Glacial-interglacial Cycles Research Articles

Southern Ocean Water Mass method: A new statistical approach using microfossil radiolaria for paleoceanographic insights for the Southwest Pacific sector of the Southern Ocean

Ocean circulation and the formation and upwelling of water masses in the Southern Ocean play a critical role in the exchange of heat and carbon with the atmosphere over glacial-interglacial cycles, but the history of the subsurface water masses is poorly understood. Radiolarians inhabit the water column from the surface to the bottom of the ocean, and their distribution is known to be associated with water masses. We use radiolarian abundance census data from the SO-RAD core top dataset to explore the relationship between radiolarian distribution and surface and subsurface water mass structure of the Southwest Pacific Sector of the Southern Ocean. The species distribution was first explored using non-Metric Multidimensional Scaling. Then Multivariate Regression Tree (MRT) analysis was used to understand the relationship between radiolarian distributions and parameters of water mass boundaries (using isopycnal depths) and upwelling (using nutrient data). We identified a series of indicator species associated with oceanographic zones which were used to develop the Southern Ocean Water Mass Index. The contribution of the Index Species Groups provided further information on water column structure and the relative influence of the various water masses. The index was then applied to the radiolarian assemblage data from 2 previously published cores, Y8 and Y9, from the Subantarctic Zone east of New Zealand. The results of the Southern Ocean Water Mass Method showed changes in water mass structure through the last glacial-interglacial cycle at both core sites. The results agree with other proxy data from the region. The SOWM Method provides a new tool for understanding the history of changes in the water mass structure and circulation in the Southern Ocean.

Next-generation phylogeography reveals unanticipated population history and climate and human impacts on the endangered floodplain bitterling (Acheilognathus longipinnis)

BackgroundFloodplains harbor highly biodiverse ecosystems, which have been strongly affected by both past climate change and by recent human activities, resulting in a high prevalence of many endangered species in these habitats. Understanding the history of floodplain species over a wide range of timescales can contribute to effective conservation planning. We reconstructed the population formation history of the Itasenpara bitterling Acheilognathus longipinnis, an endangered floodplain fish species in Japan, over a broad timescale based on phylogenetic analysis, demographic modeling, and historical demographic analysis using mitogenome and whole-genome sequences. A genome sequence was newly assembled as a reference for the resequencing analysis. This bitterling is distributed in three plains separated by high mountain ranges and exhibits ecological characteristics well adapted to floodplain environments.ResultsOur analyses revealed an unexpected population branching pattern, gene flow, and timing of the differentiation that occurred within a few hundred thousand years, i.e., long after the mountain uplift that was assumed to be the primary geological cause of the population differentiation. The analyses also showed that all local populations experienced a severe decline during the last glacial and post-glacial periods.ConclusionsOur results suggest that the floodplain bitterling was able to disperse through unknown routes after mountain uplift and that its populations were strongly influenced by climatic and geographic changes in glacial–interglacial cycles and subsequent human activities, probably related to its floodplain-dependent ecology. The genomic data highlight the unanticipated distribution process of this species and the magnitude of the impact of human activities, with important implications for its conservation.

The role of ocean circulation and regolith removal in triggering the Mid-Pleistocene Transition: Insights from authigenic Nd isotopes

Approximately 1,250,000 to 700,000 years ago, the pacing of glacial-interglacial cycles changed from 41,000 years to ∼100,000 years, a shift known as the ‘Mid-Pleistocene Transition’ (MPT). The cause – or causes – of this shift remain uncertain. However, changes in ocean circulation and removal of northern hemisphere regolith have both been proposed as potential triggers. Here, we present continuous, orbitally resolved reconstructions of deep ocean neodymium isotopes from three locations in the equatorial Atlantic, Indian and southwest Pacific oceans, spanning 1.7 million years from the Holocene to before the MPT, to test these two hypotheses. We find that global seawater neodymium isotope variability over glacial-interglacial cycles is controlled by changes in both neodymium input to the North Atlantic and deep ocean mixing. Using this neodymium isotope data, we show that enhanced northern hemisphere regolith removal began approximately 1.45 million years ago, ∼200,000 years prior to the onset of the MPT and ∼500,000 years prior to a major expansion in northern hemisphere ice sheets between ∼900,000 and 870,000 years ago. This ice sheet expansion was immediately preceded by an interval of reduced mixing of Atlantic-sourced waters into the deep southwest Pacific Ocean. We hypothesize that this circulation reorganization reflected increased stratification of the deep Southern Ocean interior, possibly in response to cooling and Antarctic sea ice expansion at this time. Taken together, these data suggest an expansion and/or thickening of northern hemisphere ice sheets during the MPT was facilitated by a combination of reduced northern hemisphere regolith cover alongside Southern Ocean circulation changes. Together, these shifts allowed the build up of larger northern hemisphere ice sheets that were more resistant to deglaciation, facilitating the longer glacial cycles of the post-MPT world.

