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Abstract Glaciated watersheds are regions of intense physical and chemical weathering. In order to gain new insight on subglacial weathering processes, we measured uranium and radium isotopes from a proglacial river draining the Greenland Ice Sheet (GrIS). Time series samples were collected from the spring to mid-summer, a time period during which subglacial drainage pathways are thought to transition from slow-inefficient (distributed) to fast-efficient (channelized) systems. The 228Ra/226Ra activity ratio of the dissolved load varied from 5.2 ± 0.9–16.9 ± 3.6, which was significantly higher than the 228Ra/226Ra ratio of a suspended sediment load sample of 2.1 ± 0.07 and crustal values of ~1. The high 228Ra/226Ra in the dissolved load relative to the source rock material is indicative of mineral surface weathering induced by rapid and continuous flushing of the subglacial drainage network during the course of the melt season and those prior. The 234U/238U ratio (δ234U) varied between 33 and 106‰ with a discharge-weighted mean of 67‰; the seasonal evolution of δ234U did not correlate to geochemical indicators of subglacial meltwater storage time. An experiment designed to measure changes in δ234U with increasing meltwater storage times found that δ234U in the dissolved phase decreased rapidly with increasing storage time. Similarly, samples collected along a transect moving downstream from the ice sheet terminus had decreasing δ234U values from 63 to 15‰ further indicating that with increased weathering, the δ234U of meltwater decreases. Coupled with the relatively low δ234U and high 228Ra/226Ra, U appears to be impacted by rapid chemical weathering of subglacial and suspended sediments. The Leverett River discharge weighted U concentration was 0.13 nM; if this system is considered representative of the broader GrIS, then the total dissolved U flux from the GrIS would be on the order of 6.4 × 104 mol/y. Using a similar set of assumptions, the dissolved 228Ra and 226Ra flux from the GrIS was ~1.1 × 1014 dpm/y and ~ 5.5 × 1013 dpm/y, respectively. These estimates suggest that the 226Ra flux to the ocean from the GrIS is globally significant and that the 228Ra flux in particular is larger than most river inputs.

A detailed record of late Pleistocene deglaciation followed by mid-Holocene ice shelf breakup and late Holocene re-growth is contained in continental shelf sediments in the northern Larsen area, northeast Antarctic Peninsula. The zero age of core tops is confirmed by new and published 210Pb profiles, and 70 accelerator mass spectrometer (AMS) 14C dates on bulk organic carbon define sedimentation rates of 7.6–92 cm/ka. The varied geology in the local ice drainage basins facilitates the use of ice-rafted debris (IRD) provenance in determining the presence or absence of ice shelves. All inshore cores contain an interval of non-local IRD in the post-glacial section, demonstrating widespread ice shelf breakup in the mid-Holocene. Both breakup and re-growth may have taken centuries and there are no widespread debris layers associated with breakup. Cores beyond and up to 30 km inside the historical ice shelf limit exhibit a varied IRD provenance throughout the Holocene, suggesting the maximum ice shelf limit may date only from the Little Ice Age. Benthic foraminiferal assemblages are related to water masses and position on the continental shelf and have been modified by taphonomic processes. Nevertheless we discern a deglaciation signal in Prince Gustav Channel of a calcareous spike in predominantly agglutinated assemblages, and this is repeated at the time of mid-Holocene ice shelf breakup. The inferred mid-Holocene warm period occurred later in the northern Larsen area than on the west coast of the Antarctic Peninsula.

