Low Sea Level Research Articles

Environmental and vegetation dynamics through the Oligocene to Early Miocene of North Africa (Egypt)

This study documents palynomorph assemblages from the Oligocene through the Early Miocene, across the significant Warm-house to Cool-house transition, using a subsurface section from the AG-5 well, north Western Desert of Egypt. Although the Paleogene and Neogene strata occupied a large area of the land, little about vegetation and ecosystem processes that shaped the climate and biodiversity during this time window is known. Here, based on a comprehensive palynological analysis of the Oligocene to Early Miocene Dabaa and Moghra formations encountered in the AG-5 well, we show that the studied area was characterized by a humid tropical to subtropical climate during the Oligocene-Miocene time interval. The obtained results provide clear evidence of the poorly known Paleogene-Neogene ecosystem in North Africa. In terms of palynostratigraphical framework, three palynozones covering the late Oligocene-Early Miocene interval are recognized. Moreover, the recovered palynomorphs inferred a deposition of the Dabaa Formation under a normal marine, inner shelf to littoral environment. However, for the basal part of the Moghra Formation, a deposition in an offshore marine environment, outer shelf (high sea level, 100–200 m depth) is assumed, whereas a deposition in shallow coastal lagoons, estuary, or delta environment (low sea level) is presumed for its uppermost part.

Characterization of salt wedge intrusion process in a geographically complex microtidal deltaic estuarine system

Deltas are strategic systems of high ecological and economic importance since they provide various environmental resources and fertile alluvial soils. Different types of hydrodynamic processes occur in deltas, including saline intrusion. We implemented a three-dimensional numerical modeling system using the EFDC + Explorer Modeling System to analyze the characteristics of saline intrusion in the Sinú River delta, Colombia. We configured the model with field data from two measurement campaigns in February and November 2021, dry and wet seasons, respectively, and with secondary information. Several climatic conditions to cover a wide range of variability in the main forcing factors were simulated, specifically river discharge and tides: (1) without the influence of the El Niño Southern Oscillation (ENSO) climatic phenomena; (2) under critically low conditions of flow discharge; and (3) with sea level rise forecasts. The model was calibrated using in-situ water velocity data and salinity profiles. We obtained Index of Agreement (d) values between 0.67 and 0.99 for salinity and higher than 0.9 for water velocity. The numerical simulation provides valuable information about this stratified salt wedge system's dynamic nature, mainly due to changes in river discharge. The simulation demonstrated that river discharges above 319 m3/s were sufficient to prevent salt wedge intrusion, which are typical values registered annually between May and November. The scenarios under critical low discharge conditions and sea level rise projections showed a maximum reach of the salt wedge intrusion of 7.40 km. The model proved efficient in evaluating the saline intrusion process in the Sinú River delta, obtaining practical results that describe the dynamics of this process. It was shown that by simulating physical processes, such as salinity stratification, numerical models provide useful information on how these estuarine systems respond to different environmental stress factors associated with current climate variability, such as long drought periods or El Niño South Oscilation (ENSO), since salinity gradients play an important role in deltas' aquatic life, since they influence the distribution of phytoplankton, which is a key player for primary productivity.

Changes in Kuroshio Current dynamics and East Asian monsoon variability during the last 26 kyr

The Kuroshio Current flows northward along the east coast of Taiwan toward the Okinawa Trough and the East China Sea, but its dynamics and trajectory were probably different during the Last Glacial Maximum (LGM) due to the globally lower sea level that could have caused a (debated) deflection of the current along the eastern edge of the Ryukyu Arc.Core MD18–3532 has been recovered in an intra-slope basin of the Ryukyu accretionary prism, currently disconnected from the Kuroshio Current, but would have been on its trajectory in case of a NE deflection. Measurements of clay mineral assemblages and illite crystallinity revealed that Taiwan has been the main sediment source at this site over the last 26 kyr. The significantly higher sedimentation rate from the Last Glacial Maximum to the Bølling–Allerød compared with the period from the Younger Dryas to the Holocene, coupled with very low δ15Nsed during LGM and Heinrich Stadial 1, provide evidence for the transport of sediments and Trichodesmium spp. cyanobacteria by the partially deflected Kuroshio Current toward the eastern edge of the Ryukyu Arc. Combined with δ13Corg, TOC, TN, and XRF analyses, an increase in primary productivity has been observed during LGM and Heinrich Stadial 1. This would have been caused by an enhanced East Asian Winter monsoon winds resulting in the deepening of the mixed layer that would have led to the upwelling of the Kuroshio Current nutrient-enriched subsurface waters to the oligotrophic surface waters, and the supply of dust-borne iron from the Chinese Loess Plateau.

