Palynofacies investigation of Callovian (Middle Jurassic) sediments from DSDP Site 534, Blake-Bahama Basin,Western Central Atlantic

During the extension of Deep Sea Drilling Project (DSDP) Leg 76 a new and previously unpenetrated lithological unit composed mainly of claystones was cored above basalt basement at Site 534 in the Blake-Bahama Basin. The Callovian part of the new unit contains interbedded ‘black shales’ which were hitherto unexpected in this part of the section. This Paper presents a brief palynological examination of lithofacies-kerogen relationships in these sediments and shows that their organic content is almost entirely a function of the re-deposition of terrestial and marine organic matter versus the ambient redox conditions of the depositional environment. Allochthonous organic matter inputs are highest in the interbedded turbidites and decline progressively toward the pelagic black shales in which marine organic matter is comparatively well preserved. The significance of various kerogen and palynomorph indices are discussed. The study emphasizes the absolute necessity for sedimentologically-aware sampling in all palynological and geochemical work on lithologically heterogeneous sequences.     

Recent changes in the North Atlantic circulation simulated with eddy-permitting and eddy-resolving ocean models

Three eddy-permitting (1/4°) versions and one eddy-resolving (1/12°) version of the OCCAM ocean model are used to simulate the World Ocean circulation since 1985. The first eddy-permitting simulation has been used extensively in previous studies, and provides a point of reference. A second, improved, eddy-permitting simulation is forced in the same manner as the eddy-resolving simulation, with a dataset based on a blend of NCEP re-analysis and satellite data. The third eddy-permitting simulation is forced with a different dataset, based on the ERA-40 re-analysis data. Inter-comparison of these simulations in the North Atlantic clarifies the relative importance of resolution and choice of forcing dataset, for simulating the mean state and recent variability of the basin-scale circulation in that region. Differences between the first and second eddy-permitting simulations additionally reveal an erroneous influence of sea ice on surface salinity, dense water formation, and the meridional overturning circulation. Simulations are further evaluated in terms of long-term mean ocean heat transport at selected latitudes (for which hydrographic estimates are available) and sea surface temperature errors (relative to observations). By these criteria, closest agreement with observations is obtained for the eddy-resolving simulation. In this simulation, there is also a weak decadal variation in mid-latitudes, with heat transport strongest, by around 0.2 PW, in the mid-1990s. In two of the eddy-permitting simulations, by contrast, heat transport weakens through the study period, by up to 0.4 PW in mid-latitudes. The most notable changes of heat transport in all simulations are linked to a weakening of the subpolar gyre, rather than changes in the meridional overturning circulation. It is concluded that recent changes in the structure of mid-latitude heat transport in the North Atlantic are more accurately represented if eddies are explicitly resolved.     

Deep-water macrofaunal diversity in the Faroe-Shetland region (NE Atlantic): a margin subject to an unusual thermal regime

The Faroe-Shetland Channel, situated in the NE Atlantic, encompasses a number of different sediment types (habitats) as well as being subject to an unusual thermal regime. Our main objective was to assess variations in macrofaunal generic diversity and composition along two transects to gauge the relative influence of regional hydrography and local habitat heterogeneity. We found that generic richness and diversity on a West of Shetland (WoS) transect correlated most strongly with temperature range, whilst along a North of Shetland (NoS) transect, richness and diversity correlated negatively with sedimentary variables, notably total organic carbon. Macrofaunal composition at WoS is also strongly influenced by water temperature with specific genera ( e.g. Galathowenia positively associated with the temperature eigenvectors), whereas at NoS it is a combination of temperature, silt + clay fraction and total organic carbon that has an impact on composition ( e.g. Proclea and Pseudosphyrapus , showing a negative relationship with the temperature eigenvectors). Although the temperature regime exerts a strong control on regional ecology, local habitat heterogeneity remains a significant factor.     

Late quaternary migrations of the subarctic front in the North Atlantic (Based on lithology and nannofossils)

A complex of lithological and micropaleontological methods were used for the study of sediments from the central North Atlantic (50–60°N). The data on the lithology, carbonate content, and occurrence of ash interbeds and ice-rafted material, combined with the nannofossil zonal biostratigraphy, allowed detailed subdivision of five core sections obtained during Cruise 48 of R/V Akademik Mstislav Keldysh. MIS 1–MIS 9 are established in the sections. In some of them, climatic changes related to migrations of the Subarctic Front are established based on the lithology and the characteristic coccolithophorid species: for example, a higher latitudinal position of the front is revealed for the Eemian interglacial (Substage 5e) as compared with that in the Holocene.     

