Core Depth Research Articles

Sources identification and distribution of aliphatic and aromatic hydrocarbons in coastal sediments of Arica Bay – Chile

ABSTRACT This study assesses the first approach regarding the origin, level of contamination, and spatial and vertical distribution of aliphatic and polycyclic aromatic hydrocarbons in coastal sediments of Arica’s Bay. Twenty-seven aliphatic hydrocarbons (AHs) and eighteen polycyclic aromatic hydrocarbons (PAHs) were studied at three depths in sediment cores collected from six locations in the coastal bay. The spatial distribution pattern of the molecular composition of aliphatic and aromatic hydrocarbons is consistent with the directions of the ocean currents from the northeast to the southwest. PAHs are mainly correlated with anthropogenic input sources to the bay. The total aliphatic hydrocarbons showed a wide concentration range from 112.07 to 2,382.43 ng·g−1 dry wt. while total PAHs ranged from 8.01 to 85.40 ng·g−1 dry wt. The vertical distribution of the total AHs shows a tendency to concentrate between 10–20 and 20–30 cm depth. Specific diagnostic characterisation ratios suggest that the bay sediments mainly consist of a mixture of autochthonous, predominantly marine sources composed of marine bacteria (n-C16, n-C18, and C20) and terrestrial plant derivatives (n-C29 and n-C31) and with a contribution of petrogenic hydrocarbons masked by biogenic hydrocarbons. The vertical distribution of the total polycyclic aromatic hydrocarbons is dominated by low molecular weight (LMW) PAHs of two and three rings, such as fluoranthene (FLT), phenanthrene (PHE), pyrene (PYR), and the highest concentrations are found between 10 and 20 cm depth of the sediment column. The PAH diagnostic ratios revealed a mixture of pyrogenic hydrocarbons (biomass and coal combustion) with petrogenic compounds from the Port of Arica and its neighbouring areas. According to the guidelines of UNEP for AHs and PAHs categorisation, the bay’s sediments may be classified from harmless to harmful due to AHs composition and low PAHs pollution.

Bioturbation in sediment cores from the Clarion-Clipperton Zone in the northeast Pacific: Evidence from excess 210Pb

Radioactivity levels of 210Pb and 226Ra were measured to evaluate the bioturbation coefficients and mixing depths in one sediment core collected from the polymetallic nodule area inside the Clarion-Clipperton Zone (CCZ), a contract area of the China Ocean Mineral Resources Association (COMR) in the eastern Pacific Ocean. With a steady-state diffusion mode, the bioturbation coefficient and mixing depth of the sediment core were estimated to be 81.5 cm2/a and 51.3 cm, respectively, higher than that of the sediment core from the previous results from abyssal or global areas, which may be attributed to the distribution of total organic carbon (TOC) abundance. In addition, the transport flux of TOC from the surface layer to the deep layer were evaluated to be 1.15 mmol/(cm2·a), resulting in 83,200 tons of carbon buried annually into the sediment in the CCZ, indicating that a potential carbon sink will be disturbed with future exploration.

Germination of Pyrodinium bahamense Cysts from a Pristine Lagoon in San José Island, Gulf of California: Implications of Long-Term Survival

The production of cysts by dinoflagellates can be part of the life cycle of some species, improving their survival under adverse environmental conditions; cyst germination may explain the recurrence of algal blooms in some cases. In order to evaluate the germination rates of Pyrodinium bahamense, its cysts were retrieved from surface sediments collected in San José Lagoon, SW Gulf of California, and germination assays were carried out through the cysts incubation under two contrasting light and nutrient concentration conditions. Also, to evaluate cysts viability, we isolated P. bahamense cysts and other dinoflagellate species from different depth layers of a 210Pb-dated sediment core (~100 years) to examine their germination for 20 days. Germination rates were higher under light (28–56%) than in darkness (23–34%); there were indications that the nutrient-enriched media was more effective in promoting germination than seawater. Furthermore, germination was observed in cysts isolated from all selected core depths, even those corresponding to ~100 years. These results demonstrate that cysts remain viable for long periods, and P. bahamense cysts germinate in any light and nutrient conditions. The results of this research provide relevant information to understand its physiology and complex population dynamics. This species should be closely monitored in the area in the context of climate change, as current natural conditions are likely to change.