Phylogeography of Pleurospermum foetens (Apiaceae) From the Sky Islands of Southwest China.

Sky islands provide insights on how glacial-interglacial cycles have shaped species distribution and help for predicting species' responses to climate warming. The alpine subnival belt of southwest China, especially in the Hengduan Mountains and adjacent areas, is sky island-like. Among them, the Yunnan-Kweichow Plateau harbors several isolated mountains with well-developed alpine subnival vegetation, sharing a similar species composition with the Hengduan Mountains. However, the relationship between the sky islands of the Hengduan Mountains and the Yunnan-Kweichow Plateau remains insufficiently explored. Pleurospermum foetens (Apiaceae) is a species endemic to the alpine screes of the Yunnan-Kweichow Plateau and the Hengduan Mountains. We used DNA sequence data from 59 individuals across 9 populations, combined with ecological niche modeling, to investigate the evolution history and future distribution of P. foetens within this sky island region. The results indicate the following: (1) P. foetens exhibits a significant phylogeographic structure and can be classified into three nrDNA clades and two cpDNA clades, respectively, (2) a nuclear-plastid discordance observed in P. foetens and its relatives based on phylogenetic analysis. P. foetens is monophyletic in the nrDNA phylogeny, while two major clades (HDM and YGP) are present in the cpDNA phylogeny, each forming a clade with other congeneric species. (3) Ecological niche modeling of P. foetens indicated that the species had the most extensive suitable habitat during the last glacial maximum (LGM). However, anticipated climate warming in the coming decades is expected to reduce the suitable range of P. foetens, posing a significant threat to isolated marginal populations (e.g., Shizi Mountain) with restricted alpine scree habitats. In conclusion, our study highlights the substantial effect of sky island and glacial-interglacial cycles on the population divergence of P. foetens. Conservation efforts for marginal populations of alpine plants in the Yunnan-Kweichow Plateau require increased attention and prioritization.

Glacial-Interglacial Cycles over the Past 150,000 years of South-Eastern Arabian Sea from δ18O Record

This study aims to reconstruct the surface water productivity and related monsoonal intensity along the southwestern continental margin of India, over the last 150,000 years by utilizing the temporal variations of δ18O and δ13C isotopes in the planktic foraminifers (Globigerinoides ruber) from a sediment core obtained from the continental slope off Kochi, south-eastern India. The chronostratigraphy of the core is established on the basis of high resolution stable isotope record of planktic foraminifera (Globigerinoides ruber) and a few AMS radiocarbon ages. Down-core records of δ18O and δ13C show millennial scale variations of primary productivity and monsoonal intensity during past 150 kyr. Boundaries of the Marine isotope stages (MISs) were delineated in the core based on the visual comparison of the δ18O with Martinson’s (D. M. Martinson, N.G. Pisias, J.D. Hays, J. Imbrie, T.C. Moor Jr, N.J. Shackleton, Age dating and the orbital theory of the ice ages: development of a high resolution 0 to 300000 year chronostratigraphy, Quaternary Research, 1987 27, p 1-29) and the SPECMAP data. From these studies it is inferred that the bottom of the core is about 150 kyrs, demarcating the paleoclimatic/paleoceanographic information covering MIS 1 to 6. Boundaries among MIS 6 and MIS 5, MIS 5 and MIS 4, MIS 4 and MIS 3, MIS 3 and MIS 2 and MIS 2 to MIS 1 (Holocene) have been demarcated at depths 11.47 m, 4.68 m, 4.03 m, 18 m, and 21 m respectively in the core studied. MIS 5 section is characterized by alternating warm and cold periods as observed in Polar Ice cores. The main findings of this work indicates that the core site has recorded higher productivity with increased fluvial input during the warm, humid interglacial periods and interstadials than the stadials during the glacial period. However, the temporal variability from 150 kyr to 130 kyr has been considered as the glacial period with cold and dry climate that corresponding to the MIS 6, MIS 4 within this an episode of extremely low terrigenous input with heavier δ18O values is noticed from 12.91 to 12.67 m. Similarly, a period of heavy δ18O values, with less surface runoff and with low δ13C values between 4.03 to 4.68 m bsf has been interpreted as MIS 4. Episodic fluctuation in SW monsoon induced productivity during MIS 3 has been observed in present study. The de-glacial event in MIS 2 marked in present core characterized by an abrupt increase in productivity during the mid-MIS 2.

