event is estimated to be around the Eocene–Oligocene (E/O) boundary. Transmission electron microscopy reveals that EM2 is dominated by magnetofossils with equant octahedral morphology, while EM3 has a higher proportion of bullet-shaped magnetofossils. An increased EM3 contribution from ~ 6.7 to 8.2 m suggests that the sediments were in the oxic–anoxic transition zone (OATZ), although the core is oxidized in its entire depth now. The chemical conditions of OATZ may have been caused by higher biogenic productivity near the equator. FORC-PCA of Hole U1365A cores identified two EMs, terrigenous (EM1) and biogenic (EM2). The coercivity distribution of the biogenic component at Hole U1365A is similar to that of the lower coercivity biogenic component in the western North Pacific. A sudden upcore terrigenous-component increase is also evident at Hole U1365A with an estimated age around the E/O boundary. The increased terrigenous component may have been caused by the gradual tectonic drift of the sites on the lee of arid continental regions in Asia and Australia, respectively. Alternatively, the eolian increase may have been coeval in the both hemispheres and associated with the global cooling at the E/O boundary.

Texture contrast soils (TCS) as indicators of eolian dust inputs in the coastal area of west central Senegal, West Africa

Different hypotheses have been addressed to explain the origin of texture contrast soils (TCS) in coastal regions. Our study investigates the TCS in the coastal region of west central Senegal, West Africa, in order to appreciate the influence of eolian dust inputs on their formation and characteristics. Nine soil profiles, from a levee to backswamp toposequence, three on each landscape position; floodplain, low terrace and middle terrace, were investigated. Soil profiles were described according to the World Reference Base. Particle-size analysis was performed by wet-sieving for the sand fraction and pipette analysis for the silt and clay fractions. Elements were determined in finely powdered soil mixed with cellulose in a ratio of 2:1. In this work, we focused principally on elemental zircon (Zr) and Titan (Ti). Our results show the presence of TCS in the coastal area of west central Senegal. We attribute the formation of these TCS to mainly two different sources of soil material: marine and continental. Marine sediments build the floodplain profiles and the subsoil of low terrace profiles, while the colluvial material derived from continental uplands form the middle terrace profiles and the topsoil of low terrace profiles. The main finding remains the influence of eolian dust inputs on the formation of TCS in this coastal area. Evidence of dust addition was confirmed by the uniformity of soil parent material tested through mS/(cU+mU) and Ti/Zr ratios. Such knowledge enhances understanding of local pedogenesis and may help develop sustainable soil management strategies.

Analysis of a major Aeolian dust input event and its impact on element fluxes and inventories at the DYFAMED site (Northwestern Mediterranean)

Continental dust can be suspended and transported by the wind, reaching seawater masses far away from its source. The deposition of the aerosols on the ocean surface can alter the abundance of chemical species in the water column and contribute to element inventories in seafloor sediments. A major Saharan dust intrusion into the Western Mediterranean Sea was recorded at the DYFAMED site (Ligurian Sea) in 20th February 2004. We determined the influence of this dust event on the concentration of 30 minor and trace level elements (TE) in sinking particles collected by sediment traps deployed at 200 m and 1000 m depth, and how a dust flux event like this contributed to the exchange of TE, including Fe, with the water column during major dust events. With coupled sediment traps and aerosol samples, we assessed the short-term implications of dust events in the water column. The event produced a flux of fast (>111 m d−1) and slow (<20 m d−1) sinking dust particles, detected during 3 weeks at 200 m and 4 weeks at 1000 m depth. Additionally, the obtained results of element concentrations and particles flux show that a single dust deposition event can produce a sinking flux equivalent to annual deposition rates of elements relevant to biogeochemical cycles and/or pollution studies: (>60% for Cr and Cu, >70% for Al, >80% for Ni and Zn, >90% for V and Mn, >100% for Fe and Pb). The corresponding Enrichment Factors (EF) for the minor and TE analyzed in the sediment traps during the dust event were calculated. EF was used to determine how minor and trace element concentrations in sinking particles vary. The values ranged between 0.35 and 421 in both 200 m and 1000 m sediment traps. For most of the analyzed elements, the obtained EF values were higher than 1. On the contrary, V, Y, Zr, Nb, and Ce showed EF ~ 1 while Cr, Ni, Cu, Zn, Sn, and Pb showed EF < 1. Despite the variability in the EF values, vertical fluxes integrated during the dust deposition event increased from 200 m to 1000 m, except for I, which decreased. This contrasts strongly with the element fluxes integrated for the complete sampling period, which decrease or increase from 200 m to 1000 m, depending on the element. This suggests that sinking dust particles were acting generally as sinks of the TE. We conclude that, apart from I, a substantial portion of the elements from atmospheric dust input from a single deposition event can reach the mesopelagic layer of the Western Mediterranean basin without increasing the budget of those elements in the water column.