Sedimentary geochemistry mediated by a specific hydrological regime in the water level fluctuation zone of the Three Gorges Reservoir, China.

The water level fluctuation zone (WLFZ) of the Three Gorges Reservoir (TGR) acts as an important sink for inflowing suspended sediment loads over the inundation periods following regular dam operations. This study depicts the sedimentary geochemical dynamics along a sedimentary profile based on the determined chronology and explores its links to the specific hydrological regime created by dam flow regulation and riverine seasonal suspended sediment dynamics. A compact 345-cm-long sediment core was extracted near the base water level (145.3m) from the WLFZ of the TGR and sectioned at 5-cm intervals. Extracted sediment subsamples were analyzed for grain size composition, organic matter (OM), total nitrogen (TN), and geochemical elements (Na, K, Ca, Mg, Pb, Zn, Ni, Co, Mn, Cr, Fe, and Cu). The sediment core chronology was determined using 137Cs elemental analysis. Sedimentary geochemistry and grain size properties of extracted sediment core exhibited greater variations during initial submergence years till the first complete impoundment of the TGR (2006-2010). Afterward (2011-2013), although upstream inflowing suspended sediments and reservoir water level were comparable, sediment deposition and concentrations of sedimentary geochemical constituents showed considerably fewer variations. Seasonal variations in sediment deposition and geochemical composition were also observed during the rainy (October-April) and dry (May-September) seasons, in addition to annual variations. Grain size, OM, and other sediment geochemical constituents all had significant correlations with each other and with sediment core depth. The concentrations of geochemical elements in various sediment stratigraphic layers exhibited staggering associations with each other and were dependent on each other in several ways. The arrangement of geochemical elements in various stratigraphic layers of the extracted core illustrated amalgamation with inputs from upstream seasonal suspended sediment dynamics and reservoir water levels. During shortened submergence periods and higher input sediment loads, geochemical elements demonstrated impulsive distributions. Alternatively, during longer submergence periods, elemental distributions were relatively uniform attributed to higher settling time to deposit according to grain size and geochemical affinities. Higher suspended sediment loads in association with seasonal floods also resulted in rough sediment deposition patterns, imparting variations in the distributions of geochemical elements. Interim mediations in geochemical element concentrations are associated with seasonal distal flash floods and local terrace bank collapses, which generate significant amounts of distal sediment loads that are quickly deposited and are not sorted hydrodynamically. Overall, although a specific mechanism was devised to circumvent the siltation process, a considerable amount of sediment is trapped at pre-dam sites. In addition, siltation caused nutrients and geochemical elements' enrichment.

Multi-Objective Optimization of Magnetorheological Mount Considering Optimal Damping Force and Maximum Adjustable Coefficient

To address the problem of multiple working conditions and complex requirements in magnetorheological fluid (MRF) mounts, a high-precision damping characteristic optimization method is explored. Based on the parallel plate model, the equation of fluid motion in the inertial channel was established according to the Navier–Stokes equation, and the MRF mount damping characteristics were analyzed. Considering the fluid model to be suitable in the steady-state, the model was experimentally verified, and the extended equation was fitted. Multi-objective optimization design was carried out by considering the large damping force and adjustable coefficient as the optimization goal and external geometric dimensions as variables. According to results, under the radial-channel MRF mount structure, the magnet core depth has the least influence on the damping force; furthermore, the damping performance can be quickly improved by changing the height of the inertial channel. The addition of the extended equations further improved the accuracy of the fluid model. The multi-objective optimization design can improve the strength and uniformity of the flux density of the MRF mount damping gap. After optimization, the damping force is increased by 44.64%; moreover, when the current is increased from 1.5 to 1.8 A, the controllable force increases by only 2.26%, and the damping performance is fully exerted.

