Siliceous microfossil succession in the recent history of two basins in Lake Baikal, Siberia

As part of the international cooperative Baikal Drilling Project, siliceous microfossil assemblage succession was analyzed in two short ( 30-cm) sediment cores from Lake Baikal. One core was recovered from the north basin (Core 324, 55°15N, 109°30E), a second from between the central and southern basins (Core 316, 52°28N, 106°5E). The northern core had higher amounts of biogenic silica (40 g SiO₂ per 100 g dry weight sediment) compared to the southern core, and increased deposition in the more recent sediments. Weight percent biogenic silica was lower in the southern core, ranging from approximately 20–30 g SiO₂ per 100 g dry weight sediment throughout the entire core. Trends in absolute microfossil abundance mirror those of biogenic silica, with generally greater abundance in the northern core (86–275×10⁶ microfossils g^–1 dry sediment) compared to the southern core (94–163×10⁶ microfossils g^–1 dry sediment).Cluster analyses using relative abundance of the dominant diatom and chrysophyte taxa revealed four zones of microfossil succession in each core. Microfossil assemblage succession in the north basin may be reflecting shifts in nutrient supply and cycling driven by climatic changes. The most recent sediments in the northern basin (Zone 1,c. 1890's–1991 A.D.) were characterized by an increased abundance ofAulacoseira baicalensis andAulacoseira spore. Zone 3 (c. 1630's–1830's A.D.) was dominated by the endemicCyclotella spp. and reduced abundance of theAulacoseira spp. Zone 3 corresponds approximately to the Little Ice Age, a cooler climatic period. The microfossil assemblages between Zones 1 and 3 (Zone 2,c. 1830's–1890's A.D.) and below Zone 3 (Zone 4,c. 830's–1430's A.D.) are similar to one another suggesting they represent transitional intervals between warm and cold periods. Southern basin sediments record similar changes in the endemic taxa. However, the increased abundance of non-endemic planktonic taxa (e.g.Stephanodiscus binderanus, Synedra acus, Cyclostephanos dubius) during two periods in recent history (post World War II and late 1700's) suggests evidence for anthropogenic induced changes in southern Lake Baikal.     

Inferring paleosalinity trends using the chrysophyte cyst to diatom ratio in coastal shallow temperate/subtropical lagoons influenced by sea level changes

Data on chrysophyte cyst to diatom ratios as an index to track Holocene paleosalinity changes are presented. Six sediment cores taken in four coastal systems influenced by Holocene sea level changes indicate that during the transition from marine/brackish to brackish/freshwater and freshwater conditions, increases in the cyst to diatom ratio were recorded. These data suggest that Holocene changes in paleosalinities in coastal aquatic systems may be tracked by using this simple index, however other factors (such as changes in nutrient levels) may complicate some interpretations. Nevertheless, data required to calculate this simple index are easy to obtain, and so relatively little effort is required to obtain some paleolimnological information on these two important algal groups.     

The palynology and geology of the Lower Cretaceous (Aptian–Albian) of Munday’s Hill Quarry,Bedfordshire, UK

Early Cretaceous sediments of Aptian–Albian age outcrop at Munday’s Hill Quarry, Bedfordshire, England. Previous papers describing the section have resulted in different terminologies being applied. The Lower Cretaceous in Bedfordshire is represented by sediments belonging to the Lower Greensand Group and the Gault Clay Formation. Within the Lower Greensand Group in the study area the Woburn Sands Formation, are of Aptian–Albian age. Selected samples have been analysed for palynology. The analysis reveals diverse palynomorph assemblages, including well-preserved dinoflagellate cysts and sporomorphs. Comparison of the assemblages with published records indicates that the lower samples are of Late Aptian age. Forms recorded include common Kiokansium unituberculatum, Cerbia tabulata, Aptea polymorpha and Cyclonephelium inconspicuum. An Early Albian age is indicated for the uppermost sample.     

A new biostratigraphic correlation for Late Cretaceous–Paleocene strata of the Gulf of Guinea: Evidence from dinoflagellate cysts

A new biostratigraphic correlation for Late Cretaceous and Palaeocene strata of the Côte d’Ivoire–Ghana continental margin has been developed from the identification of significant dinoflagellate cyst events in ODP Hole 959D. The Late Cretaceous stage boundaries are mostly consistent with previous studies. However, the Maastrichtian/Danian boundary is placed much lower than previously recognized on the basis of the first occurrences of Carpatella cornuta and Damassadinium californicum. The base of the Selandian is recognized from the last occurrence of Cerodinium diebelii and the first occurrence of Adnatosphaeridium multispinosum. The base of the Thanetian is recognized from the first occurrence of Areoligera gippingensis. The rarity of the age-marker taxa is the main reason for different age determinations among studies of the same section.     