Изменение окружающей среды северо-западного сектора Японского моря в период последней дегляциации

Environment changes in the northwestern part of the Sea of Japan and adjacent land during last 21.0 kyr was reconstructed based on the analysis of pollen and diatom data with a high temporal resolution. Relatively dry climate caused a wide distribution of forest-steppe landscapes in the region between 21.0 to 16.6 ka. Boreal forests covered mountain slopes. Broad-leaved trees survived in refugia located in lower mountain belts. The low sea level during the Last Glacial Maximum (LGM) changed the general patterns in the sea circulation and longshore current directions, which transported the waters formed in the shallow areas of the northwestern and northern parts of the Sea of Japan. A slight increase in sublittoral benthic diatoms indicates the lowered sea level during the LGM. Occurrence of Betula indicates the start of warming after 18.5 ka; it was interrupted by the cold event Heinrich 1 and marked by the spread of coniferous Larix, Picea, and sphagnum bogs. The beginning of late glacial climatic amelioration Bølling-Allerød (BA) is contributed to dispersal of Quercus and Polypodiaceae ferns. The distribution of conifers Larix and Picea as well as of sphagnum bogs is correlated with the Younger Dryas (YD) cooling. Significant changes in vegetation occurred in the Holocene. The high percentage of sublittoral planktonic diatoms reflects a gradual rise in sea level during the BA and YD. A greater component of oceanic diatom species in the Holocene indicates the inflow of the Pacific waters through both the Tsushima and Tsugaru straits. Some increase in the participance and species diversity of relatively warm-water diatoms was noticed in the warming periods. The study of pollen and diatom records demonstrates a clear response to climatic fluctuations and changes in the Sea of Japan level in the Late Pleistocene and Holocene.

A subaerial origin for the mid-Ediacaran Johnnie valleys, California and Nevada: Implications for a diachronous onset of the Shuram excursion

Mid-Ediacaran incised valleys in the Johnnie Formation of eastern California are of interest for their broad time concordance with comparable features elsewhere (e.g., the Wonoka canyons of South Australia), and the largest negative carbon isotope anomaly in Earth history (the Shuram excursion). The Johnnie valleys have been previously interpreted as originating through mass wasting in a submarine setting at a continental margin, and perhaps as a result of syndepositional tectonism. New data suggest an alternative scenario: that the valleys were cut by a combination of fluvial incision and subaerial mass wasting concomitant with sea-level lowering in excess of 200 m, and were subsequently drowned and filled by marine sediments representing paleowater depths as great as tens of meters. Critical evidence from a series of outcrops in the southern Nopah Range includes (1) a new estimate of the erosional relief of the valleys of at least 208 m; (2) the presence in the basal fill of polymictic conglomerate/breccia with a quartz sand matrix that is locally associated with stratified quartz sandstone, suggesting both local and far-traveled fill components; and (3) beds and blocks of giant ooid packstone-grainstone indicative of shallow marine sedimentation during the early stages of valley filling. The conglomerate/breccia is channelized and associated locally with cross-stratification. Our interpretation is based upon a total of forty-five measured sections, physical stratigraphic mapping supported by sub-meter scale resolution 3-D drone imagery, as well as carbon isotope analyses. Comparable valleys, arguably of the same age, and likewise attributed to subaerial incision in earlier studies, are present at or near the top of the Caddy Canyon Quartzite of northern Utah and southeastern Idaho (a straightline distance of ∼ 850 km). Our working hypothesis is that both sets of valleys correspond in time with Gaskiers glaciation (∼580 Ma). Given that negative δ13C values have been obtained from both below and (new data) within the basal valley fill, and correlated by most workers with the Shuram excursion, we infer that the Shuram encompasses rather than postdates the Gaskiers event in eastern California, and that the onset of the excursion may be diachronous at a global scale.

