Holocene Tephra Research Articles

Exploiting the Greenland volcanic ash repository to date caldera-forming eruptions and widespread isochrons during the Holocene

Polar ice-cores have long been recognised as unrivalled repositories of past volcanic events. Although tephra products from local eruptions tend to dominate these records, improvements in micro-sampling and analytical techniques are uncovering a growing number of cryptotephras erupted from exceptionally distant volcanoes. We present a series of nine Middle Holocene cryptotephra deposits detected within the NGRIP ice-core that originate from five different volcanic regions across the Northern Hemisphere (Alaska, Cascades, Iceland, Japan, Kamchatka). Unique compositional signatures are employed to identify ash from three large caldera-forming events in Kamchatka (KS2 from Ksudach), the Cascades (Mazama) and North East Japan (Mashu), along with ash from the Hekla 4 eruption in Iceland. High-precision ice-core ages (adopting a 1950 CE datum for the GICC05 timescale assigned to the Greenland ice cores) are derived for each eruption: Hekla 4 (4325 ± 8 a b1.95k), KS2 (7089 ± 26 a b1.95k), Mashu (i-f) (7473 ± 33 a b1.95k) and Mazama (7562 ± 35 a b1.95k), all of which can be employed as chronological fix-points in other proxy records where these deposits are also preserved. Four further cryptotephra deposits and one macro-deposit are also identified and traced to sources in Iceland and Alaska. The cryptotephra originating from Alaska is correlated to a deposit identified in lake records from the Kenai Peninsula, thought to originate from Redoubt Volcano. The remaining four deposits are typical of the products of Katla, Grímsvötn and Veiðivötn in Iceland. This ensemble of Middle Holocene tephra deposits highlights the pivotal position of the Greenland ice-sheet and its ice-cores to capture deposition from the convergence of several far-travelled ash clouds. Precise age estimates derived from the annually resolved ice-core record greatly enhances the value of these tephra isochrons.

Soils on Recent Tephra of the Somma–Vesuvius Volcanic Complex, Italy

The Somma–Vesuvius volcanic complex emitted huge quantities of volcanic materials over a period from before 18,300 years BP to 1944. The activity during the last period, from post-AD 1631 to 1944, primarily produced lava and pyroclastics via effusive and strombolian eruptions. We investigated the pedogenesis on rocks formed from post-AD 1631 to 1944, occurring on the slopes of Mt. Vesuvius up to Gran Cono Vesuviano and in the northern valley separating Vesuvius from the older Mt. Somma edifice. Pertinent morphological, physical, chemical, and mineralogical (XRD and FT-IR) soil properties were studied. The results indicated the existence of thin and deep stratified soils on lava, as well as the presence of loose detritic covers formed via pyroclastic emplacement and redistribution. The soils showed minimal profile differentiation, frequently with layering recording the episodic addition of sediments. We found that the dominant coarse size of primary mineral particles was preserved, and there was a low level of clay production. The main mineralogical assemblage present in sands also persisted in clays, indicating the physical breaking of the parent material. Chemical weathering produced mineral modifications towards the active forms of Al and Fe and was also attested in selected soils by glass alteration, allophane production, and the presence of analcime in clay as a secondary product from leucite. The differences in glass alteration and analcime production found in the selected soils on lava were related to soil particle size and soil thickness. Concerning the youngest soil present on Gran Cono Vesuviano, other factors, such as the substratum’s age and site elevation, appeared to be implicated.

