Abundance Of Ostracods Research Articles

Late Quaternary paleoceanographic history based on ostracode records from the Chukchi Plateau, western Arctic Ocean

Fossil ostracode assemblages were investigated in three sediment cores from the Chukchi Plateau, in the western Arctic Ocean, in order to reconstruct its late Quaternary paleoceanographic history. The cores were obtained from water depths of 435–741 m, within the range of modern Atlantic Water (AW). The ostracode abundance shows distinct glacial/interglacial fluctuations, suggesting the suppression of benthic bioproductivity during glacial periods, probably associated with the development of perennial sea ice. Based on the modern ostracode distribution in the Arctic Ocean, 11 common ostracode taxa out of a total of 33 are related to specific water mass or sea ice conditions. Analyses of key ostracode species and a benthic foraminifera species, Cassidulina teretis, reveal a pronounced faunal turnover between MIS 3 and MIS 1. A distinct assemblage dominated by Polycope spp. and accompanied by other species preferring Arctic Intermediate Water (AIW) (Microcythere medistriatum, Pseudocythere caudata, Cytheropteron sedovi, C. scoresbyi, and Pedicythere spp.) characterizes the period between late MIS 5 and MIS 3, whereas MIS 1 is characterized by a rise in Krithe spp. and two species associated with AW (Cytheropteron perlaria and Cassidulina teretis). The faunal turnover indicates an upward shift of AIW and a decline of the influence of warm AW during the period between late MIS 5 and MIS 3, presumably caused by a weakening or cessation of the westward dispersion of AW. The distributions of two sea-ice related species, Acetabulastoma arcticum and Rabilimis mirabilis, indicate minimal perennial sea-ice cover and probably summer sea-ice-free conditions throughout MIS 1 and the development of a summer sea-ice margin environment during interglacial/interstadial periods.

Benthic ostracods (crustacean) as a nearshore pollution bio-monitor: examples from the Red Sea Coast of Egypt.

Benthic ostracods are deemed as one of the most useful micro-fauna for biomonitoring in shallow marine ecosystem, which are sensitive to environmental changes that can be reflected by their diversity and abundances. The pollution leads to high dominance index and low abundance ostracod communities. Therefore, eighteen sediment samples were collected from Ras Gharib and Quseir sites, along the Red Sea coast, to assess the ostracods response toward the anthropogenic environmental disturbances. Jugosocythereis borchersi, Alocopocythere reticulata, and Loxocorniculum ghardaqensis are the most abundant ostracods in the study localities. To evaluate the linkage between ostracods and contaminated sediments, metal concentrations in the sediments were measured using inductively coupled plasma optical-emission spectrometry (ICP-OES). We observed a significant spatial difference in elemental distribution in sediment samples, and some elements are of higher contributions than the average marine sediment composition. The quantitative analysis of benthic ostracod associations was processed statistically with geochemical data and differentiated the study area into two environments, based on the degrees of contamination. Quseir is encompassing the most contaminated stations. It is characterized by sediments richer in heavy metals, higher silt, and higher organic matter contents. Contaminated environments favor the presence of pollution-tolerant species (e.g., J. borchersi, C. torosa, L. ghardaqensis, G. triebeli, M. striata, A. reticulata, and partly, C. dimorpha). Conversely, Ras Gharib is less polluted with metals and organic matter, and is characterized by pollution-sensitive species (X. rhomboidea). Noteworthy, a low density of ostracods was observed at the expense of the diversity around contaminated stations of the Quseir site.

Ostracods from the non-marine Lower Cretaceous interval at Liying section of Luanping basin, North China: A stratigraphic correlation

Non-marine strata of Lower Cretaceous age in western Liaoning and northern Hebei, North China, are famous for its Jehol Biota, including abundant ostracods. However, there are still some controversies about the stratigraphic correlation in these regions, for instance, it is still debated whether the interval from the Liying section of Luanping Basin belongs to the Dadianzi Formation or the member 1 of the Xiguayuan Formation. Ostracods act as an important tool for the correlation of the stratigraphy within or between basins. Here we report and illustrate the ostracods from the Liying section in detail for the first time, and aim to determine the section's stratigraphic correlation. Results show that, the Liying section has a thickness of 157.65 m and can be divided into 33 layers. Ostracods from this section are mainly distributed in the lower and middle part, and 7 genera and 13 species have been preliminarily recognized. These ostracod species can be summarized as the Cypridea-Limnocypridea-Lycopterocypris Assemblage Zone temporarily. Based on the identified ostracods, occurrence of other abundant representative fossils of the Jehol Biota, and isotope dating results, the major interval of the Liying section should be assigned to member 1 of the Xiguayuan Formation, and can be correlated with the Yixian Formation from western Liaoning.