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.

Optimal type and dose of hypoxic training for improving maximal aerobic capacity in athletes: a systematic review and Bayesian model-based network meta-analysis.

Objective: This study aimed to compare and rank the effect of hypoxic practices on maximum oxygen consumption (VO2max) in athletes and determine the hypoxic dose-response correlation using network meta-analysis. Methods: The Web of Science, PubMed, EMBASE, and EBSCO databases were systematically search for randomized controlled trials on the effect of hypoxc interventions on the VO2max of athletes published from inception until 21 February 2023. Studies that used live-high train-high (LHTH), live-high train-low (LHTL), live-high, train-high/low (HHL), intermittent hypoxic training (IHT), and intermittent hypoxic exposure (IHE) interventions were primarily included. LHTL was further defined according to the type of hypoxic environment (natural and simulated) and the altitude of the training site (low altitude and sea level). A meta-analysis was conducted to determine the standardized mean difference between the effects of various hypoxic interventions on VO2max and dose-response correlation. Furthermore, the hypoxic dosage of the different interventions were coordinated using the "kilometer hour" model. Results: From 2,072 originally identified titles, 59 studies were finally included in this study. After data pooling, LHTL, LHTH, and IHT outperformed normoxic training in improving the VO2max of athletes. According to the P-scores, LHTL combined with low altitude training was the most effective intervention for improving VO2max (natural: 0.92 and simulated: 0.86) and was better than LHTL combined with sea level training (0.56). A reasonable hypoxic dose range for LHTH (470-1,130kmh) and HL (500-1,415kmh) was reported with an inverted U-shaped curve relationship. Conclusion: Different types of hypoxic training compared with normoxic training serve as significant approaches for improving aerobic capacity in athletes. Regardless of the type of hypoxic training and the residential condition, LHTL with low altitude training was the most effective intervention. The characteristics of the dose-effect correlation of LHTH and LHTL may be associated with the negative effects of chronic hypoxia.

Drivers of large mammal distribution: an overview and modelling approach for palaeoecological reconstructions of extinct ecosystems

Abstract One of the primary goals of the palaeosciences is to produce robust understandings of palaeoecologies of extinct ecosystems. The time has arrived where such palaeoecologies can be significantly improved—agent-based models (ABMs) that synthesize our modern understandings of animal ecology with past conditions provide a unique opportunity for this. The Palaeo-Agulhas Plain (PAP), a now submerged landscape off the south coast of South Africa, formed a novel ecosystem during the lower sea levels of the Pleistocene. Here we provide a review of the utility of ABMs for understanding herbivores in prehistoric environments using the Paleoscape Model. The Paleoscape Model is fortunate to have features models of climate, geology and vegetation upon which we can understand how herbivores used the PAP environment. To incorporate aspects of herbivore behaviour and habitat suitability into the model requires analogies from extant systems. In addition to reconstructions of the availability of resources and associated risks, data on herbivore behaviour and physiology are imperative to our understanding of these systems. Behaviour, driven by changes in the environment, is interpreted by species, leading to selection of suitable habitats ultimately driving the herbivore’s decisions within ABMs. Finally, we discuss herbivore integration into these models that can be used in numerous other scenarios (past, present and future).

