ABSTRACT Increasing ocean and air temperatures have contributed to the removal of floating ice shelves from several Greenland outlet glaciers; however, the specific contribution of these external forcings remains poorly understood. Here we use atmospheric, oceanographic and glaciological time series data from the ice shelf of Petermann Gletscher, NW Greenland to quantify the forcing of the ocean and atmosphere on the ice shelf at a site ~16 km from the grounding line within a large sub-ice-shelf channel. Basal melt rates here indicate a strong seasonality, rising from a winter mean of 2 m a −1 to a maximum of 80 m a −1 during the summer melt season. This increase in basal melt rates confirms the direct link between summer atmospheric warming around Greenland and enhanced ocean-forced melting of its remaining ice shelves. We attribute this enhanced melting to increased discharge of subglacial runoff into the ocean at the grounding line, which strengthens under-ice currents and drives a greater ocean heat flux toward the ice base.
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This content will become publicly available on December 1, 2024
Pyroxenite–harzburgite sequences in the Dazhuqu ophiolite (Southern Tibet) formed through hydrous melt infiltration and melt–peridotite reaction
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Abstract Melt inclusions with large, positive Sr anomalies have been described in multiple tectonic settings, and the origins of this unusual geochemical feature are debated. Three origins have been proposed, all involving plagioclase as the source of the elevated Sr: (i) direct assimilation of plagioclase‐rich lithologies, (ii) recycled lower oceanic gabbro in the mantle source, and (iii) shallow‐level diffusive interaction between present day lower oceanic crust (i.e., plagioclase‐bearing lithologies) and the percolating melt. A “ghost plagioclase” signature (i.e., a large, positive Sr anomaly without associated high Al2O3) is present in melt inclusions from Mauna Loa. We present new87Sr/86Sr measurements of individual olivine‐hosted melt inclusions from three Hawaiian volcanoes, Mauna Loa, Loihi, and Koolau. The data set includes a Mauna Loa melt inclusion with the highest reported Sr anomaly (or highest (Sr/Ce)N, which is 7.2) for Hawai'i. All melt inclusions have87Sr/86Sr values within the range reported previously for the lavas from each volcano. Critically, the87Sr/86Sr of the high (Sr/Ce)Nmelt inclusion lies within the narrow range of87Sr/86Sr for Mauna Loa melts that lack high (Sr/Ce)Nsignatures. Therefore, to explain the high (Sr/Ce)Nratio of the ghost plagioclase signature using an ancient recycled gabbro, the gabbro‐infused mantle source would have had to evolve, by chance, to have the same87Sr/86Sr as the source of the Mauna Loa melts that lack a recycled gabbro (ghost plagioclase) signature. Alternatively, shallow‐level diffusive interactions between Mauna Loa plagioclase‐rich cumulates and a percolating mantle‐derived melt provides a simpler explanation for the presence of the high (Sr/Ce)NMauna Loa melts.
