The Cretaceous–Palaeogene boundary at Gorgonilla Island,Colombia, South America

The discovery of a new Cretaceous/Palaeogene (K/Pg) bathyal marine sequence on Gorgonilla Island, SW Colombia, extends the presence of Chicxulub impact spherule deposits to the Pacific region of northern South America and to the Eastern Pacific Ocean. The Gorgonilla spherule layer is approximately 20 mm thick and consists of extraordinarily well‐preserved glass spherules up to 1.1 mm in diameter. About 70–90% of the spherules are vitrified, and their chemical composition is consistent with Haiti (Beloc) impact glass spherules. Normal size‐grading, delicate spherule textures, welded melt components and an absence of bioturbation or traction transport suggest that the Gorgonilla spherule layer represents an almost undisturbed settling deposit.     

NGC 985: Interactions and the origin of AGNs

Observations of the Seyfert galaxy NGC 985 have revealed large-scale extended ionized zones, covering a large fraction of the ring-shaped structure of this galaxy. These ionized regions are a major contributor to the total far-infrared emission of this object. An interaction driven starburst is proposed to explain the main features of this galaxy.Based on observations obtained at the Observatorio de El Roque de los Muchachos, La Palma, Spain.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.     

Metal concentrations in water and sediments from tourist beaches of Acapulco, Mexico

A survey on the metal concentrations (As, Ba, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Sr, V, Zn) in beach water and sediments is reported from the tourist destination of Acapulco city on the Pacific coast of Mexico. The concentration of dissolved trace metals (DTMs) in beach water and acid leachable trace metals (ALTMs) in sediments indicated that they are anthropogenic in nature due to the increased tourist activities in the crowded beach locations. The statistical analysis indicates Fe and Mn play a major role as metal scavengers in both the medium (water and sediment) and the higher value of other metals is site specific in the study area, indicating that they are transported from the local area. Comparison results suggest that the beach water quality has deteriorated more than the sediments and special care needs to be taken to restore the beach quality.     

Epibiotic traits of the invasive red seaweed Acanthophora spicifera in La Paz Bay,South Baja California (Eastern Pacific)

The aim of this study was to analyze the interaction of a non‐native macroalga (Acanthophora spicifera) with native macroalgae (Sargassum spp.) and sponge assemblages in a subtropical embayment of the Mexican Pacific. The intensity of A. spicifera epiphytism on the native seaweed Sargassum varied significantly over time and was inversely related to the Sargassum density and size. The higher intensity (up to 28 individuals per host plant) occurred when Sargassum was smaller and was lower in density (senescence period). The lower intensity was recorded during the growth period of Sargassum and the subsequent increase in intensity was attributed to a high fragmentation period of A. spicifera, which was evidenced by a decrease in its average size and biomass and by the presence of larger free‐floating accumulations on the subtidal zone. The facultative interaction between A. spicifera and Sargassum appears to be neutral, as no negative or positive effects were found for epiphytic or basibiont seaweeds. However, this invasive seaweed characteristically monopolizes almost all types of hard substrate, and its effects on other algae and benthic organisms should be investigated. Moreover, A. spicifera was often epizoic on epilithic sponges. This invasive seaweed was found anchored on the sponge tissue by rhizome‐like structures. In addition, free‐floating fronds of A. spicifera were frequently found carrying small pieces of the basibiont sponge in its basis (60% of them with eggs and embryos), which suggests a novel facilitation mechanism for some sponge species, as the A. spicifera epizoism could favor fragmentation, dispersal and recruitment of these invertebrates. This study shows that A. spicifera is not only a species that adapts rapidly to the new conditions of the receiving environment but, due to its epibiotic traits, it can directly interact with and influence the life histories of some native species.     

Dependence of Mean Sea Surfaces from Altimeter Data on the Reference Model Used

A mean sea surface model is used as the frame of reference in processing altimeter data. This article focuses on ascertaining the extent to which results depend on the different mean sea surface models used. In particular, we have analyzed the results from the OSU95MSS and the CLS_SHOMv.98.2 models in an area in the North Atlantic Ocean comprising the Canary and Azores Islands. Special attention has been paid to data editing and several criteria were proposed. The amount of detected data is quite small because we used a well corrected data set. However, it was enough to show important relations between the applied criteria and the kind of area. Therefore we analyzed the best way to apply these criteria according to the areas where the points have been found. Singular areas related to several factors have been detected by all the suggested criteria. In particular, rough sea bottom features, dynamic circulation, and amphidromic points of the tidal waves, among others. As a result of this analysis, we have not considered it appropriate to remove all the detected points. Two time-averaged and corrected mean sea surfaces were determined in the test area.     