Deciphering the synergistic impact of elevated temperature and oil pollution on meiobenthic community structure: A benthocosm study

Meiobenthos has been considered as an excellent tool for biomonitoring assessment. Elevated temperature and oil pollution are considered as the most pervasive aspects of global environmental changes and matter of concern for contemporary society. Presently, very limited information is available about the synergistic effect of these stressors on meiobenthic community structure and tolerance potential from tropical intertidal environment. Here, we assessed their impacts on meiobenthic community by conducting a 60 days long benthocosm experiment selecting three sets of temperature (25°, 30° and 35 °C) and two sets of diesel oil (low and high) combinations. Gradual changes in their community composition were revealed discernibly with exposures to both the disturbances after 30 and 60 days of experimental period. Diversity profiles for the nematodes were less affected, but copepods showed a graded response of decreasing density with increasing dose of both the stressors. Other meiobenthic taxa such as halacarid mite, turbellaria and polycheate juveniles were adversely affected and eliminated from the treatments, howbeit abundance of ostracods, foraminiferans and bivalve settlers varied significantly. A 3-factor PERMANOVA indicated a significant effect of temperature, diesel, between their interaction and interaction among stressors and time on meiofaunal abundances. In case of free-living nematodes, temperature rise and diesel contamination synchronously led to an elimination of k-selected species like Halalaimus gracilis, H. longicaudatus, Oxystomina aesetosa and Pomponema sp. with a significant decrease in abundance of H. capitulatus and Oncholaimus sp. The r-selected species Daptonema invagiferoum, Sabatieria praedatrix, Theristus acer, Monhystera sp. and Thalassomonhystera sp. had endured even at high doses of diesel treatment in three different temperatures set up. The effects were evident in term of changes in life strategies with an increment of opportunistic species and increased trophic diversity of deposit feeders in treated sediments. Overall, elevated temperature together with diesel oil contamination were found to alter species dynamics within shallow intertidal meiobenthic communities, which might have significant Armageddon on benthic ecosystem functioning.

Relationship of sediment influx to ostracode populations on the variably deforested Luiche and Mahale platform coasts of Lake Tanganyika, Tanzania

We investigated the hypothesis that ostracode populations are sensitive to variations in sediment discharge related to watershed differences at Lake Tanganyika. Many ostracode species are documented to be sensitive to high turbidity which increases during runoff from strong rainfall events and changes in ostracode populations can impact organisms higher in the food web. We compared surficial death assemblages of ostracodes around two sites with extensive shell beds, the highly deforested Luiche Platform area, heavily populated since the 20th Century, and the less deforested Mahale Platform area, with recent population increases, to understand the impacts of increasing sedimentation within and between sites. The study found that whereas the Mahale Platform area is less disturbed, the faunal differences between sites is not large. The data showed high species richness and abundance of ostracodes at 10–20 m depth at both sites, within shell bed zones, with no statistical difference in raw species richness between the sites. The Mahale Mountain area ostracode populations were however statistically more diverse (Shannon H) than at Luiche. We conducted a multi-response permutation procedure and found that the sites are statistically different, but with very small differences in species richness and ostracode abundance. Non-metric multidimensional scaling ordination of species assemblages shows that most samples overlap on both major axes. This study synthesized with ongoing research about shell bed communities in less disturbed regions of the lake will give insights into how conservation projects can be optimized to preserve the lake’s benthic ecosystem from the effects of deforestation.