Assessment and exploitation of coastal low resolution mode sea level data from CryoSat-2 on the entrance to the Gulf of California

The CryoSat-2 mission (CS2), initially conceived for sea ice measurements, is also useful for sea level monitoring in oceanic and coastal areas. Only specific regions have two high resolution modes (SAR Delay/Doppler and SAR-Interferometric modes), while the rest of the areas are measured in low-resolution mode (LRM). The entrance to the Gulf of California presents this mode of operation. Sea Level Anomalies (SLA) obtained from CS2 are compared with tide gauges at three locations, Cabo San Lucas (CSL) south of the Baja California peninsula, Mazatlán (MZ) and San Blas (SB) on the continental margin. The comparison shows good agreement between SLAs in CSL and MZ, with standard deviations of the differences (SDD) lower than 0.09 m and Pearson’s correlations higher than 0.7 (95% of confidence level). San Blas is in a complex location and with less data, presenting an SDD greater than 0.13 m and a correlation below 0.55. We present the cross-shore seasonal and interannual variability in CSL and MZ using the CS2 SLA time series from 2011 to 2020. The variability shows the presence of events such as El Niño (2015 to early 2016), La Niña (2011) and the warm event of 2014 (nicknamed “the Blob”). Additionally, the residual time series of CS2 obtained after extracting the annual, semi-annual and monthly components, shows the East side (at MZ) is more affected by El Niño/La Niña variability while the West side (at CSL) is more influenced by the Blob/El Niño. Estimated long-term SLA trend at both locations are around 3.1 mm/yr, supporting similar findings by previous studies.

Simulating synergistic impacts of climate change and human induced stressors on a northern Gulf of Mexico estuarine food web

Apalachicola Bay, an estuary located in northwest Florida, is likely to experience a continuing increase in the severity of the effects of changing climate and human-induced stressors, such as sea level rise and changes in freshwater inflow. A coupled hydrodynamic and food web modeling approach was used to simulate future scenarios of freshwater input and sea level rise in Apalachicola Bay from 2020 to 2049 to demonstrate the range of temporal and spatial changes in water temperature, salinity, fisheries species biomasses, total food web biomass and upper trophic level diversity. Additionally, a survey of Apalachicola Bay stakeholders was conducted concurrently with model development to assess stakeholder knowledge and concerns regarding species and environmental changes within the system. Results of the model simulations indicated an increase in water temperature across all scenarios and an increase or decrease in salinity with scenarios of low or high river flow, respectively. These results aligned with the impacts anticipated by stakeholders. White shrimp biomass increased with low river flow and decreased with high river flow, while Gulf flounder biomass decreased across all scenarios. The simulated trends in white shrimp biomass contrasted with stakeholder perceptions. The food web model results also showed an increase in total food web biomass and decrease in upper trophic level diversity across all future scenarios. For all modeled simulations, the largest differences in future environmental variables and species biomasses were between scenarios of low and high river flow, rather than low and high sea level rise, indicating a stronger influence of river flow on the abiotic and biotic characteristics of the estuary. Stakeholders anticipated a future reduction in river flow and increase in sea level rise as negatively impacting the Franklin County economy and stakeholders’ personal interaction with the Apalachicola Bay ecosystem. The use of the ensemble modeling approach combined with the stakeholder survey highlights the use of multiple knowledge types to better understand abiotic and biotic changes in the estuarine system. Results provide insight on the synergistic effects of climate change and human-induced stressors on both the estuarine food web and human community of Apalachicola Bay.

Sand ridges from the coastal zone of southern Thailand reflect late quaternary sea-level history and environmental conditions in Sundaland