Distribution and characterization of Chilean populations of the brine shrimp Artemia (Crustacea, Branchiopoda, Anostraca)

Hypersaline habitats in Chile, from marine solar salt pans to saline lagoons and pools in Andean salars, were prospected in search of Artemia populations. These saline ecosystems were characterized through physico-chemical parameters and ionic composition of their brines. Biometrics of cysts and nauplii, as well as morphometrics by using multivariate discriminant analysis for adult specimens evidenced that the Chilean populations of brine shrimp belong to A. franciscana. Cross-breeding results supported the former hypothesis of conspecific Chilean populations, and their differences with A. persimilis, also endemic to the New World, but restricted to Argentinean sites.     

Last interglacial (MIS 5e) surface water conditions at the Vøring Plateau (Norwegian Sea), based on dinoflagellate cysts

Sediments from the last interglacial, marine isotope stage 5e (MIS 5e), have been studied for their dinoflagellate cyst content in a core retrieved from the Vøring Plateau, Norwegian Sea. Qualitative and quantitative analyses of the data, and comparison with the surface sample and published Holocene data from the core, reveal distinct differences in hydrological surface conditions between the late Holocene and MIS 5e. A higher number of co-dominant, subordinate species in the last interglacial samples suggests there was a more pronounced seasonality of the surface water at this time. This is supported by the significant presence of Bitectatodinium tepikiense , a species that was virtually absent from the area for most of the Holocene. The seasonality signal is further substantiated by transfer-function reconstructions, which also indicates a stronger stratification of the upper water column during MIS 5e. Moreover, the assemblage data clearly show that optimal, fully marine interglacial conditions prevailed only late in MIS 5e (between ca. 117.5 and 116.5 Kya), which is in contrast with the climatic optimum early in the Holocene. Stable oxygen isotope values from planktic foraminifera for this MIS 5e optimum are comparable with the average Holocene values, but are generally ca. 0.3‰ higher than those of the earlier part of the last interglacial ( sensu stricto ). These higher δ¹⁸O values are likely to be the result of the enhanced and prolonged influence of Saalian deglacial meltwater, thus corroborating the existence of a quite differently structured sea surface, as suggested by the dinocyst data.     

湄洲湾海域甲藻孢囊的时空分布初步调查

为了解湄洲湾海域表层沉积物中甲藻孢囊的时空分布特征,于2018年5月(春)、8月(夏)、11月(秋)和2019年2月(冬)采集湄洲湾海域7个站位表层沉积物样品,进行甲藻孢囊分析,共鉴定出甲藻孢囊6大类42种和2种未知种。异养型甲藻孢囊种类数和丰度均高于自养型甲藻孢囊,其中又以原多甲藻类孢囊的种类和丰度最高。季节间差异不明显：种类数介于34～38种之间,丰度则在397.8～569.5 cysts/g之间变化,全年平均丰度448.0 cysts/g。工业区附近的站位种类数和丰度均低于养殖区附近的站位和对照点。优势种高达16种,原多甲藻类占绝对优势,但全部优势种优势度均不大。多样性指数、丰富度指数和均匀度指数均较高,全年的平均值分别为3.45、1.55和0.92。与历史资料对比,新发现19种孢囊,但丰度相差不大。另需注意的是,在湄洲湾海域共发现6种有毒甲藻孢囊,虽然全年丰度均不高,但仍有暴发有毒赤潮的危险,需引起重视。     

不同处理对卤虫卵的孵化特征影响的初步研究

本文对四个品系的卤虫卵在自来水浸泡2h和脱壳处理下的孵化特征进行了初步研究;并对干卵、自来水浸泡2h的湿卵、不脱壳孵化12h的湿卵以及脱壳孵化12h的湿印进行了常规组织学制片。结果表明,不同处理下卤虫卵的孵化特征不同,其结构也有一定的差异。     

闽江口海域表层沉积物中甲藻休眠孢囊的初步研究

对福建闽江口50个站位的海底沉积物样品进行分析,共鉴定出甲藻孢囊17种,隶属7属,主要的种类有锥状斯氏藻(Scrippsiella trochoidea),科夫／无纹多沟藻(Polykrikos kofoidii／schwartzii)、斯氏膝沟藻(G．scrippsae)和具刺膝沟藻(Gonyaulax spinifera)：锥状斯氏藻为最丰富的种：并检出有毒种塔玛亚历山大藻(Alexandrium tamarense)。研究结果表明,闽江口表层沉积物中的甲藻休眠孢囊主要分布在砂-粉砂-粘土沉积物类型中;有毒甲藻塔玛亚历山大藻有可能在每年5-6月、10-11月对该海域的海洋生物和人类健康及生命安全构成潜在威胁,应加强监测。