Ostracods from the end‐Permian mass extinction in the Aras Valley section (north‐west Iran)

AbstractThe Aras Valley section (north‐west Iran) exposes a sedimentary succession that allows the study of ostracod diversity patterns during/across the end‐Permian mass extinction. For the present study, 59 samples were investigated for their ostracod abundances, which ranged from 4 to 31 500 specimens per 500 g. In 45 sample horizons, the ostracods were identified to the species level. In total, 3 425 specimens were determined and 62 species were identified, of which one genus and ten species are described for the first time: Fabalicypris veronicae Gliwa, sp. nov., Orthobairdia capuliformis Gliwa, sp. nov., Araxobairdia formosa Gliwa, gen. et sp. nov., Bairdiacypris kathleenae Gliwa, sp. nov., Eumiraculum mettei Gliwa, sp. nov., Liuzhinia julfensis Gliwa, sp. nov., Carinaknightina hofmanni Gliwa, sp. nov., Cavellina fosteri Gliwa, sp. nov., Cavellina hairapetiani Gliwa, sp. nov. and Hungaroleberis striatus Forel, sp. nov. The assemblages show, at the end‐Permian mass extinction event, a complete turnover from a low‐diversity Fabalicypris‐dominated pre‐extinction community to a more diverse Bairdiacypris‐dominated post‐extinction community. The turnover coincides with the significant temperature increase that was previously recorded from north‐west Iranian sections. The low diversity in the horizon immediately below the extinction horizon indicates that environmental changes, such as thermal stress, may have had an impact on the ostracod assemblages prior to the extinction event. In comparison with other diverse ostracod assemblages from the Palaeotethyan realm, the ostracods of the Aras Valley section are not associated with microbialites.

Habitat factors differentiating the occurrence of Ostracoda (Crustacea) in the floodplain of a small lowland River Krąpiel (N-W Poland)

We analysed the occurrence of ostracods in a small river, taking into account all the types of water bodies in the floodplain − these included helocrenes, oxbow lakes, and ponds, as well as the main river channel. The objective of the study was to investigate the variation in ostracod communities and identify those factors determining species distribution. The environmental factors considered were the type of water body, responsible for 17% of the variance, the physical and chemical water properties (29%), and the biotic and abiotic factors associated with the substrate type (23%). Among the factors associated with the substrate, sediment sorting, plant coverage and insolation were the most important. The ostracod fauna of the helocrenes differed from that of the other water bodies in the floodplain. In the water bodies of the Krąpiel valley and in the main river channel, 33 ostracod species were recorded, of which 26 were found in the main river channel. Refugia in the floodplain were the main source of the diversity and abundance of ostracods in the main river channel. The mean density in the main river channel was very low, at 330 indiv. m−2, while in the water bodies of the floodplain it was the greatest, reaching up to 5568 indiv. m−2.

Interglacial Paleoclimate in the Arctic

AbstractMarine Isotope Stage 11 from ~424 to 374 ka experienced peak interglacial warmth and highest global sea level ~410–400 ka. MIS 11 has received extensive study on the causes of its long duration and warmer than Holocene climate, which is anomalous in the last half million years. However, a major geographic gap in MIS 11 proxy records exists in the Arctic Ocean where fragmentary evidence exists for a seasonally sea ice‐free summers and high sea‐surface temperatures (SST; ~8–10 °C near the Mendeleev Ridge). We investigated MIS 11 in the western and central Arctic Ocean using 12 piston cores and several shorter cores using proxies for surface productivity (microfossil density), bottom water temperature (magnesium/calcium ratios), the proportion of Arctic Ocean Deep Water versus Arctic Intermediate Water (key ostracode species), sea ice (epipelagic sea ice dwelling ostracode abundance), and SST (planktic foraminifers). We produced a new benthic foraminiferal δ18O curve, which signifies changes in global ice volume, Arctic Ocean bottom temperature, and perhaps local oceanographic changes. Results indicate that peak warmth occurred in the Amerasian Basin during the middle of MIS 11 roughly from 410 to 400 ka. SST were as high as 8–10 °C for peak interglacial warmth, and sea ice was absent in summers. Evidence also exists for abrupt suborbital events punctuating the MIS 12‐MIS 11‐MIS 10 interval. These fluctuations in productivity, bottom water temperature, and deep and intermediate water masses (Arctic Ocean Deep Water and Arctic Intermediate Water) may represent Heinrich‐like events possibly involving extensive ice shelves extending off Laurentide and Fennoscandian Ice Sheets bordering the Arctic.

