Marine Isotope Stage Research Articles

Last Interglacial coastal hydroclimate variability in Bermuda revealed by clumped isotope oyster sclerochronology

The islands of Bermuda preserve carbonates from several glacial and interglacial intervals with demonstrated potential for reconstructing past North Atlantic climate. Here, we describe new clumped and conventional stable isotope data from Dendostrea (oyster) shells collected from a Last Interglacial / Marine Isotope Stage 5e (MIS 5e) deposit. Interpretation of these and past data is supported by new amino acid racemization age dating results from nine localities around Bermuda.We find that the fossil oyster population on Verrill Island (within the present Great Sound of Bermuda) records MIS 5e temperatures and water δ18O values that are similar to modern. These data contrast with the much cooler temperatures and lighter reconstructed water δ18O values reconstructed for sites on the southern shore. This contrast may in part be due to timing, with the Verrill Island deposit plausibly representing an earlier and warmer portion of MIS 5e. The data also reflect meaningful, highly local differences in environment, with modern Great Sound shells perhaps living in partially restricted waters buffered from cooler and groundwater-influenced conditions along the South Shore. The mobility of Cittarium pica marine snails used in previous work likely also introduces exaggerated variability in those cases. Critically, incorporation of clumped isotope data across multiple sites and genera enables an understanding of Bermudian MIS 5e climate that would be meaningfully different if given data from only one site. We seek to illustrate both the complexities and potential of working with clumped isotope paleoclimate data from coastal deposits.

Insights Into Changing Interglacial Conditions in Subarctic Canada From MIS 11 Through MIS 5e From Seasonally Resolved Speleothem Records

AbstractHigh‐resolution records from past interglacial climates help constrain future responses to global warming, yet are rare. Here, we produce seasonally resolved climate records from subarctic‐Canada using micron‐scale measurements of oxygen isotopes (δ18O) in speleothems with apparent annual growth bands from three interglacial periods—Marine Isotope Stages (MIS) 11, 9, and 5e. We find 3‰ lower δ18O values during MIS 11 than MIS 5e, despite MIS 11 likely being warmer. We explore controls on high‐latitude speleothem δ18O and suggest low MIS 11 δ18O values reflect greater contribution of cold‐season precipitation to dripwater from longer annual ground thaw durations. Other potential influences include changes in precipitation source and/or increased fraction of cold‐season precipitation from diminished sea ice in MIS 11. Our study highlights the potential for high‐latitude speleothems to yield detailed isotopic records of Northern Hemisphere interglacial climates beyond the reach of Greenland ice cores and offers a framework for interpreting them.

Vegetation and glacier dynamics are sensitive to summer (not winter) warming and the evidence for larch refugia in the ‘Northern Pole of Cold’ inferred from sedimentary ancient DNA and geochemistry

Climate seasonality critically influences the functioning and dynamics of ecosystems in continental areas. The ecological importance of winter temperatures on high-latitude vegetation changes has recently been argued to be largely overlooked in comparison to summer temperatures. The Oymyakon region from eastern Siberia, with its strong continentality of extremely cold winters and moderately warm summers, is ideally suited to study the response of past vegetation to seasonal temperature changes based on long ecological time-series. However, few paleorecords are available from this area. The history of regional glacial activity and potential plant refugia since Marine Isotope Stage (MIS) 3 is not well understood. Here, we present geochemical and plant DNA metabarcoding records retrieved from a sediment core from Lake Ulu in the Oymyakon region, which provides detailed information on glacier and vegetation dynamics over the last 43 cal. ka BP. Our results suggest that glacial fluctuations were primarily driven by summer insolation, and Lake Ulu was likely initiated by glacial retreat during MIS 3. The catchment experienced multiple glacial advance/retreat cycles until the Last Glacial Maximum, and the glaciers fully retreated by 20 cal. ka BP. In addition, a tundra-steppe landscape dominated by Dryas, Papaver, Saliceae, and Anthemideae occupied the catchment for most of the time and began to collapse around 19 cal. ka BP following the expansion of trees and shrubs such as Larix, Betula, Alnus, and Vaccinium. Postglacial plant assemblages in the Oymyakon region exhibit a high sensitivity to summer temperature variations, with minimal impact from winter temperatures. This can be explained by the dominance of summer insolation amplitude, extreme continentality, extended plant growing season, and plant genetic adaptation to cold. Notably, our ancient DNA record show the earliest postglacial expansion of larch in eastern Siberia (around 18.6 cal. ka BP), which is likely related to the presence of local refugia. This implies that the Oymyakon region may be one of the earliest sources for larch recolonization and that more research should be implemented to provide insights into larch expansion and migration, and to better predict the future scenarios for Siberian larch forests.

