Marine Isotope Stage Research Articles

Glacial-interglacial environmental changes in the Drake Passage over the past 600 kyrs

Oceanographic conditions in the Southern Ocean are closely related to the oceanic frontal system. Glacial-interglacial changes in cryosphere influence variations in oceanic fronts in the Southern Ocean and vice versa, causing changes in surface water productivity, nutrient utilization, bottom water chemistry, and/or bottom current intensity. Here, we documented geochemical, nitrogen isotope, and grain size records over the last 600 kyrs from the Drake Passage with previously published data to compare between glacial and interglacial oceanic conditions from surface to bottom. Biogenic opal (diatom) and export productions were high during interglacial periods and low during glacial periods. Surface water production was dominated by open ocean species during both glacial and interglacial periods without a clear glacial-interglacial change in sea ice species. After Marine Isotope Stage (MIS) 9, interglacial biogenic opal and diatom abundance increased distinctively with decreased terrestrial influence. Nutrient utilization increased (decreased) during interglacial (glacial) periods with increased (decreased) surface water production, particularly after MIS 9. This indicates that surface water production was regulated by light availability in association with sea ice duration/extent. According to good correlation between sortable silt mean grain size (SS MGS) and %sortable silt, SS MGS can be used for bottom current intensity indicator in this study; increased (decreased) bottom current during glacial (interglacial) periods. Increased glacial bottom current is likely related to southwestward flowing bottom current. Interglacial bottom current intensity became also significantly weakened after MIS 9. However, outstanding interglacial warmth in the Drake Passage occurred from MIS 9, not following the global trend to occur after MIS 11. This implies that more studies from the Southern Ocean in response to the Mid-Brunhes Event are required in the future.

Marine Isotope Stage 4 (71–57 ka) on the Western European margin: Insights to the drainage and dynamics of the Western European Ice Sheet

Marine Isotope Stage 4 (71–57 ka) on the Western European margin: Insights to the drainage and dynamics of the Western European Ice Sheet

Humid phases on the southwestern Arabian Peninsula are consistent with the last two interglacials

Past environmental and climatic conditions within the Arabian Peninsula are key to understanding the setting for hominin dispersal across the Saharo-Arabian dryland belt. The tufa deposits within the volcanic harrats on the southwest coast of Saudi Arabia fill a significant spatial gap in the distribution of palaeoenvironmental records on the west coast of the Arabian Peninsula adjacent to the Red Sea. In the catchment of Wadi Dabsa in the Harrat Al Birk, there are widespread fossil palustrine to shallow-lacustrine tufa deposits with fluvial elements. Several phases of tufa accumulation, separated by fluvial downcutting, are observable within these powerful palaeoenvironmental proxies. U–Th dating of targeted dense, banded tufa facies, yield ages that are stratigraphically consistent at the landscape scale, and indicate that tufa accumulation occurred during distinct humid phases broadly coeval with the last two warm interglacial Marine Isotope Stages (MIS 7 and MIS 5). For the first time this shows humid intervals in southwest Arabia coincident with the southern coast. There is a simlar pattern emerging further north in the Arabian Peninsula, The Sinai and Levant and further on into continental Europe. Furthermore, tufa δ18O ranges from −14.6 to −1.9‰, covering a range similar to those reported for tufa from north African oasis sites and speleothems elsewhere on the Arabian Peninsula and The Levant. The lowest δ18O values are derived from MIS 5e samples, a pattern in agreement with speleothems in Yemen and Oman, and consistent with an isotopic-enabled climate model simulation for this time slice. The δ13C and Sr isotopic compositions of dated tufa samples indicate deposition from shallow-circulating meteoric water, with no geothermal influence. This, along with the δ18O values, suggest a freshwater supply that was a potable water source in this landscape. The δ13C signatures at Wadi Dabsa are more negative than for parts of north Africa, suggesting Wadi Dabsa may have experienced comparatively higher biomass, thicker soils and wetter conditions with lower evaporative losses. This new record of tufa deposition during the middle and late Pleistocene, suggests for the first time that the west coast of Arabia experienced a similar history of humid phases over the past 250 ka as southern Arabia and the Nefud in the northern interior. These regional changes in hydroclimatic regime occur at timescales coincident with hominin dispersals.