Palynological records from glacial lakes, northern Priokhotye (western Beringia)

Palynological analyzes of sediments from glacial lakes in Northern Priokhot'ye provide the first continuous records of regional vegetation responses to climate change at the end of the Pleistocene and during the Holocene. The pollen stratigraphy from these coastal sites is like that described for more northern regions of Western Beringia. Herb dominated tundra with Poaceae-forb meadows characterized the Late Pleistocene and was replaced c. 12,100 cal BP by Betula shrub tundra and then by shrub Betula-Alnus tundra. In the Middle Holocene (c. 8900-4700 cal BP), Larix-Betula platyphylla forests with an undergrowth of Pinus pumila, shrub Betula, and Alnus became widespread. Pinus pumila also formed a high shrub tundra zone above altitudinal treeline. Finds of Betula platyphylla macrofossils suggest that summer temperatures were 2–4 °C warmer than today between c. 7700 and 6700 cal BP. Variations in Pinus pollen percentages during the Middle and Late Holocene suggest changes in altitudinal treeline related to intervals of relatively cooler or warmer climates. The timing of the postglacial thermal maximum and possible shifts in altitudinal treeline suggest paleoclimatic patterns that are more like southern areas of the Russian Far East than northern regions of Western Beringia. A Late Holocene tephra was found for the first time in the lake sediments and peat exposures of Northern Priokhotye. The most likely source of this important chronostratigraphic horizon is the Shiveluch volcanic eruption (Kamchatka Peninsula) dated to 2500–2600 BP (2580–2730 cal BP).

Revisiting the Holocene tephrochronology of northwestern Argentina: Insights from geochemical characterization of the tephras from the Tafí valley

In the southernmost sector of the Central Volcanic Zone (CVZ), spanning from 23° to 28°S, there is an estimated count of 30–40 potentially active volcanoes. Due to its remote location, the primary volcanic threat in this area during explosive eruptions is the dispersal and fallout of tephra. Among various approaches, tephrochronological studies have proven to be the most effective in compiling a comprehensive record of recent explosive eruptions in this region. The intermontane valleys nestled at the eastern foothills of the Andes, situated around 200–300 km from the volcanic arc, harbor a Holocene stratigraphic record containing multiple layers of tephra. These layers are evidence of the recurrence of substantial volcanic eruptions (VEI ≥4) during recent times, particularly within the last 10,000 years. Improving the tephrochronological knowledge of the southernmost edge of the CVZ constitutes a crucial initial step in evaluating the ash-fall hazard of this region. In this context, the Tafí valley emerges as a prominent candidate for serving as a dependable tephrochronological "anchor point" for regional correlations. Its strength lies in its conspicuous record of Holocene tephras and its well-documented morpho-stratigraphic setting, which has been rigorously constrained by absolute age dating. Despite these advantages, some of the Holocene tephras found within Tafí valley remain uncharacterized in terms of both glass shard and mineral geochemistry. This limitation has consequently hindered their utility in facilitating regional correlations. Thus, we present the glass shard and mineral composition of these uncharacterized Holocene tephras previously identified within Tafí valley. Our findings have not only enhanced regional correlations beyond the Tafí valley but have also provided more precise source constraints. Ultimately, our work represents an upgrade of the Holocene tephrochronological framework of Northwestern Argentina and a stride toward a more reliable assessment of volcanic hazard and risk within the region.

Redox-controlled differential weathering of andesitic pumice: Possible catalytic effects of ferrous/ferric iron on rapid halloysite accumulation in a Holocene tephra layer

Differential weathering process of Holocene andesitic tephra in Atsuma, Hokkaido, northern Japan, were investigated with a specific focus on the flame-like occurrence of halloysite bands and their formation mechanism. The parent material was coarse-grained pumice (Ta-d2) deposited 9 ka to form a highly permeable metre-thick layer atop fine-grained impervious periglacial loam, which is covered by humic soil–tephra sequences. The shallower part of the Ta-d2 layer was weathered to a reddish or yellowish brown colour, which is characterized by intensive leaching of Si and Al, with abundant precipitation of iron (hydr)oxide and amorphous secondary minerals in an oxidizing environment. A reductive grey colour was observed only at the Ta-d2 bottom below the halloysite band, where pumice grains survived significant elemental leaching and contained ferrous iron in the solid phase with abundant dissolved Fe in the liquid phase. Between these oxidized and preserved zones, an irregularly shaped, fine-grained, white iron-rich halloysite layer with a decimetre-scale thickness developed. In this clay band, the molar ratio of Si to (Al + Fe) was nearly 1:1, with a small amount of remnant Ca. Mössbauer analysis revealed that Fe2+ was initially incorporated into the aluminosilicate sheet via Al3+ substitution and transformed into Fe3+ within the structure. The halloysite band was formed at depths in the tephra layer corresponding to the redox front. The abundance of Si and Al in pore water in any zone of the tephra layer meets the stability requirements of halloysite, indicating that the redox condition controls the rapid local accumulation of halloysite through the isomorphous substitution followed by valence change of iron. We propose a new hypothesis stating that iron catalyses halloysite nucleation via a stepwise function, including layer charging to absorb hydrated cations and subsequent charge loss resulting in cation desorption and passive intercalation of water molecules within the 1:1 layer.

