Search

Closure of the Central American Seaway (CAS) and hydrology of the Caribbean Sea triggered Northern Hemisphere Glaciation and played an important role in the Pliocene to modern‐day climate re‐establishing the deep and surface ocean currents. New data on Mn/Ca obtained with femtosecond laser ablation inductively coupled plasma mass spectrometry on well‐preserved tests of the epibenthic foraminifer Cibicidoides wuellerstorfi and infaunal C. mundulus contribute to the interpretation of paleoenvironmental conditions of the Caribbean Sea between 5.2 and 2.2 Ma (million years) across the closure of the CAS. Hydrothermal activity at the Lesser Antilles may be a primary source of Mn in the well‐oxygenated Plio‐Pleistocene Caribbean Sea. Incorporation of Mn in the benthic foraminifer shell carbonate is assumed to be affected by surface ocean nutrient cycling, and may hence be an indicator of paleoproductivity., Plain Language Summary: The closure of the Panama Isthmus caused the expansion of ice sheets in the Northern Hemisphere and changed the water current dynamics and climate in the Caribbean Sea since the Pliocene (∼5.3 million years ago). New Mn/Ca data measured using femtosecond laser ablation inductively coupled plasma mass spectrometry on the deep‐sea benthic foraminifer species Cibicidoides wuellerstorfi and Cibicidoides mundulus help us understand past environmental conditions of the Caribbean Sea prevailed between 5.2 and 2.2 million years ago. While manganese might be sourced from the surrounding hydrothermal vents, its incorporation in the foraminifer shell carbonate might be related to nutrient cycling and may indicate past biological productivity in the ocean., Key Points: Femtosecond‐laser ablation inductively coupled plasma mass spectrometry provides a new approach on distinguishing Mn of the ontogenetic shell calcite from Mn of the authigenic coatings. Ontogenetic Mn within the foraminifer shell calcite may result from the regional nutrient cycle. Mn in the deep eastern Caribbean Sea may mainly derive from hydrothermal sources along the Antilles Island Arc., MPIC, https://doi.org/10.17632/bps7nw7922.1

Calcareous foraminifer shells (tests) represent one of the most important archives for paleoenvironmental and paleoclimatic reconstruction. To develop a mechanistic understanding of the relationship between environmental parameters and proxy signals, knowledge of the fundamental processes operating during foraminiferal biomineralization is essential. Here, we apply microscopic and diffraction‐based methods to address the crystallographic and hierarchical structure of the test wall of different hyaline foraminifer species. Our results show that the tests are constructed from micrometer‐scale oriented mesocrystals built of nanometer‐scale entities. Based on these observations, we propose a mechanistic extension to the biomineralization model for hyaline foraminifers, centered on the formation and assembly of units of metastable carbonate phases to the final mesocrystal via a non‐classical particle attachment process, possibly facilitated by organic matter. This implies the presence of metastable precursors such as vaterite or amorphous calcium carbonate, along with phase transitions to calcite, which is relevant for the mechanistic understanding of proxy incorporation in the hyaline foraminifers., Plain Language Summary: Foraminifers are single celled marine organisms typically half a millimeter in size, which form shells made of calcium carbonate. During their life, the chemical composition of their shells records environmental conditions. By analyzing fossil shells, past conditions can be reconstructed to understand ancient oceans and climate change. To do that correctly, we need to know exactly how foraminifers form their shell. We find that foraminifers build micrometer‐sized mesocrystals which are made of smaller building blocks. This means that the smallest building blocks form first and assemble to form a larger grain, which is oriented in a specific direction. To align all the building blocks, it is possible that they are first unstable and undergo transformation on assembly, during which their composition may change. By understanding and quantifying this process, the composition of the final fossil shell may be understood, ultimately leading to more reliable reconstructions of past environmental change., Key Points: Hyaline foraminiferal shells are built of micrometer sized mesocrystalline units. Biomineralization likely includes the formation and assembly of nanoparticles. Nanometer sized units suggest non‐classical crystal growth., https://doi.org/10.17617/3.D7HN3I