Glacial and volcanic landforms in the upper catchment of Claro River, Central Chile (35.5°S): A Late Quaternary geomorphological case study

AbstractThe upper catchment of the Claro river is located within the Transitional Southern Volcanic Zone in the Maule Region of Chile (35.5°S), at the foothills of Manantial Pelado volcano, a Pleistocene stratovolcano whose morphology suggests the occurrence of important glacial processes in the area. The observed glacial landforms can be sequenced and associated with episodes of volcanic activity. Different units of volcanic and glacial origin were identified based on field observations, detailed mapping, and digital elevation model and satellite image analysis. The contact relations between them made it possible to discern four events that can be linked to Marine Isotope Stages 8, 6, 4‐2, and to the Neoglacial. We propose seven stages in the geomorphological evolution from the late Pleistocene to the late Holocene, where there is coexistence between volcanic and glacial episodes, such as the emplacement of the Manantial Pelado volcano overlying the Abanico and Cola de Zorro formations; a subsequent debris avalanche; the enlargement of the Del Indio valley during the Penultimate Glaciation; the construction of Cerro Redondo (a minor eruptive center at the head of Del Indio valley); ongoing fluvial incision; and Neoglacial advances. The relative chronology proposed in this work contributes to clarifying the Pleistocene–Holocene geomorphological history in this catchment and to further understand the interplay between volcanic and glacial processes in the central Chilean Andes during the Quaternary.

Range-Wide Phylogeography and Ecological Niche Modeling Provide Insights into the Evolutionary History of the Mongolian Racerunner (Eremias argus) in Northeast Asia.

The Mongolian racerunner, Eremias argus, is a small lizard endemic to Northeast Asia that can serve as an excellent model for investigating how geography and past climate change have jointly influenced the evolution of biodiversity in this region. To elucidate the processes underlying its diversification and demography, we reconstructed the range-wide phylogeographic pattern and evolutionary trajectory, using phylogenetic, population genetic, landscape genetic, Bayesian phylogeographic reconstruction and ecological niche modeling approaches. Phylogenetic analyses of the mtDNA cyt b gene revealed eight lineages that were unbounded by geographic region. The genetic structure of E. argus was mainly determined by geographic distance. Divergence dating indicated that E. argus and E. brenchleyi diverged during the Mid-Pliocene Warm Period. E. argus was estimated to have coalesced at~0.4351 Ma (Marine Isotope Stage 19). Bayesian phylogeographic diffusion analysis revealed out-of-Inner Mongolia and rapid colonization events from the end of the Last Interglacial to the Last Glacial Maximum, which is consistent with the expanded suitable range of the Last Glacial Maximum. Pre-Last Glacial Maximum growth of population is presented for most lineages of E. argus. The Glacial Maximum contraction model and the previous multiple glacial refugia hypotheses are rejected. This may be due to an increase in the amount of climatically favorable habitats in Northeast Asia. Furthermore, E. argus barbouri most likely represents an invalid taxon. The present study is the first to report a range-wide phylogeography of reptiles over such a large region in Northeast Asia. Our results make a significant contribution towards understanding the biogeography of the entire Northeast Asia.