The filter-feeders signal: response of ostracods to marine environmental changes in the Devonian F–F event

The percentage of filter-feeder species in benthic ostracod assemblages shows evident changes during the Late Devonian Frasnian–Famennian (F–F) transition with two sharp rises in the event stratal interval based on materials collected from the Yangdi section, South China. Neither anoxia nor oligotrophy, eustasy should have been the only primary cause of filter-feeders signal in the F–F event. The sea level fall and rise would create deteriorative environmental conditions such as lower oxygenation and less nutrients, which altogether reduced the diversity and abundance of the benthic ostracods in the F–F transition. The percentage of filter-feeders showed a decrease during the regression, and vice-versa. Therefore, the filter-feeders may be potentially an indicator of sea level changes in the F–F event.

High-resolution variation in ostracod assemblages from microbialites near the Permian-Triassic boundary at Zuodeng, Guangxi region, South China

After the end-Permian mass extinction (EPME), the marine environment was considered extremely toxic, mainly due to anoxic and high-temperature conditions and ocean acidification; consequently, the ecosystem contained few organisms. This paper describes a new ostracod fauna from the microbialite-bearing Permian-Triassic (P-Tr) strata at Zuodeng, Guangxi region, China. One thousand and seventy ostracod specimens were extracted from forty-eight samples. Fifty-three species belonging to fourteen genera were identified. Ostracods, primarily from the family Bairdiidae, were extremely abundant in the microbialites, which suggests that ostracods were opportunists that could survive the EPME within this special microbial ecosystem with sufficient food and scarce competitors and predators rather than undergoing a rapid and early recovery after the EPME event. Ostracods having simultaneous Paleozoic and Meso-Cenozoic affinities coexisted in this fauna. The similarities and differences among the ostracod faunas in the microbialite sections of the P-Tr boundary around the Paleo-Tethys indicate that there was a long-distance dispersal of ostracods, but the faunas maintained endemism at the species level. Previous studies have regarded microbialites as whole units, and it is difficult to detect environmental changes within a microbialite interval based on paleoecological groups of (super)families. In this study, high-resolution sampling was applied to identify changes in the ostracod abundance, diversity, assemblages and proportion of five dominant species in the section, which exhibited an evolutionary trend from the “Bairdia” group to the “Liuzhinia antalyaensis-Bairdiacypris ottomanensis” group. Furthermore, the transition of the ostracod fauna could be divided into six stages according to changes in the dominant species groups, suggesting that the microbialite environment was not entirely monotonous but fluctuated during the postextinction interval.

Early Triassic microbialites from the Changxing Region of Zhejiang Province, South China

Microbialites, often considered as a signal of extreme marine environment, are common in the Lower Triassic strata of South China where they flourished in the aftermath of the end-Permian mass extinction. Early Triassic microbialite facies are known to vary palaeogeographically, perhaps due to differing climates, ocean chemistry, and water depths. This paper provides the first record of a brief, but spectacular development of microbialites in the aftermath of the end-Permian mass extinction at Panjiazhuang section, Changxing Region of Zhejiang Province (eastern South China). Here, the Upper Permian Changxing Formation comprises typical shallow platform facies rich in calcareous algae and foraminifera, the development of which was terminated by the major end-Permian regression. A 3.4-m-thick microbialite began to form at the onset of the transgression in the earliest Triassic. The microbialite at Panjiazhuang section is composed of thrombolite that contains abundant calcified cyanobacteria, small gastropods, microconchid tubes and ostracods, representing a low-diversity shallow marine community in the aftermath of the end-Permian crisis. The microbialites are succeeded by thin-bedded micrites bearing thin-shelled bivalves, which record a rapid sea-level rise in the Early Triassic. Abundant populations of small pyrite framboids are observed in the upper part of the microbialites and the overlying thin-bedded micrites, suggesting that dysoxic water conditions developed at that time. The appearance of microbialites near the Permian–Triassic boundary (PTB) at Panjiazhuang section was the result of peculiar marine conditions following the end-Permian regression, whilst their disappearance was due to the increasing water depth and the development of dysoxia.

