Plant species, biomass and environmental characteristics of relevés along the North America Arctic bioclimate gradient

Question: How do interactions between the physical environment and biotic properties of vegetation influence the formation of small patterned-ground features along the Arctic bioclimate gradient? Location: At 68° to 78°N: six locations along the Dalton Highway in arctic Alaska and three in Canada (Banks Island, Prince Patrick Island and Ellef Ringnes Island). Methods: We analysed floristic and structural vegetation, biomass and abiotic data (soil chemical and physical parameters, the n-factor [a soil thermal index] and spectral information [NDVI, LAI]) on 147 microhabitat releves of zonalpatterned-ground features. Using mapping, table analysis (JUICE) and ordination techniques (NMDS). Results: Table analysis using JUICE and the phi-coefficient to identify diagnostic species revealed clear groups of diagnostic plant taxa in four of the five zonal vegetation complexes. Plant communities and zonal complexes were generally well separated in the NMDS ordination. The Alaska and Canada communities were spatially separated in the ordination because of different glacial histories and location in separate floristic provinces, but there was no single controlling environmental gradient. Vegetation structure, particularly that of bryophytes and total biomass, strongly affected thermal properties of the soils. Patterned-ground complexes with the largest thermal differential between the patterned-ground features and the surrounding vegetation exhibited the clearest patterned-ground morphologies.

Calcareous nannofossils of ODP Sites 149-897 and 149-901

Mesozoic calcareous nannofossil assemblages recovered during Ocean Drilling Program Leg 149 from the Iberia Abyssal Plain off the coast of Portugal were examined to determine the age of the rifting processes that affected the western Iberia Margin. Dark carbonaceous claystones (black shales) recovered from Site 901 contain highly diverse and abundant Tithonian calcareous nannofossil assemblages. Careful examination and documentation of this material has extended the ranges of numerous Jurassic and Cretaceous species and detailed a significant Late Jurassic assemblage turnover observed in the calcareous nannofossil record. The Lower Cretaceous sequence consists of intervals of serpentinized peridotite intercalated between various breccias and dark claystones. With the exception of a few samples, calcareous nannofossils are few and moderately preserved. The age of nannofossils within these varied sedimentary lithologies ranges from the late Barremian to the late Aptian. Eight new species are described: Ansulasphaera covingtonii, Clepsilithus meniscus, Conusphaera sinespina, Crepidolithus parvulus, Diazomatholithus galicianus, Percivalia arata, Rotelapillus pleoseptatus, and Tranolithus incus. Also proposed are five new combinations.

Radiolarian assemblages of ODP Leg 117 sites

Significant numbers of radiolarians ranging in age from late middle Miocene to Recent were recovered from six sites drilled on the Oman margin and Owen Ridge. Sparse faunas were recovered from five additional sites on the Oman margin and one site on the Indus Fan. Detailed range charts and biozonations are presented for most sites. The radiolarian assemblages are peculiar in that numerous common tropical forms, some of which are biomarkers, are absent or very rare. In addition, some species not usually found in tropical assemblages are present. These forms, indicative of up welling conditions, fall into three categories: (1) endemic upwelling: species endemic to upwelling and not previously described from the Indian Ocean; (2) displaced temperate: temperate forms not usually found in tropical waters; and (3) enhanced tropical: tropical forms which are more abundant and/or robust in areas of upwelling. Comparison of the Oman margin/Owen Ridge fauna with that recovered from the Peru margin upwelling area (ODP Leg 112) suggests that the assemblage may be globally diagnostic of upwelling conditions. The onset of upwelling is marked by the appearance of siliceous biota at about 11.9 Ma, and there is some indication of a decrease in the strength of the upwelling signal at about 9.6 Ma. A strong pulse in, or strengthening of, the upwelling mechanism is indicated by a marked fauna change at 4.7 Ma. There is a weaker signal, implying a change in upwelling conditions, at about 1.5 Ma.