Quaternary transgression process controlled by tectonic subsidence over the last 1.35 Ma: New insights from the eastern Bohai Sea

The Quaternary sedimentary history of the Yellow Sea and Bohai Sea offers significant insights into global sea-level changes. This history is intricately linked to tectonic subsidence. However, the process of the Quaternary transgressions of these areas remains controversial due to the lack of cores with comprehensive sedimentary sequences and reliable chronological frameworks in representative sites. This study evaluated the grain size, benthic foraminifera assemblages, quartz optically stimulated luminescence (OSL) dates, and magnetostratigraphy of Core CSH05 (102.4 m) from the eastern boundary of the Bohai Sea. By comparing these results with previous research, new insights were gained into sea-level changes and tectonic events in the Bohai Sea. The paleomagnetic analysis revealed the existence of Brunhes and Matuyama chrons in the core, including the Jaramillo and Cobb Mountain subchrons and Blake excursion. The boundary between the Brunhes and Matuyama chrons was determined at 57.2 m in the core, aligning with adjacent cores. The basal age of the core is estimated to be ~1.35 Ma. Thirteen sedimentary units (U1-U13), consisting of seven neritic deposits and six terrestrial/littoral deposit layers, were identified in the core through sedimentology and environmental proxies (grain size and benthic foraminifera), indicating alternating transgression-regression cycles. OSL samples suggest that the neritic deposits layer (16.2–20.6 m) probably originated during the early Marine Isotope Stage 3 (MIS3), exhibiting a weaker transgression than MIS5 and MIS1. The initial transgression (U13) dates back to no later than 1.35 Ma, representing the earliest documentation in the Bohai Sea. U11 shows a transgression to 1 Ma, aligning with results from adjacent cores, indicating that the Miaodao Island uplift experienced further subsidence between 1 and 0.83 Ma, allowing seawater to inundate the central basin of the Bohai Sea during high sea level periods. The current sea-land configuration structure emerged after 0.3 Ma due to the complete subsidence of the Miaodao Islands Uplift. The Quaternary transgressions in the Bohai Sea demonstrate a coupling relationship with the uplift of the Qinghai Tibet Plateau, glacial-interglacial cycles, and integration of the Yellow River. This study traces the initial transgression in the Bohai Sea to 1.35 Ma and provides a new detailed evolutionary model of the timing and routes for the Quaternary transgression of the Bohai Sea and Yellow Sea, thereby enhancing our understanding of sedimentary evolution and paleoenvironmental changes in the region.

Effects of climate change and methane-rich fluid activity on sedimentary sulfur geochemical records in the northern South China Sea since mid-Pleistocene

Microbial sulfate reduction (MSR) and associated pyritic sulfide formation are important diagenetic processes in marine sediments. The sulfur isotopic composition of pyrite (δ34Spyr) is proven to be sensitive to changes in sedimentation rates and the content and reactivity of organic carbon, especially on the continental shelves and upper slopes (water depth < 350 m). However, the diagenetic responses of sulfur to variations in climatic and depositional conditions in the deep-sea sediments are still poorly understood. This study combines element contents and isotopes to characterize diagenetic interplays of sulfur, organic carbon, and methane in the continental slope sediments of the northern South China Sea since the mid-Pleistocene. Our data suggest that the total organic carbon (TOC) increased during glacial times, implying enhanced primary productivity due to increased nutrient supply by the East Asian Winter Monsoon, in addition to efficient transfer of organic carbon and better preservation of organic carbon due to reduced bottom water oxygen. Total sulfur and chromium reduction sulfur contents varied concomitantly with the TOC, suggesting an increased burial of organic carbon that enhanced the organoclastic sulfate reduction (OSR) and the formation of authigenic pyrite. The environmental changes did not induce a significant shift in δ34Spyr, due most likely to relatively low sedimentation rates and large fractionation in sulfur isotope through OSR during the glacial-interglacial cycles. Instead, it is hypothesized that the sulfate-driven anaerobic methane oxidation promoted the formation of a higher amount of authigenic pyrite. Consequently, it created a closed diagenetic system leading to positive excursions in δ34Spyr at the sulfate-methane transition zone. Our results suggest the vulnerability of pyrite formation and its sulfur isotopic composition to the changes in monsoon-driven primary productivity and the methane-rich fluid migrations in the continental margin sediments. This study complements the growing evidence for the local diagenetic controls on sedimentary sulfur geochemical records by highlighting the importance of early diagenesis in paleoenvironment reconstruction based on the content and sulfur isotopic composition of pyrite.