Late Pleistocene prey mobility in southwestern France and its implications for reconstructing Neandertal ranging behaviors

As hunter-gatherers, Neandertal mobility and corresponding adaptations were influenced by the mobility of their prey; thus, it is critical to track how the movement patterns of each species varied over time at specific sites. Here, prey paleomobility is reconstructed by measuring radiogenic strontium isotope ratios (87Sr/86Sr) in herbivore teeth recovered from two archaeological sites (Pech de l’Azé IV and Roc de Marsal) in the Dordogne Valley (Aquitaine Basin) of southwestern France that span marine isotope stages (MIS) 5-3. These ratios are compared to a published isoscape as well as new environmental samples (soil, Helix shells, rodent teeth, water, and wine). Our results show that reindeer (Rangifer) likely moved within the sedimentary basins of France and did not venture into mountainous regions. Instead, reindeer, bison (Bison) and other prey species were available year-round in the Aquitaine and Paris basins. Red deer (Cervus) and horse (Equus) may have ventured into the mountains. These results suggest that Neandertals could find year-round faunal resources in these basins, at least during MIS 4 and 3.

Sedimentary Characteristics, Ages, and Environmental Significance of Gravel Deposits and Loess in Shandong, Eastern China: Regional Response to Global Change Since the Last Glacial Period

AbstractInvestigation of rarely studied gravel layers found in the loess in Shandong Province, eastern China, reveals the fabric characteristics of two gravel layers (G1, G2) and the sedimentary characteristics of loess at the typical and well‐preserved Heiyu section (HY), where, to determine the paleoclimatic changes during Marine Isotope Stage 3a. Optically stimulated luminescence dates of the HY formation range from 0.26 ± 0.02 ka to 39.00 ± 2.00 ka. In addition, the ages of G1 and G2 were estimated using the Bayesian model to be 39.60–40.50 and 29.00–29.50 ka. G1 and G2 are mainly composed of fine and medium gravel, both of which were subangular to subrounded limestone, with gravel directions to NE and E. The average flow velocity, average depth, and flood peak flow of G1 are 1.10 m/s, 0.49 m, and 37.04 m3/s, respectively, calculated using the flow energy method, whereas those of G2 are 0.98 m/s, 0.38 m, and 18.38 m3/s, respectively. Analysis of climate proxy indices show that the sedimentary environment of the gravel and loess in HY might be a regional response to global change.

Episodic sediment accumulation linked to global change in the endorheic Qaidam Basin of the Tibetan Plateau revealed by feldspar luminescence dating

Given its high accumulation rate in sediments, the endorheic basin in arid regions plays a crucial role in reconstructing paleo-environment. However, it would not provide high-resolution climatic records if significant wind-eroded depositional hiatuses were inevitable within a severe wind environment. Unconformable contacts have been found during field survey in the top part of the stratigraphy in the Qaidam Basin, a prototypical endorheic basin in central Asia. To elucidate whether the sediment is continuous, we employed luminescence dating methods of feldspar pIR200IR250 and quartz OSL to date sediments, including lacustrine sediments and salt crusts, from the Qarhan Playa that is the Quaternary depositional center of the Qaidam Basin. Various experiment tests, including preheat plateau, dose recovery, and residual dose, were conducted. The dating results show that the feldspar pIR200IR250 can provide dependable ages with negligible residual doses. The pIR200IR250 dating ages within the last glacial cycle reveal several environmental shifts. A Qarhan paleolake in Marine Isotope Stage (MIS) 5 was demonstrated by the cluster ages of ∼140–80 ka of lacustrine sediments. The salt crust ages of 136 ± 10 ka and 97 ± 6 ka indicate that, before completely disappeared, the paleolake with shallow dish-shape depression had been dried up more than once, illustrating “shallow——dry——shallow” cycles. The playa in the eastern Qaidam Basin evolved mainly in warm periods, such as MIS 5 and MIS 1, supported by the salt crust ages of MIS 5 (136 ± 10 ka and 97 ± 6 ka) and MIS 1 (10 ± 1 ka and 0.6 ± 0.1 ka). Depositional hiatus in the last glacial cycle were identified by unconformable contacts in three sections between the lacustrine strata and their overlying playa strata, with corresponding age gaps of 158 ± 20–97 ± 6 ka, 131 ± 10–10 ± 1 ka, and 84 ± 7–0.6 ± 0.1 ka, respectively. In all the three sections the sediments for the whole of the last glacial period is missing, eroded by wind. This process should have occurred periodically during the glacial-interglacial cycles of the orbital global climatic changes. The results also show that hiatuses are common for endorheic basins on the Earth with age gaps of up to ∼100 ka, suggesting that robust chronology should be established before any climatic correlation due to severe wind erosion leading to episodic sediment accumulation.