A Holocene tephrochronological framework for Finland

Regional tephrochronological frameworks serve as dating and correlating tools that enable critical assessment of the validity of single cryptotephra findings. In this study, our aim was to construct an outline for a Finnish Holocene tephra framework by investigating 12 peatlands and one lake site for presence of cryptotephra. As a result, glass shards from 19 individual tephras were geochemically characterized and correlated to their source volcanoes in Iceland and Alaska. Fifteen of these tephras were identified in Finland for the first time. The oldest identified cryptotephra in the Finnish environmental records is the 7 ka Hekla 5 tephra, and the youngest one is the Askja 1875. The identification of two Alaskan tephras (White River Ash eastern lobe and Aniakchak tephra) in Finland demonstrates an opportunity for intercontinental tephra correlations. The first Finnish Holocene tephrochronology presented here reveals a great potential for using tephrochronology as a dating method in Finland and is expected to aid in future cryptotephra research in the region. Additionally, the cryptotephra findings in this study help to refine the dispersal areas of several Holocene tephras.

An integrated proximal-distal radiocarbon dating approach provides improved age constraints for a key Holocene tephra isochron

Volcanic ash (tephra) horizons are an essential tool for the spatial and temporal correlation of many natural archives. However, tephrochronology is accompanied by age uncertainties that often limit its capacity to effectively constrain age models. This is particularly problematic for paleoseismology in complex tectonic settings such as New Zealand, where the accuracy and precision of earthquake ages is important for interpreting past fault interactions and earthquake sequences. We use the widespread Waimihia tephra, erupted at ∼3.4 ka from Taupō volcano, as a case study for generating improved age constraints for Holocene tephra isochrons. Our dating strategy minimizes uncertainties by (i) conducting detailed assessments to identify the most reliable dateable material, (ii) using precise AMS dating techniques, and (iii) constructing Bayesian age models. By applying consistent procedures to date tephra deposits at proximal, onshore distal and offshore distal locations, we also facilitate the detection of any geographic radiocarbon bias. Based on high agreement between the independently derived tephra ages from each location, we demonstrate no offsets in radiocarbon results between proximal and distal deposits, precluding bias from near-vent magmatic degassing. Our integrated age model exploits the benefits of each individual dating approach and uses the full suite of 42 new radiocarbon dates to yield an age of 3574–3478 cal yr BP (highest 95% range) for the Waimihia eruption. Compared to previous estimates, this older and more precise age has implications for refining existing paleoearthquake correlations and other chronologies that rely on the Waimihia isochron to provide age control. We recommend applying this multi-location approach to existing tephrochronologies where possible, to achieve more accurate and precise eruption age estimates that allow for the detection of radiocarbon bias.

Palynological Characteristics and Volcanic Ash from Sediments of Chistoye Lake, Northern Priokhotye