Visual estimates of carbonate particles and coccolith abundance at DSDP Hole 75-530A

The upper Albian to Coniacian section (Cores 105 to 89) at Site 530 contains rare and poorly preserved coccoliths at a few levels and fine-fraction carbonate ("micarb") at all the levels studied. Dissolution ranking of the most resistant coccolith species is possible. Changes in the dissolution intensity resulting from variations in the organic carbon and carbonate input seem a likely explanation for changes in the relative abundance of fine-fraction carbonates types.

Cretaceous nannofossils from the Northwest African Margin

Deep Sea Drilling Project Leg 79 recovered Cretaceous nannofossils at two localities, Sites 545 and 547. Species diversity of the Cretaceous coccoliths is high, and the assemblages range in age from early Valanginian-early Hauterivian to latest Maestrichtian. Site 545 and portions of Site 547 can be combined to form a composite section ranging from the upper Aptian-lower Albian to the middle to upper Cenomanian. As defined by nannofossil events, this section represents a complete record of sedimentary deposition. The interval appears to be the most extensive and complete Cretaceous section yet drilled off the Northwest African margin. The Campanian and Maestrichtian sediments found at Site 547 (Hole 547A) are the youngest Cretaceous strata found on the Northwest African margin. Like the middle Cretaceous sections, the uppermost Maestrichtian of this interval also represents a complete record of sedimentation.

Diatom biostratigraphy of sediments from ODP Leg 170 sites

The following data paper summarizes diatom biostratigraphic data from sediments drilled in the Costa Rica accretionary wedge during Ocean Drilling Program Leg 170. Quaternary through lower Miocene diatom zones characteristic of the equatorial Pacific region are recognized in the reference section, Site 1039, which was drilled on the downgoing Cocos plate. At Sites 1040-1043, where the recovered silty clay units are primarily wedge and apron sediments that overlie the underthrust sections, diatoms are generally low in abundance, and complete zonation of the cores was not possible above the décollement surface.

Abundance of copepods from multinet samples during POLARSTERN cruise ANT-XX/1

Abundance and species composition of copepods were studied during the expedition ANT XXI/1 on a latitudinal transect in the eastern Atlantic from 34°49.5' N to 27°28.1' S between 2-20 November 2002. Stratified zooplankton tows were carried out at 19 stations with a multiple opening-closing net between 300 m water depth and the surface. Cyclopoid and calanoid copepods showed similar patterns of distribution and abundance. Oithona was the most abundant cyclopoid genus, followed by Oncaea. A total of 149 calanoid copepod species were identified. Clausocalanus was by far the most abundant genus, comprising on average about 45% of all calanoids, followed by Calocalanus (13%), Delibus (9%), Paracalanus (6%), and Pleuromamma (5%). All other genera comprised on average less than 5% each, with 40 genera less than 1%. The calanoid copepod communities were distinguished broadly in accordance with sea surface temperature, separating the subtropical from the tropical stations, and were largely determined by variation in species composition and species abundance. Nine Clausocalanus species were identified. The most numerous Clausocalanus species was C. furcatus, which on average comprised half of all adult of this genus. C. pergens, C. paululus, and C. jobei, contributed an average of 19%, 9%, and 9%, respectively. The Clausocalanus species differed markedly in their horizontal and vertical distributions: C. furcatus, C. jobei, and C. mastigophorus had widespread distributions and inhabited the upper water layers. Major differences between the species were found in abundance. C. paululus and C. arcuicornis were biantitropical and were absent or occurred in very low numbers in the equatorial zone. C. parapergens was found at all stations and showed a bimodal distribution pattern with maxima in the subtropics. C. pergens occurred in higher numbers only at the southern stations, where it replaced C. furcatus in dominance. In contrast to the widespread species, the bulk of the C. paululus, C. arcuicornis, C. parapergens, and C. pergens populations was concentrated in the colder, deeper water layers below the thermocline, thereby avoiding the warm surface waters. C. lividus was found only at the most northern and C. ingens only at the most southern stations. Both species were found almost exclusively in the upper 50 m. The distinct differences in abundance and horizontal and vertical distribution suggest a strong ecological differentiation among the Clausocalanus species.