On the presence of <Emphasis Type="Italic">Stephanodiscus niagarae</Emphasis> Ehrenberg in central Mexico

Stephanodiscus niagarae is frequently reported from late Pleistocene (>10,000 yr BP) sediments in central Mexico, with lower abundances through the Holocene. Its presence in Holocene and modern environments in central Mexico was not well documented until our study, where we report on three populations of S. niagarae, one middle Holocene population with particularly high abundance from the Upper Lerma Basin, and two modern sites, Valle de Bravo and Santa Elena. The three sites are located in the same geographical area, in the State of Mexico. The fossil material dates to ca. 6600–4900 yr BP, with S. niagarae reaching up to 90% of the diatom counts. Stephanodiscus niagarae is present in association with Fragilaria pinnata, F. brevistriata, and Aulacoseira granulata. In Valle de Bravo (ca. 30 m deep) S. niagarae is present in very low numbers in water column and surface sediments samples (<1%); the diatom assemblage is dominated by Fragilaria crotonensis in association with A. granulata, A. granulata var. curvata and Cyclotella ocellata. In Santa Elena, a shallow, intermittent irrigation channel, S. niagarae is the second most abundant alga; the diatom assemblage is dominated by S. niagarae in association with A. granulata, A. granulata var. curvata and F. crotonensis. Both modern sites show a trend to eutrophy and these diatom assemblages are taken as indicative of this trend. It is suggested researchers should be cautions when the presence of S. niagarae in sedimentary records is taken as indicative of deep waters conditions, as the present data show that this species can thrive in rather shallow environments in Mexico.     

Geomorphological and ecological features of blowouts in a western Mediterranean coastal dune complex: a case study of the Es Comú de Muro beach-dune system on the island of Mallorca, Spain

Many of the coastal dune systems along western Mediterranean shores are in an advanced state of fragmentation and show distinct signs of erosion, largely because of blowout development along the dune front. The Es Comú de Muro beach-dune system on the island of Mallorca (Spain) is a good example of this. In order to better understand and quantify the current situation, 58 blowouts along a ca. 1.5-km-long dune front were investigated. In each case, a number of morphometric and ecological variables were analyzed as a basis for comparison and classification, in particular blowout dimensions and orientation, inner morphometry and topography, morphological types, the role of vegetation in defining the state of the foremost dune line, and the link between vegetation and blowout typology. In comparison with a recent preliminary investigation, the results of the present study provide a more comprehensive picture of the advanced state of fragmentation along the dune front. The blowouts are not evenly distributed, highest densities occurring along the southernmost part of the beach, lowest densities along the northern part. The blowouts were subdivided into two categories on the basis of their shape and general structure, trough blowouts being the most prevalent, followed by mixed trough-saucer shapes. Distinctly saucer-shaped blowouts could not be distinguished. In addition, the blowouts were subdivided into two morphological categories, i.e. simple and branched. It was also possible to link the morphological state of the dune front to certain ecological parameters, in particular vegetation which, in the present case, comprised herbaceous and woody plants. Cluster analyses of species associations (Bray-Curtis similarity indices) were carried out on the basis of the presence/absence of each species. It is shown that, on account of presence counts and the degree of similarity of species associations, some species play a more important role in stabilizing the mobile dune sands than others, a foremost candidate being Ammophila arenaria. It is concluded that active support for such plants should form part of any management strategy aiming to reduce and reverse coastal dune fragmentation processes.     

Middle pleistocene variations in palaeoclimate,palaeoenvironment and vegetation of the las tablas de daimiel national park (Spain)

The Middle Pleistocene palaeoclimate and palaeoenvironment evolution of the Las Tablas de Daimiel wetlands is described using a combination of sedimentology, pollen and δ¹³C and δ¹⁸O isotopic records of Unit B of core LT‐199906. This unit mostly contains fluvial and palustrine sediments. U/Th and amino acid racemization (AAR) dating and a comparison of the δ¹⁸O curve of Unit B with oceanic records suggests that Unit B spans the period from the end of Marine Isotope Stage (MIS) 10 (340 ka) to the first stages of MIS 7 (ca. 210 ka). MIS 9 was characterised by a regional vegetation dominated by Cupressaceae, with Pinus as a tree element. The water level was high and temperatures were very probably higher than during the Holocene. MIS 8 and the first substages of MIS 7 (7e, 7d and 7c) were dominated by xerophilous steppe vegetation in lowlands (elevations around 610 m above sea level) near to the wetland. At higher altitudes, far away from the wetland, there were fewer Pinus than in MIS 9, and a greater presence of warm, temperate and cool climate tree elements. The aquatic system in MIS 9 became shallower, with eutrophication and the accumulation of organic matter occurring; temperatures were similar to or lower than those of the Holocene. Copyright © 2011 John Wiley & Sons, Ltd.