At many times during the Quaternary, when the global sea level was much lower than today (at least 30 m), the Thai-Malay Peninsula was connected by land to the Indonesian archipelago. This now submerged region is known as Sundaland and played a key role in the expansion of flora, fauna, and humans during the Quaternary. However, information regarding past environmental conditions is sparse as post-glacial sea-level rise submerged and eroded most sedimentary archives. In this study, a combination of geomorphological mapping, investigating sedimentary features, and optically stimulated luminescence dating is used to decipher the evolution of sand ridges found in the coastal zone of the Nakhon Si Thammarat Province, southern Thailand. The two main ridges (eastern and western) are composed of moderately to poorly sorted medium to coarse, structureless massive sands. The eastern ridge deposited between ca. 8.3 ka and 0.16 ka and formed by coastal processes related to sea-level change and storm surge during the Holocene. Surprisingly, the western ridge yields a minimum depositional age of ca. 82 ka, and further deposition dates to different periods of the Late Pleistocene. We suggest that the initial formation of the western ridge possibly occurred during the Last Interglacial (Marine Isotope Stage 5e). During periods of low global sea level, when the region was far away from the coast, the ridge accumulated further sand, most likely due to aeolian activity. This would imply a rather limited vegetation cover in the interior of Sundaland and support previous assumptions of savannah-like conditions during global-scale glacial periods.

Spatio-temporal long-term evaluations of the mean sea level pressure, sea level change, and sea surface temperature over two enclosed seas

This study aims to examine the temporal and spatial variability of mean sea level pressure (MSLP) and to determine the relationship between MSLP and the oceanic data, such as sea surface temperature (SST), and sea level anomaly (SLA). The long-term and decadal averages, long-term trends, and their statistical significance levels were evaluated in the eastern Mediterranean and Black seas as enclosed sea examples. In the Black Sea, the western part was exposed to higher MSLP accompanied by relatively low sea level rise compared to the eastern part of the sea. In the eastern Black Sea, significant sea level rise was detected, where the MSLP was low due to the inverse barometer (IB) effect. In the eastern Mediterranean Sea, MSLP was significantly decreased eastward and was accompanied by relatively high sea level rise compared to other parts of the basin. The highest MSLP was found in the Aegean Sea, where the sea level rise was relatively low. In recent years, significant warming tendency in SST triggers a significant decreasing trend in MSLP and the rising tendency in sea level over the eastern Mediterranean and Black seas.

Relict and Modern Sediments on the Continental Shelf of the Northern South China Sea: A Reconsideration

AbstractUnderstanding the temporal‐spatial patterns of modern and relict sediments is of importance for assessing changes in the Quaternary environment and sea‐level. Sedimentological and geochemical data is presented, along with in situ shell‐based accelerator mass spectrometry 14C ages of 30 samples from the surface sediments on the northern shelf of the South China Sea (NSSCS). The authors’ data show that the NSSCS surface sediments exhibit considerable diversity in composition. Modern sediments are primarily constrained to the NW inner shelf, which is fed by fluvial sands sourced from Coastal South China river systems and dominated by the Pearl River Estuary delivery. The transport and discharge of the terrestrial sediments to the NSSCS is highly influenced by the Guangdong Longshore Current and its secondary cyclonic eddies. Relict sediments dominated by well‐sorted, medium‐ and coarse‐grained sands were identified in the NW Shenhu and NW Dongsha areas of the outer NSSCS. The sedimentology and geochemistry of the relict sediments imply that they were deposited in a dry and cold environment either during the low sea levels of the late Pleistocene (∼40 ka) or the early Holocene (∼10 ka). To the east, the Taiwan Shoal and vicinity are dominated by a sand mixture, at which the relict sediments were reworked by terrigenous supply and modern hydrodynamic environment due to the compound action of the Guangdong Longshore Current, seasonal cyclones, and Kuroshio Intrusion. The present isobaths of ∼−90 m in the NSSCS might be the reflective of the early Holocene coastal delta or the last glacial maximum shoreline.

