Causal networks of phytoplankton diversity and biomass are modulated by environmental context

Untangling causal links and feedbacks among biodiversity, ecosystem functioning, and environmental factors is challenging due to their complex and context-dependent interactions (e.g., a nutrient-dependent relationship between diversity and biomass). Consequently, studies that only consider separable, unidirectional effects can produce divergent conclusions and equivocal ecological implications. To address this complexity, we use empirical dynamic modeling to assemble causal networks for 19 natural aquatic ecosystems (N24◦~N58◦) and quantified strengths of feedbacks among phytoplankton diversity, phytoplankton biomass, and environmental factors. Through a cross-system comparison, we identify macroecological patterns; in more diverse, oligotrophic ecosystems, biodiversity effects are more important than environmental effects (nutrients and temperature) as drivers of biomass. Furthermore, feedback strengths vary with productivity. In warm, productive systems, strong nitrate-mediated feedbacks usually prevail, whereas there are strong, phosphate-mediated feedbacks in cold, less productive systems. Our findings, based on recovered feedbacks, highlight the importance of a network view in future ecosystem management

The use of electron probe microanalysis and laser ablation-inductively coupled plasma-mass spectrometry for the investigation of 8th–14th century plant ash glasses from the Middle East

This is the first broad survey using major, minor and trace element analysis of 8th-15th AD plant ash glass from the Middle East across a 2000 mile area stretching from Egypt to northern Iran. This was part of the ancient Silk Road that extended from the Middle East, through central Asia to China. Up to now, some compositional distinctions have been identified for such glasses mainly using major and minor element oxides and radiogenic isotopes. Our new trace element characterisation is for glass found in selected cosmopolitan hubs, including one where there is archaeological evidence for primary glass making. It provides not only far clearer provenance definitions for regional centres of production, in the Levant, northern Syria and in Iraq and Iran, but also for sub-regional zones of production. This fingerprinting is provided by trace elements associated with the primary glass making raw materials used: ashed halophytic plants and sands. Even more surprising is a correlation between some of the sub-regional production hubs and the types of glass vessels with diagnostic decoration apparently manufactured in or near the cosmopolitan hubs where the glass was found such as colourless cut and engraved vessels (in Iraq and Iran) and trail-decorated vessels (in the Levant). This therefore provides evidence for centres of specialisation. Our trace element characterisation provides a new way of defining the Silk Road by characterising the glass that was traded or exchanged along it. Taken together this data provides a new decentralised model for ancient glass production

Anoxia begets anoxia: a positive feedback to the deoxygenation of temperate lakes

Declining oxygen concentrations in the deep waters of lakes worldwide pose a pressing environmental and societal challenge. Existing theory suggests that low deep-water dissolved oxygen (DO) concentrations could trigger a positive feedback through which anoxia (i.e., very low DO) during a given summer begets increasingly severe occurrences of anoxia in following summers. Specifically, anoxic conditions can promote nutrient release from sediments, thereby stimulating phytoplankton growth, and subsequent phytoplankton decomposition can fuel heterotrophic respiration, resulting in increased spatial extent and duration of anoxia. However, while the individual relationships in this feedback are well established, to our knowledge, there has not been a systematic analysis within or across lakes that simultaneously demonstrates all of the mechanisms necessary to produce a positive feedback that reinforces anoxia. Here, we compiled data from 656 widespread temperate lakes and reservoirs to analyze the proposed anoxia begets anoxia feedback. Lakes in the dataset span a broad range of surface area (1–126,909 ha), maximum depth (6–370 m), and morphometry, with a median time-series duration of 30 years at each lake. Using linear mixed models, we found support for each of the positive feedback relationships between anoxia, phosphorus concentrations, chlorophyll a concentrations, and oxygen demand across the 656-lake dataset. Likewise, we found further support for these relationships by analyzing time-series data from individual lakes. Our results indicate that the strength of these feedback relationships may vary with lake-specific characteristics: For example, we found that surface phosphorus concentrations were more positively associated with chlorophyll a in high-phosphorus lakes, and oxygen demand had a stronger influence on the extent of anoxia in deep lakes. Taken together, these results support the existence of a positive feedback that could magnify the effects of climate change and other anthropogenic pressures driving the development of anoxia in lakes around the world

Post-collisional tectonomagmatic evolution in the northern Arabian–Nubian Shield: time constraints from ion-probe U–Pb dating of zircon

<p>Ion-probe U–Pb dating of plutonic rocks from the northern Arabian–Nubian Shield in Sinai and southern Israel constrains the timing of late East African batholithic post-collisional calc-alkaline (CA2) magmatism and within-plate alkaline to peralkaline (AL) magmatism to <em>c</em>. 635–590 Ma and <em>c</em>. 608–580 Ma, respectively. The earliest dated CA2 rocks are slightly deformed to undeformed, indicating that penetrative deformation ceased by <em>c</em>. 630 Ma. Within the CA2 suite a change from mafic to felsic magmatism is manifested in most of the region, peaking in a voluminous pulse of granodiorite to granite intrusion at 610–600 Ma. The AL magmatism started contemporaneously with the peak in CA2 felsic activity at <em>c</em>. 608 Ma and lasted until 580 Ma. It includes mostly alkaline and peralkaline granites, probably representing variable degrees of differentiation of similar parental magmas. Thus CA2 and AL granites do not represent different tectonic settings, but coeval derivation from variable sources during crustal extension. The majority of rocks dated in this study show minor to non-existent zircon inheritance and thus indicate very minor interaction with previously formed felsic crust. The rare zircon xenocrysts span a typical East African age range (900–607 Ma) and confirm the absence of older crustal components in the juvenile Arabian–Nubian Shield. </p