Compressive failure strain of unidirectional carbon fibre composites from bending tests

One of the major difficulties in establishing material properties for composites is to obtain reliable compressive strengths either from the current direct compressive testing methods due to the stress concentration or from the indirect flexural tests due to the localised stress concentration and strain gradient effect. In the present paper, unconventional flexural tests on carbon fibre/wood sandwich and monolithic composite beams have been developed and compressive failure strains of unidirectional carbon fibre composites have been obtained with high values and low variability. The compressive strain of 1.36% obtained for the IM7/8552 material is 14% higher than the highest published value found and the variability is only 3%. Strain gradient effects on the compressive failure strain from measurements with the same stressed volume have also been quantified for the first time using the proposed carbon fibre/wood sandwich beam with various wood core depths. The increase in failure strain due to the strain gradient effect reduced with the increase of total beam thickness and approached a constant value when the beam was thicker than 20 mm.

Morphological Variability of Alveolophora antiqua from a Freshwater Early Miocene Paleolake in the Barguzin Valley (Baikal Rift Zone)

Using scanning electron microscopy, the morphology of Alveolophora antiqua (Moisseeva) Moisseeva from the freshwater Early Miocene paleolake in the Barguzin Valley was studied. We extended the species diagnosis relative to features such as spines, structure of areolae, costae, alveolae, rimoportulae and the external opening of rimoportulae and show a wide morphological variability with regard to valve shape (round, oval, ovoid and triangular). The percentage of these shapes varied with the core depth. Oval valves dominated in lower layers, while triangular ones occur in upper layers. We propose that the shape variability of valves might be due a sharp short-term cooling event or polyploidization. The finding of A. antiqua in the Early Miocene deposits of the Barguzin Valley expands both the georaphic and stratigraphic ranges of this species.

U.S. Geological Survey Core Research Center: a gateway to subsurface discovery for geoscience research

Abstract The U.S. Geological Survey (USGS) operates the Core Research Center (CRC) in Denver, Colorado, USA, a public access repository of rock cores from over 9800 wells and drill cuttings from over 53 000 wells, primarily from states in or adjacent to the Rocky Mountain Region. Annually, approximately 1400 visitors use the collection for traditional and innovative research. The CRC has an online, searchable database which includes downloadable core photos, analytical data, and thin-section images. When visitors sample for analyses, the results must be returned to the CRC for public dissemination providing immediate, free access to users while sparing the finite, irreplaceable collection from redundant testing. A representative quantity of every core depth is preserved in perpetuity. Studies on CRC materials, paired with new extraction methods, have unlocked new productive deposits. Materials drilled and curated decades ago remain in high demand while materials receiving little attention today may be crucial for future research. The collection provides immediate, inexpensive access to subsurface materials at a fraction of the cost of new drilling, sparing money, time and environmental impacts.

Evidence for late-glacial oceanic carbon redistribution and discharge from the Pacific Southern Ocean

Southern Ocean deep-water circulation plays a vital role in the global carbon cycle. On geological time scales, upwelling along the Chilean margin likely contributed to the deglacial atmospheric carbon dioxide rise, but little quantitative evidence exists of carbon storage. Here, we develop an X-ray Micro-Computer-Tomography method to assess foraminiferal test dissolution as proxy for paleo-carbonate ion concentrations ([CO32−]). Our subantarctic Southeast Pacific sediment core depth transect shows significant deep-water [CO32−] variations during the Last Glacial Maximum and Deglaciation (10-22 ka BP). We provide evidence for an increase in [CO32−] during the early-deglacial period (15-19 ka BP) in Lower Circumpolar Deepwater. The export of such low-carbon deep-water from the Pacific to the Atlantic contributed to significantly lowered carbon storage within the Southern Ocean, highlighting the importance of a dynamic Pacific-Southern Ocean deep-water reconfiguration for shaping late-glacial oceanic carbon storage, and subsequent deglacial oceanic-atmospheric CO2 transfer.