Phylogeography of Korean field mouse Apodemus peninsulae (Rodentia: Muridae): an update

Abstract To better understand the evolutionary and demographic histories of the Korean field mouse Apodemus peninsulae we examined mitochondrial (mt) cytochrome b gene sequences of 200 specimens from 65 localities in China, Japan, Korea, Mongolia, and Russia. The phylogenetic and phylogeographic analyses revealed three major groups of haplotypes: “Chinese” (C), “Korean” (K) and “Russian” (R). C includes only the samples from southern and central China, K combines all samples from Korean Peninsula and some samples from Siberia, and R comprises all samples from Russian Far East, Japan, and most samples from Siberia. Both R and K also include the samples from Northern China and Mongolia. Coalescent-based approaches suggest a link between separation of these groups and intensive Kung-Huang Pleistocene uplift event of the Tibetan Plateau. The rapid expansion events in R are associated with marine isotope stages (MIS) 3 and 4, and in K with MIS 6; no sings of rapid expansion were found in C. The widespread settlement of the northeast occurred in two waves, close in time: 1) to Northern China and Korean Peninsula, and then 2) to most of Siberia, the Russian Far East and Japan; parts of Siberia, Mongolia and northern China were colonized twice.

Paleomagnetic secular variation and revised chronostratigraphy of Bering Sea (IODP expedition 323) deep-sea sediments (MIS 5)

This study presents new high-resolution, full-vector paleomagnetic secular variation (PSV) records from IODP Expedition 323 Sites U1339, U1343, U1344, and U1345 in the Bering Sea (51°N-60°N) during Marine Isotope Stage 5 (71–130 ka). The chronology of the records has been determined by oxygen isotope stratigraphy with an age uncertainty of ∼±2000 years. The data come from shipboard paleomagnetic measurements of deep-sea sediments with accumulation rates of 26–54 cm/ky. The sample interval in the composite records is 5 cm with a time resolution of ±100–200 years. The composite PSV records for each site were developed by correlation and analysis of 3–4 paleomagnetic records from individual holes at each site. The composite records are a combination of the best correlatable PSV data from each site. We have been able to significantly correlate the PSV records from all four sites. We have identified 56 inclination features (highs/lows) and 54 declination features (east/west extremes) in all the records. Relative paleointensity has been determined by normalizing the sediment natural remanence, after 20-mT af demagnetization, to magnetic susceptibility. This normalization process is complicated by environmental variability, thus our relative paleointensity records are limited to large-scale correlations among the four sites. We correlated our relative paleointensity records to the global PISO-1500 paleointensity record that is itself dated by oxygen isotope stratigraphy. We can identify 6 key intensity highs/lows in our composite records and the PISO-1500 record that provide additional dating isochrons for our records. There are three short magnetic field excursions recorded with replication at these four sites – The youngest excursion occurred at 100 ± 2 ka and is associated with the Fram Strait Excursion. Two older excursions occurred at 116 ± 2 ka and 119.5 ± 2 ka. We associate both of these with the Blake Event. All three of the excursions have very short time intervals (∼200–400 yrs) with somewhat out-of-phase inclination and declination variability. All three of these are Class I excursions. We have studied the statistical characteristics our composite records by calculating the 3ky and 9ky averaged inclinations, declinations, unit vectors, and relative paleointensity over 71–130 ka after removing all excursional directions. The averaged inclinations and declinations are consistent among the four sites. The averaged angular dispersion is bimodal in its overall pattern. Most of the time angular dispersion is low (∼±10°–12°) except for three shorter intervals that have significantly higher angular dispersion (∼±24–30°) and lower paleointensities. The high angular dispersion intervals are associated with the three short excursional intervals. The timing and pattern of interrelated high angular dispersion, low paleointensity, and excursions is synchronous with the PSV pattern recorded during MIS 5 in the central North Atlantic Ocean. We think this defines a distinctive low-intensity/low-energy state for the geomagnetic field.