Nd-Sr-Hf-O isotope provinciality in the northernmost Arabian-Nubian Shield: implications for crustal evolution

International audienceMulti-isotope study including whole-rock Nd-Sr, single zircon Hf, and SIMS delta(18)O analyses of zircons sheds light on magma sources in the northernmost Arabian-Nubian Shield (ANS) during similar to 820-570 Ma. Reconnaissance initial Nd and Sr isotope data for the older rocks (similar to 820-740 Ma) reaffirms previous estimates that early crustal evolution in this part of the shield involved some crustal contamination by pre-ANS material. Prominent isotope provinciality is displayed by post-collisional calc-alkaline and alkaline igneous rocks of similar to 635-570 Ma across a NW-SE transect across basement of the Sinai Peninsula (Egypt) and southern Israel. Silicic rocks of the NW-region are characterized by lower epsilon Nd(T)-epsilon Hf(T) and higher Sr(i) and delta(18)O compared with rocks of the SE-region, and the transition between the regions is gradual. Within each region isotope ratios are independent of the extent of magma fractionation, and zircon cores and rims yield similar delta(18)O values. Comparison with southern segments of the ANS shows that the source for most similar to 635-570 Ma rocks can be modeled as the isotopically aged lower-intermediate crust in the ANS core (SE-region) and its northern, more contaminated ANS margins (NW-region). Nevertheless, Nd-Sr isotope enrichment of the lithospheric mantle is indicated by some basic magmas of the NW-region displaying the most enriched Nd-Sr isotope compositions. Comparison of Nd and Hf depleted mantle model ages for rocks of the SE-region may indicate that crustal formation events in the ANS geographical core took place at 1.1-1.2 Ga and were followed by crustal differentiation starting at similar to 0.9 Ga

Tectonometamorphic evolution of the Areskutan Nappe-Caledonian history revealed by SIMS U-Pb zircon geochronology

Secondary ionization mass spectrometry (SIMS) U–Pb dating of zircons from the Åreskutan Nappe in the central part of the Seve Nappe Complex of western central Jämtland provides new constraints on the timing of granulite–amphibolite-facies metamorphism and tectonic stacking of the nappe during the Caledonian orogeny. Peak-temperature metamorphism in garnet migmatites is constrained to c. 442 ± 4 Ma, very similar to the ages of leucogranites at 442 ± 3 and 441 ± 4 Ma. Within a migmatitic amphibolite, felsic segregations crystallized at 436 ± 2 Ma. Pegmatites, cross-cutting the dominant Caledonian foliation in the Nappe, yield 428 ± 4 and 430 ± 3 Ma ages. The detrital zircon cores in the migmatites and leucogranites provide evidence of Late Palaeoproterozoic, Mesoproterozoic to Early Neoproterozoic source terranes for the metasedimentary rocks. The formation of the ductile and hot Seve migmatites, with their inverted metamorphism and thinning towards the hinterland, can be explained by an extrusion model in which the allochthon stayed ductile for a period of at least 10 million years during cooling from peak-temperature metamorphism early in the Silurian. In our model, Baltica–Laurentia collision occurred in the Late Ordovician–earliest Silurian, with emplacement of the nappes far on to the Baltoscandian platform during the Silurian and early Devonian, Scandian Orogeny lasting until c. 390 Ma