Behaviourally modern humans in coastal southern Africa experienced an increasingly continental climate during the transition from Marine Isotope Stage 5 to 4

Linking human technological and behavioural advances to environmental changes is challenging, as it requires a robust understanding of past climate at local scales. Here, we present results from regional high-resolution numerical simulations along with climate data directly from the archaeological sequence of Blombos Cave (BBC), a well-studied site in coastal southern Africa. The model simulations cover two distinct periods centred at 82 and 70 thousand years (ka) ago (Marine Isotope Stage [MIS] 5 and the onset of MIS 4, respectively), when orbital parameters and global sea level were markedly different from one another. Climatic changes from 82 to 70 ka are determined through four simulations that use past and present-day coastline configurations. The hydrogen isotopic composition of leaf waxes (δ2Hwax) and n-alkane distributions and abundances are used to reconstruct hydroclimate around BBC. The leaf wax n-alkane record, one of the first produced in an archaeological setting in this region to date, can be interpreted as a drying signal from MIS 5c to 4. This agrees with our modelling results, which indicate a drier and more continental climate over coastal southern Africa at 70 ka, compared to 82 ka. The simulated aridification is most evident from the reduced precipitation amounts in both summer (∼20%) and winter (∼30%). The annual number of summer days (Tmax ≥ 25 °C) and cold nights (Tmin < 5 °C) in the vicinity of BBC increases more than 5 and 3-fold, respectively, under the more continental climate at 70 ka. Weaker westerly winds in winter, a cooler Agulhas Current, and a land surface expansion associated with the coastline shift due to lower sea levels at 70 ka all contribute to the simulated climate shift. Our approach highlights the importance of multiple lines of evidence for achieving robust results, while demonstrating how both large-scale forcing and local influences worked together in shaping the local climate that early humans lived in. Adaptation to a drier climate and increased continentality around BBC might have induced greater mobility, which led to increased population interactions, cultural transmission rates, skill exchange, and material complexity during the so-called Still Bay period.

A steady-state model reconstruction of the patagonian ice sheet during the last glacial maximum

During the Last Glacial Maximum (LGM), the Patagonian Ice Sheet (PIS) was the largest Quaternary ice mass in the Southern Hemisphere outside of Antarctica. Although the margins of the LGM ice sheet are now well established through end-moraine mapping and dating, apart from a few modelling and empirical studies, there remains a lack of constraint on its thickness and three-dimensional configuration. Here, we provide a high-resolution steady-state model reconstruction of the PIS at its maximum - LGM - extent applied using Nye's perfect-plastic ice rheology. The yield-strength parameter for the perfect-plastic flow model was calibrated against independent empirical reconstructions of the Lago Pueyrredón Glacier, where the former vertical extent of this major outlet glacier is well constrained by cosmogenically-dated trimlines and lateral and end-moraine limits. Using this derived yield-strength parameter, the perfect-plastic model is then applied to multiple flowlines demarking each outlet across the entirety of the PIS in a GIS framework. Our results reveal that the area of the PIS was ∼504,500 km2 (±8.5%) with a corresponding modelled ice volume of ∼554,500 km3 (±10%), equivalent to ∼1.38 m (±10%) of eustatic sea-level lowering at the LGM. Maximum surface elevation was at least 3500m asl although the majority of the ice sheet surface was below 2500 m asl. We find that our ice sheet reconstruction is in good general agreement with previous estimates of net PIS volume derived from transient modelling studies. We attribute the slightly lower aspect-ratio of our ice sheet (and its concomitant 5% reduction in volume and sea-level equivalent) to the lower yield strength applied, based on more temperate and dynamic ice sheet conditions.

Benthic biota (nummulites) response to a hyperthermal event: Eccentricity-modulated precession control on climate during the middle Eocene warming in the Southern Mediterranean

