Vegetation and fire history since the last glacial maximum in an inland area of the western Mediterranean Basin (Northern Iberian Plateau, NW Spain)

We reconstructed vegetation responses to climate oscillations, fire and human activities since the last glacial maximum in inland NW Iberia, where previous paleoecological research is scarce. Extremely sparse and open vegetation composed of steppic grasslands and heathlands with scattered pioneer trees suggests very cold and dry conditions during the Oldest Dryas, unsuitable for tree survival in the surroundings of the study site. Slight woodland expansion during the Bolling/Allerod was interrupted by the Younger Dryas cooling. Pinewoods dominated for most of the early Holocene, when a marked increase in fire activity occurred. Deciduous trees expanded later reaching their maximum representation during the mid-Holocene. Enhanced fire activity and the presence of coprophilous fungi around 6400-6000 cal yr BP suggest an early human occupation around the site. However, extensive deforestation only started at 4500 calyrBP, when fire was used to clear the tree canopy. Final replacement of woodlands with heathlands, grasslands and cereal crops occurred from 2700 cal yr BP onwards due to land-use intensification. Our paleoecological record can help efforts aimed at restoring the natural vegetation by indicating which communities were dominant at the onset of heavy human impact, thus promoting the recovery of currently rare oak and alder stands.

Aeolian dust in Colorado Plateau soils: Nutrient inputs and recent change in source

Aeolian dust (windblown silt and clay) is an important component in arid-land ecosystems because it may contribute to soil formation and furnish essential nutrients. Few geologic surfaces, however, have been characterized with respect to dust-accumulation history and resultant nutrient enrichment. We have developed a combination of methods to identify the presence of aeolian dust in arid regions and to evaluate the roles of this dust in ecosystem processes. Unconsolidated sandy sediment on isolated surfaces in the Canyonlands region of the Colorado Plateau differs greatly in mineralogical and chemical composition from associated bedrock, mainly aeolian sandstone. Detrital magnetite in the surficial deposits produces moderately high values of magnetic susceptibility, but magnetite is absent in nearby bedrock. A component of the surficial deposits must be aeolian to account for the abundance of magnetite, which formed originally in far-distant igneous rocks. Particle-size analysis suggests that the aeolian dust component is typically as much as 20–30%. Dust inputs have enriched the sediments in many elements, including P, Mg, Na, K, and Mo, as well as Ca, at sites where bedrock lacks calcite cement. Soil-surface biologic crusts are effective dust traps that apparently record a change in dust sources over the past several decades. Some of the recently fallen dust may result from human disturbance of land surfaces that are far from the Canyonlands, such as the Mojave Desert. Some land-use practices in the study area have the potential to deplete soil fertility by means of wind-erosion removal of aeolian silt.

Cenozoic nannofossils from the Exmouth Plateau, eastern Indian Ocean

Six sites (759-764) were drilled on the Exmouth Plateau during Ocean Drilling Program Leg 122. Nannofossilrich Cenozoic sediments were recovered at all six sites, reflecting the open-ocean conditions that prevailed over the Exmouth Plateau during the Cenozoic. Calcareous nannofossils are abundant, diverse (250 different species identified), and generally well preserved throughout the composite lower Paleocene to Quaternary section. The diversity and preservation of nannofossils permits a high degree of stratigraphic resolution at each site. Site 762 on the central part of the Exmouth Plateau contains an almost unbroken Cenozoic record (only Miocene Zones NN3, NN8, and NN10 are missing). This site may prove to be a useful Cenozoic biostratigraphic and biomagnetochronologic reference section for the eastern Indian Ocean.

Benthic foraminiferal assemblages and paleoproductivity reconstructions for the last 550 kyr of the Ontong Java Plateau, western equatorial Pacific

We analyzed foraminiferal and nannofossil assemblages and stable isotopes in samples from ODP Hole 807A on the Ontong Java Plateau in order to evaluate productivity and carbonate dissolution cycles over the last 550 kyr (kilo year) in the western equatorial Pacific. Our results indicate that productivity was generally higher in glacials than during interglacials, and gradually increased since MIS 13. Carbonate dissolution was weak in deglacial intervals, but often reached a maximum during interglacial to glacial transitions. Carbonate cycles in the western equatorial Pacific were mainly influenced by changes of deep-water properties rather than by local primary productivity. Fluctuations of the estimated thermocline depth were not related to glacial to interglacial alternations, but changed distinctly at ~280 kyr. Before that time the thermocline was relatively shallow and its depth fluctuated at a comparatively high amplitude and low frequency. After 280 kyr, the thermocline was deeper, and its fluctuations were at lower amplitude and higher frequency. These different patterns in productivity and thermocline variability suggest that thermocline dynamics probably were not a controlling factor of biological productivity in the western equatorial Pacific Ocean. In this region, upwelling, the influx of cool, nutrient-rich waters from the eastern equatorial Pacific or of fresh waters from rivers have probably never been important, and their influence on productivity has been negligible over the studied period. Variations in the inferred productivity in general are well correlated with fluctuations in the eolian flux as recorded in the northwestern Pacific, a proxy for the late Quaternary history of the central East Asian dust flux into the Pacific. Therefore, we suggest that the dust flux from the central East Asian continent may have been an important driver of productivity in the western Pacific.