Changes in foraminiferal assemblages and environmental conditions during the T-OAE (Early Jurassic) in the northern Lusitanian Basin, Portugal

The foraminiferal assemblages and other microfossils from the Rabaçal area (Maria Pares section) in the Lusitanian Basin (Portugal) provide new insights regarding the Toarcian Oceanic Anoxic Event (T-OAE). Complementary analysis of the δ13C, total organic carbon (TOC) and geochemical redox and palaeoproductivity proxies reflect environmental changes that affected the microfossil assemblages. Detailed analyses of foraminiferal assemblages (their diversity, abundance, morphogroups and lifestyle) and geochemistry led us to discern phases of the biotic crisis and subsequent stages of recovery. Environmental instability, which began in the lattermost part of the Polymorphum Zone, is marked by a lesser abundance of foraminifera and ostracods, increased opportunist foraminifera, fluctuations in TOC values and the enrichment factor of phosphorous (PEF), as well as the onset of a negative carbon isotopic excursion (CIE). The peak phase of the biotic crisis corresponds with the lowest values for foraminiferal diversity and abundance (including a barren sample for benthic microfossils). The abundance and diversity of echinoderms, brachiopods, dinoflagellate cysts and calcareous nannofossils dropped sharply during the peak phase. This biotic crisis also entails extinction of the Order Metacopina and a local disappearance of echinoderms and brachiopods. Anoxic conditions at sea bottom did not develop, given the almost continuous record of foraminifera and trace fossils, yet oxygen-depleted conditions occurred. The lower part of the Levisoni Zone contains thin nodular limestones corresponding to a tempestitic–turbiditic facies. In this context, the re-oxygenation of bottom waters was favoured, as indicated by the presence of Thalassinoides and the low values of TOC and redox-sensitive elements (Mo, Ni and U). The survival phase in the wake of the biotic crisis is characterized by greater diversity and abundance of foraminifera and echinoderms (holothuroids and ophiuroids). The lowest δ13C values are recorded during this phase, with a dominance of opportunist (Eoguttulina) and facultative opportunist (Paralingulina tenera) foraminifera. Finally, recovery after the biotic crisis is evidenced by high values for specialists and potentially deep infaunal foraminifera, indicating oxic conditions in the sediment.

Late Turonian Microfossils and Paleoclimate in the Songliao Basin, NE China

Although the paleoclimate of the marine Cretaceous has been well studied, the paleoclimate of the non-marine is still not well understood. The Songliao Basin was one of the largest non-marine rift basins during Cretaceous. The Well-preserved Cretaceous lacustrine deposits in this basin provide a unique opportunity to study terrestrial paleoenvironments and paleoclimate during the Late Cretaceous. Here, the microfossils from the Late Turonian Qingshankou Formation of the Songliao Basin were used to investigate the paleoenvironments and paleoclimate of east Asia. There are two spore and pollen assemblages recognized: a Cedripites-Cyathidites-Classopollis assemblage from Upper Member 1, and a Cedripites-Cyathidites-Classopollis assemblage from Lower Member 2 of the Qingshankou Formation, respectively. Besides, relatively abundant ostracods have been identified. In the Songliao Basin, the climate was relatively warm and wet during Late Turonian, with good source rock deposited in the Songliao lake.

Response of Ostracods (Crustacea) to the Devonian F—F event: Evidence from the Yangdi and Nandong sections in Guangxi, South China

Abstract This study focuses on the Late Devonian ostracods and their responses to the F—F (Frasnian-Famennian) event based on abundant materials collected from the Yangdi and Nandong sections in South China. More than half (53%) of the benthic ostracod species disappeared at the F—F boundary in the Yangdi section of slope facies, whereas most benthic ostracod species survived the F—F crisis in the Nandong section of basinal facies, with the extinction of some pelagic entomozooidea. In view of a higher extinction rate (more than 65%) of ostracod species in the shallow-water Xikuangshan section, we deduce that ostracods in varied environments responded to the F—F event differently. Namely, from the carbonate platform, slope, to basinal settings, the extinction rate of benthic ostracods at the F—F transition decreased with increasing water depth. Nevertheless, the F—F event caused substantial loss among pelagic entomozooidea lineages. The extinction pattern of benthic and pelagic ostracods in F—F event in South China is similar to the situation in Europe. But the extinction rates of benthic ostracods in shallow water and slope in Europe seems to be higher than that in the same situation in South China. The abundance and diversity of ostracods decreased and some species even disappeared in anoxic environments across the F—F boundary in South China, when there were rapid changes in the palaeotemperature of surface sea water.