Late Quaternary river evolution and its response to climate changes in the upper Mekong River of the Qinghai–Tibetan Plateau

Multiple continental-scale large rivers originate from the Qinghai–Tibetan Plateau (QTP), known as the “Asia Water Tower”, because of glacial melting. However, the timing of fluvial processes in the headwaters of these large rivers and their correlation with global climate changes remain uncertain. Among these rivers, the Mekong River, the third-longest in Asia, flows through the southeastern QTP. In this study, we investigated fluvial terraces, buried paleochannels, hillslope-derived colluvium, and remnants of dammed lake in the Nangqian Basin, which is in the headwaters of the Mekong. We reconstructed the fluvial aggradation and incision history employing optically stimulated luminescence (OSL) dating. Our results suggest that orbital-scale climate changes have significantly influenced fluvial processes in the Nangqian Basin since the Late Pleistocene. During marine isotope stage (MIS) 3 (57–29 ka), a relatively warm period within the last glacial epoch, the Nangqian Basin experienced aggradation of fluvial sediment. Subsequently, during the later part of the Last Glacial Maximum (LGM) (21–17 ka), episodic landslides and debris flows caused valley infilling, resulting in river blockage and the formation of a dammed lake. At around 16 ka, the Mekong in the Nangqian Basin shifted from aggradation to fluvial incision. Since the late Holocene, the basin returned to aggradation, forming a new terrace at around 1.1 ka. This may be due to the combination of decreased stream power and increased sediment supply, potentially linked to intensified human activities and its associated vegetation degradation. Overall, our study highlights the close links between glaciation and fluvial processes in the region. Specifically, we propose that the observed aggradation pattern during the last glacial period on the plateau primarily resulted from substantial detrital input from glacier activities. The transition from aggradation to incision during the last deglacial period is likely influenced by increased discharge from glacier meltwater. The presence of colluvium interbedded within the late LGM fluvial sediment sequences highlights the significant impact of climate changes on fluvial processes in the headwater areas of the QTP, especially those events stemming from hillslope activity, such as landslides and debris flows.

Multi-proxy speleothem-based reconstruction of mid-MIS 3 climate in South Africa

Abstract. The southern coast of South Africa displays a highly dynamical climate as it is at the convergence of the Atlantic and Indian oceans, and it is located near the subtropical/temperate zone boundary with seasonal influence of easterlies and westerlies. The region hosts some key archeological sites with records of significant cognitive, technological and social developments. Reconstructions of the state and variability of past climate and environmental conditions around sites of archeological significance can provide crucial context for understanding the evolution of early humans. Here we present a short but high-resolution record of hydroclimate and temperature in South Africa. Our reconstructions are based on trace elements, calcite and fluid inclusion stable isotopes, as well as fluid inclusion microthermometry, from a speleothem collected in Bloukrantz cave, in the De Hoop Nature Reserve in the southern Cape region of South Africa. Our record covers the time period from 48.3 to 45.2 ka during marine isotope stage 3. Both δ18Oc and δ13Cc show strong variability and covary with Sr/Ca. This correlation suggests that the control on these proxies originates from internal cave processes such as prior carbonate precipitation, which we infer to be related to precipitation amount. The hydroclimate indicators furthermore suggest a shift towards overall drier conditions after 46 ka, coincident with cooling in Antarctica and drier conditions in the eastern part of South Africa corresponding to the summer rainfall zone (SRZ). Fluid inclusion-based temperature reconstructions show good agreement between the oxygen isotope and microthermometry methods, and results from the latter display little variation throughout the record, with reconstructed temperatures close to the present-day cave temperature of 17.5 ∘C. Overall, the BL3 speleothem record thus suggests relatively stable temperature from 48.3 to 45.2 ka, whereas precipitation was variable with marked drier episodes on sub-millennial timescales.

Improving tephrostratigraphy and cryptotephrostratigraphy since 1 Ma of Hole U1437B in the Izu-Bonin arc, NW Pacific: Differentiation of widespread tephras with similar shard chemistries