Using stable isotopes in deciphering climate changes from travertine deposits: the case of the Lapis Tiburtinus succession (Acque Albule Basin, Tivoli, Central Italy)

Quaternary stable isotope records of marine and lacustrine carbonate deposits as well as speleothems were extensively studied to reconstruct global and regional climatic evolution. This study demonstrates how stable isotope records of travertine provide fundamental information about climate and the consequences of its evolution on groundwater level fluctuations. The deposition of the Lapis Tiburtinus travertine succession occurred during the Late Pleistocene (150–30 ka), coeval with the last activity of the Colli Albani volcanic complex. Two boreholes (Sn1 and Sn2) were drilled into the Acque Albule Basin (23 km E of Rome), crossing the entire Lapis Tiburtinus succession. The Sn1 borehole in the central part of the basin crosscuts a travertine succession of 62.1 m in thickness, while the Sn2 borehole in the southern part of the basin is characterized by a travertine succession 36.3 m in thickness. Carbon and oxygen stable isotope ratios were analysed on 118 samples (59 samples both for Sn1 and Sn2 boreholes) representative of the entire Lapis Tiburtinus travertine succession crossed by the boreholes. Values, measured and correlated in the two drilled boreholes, permitted determination of the sensitivity of the travertine depositional system to glacial and interglacial cycles, unravelling the complex oxygen and carbon cycle dynamic recorded in such sedimentary succession. Moreover, the results obtained correlated with available pollen curves of the Mediterranean area (from the Castiglione crater, 25 km E of Rome). Regional and global oxygen isotope continental and marine curves, calibrated with the stratigraphy of the Acque Albule Basin, and available U/Th dating allow the identification of at least three phases of the last interglacial (Marine Isotope Stage 5-MIS5). The carbon isotope record, compared with CO2 flux reconstructed and associated with the volcanic activity of the Colli Albani volcanic complex, instead shows an influence from groundwater level changes. In particular, positive shifts that occurred during arid phases are associated with a lower groundwater level and increased CO2 degassing, inducing a major fractionation effect on carbon isotopes. Instead, the negative shifts occurring during more humid periods indicate the inhibition of CO2 degassing and increase in pressure, attesting to a rise in groundwater level. In this view, travertine deposits, frequently studied to define the tectonic setting and activity of the area where they develop, can thus also be used as a tool to understand climate changes and groundwater variations apparent in their stable oxygen and carbon isotope signature.

A Quaternary sequence of terrestrial molluscs from East Africa: a record of diversity, stability, and abundance since Marine Isotope Stage 5 (78,000 BP)

A Quaternary sequence of terrestrial molluscs from East Africa: a record of diversity, stability, and abundance since Marine Isotope Stage 5 (78,000 BP)

Distinct oxygenation modes of the Gulf of Oman over the past 43 000 years – a multi-proxy approach