Earth's future environment depends critically on how the marine ecosystems react to the current greenhouse conditions. Past warming events from the Middle Eocene can shed light on the nature of these reactions. Middle Eocene sedimentary archives from the Tethyan margins record the Middle Eocene Climatic Optimum (MECO) with varying carbon isotope excursions from site to site. The present study integrates stable isotopes, the abundance of benthic fauna, and astrochronology to look for the timing of the MECO peak warming and the maximum abundance of nummulites in the Southern Mediterranean (Tunisia). A mesotrophic environment during the lower Bartonian with high eustatic sea level promotes the formation of a shallow water carbonate platform in central Tunisia from 40.6 Ma to 39.8 Ma. Nummulites occur in low abundance in the Lower Reneiche Limestone unit (LRL, Bey et al., 2015) from 40.6 to 40.2 Ma, then increase, reaching maximum abundance at the Upper Reneiche Limestone unit (URL, 40.1 to 40 Ma). Maximum accumulation of nummulites and negative excursion of δ18O in the URL occurred during the MECO's warming peak (40.07 to 40 Ma), 200 kyr after the middle Eocene third-order maximum flooding surface. The nummulitic beds represent warmer climates and higher sea levels (arid to semi-arid climate), and the short marl intervals reflect enhanced detrital input (humid climate and lower sea level). The eccentricity modulations were extracted using a lowpass filter applied on a wide-band precession filter then we computed the instantaneous amplitude using Hilbert Transform. The Spearman-rank correlation assesses the potential introduction of amplitude modulations during tuning. Power Decomposition Analysis (PDA) indicates a dominant short eccentricity forcing on the regional climate during the MECO with a minor obliquity component. Variations in magnetic susceptibility and CaCO3 content suggest a combined control of climate and sea-level cycles controlled by eccentricity-modulated precession cycles.

Millennial-scale paleotemperature change in the Japan Sea during Marine Isotope Stage 3: Impact of meridional oscillation of the subpolar front

The Japan Sea is a semi-closed marginal sea that has been significantly affected by fluctuations of the East Asian monsoon. Due to its geographic setting, the influence of the monsoon is significant especially during the last glacial period, when the low sea level stand restricted surface water exchange with adjacent seas. Millennial-scale change in the summer monsoon controlled the input of freshwater and nutrients into the Japan Sea during Marine Isotope Stage (MIS) 3, resulting in the deposition of alternating dark- and light-colored sedimentary layers. However, the relationships between the sediment color alternations and winter sea surface conditions, such as temperature and salinity, are not understood. Here, we provide high-resolution Mg/Ca-based winter sea surface temperature (SST) records during MIS3 from two sediment cores from the southern Japan Sea. The SSTs at both sites showed millennial-scale fluctuations with significantly different amplitudes. The southern site had a larger SST amplitude with warmer in dark- and cooler in light-colored intervals. The SST difference between the two cores was greater in dark-colored intervals. The millennial-scale changes in SST difference are probably attributable to meridional migration of the subpolar front, induced by winter monsoons and inflow of the Tsushima Warm Current, which had a northerly (southerly) position during interstadials (stadials). The results suggest that the millennial-scale winter monsoon variability contributed to sediment color alternation via greater cooling during stadials, which enhanced ventilation, in conjunction with the summer monsoon-induced productivity change. Therefore, both the winter and summer monsoons are key drivers of the oceanographic condition in the Japan Sea.

A new deglacial climate and sea-level record from 20 to 8 ka from IODP381 site M0080, Alkyonides Gulf, eastern Mediterranean

Records of relative sea-level rise for the last deglaciation are mostly limited to coral reef records and geophysical model estimates, but observational data from regions with temperate climates is sparse. We present a new relative climatic and regional sea-level rise record for glacial Termination 1 (Marine Isotope Stages [MIS] 2–1) based on ostracode paleoecology from the upper 8 m of the International Ocean Discovery Program (IODP) Site M0080 collected on Expedition 381, in the Gulf of Alkyonides, eastern Corinth basin of the Mediterranean Sea. Results show a series of major faunal transitions from lacustrine (Ponto-Caspian, Lake Corinth) glacial-age assemblages to fully marine (Mediterranean) interglacial assemblages between 20 and 8 ka. During glacial and early deglacial intervals, the Gulf of Alkyonides was characterized by non-marine lacustrine conditions with episodic sediment input from coastal, saline lake environments. Relatively stable lake shoreline conditions marked by the distinctive Tuberoloxoconcha sp. Existed from ∼17.5 to 15 ka. During the peak deglacial interval, the BØlling-AllerØd (B-A, ∼15–13.5 ka), rapid sea-level rise is indicated by a fully marine ostracode fauna colonization, which persisted from 13.5 to 7.5 ka (Late Pleistocene-Early to Middle Holocene).The transition from lacustrine to marine environments confirms that during the last glacial maximum (LGM) low sea level (130 - 125 m below present day), the Corinth-Alkyonides depocentres were lacustrine. Marine water breached the shallow Rion and Acheloos-Cape Pappas sills, which today are ∼50–60 m deep, separating the Mediterranean and Corinth-Alkyonides system beginning about 15 ka. Based on Alkyonides sedimentation rates, mean rates of sea-level rise during the B-A flooding of the Corinth-Alkyonides system are comparable to those obtained from coral reef sea level (SL) records, at least 10–20 mm yr−1. Changes in sedimentation and sill depths in this tectonically active region may have played a role in reconnection of the Mediterranean and Corinth/Alkyonides system over a prolonged period. However, the ages and scale of the faunal changes and their clear correspondence with previously published global sea-level curves and the regional sea-level curve based on deglacial land elevation changes predicted by the ICE-7G model suggests the M0080A deglacial is dominated by the glacio-eustatic sea-level rise and records details of global climate changes during Termination 1.