We investigated the deep-sea sedimentary sequence of Hole U1437B, corresponding to the last 1 Ma, in the Izu-Bonin arc, NW Pacific Ocean, and refined its tephrostratigraphy. We correlated many tephras and cryptotephras with terrestrial and marine tephras on the basis of the major- and trace-element compositions of their glass shards by referring to the reported tephrostratigraphy of marine sediments in core MD012422 (since 0.35 Ma) off Shikoku Island, in Holes ODP1151C (0.2–0.8 Ma) and C9001C (since ca. 0.8 Ma) off northern and northernmost Honshu, respectively, and on the Boso Peninsula (since 1 Ma). Many widespread tephras and cryptotephras were detected in the hole such as those originated from the Kyushu volcanic zone (from north to south, Yufu-Tsurumi, Shishimuta, Aso, Kakuto, Kobayashi, Aira, Ata, and Kikai volcanoes/calderas), Hakkoda-Kokumoto tephra originated from Hakkoda caldera, northernmost Honshu, and some tephras probably originated from source(s) in northern Honshu. Among the widespread tephras, those with similar shard chemistries occurred at different horizons. Kasamori 5 tephra (Ks5) was newly detected by this study in a position above the previously reported "Ks5" horizon in Hole U1437B. The newly detected Ks5 tephra occurs in the marine isotopic stage (MIS) 12 segment of the δ18O stratigraphy, consistent with the reported stratigraphic age of Ks5 (MIS 12b–c) in Hole C9001C. Although the reported "Ks5" horizon also occurs in the MIS 12 segment in Hole U1437B, it is actually a different unidentified tephra, as indicated by its slightly different shard chemistry. Further, we correlated Kasamori 10 tephra (Ks10: mid-MIS 13) in Hole U1437B to subspike G19.3 in Hole C9001C but not to subspike G4.4 in Hole ODP1151C. Although subspike G4.4 in Hole ODP1151C was previously estimated on the basis of its shard major-element composition to correspond to subspike G19.3 in Hole C9001C, their shard trace-element compositions differ. Instead, on the basis of their shard chemistries, we correlated subspike G4.4 in Hole ODP1151C to spike G90 in Hole U1437B (MIS 14), which occurs below the Ks10. This tephra has not been reported in the marine Kasamori Formation on the Boso Peninsula. Further, spike G7 in Hole ODP1151C, which is below subspike G4.4 and above spike G9 (a correlative of Ks22 and Kaisho-Kamitakara tephra, MIS 16), is here correlated to Ks18 in the MIS 15 horizon of Hole U1437B on the basis of their shard chemistries. The stratigraphic ages of Ks5, Ks10, the spike G90 tephra, and Ks18 at most (but not all) locations are roughly consistent with the age of a globally correlated biohorizon, the last appearance datum of Pseudoemiliania lacunosa (ca. 0.45 Ma). These findings emphasize that Hole U1437B sediments are as good as or better than the marine sediments on the Boso Peninsula as archives of the regional tephrostratigraphy. Thus, they are useful for improving the Middle Pleistocene tephrostratigraphy in the NW Pacific region.

Anomalous 234U/238U isotopic composition in Southern Ocean sediments

Uranium is a redox-sensitive trace element that under certain sedimentary conditions will reflect changes in past biological productivity and/or deep ocean ventilation. Applications for the isotopic composition of U (234U:238U activity ratio, δ234U or the per mil deviation from secular equilibrium) as a paleoceanographic proxy, however, remain largely unexplored in pelagic sediments. We present δ234U of bulk U for a 504-kyr record of South Atlantic core ODP 1094, a record that has exhibited sensitivity to bottom water formation with minimal 238U remobilization due to changes in redox condition. Sedimentary δ234U at time of burial was modeled given authigenic and detrital sources, where it was found that δ234U has a reoccurring pattern of anomalous behavior around deglacial transitions. In many cases, the anomalous δ234U compositions in sediment exceeded seawater, which is not consistent with its expected sources. A mass balance of 234U across these anomalous sections showed that vertical rearrangement of 234U can explain anomalous sedimentary δ234U during Marine Isotope Stage (MIS) 7/8 and 11/12 transitions, as well as partially during MIS 5/6 and MIS 9/10. The distribution of these anomalies is likely consistent with the idea that deglacial spikes in aU, resulting from periods of high organic carbon delivery and thereby strong reduction in the sediments, act as a persistent sink of 234U alpha-recoiled from vertically adjacent sediment layers after burial. While this mechanism explains the negative δ234U anomalies, there is a large subset of positive δ234U anomalies that cannot be explained by vertical diffusion of 234U in pore waters alone. This excess 234U points to an extremely high δ234U source to seawater during deglaciation or additional diagenetic effects such as diffusion from lateral heterogeneity in the redox state of sediment at depth. We find that δ234U of pelagic sediment may be useful to identify fine-scale pore water migration of alpha-recoil products.