Abstract. Changing climatic conditions can shape the strength and extent of the oxygen minimum zone (OMZ). The presence and variability of the OMZ in the Arabian Sea is of importance to the latter's ecosystem. The state of oxygenation has, for instance, an impact on the pelagic and benthic faunal community or the nitrogen and carbon cycles. It is important to understand the dynamics of the OMZ and related marine environmental conditions because of their climate feedbacks. In this study, we combined three independent proxies to reconstruct the oxygenation state of the water column and bottom water in the Gulf of Oman for the past 43 kyr approximately. This multi-proxy approach is done for the first time at the northeastern Oman margin located in the Gulf of Oman. We used bulk sedimentary nitrogen isotopes (δ15N) and the alkane ratio (lycopane +n-C35)/n-C31 and benthic foraminiferal faunal analysis to reconstruct the strength of the OMZ in the water column and bottom water oxygenation, respectively. Our results show that the Gulf of Oman experienced strong pronounced OMZ and bottom water deoxygenation during the Holocene. In contrast, during Marine Isotope Stage 2 (MIS 2), including the Last Glacial Maximum (LGM), the Gulf of Oman was very well ventilated, with a highly diverse benthic foraminiferal community. This may have been caused by stronger wind-induced mixing and better ventilation by oxygen-rich water masses. Our results also show moderate oxygenation during MIS 3, with deoxygenation events during most of the warmer Dansgaard–Oeschger (D–O) events. We propose two distinct oxygenation modes for the Gulf of Oman: (1) a stable period of either strongly pronounced water column OMZ and bottom water deoxygenation or well-oxygenated water column and bottom water conditions and (2) an unstable period of oscillating oxygenation states between moderately oxygenated (stadials) and deoxygenated (interstadials, D–O events) conditions. The unstable period may be triggered by an interstadial Atlantic meridional overturning circulation (AMOC) mode, which is required to initiate D–O events.

Vegetation response to climate changes in the eastern Arctic during the Middle Gelasian age of the Early Pleistocene

Palynological analysis of sediments from El'gygytgyn Lake document vegetation changes in the Eastern Arctic from early marine isotope stage (MIS) 74 to late MIS 80 (c.2.1–1.9 MA) and close the last remaining gap in the El'gygytgyn pollen record. Cooler climates were characterized by a mix of Larix forest-tundra, shrub Betula tundra, and herb-dominated communities. During interglaciations, Larix forests with tree Betula and Alnus, and perhaps with a minor component of Picea and tree Pinus, characterized areas that today are tundra. These forests included a rich shrub understory of Betula, Duschekia, Salix, and Pinus pumila. Although MIS 77 has been considered a “super” interglaciation, the data do not indicate that this stage was exceptionally warm. Interstadial conditions are denoted by pollen assemblages that indicate the regional vegetation was dominated by Larix forest -tundra and an absence of Pinus pumila. The palynological results from this Early Pleistocene interval demonstrate the need to: 1) modify the El'gygytgyn age model; 2) reevaluate the relationship of sediment facies to climate change; and 3) reconsider the occurrence and/or definition of “super” interglaciations.

Sediment provenance variations driven by sea level in the eastern Arabian Sea since the MIS 9 period: Evidence from geochemical proxies

Although the uplift of the Tibetan Plateau has led to strong land-sea interactions, the characteristics of sediment transport and their controlling factors in typical marine areas in the northern Indian Ocean since the Quaternary are not clear. This work aimed to reconstruct the pattern of change in the sources of sediments since the Marine Isotope Stage 9 (MIS 9) period and to explore the mechanism of their response to changes in the marine environment in the Arabian Sea. To this end, a comprehensive multi-indicator study of the chronology and geochemical elements was carried out in core AS05-7 from the eastern Arabian Sea. Major trace element factor analysis and rare earth element (La/Yb)N-δEuN mapping suggested that sediments in the eastern Arabian Sea were mainly derived from terrestrial inputs from the Indus River and the Deccan Plateau. The sediments showed a clear glacial-interglacial cycle of change, with the contribution of the Indus River increasing during the interglacial period and that of the Deccan Plateau increasing during the glacial period. On average, the Indus River and Deccan Plateau contributed 71 % and 29 %, respectively, to the total amount of sediment. Indicators such as mass accumulation rate and Ca/Ti showed that the inputs from the terrestrial sources showed clear glacial-interglacial characteristics, with inputs during the glacial period being higher than those during the interglacial period. The lowering of the sea level during the glacial period led to an increase in the exposed area of the shelf, the shifting of deposition centers closer to the core, an increase in the rate of mass accumulation, and an increase in riverine inputs to the sea when clastic sediments from the Deccan Plateau increased. The elevation of the sea level during the interglacial period led to the inundation of the shelf, the shifting of deposition centers away from the core, a decrease in the rate of mass accumulation, and a reduction in riverine inputs to the sea when detrital sediments from the Deccan Plateau decreased. Changes in terrestrial inputs and sources revealed the orbital-scale control of sea-level change on sedimentary processes in the Arabian Sea and provided direct evidence for the “source-sink” model of sedimentation in the tropical Indian Ocean.