Chistoye Lake (59° 32' N, 151° 48' E) is located 10 km from the northern coast of Taui Bay (Okhotsk Sea) in the central part of a tectonic depression that has been infilled with Paleogene and Neogene deposits. The lake originated as the result of glacial activity during the latest Pleistocene (MIS2). A 550-cm-long lacustrine sediment core was raised from Chistoye Lake using a piston sampler. The core is dominated by silt with layers of peat and sand at its base. The silt includes two tephra layers at 360-364 cm and 77-80 cm. The tephra layers have different geochemical, magnetic, and mineralogical properties. Volcanic ash like the lower tephra in the Chistoye core has been found in other lacustrine sites from the Upper Kolyma, Upper Indigirka, and Northern Priokhotye regions. Radiocarbon dating of organic remains that bracket this second tephra, corresponding to the lower tephra in Chistoye Lake, indicates an age of 7 650 ± 50 years ago, which is comparable with the age of the Kurile Lake - Iliyinskaya caldera forming eruption in Kamchatka. The younger tephra also has been noted in cores from other lakes in Northern Priokhotye and dated to 2 745 ± 10 years ago. A distinctive feature of this Late Holocene tephra is its high magnetic susceptibility. Extrapolation of a sedimentation rate based on the tephra ages suggests that the Chistoye record is approximately 11 700 years old. Palynological analysis of the Chistoye Lake material showed that all samples contain pollen redeposited from Neogene sediments (Picea sect. Eupicea, Tsuga, Tilia, Corylus, Juglans, Ulmus). These taxa can be easily discounted as contaminant, but other pollen types (e. g., Pinus subgen. Haploxylon, Betula, Alnus, Cyperaceae, Poaceae) are more problematic for interpreting the paleovegetation, because they represent plants that were present during the Holocene and/or the Late Pleistocene and during the Neogene. Nonetheless, the changes in the percentages of Sphagnum spores suggest a gradual increase in effective moisture during the Younger Dryas and Holocene. A multiproxy study of the sediments from Chistoye Lake, in conjunction with their palynological characteristics, shows the importance of analyzing magnetic properties to help determine the presence of tephra in the sediments. Volcanic ash layers in the lake sediments from northeastern Siberia are reliable chronostratigraphic markers that can supplement radiocarbon dates and improve the regional understanding of climate and vegetation changes during the Holocene.

Creating a digital database of tephra fallout distribution and frequency in Japan

Tephra fallout is a potential hazard to livelihoods, critical infrastructure, and health, even in areas that are far from volcanoes. Therefore, it is important to quantitatively evaluate tephra fall hazards for both residents and infrastructure around hazardous volcanoes. Modern probabilistic volcanic hazard assessments of tephra fallout strongly rely on computer modeling; however, assessments based on isopach maps can also be also helpful in assisting decision-makers. To assess the tephra fall hazards in Japan, we created a digital database “Isopach map-Based Tephra fall Hazard Analysis (IB-THA)” and a tool to draw the cumulative number of tephra fallout events exceeding a specific thickness at a particular location. The database was re-digitized using an existing catalog of 551 tephra fall deposit distribution maps. The re-digitized datasets were utilized here to estimate the cumulative number of tephra fallout events exceeding a specific thickness at 47 prefectural offices for the last 150 kyr. This allowed the characterization of regional tephra fall hazards in Japan for the first time. High cumulative numbers (20) of tephra fall deposits > 0 mm were identified in the NE-E region (e.g., Maebashi), whereas low numbers (2) were recognized in the SW and W regions of Japan (e.g., Naha). The thickest tephra fall deposit (2850 mm) was observed at Kagoshima. We used IB-THA to create a hazard curve for Tokyo. This hazard curve provides the minimum frequency needed to exceed the tephra fall thickness at any location. To refine the digital database presented here, further studies are required to incorporate recent (i.e., 2003 or younger) tephra distributions, review questionable isopach maps, and improve the interpolation method for digitizing tephra fall distributions.