Benthic foraminifera in the Tasman Sea, Emerald Basin and Challenger Plateau

Im Rahmen des TASQWA-Projektes (Quarternary Variability of Water Masses in the Southern Tasman Sea and the Southern Ocean) wurde eine erstmalige quantitative und taxonomische Bestandsaufnahme der rezenten, benthischen Tiefseeforaminiferen der Korngrößenfraktion > 250 µm in 27 Sedimentoberflächenproben aus dem austral-antarktischen Gebiet durchgeführt. Es konnten 137 Arten bestimmt werden, wobei aber keine Art dominante Anteile in den Proben erreichte. Über benthische Tiefseeforaminiferen im untersuchten Gebiet existiert kaum Literatur. Es gibt zwar aus dem 19. Jhrd. sehr gut dokumentierte Foraminiferen in diesem Bereich, diese decken aber längst nicht alle gefundenen Exemplare ab. Erst um die Jahrtausendwende beschäftigten sich Autoren wieder intensiver mit den australischen und neuseeländischen, benthischen Foraminiferen. Aber auch sie drangen nicht bis in die Tiefsee vor, sondern blieben vorwiegend im Schelfbereich. Aufgrund dieser spärlichen Literatur ist jede einzelne Art ausführlich mit Synonymieliste und Abbildung dokumentiert worden. Die PAST-Analyse generierte mit den 137 Arten und den 27 Stationen sechs Faunenvergesellschaftungen, die überwiegend bathymetrisch zoniert sind. Ab 562 m beginnt am Campbell Plateau in der Hochproduktionszone die Bulimina-Vergesellschaftung. Diese Vergesellschaftung zeichnet sich durch die höchste Individuenzahl aus. Ab 959 m findet sich die Rhizammina-Vergesellschaftung, die im Untersuchungsgebiet am weitesten verbreitet ist. Die weniger oft anzutreffende Cibicides-Vergesellschaftung läßt sich ab 1660 m Tiefe finden. Nur in einer einzigen Probe an der Tasmanschwelle in 2146 m Tiefe, tritt die Reophax-Vergesellschaftung auf, in der die Textulariina überwiegen. Die weniger oft anzutreffende Ehrenbergina-Vergesellschaftung läßt sich ab 1841 m finden. In dieser Vergesellschaftung, in der die Artenanzahl fast an das Niveau der Hochproduktionszone heranreicht, halten sich Rotaliina und Textulariina die Waage. Im Emerald Becken ab 3909 m Tiefe beginnt die Jaculella- Vergesellschaftung. Diese liegt in einem echten Hungergebiet und besteht hauptsächlich aus Textulariina. Im gesamten Untersuchungsgebiet lassen sich durch die Probenauswertung vier unterschiedliche Lebensräume (Challenger Plateau, Campbell Plateau, Emerald Becken und Tasmanschwelle) ausmachen. Da jedoch nur zwei Sedimentoberflächenproben am Challenger Plateau genommen wurden, konnte dieser Bereich nur eingeschränkt mit den anderen drei Bereichen verglichen werden. Die Foraminiferengemeinschaften des Challenger Plateaus und der Tasmanschwelle können jedoch im oberen Bereich der Wassersäule auch nur eingeschränkt miteinander verglichen werden, da man an der Tasmanschwelle Sedimentoberflächenproben erst ab 1634 m genommen hat und am Campbell Plateau Proben ab 562 m vorhanden sind. Die oberen Bereiche (ab 562 m bis ca. 1300 m) des Campbell Plateaus sind Hochproduktionsbereiche, die die höchsten Individuenzahlen pro 10 cm**3 Sediment und die höchste Artenvielfalt aufweisen. Am Südwesthang des Campbell Plateaus läßt sich eine Abfolge der verschiedenen Foraminiferenvergesellschaftungen bis hinunter in das Emerald Becken nachweisen. An der Tasmanschwelle selbst läßt sich keine ausgeprägte Hochproduktionszone erkennen. Generell gibt es hier weniger Arten und weniger Individuen pro 10 cm**3 Sediment als am Cambell Plateau. Das Emerald Becken, als tiefster Bereich des Untersuchungsgebietes und als echtes Hungergebiet, nimmt eine Sonderrolle ein.

(Table 1) Abundance of tunicate spicules along the Great Barrier Reef-Queensland Plateau transect

The abundance patterns of tunicate spicules are documented for the Pliocene-Pleistocene sediments at seven sites along the Great Barrier Reef-Queensland Plateau transect. The spatial distribution pattern indicates that tunicate spicules were limited to waters shallower than 900 m. The occurrences of tunicate spicules at Sites 822 and 823 that are deeper than 900 m are ascribed to downslope transport, and their distribution patterns can be used to monitor downslope transport processes. The first common occurrence of tunicate spicules at Sites 822 and 823 around 1.6 Ma may suggest the initiation of the central Great Barrier Reef at this time. The morphology of tunicate spicules varies greatly and appears to be gradational among different forms. Older tunicate assemblages are less diverse than those in younger sediments, presumably because of diagenesis. Tunicate spicules do not appear to be a promising biostratigraphic tool for the Pliocene-Pleistocene.

Late Miocene and Pliocene dinoflagellate cysts, acritarchs and terrestrial palynomorphs from ODP Hole 642B, Vøring Plateau, Norwegian Sea

The globally warm climate of the early Pliocene gradually cooled from 4 million years ago, synchronous with decreasing atmospheric CO2 concentrations. In contrast, palaeoceanographic records indicate that the Nordic Seas cooled during the earliest Pliocene, before global cooling. However, a lack of knowledge regarding the precise timing of Nordic Seas cooling has limited our understanding of the governing mechanisms. Here, using marine palynology, we show that cooling in the Nordic Seas was coincident with the first trans-Arctic migration of cool-water Pacific mollusks around 4.5 million years ago, and followed by the development of a modern-like Nordic Seas surface circulation. Nordic Seas cooling precedes global cooling by 500,000 years; as such, we propose that reconfiguration of the Bering Strait and Central American Seaway triggered the development of a modern circulation in the Nordic Seas, which is essential for North Atlantic Deep Water formation and a precursor for more widespread Greenland glaciation in the late Pliocene.