The palynology of the Permian succession in the CSDP-2 Well, South Yellow Sea, China

The fully cored CSDP-2 Well, drilled in the central uplift region of the South Yellow Sea, China, provides indispensable and very significant research opportunities to understand the evolution of life, paleoclimate, paleogeography, and tectonics during the Permian in the South Yellow Sea area of the Yangtze paleoblock. We here analyze 118 samples from 893.7 to 1798.8 m depth of the CSDP-2 borehole core and recognize three Permian palynological assemblages, Laevigatosporites minimus – Florinites florini (MF) for the Kungurian mid-lower Qixia Formation, Crucisaccites quadratoides – Limitisporites rhombicorpus (QR) for the Capitanian lower Longtan Formation and Macrotoispora media – Anticapipollis tornatilis (MT) for the Wuchiapingian upper Longtan Formation, in an ascending order. These palynological assemblages indicate a warm and semi-humid rainforest paleoenvironment and a drying tendency of the paleoclimate. The present study area belongs to the Yangtze paleoblock in paleogeography and is a part of the Cathaysia flora based on mega-plant fossil records. However, our palynological assemblages show similarities to those of both South China and North China subzones and, especially, their pollen contents with arid coniferous affinities highly similar to those in the north part of the South China subzone. The presence of conifers might suggest a more arid climate in the North China subzone had started to affect the Yellow Sea area in the Lopingian (Permian).

Enhanced drying of the Tengger desert, northwest margin of East Asian summer monsoon during warming interglacials after 500 ka

The arid-semiarid regions face drying threats under global warming, but their future changes in terms of drying or not are controversial. High orbital-scale resolution records spanning across the Mid-Brunhes event in the arid deserts provide a climate analogue since the formation of deserts. However, there was no definite work in the deserts so far. Here, we present the results of a chronological and paleoenvironmental study of a 122.63 m-long core drilled in the largest lake basin in the central Tengger Desert (northern China), located in the northwestern margin of East Asian Summer Monsoon regions. Following comprehensive paleomagnetism analysis, the Matuyama/Brunhes boundary was detected at a core depth of 87.5 m, and the basal age of the core is estimated at ∼940 ka based on orbital tuning. The lithology, grain size, carbonate and total organic carbon content were analyzed to examine the sedimentary facies and reconstruct the paleoenvironmental evolution. Ten relatively humid layers were identified by sedimentary facies, further results confirmed by fine grain size, high carbonate, and total organic carbon content, which generally developed during interglacial and were controlled by the East Asian summer monsoon precipitation during the past 940 ka. Since ∼500 ka, the interglacial climate regime displayed an intensified aridification manifested as shrinking lakes and persistent mobile dunes in the Tengger Desert. We argue that this aridification was caused by the combination of a massive supply of clastic material for the desert and the occurrence of higher potential evapotranspiration during warmer interglacials after the Mid-Brunhes Event. This research finding provides geological evidence for the aridification of the deserts in the East Asian Summer Monsoon margin under global warming.

Palaeoclimatic Studies of the Late Quaternary Sediments from Chirakkara, Kollam District, Kerala, India

The Quaternary period is considered one of the most eventful periods of all geologic periods. The present study intends to understand the paleo-environmental conditions that prevailed in the southern part of the Kerala State, India, during the Late Quaternary period. The present study aims to understand the climatic variability of the Holocene epoch in the Chirakkara region, the easternmost part of Polachira wetland, Kollam district, South Kerala, by using granulometric data and geochemical proxies. A core of 2.5 m in length has been collected from the study area, and both textural and TOC/TN analyses were carried out. The variation in grain size is attributed to the variations in the energy level of the transporting medium and turn to the climatic conditions, especially rainfall. The sediments encountered in the core are dominated by sand-sized particles indicating dynamic high energy conditions and high precipitation events. The ternary plot of the sediment samples also suggests violent environmental conditions during the deposition of the sediments. The predominance of low values of TOC/TN ratio found at both ends of the core indicates an autochthonous source for organic carbon, possibly due to the aggravated aquatic phytoplankton activity, and increased lake bioproduction, and/or decline in the delivery of organic matter from the terrestrial environment. High values of the TOC/TN ratio noted at the middle portion of the core at depths from 120 cm to 210 cm indicate the allochthonous source for the organic carbon. Among allochthonous sources, the C3-type plant is dominant, indicating a cool and wet climate. At the same time, the extremely high TOC/TN values at 170 cm core depth indicate a short period of hot and sunny climatic conditions. The analysis of the granulometric data and organic matter proxies suggest that the study area has experienced wet climatic conditions with occasional dry spells during the Late Quaternary Period.