Holocene Marine Tephra Offshore Ecuador and Southern Colombia: First Trench‐to‐Arc Correlations and Implication for Magnitude of Major Eruptions

AbstractTephra layers preserved in marine sediments are strong tools to study the frequency, magnitude and source of past major explosive eruptions. Thirty‐seven volcanoes from the Ecuadorian and Colombian arc, in the northern Andes, experienced at least one eruption during the Holocene. The volcanic hazard is therefore particularly high for the populated areas of the Andes and in particular cases for the coastal region, and it is crucial to document such events to improve hazard assessment. The age and distribution of deposits from major Holocene eruptions have been studied in the Cordillera, but no descriptions of distal fallouts have been published. In this study, we focused on 28 Holocene tephra layers recorded in marine sediment cores collected along the northern Ecuador—Southern Colombia margin. New lithological, geochemical and isotope data together with 14C datings on foraminifers allow us to determine the age and volcanic source of marine tephra, and to propose a first land‐sea correlation of distal tephra fallouts. We show that at least seven explosive eruptions from Guagua Pichincha, Atacazo‐Ninahuilca, Cotopaxi, and Cerro Machín volcanoes left tephra deposits recorded in marine cores over 250 km away from their source. Volume estimates of emitted tephra range between 1.3 and 6.0 km3 for the tenth century Guagua Pichincha, ∼5 ka Atacazo‐Ninahuilca, ∼6.7 and ∼7.9 ka Cotopaxi events, suggesting that they were eruptions of Volcanic Explosivity Index of 5. The distribution of these deposits also brings new constraints for a better evaluation of the volcanic hazard in Ecuador.

The Late Pleistocene to Holocene tephra record of ND14Q site (southern Adriatic Sea): Traceability and preservation of Neapolitan explosive products in the marine realm

A tephrochronological investigation was carried out at site ND14Q (1013 m of water depth), located in the southern Adriatic Sea, offshore the Gargano promontory. It was drilled in the frame of The NextData Project (www.nextdataproject.it, 2011-2013), focused on paleoclimate research. To obtain a composite and well preserved deep marine record, three cores were raised at the study site. Twelve primary cryptotephra and one tephra were analysed in terms of major-element content and correlated with a total of sixteen eruptive events. The studied materials display K-alkaline and subalkaline features pointing to a correlation with the Somma-Vesuvius, Campi Flegrei and Lipari Island (Aeolian Arc) volcanic activity occurred during the Late Pleistocene-Holocene. In detail, major marker tephra of the central Mediterranean have been recognized, among which the Phlegraean Neapolitan Yellow Tuff (ca. 15 ka), Pomici Principali (ca. 12 ka BP) and Astroni-Agnano-Monte Spina (ca. 4.2 ka - 4.4 ka BP) eruptions and, for the first time in this area, the Vesuvian 79 CE event. The very well preserved Mercato (ca. 9 ka BP) and Fiumebianco-Gabellotto (ca. 8.4 ka BP) cryptotephra have also been found in the sapropel S1 interval of the succession, which definitely records the last ca. 22 kyr (Pomici di Base tephra). A number of other Plinian and sub-Plinian events also occur and the availability of multiple cores provided new insights into their temporal relation such as between AP2 and Astroni 6 eruptions. The identification of tephra sourced by well-dated volcanic events, along with several AMS 14C age results, allowed an accurate chronological framework for the composite tephrostratigraphic record, thus providing accurate ages for those deposits with an uncertain correlative event. In addition, stratigraphic evidences in the core replicates at ND14Q site showed that several intervening factors affect preservation and traceability of cryptotephra deposits in the marine realm posing main critical issues on volcanological and paleoclimate research.

Characterizing porous microaggregates and soil organic matter sequestered in allophanic paleosols on Holocene tephras using synchrotron-based X-ray microscopy and spectroscopy

