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Background: The forelands of retreating glaciers are invaluable natural laboratories in which to explore the processes of primary succession. Numerous studies have been conducted on foreland chronosequences to identify temporal and spatial trends of the successional communities. This study focused on the spatio-temporal distribution of three woody plant species on the foreland of a retreating glacier in southern Iceland where historical observations provide precise age control of the moraines. To evaluate colonization and successional trends, we examined which species increase in abundance with time and tested the role of proximity to a seed source in colonization. Additionally, we quantified the rate at which biomass carbon is added to the landscape. Results: The density of stems of Betula pubescens increases with moraine age across the foreland chronosequence while the density of stems of both Salix lanata and Salix phylicifolia decreases. We found low statistical significance to the relationship between the density of B. pubescens and distance from a forested ridge nor did we find a relationship between the lengths of the stems and the moraine ages. Woody biomass increased fastest during early successional stages and reached a maximum of 28.5 g C m− 2 on the oldest moraine. Conclusions: Early colonization of moraines was controlled by environmental filters which favored both Salix species. Colonization by B. pubescens followed as environmental factors, e.g., favorable soil properties, improved. We found no conclusive evidence that proximity to a potential source of B. pubescens propagules was a significant factor in controlling colonization. The assumption that the abundance of individuals increased with time through later successional stages proved valid for B. pubescens, but not for either species of Salix. These findings are consistent with the classical spatial successional model of community homogenization. Thus, general successional processes at the landscape scale control the temporal dynamics of individual species. [ABSTRACT FROM AUTHOR]

In this paper we present a model for the growth of a maar-diatreme complex in a shallow marine environment. The Miocene-age Costa Giardini diatreme near Sortino, in the region of the Iblei Mountains of southern Sicily, has an outer tuff ring formed by the accumulation of debris flows and surge deposits during hydromagmatic eruptions. Vesicular lava clasts, accretionary lapilli and bombs in the older ejecta indicate that initial eruptions were of gas-rich magma. Abundant xenoliths in the upper, late-deposited beds of the ring suggest rapid magma ascent, and deepening of the eruptive vent is shown by the change in slope of the country rock. The interior of the diatreme contains nonbedded breccia composed of both volcanic and country rock clasts of variable size and amount. The occurrence of bedded hyaloclastite breccia in an isolated outcrop in the middle-lower part of the diatreme suggests subaqueous effusion at a low rate following the end of explosive activity. Intrusions of nonvesicular magma, forming plugs and dikes, occur on the western side of the diatreme, and at the margins, close to the contact between breccia deposits and country rock; they indicate involvement of volatile-poor magma, possibly during late stages of activity. We propose that initial hydromagmatic explosive activity occurred in a shallow marine environment and the ejecta created a rampart that isolated for a short time the inner crater from the surrounding marine environment. This allowed explosive activity to draw down the water table in the vicinity of the vent and caused deepening of the explosive center. A subsequent decrease in the effusion rate and cessation of explosive eruptions allowed the crater to refill with water, at which time the hyaloclastite was deposited. Emplacement of dikes and plugs occurred nonexplosively while the breccia sediment was mostly still soft and unconsolidated, locally forming peperites. The sheltered, low-energy lagoon filled with marine limestones mixed with volcaniclastic material eroded from the surrounding ramparts. Ultimately, lagoonal sediments accumulated in the crater until subsidence or erosion of the tuff ring caused a return to normal shallow marine conditions. [ABSTRACT FROM AUTHOR]

Examines the carbon isotope compositions of pedogenic calcite from paleosol formations spanning across the Triassic/Jurassic boundary to represent a rise in atmospheric carbon dioxide concentrations. Effects of the eruptions of the Central Atlantic Magmatic Province; Factors controlling carbon isotopic composition of soil carbonate; Stratigraphic units sampled; Calculation findings of atmospheric paleo-carbon dioxide.

Anomalous levels of iridium in sedimentary strata are associated with mass extinction events caused by impact events. In the case of the end-Triassic extinction event, the anomalies as well as the extinctions are linked to the eruption of the Central Atlantic Magmatic Province (CAMP) flood basalts. We report new data on concentrations of iridium in continental strata of the Fundy, Deerfield, Hartford and Newark basins, both above and below the oldest CAMP flows in these basins, that demonstrate that these anomalies are more common than previously known. We conclude that the enrichments were at least in some instances likely derived locally by concentration due to leaching directly from the lavas into sediments proximal to the CAMP flows due to post-eruptive hydrothermal activity. In other instances, the enrichments likely record the global fallout of aerosols and/or ash particles during the eruptions of the CAMP basalts. The common association of the highest levels of enrichment with organic matter suggests either redox control or stabilization by formation of organometallic complexes following post-eruptive redistribution. These findings demonstrate the importance of considering the distribution and magnitude of iridium anomalies in considering the source of the iridium and possible extinction mechanisms. [ABSTRACT FROM AUTHOR]

Introduction: Primary succession on glacial forelands is increasingly relevant as rapid glacial retreat is exposing growing land areas to plant colonization. We investigated temporal trends, controls, and outcomes in floral succession on a subarctic glacial foreland. Specifically, we examined changes in community composition (mosses, low shrubs, forbs, trees, and graminoids) over long-term (decadal) and short-term (< 10 years) scales and attempted to identify the underlying processes responsible for the observed successional patterns. Methods: The study area was the foreland of the Skaftafellsjӧkull, located in Vatnajӧkull National Park near the south coast of Iceland. We established nine transect lines at varying distances from the ice front representing surfaces of age ranging from less than one decade to over 100 years. Each transect consisted of five measurement stations of 1 m2 where we measured vegetative cover (VC), species richness (SR), and species density (SD) and calculated species evenness (SE). Measurements were made initially in 2007 and repeated at the same geographic coordinates in 2014. Results: VC increased with distance from the ice front from 16% to over 90%. SR and SD increased from the youngest pioneer community through a mid-successional stage corresponding to an age of over 60 but less than 100 years. Increased VC but declining SR, SD, and SE characterized the oldest (over 100 years) bryophyte-dominated surfaces. Species turnover, which involved forbs almost exclusively, increased moderately from early through mid-successional sites and declined on older sites. Comparison of the measurements made in 2014 to those made in 2007 demonstrates increased SR at mid-successional sites while SD remained relatively constant. Conclusion: At a small scale, colonization is controlled by local factors such as microtopography and aspect, particularly in proximity to the glacier. At the landscape level, changes in VC and community structure are controlled by time and nutrient availability. Low nutrient levels and limited site availability favor bryophyte dominance on the oldest surfaces. The greatest community-level changes observed over the 7-year interval were increases in surface cover by mosses and low shrubs, particularly in mid-successional and older sites. These changes suggest that the community on the oldest surfaces has not yet reached equilibrium. [ABSTRACT FROM AUTHOR]