Demographic processes, refugia and dispersal routes during the Pleistocene in a sigmodontine rodent assemblage from the South American Pampas

Abstract The Pampas of South America represents one of the most extended subtropical–temperate grasslands in the world. This ecoregion was influenced by Pleistocene climate oscillations. The sigmodontine rodent assemblage inhabiting this region is a good model system to analyse the impact of these climate changes on evolutionary histories. We performed a comparative phylogeographical study on seven species to evaluate the concordance of phylogeographical patterns among them, to assess if they experienced congruent and synchronous demographic changes, and posit putative centres of origin and dispersal routes. Four species (Calomys musculinus, Oligoryzomys flavescens, Oxymycterus nasutus and Oligoryzomys nigripes) showed evidence of demographic expansion. In the first three, population increases started during Marine Isotope Stage 5 (MIS 5) while in Ol. nigripes, the rise started during MIS 7; this rise would have continued to the present in all cases. Necromys lasiurus, Scapteromys tumidus and Scapteromys aquaticus did not show a pattern of expansion. Four centres of origin were identified; in general, populations sharing the same putative refugium followed common dispersal routes. Our results indicate that the Pampas offered relatively stable habitats over time, mainly in areas associated with watercourses or coastlines, suggesting that recent Pleistocene climate oscillations have had a moderate impact on this ecoregion compared to other regions of South America.

Vegetation cover dynamics on the northeastern Qinghai-Tibet Plateau since late Marine Isotope Stage 3

Knowledge of long-term changes in vegetation cover is essential for paleoenvironmental reconstruction and Earth system modeling. The vegetation on the northeastern Qinghai-Tibet Plateau (QTP) is highly sensitive to climatic changes, but studies of long-term changes in the vegetation cover of this region are lacking. To better understand the changes in the regional vegetation cover since late Marine Isotope Stage (MIS) 3, we obtained a pollen record from Luanhaizi Lake and used it to quantitatively reconstruct changes in the cover of trees and grasses using the random forest method. The pollen spectra show that the vegetation of the Luanhaizi Lake area was probably alpine tundra from late MIS3 to the Last Glacial Maximum, after which it changed to alpine steppe with alpine shrub and sparse forest at lower elevations during the last deglaciation. Alpine steppe and alpine meadow dominated the vegetation during the Holocene, with sparse forest in the surrounding low-elevation areas. The quantitative vegetation cover reconstruction suggests that the vegetation cover of the Luanhaizi Lake area was low (20–30%) during 47.0–20.0 ka. The tree cover then increased from ∼3% to ∼10%, and the grass cover increased from ∼20% to ∼45% during the last deglaciation (20.0–11.9 ka). The increasing Northern Hemisphere summer insolation caused increases in the regional temperature, meltwater supply, and monsoon precipitation, which promoted the development of steppe vegetation. The continued increases in insolation and monsoonal precipitation during the Holocene further increased the tree cover, which reached a maximum of 17.4% at ∼7.2 ka. Vegetation cover reconstructions from two other sites on the eastern QTP for the last deglaciation indicate contrasting patterns of changes, likely due to contrasts in elevation, climate, and environment.

One million years of Mediterranean outflow strength

An orbitally tuned age model is established, based principally on sortable silt mean grainsize (SS¯, proxy for flow speed), for sediments deposited under the influence of the Mediterranean Outflow (MO) at IODP Site U1389 in the Gulf of Cadiz. The possibility of tuning sortable silt grainsize to insolation was indicated by close agreement between these two parameters on an earlier isotopically-based age model for the upper 130 m of the core. This led to tuning of the whole 390 m-long record with addition of a magnetic susceptibility control at Marine Isotope Stage 16, and the last occurrence of R. asanoi datum at around 900 ka (now dated at 910 ka in this core).The strongest variability in SS¯ is precessional with speed maxima at insolation minima superimposed on an increase in flow speed from 620 ka to the present. Although the Gibraltar sill exercises a major control on the inflow and outflow to the Mediterranean, there is little change in flow depth over most 20 ka precessional cycles, and therefore minor hydraulic control. Accelerations in average flow speed are also seen in interglacial to glacial (IG-G) cycles, particularly after 550 ka, with strong speed maxima at maximum glacial lowering of sealevel. This has allowed calculation of the sensitivity of flow speed to sea-level (SL) change of ∼0.074 cm s−1/m. From 990 to 620 ka the average amplitude of precessional speed changes is 3.7 cm s−1, but this increases to 7.7 cm s−1 from 620 ka to present.Deep ocean flow speeds are mainly density driven. Previous work has demonstrated that the major drivers of this system's density on precessional timescales are the evaporation - precipitation - inflow balance in the eastern Mediterranean plus cooling in the Gulf of Lions. Published benthic δ18O for 125–235 ka (corrected for ice volume changes) which tracks the combination of seawater temperature and salinity that controls density, demonstrates that flow speed and density maxima are coincident for that period and probably for the whole record. Although precessional SL changes are too small to affect flow speed significantly, SL does control accelerations at glacial maxima because shallower flow depth reduces inflow and leads to longer evaporation time, resulting in increased outflow density and speed. The sensitivity of flow speed to sill depth changes has allowed estimation of the long-term shallowing of the Gibraltar sill of ∼68 m over the last 620 ka in agreement with dated terrace uplift.