Effects of Spectral Resolution on Simple Magnetic Field Diagnostics of the Mg ii H and K Lines

We study the effects of finite spectral resolution on the magnetic field values retrieved through the weak-field approximation (WFA) from the cores of the Mg ii h and k lines. The retrieval of the line-of-sight component of the magnetic field, B LOS, from synthetic spectra generated in a uniformly magnetized FAL-C atmosphere is accurate when restricted to the inner lobes of Stokes V. As we degrade the spectral resolution, partial redistribution effects, which more prominently affect the outer lobes of Stokes V, are brought into the line core through spectral smearing, degrading the accuracy of the WFA and resulting in an inference bias, which is more pronounced as the resolution becomes poorer. When applied to a diverse set of spectra emerging from a sunspot simulation, we find good accuracy in the retrieved B LOS when comparing it to the model value at the height where the optical depth in the line core is unity. The accuracy is preserved up to field strengths of B ∼ 1500 G. Limited spectral resolution results in a small bias toward weaker retrieved fields. The WFA for the transverse component of the magnetic field is also evaluated. Reduced spectral resolution degrades the accuracy of the inferences, because spectral mixing results in the line effectively probing deeper layers of the atmosphere.

Parametric Model for Eddies‐Induced Sound Speed Anomaly in Five Active Mesoscale Eddy Regions

AbstractMesoscale eddies are ubiquitous in the ocean. Their acoustic properties have attracted considerable research attention. However, the three‐dimensional structure for eddy‐induced sound speed anomalies has remained obscure, hindering further understanding of the impact of eddies on acoustic propagation. To solve this problem, a region‐dependent parametric model for eddy‐induced sound speed anomaly (SSA) structure is established by performing a composite analysis based on abundant profiles measured by Argo floats and the corresponding satellite altimetry data. The parametric SSA model can be applied to fast reconstruct the underwater sound speed (SS) field of the eddy based only on the intensity and radius of the eddy. A comparison with a surveyed eddy shows that the errors of the reconstructed SSA are 2.36 m/s (8.33%) in strength and 37 m (9.37%) in core depth. The reconstructed SS field is employed to study the sound propagation characteristics in the presence of a cyclonic eddy with the ray‐tracing method. The results show that the parametric model can advance eddy‐acoustic effect research in the case of observation data shortages.

Impact of Assimilating Adaptively Thinned AIRS Cloud-Cleared Radiances on the Analysis of Polar Lows and Mediterranean Sea Tropical-Like Cyclone in a Global Modeling and Data Assimilation Framework

