Initial vegetation, and spore density, diversity and evenness of different arbuscular mycorrhizal fungi morphotaxa 29,36 and 39 months after experimental vegetation removal, central Argentina

1. Dominant plant functional types (PFTs) are expected to be primary determinants of communities of other above- and below-ground organisms. Here, we report the effects of the experimental removal of different PFTs on arbuscular mycorrhizal fungi (AMF) communities in a shrubland ecosystem in central Argentina. 2. On the basis of the biomass-ratio hypothesis and plant resource use strategy theory, we expected the effect of removal of PFTs on AMF colonization and spores to be proportional to the biomass removed and to be stronger when more conservative PFTs were removed. The treatments applied were: undisturbed control (no plant removed), disturbed control (mechanical disturbance), no shrub (removal of deciduous shrubs), no perennial forb (removal of perennial forbs), no graminoid (removal of graminoids) and no annual forb (removal of annual forbs). AMF colonization was assessed after 5,17 and 29 months. Total density of AMF spores, richness and evenness of morpho-taxa, and AMF functional groups were quantified after 5,17,29,36 and 39 months. 3. Five months after the initial removal we found a significant reduction in total AMF colonization in all plots subjected to PFT removals and in the disturbed control plots, as compared with the undisturbed controls. This effect disappeared afterwards and no subsequent effect on total colonization and colonization by arbuscules was observed. In contrast, a significant increase in colonization by vesicles was observed in months 17 and 29, mainly in no graminoid plots. In general, treatments did not significantly affect AMF spores in the soil. On the other hand, no annual forb promoted transient (12-18 months) higher ammonia availability, and no shrub promoted lower nitrate availability in the longer term (24-28 months). 4. Synthesis. Our experiment, the first to investigate the effects of the removal of different PFTs on AMF communities in natural ecosystems, indicates that AMF communities are resilient to changes in the soil and in the functional composition of vegetation. Furthermore, it does not provide consistent evidence in support of the biomass-ratio hypothesis or differential trait-based direct or indirect effects of different PFTs on AMF in this particular system.

Diversity and faunal composition of benthic foraminifera in Hole 44-390A on the Blake Nose Plateau

Benthic foraminiferal assemblages are a widespread tool to understand changes in organic matter flux and bottom-water oxygenation and their relation to paleoceanographic changes in the Upper Cretaceous oceans. In this study, assemblage data (diversity, total number, and number per species and gram) from Deep Sea Drilling Project (DSDP) Site 390 (Blake Nose, western North Atlantic) were processed for the lower Maastrichtian (Globotruncana falsostuarti - Gansserina gansseri Planktic Foraminiferal Zone). These data document significant changes in nutrient flux to the sea floor as well as bottom-water oxygenation during this time interval. Parallel to the observed changes in the benthic foraminiferal assemblages the number of inoceramid shells decreases, reflecting also a significant increase in bottom-water oxygenation. We speculate, that these data could reflect the onset of a shift from warmer low-latitude to cooler high-latitude deep-water sources. This speculation will predate the major reorganization of the oceanic circulation resulting in a circulation mode similar to today at the Early/Late Maastrichtian boundary by ~1 Ma and therefore improves our understanding of Late Cretaceous paleoceanography.

Foraminifera and microfossil occurence in Late Jurassic sediments of the North and South Atlantic