Allophanic tephra-derived soils can sequester sizable quantities of soil organic matter (SOM). However, no studies have visualized the fine internal porous structure of allophanic soil microaggregates, nor studied the carbon structure preserved in such soils or paleosols. We used synchrotron radiation-based transmission X-ray microscopy (TXM) to perform 3D-tomography of the internal porous structure of dominantly allophanic soil microaggregates, and carbon near-edge X-ray absorption fine-structure (C NEXAFS) spectroscopy to characterize SOM in ≤ 12,000-year-old tephra-derived allophane-rich (with minor ferrihydrite) paleosols. The TXM tomography showed a vast network of internal, tortuous nano-pores within an allophanic microaggregate comprising nanoaggregates. SOM in the allophanic paleosols at four sites was dominated by carboxylic/carbonyl functional groups with subordinate quinonic, aromatic, and aliphatic groups. All samples exhibited similar compositions despite differences between the sites. That the SOM does not comprise specific types of functional groups through time implies that the functional groups are relict. The SOM originated at the land/soil surface: ongoing tephra deposition (intermittently or abruptly) then caused the land-surface to rise so that the once-surface horizons were buried more deeply and hence became increasingly isolated from inputs by the surficial/modern organic cycle. The presence of quinonic carbon, from biological processes but vulnerable to oxygen and light, indicates the exceptional protection of SOM and bio-signals in allophanic paleosols, attributable both to the porous allophane (with ferrihydrite) aggregates that occlude the relict SOM from degradation, and to rapid burial by successive tephra-fallout, as well as strong Al-organic chemical bonding. TXM and C NEXAFS spectroscopy help to unravel the fine structure of soils and SOM and are of great potential for soil science studies.

A Holocene tephra layer within coastal aeolian deposits north of Caleta Olivia (Santa Cruz Province, Argentina)

In this paper we illustrate the stratigraphy, geochronology, and geochemistry (major, minor, trace elements and Sr-isotopes) of a Holocene tephra layer found within coastal sedimentary deposits north of Caleta Olivia (Santa Cruz Province, Argentina). The stratigraphic succession comprises beach deposits with basal erosive surface resting on the local substrate (“Formación Patagonia”) followed by a poorly developed paleosoil. The paleosoil is covered by a lenticular fine-grained (Mdφ: 5.2, 0.027 mm), well sorted (σφ: 1.2) volcanic ash layer and aeolian sands. The geochemical composition of shard fragments points to an origin from the Hudson volcano, located in the southern Andes, ca. 400 km to the west. The geochemistry, Sr-isotopes and the radiometric constraints (younger than the age of the underlying marine layer dated at ca. 4,100 a cal BP) further allow correlating this tephra with the so-called H2 eruption (ca. 3,900 a cal BP). This finding is of interest owing to the poor preservation potential of tephra within the Late Holocene sedimentary deposits of the Atlantic coast of Patagonia and represents the first finding of H2 eruption in this area, improving our knowledge of the dispersion of the fine-grained distal deposit of the Hudson volcanic explosive activity, thus allowing a better estimate of the eruptive dynamics and the risks associated with the Hudson volcano.

Calbuco, a monotonous andesitic high-flux volcano in the Southern Andes, Chile

Calbuco (41.3°S) is a highly active composite frontal arc volcano in the Andean Central Southern Volcanic Zone (CSVZ). It is currently ranked by Chile's Geological Survey (SERNAGEOMIN) as among the most dangerous volcanic centers in the Southern Andes, with sub-Plinian explosive activity occurring as recently as 2015. Compositional and geochronologic data from 65 samples constrain the Pleistocene-Holocene eruptive evolution of Calbuco. New 40Ar/39Ar ages from lava flows, revised mapping, and existing 14C dates for Holocene tephras reveal that much of the current edifice is <20 ka in age. Thus, Calbuco has produced a greater Holocene eruptive flux, 3.4 km3/ka averaged over the last 10 ka and 4.8 km3/ka over the last 4 ka, than other arc volcanoes both in the CSVZ and globally. Morphologic and stratigraphic observations along with new whole-rock geochemical data suggest that this remarkable magma flux is expressed as repeated eruptions of lavas and tephra with a narrow SiO2 range (54–58 wt%). This compositional monotony, conspicuous resorbed amphibole, and elevated fluid-mobile trace element abundances differ from the post-glacial compositions and mineralogy observed at other CSVZ arc front volcanoes. Mid-crustal processing at or just below the depth where amphibole is stable plays a key role in the genesis of andesite at Calbuco. The precision of 40Ar/39Ar dates from Latest Pleistocene to Holocene low K2O mafic lavas remains a challenge to constructing eruptive chronologies for comparison to records of glacier expansion and retreat. Notwithstanding, our findings from Calbuco imply that petrologic factors, including mantle melt flux, depth of magma storage, and melt H2O content, may promote distinctive eruptive responses at adjacent CSVZ volcanoes following rapid retreat of the Patagonian Ice Sheet at 18 ka.