Precipitation variability and environmental change across late Quaternary glacial-interglacial cycles in lowland Central America: Insights from Lake Petén Itzá (Guatemala) sediments

Lowland Central America, a biodiversity hotspot in the northern Neotropics, is a region where the climate is influenced by the location and expansion-contraction of the Intertropical Convergence Zone (ITCZ) on seasonal to millennial timescales. Paleo-records from the Caribbean Sea and the eastern equatorial and subtropical Pacific Ocean illustrate the response of regional precipitation to fluctuations in global temperature, driven by glacial-interglacial cyclicity over the past 500 kyr. Here, we present a paleoclimate and paleoenvironment record from Lake Petén Itzá, lowland Guatemala, which spans the last ∼413 kyr. Sediment in the lake recorded lacustrine and terrestrial ecosystem responses to large-scale climate variability. Precipitation patterns during MIS11-9 (∼413-304 ka BP) align with the latitudinal position of the ITCZ, with superimposed effects from the strength of the Caribbean Low-Level Jet (CLLJ). A sediment hiatus, likely attributable to mass removal processes in the lake's shallower areas, spans the period from MIS8 (starting at 304 ka BP) to the end of MIS6 (at 149 ka BP). MIS6 was characterized by humid conditions, perhaps ascribable to a more southerly extension of cold fronts and intensification of the CLLJ. During MIS5, pronounced fluctuations among all sediment variables, accompanied by an abrupt decline in precipitation, may correspond with cold events inferred from North Atlantic Ocean sediment cores. Although discontinuous, the Lake Petén Itzá sediment record provides a window into late Quaternary climate and environmental change in lowland Central America.

From paleolake to peatland: Paleo environmental changes over glacial and interglacial cycles (Mid-Pleistocene) in the Colônia Basin, Brazil

Diatom and geochemical elements were used to analyze the transition from lake to peatland in the Colônia basin, São Paulo, Brazil; local versus regional driving factors were examined. Sediment core COL17–1, section 1470–800 cm depth shows five distinct diatom intervals offering insights into environmental changes and ecological characteristics based on sediment sources, diatom productivity, and bog wetness. Colônia basin evolution exhibited a progressive transition from mineral elements, associated with catchment instability during the lake stage, to higher levels of organic-rich sediments towards the uppermost section of the core. This shift was accompanied by the increasing presence of elements reflecting redox/productivity dynamics under changing conditions. Simultaneously, Br concentrations increased during peat formation indicating alterations in organic matter were influenced by atmospheric circulation and precipitation. During the transition from lake to peatland, the paleolake shallowing process showed successive colonization by benthic acidophilus diatom taxa, indicating a broader littoral zone and subsequent disappearance of diatoms under dry conditions. After a benthic stage, the diatom content shifted to one of planktonic dominance characterized by Aulacoseira sp., marking the return to cold-wet conditions and a moderately deep, flooded environment. Subsequently, the basin evolved into a completely flooded, turbulent peatland dominated by the Aulacoseira granulata complex. An uppermost layer sterile in diatom was associated with warmer and drier conditions and decrease in the concentration of mineral elements. Present results compared with core CO14 and Lake Titicaca showed benthic-rich levels during the penultimate glacial period and low benthic abundances. This differed the glacial-interglacial transition from those of COL17–1, which was dominated by planktonic-rich levels, suggesting the need for either a reassessment of our age model or the influence of local factors on diatom content. These findings highlight the sensitivity of diatoms to climate shifts, particularly in tropical regions, across different glacial-interglacial cycles.