Biostratigraphical, taxonomical, and palaeocological results were obtained from Oxfordian to Tithonian foraminifers of the Northern and Southern Atlantic Ocean boreholes of the DSDP Legs 1, 11, 36, 41, 44, 50, and 79. An oversight on the cored Jurassic sections of the DSDP Legs 79 and the corresponding foraminiferal descriptions are given. The reddish brown, clayey and carbonaceous Cat Gap Formation (Oxfordian to Tithonian) of the Northern Atlantic Ocean, rich in radiolarians, yields less or more uniform, in most cases allochthonous foraminiferal faunas of Central European shelf character. No Callovian and Upper Tithonian foraminiferaI zones can be established. The zone of Pseudomarssonella durnortieri covers the Oxfordian/Kimmeridgian, the zone of Neobulimina atlantica the Kimmeridgian/Lower Tithonian interval. Characteristic foraminiferal faunas are missing since the Upper Tithonian to Valanginian for reason of a widely distributed regression which caused hiatuses observed all over the Northern Atlantic Ocean and in parts of Europe. The Upper Jurassic cannot be subdivided into single stages by foraminiferal biostratigraphy alone. The fovaminiferal zones established by Moullad (1984) covering a Callovian-Tithonian interval may be of some local importance in the Tethyan realm: It has too long-ranging foraminiferal species to be used as index marker in the word-wide DSDP boreholes. Some taxonomical confusion is caused because in former publications some foraminiferal species have got different names both in the Jurassic and Cretaceous. The foraminiferal biostratigraphy of drilled sections from DSDP boreholes is restricted by the drilling technique and for palaeo-oceanographical, biological, and geological reasons. Foraminiferal faunas from the DSDP originally described as ,,bathyal, or ,,abyssal,, have to be derived from shallower water. This contrasts the palaeo-water depths of 3000-4000 m which result from sedimentological and palaeo-geographical investigations.

Benthic foraminifers from the Japan Sea

Five holes were drilled at two sites in the Sea of Japan during Ocean Drilling Program (ODP) Leg 128. Site 798 is located on Oki Ridge at a depth of about 900 m. Sediment age at Site 798 ranges from Pliocene to Holocene. Site 799 is located in the Kita-Yamato Trough at depth of 2000 m and below the present calcite compensation depth (CCD); the sediment ranges from Miocene to Holocene in age. Samples from all holes contain benthic foraminifers. Faunal evidence of downslope displacement is frequent in Holes 799A and 799B. The vertical frequency distribution of some dominant species shows that significant faunal changes occur in Holes 798A-C on Oki Ridge. Based on the faunal change and the thickness of sediments, it appears that the Oki Ridge was uplifted more than 1,000 m during last 4 m.y. Benthic foraminifers also demonstrate that the water depth of Site 799 rapidly changed from upper bathyal to lower bathyal during middle Miocene time. The appearance of benthic foraminifer species common to anaerobic environments suggests that the dysaerobic to anaerobic bottom conditions existed during the evolution of the Sea of Japan. Faunal distributions also suggest that the 'Tertiary-type' species recognized in the Neogene strata of the Japan Sea coastal regions disappeared sequentially from the Sea of Japan during Pliocene to late Pleistocene.

Occurrence and abundance of late Early Cretaceous radiolarians at DSDP Leg 62 Holes

Well-preserved Mesozoic radiolarian faunas have been recovered at four sites of Deep Sea Drilling Project Leg 62. Late Early Cretaceous assemblages, which occur always with foraminifers or calcareous nannoplankton, allow the description of 21 new species, the introduction of a new zone scheme, and calibration of the radiolarian zones with the geochronological scale.

Mollusc biostratigraphy and Bolboforma abundance in sediments obtained near Gross Pampau, north Germany

A thirty-six meter thick section of Miocene mica clay of Gross Pampau was studied for molluscs and bolboformas. The molluscs define the regional substages of late Reinbekian to late Langenfeldian. The bolboformas enable the cross-correlation with the nannoplankton subdivision and the geological time scales of BERGGREN et al. (1995). New species are Periploma ariei, Ringicula tiedemanni, Bolboforma robusta badenensis, and Bolboforma contorta.