Geochemical fingerprinting of Holocene tephras in the Willaumez Isthmus District of West New Britain, Papua New Guinea. In From Field to Museum—Studies from Melanesia in Honour of Robin Torrence, ed. Jim Specht, Val Attenbrow, and Jim Allen

Geochemical fingerprinting of Holocene tephras in the Willaumez Isthmus District of West New Britain, Papua New Guinea. In From Field to Museum—Studies from Melanesia in Honour of Robin Torrence, ed. Jim Specht, Val Attenbrow, and Jim Allen

An Integrated Late Pleistocene to Holocene Tephrostratigraphic Framework for South‐East and East Asia

AbstractVolcanic ash has been widely used as unique independent marker horizons for dating and synchronizing paleoenvironments and archeological records. Here, we report a series of key widespread late Pleistocene to Holocene tephras horizons from a lake sequence in southern China that have significant potential for dating and synchronizing paleoenvironmental records from East Asia. Translatitudinal paleoclimatological, paleoenvironmental, and archeological correlations from the tropical Philippines, mainland China, and midlatitude Japan are achievable through these extensively distributed tephras, including synthetic studies of the Younger Dryas and mid‐Holocene climate events. Additionally, we establish refined ages for four pre‐1991 Pinatubo eruptions and date three late Pleistocene Luzon eruptions based on the lake sequence age model, which will facilitate future studies of tropical volcanic eruptions’ forcing of climate change. Our results highlight the volcanic hazards around densely populated East Asia, and bring solutions to resolving dating uncertainty in the synchronization of rapid climate events across the region.

Rapid carbon accumulation in a peatland following Late Holocene tephra deposition, New Zealand

Contemporary measurements of carbon (C) accumulation rates in peatlands around the world often show the C sink to be stronger on average than at times in the past. Alteration of global nutrient cycles could be contributing to elevated carbon accumulation in the present day. Here we examine the effect of volcanic inputs of nutrients on peatland C accumulation in Moanatuatua Bog, New Zealand, by examining a high-resolution Late Holocene C accumulation record during which powerful volcanic eruptions occurred, depositing two visible rhyolitic tephra layers (Taupo, 232 ± 10 CE; Kaharoa, 1314 ± 12 CE). Carbon accumulation rates since c. 50 CE, well before any human presence, increased from a background rate of 23 g C m−2 yr−1 up to 110 g C m−2 yr−1 following the deposition of the Taupo Tephra, and 84 g C m−2 yr−1 following the deposition of the Kaharoa Tephra. Smaller but nevertheless marked increases in C accumulation additionally occurred in association with the deposition of three andesitic-dacitic cryptotephras (each ≤ ∼1 mm thick) of the Tufa Trig Formation between the Taupo and Kaharoa events. These five periods of elevated C uptake, especially those associated with the relatively thick Taupo and Kaharoa tephras, were accompanied by shifts in nutrient stoichiometry, indicating that there was greater availability of phosphorus (P) relative to nitrogen (N) and C during the period of high C uptake. Such P was almost certainly derived from volcanic sources, with P being present in the volcanic glass at Moanatuatua, and many of the eruptions described being associated with the local deposition of the P rich mineral apatite. We found peatland C accumulation to be tightly coupled to N and P accumulation, suggesting nutrient inputs exert a strong control on rates of peat accumulation. Nutrient stoichiometry indicated a strong ability to recover P within the ecosystem, with C:P ratios being higher than most other peatlands in the literature. We conclude that nutrient inputs, deriving from volcanic eruptions, have been very important for C accumulation rates in the past. Therefore, the elevated nutrient inputs occurring in the present day could offer a more plausible explanation, as opposed to a climatic component, for observed high contemporary C accumulation in New Zealand peatlands.