Seasonal climate variations during Marine Isotope Stages 3 and 2 inferred from high‐resolution oxygen isotope ratios in horse tooth enamel from Lower Austria

ABSTRACTWe present sequential oxygen isotope records (δ18Ophosphate vs. VSMOW) of horse tooth enamel phosphate of six individuals from two adjacent Palaeolithic sites in Lower Austria. Three molars from the site Krems‐Wachtberg date to 33–31k cal a bp, and three molars from Kammern‐Grubgraben to 24–20k cal a bp. All teeth show seasonal isotope variations, which are used to reconstruct the annual oxygen isotope composition of drinking water (δ18Odw) and palaeotemperatures. Measured δ18Ophosphate values ranged from 8.6 to 13.0‰ and from 10.8 to 13.9‰ at Krems‐Wachtberg and Kammern‐Grubgraben, respectively. An inverse modelling approach was used to reconstruct summer and winter temperatures after a correction for glacial oceanic source water δ18O. Reconstructed annual δ18Odw was −16.4 ± 1.5‰ at Krems‐Wachtberg and −15.3 ± 1.4‰ at Kammern‐Grubgraben, resulting in annual temperatures of −5.7 ± 3.1 and −3.5 ± 2.9°C, respectively. Summer and winter temperatures reconstructed from individual teeth exhibit high seasonal variations with moderate summer temperatures and extremely low winter temperatures typical for a polar tundra climate. Isotopic differences between individuals are attributed to interannual climate variability or to different drinking water sources. Our reconstructed temperatures are, overall, consistent with previously reported values from European horse teeth, when taking regional differences into account.

Sea-level and monsoonal control on the Maldives carbonate platform (Indian Ocean) over the last 1.3 million years

Abstract. The Maldives Archipelago (Indian Ocean), composed of two rows of atolls that enclose an inner sea, offers an excellent study site to explore the forcings of carbonate production at platforms. Glacial–interglacial sea-level changes have been claimed to be the main factor controlling the carbonate platform factories; however, climatic factors may also have an impact. In this work we used geochemical compositional records, obtained by X-ray fluorescence (XRF) core-scanning from the International Ocean Discovery Program (IODP) Site U1467 in the Maldives Inner Sea, to analyze the orbitally driven fluctuations on the carbonate production and export from the neritic environment into the Maldives Inner Sea over the last 1.3 million years. High Sr aragonite-rich carbonates (HSAC) from neritic settings were deposited in the Maldives Inner Sea during sea-level highstand intervals, increasing the Sr/Ca values. In contrast, low Sr/Ca values are observed coincident with sea-level lowstand periods, suggesting that large areas of the atolls were exposed or unable to grow, and therefore, there was a demise in the carbonate production and sediment export to the Maldives Inner Sea. However, comparison of the Sr/Ca values and the sea-level reconstructions for different interglacial periods before and after the mid-Brunhes event (MBE, ∼ 430 ka) indicates that sea level is not the only factor controlling the production of HSAC during sea-level highstands. The study of monsoon and primary productivity proxies (Fe-normalized, Fe/K, and Br-normalized records) from the same site suggests that the intensity of the summer monsoon and the Indian Ocean dipole probably modulated the carbonate production at the atolls. Moreover, Marine Isotope Stage 11 stands out as a period with high sea level and extraordinary carbonate production in the Maldives platform. This outstanding carbonate production in the Maldives atolls (and in other low-latitude carbonate platforms) probably contributed to the mid-Brunhes dissolution event through a strong shelf-to-basin fractionation of carbonate deposition.