The Dust Deposition Process and Biogeochemical Impacts in the Northern South China Sea

Modern dust plays essential roles in marine sediments, providing nutrient and crucial elements for primary productivity and aquatic ecosystems. However, present marine atmospheric dust observational evidence concerning the biogeochemical response to dust deposition process is spared for a long time. Here a total of 147 aerosols samples were collected near the northern South China Sea (SCS) coast between 13 February, 2016, and 12 February, 2017, have been investigated for the grain size distribution, depositional flux, ten-day back trajectories, clusters analysis, combining with primary productivity (Chlorophyll-a concentration) to indicate the present-day dust deposition process and biogeochemical impacts in the northern SCS on the first time. Our results illustrate the deposition flux and grain size distribution change in different season, grain size distribution in winter are coarser particles than that in the summer, while the maximum and minimum dry deposition flux are 12 December, 2016, (60.4 mg m−2 d−1) and 26 August, 2016, (5 mg m−2 d−1), respective. In addition, the back trajectories and three clusters analyze results indicating 53% of air masses originating locally near the coastal areas of China from the marine boundary layer (0–0.5 km) in the summer monsoon, while 48% dust from the northeast wind is prevailing during the winter monsoon over a relatively higher level (0–1.5 km). Furthermore, an apparent Chl-a blooming after aeolian dust input with a period of 1–2 days in the SCS. Therefore, atmospheric dust contains readily bioavailable iron and enhance the biogeochemical impact in the oligotrophic SCS.

Links between iron supply from Asian dust and marine productivity in the Japan Sea since four million years ago

AbstractAeolian dust input exerts significant influence on oceanic biogeochemical cycles and further potentially controls atmospheric CO2 concentrations. However, the possible link between long-term aeolian dust supply and primary productivity in the western North Pacific remains poorly understood. Here, we present a comprehensive study of major and trace elements and total organic carbon (TOC) concentrations of sediments from Integrated Ocean Drilling Program (IODP) Site U1430 in the southern Japan Sea, in order to reconstruct oceanic palaeoproductivity evolution and test its possible link to Asian dust input since 4 Ma. Palaeoproductivity proxies indicate remarkable increases in productivity at ∼3–2 Ma followed by high-frequency oscillations in productivity since 1.2 Ma. We suggest that higher dust-derived iron supply from Central Asia at 3–2 Ma, which was likely driven by the growth of the Northern Hemisphere ice sheets, could account for enhanced primary productivity and export production in the Japan Sea. Such increased oceanic palaeoproductivity could enhance organic carbon burial, which might contribute to the decrease in atmospheric CO2 concentrations, and provide a positive feedback to the global cooling. However, the Tsushima Warm Current (TSWC) intrusion via the southern Tsushima Strait, which was controlled by glacioeustatic sea level changes, has been the principal cause of the rapid changes in primary productivity and benthic redox condition since 1.2 Ma, regardless of continuously increased Asian dust input.