International audience; Findings of oceanic volcanics and mafic cumulates originated from melts depleted in incompatible elements and enriched in silica and radiogenic Sr isotopes were attributed to an interaction between the mantle-derived melt(s) and the overlying hydrated lithosphere [1], but the proofs of the model yet remain elusive. Here we report results of experiments constraining mechanisms and rates of reactions between serpentinite and tholeiitic basalt at 0.5-1.0 GPa and 1200-1300°C. Our data show that the reaction proceeds via a multi-stage mechanism involving (i) transformation of serpentinite to harzburgite (with Fo92-95) containing pore fluid, (ii) partial melting and dissolution of the harzburgite with formation of interstitial hydrous melts (up to 62 wt% SiO2), and (iii) final assimilation of the harzburgite and formation of a hybrid basaltic melt with elevated 12-13 wt% MgO, ~500 ppm Cr and ~200 ppm Ni contents. Hybrid magmas produced by the assimilation of the serpentinized lithospheric mantle may be recognized by high Mg-numbers, Cr and Ni contents in minerals, an excess of SiO2 and H2O in the melts, and unusual Sr, O and He isotope compositions. Our experimental work provides convincing evidence that depleted MORB and orthopyroxene-rich cumulates depleted in incompatible elements can be routinely produced from "normal" mid-ocean ridge basaltic melts modified by reaction with hydrated lithospheric peridotite. The assimilation rate of serpentinized peridotite is controlled by silica diffusion in the reacting hydrous basaltic melt. Our study challenges traditional interpretation of the variations in chemical and isotopic composition of MORB and OIB in terms of deep mantle plume source heterogeneity and/or degree of partial melting. [1] Benoit M. et al., 1999. Nature 402, 514-518.

Here we present a new composite record from two well-dated speleothem records from two caves in Northern Morocco. The high-resolution record covers the last millennium allowing to detect multi-decadal to centennial periodicities. Over the industrial period, delta O-18 values of our speleothems are shown to be dominated by the main mode of decadal variability in the North Atlantic region: the North Atlantic Oscillation (NAO). Statistical analyses confirm the previously reported multi-decadal variability related to the influence of the Atlantic Multidecadal Oscillation (AMO) in the region. High power and persistent centennial-scale periodicities, similar to the Vries-Suess 200-year solar cycle, are observed as well. Indeed, comparison between solar activity reconstructions and our record confirms the in-phase relationship on centennial time-scales. Low delta O-18 values, and hence negative phases of NAO that bring precipitation towards the Western Mediterranean, are observed during well-known solar minima periods. The results are consistent with previous models which describe low irradiance as a trigger for southward shifts of precipitation-bearing westerlies during winter.

There is no end of studies charting the various influences on the work and thought of W. B. Yeats, or the importance which English and Irish writers, but also those from non-English speaking countries, had for him. Leaving aside the more exotic areas of Indian theosophy and Japanese theatre and concentrating on continental European countries, one will find an extensive literature on the traces of French symbolist poetry, German and Italian literature and philosophy, and even Scandinavian dram...

IN MEMORIAM A. Norman Jeffares 11 August 1920-1 June 2005

Carbonatites are common in continental settings but have, so far, only been identified at two oceanic localities, the Cape Verde and Canary Islands, both resting on > 130 Ma old, thick and cool oceanic crust. Here, we report on the first carbonatites observed in a hotter and younger mid-ocean setting, occuring as xenolithic fragments in nephelinitic tuffs at Salt Lake Crater (SLC), Oahu, Hawaii. The existence of Hawaiian carbonatites has been hypothesized before from various lines of evidence: (1) production of carbonatitic melts require carbonate in their source1; (2) diamond and SiC-bearing SLC xenoliths indicate mixed carbonatitic-silicic metasomatic agents in the sub-Hawaiian mantle 2 and (3) so do trace element compositions of Niihau 3 and SLC 4 post-erosional magmas. The potential role of mantle carbonatites on assimilation-fueled ascent of kimberlitic magmas has been the subject of two recent experimental studies 5,6. For experimental reasons, both these experiments failed to reproduce conditions prevailing at mantle depth by applying either too low pressure of 1 atm 5 or using Na2 CO3 as a substitute for Ca-Mg carbonate 5,6. Here, we show the CO2 producing reaction CaCO3+ Opx -> Cpx + CO2 “caught in the act” and in-situ in sub-Hawaiian carbonatite bearing xenoliths. We document the reaction by means of SEM and TEM analyses and discuss the carbonatites’ isotope composition for C, O and Sr with respect to their parentage.