Analysis of a Cretaceous (late Aptian) high-stress ecosystem: The Romualdo Formation of the Araripe Basin, northeastern Brazil

The Cretaceous (upper Aptian) Romualdo Formation of the Araripe Basin, northeastern Brazil, is a marine-influenced, predominantly fine-grained siliciclastic unit. In the eastern part of the basin, it corresponds to a depositional sequence composed of two transgressive-regressive cycles. Low-diversity benthic macrofaunas document high-stress conditions. Their palaeoecological and taphonomic analysis allows for the detailed reconstruction of the palaeoenvironments and of the temporal changes in the palaeoecosystem. The transgressive part of the lower cycle is a black shale with calcareous concretions that contain excellently preserved fishes and other vertebrates (the famous “Santana fossils”), but apart from abundant ostracods and rare decapod crustaceans, benthic faunal elements are very rare due to anoxic to dysoxic conditions. A low-diversity parautochthonous molluscan fauna of small bivalves and gastropods records fluctuating dysoxic conditions during early regression. Towards the top of the measured sections (late regression), thin gastropod shell beds become conspicuous. At the top of the sections decimetre-thick shell concentrations show signs of reworking and a greater marine influence (transgressive part of the upper cycle). The distribution pattern of three benthic associations and two assemblages is almost equally shaped by three environmental parameters: The low overall species diversity, small size of the fauna, and the lack of stenohaline elements suggest lowered and fluctuating salinity conditions. Fluctuating redox conditions with anoxia to dysoxia, identified especially in the lower parts of the succession, and substrate were the other two factors shaping the faunal distribution. The late Aptian sedimentary and faunal history of the eastern part of the basin indicates restricted marine influence, coupled with increasing freshwater input during phases of sea-level lowstand, and low-energy conditions offshore, which led to widespread anoxia, especially in the lower part of the formation. Thus, palaeoecological analyses are an excellent tool to disentangle the various environmental parameters that shaped the palaeoenvironments of the basin, to understand more closely its Fossil-Lagerstätten, and to corroborate and fine-tune the sequence stratigraphic framework.

Holocene Ostracods from the Hang Hau Formation in Lei Yue Mun, Hong Kong, and their palaeoenvironmental implications

Wang. H., Zhang, H., Cao, M. & Horne, D.J., October 2018. Holocene Ostracods from the Hang Hau Formation in Lei Yue Mun, Hong Kong, and their palaeoenvironmental implications. Alcheringa 43, 320–333. ISSN 0311-5518.The Holocene Hang Hau Formation is the youngest part of the Quaternary succession in Hong Kong and yields abundant and diverse ostracods. This study of ostracod assemblages from two cores in Lei Yue Mun identifies eight genera and nine species of marine Ostracoda that were previously unreported from the Hang Hau Formation, increasing the known diversity from 67 to 76 species. Among these species, Neocyprideis timorensis (Fyan 1916) is reported for the first time in China. The recovery of abundant juvenile and adult specimens has facilitated illustration and discussion of an ontogenetic series for Neomonoceratina delicata Ishizaki & Kato, 1976, extending from the A-5 instar (fourth moult after hatching) to the sexually dimorphic A (adult) instar. Palaeoenvironmental analysis of the ostracod assemblages supports and strengthens previous interpretations indicative of a warm, shallow, nearshore-marine environment.He Wang [wang0701@163.com] State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology and Center for Excellence in Life and Paleoenvironment, Chinese Academy of Sciences, 39 East Beijing Road, Nanjing 210008, PR China; Haichun Zhang [hczhang@nigpas.ac.cn] State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology and Center for Excellence in Life and Paleoenvironment, Chinese Academy of Sciences, 39 East Beijing Road, Nanjing 210008, PR China; Meizhen Cao [mzcao@nigpas.ac.cn] Nanjing Institute of Geology and Palaeontology and Center for Excellence in Life and Paleoenvironment, Chinese Academy of Sciences, 39 East Beijing Road, Nanjing 210008, PR China; David J. Horne [d.j.horne@qmul.ac.uk] School of Geography, Queen Mary University of London, Mile End Road, London E1 4NS, UK. *Also affiliated with: University of Science and Technology of China, No. 96, JinZhai Road Baohe District, Hefei, Anhui 230026, PR China.