Chemostratigraphy and mineralogical characterization of Piacenzian sapropels cluster A (2.75–2.57 Ma) in the Gelasian GSSP type-section of Monte San Nicola (Sicily, Italy): Paleoenvironmental and paleogeographic implications

Mineralogical, geochemical and stable isotope (δ18O, δ13C) data from Marine Isotope Stages (MIS) G4 to 103 are here presented. The studied interval includes the sapropelic cluster A (A2-A5) from the Gelasian GSSP type-section, outcropping at Monte San Nicola (Sicily, Italy). The studied section exhibits a good response of the δ18O measured on the bulk carbonate to the Earth's astronomical parameters. The sapropelic red/brown layers (A2- A5) are alternated to grey marls and this cyclicity is clearly evident by the difference in colour, organic matter content, redox-sensitive elements and runoff indicators, tied to the precession/insolation cycles. Further, the obliquity signal is well evident in paleoproductivity indicators and mineralogical composition, driven by glacial-interglacial cycles. The obtained dataset has allowed the reconstruction of the paleoenvironmental conditions during marls/sapropels deposition, which appears to be influenced by the precessional forcing that induced strong changes in the marine water circulation. This scenario is also integrated by an original paleogeographic model including the presence of a high topographic structure in SE Sicily that limited water exchanges between the Ionian and Central Mediterranean Seas during sea level drawdowns, caused by glacial phases, triggered by obliquity minima.

Quaternary morpho-stratigraphic evolution of the eastern Campo Imperatore basin (Gran Sasso range, central Italian Apennines) and tectonic implication

ABSTRACT Geological survey and geochronological analyses were conducted in the Campo Imperatore plain to understand its Quaternary morpho-sedimentary and tectonic evolution. In the Late Pliocene-Early Pleistocene, low relief energy and steady and warm climatic conditions promoted a long phase of areal peneplanation, resulting in the formation of gently sloping landscape. With further regional uplift and changes in frequency/amplitude of the glacial-interglacial cycles (Early-Middle Pleistocene transition) and after establishment of the expansion-contraction cycles of the Apennine glaciers (Middle Pleistocene), the morpho-sedimentary processes become highly dynamic. In Middle Pleistocene, more than 100 meters of breccias deposited all along the slopes of the Gran Sasso range, followed by higher frequency processes of sedimentation, erosion and pedogenesis of Middle-Late Pleistocene to Holocene fluvio-glacial deposits. These have been progressively offset by synthetic and antithetic normal faults belonging to the Gran Sasso fault system, a 40-km-long seismogenic structure which released in the past earthquakes of Mw~7.

Weathering and pedogenesis of the Holocene aeolian loess-paleosol sections in the Guanzhong Basin on the Chinese Loess Plateau

The aeolian loess-paleosol sections on the Chinese Loess Plateau (CLP) represent invaluable archives for elucidating the dynamics of the East Asian Monsoon (EAM) across Quaternary glacial-interglacial cycles. In this study, a Holocene aeolian loess-paleosol section in the Guanzhong Basin on the CLP was meticulously investigated to assess the intensity of weathering and pedogenesis, and to discern its paleoclimatic implications. Through comprehensive analysis of chemical element composition and micromorphology, it was revealed that the majority of stratigraphic units within the Holocene aeolian loess-paleosol section exhibit indications of weak weathering and pedogenesis, while the mid-Holocene paleosol approaches to moderate weathering and pedogenesis. Hierarchically, the intensity of weathering and pedogenesis among the stratigraphic units can be ranked as follows: paleosol > topsoil > recent loess > transitional loess. Furthermore, the chemical index of alteration (CIA) values of the mid-Holocene paleosol exhibit a gradient decline from southeast to northwest, aligning with present-day temperature and precipitation distributions under the predominant influence of the East Asian summer Monsoon (EASM). Thus, it can be inferred that the robust impact of the EASM on weathering and pedogenesis of paleosol was pronounced during the mid-Holocene Climatic Optimum. These results are of significance in exploring the Holocene weathering and pedogenesis and paleoenvironmental evolution on the CLP.

Carbon isotope budget indicates biological disequilibrium dominated ocean carbon storage at the Last Glacial Maximum

Understanding the causes of the ~90 ppmv atmospheric CO2 swings between glacial and interglacial climates is an important open challenge in paleoclimate research. Although the regularity of the glacial-interglacial cycles hints at a single driving mechanism, Earth System models require many independent physical and biological processes to explain the full observed CO2 signal. Here we show that biologically sequestered carbon in the ocean can explain an atmospheric CO2 change of 75 ± 40 ppmv, based on a mass balance calculation using published carbon isotopic measurements. An analysis of the carbon isotopic signatures of different water masses indicates similar regenerated carbon inventories at the Last Glacial Maximum and during the Holocene, requiring that the change in carbon storage was dominated by disequilibrium. We attribute the inferred change in carbon disequilibrium to expansion of sea-ice or change in the overturning circulation.