末次冰盛期山东半岛高分辨率气候环境变化

末次冰盛期是末次冰期以来地球表面最寒冷的时期。通过对山东半岛地下画廊溶洞石笋DXHL3进行高精度230Th定年和高分辨率氧-碳稳定同位素分析,重建了该地区23.2～18.8 ka时期高分辨率夏季风气候环境变化历史。结果发现,山东半岛末次冰盛期夏季风气候存在显著的千年尺度波动;REDFIT分析表明,氧、碳同位素值均存在显著的2.2 ka周期。末次冰盛期山东半岛总体处于冷干状态,具体又可细分为4个阶段,即冷干（23.2～22 ka）-相对暖湿（22～21 ka）-冷干（21～19 ka）-相对暖湿（19～18.8 ka）。石笋DXHL3的δ18O变化趋势总体上与亚洲季风区内其他石笋记录相似,也与西太平洋暖池婆罗洲的石笋记录类似。这反映了末次冰盛期西太平洋暖池气候环境变化可能对山东半岛的夏季风气候变化产生了重要影响,推测西太平洋暖池表层海水温度变化引起的大气环流和黑潮的变化,是将气候环境变化信号从低纬地区传递到中高纬地区的纽带。     

Late Quaternary carbonate sedimentation at the Sierra Leone Rise (eastern equatorial Atlantic Ocean)

In the eastern equatorial Atlantic Ocean, changes in the concentration of carbonate in Late Quaternary sediments resulted from reduced production of carbonate in surface waters and increased dilution with non-carbonate sediments during glacial maxima. During glacial stages, production of carbonate in surface water (measured as its accumulation rate in shallow, undissolved cores) decreased by one half. The glacial accumulation rate of non-carbonate components increased 1.5 to 4 times over Holocene values; the greatest increases occurred in the deepest cores.

Carbonate dissolution during stages 2, 3 and 4 increased the proportion of foraminiferal fragments and decreased the accumulation rate of susceptible species in the deep sites. In shallow sites, slightly increased dissolution can be detected during stage 3 while greatly increased dissolution occurred during stage 4. Bathymetric profiles of foraminiferal fragmentation and accumulation document a shoaling of the foraminiferal lysocline by 1000 m during glacial isotopic stages. We present a mass balance model of sediment accumulation for carbonate and insoluble components and from this model we estimate the rate of downslope transport and dissolution of carbonate at the Sierra Leone Rise. Our results show that during stage 4 the rate of carbonate loss to dissolution was greater than the rate observed today or during other interglacial stages. The calculated rates of dissolution for stages 2 and 3 are not significantly different from those calculated for stage 1.     

Deep-Water Circulation in the Hunter Channel (Southwest Atlantic) in the Late Pleistocene and Holocene Based on Benthic Foraminifera

Oceanology - Based on benthic foraminifera from three sediment cores, the deep-water circulation near the Hunter Channel (Southwest Atlantic) in the Late Pleistocene and Holocene has been...     

Propagation of Antarctic Bottom Water in the Discovery Gap (Northeast Atlantic) Based on Measurements from 2019

Oceanology - The results of the analysis of the thermohaline water parameters of the bottom layer in the Discovery Gap (Azores-Gibraltar Fracture Zone, Northeast Atlantic) are presented. The data...     

Physical and hydrological characteristics of climatic frontal zones in the Tropical Atlantic

Climatic frontal zones are selected in the thermohaline fields of the Tropical Atlantic by analyzing the many-year-average seasonal database reduced to the nodes of a one-degree grid. We determine physical characteristics of the frontal zones, study their spatial and temporal variability, and reveal basic regularities of the appearance of frontal zones in the fields of thermohaline characteristics. Translated by Peter V. Malyshev and Dmitry V. Malyshev     