Vegetation changes through stadial and interstadial stages of MIS 4 and MIS 3 based on a palynological analysis of the Girraween Lagoon sediments of Darwin, Australia

A palynological record from Girraween Lagoon sediments (Darwin region of the Northern Territory, Australia) provides detailed long-term insight into tropical savanna vegetation community patterns, climatic and fire relationships, through Marine Isotope Stage 4 (MIS 4: 71–57 thousand years ago, ka) and Marine Isotope Stage 3 (MIS 3: 57–29 ka). Owing to a lack of data in reconstructing northern Australian environments, this paper looks to define and describe to a greater degree the nature and scope of these stadial and interstadial stages for the region. Girraween Lagoon simultaneously provides proximal palaeoecological data for the time and region of Aboriginal people's first arrival into Australia, also encompassing the late Pleistocene continental decline of megafauna. This study provides a dataset enabling full exploration of long-term people-landscape and faunal-floral interactions. Sea levels and associated variations imposed on the transportation of moisture and heat, held implications for MIS 4 and MIS 3 monsoon strength, which was particularly consequential for Girraween regional ecology. Results reveal a prolonged transition from wooded- to grassy-savanna, into a cool drier semi-arid savanna. Increasingly episodic delivery of moisture influenced the permanency of freshwater in the landscape.

Biogenic carbonates (queras) in loess-palaeosol sequences of the Ebro Basin and their potential use as a palaeoenvironmental proxy

Secondary carbonate accumulations are very common in arid and semi-arid soils but are often poorly described and classified. This is the case for queras that are observed in several loess-palaeosol sequences of the Ebro Basin. Micromorphologically, queras are complex pedogenic features basically consisting of infillings of calcified root cells in channels, surrounded by decarbonated hypocoatings. They apparently result from biologically mediated calcification/decalcification processes at a microscale. The aim of this study is to systematically characterize biocalcifications found in dated loess-palaeosol sequences, to determine the main factors of formation, and to discuss their possible use as a palaeoenvironmental proxy. Different queras show a similar number of biosparite layers (four to five) around a central channel, and a decarbonated hypocoating around the queras. This supports the hypothesis that queras originate from the calcification of root tips and are related to the acidification of surrounding soil for nutrient absorption. Under cathodoluminescence microscopy, biosparite has a different behaviour than non-biological calcite crystals: the latter appears reddish while biosparite remains black. The queras, with ages corresponding to Marine Isotope Stages 1–3, are younger than that of the loess where they are found in. The stable isotope values likely correspond to C3 plants, and the estimated temperatures of formation reflect a Mediterranean temperate climate. This suggests that the biocalcifications developed during short moist seasons amidst arid periods of the Quaternary.

The Middle Pleistocene human metatarsal from Sedia del Diavolo (Rome, Italy)

The peopling of Europe during the Middle Pleistocene is a debated topic among paleoanthropologists. Some authors suggest the coexistence of multiple human lineages in this period, while others propose a single evolving lineage from Homo heidelbergensis to Homo neanderthalensis. The recent reassessment of the stratigraphy at the Sedia del Diavolo (SdD) site (Latium, Italy), now dated to the beginning of marine isotope stage (MIS) 8, calls for a revision of the human fossils from the site. In this paper, we present the morphometric, biomechanical and palaeopathological study of the second right metatarsal SdD2, to both re-evaluate its taxonomical affinities and possibly determine the levels of physical activity experienced by the individual during lifetime. Results demonstrate the persistence of archaic features in SdD2 suggesting new insights into the technology and hunting strategies adopted by Homo between MIS 9 and MIS 8.