North Atlantic temperature control on deoxygenation in the northern tropical Pacific

Ocean oxygen content is decreasing with global change. A major challenge for modelling future declines in oxygen concentration is our lack of knowledge of the natural variability associated with marine oxygen inventory on interannual and multidecadal timescales. Here, we present 10 annually resolved 200 year-long records of denitrification, a marker of deoxygenation, from a varved sedimentary archive in the North Pacific oxygen minimum zone covering key periods over the last glacial–interglacial cycle. Spectral analyses on these records reveal strong signals at periodicities typical of today’s Atlantic multidecadal oscillation. Modern subsurface circulation reanalyses regressed on the positive Atlantic and Pacific Climatic Oscillation indices further confirm that North Atlantic temperature patterns are the main control on the subsurface zonal circulation and therefore the most likely dominant driver of oxygen variability in the tropical Pacific. With currently increasing temperatures in the Northern Hemisphere high latitudes and North Atlantic, we suggest deoxygenation will intensify in the region.

Late Pleistocene–Holocene palynology and paleoceanography of İmralı Basin, Marmara Sea: Pollen-spore, dinoflagellate cyst and other NPP zonations

The Marmara Sea is the oceanographic gateway that links the hypersaline Eastern Mediterranean Sea with the hyposaline Black Sea via Straits of Dardanelles and Bosphorus, respectively, and also occupies a transitional vegetation and climatic regime between the Mediterranean and Euxinic phytogeographic ecosystems. Recent palynological studies of long cores from the shallow İmralı Basin perched on the southeastern slope of the Marmara Sea reveal that major paleoecological changes accompanied the isolation and reconnection of the Marmara Sea during the last two Pleistocene glacial–interglacial cycles. Here, we use data primarily from two İmralı Basin cores to determine new quantitative zonations for the pollen-spore, dinoflagellate cyst (dinocyst) and other non-pollen palynomorph (NPP) assemblages in sediments representing the last ∼30 cal ka. A gap in one core is closed using data from three short gravity cores. Twenty-four radiocarbon ages and 20 correlation-ties for sapropel and ash layers from these five cores provide an essentially complete record for the past 30 cal ka. Use of a full suite of palynomorph data (pollen and spores, fungal spores, dinocysts and other phytoplankton, aquatic parasites/saprophytes, zoo-planktonic and zoo-benthic NPPs) shows for the first time that fluctuations in aquatic palynoassemblages during the glacial periods are more complex than simple salinity or temperature responses. The changes involve food web-level turnovers in trait- and size-based food web components in which potential parasites/saprophytes appear critically important.Pollen stratigraphies reveal a significant loss of Euxinic tree taxa by MIS 3c, with only partial recovery in MIS 1. The Euxinic forest elements are replaced by cultivars and other indicators of anthropogenic influences during the MIS 1 that is also marked by a dry interval and corresponding in part with the 4.2 cal ka Eastern Mediterranean Drought Event. The dinocyst zones for the last ∼30 cal ka show a clear turnover from assemblages dominated by brackish Ponto–Caspian taxa to marine assemblages at ∼11.7 cal ka. This phytoplanktonic signal lags slightly behind (a) the vegetation and shift in the other NPP commencing ∼13.2 cal ka, the initial marine incursion at 13.8 cal ka, and the arrival of coccolithophores at ∼13 cal ka. Comparison to published MIS 6 and 5 data reveals higher MIS 2–1 species diversity, reappearance of the MIS 6 marker Impagidinium inaequalis, and the emergences of Pyxidinopsis psilata f. quadrata, cf. Boreadinium breve, and Peridinium spp. of Brenner 2005. The pre-reconnection microbiota is dominated by the unicellular alga Sigmopollis, spikes of colonial Pediastrum algae, the saprophytes/parasites cf. Multiplicisphaeridium and Chytridiomycota. This microbiota is displaced by the post-reconnection assemblage dominated by Botryococcus coenobia, various Platyhelminth egg capsules and ostracod lining-types that persist through the Holocene. A distinctive transitional microbiota with Discocotyle-type turbellarian egg capsules marks the Bølling–Allerød warming, followed at ∼13.3 ka by a marine assemblage with micro-foraminiferal linings and crustacean eggs. The interglacial marine phase of MIS 1 in İmralı Basin has much higher dinocyst species diversity than MIS 5e, reflecting Neolithic impacts (agriculture, land clearance) and expanded shipping trade. Initial marine flooding in the Marmara Sea during both interglacials are marked by sapropel deposition but variations of ravinement surface erosion, and marine deep water residence time in a stratified Marmara Sea are potentially important factors underlying hypoxia/anoxia and sapropel deposition.