Sediment Grain-Size Composition in the Permafrost Region of the Greater Khingan Range and Its Significance as a Material Source

Sediment grain-size distribution (GSD) provides rich information about sedimentary sources and can potentially do the same with regard to environmental and climatic changes. However, neither traditional descriptive statistics nor curving-fitting methods can fully address its complexity. We selected the Greater Khingan Range in northeastern China as the study area and used parameterized end-member analysis (EMA) of the GSD of four drilling cores to extract different end-member (EM) components. The results show that EM1 (mode particle size (Mo): 1.26–1.66 μm) originates from weathering and pedogenesis. The EMs with Mo values of 4.37–5.01 μm represent components transported by the upper westerly wind. EMs with Mo values of 7.58 μm and 11.48 μm represent wet dust deposition and dry dust deposition. The wind transport of particles in winter consists of low-level near-source transport and local-source transport (possibly from the flood plain of the Amur River). Due to the limitations of the EM model, the two sources have one or two EM components: AEM3 + AEM4, BEM3 + BEM4, CEM4, and DEM4. DEM5 is the only large particle-size component and may represent coarse-grained detritus generated via rock weathering. The components related to the winter monsoon and the 14C dating data suggest a weak-strong-weak-strong trend of the winter monsoon since the Marine Isotope Stage 3a (MIS 3a). Our results suggest that the strengthening of the winter monsoons in the previous few thousand years has caused the transportation of coarser grain sizes and further exacerbated permafrost degradation, providing a scientific reference for understanding climate change and the formation and evolution of permafrost in the Greater Khingan Mountains since the MIS 3a.

Iberian Margin surface ocean cooling led freshening during Marine Isotope Stage 6 abrupt cooling events

The high-resolution paleoclimate records on the Iberian Margin provide an excellent archive to study the mechanism of abrupt climate events. Previous studies on the Iberian Margin proposed that the surface cooling reconstructed by the alkenone-unsaturation index coincided with surface water freshening inferred from an elevated percentage of tetra-unsaturated alkenones, C37:4%. However, recent data indicate that marine alkenone producers, coccolithophores, do not produce more C37:4 in culture as salinity decreases. Hence, the causes for high C37:4 are still unclear. Here we provide detailed alkenone measurements to trace the producers of alkenones in combination with foraminiferal Mg/Ca and oxygen isotope ratios to trace salinity variations. The results indicate that all alkenones were produced by coccolithophores and the high C37:4% reflects decrease in SST instead of freshening. Furthermore, during the millennial climate changes, a surface freshening did not always trigger a cooling, but sometimes happened in the middle of multiple-stage cooling events and likely amplified the temperature decrease.

Long-term glacial and fluvial system coupling in southern Greece and evidence for glaciation during Marine Isotope Stage 16