Mid-Pleistocene benthic foraminiferal record in the Southwest Pacific

Benthic foraminiferal faunas from three bathyal sequences provide a proxy record of oceanographic changes through the mid-Pleistocene transition (MPT) on either side of the Subtropical Front (STF), east of New Zealand. Canonical correspondence analyses show that factors related to water depth, latitude and climate cycles were more significant than oceanographic factors in determining changes in faunal assemblage composition over the last 1 Ma. Even so, mid-Pleistocene faunal changes are recognizable and can be linked to inferred palaeoceanographic causes. North of the largely stationary STF the faunas were less variable than to the south, perhaps reflecting the less extreme glacial-interglacial fluctuations in the overlying Subtropical Surface Water. Prior to Marine Isotope Stage (MIS) 21 and after MIS 15, the northern faunas had fairly constant composition, but during most of the MPT faunal composition fluctuated in response to climate-related food-supply variations. Faunal changes through the MPT suggest increasing food supply and decreasing dissolved bottom oxygen. South of the STF, beneath Subantarctic Surface Water, mid-Pleistocene faunas exhibited strong glacial-interglacial fluctuations, inferred to be due to higher interglacial nutrient supply and lower oxygen levels. The most dramatic faunal change in the south occurred at the end of the MPT (MIS 17- 12). with an acme of Abditodentrix pseudothalmanni, possibly reflecting higher carbon flux and lower bottom oxygen. This study suggests that the mid-Pleistocene decline and extinction of a group of elongate, cylindrical deep-sea foraminifera may have been related to decreased bottom oxygen concentrations as aresult of slower deep-water currents.

Correlation of Bolboforma zonation and nannoplankton stratigraphy in the Neogene of the North Atlantic

The Neogene Bolboforma zones established in the North Atlantic have been correlated with the calcareous nannoplankton stratigraphy obtained by investigation of the same samples from DSDP Sites 12-116 (44 samples), 49-408 (76 samples), 81-555 (43 samples) and 94-608 (103 samples). The absolute ages for the zonal boundaries were determined by the paleomagnetic record of Site 94-608. This correlation and the age determinations are additional useful tools to develop a precise biostratigraphy of Neogene sediments in the Northern Atlantic.

Radiolarian chronology and fauna across the middle/late Eocene boundary at ODP Hole 171-1052A

Quantitative radiolarian assemblage analysis has been conducted on middle and upper Eocene sediments (Zones RP16 to RP18) from Ocean Drilling Program Site 1052 in order to establish the radiolarian magnetobiochronology and determine the nature of the faunal turnover across the middle/late Eocene boundary in the western North Atlantic Ocean. We recognize and calibrate forty-five radiolarian bioevents to the magneto- and cyclo-stratigraphy from Site 1052 to enhance the biochronologic resolution for the middle and late Eocene. Our data is compared to sites in the equatorial Pacific (Leg 199) to access the diachrony of biostratigraphic events. Eleven bioevents are good biostratigraphic markers for tropical/subtropical locations (south of 30°N). The primary markers (lowest occurrences of Cryptocarpium azyx and Calocyclas bandyca) which are tropical zonal boundary markers for Zones RP17 and RP18 provide robust biohorizons for correlation and age determination from the low to middle latitudes and between the Atlantic and Pacific Oceans. Some other radiolarian bioevents are highly diachronous (<1 million years) between oceanic basins. A significant faunal turnover of radiolarians is recognized within Chron C17n.3n (37.7 Ma) where 13 radiolarian species disappear rapidly in less than 100 kyr and 4 new species originate. The radiolarian faunal turnover coincides with a major extinction in planktonic foraminifera. We name the turnover phase, the Middle/Late Eocene Turnover (MLET). Assemblage analysis reveals the MLET to be associated with a decrease in low-mid latitude taxa and increase in cosmopolitan taxa and radiolarian accumulation rates. The MLET might be related to increased biological productivity rather than to surface-water cooling.

Benthos fauna in the North Sea from 2 surveys in 1986 and 1987

During two surveys in the North Sea, in summer 1986 and in winter 1987, larger epibenthos was collected with a 2 m beam trawl. The distributions of the species were checked for average linkage by means of the JACCARD-index cluster analysis. In summer two main clusters can be recognized. These are situated to the north and to the south of the Dogger Bank. In winter two main clusters may be recognized as well, but these clusters divide the North Sea into a western and an eastern part. We conclude, that these differences of epibenthos characteristics are correlated with seasonal changes in water body distributions.