Abstract Ocean circulation changes along the continental shelf of the Nordic and Barents Seas have been investigated in order to reconstruct regional changes in the inflow of Atlantic Water (AW) through the last 16,000 calibrated (cal) years (yr) B.P. We have selected five time-slices representing the late glacial (16,000–15,000 cal yr B.P.), the Bolling-Allerod warm interstadials (14,500–13,500 cal yr B.P.), the Younger Dryas cold stadial (12,500–11,500 cal yr B.P.), the early Holocene (9500–7500 cal yr B.P.) and the late Holocene (4000–2000 cal yr B.P.). Twelve previously published records of the distribution of benthic foraminifera faunas and ice-rafted debris have been compiled. The earliest sign of Atlantic Water inflow was recorded at the northern Iceland shelf at 16,000–15,000 cal yr B.P. The inflow of warm AW to the Nordic Seas shelf has been persistent since, but with variable strength and geographic pattern. An apparent zonal seesaw pattern in the strength of the Norwegian Atlantic Current (NwAC) and the Irminger Current (IC) during the late glacial, Bolling-Allerod and Younger Dryas periods was found. During the Holocene, no zonal differences in the inflows of NwAC and IC were found. A strong meridional gradient with warmer conditions at lower latitudes and relatively cold conditions at high northern latitudes existed.

Fast spherical harmonic synthesis (SHS) at multiple points based on the lumped coefficients approach is a very well-established technique. However, this method cannot be applied to SHS at irregular surfaces, as the points must be regularly spaced and refer to a regular surface such as the sphere or the ellipsoid of revolution. In this paper we present a MATLAB ? -based graphical user interface software for ultra-high degree (e.g. tens of thousands or even higher) SHS on grids at irregular surfaces, like the Earth surface. This software employs the highly efficient lumped coefficient approach for SHS at regular surfaces and the Taylor series expansions to continue the functionals to the irregular surfaces, e.g. the Earth surface. The generalized idea of continuing functionals using the Taylor series was presented by Hirt (2012) (J. Geod. 86, 729-744). We took advantage of the software GrafLab (Bucha and Janak, 2013. Comput. Geosci. 56, 186-196), which employs the lumped coefficients approach, and developed a new software isGrafLab (Irregular Surface GRAvity Field LABoratory). Compared to the commonly used "two loops" approach, the factor of increased computational speed can reach a value of several hundreds. isGrafLab allows accurate evaluation of 38 functionals of the geopotential on grids at irregular surfaces. High orders of the Taylor series can be used for the continuation. The new software offers all the other options available in GrafLab, such as the employment of three different approaches to compute the fully normalized associated Legendre functions, the graphical user interface or the possibility to depict data on a map. HighlightsA new MATLAB-based software for spherical harmonic synthesis is presented.Spherical harmonic synthesis is efficiently performed on grids at irregular surfaces.The program employs the lumped coefficients approach and Taylor series expansions.The program has been developed with a graphical user interface.

Bursts in species diversification are well documented among animals and plants, yet few studies have assessed recent adaptive radiations of eukaryotic microbes. Consequently, we examined the radiation of the most ecologically dominant group of endosymbiotic dinoflagellates found in reef-building corals, Symbiodinium Clade C, using nuclear ribosomal (ITS2), chloroplast (psbA(ncr)), and multilocus microsatellite genotyping. Through a hierarchical analysis of high-resolution genetic data, we assessed whether ecologically distinct Symbiodinium, differentiated by seemingly equivocal rDNA sequence differences, are independent species lineages. We also considered the role of host specificity in Symbiodinium speciation and the correspondence between endosymbiont diversification and Caribbean paleo-history. According to phylogenetic, biological, and ecological species concepts, Symbiodinium Clade C comprises many distinct species. Although regional factors contributed to population-genetic structuring of these lineages, Symbiodinium diversification was mainly driven by host specialization. By combining patterns of the endosymbiont's host specificity, water depth distribution, and phylogeography with paleo-historical signals of climate change, we inferred that present-day species diversity on Atlantic coral reefs stemmed mostly from a post-Miocene adaptive radiation. Host-generalist progenitors spread, specialized, and diversified during the ensuing epochs of prolonged global cooling and change in reef-faunal assemblages. Our evolutionary reconstruction thus suggests that Symbiodinium undergoes "boom and bust" phases in diversification and extinction during major climate shifts.