Pleistocene glacial activity was a major influence on runoff and sediment supply in many river systems across the Mediterranean. The geomorphological impacts of changes in sediment supply between glaciated headwater terrains and downstream depocentres spanning several glacial cycles are, however, poorly understood. By applying uranium-series and optically stimulated luminescence dating to fluvial and glacial sediments preserved on Mount Chelmos (2355 m a.s.l.) in southern Greece, we show how changes in the long-term coupling between glacial and fluvial systems are preserved within a major glaciofluvial outwash fan system that functioned during multiple cold stages. We also present evidence in the form of a cemented till unit, stratigraphically below younger Middle Pleistocene glacial deposits, yielding a U-series age close to the limit of the technique, indicating glaciation during Marine Isotope Stage (MIS) 16 - one of the most severe cold stages recorded in the Mediterranean. This is the first time such early glaciation has been directly recorded in Greece and the wider Balkans and is defined here as the Valvousian Stage based on glacial deposits on Mount Chelmos. Geomorphological and geochronological data point to the formation of a more extensive plateau ice field over Chelmos during MIS 12, another severe glacial period in the Balkans that corresponds with the Skamnellian Stage glaciation of Northern Greece. During this phase, very strong coupling of glacial and fluvial systems led to meltwater flood events transferring large volumes of sediment to lower valley zones culminating in the formation of an extensive glaciofluvial outwash fan complex and glaciofluvial terraces. A smaller plateau ice field during MIS 6 and localised valley glaciers between MIS 5d to 5c correlate with the Vlasian and early Tymphian Stage glaciations in Greece, respectively. The delivery of much less meltwater and sediment through a single valley during MIS 6 and MIS 5b to MIS 4 signalled the transition to progressively weaker glacial and fluvial system coupling. After MIS 4 the uncoupling of depositional zones from sediment sources in glaciated catchments led to fluvial incision of glaciofluvial outwash deposits in several valleys. Despite this incision, the glaciofluvial outwash fans preserve a record of glacial and fluvial system interactions during the Middle Pleistocene and early stages of the Late Pleistocene.

40Ar/39Ar Age Constraints on MIS 5.5 and MIS 5.3 Paleo‐Sea Levels: Implications for Global Sea Levels and Ice‐Volume Estimates

AbstractWe integrate 10 new with five published 40Ar/39Ar age determinations, both on primary volcanic deposits and on detrital sanidine, which provide precise geochronologic control on the Marine Isotope Stage (MIS) 5.5 and MIS 5.3 sea‐level indicators that occur at three coastal caves in a tectonically stable region of the central Tyrrhenian Sea of Italy. The age of a Strombus‐bearing bioclastic conglomerate, associated with a tidal notch occurring at 9.5 m a.s.l. at Cape Circeo, is constrained to between 121.5 ± 5.8 and 116.2 ± 1.2 ka. Moreover, backbeach deposits intercalated in the sedimentary filling of Guattari and Capre coastal caves are directly correlated with a tidal notch at ∼2.5 m associated with another bioclastic conglomerate at Cape Circeo and dated to 110.4 ± 1.4–104.9 ± 0.9 ka. The latter deposit is also correlated with the adjacent marine terrace, occurring at 3–5 m on the coast between Capes Circeo and Anzio, for which a maximum age of 100.7 ± 6.6 ka was previously reported. These data provide evidence for a maximum sea level around 9.5 m above the present sea level and a duration of MIS 5.5 highstand until 116 ka, in agreement with estimates from other regions in the world. In contrast, they suggest a maximum sea level during MIS 5.3 highstand that is similar to the present level, and only ∼7 m lower than the MIS 5.5 highstand, challenging the reconstructions of the MIS 5 ice‐sheet volumes and derived global sea levels that are based on benthic oxygen isotope records.

The stratigraphy and formation of Middle Stone Age deposits in Cave 1B, Klasies River Main site, South Africa, with implications for the context, age, and cultural association of the KRM 41815/SAM-AP 6222 human mandible

Cave 1B, in the Klasies River Main site complex (KRM), is best known for the recovery of the KRM 41815/SAM-AP 6222 human mandible. After initial skepticism over the modernity of this specimen, it is accepted that the mix of archaic and modern traits it displays is characteristic of early Homo sapiens individuals. Different authors have associated this specimen with the Middle Stone Age (MSA) I and II/Mossel Bay cultural phases, but the published data do not allow an unambiguous attribution. KRM 41815's frequent use in studies of the evolution of the human mandible, and its well-developed chin, makes clarifying its age and context important objectives. The field and micromorphology observations presented here provide greater insight into the stratigraphy and formation of the sequence exposed in the PP38 excavation. There are three major divisions: the basal Light Brown Sand (LBS) Member (not excavated), the Rubble Sand (RS) Member (MSA I), and the Shell and Sand Dark Carbonized (SASDC) Submember (MSA II). Cultural stratigraphy based on lithic artifacts remains the only way to make secure (but broad) temporal correlations with the rest of the site complex. This investigation shows that a range of anthropogenic, geogenic, and biogenic processes contributed to the deposition and post-depositional alteration of the identified microfacies. Short depositional hiatuses are reasonably common, and a significant hiatus was identified between the RS and SASDC. The impact of post-depositional processes on the RS is significant, with anthropogenic deposits poorly preserved. In comparison, the SASDC is dominated by hearths contained within deposits rich in reworked anthropogenic materials known as carbonized partings. Small shell disposal features are also present. The distribution of these anthropogenic features suggests continuity in the management of space throughout the MSA II occupations, from before 110 ka. New stratigraphic correlations indicate that KRM 41815 is unambiguously associated with the MSA I. Therefore, it predates 110 ka, with a lower age limit potentially in Marine Isotope Stage 6.