Holocene tephrostratigraphic framework and monsoon evolution of East Asia: Key tephra beds for synchronising palaeoclimate records

In East Asia our understanding of Holocene climate change, forcing mechanisms and propagation, require the precise chronological control of palaeoclimate records to allow robust integration of data sets. The existing chronologies, predominantly based on 14C method, however, are not sufficient to constrain key questions about abrupt climate shifts that occur within a century in the transitions between states. Widely dispersed tephra layers allow precise dating and synchronisation of sedimentary archives, providing a chronological framework for integrating records, especially where the visible tephra record is complemented by the addition of cryptotephra (non-visible ash). Despite significant tephra studies in this region, however, a comprehensive Holocene tephra framework is not available. To address this issue, we carry out a thorough review on Holocene tephra investigations undertaken in Japan. Using widespread tephra beds we present an integrated tephra framework and suggest the way forward for establishing this as a wider approach for East Asia. The framework is based on twenty-two ash layers that are mainly from Japan, and to a lesser extent China/N Korea, S Korea and Russia. Each tephra is assessed in terms of chronology, geochemistry and distribution. The framework is compared with high resolution palaeoclimate records from East Asia. Using this we demonstrate regional variations in monsoon evolution and more importantly, the potential of tephra isochrons in constraining such variations. Given the scarce identification of tephra layers in those well-resolved palaeoclimate records, we advocate a more systematic employment of the cryptotephra method, which would potentially lead to a significant advance in East Asian tephrochronology and the correlation of palaeoclimate archives in the region.

Chronological and geomorphological approach to the Holocene tephras from Tafí and Santa María valleys, NW Argentina

AbstractA comprehensive morphostratigraphic and chronological study of the complete set of Holocene tephras from Tafí and Santa María valleys (northwestern Argentina), including analyses of compositional characteristics, is presented. Five ash tephras are recognized: V0 (El Rincón), V1a (Carreras 1a ash), V1b (Carreras 1b ash), V2a (Carreras 2 ash), and V2b (El Paso 3 ash). Two of them (V1b and V2b) are described for the first time in the study area. The new 14C and accelerator mass spectrometry ages presented, along with the previously published information, allows for the establishment of a chronological framework. The V0 tephra was deposited in the Early Holocene (about 10,000 yr BP), V1a and V1b were deposited in the Middle Holocene (about 4200 and 3500 yr BP, respectively), and V2a and V2b were deposited in the Late Holocene (after about 800 yr BP). The mineralogical, textural, and geochemical characterizations of the five tephras suggest that their tephra provenance was mainly from the back-arc region. However, the determination of the exact source of each tephra requires more accurate high-resolution tephrochronological studies. At least five major eruptions affected the Tafí and Santa María valleys in the last 10,000 yr.

Middle to late Pleistocene record of explosive volcanic eruptions in marine sediments offshore Kamchatka (Meiji Rise, NW Pacific)

ABSTRACTThis paper presents the first detailed study of a late Pleistocene marine tephra sequence from the NW Pacific, downwind from the Kamchatka volcanic arc. Sediment core SO201‐2‐40, located on the Meiji Rise ~400 km offshore the peninsula, includes 25 tephras deposited within the last 215 ka. Volcanic glass from the tephras was characterized using single‐shard electron microprobe analysis and laser ablation inductively coupled mass spectrometry. The age of tephras was derived from a new age model based on paleomagnetic and paleoclimate studies. Geochemical correlation of distal tephras to Kamchatkan pyroclastic deposits allowed the identification of tephras from the Karymsky, Gorely, Opala and Shiveluch eruptive centers. Three of these tephras were also correlated to other marine and terrestrial sites and hence are identified as the best markers for the north‐west Pacific region. These are an early Holocene tephra from the Karymsky caldera (~8.7 ka) and two tephras falling into the Marine Isotope Stage (MIS) 6 glacial time: an MIS 6.4 tephra from Shiveluch (~141 ka) and the MIS 6.5 Rauchua tephra (~175 ka) from Karymsky. The data presented in this study can be used in paleovolcanological and paleoceanographic reconstructions.