Abstract Polar lows, and mesoscale convective cyclones bearing resemblance to tropical cyclones but originating outside of the tropics, are storms that are challenging to represent accurately in global analyses and models because of their small size, rapid growth at subsynoptic scales, occurrence in data poor oceanic regions, and difficulties in objectively validating them in analysis. Building on previous positive results obtained with respect to the representation of tropical cyclones (TCs) in a global model, a set of observing system experiments (OSEs) performed using the NASA Goddard Earth Observing System (GEOS, version 5) are investigated, focusing on three case studies—a polar low in the Sea of Okhotsk, a polar low in the Southern Ocean, and a Mediterranean Sea tropical-like cyclone that occurred during the boreal fall season of 2014. Experiments assimilating adaptively thinned cloud-cleared hyperspectral infrared radiances from the Atmospheric Infrared Sounder (AIRS) instrument on board the NASA Aqua satellite, with higher density in the vicinity of each storm and its pre-cyclogenesis environment, and lower density elsewhere, demonstrate a positive impact on the analyzed representation of each storm. The adaptive thinning experiments improve the storm intensity and structure, including vertical alignment, depth, symmetry, strength, and compactness of warm core compared to the reference experiments. The results suggest that jet-level processes associated with extremely strong horizontal velocity gradients as represented in the model analysis can be useful to locate dynamically active regions of the extratropical atmosphere where denser data coverage is likely to improve the analyzed representation of polar lows and other similar marine mesoscale convective cyclones. Significance Statement Extratropical maritime mesoscale convective cyclones are short-lived, elusive features that are difficult to represent accurately in global analyses. Previous work by this team demonstrated a positive impact of an adaptive thinning methodology for infrared radiances applied to the tropical cyclone (TC) analysis. The methodology allows a relatively greater volume of radiance data to be assimilated around TCs within a TC-centered moving domain in a global model, yielding an improvement in TC structure and intensity forecast. A similar approach is explored here for two polar lows and a Mediterranean Sea tropical-like cyclone, wherein infrared radiances are more densely assimilated in the vicinity of each storm and its pre-cyclogenesis environment, resulting in a positive impact on the representation of the storm. Strong jet-level horizontal velocity gradients appear to precede each storm, and could be used to automate the adaptive thinning strategy in the future.

Isotopic Records of Ancient Wildfires in C4 Grasses Preserved in the Sediment of the Ross Sea, Antarctica

AbstractWe report carbon isotopic values in total organic carbon (TOC) and pyrogenic carbon (PyC) preserved in two sediment cores from the Ross Sea, Antarctica. The δ13C values of PyC ranged from −10.9‰ to −17.2‰, with distinct differences from the δ13C values of TOC (−24.1‰ to −26.1‰) in the sediments. The radiocarbon ages of PyC were 9,128 and 8,410 years old on average in the two cores but were thousands of years younger than the ages of TOC at the same core depth. These isotopic records provide strong evidence indicating that the PyC was produced from ancient wildfires predominantly in C4 vegetation and transported to Antarctica in the atmosphere. We suggest that ancient wildfires in predominantly C4 grasslands likely frequently occurred on a large scale and at a high intensity in the Southern Hemisphere during the last deglaciation to mid‐Holocene period of 14,800–4,200 years ago.

Observed near-inertial kinetic energy in the Philippine Sea

Using 32 months of observational data from two acoustic Doppler current profiler (ADCP) moorings deployed at 18°N, 125°E and 18°N, 126°E, this study investigated the statistical characteristics of the near-inertial kinetic energy (NIKE) in the Philippine Sea. During the whole observational period, the ratio of the typhoon-induced NIKE to the total NIKE was only approximately 1/3, while processes other than typhoons contributed approximately 2/3 of the total NIKE. The research depth was divided into four layers to explore the relative importance of NIKE, and NIKE was found to contribute the highest proportion of total kinetic energy in the 400∼600 m layer, not the 50∼200 m layer. Four typical strong NIKE cases were found in months without any typhoon records, and the time-averaged NIKE at the core depth of these cases was much higher than that of the non-typhoon period. The vertical group velocity (Cgz) and generation mechanism of these events were examined. The NIOs basically propagated in the layer where they were generated with small Cgz values (between 0 and 5 m ⋅ d−1) and dissipated rapidly (within 10 days). Correlation analysis suggested that low-frequency flow vertical shear transferred energy into the near-inertial frequency band, leading to the spontaneous formation of NIKE. The ratio of NIKE generated by low-frequency flow vertical shear to the total NIKE in the non-typhoon period is 14.1%. In the presence of an anticyclonic eddy, wind-generated NIOs were captured at the edge and accumulated at the bottom of the eddy. The highest NIKE among these cases was caused by both low-frequency vertical shear and the eddy.

Characteristics of Dissolved Organic Matter in Sediments of Typical Lakes in Southeastern Hubei Province, China.