Thermostads and circulation in the upper layer of the Atlantic Ocean

There are three major permanent thermostads with roughly the same potential densities in the upper layer of the Atlantic Ocean. One is the thermostad of the 13°C Water in the equatorial Atlantic. The original type of the 13°C Water is formed in the thermocline in the eastern sector of the South Atlantic subtropical gyre by vertical mixing of dense, low-salinity water from the winter outcrop farther south and overlying less dense, high-salinity water. There might also be a lateral contribution of relatively high-salinity water from the Indian Ocean. The original 13°C Water thus formed is transported northwestward along the northern edge of the subtropical gyre and fed into the North Brazilian Current, which flows equatorward along the coast of Brazil. In the region of the equator, the Equatorial Undercurrent and the subsurface North and South Equatorial countercurrents branch off from the North Brazilian Current and carry the 13°C Water eastward to the thermostad region. Vertical mixing does not explain the development of the thermostad, but is found to be essential in determining the ultimate characteristics of the 13°C Water. The other two thermostads are those of the 18°C Water in the Sargasso Sea and the Subantarctic Mode Water in the western South Atlantic. Unlike the 13°C Water, both of these mode waters are formed as thermostads in the surface layer by winter convection, but vertical mixing in the subtropical gyres may play a role in determining their characteristics. All the three thermostads appear to be required to balance the system of flows in opposing directions.     

Investigating the molecular systematic relationships amongst selected Plesionika (Decapoda: Pandalidae) from the Northeast Atlantic and Mediterranean Sea

Despite the high number of species and ecological diversity of pandalid shrimps, there has been no previous attempt to resolve evolutionary relationships of several genera using molecular tools. Although mitochondrial DNA cytochrome oxidase I (COI) is widely used in barcoding studies to delimit species boundaries, additional insights into phylogenetic affinities can be obtained, especially when used in combination with data from additional genes. The knowledge of molecular diversity is essential to understand phylogenetic relationships and will help systematic clarifications. Based on partial fragments of the 16S and COI genes, we have focused specifically on addressing the systematic relationships of the economically and ecologically important shrimp genus Plesionika within a framework of five genera from within the Pandalidae. Our results showed that species within Plesionika are substantially divergent when compared with other genera, exhibiting the highest average nucleotide divergence, with 0.1123 and 0.0846 in COI and 16S genes, respectively. In addition, sequence divergence was found to vary greatly within the genus Plesionika (COI/16S): 0.0247/0.0016 between Plesionika antigai and Plesionika heterocarpus and 0.1616/0.098 between Plesionika heterocarpus and Plesionika edwardsii. We did not find amino acid sequence divergence between P. heterocarpus and P. antigai compared with P. heterocarpus and P. edwardsii (8.10%, K2P distance). Three species of Plesionika (P. antigai, P. heterocarpus and Plesionika scopifera) appear well separated from other Plesionika species in both maximum likelihood and Bayesian analyses. The present study confirms the utility of COI over 16S as a genetic marker to resolve relationships between different species of Plesionika from the Northeast Atlantic and Mediterranean Sea, in addition to species delimitation. The findings highlight the need to further review paraphyly within Plesionika in an attempt to recognize a concordance in the evolutionary history of Plesionika with major ecological and geological events.     

Patterns in megabenthic assemblages on a seamount summit (Ormonde Peak,Gorringe Bank,Northeast Atlantic)

Gettysburg and Ormonde are two shallow peaks located on the Gorringe seamount about 200 and 240 km WSW off Cape St. Vincent (Portugal, NE Atlantic), within the Portuguese Economic Exclusive Zone. Despite the ecological importance of the biological assemblages on these peaks and the need to preserve seamounts as valuable habitats, no management plans have been yet implemented at this site, which only recently has been included in the list of Sites of Community Importance of Portugal. Video imagery collected using a ROV during the 2011 Oceana campaigns was used here to analyse qualitative and quantitative patterns of benthic assemblage composition at the summit of the seamount (between 30 and 230 m depth). The results suggest that Ormonde is a biologically important area made up of vulnerable marine ecosystem elements that change significantly with depth. These include: kelp beds, in the euphotic zone; encrusting coralline algal communities and solitary colonies or mixed associations of suspension‐feeders (scleractinians, gorgonians, antipatharians, encrusting demosponges and ascidians), at the lower limit of the euphotic zone; mixed coral gardens and erect sponges, in the disphotic zone; and dense sponge aggregations, on the upper slope. These results were further used to propose amendments to the European Nature Information System habitat classification as a tool to work towards resolving the seamounts management issue. The results also provide information on taxa and habitats with high ecological value and classified as threatened or vulnerable, which is essential for the implementation of the cornerstones of Europe's biodiversity conservation policy, namely the OSPAR Convention and the EU Habitats Directive.