88 Sr/ 86 Sr fractionation and calcite accumulation rate in the Sea of Galilee

This study used the Sea of Galilee (Lake Kinneret, northern Israel) as a “natural laboratory” to investigate the fractionation of the stable Sr isotope ratio (88Sr/86Sr) during precipitation of inorganic (primary) calcite from the lake's water. It was found that the absolute value of the 88Sr/86Sr fractionation factor, Δ88/86Sr, increases as a function of calcite accumulation rate (Δ88/86Sr [‰] = −0.05 to 0.042·log(R) [μmol·m−2·d−1], where R is the accumulation rate). Furthermore, the 87Sr/86Sr and 88Sr/86Sr ratios in the freshwater and brines that enter the lake were used to calculate the contributions of these sources to the lake Sr budget. The 87Sr/86Sr and 88Sr/86Sr ratios were measured in primary calcite, aragonite shells of live Melanopsis, lake water and various water sources to the lake. While the lake's 87Sr/86Sr ratios are determined by the mixture of freshwater of the Jordan River and saline springs, the 88Sr/86Sr ratios of the lake reflect a more complex mass balance that includes the effect of isotopic fractionation associated with the precipitation of primary calcite. Data analysis suggests that long-term accumulation of inorganic calcite depleted in the heavy isotope 88Sr, results in an increase of the δ88/86Sr value of the lake water by 0.05‰. In contrast to the primary inorganic calcite, biogenic aragonite of the Melanopsis shells show a rather constant 88Sr/86Sr water-CaCO3 fractionation of Δ88/86Sr = −0.21‰. Similar Δ88/86Sr values were reported for the precipitation of coralline and inorganic aragonite from seawater and the precipitation of inorganic calcite from various continental waters. The Δ88/86Sr value of inorganic calcite is modulated by the rate of carbonate precipitation, as noted above and shown by precipitation experiments. Massive precipitation of primary calcite with a wide spread of accumulation rates occurs during the spring phytoplankton bloom in Lake Kinneret. The bloom dictates the degree of calcite saturation in the lake and hence the stable Sr isotopic composition of the precipitating calcite. The correlation between Δ88Sr/86Sr and the calcite accumulation rate can be therefore used as a tool to reconstruct environmental and ecological variations in the historical lake by analyzing the 88Sr/86Sr ratio in the primary CaCO3 recovered from the lake's sedimentary archives

Provenance of Neoproterozoic sediments in the Särv nappes (Middle Allochthon) of the Scandinavian Caledonides: LA-ICP-MS and SIMS U-Pb dating of detrital zircons

We present U-Pb age data for detrital zircons from dike-intruded Neoproterozoic sedimentary rocks of the Caledonian Middle Allochthon in central Sweden and Norway. Detrital zircons from 11 samples from the Särv, Sætra and upper Leksdal nappes (informally referred to as the Särv nappes) are clustered within ca. 0.9-1.75. Ga, but display a bimodal distribution with major ca. 1.45-1.75. Ga and ca. 0.9-1.2. Ga components. An apparent increase of younger (0.9-1.2. Ga) components to the northwest reflects varying source terranes. Detrital zircons from an additional sample from the lower part of the Leksdal Nappe, of uncertain affiliation to the Särv has a prominent 1.75-1.85. Ga component supporting previous suggestions that this part of the nappe belonged to a more proximal basin. Comparison of the Särv age probability patterns with data from basement windows and basement slices within the Middle Allochthon in central Sweden and Norway supports the derivation of the sediments from the attenuated Baltican continental crust on which they were presumably deposited. Similar comparisons suggest that derivation from the southern segment of the Fennoscandian Shield or from eastern segments of Laurentia is less likely, mostly because they include also older components.We infer that the ca. 200. km wide belt of attenuated Baltican continental crust included northern extensions of Mesoproterozoic to early Neoproterozoic terranes exposed in the southern part of the Fennoscandian Shield and the easternmost part of Laurentia, which at ca. 900. Ma were still adjacent. Pre-1.75. Ga terranes of the Fennoscandian Shield were probably isolated from the Särv distal basin(s) by intra-cratonic basins and uplifted margins associated with early development of this extended continental crust. The significantly older ages in the lower part of the Leksdal Nappe and its inferred more proximal position support this model. The proposed northern extension of Mesoproterozoic-early Neoproterozoic terranes can explain in a simpler way the occurrence of such detritus in many Caledonide-Appalachian allochthons exposed at the margins of the North Atlantic, with no need to infer large displacement along the axis of the Caledonide Orogen or to postulate selective transport of Grenville-age material from the south over large distances. One of our Särv samples located at the Norwegian coast revealed Caledonian reworking at ca. 395. Ma. This age agrees with ages of late-tectonic amphibolite-facies metamorphism and pegmatite intrusion recorded in this part of the Caledonides

Post-collisional magmatism in the central East African Orogen: the Maevarano Suite of north Madagascar

Late tectonic, post-collisional granite suites are a feature of many parts of the Late Neoproterozoic to Cambrian East African Orogen (EAO), where they are generally attributed to late extensional collapse of the orogen, accompanied by high heat flow and asthenospheric uprise. The Maevarano Suite comprises voluminous plutons which were emplaced in some of the tectonostratigraphic terranes of northern Madagascar, in the central part of the EAO, following collision and assembly during a major orogeny at ca. 550 Ma. The suite comprises three main magmatic phases: a minor early phase of foliated gabbros, quartz diorites, and granodiorites; a main phase of large batholiths of porphyritic granitoids and charnockites; and a late phase of small-scale plutons and sheets of monzonite, syenite, leucogranite and microgranite. The main phase intrusions tend to be massive, but with variably foliated margins. New U–Pb SHRIMP zircon data show that the whole suite was emplaced between ca. 537 and 522 Ma. Geochemically, all the rocks of the suite are enriched in the LILE, especially K, and the LREE, but are relatively depleted in Nb, Ta and the HREE. These characteristics are typical of post-collisional granitoids in the EAO and many other orogenic belts. It is proposed that the Maevarano Suite magmas were derived by melting of sub-continental lithospheric mantle that had been enriched in the LILE during earlier subduction events. The melting occurred during lithospheric delamination, which was associated with extensional collapse of the East African Orogen