Sequence stratigraphy and evolution of the southern Central Vietnam Shelf during Late Pleistocene-Holocene

The central Vietnam continental shelf is located on the western margin of the East Vietnam Sea (South China Sea). This study provides new findings regarding the Late Pleistocene-Holocene evolution of the southern central Vietnam shelf off Binh Dinh province using high-resolution seismic profiles and sediment cores. The study found that the Late Pleistocene-Holocene sequence stratigraphic model of the study area can be divided into three systems tracts: the regressive systems tract (RST), the transgressive systems tract (TST), and the highstand systems tract (HST). The RST is the oldest and thickest of the three systems tracts and is characterized by forced regressive and lowstand deposits. These deposits likely formed between the Marine Isotope Stages (MIS) 5e highstand and the Last Glacial Maximum (LGM) termination. The RST is well-preserved at water depths deeper than 60 m and has a maximum thickness of about 40 m. The TST is the middle systems tract and was likely deposited during a postglacial transgressive period, from the LGM lowstand termination to around 8 cal ky BP. The TST is thickest in shallow water depths in the southern part of the study area and within incised-valley systems. The HST is the youngest of the three systems tracts and is dominated by thick mud clinoforms that prograde onto the shelf following mid-Holocene sea-level highstand until the present day. The HST was primarily deposited in shallow water depths of 0–50 m and decreases in thickness towards the outer shelf, ending at a water depth of around 80 m.The study also found that Late Pleistocene-Holocene relative sea-level change is the main factor controlling the overall stratigraphic organization of units on the study area. The presence of the beach-ridge structure at a water depth of approximately 140 m below the modern sea level in the southernmost part of the study area suggests that the region experienced a sea-level lowstand in the past. This lowstand was likely a result of subsidence due to a high sedimentation rate. This discovery is consistent with earlier studies conducted on the central Vietnam shelf. There are similarities in the deposition of Late Pleistocene-Holocene deposits between Binh Dinh and other shelves worldwide, indicating that there may be consistent controlling factors that govern the geological history of these regions. However, the thickness and distribution of deposits in the study area may be different due to local factors that interacted to shape the area differently than others.

Co-evolution of orbital-to-millennial East Asian monsoon and westerlies variability over the past 150 ka

Understanding the evolution and interaction of the mid-latitude westerlies and East Asian monsoon (EAM) is crucial for comprehending Asian climate dynamics. While abundant evidence from loess, lake and speleothem records in arid Central Asia (ACA) and East Asia has revealed the interplay between the mid-latitude westerlies and the EAM on orbital and millennial scales, most of these records only cover the period since the last glacial maximum. Thus, the trade-off relationship between the mid-latitude westerlies and the EAM on glacial-interglacial to millennial timescale since the last interglacial period remains unclear. In this study, we present 150 ka-long grain-size and organic carbon records from two loess sections in the western Chinese Loess Plateau (CLP) and Yili Basin to assess the wind intensity and moisture variability between East Asia and ACA at glacial-interglacial to millennial timescales. Our results indicate that the East Asian winter monsoon (EAWM) and westerly wind exhibit synchronous glacial-interglacial and precession-scale fluctuations. However, the moisture exhibits consistent variations between East Asia and ACA on glacial-interglacial timescale, whereas inconsistent pattern at precessional timescale. The moisture variations in ACA lagged those in the East Asia by 2 kyr during marine isotope stages (MIS)5. Millennial-scale wind and moisture variability in East Asia and ACA are broadly correlated with cooling events in the North Atlantic. Based on the modeling results of the TraCE-21 ka, we suggest that the wind and moisture variations in East Asia and ACA are controlled by the combined effects of ice sheets, insolation, and meltwater flux from orbital to millennial timescales. Therefore, our study provides new insights into the complex interplay between the EAM and mid-latitude westerlies, which can contribute to a better understanding of Asian climate dynamics.

Was there a nonglacial episode in the western Hudson Bay Lowland during Marine Isotope Stage 3?