Semi-continuous, linear accumulations of poorly-sorted debris are present on the surface of the remnant Larsen-A Ice Shelf, Antarctic Peninsula. These accumulations form a complex of debris bands extending parallel to the front of the ice shelf for several kilometres. Landsat imagery shows that the debris bands originated as lateral moraines along the Nordenskjöld Coast. Almost 80% of clasts sampled from these debris accumulations have shape/roundness characteristics consistent with glacier transport in the zone of basal traction. Angular and very angular clasts account for 15% and 22% of clasts in the pebble- and cobble/boulder-sized fractions, respectively, and originated by rockfall from valley/nunatak sides, with subsequent passive glacier transportation. Lithological analysis indicates that the debris is derived locally from the Nordenskjöld Coast, Cape Fairweather region and interior of the Antarctic Peninsula. Episodic melt-out and resedimentation of this debris from the front of the ice shelf would deliver pulses of coarse-grained sediment to the sea floor. Therefore, coarse-grained debris can also be released along the calving margin of small polar ice shelves fringing mountainous terrain, and could potentially be confused with sediment deposited at the grounding line of Antarctic ice-shelves. Sedimentological criteria to differentiate between these environments are proposed in this paper.

AbstractThe genus Aladraco nom. nov. is described and discussed, along with two species recognized from coeval strata of the lower traditional middle Cambrian, A. schloppensis (Wurm) from the Tannenknock Formation of the Franconian Forest region, Germany, and A. ougnatensis sp. nov. from the Jbel Wawrmast Formation of the eastern Anti‐Atlas, Morocco. Aladraco was formerly known as Oxyprymna Kiderlen, a preoccupied generic name requiring renaming of the genus. The genus bears morphological characters such as the size, shape and external ornamentation of the conch which clearly indicate a systematic position in the class Hyolitha. A number of characters, such as a tripartition into an axial chamber and lateral acuminate processes, and the course of the apertural margin, differ considerably from those seen in the two orders Hyolithida and Orthothecida, and appear to indicate distinct differences in functional morphology. However, similarities of the morphological characters with the known representatives of the Hyolithida suggest that the species are derived from this systematic group and should be dealt with as a hitherto unrecognized distinct suborder and family, introduced as Aladracina subord. nov. and Aladracidae fam. nov.

Ferromanganese coatings have been found on glacial erratics in Lydonia Canyon, off the United States northeastern coast. The coatings, which are about 17 μm thick, consist of an outer manganese-rich layer which covers the top of the erratic, a middle transitional layer, and an internal iron-rich layer that encircles the entire surface of the erratic. Chemical analyses of the coatings, when compared with similar data on abyssal marine ferromanganese deposits, reveal comparable Mn/Fe ratios, higher P and Ti concentrations, and an order of magnitude less of Co, Ni, Cu, and most other metals. A comparison of the Lydonia Canyon coatings with desert varnishes reveals obvious chemical, mineralogical, and morphological differences.

Abstract This study introduces a practical methodology for modeling of self-healing microcapsules-based composites elasticity with experimental verification. The elastic modulus of the matrix material was determined using dynamic mechanical analysis (DMA). In addition, single-microcapsule micromanipulation compression was performed accompanied by 2D finite element modeling (FEM) to extract the elastic modulus of single-microcapsule. Detailed 3D FEMs were constructed to predict the effective elastic properties of the microcapsules-based composites. To define the material properties of these FEMs, both of the elastic moduli of the matrix and the microcapsules were used. Microstructures having packing arrangement of simple cubic (SC), body-centered cubic (BCC), face-centered cubic (FCC), and random-monodispersed (RM) microcapsules were investigated. The microcapsules size and shell wall thickness reflect the microstructural geometry at definite volume fractions. Dynamic mechanical analysis was performed to determine the elastic modulus of prepared composites containing 5, 10, and 20 vol% microcapsules. Finally, experimental verification was obtained by comparing the experimental work to the FEM results. Good agreement was achieved. It was found that the volume fraction and the packing arrangement of the microcapsules in the composite were the only parameters that affect the composite effective elastic modulus, while the size and shell thickness of the microcapsules are not effective.