Mining expressed sequence tag (EST) microsatellite markers to assess the genetic differentiation of five Hynobius species endemic to Taiwan

Taiwan harbors five endemic species of salamanders (Hynobius spp.) that inhabit distinct alpine regions, contributing to population fragmentation across isolated “sky islands”. With an evolutionary history spanning multiple glacial-interglacial cycles, these species represent an exceptional paradigm for exploring biogeography and speciation. However, a lack of suitable genetic markers applicable across species has limited research efforts. Thus, developing cross-amplifying markers is imperative. Expressed sequence-tag simple-sequence repeats (EST-SSRs) that amplify across divergent lineages are ideal for species identification in instances where phenotypic differentiation is challenging. Here, we report a suite of cross-amplifying EST-SSRs from the transcriptomes of the five Hynobius species that exhibit an interspecies transferability rate of 67.67%. To identify individual markers exhibiting cross-species polymorphism and to assess interspecies genetic diversity, we assayed 140 individuals from the five species across 84 sampling sites. A set of EST-SSRs with a high interspecies polymorphic information content (PIC = 0.63) effectively classified these individuals into five distinct clusters, as supported by discriminant analysis of principal components (DAPC), STRUCTURE assignment tests, and Neighbor-joining trees. Moreover, pair-wise FST values > 0.15 indicate notable between-cluster genetic divergence. Our set of 20 polymorphic EST-SSRs is suitable for assessing population structure within and among Hynobius species, as well as for long-term monitoring of their genetic composition.

Diverse fluvial aggradation and incision response to interglacial—Glacial transitions in the headwaters of the Yangtze River, SE Tibetan Plateau

As a key geomorphic archive, staircase sequences of terraces and sediments record the history of fluvial aggradation and incision, which are related to tectonic activities, climatic fluctuations, and varying base levels. While numerous studies have investigated their influence on the formation of fluvial terraces, the manner in which rivers adapt to diverse climatic transitions (specifically, the shifts from warm to cold and from cold to warm) remains a subject of ongoing debate, particularly when considered within varying tectonic and climatic contexts. Here, we address this issue by reconstructing terrace distributions and identifying sedimentary features with OSL dating in the headwaters of the Yangtze River in the southeastern Tibetan Plateau. We discovered two distinct sets of thick valley-filling sequences at different elevations indicating two phases of aggradation during the penultimate and last glacial periods, when the Yangtze River was in a transport-limited condition. During the warmer interglacial and deglacial periods, increased monsoon precipitation led to higher discharge, causing the river to incise into these valley fills. In addition, superimposed tectonic activities produced diverse river response to the climatic transition from interglacial to glacial between the upstream shallow valley and the downstream deeply incised gorge. In the upper valley, stable tectonic conditions resulted in minimal incision, with younger deposits overlying older ones. Conversely, in the downstream gorge, with more intense tectonic activities, sediments only partially covered the riverbed. These sediments acted as abrasion tools, facilitating rapid incision during the warm-to-cold transition, thereby creating two separated valley fills. This finding enhances our understanding of how tectonic forces influence river responses to interglacial—glacial cycles.

Sediment flux variation as a record of climate change in the Late Quaternary deep‐water active Corinth Rift, Greece