AbstractEstablishing the timing of glacial and nonglacial intervals in the core regions of the Laurentide Ice Sheet (LIS) is essential to constrain ice-sheet configuration at times of globally reduced ice volume, such as during Marine Isotope Stage (MIS) 3 (~57–29 ka). Hudson Bay Lowland (HBL) deglaciation, at the centre of the LIS, has been inferred at MIS 3 based on near-infinite wood radiocarbon ages and limited luminescence ages. To better constrain the age of the penultimate deglaciation of the western HBL, this study initially identified the youngest intertill nonglacial sediments, based on extensive fieldwork and till characterization. Next, vetted radiocarbon ages were combined with revised stratigraphy to show that five previously identified “MIS 3” sites were likely deposited during an earlier ice-free period. Finally, new optical ages targeting the youngest intertill nonglacial bed at three localities yielded ages ranging from 166 to 146 ka; all older than MIS 3. These ages indicate that the penultimate deglaciation of the western HBL likely occurred during MIS 5e. This interpretation better explains accompanying paleobotanic data sets that indicate vegetation similar to vegetation existing under present interglacial conditions. Currently no firm evidence exists in the terrestrial stratigraphic record for the deglaciation of the western HBL during MIS 3.

Mapping and chronological classification of marine terraces along the southern side of the Sibari Plain (northern Calabria, Italy) by means of digital and analogue tools

ABSTRACT We study the marine terraces of the southern side of the Sibari Plain in Northern Calabria (Italy) through the use of traditional and quantitative analyses of the Digital Terrain Model (DTM). The main aim of the present work consists in the extensive use of GIS tools that were never used before in the area, and in checking the applicability of this procedure. The terraced surfaces identified using photo interpretation and those recognized semi-automatically through the GIS tools were compared to finally produce a consensus map. In the final map, we identified 272 terraced surfaces and 62 morphological features associated with inner margins (i.e. paleoshorelines). The main map shows a well-developed flight of seven orders of marine terraces with elevation ranging from 45 to 360 m asl and age ranging from Marine Isotope Stage (MIS) 5a to 11.

Reconstraining the Quaternary glacial history of Lahaul Himalaya, northern India

The study reports new progress in the glacial chronology from new sites of the Chandrabhaga basin (CBB), in the transition between the monsoon-dominated Pir-Panjal and westerly-dominated Trans-Himalaya, in Lahaul Himalaya, northern India. In Lahaul, asynchronous timing and extent of late Quaternary glaciation have been reported (Owen et al., 1996, 1997, 2001; Eugster et al., 2016). The established oldest and most extensive Chandra glacial stage remains undated and speculative. We reconstrain the late Quaternary glacial history of the CBB using geomorphological mapping, Infrared Stimulated Luminescence (IRSL), and 10Be Terrestrial Cosmogenic Nuclide (TCN) surface exposure dating. Four local glacial stages, the Chandra, Batal, Dali, and Mayar, are dated to 152 ± 37 ka, 43 ± 3 ka, 21 ± 2 ka, and Little Ice Age (LIA), respectively. The Chandra glacial stage occurred during the late Marine Isotope Stage 6 (MIS 6; 186 ± 30 – 113 ± 10 ka), characterized by thick lacustrine deposits, rock benches, and ice-polished bedrock along the trunk valleys. We provide the first account of the numerical dating for the much-awaited timing of the oldest Chandra glacial stage (Local Last Glacial Maxima; LLGM) in the region (Owen et al., 1996, 1997, 2001). The LLGM in the CBB is much older than previously thought, consistent with some north-western Himalayan glacial records (Owen et al., 2006; Dortch et al., 2010; Hedrick et al., 2011; Orr et al., 2017, 2018). The Batal glacial stage occurred during the early MIS 3 and is dated from 47 ± 2 to 41 ± 2 ka, represented by the thick lacustrine deposits and impressive terraces. The Dali glacial stage occurred during the Global Last Glacial Maxima (GLGM), characterized by a series of latero-frontal recession moraines, and is dated from 33 ± 3 to 13 ± 1 ka. The Mayar advance is characterized by confined tributary valley glaciers, possibly linked to the LIA advance reported in the Kulti valley (Saha et al., 2019). The equilibrium line altitude (ELA) rose by ∼486 m from the Chandra stage to the present day. Reconstructed ELA altitudes and glacial landforms demonstrate that the glaciations have become progressively less extensive through time for this part of the western Himalayas. The change of glaciation pattern during the later part of the Quaternary is like other regions of the orogen, such pattern of glaciation reflects regional climatic forcing.