This study aimed to reveal the distribution characteristics and sources of dissolved organic matter (DOM) in sediments of typical lakes in the southeastern of the Hubei province and provide a reference for pollution control of eutrophic lakes. The sediments of four typical lakes (Liangzi, Baoan, Daye, and Qingshan) in the southeastern of the Hubei Province were investigated in May 2019. Ultraviolet-visible (UV-Vis) absorption spectroscopy and excitation-emission matrixes characteristics of DOM were obtained by UV-Vis spectrophotometry and three-dimensional fluorescence spectroscopy. Moreover, the DOM fluorescence components were resolved by parallel factor analysis (PARAFAC). The results showed that: (1) The absorption coefficient a350 in surface sediments followed the order: Baoan Lake (16.99 ± 3.82 m−1) > Qingshan Lake (15.37 ± 3.8 m−1) > Liangzi Lake (12.54 ± 5.58 m−1) > Daye Lake (12.43 ± 1.43 m−1). Specifically, with increasing depth in the sediment cores, a350 increased and then gradually decreased in Daye Lake and Baoan Lake, but fluctuated in Liangzi Lake and Qingshan Lake with a roughly decreasing trend. (2) Two humic-like components (C1, C2) and one protein-like component (C3) were identified via PARAFAC. This analysis also showed that the surface sediment fluorescent dissolved organic matter (FDOM) was dominated by protein-like, while the sediment core FDOM was dominated by humic-like in Liangzi Lake. The proportion of humic-like in FDOM was higher than protein-like in surface sediments and sediment cores of Baoan, Daye, and Qingshan Lakes. (3) The DOM of surface sediments in the Liangzi Lake comprised mostly autochthonous components, mainly produced by the vital activities of aquatic organisms. The DOM of surface sediments in Baoan Lake and Qingshan Lake showed weak humic and moderate autochthonous characteristics. The humification of DOM in sediment cores of Liangzi, Baoan, and Qingshan Lakes gradually decreased from depth to the surface. The DOM in surface sediments of Daye Lake had strong humic and moderate autochthonous characteristics. (4) In general, the DOM of lake sediments in southeastern Hubei Province has dual-contribution characteristics representing terrigenous and endogenous sources. In the restoration and treatment of lake ecology, both internal and terrestrial pollution should be considered. At the same time, it is noteworthy that cyanobacteria depletion and aquatic residues caused potential internal pollution.

An Intrathermocline Eddy Observed in the Northeastern Bay of Bengal

AbstractAn intrathermocline eddy (ITE) was detected to the northwest of Preparis Channel by in situ measurements in January 2018. The ITE had a horizontal extent of approximately 200 km and a maximum velocity of approximately 60 cm/s at core depths between 75 and 130 m. This ITE was generated by the transformation from a preexisting surface‐intensified anticyclonic eddy (SAE). The blocking of the northeast monsoon by the Arakan Yoma Mountains resulted in a weak wind stress on the leeward side of the mountains. This caused positive Ekman pumping around Preparis Channel together with eddy wind‐driven upwelling, shoaling the upper thermocline in the SAE, and thus turning it into an ITE. Among the 71 anticyclonic eddies detected by Argo profiles around Preparis Channel from 2003 to 2018, approximately 60% were ITEs, indicating that Preparis Channel could be the main source for ITE generation in Bay of Bengal.

Inferences on paleo-tsunami from the shoreline of Poompuhar, central Tamil Nadu coast, India through sedimentological and micropaleontological signatures

A 650 cm long sediment core collected from the Poompuhar beach was analyzed for sedimentological and foraminiferal studies. The specific absence of foraminifera and occurrences of coarser sands of low φ value of mean grain size from the bottom of the core up to 200 cm core depth reflects the dominant influence of the Cauvery river in the study area in the geological past. Further, the consistent occurrence of the appreciable number of marine microfossil - foraminifera and greater φ value of mean grain size of finer sands in top 200 cm core depth reflect the strong influence of marine environment indicating the coastal subsidence followed by marine transgression in this region. This distinct break in sedimentological and micropaleontological parameters at around 200 cm core depth could be due to the mega-tsunami events and associated phenomena such as coastal submergence, shifting of the river course, and reduced supply of sediments river in the study area around 1540 ± 25 years ago.