A late Miocene ostracod record from the northeastern Tibetan Plateau

Lake Qinghai, the largest inland brackish lake in China, is located on the northeastern margin of the Tibetan Plateau and is affected by both the Asian Monsoon and Westerlies climate systems. It is very sensitive to climate and environmental changes. Moreover, its sediments accumulated over the Cenozoic Era and contain abundant information about past tectonics and environmental changes. Here we present a record of late Miocene ostracods from Lake Qinghai sediment cores. A taxonomic analysis of the ostracods yielded 7 families, 14 genera, and 31 species. Six distinct sediment facies were recognized and their corresponding paleolimnological and paleoenvironmental changes were inferred from the ostracod assemblages. The first appearance of ostracod shells at about 7.60 Ma reflects a switch from an eolian sedimentation facies (ca. 8.10–7.60 Ma) to a shallow lacustrine environment (ca. 7.60–5.85 Ma). Ostracod shells were absent from ca. 5.85 to 4.64 Ma in eolian sediments. A transition to a deep lacustrine facies began at ca. 4.64 Ma, and ended at ca. 3.58 Ma. Thus, Lake Qinghai existed in the late Miocene and became larger and deeper in the early Pliocene (ca. 4.64 Ma). During the time interval ca. 3.58–0.70 Ma, littoral lacustrine sedimentation occurred at the core sites. After ca. 0.70 Ma, there were alternating shallow lacustrine and lakeshore environments at the sites, until ca. 0.12 Ma. Changes in ostracod assemblages and their abundance during the intervals ca. 4.64–3.56 Ma and ca. 0.70–0.12 Ma indicate that the sedimentary environment fluctuated over short time scales. Given Lake Qinghai’s sensitivity to environmental and tectonic changes, related to its special location, we concluded that changes in the relative and absolute abundances of ostracods reflect the evolution of the Asian monsoon-arid environment and Plateau growth, as well as global climate changes.

A 14 ka high-resolution δ18O lake record reveals a paradigm shift for the process-based reconstruction of hydroclimate on the northern Tibetan Plateau

The influence of the mid-latitude westerlies (MLW) competing with the Asian summer monsoons (ASM) over the Tibetan Plateau (TP) remains a matter of discussion on how and to which extent both atmospheric systems have been controlling hydro-climate during the Holocene. Depleted oxygen isotopes in lake deposits were commonly interpreted in terms of enhanced summer monsoon moisture supply, implying a migration of the ASM deep into the interior of the plateau during Holocene periods. In order to test this relationship we used a high resolution oxygen isotope record (mean 20 yr resolution) in combination with carbonates and mineral phases, titanium flux, grain size and ostracod abundances derived from a 6.84 m long sediment core in the endorheic Kuhai Lake basin, north-eastern TP. The results confirm 1) continuous positive co-variance between enriched δ18Ocarb and total carbonates during the last 14 ka, indicative of dominant seasonal influence on multi-decadal to centennial scale isotopic signatures in lake water and respective carbonate precipitation, 2) negative co-variance between allochthonous sediment flux and δ18Ocarb (and carbonates) attributed to relative increase of flux rates during non-summer seasons, 3) correspondence of lake level variations with carbonate mineral phases and the occurrence/disappearance of ostracod assemblages, and 4) inverse relationships between isotopic signatures in ASM-dominated and MLW-controlled lake records across the TP. Enriched δ18Ocarb in Kuhai Lake sediments was primarily a result of high evaporation during the summer seasons, while ASM-related rainfall amount did not play an important role, likely counterbalanced by isotopic signatures from different water sources. Conversely, depleted δ18Ocarb was mainly attributed to water supply during non-summer seasons of colder temperatures and generally light isotopic signatures from MLW-derived sources. This finding may lead to a paradigm shift in such way that depleted δ18O in carbonates is primarily not the result from ASM-related rainfall as previously assumed. The reconstructed hydro-climatic history of Kuhai Lake indicates the dominance of westerly-derived climate during the Younger Dryas interval (12.8–11.5 ka) under very shallow pond-like conditions. Despite climate amelioration during the early Holocene (11.5–7.5 ka) hydrological conditions remained unstable with frequent alternations between dominance of summer and winter seasons. During the middle Holocene (7.5–5.5 ka) the lake experienced highest lake levels dominated by summer monsoon-related water supply, assigned to the Holocene hydro-climatic optimum. Frequent high-amplitude fluctuations afterwards (5.1–2.9 ka) refer to cooling/drying events under enhanced MLW influence accompanied by a strong lake level decline. The late Holocene (2.9 ka- Present) period experienced moderate isotopic variations and fluctuating lake levels in response to variable influence of summer- or winter-related hydro-climatic conditions.This seesaw-like pattern with amplitudes of >10‰ in δ18Ocarb resembles fluctuations in cave records and variations between air and seawater (Dole effect). High correspondence with cooling events derived from North Atlantic drift ice and meltwater discharge indicate close ties to northern hemispheric climate transmitted by the MLW across the TP.