Rare-earth element geochemistry reveals the provenance of sediments on the southwestern margin of the Challenger Deep

The hadal zone represents one of the last great frontiers in modern marine science, and deciphering the provenance of sediment that is supplied to these trench settings remains a largely unanswered question. Here, we examine the mineralogical and geochemical composition of a sediment core (core CD-1) that was recovered from the southwestern margin of the Challenger Deep within the Mariana Trench. Major element abundances and rare-earth element patterns from these sediments require inputs from both terrigenous dust and locally sourced volcanic debris. We exploit a two-endiuember mixing model to demonstrate that locally sourced volcanic material dominates the sediment supply to the Challenger Deep (averaging similar to 72%). The remainder, however, is supplied by aeolian dust (averaging similar to 28%), which is consistent with adjacent studies that utilized Sr-Nd isotopic data. Building on a growing database, we strengthen our understanding of Asian aeolian dust input into the northwestern Pacific, which ultimately improves our appreciation of sedimentation in, and around, the hadal zone.

Evidence for early (≥12.7 Ma) eolian dust impact on river chemistry in the northeastern Tibetan Plateau

As one of the largest dust sources on the Earth's surface, dryland in Central Asia gives rise to thick eolian deposits over East Asia (e.g., the Chinese Loess Plateau, CLP) and significantly influences the regional hydrochemistry in the downwind drainage areas. However, the formation of thick eolian dust deposits requires not only climatic prerequisites for dust emission and transport but also climatic and topographic conditions favourable for deposition and accumulation. The scarcity of widespread eolian deposition around the CLP before 7-8 Ma hinders a full understanding of the processes and mechanisms of Central Asian aridification. The deposition of eolian dust also impacts the hydrogeochemistry of fluvial systems and the precipitation of authigenic phases in continental sedimentary systems could be an archive for studying eolian dust dynamics when pure eolian deposits are scarce. Here, we present the Ca-Mg-Sr concentrations and 87Sr/86Sr isotope compositions of bulk carbonates in a new fluvial sequence (12.7-4.8 Ma) of the Xining Basin. The Mg/Ca and Sr/Ca ratios of the carbonate describe a power law relationship with a power coefficient of ∼0.8, lower than the coefficient characteristic of prior calcite precipitation (PCP). An input of eolian dust with the dissolution of Mg-rich carbonate is likely responsible for the deviation from a pure PCP process. The bulk carbonates also show a general decrease of 87Sr/86Sr ratios from 12.7 to 4.8 Ma, with a transition around 8.6 Ma revealed by lower Sr/Mg ratios. The comparison of these proxies to a previously reported fluvial section (12.2-5.1 Ma) in the Linxia Basin, ∼200 km to the southeast, shows that the 87Sr/86Sr ratios of the bulk carbonates and water-soluble salts in the Linxia Basin are around 0.7098, which is 0.0018 lower than those in the Xining Basin before 8.6 Ma, but shows a significant rise between 8.6 and 7.0 Ma. The two basins share the same range of carbonate 87Sr/86Sr ratios when sediments are younger than 7 Ma. For the last 7 Myrs, the evolution of the 87Sr/86Sr ratios in bulk carbonates of fluvial sediments and Pliocene-Quaternary eolian deposits found in the Xining Basin are similar to those in typical eolian red clays/loess-palaeosol sequences on the CLP. These results suggest a transition of the hydrochemical regime at 8.6 Ma in the Linxia Basin from a catchment only influenced by the weathering of its bedrock to one significantly impacted by eolian dust input. In the Xining Basin, the carbonate elemental and 87Sr/86Sr ratios are consistent with a hydrochemistry more impacted by the presence of the eolian dust. There, the dust input occurred earlier, at ≥12.7 Ma, though it has strengthened since 8.6 Ma. The eolian dust impact on fluvial systems in the Xining Basin was much earlier than in the Linxia Basin and also preceded the initial accumulation of widespread eolian red clays on the CLP (7-8 Ma), suggesting a temporally propagating and spatially stepwise expansion of eolian dust delivery across the Asian inland during the late Cenozoic.