Identification of depositional features in the Albian and Aptian sections over the hydrocarbon exploration block M2 on the Mannar Basin, Sri Lanka

The Mannar Basin extends over 45,000 km2 off the western coast of Sri Lanka. It has evolved due to the multiphase rifting between Indo-Lanka landmasses during the Barremian-Paleocene time. The sediment thickness of the basin ranges from about 4 to 10 km. The northern part of the basin is a targeted area for hydrocarbon exploration in Sri Lanka. Though two natural gas discoveries were made in 2011, the basin remains a frontier due to lack of well penetration and 3D seismic coverage. As a result, the depositional features of sediment in the basin are little known. This study focuses on identifying paleo depositional features in the Albian and Aptian strata using 650 km2 3D seismic data from the Mannar Basin. Root Mean Square (RMS) amplitude was used to characterize the depositional features in three-time windows on IHS Kingdom software (v.8.3). The results show the existence of a multi-level paleo submarine fan system in the Albian and Aptian strata. They are located relatively close to the western coastline compared to the fan system in the Eocene strata. The deposition of this paleo submarine fan system has taken place in a shelf marine environment and has been influenced by relatively high sea levels during the Albian and Aptian compared to the relatively low sea levels in the Paleocene and Eocene.

Glacial changes in sea level modulated millennial-scale variability of Southeast Asian autumn monsoon rainfall

Most paleoclimate studies of Mainland Southeast Asia hydroclimate focus on the summer monsoon, with few studies investigating rainfall in other seasons. Here, we present a multiproxy stalagmite record (45,000 to 4,000years) from central Vietnam, a region that receives most of its annual rainfall in autumn (September-November). We find evidence of a prolonged dry period spanning the last glacial maximum that is punctuated by an abrupt shift to wetter conditions during the deglaciation at ~14 ka. Paired with climate model simulations, we show that sea-level change drives autumn monsoon rainfall variability on glacial-orbital timescales. Consistent with the dry signal in the stalagmite record, climate model simulations reveal that lower glacial sea level exposes land in the Gulf of Tonkin and along the South China Shelf, reducing convection and moisture delivery to central Vietnam. When sea level rises and these landmasses flood at ~14 ka, moisture delivery to central Vietnam increases, causing an abrupt shift from dry to wet conditions. On millennial timescales, we find signatures of well-known Heinrich Stadials (HS) (dry conditions) and Dansgaard-Oeschger Events (wet conditions). Model simulations show that during the dry HS, changes in sea surface temperature related to meltwater forcing cause the formation of an anomalous anticyclone in the Western Pacific, which advects dry air across central Vietnam, decreasing autumn rainfall. Notably, sea level modulates the magnitude of millennial-scale dry and wet phases by muting dry events and enhancing wet events during periods of low sea level, highlighting the importance of this mechanism to autumn monsoon variability.