Encrusting agglutinated foraminifera on indurated sediment at a hydrothermal venting area on the Juan de Fuca Ridge, northeast Pacific Ocean

Indurated sediment from the apron and basal areas of hydrothermal mounds in Middle Valley, on the Juan de Fuca Ridge, northeastern Pacific Ocean, is the site of attachment for a variety of encrusting agglutinated foraminifera. Hydrothermal venting in Middle Valley has created a unique environment which is characterized by elevated temperatures of substrate and bottom water, low pH values, and consolidated substrate. Foraminifera avoid areas in direct contact with the extremely high temperatures of hydrothermal vent fluids, but encrust the surrounding indurated sediment. Species diversity is low and population density varies on a small scale. One new genus, Ropostrum, with its type species R. amuleturn, is described from this locality. The substrate bears other micro-organisms of unknown affinity which are illustrated here. A comparison with other deep-sea consolidated substrates shows that encrusting agglutinated foraminifera prefer Fe-and Mn-rich surfaces

Benthic foraminiferal distribution at Middle Valley, Juan de Fuca Ridge, a northeast Pacific hydrothermal venting site

Fourteen benthic foraminiferal bearing surface samples collected from the Area of Active Venting (AAV) in Middle Valley at a depth of 2430 m at the northern end of Juan de Fuca Ridge, northeast Pacific Ocean, yielded 156 identifiable taxa. Sample sites were selected near active or recently active vents, where temperatures up to 274 °C have been measured. The sea floor beyond hydrothermal mounds is characterized by unaltered soft hemipelagic mud and is dominated by a calcareous foraminiferal assemblage which includes numerous allochthonous species derived from the shelf via turbidite flows into the valley. Within the AAV, agglutinated foraminifera dominate with proximity to hydrothermal vent activity. Species of the family Hormosinidae, subfamily Reophacinae, dominate in the hydrothermal habitat because of their success at colonization. Attached agglutinated foraminifera densely colonize the indurated sediment in close proximity to vent sites. However, like the macrofauna observed near hydrothermal vents, foraminifera do not venture into the extreme habitats where temperatures are greater than 20 °C. Where clam beds are found in association with active hydrogen sulphide venting, benthic foraminifera occur rarely. These beds occur in loose pyritic mud that is toxic to all but species (e.g. the clam Calyptogena) that co-exist symbiotically with sulphur-oxidizing bacteria. The sparse distribution of calcareous benthic foraminifera in the vent areas is caused by enhanced carbonate dissolution at pH values of 5.2. Low foraminiferal abundance and species diversity at the immediate site of active venting is attributed to rapid changes in phys

Long-term ecosystem level experiments at Toolik Lake, Alaska, and at Abisko, Northern Sweden: generalizations and differences in ecosystem and plant type responses to global change

Long-term ecosystem-level experiments, in which the environment is manipulated in a controlled manner, are important tools to predict the responses of ecosystem functioning and composition to future global change. We present the results of a meta-analysis performed on the results of long-term ecosystem-level experiments near Toolik Lake, Alaska, and Abisko, Sweden. We quantified aboveground biomass responses of different arctic and subarctic ecosystems to experimental fertilization, warming and shading. We not only analysed the general patterns but also the differences in responsiveness between sites and regions. Aboveground plant biomass showed a broad similarity of responses in both locations, and also showed some important differences. In both locations, aboveground plant biomass, particularly the biomass of deciduous and graminoid plants, responded most strongly to nutrient addition. The biomass of mosses and lichens decreased in both locations as the biomass of vascular plants increased. An important difference between the two regions was the smaller positive aboveground biomass response of deciduous shrubs in Abisko as compared with Toolik Lake. Whereas in Toolik Lake Betula nana increased its dominance and replaced many of the other plant types, in Abisko all vascular plant types increased in abundance without major shifts in relative abundance. The differences between the responses of the dominant vegetation types of the Toolik Lake region, i.e. tussock tundra systems, and that of the Abisko region, i.e. heath systems, may have important implications for ecosystem development under expected patterns of global change. However, there were also large site-specific differences within each region. Several potential mechanistic explanations for the differences between sites and regions are discussed. The response patterns show the need for analyses of joint data sets from many regions and sites, in order to uncover common responses to changes in climate across large arctic regions from regional or local responses

Long-term ecosystem level experiment at Toolik Lake, Alaska, and at Abisko, Northern Sweden: generalisations and differences in ecosystem and plant type responses to global change.

Long-term ecosystem-level experiments, in which the environment is manipulated in a controlled manner, are important tools to predict the responses of ecosystem functioning and composition to future global change. We present the results of a meta-analysis performed on the results of long-term ecosystem-level experiments near Toolik Lake, Alaska, and Abisko, Sweden. We quantified aboveground biomass responses of different arctic and subarctic ecosystems to experimental fertilization, warming and shading. We not only analysed the general patterns but also the differences in responsiveness between sites and regions. Aboveground plant biomass showed a broad similarity of responses in both locations, and also showed some important differences. In both locations, aboveground plant biomass, particularly the biomass of deciduous and graminoid plants, responded most strongly to nutrient addition. The biomass of mosses and lichens decreased in both locations as the biomass of vascular plants increased. An important difference between the two regions was the smaller positive aboveground biomass response of deciduous shrubs in Abisko as compared with Toolik Lake. Whereas in Toolik Lake Betula nana increased its dominance and replaced many of the other plant types, in Abisko all vascular plant types increased in abundance without major shifts in relative abundance. The differences between the responses of the dominant vegetation types of the Toolik Lake region, i.e. tussock tundra systems, and that of the Abisko region, i.e. heath systems, may have important implications for ecosystem development under expected patterns of global change. However, there were also large site-specific differences within each region. Several potential mechanistic explanations for the differences between sites and regions are discussed. The response patterns show the need for analyses of joint data sets from many regions and sites, in order to uncover common responses to changes in climate across large arctic regions from regional or local responses