Biostratigraphic and palaeoenvironmental significance of Campanian-early Maastrichtian (Late Cretaceous) ostracods from the Jiaozhou Formation of Zhucheng, Shandong, China

Cretaceous strata are well developed in the Jiaolai Basin (Jiaodong Peninsula, East China) and contain abundant fossils including hadrosaurids, tyrannosauroids, various types of dinosaur eggs, bivalves, gastropods, ostracods, clam shrimps, insects and plants. During a geological investigation in Zhucheng City, eastern Shandong Province, East China, a new exposure of part of the Jiaozhou Formation was discovered near Jiankou Village. This formation constitutes uppermost Cretaceous to earliest Paleogene strata (encompassing the K/Pg boundary) in the Jiaolai Basin. Samples from a new Jiankou section yielded abundant ostracods assigned to twelve genera and twenty-seven species, reported for the first time from the Jiaozhou Formation in this area. The assemblage is composed entirely of non-marine taxa, including species of Cypridea, Talicypridea and Candoniella. Ostracod biostratigraphy indicates this section to be Campanian to early Maastrichtian in age, but not including the K/Pg boundary commonly present in the upper part of the Jiaozhou Formation. Palaeoenvironmental analysis of the species composition of the assemblages obtained, combined with a study of valve ornamentation, suggests that during the late Campanian, an ephemeral pond or small ephemeral lake alternated with a permanent lake in the studied area, and during the Campanian to Maastrichtian interval, there was a seasonally expanding and shrinking lake with both permanent and ephemeral basins in the studied area.

Composition and distribution patterns of marine planktonic ostracods (Crustacea, Ostracoda) in the Adriatic Sea - a historical perspective

This study provides the first comprehensive results on species composition, seasonal and horizontal distribution of the planktonic ostracod community in the open waters of the whole Adriatic Sea. Samples were collected during the “Andrija Mohorovičić” oceanographic expedition (1974-1976) in all four seasons at 35 stations located along eight latitudinal transects in the northern, central and southern part of the Adriatic Sea. Fifteen ostracod species and two subspecies belonging to the family Halocyprididae were identified. The dominant species were Archiconchoecia striata, Porroecia spinirostris and Proceroecia macroprocera. Additionally, Paraconchoecia oblonga was recorded for the first time in the Adriatic Sea. The highest abundance and diversity of planktonic ostracods were found in the deep South Adriatic. Conversely, ostracods were scarce in the shallow North Adriatic area. As the transitional zone between these two regions, the Central Adriatic was characterized by high ostracod diversity, but a short period of dominance in the zooplankton assemblage. The horizontal distribution of planktonic ostracods in the Adriatic Sea could be linked to periodical ingressions of Eastern Mediterranean water masses and gyre currents, especially in the Central and the South Adriatic.