AbstractThe value of deep‐water sedimentary successions as reliable records of environmental change has been questioned due to their long response times and sediment pathways leading to complex responses to climatic change and tectonic signals over differing timescales. We studied the Gulf of Corinth, Greece, to test the value of deep‐water stratigraphic successions as records of external controls on sediment flux in a setting with short response times and transport distances. The confinement of the rift basin allows for a near‐complete accounting of clastic sediment volumes. The recent acquisition of high‐resolution seismic reflection data, utilisation of International Ocean Discovery Programme Expedition 381 cores and a robust chronological framework, enable evaluation of the stratigraphy at a high temporal resolution. Combining borehole and high‐resolution seismic reflection data, distinct seismic units can be correlated to multiple paleoenvironmental proxies, permitting quantification of sediment flux variation across successive glacial–interglacial cycles at ca. 10 kyr temporal resolution. Trends in average sediment flux since ca. 242 ka show ca. 2–9 times greater sediment flux in cooler glacials compared to warmer interglacial conditions. The Holocene is an exception to low sediment flux for the interglacials, with ca. 5 times higher rates than previous interglacials. The short and steep configuration of the Sythas canyon and its fan at the base of an active submarine normal fault results in deep‐sea deposition at all sea‐level stands. In contrast, adjacent canyon systems shut down during warm intervals. When combined with palynology, results show that periods of distinct vegetation re‐organisation correlate to sediment flux changes. The temporal correlation of sediment flux to palynology in the Gulf of Corinth over the last ca. 242 kyr is evidence that variability of sediment supply is largely governed by climate‐related changes in hinterland catchments, with sea‐level and tectonics being second‐order controls on sediment flux variability.

Newly discovered diamictite and cap carbonate couplet in the southern Alxa Block, northwestern China: Implications for stratigraphic correlation and Marinoan glaciation

Neoproterozoic glaciogenic diamictite and cap carbonate couplets have played a pivotal role in understanding glacial-interglacial cycles and establishing regional stratigraphic correlation. The Alxa Block in northwestern China preserves a sequence of Neoproterozoic diamictites along its southern margin, but the age and origin of the succession remain debatable due to the lack of discovery of cap carbonate. We report newly discovered cap carbonates that overlie the diamictites of the Shaohuotonggou Formation in the Longshoushan region in the southern Alxa Block. Based on detailed geological investigations, we identified massive diamictites, stratified diamictites, and cap carbonates in the lower part of the formation. The presence of ice-rafted dropstones, bullet-shaped and facetted clasts, glacial striations, and relatively low chemical index of alteration values of sedimentary matrix support a glaciogenic origin of the diamictites. The 2- to 2.6-m-thick cap carbonates are mainly composed of thinly laminated microcrystalline dolomites and show sheet cracks, cemented breccias, and tepee-like structures at the basal part of the unit. These features and their consistently negative δ13C values (−5.2‰ to −2.2‰) are characteristic of Marinoan-age cap carbonates (ca. 635 Ma). The quasi-continuous deposition of the massive diamictites, stratified diamictites, and cap carbonates suggests that the formation of this couplet was closely related to the Marinoan glaciation and subsequent deglaciation. We propose a three-stage depositional model for the glaciogenic succession and recommend that the diamictite and cap carbonate couplet in the Alxa Block provides a credible mark of the Cryogenian−Ediacaran boundary for further stratigraphic correlation and investigation.

Two sides of the same coin? Transient hybridization in refugia and rapid postglacial ecological divergence ensure the evolutionary persistence of sister Nothofagus.

Glacial periods have been considered as inhospitable environments that consist of treeless vegetation at higher latitudes. The fossil record suggests many species survived the Last Glacial Maximum within refugia, usually at lower latitudes. However, phylogeographic studies have given support to the existence of previously unknown high-latitude refugia that were not detected in the fossil record. Here, we test the hypothesis that cold-tolerant trees of Patagonia survived cold periods in microclimatically favourable locales where hybridization occurred between sister taxa. To study local presence through glacial periods in multiple refugia, we used pollen records and genetic information (isozymes, microsatellites, and combined nuclear and chloroplast DNA sequences) of population pairs of Nothofagus antarctica and N. pumilio that belong to the ancient subgenus Nothofagus which can potentially hybridize in nature, along their entire latitudinal range in Patagonia. Studied species share the N. dombeyi type pollen, which was abundant at >20% in the northernmost latitudinal bands (35-43°S), even during the Last Glacial Maximum. Mid- and southern latitudinal records (44-55°S) yielded lower abundances of ~10% that increased after c. 15.0 cal. ka BP. Therefore, fossil pollen evidence suggests a long-lasting local presence of Nothofagus throughout glacial-interglacial cycles but mostly as small populations between 44°S and 51°S. We found species-specific and shared genetic variants, the latter of which attained relatively high frequencies, thus providing evidence of ancestral polymorphisms. Populations of each species were similarly diverse, suggesting survival throughout the latitudinal range. Estimates of coalescent divergence times were broadly synchronous across latitudes, suggesting that regional climates similarly affected populations and species that hybridized through climate cycles, fostering local persistence.