Cretaceous nannofossils of southeast France

The Aptian-lower Albian succession of the Vocontian Basin (SE France) consists of marine hemipelagic sediments including several black shale horizons. The latter are partly of regional and partly of global distribution. This sedimentary succession records the nannoplankton evolution of the Aptian-early Albian interval and thus provides an excellent opportunity to calibrate the calcareous nannofossil record with Tethyan ammonite and planktic foraminiferal biostratigraphy. The calcareous nannofossil biostratigraphy presented in this paper supports previous zonations, but it also provides a much higher resolution and thus improves the correlation of different black shale horizons on a supraregional scale. Up to 23 major (supraregionally significant) and minor (regionally significant) first and last occurrences of calcareous nannofossil taxa are recognized. Nannoconid abundances decrease rapidly in the upper Lower Aptian (nannoconid crisis I, NCI) and in the middle Upper Aptian (nannoconid crisis II, NCII). Both decreases correlate with carbonate-platform drowning events. The upper Lower Aptian interval above the NCI is characterized by high abundances of large specimens of Assipetra infracretacea and Rucinolithus terebrodentarius probably of supraregional significance. The uppermost Aptian-Lower Albian is characterized by high abundances of the calcareous nannoplankton taxon Repagulum parvidentatum, reflecting boreal influence on the Tethyan Realm. This suggests a temporary decrease in surface-water temperatures in the Vocontian Basin.

(Appendix) Late Cretaceous calcareous nannofossils of DSDP Holes 80-549 and 80-551

he early late Cretaceous (Cenomanian-early Turonian) is thought to have been one of the warmest periods of the Phanerozoic. This period was characterised by tropical sea surface temperatures of up to 36 °C and a pole-to-equator-gradient of less than 10 °C. The subsequent Turonian-Maastrichtian was characterised by a continuous climatic cooling, peaking in the Maastrichtian. This climatic cooling and the resulting palaeoceanographic changes had an impact on planktic primary producer communities including calcareous nannofossils. In order to gain a better understanding of these Cenomanian-Maastrichtian palaeoceanographic changes, calcareous nannofossils have been studied from the proto North Atlantic (Goban Spur, DSDP Sites 549, 551). In order to see potential differences between open oceanic and shelf dwelling nannofossils, the data from Goban Spur have been compared to findings from the European shelf (northern Germany). A total of 77 samples from Goban Spur were studied for calcareous nannofossils revealing abundant (mean 6.2 billion specimens/g sediment) and highly diverse (mean 63 species/sample) nannofossil assemblages. The dominant taxa are Watznaueria spp. (mean 30.7%), Prediscosphaera spp. (mean 18.3%), Zeugrhabdotus spp. (mean 8.3%), Retecapsa spp. (mean 7.2%) and Biscutum spp. (mean 6.6%). The Cenomanian assemblages of both Goban Spur (open ocean) and Wunstorf (shelf) are characterised by elevated abundances of high fertility taxa like Biscutum spp., Zeugrhabdotus spp. and Tranolithus orionatus. Early Turonian to Maastrichtian calcareous nannofossil assemblages of Goban Spur are, however, quite different to those described from European sections. Oceanic taxa like Watznaueria spp., Retecapsa spp. and Cribrosphearella ehrenbergii dominate in Goban Spur whereas the fertility indicators Biscutum spp. and T. orionatus are more abundant in the European shelf assemblages. This shift from a homogeneous distribution of calcareous nannofossils in the Cenomanian towards a heterogeneous one in the Turonian-Maastrichtian implies a change of the ocean circulation. The "eddy ocean" system of the Cenomanian was replaced by an oceanic circulation similar to the modern one in the Turonian-Maastrichtian, caused by the cooling. The increased pole-to-equator-gradients resulted in an oceanic circulation similar to the modern one.