Abstract: We determined the δ15N and δ13C values of individual amino acids (AAs) isolated from chick blood of 4 penguin species that forage in different oceanic regions (from the subtropics of the Indian Ocean to Antarctica) to test if: (1) the δ15N values of phenylalanine (δ15N phe) revealed different foraging areas among the species; (2) the difference between glutamic acid and phenylalanine δ15N values (Δδ15Nglu-phe) accurately predicted trophic levels; and (3) the δ13C value of AAs could resolve species foraging locations, similar to bulk δ13C values. The δ13C values of all AAs decreased with latitude, were positively correlated with bulk δ13C data, and, therefore, tracked the isotopic baseline. However, we were not able to discern additional ecological information from these δ13C values. In contrast, the δ15N values of AAs distinguished the isotopic value of the nitrogen at the base of the food web from the trophic level of the consumer, providing new insight for the study of the trophic ecology of seabirds. The difference in the bulk δ15N values of northern and southern rockhopper penguins Eudyptes chrysocome ssp. was due to both a difference in their foraging location (different δ15N phe) and their trophic levels (different Δδ15Nglu-phe). The δ15N phe values of king Aptenodytes patagonicus and Adélie penguins Pygoscelis adeliae were higher than those of rockhoppers, which could reflect a foraging on mesopelagic prey for king penguins and, in the highly productive Antarctic shelf waters, for Adelie penguins. The Δδ15Nglu-phe accurately reflected the relative trophic level of penguins, but further work is required to determine the trophic enrichment factors for compound-specific isotope analysis.

Abstract: We describe coordinated observations made on 14 July 2001 simultaneously in the midaltitude cusp by Cluster and at the cusp's ionospheric magnetic footprint by Super Dual Auroral Radar Network (SuperDARN) and Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) during a period of three successive solar wind dynamic pressure pulses. In association with each of these pulses, Cluster observes plasma injections while auroral images from the IMAGE spacecraft show enhanced precipitation in the cusp. Following these plasma injections, channels of fast convection flows are observed in the ionosphere by the SuperDARN radars. On the basis of the spatial and temporal relationships between these various signatures, we analyze the response of the dayside magnetosphere and ionosphere to the pressure pulses as follows: (1) the solar wind dynamic pressure pulses are the drivers of plasma injections from the magnetosheath into the cusp; (2) the ionospheric convection bursts start shortly after the auroral intensifications and their duration is much longer (10 min versus 4–6 min for the auroral intensifications); (3) the convection bursts occur on the poleward side of the cusp precipitation; and (4) the Alfvén waves that are responsible of the transmission of the magnetic stress from the reconnection site to the ionosphere are strongly reflected in the upper ionosphere. This, in addition to possible parallel potential drops, may explain the imperfect mapping of the magnetospheric electric field into the ionosphere during the injections. These observations demonstrate that the convection bursts are “fossil” signatures of the compression–injection process, which is also a signature of reconnection at the dayside magnetopause driven by the interplanetary magnetic field alone.

Abstract: We demonstrate the effect of an ecosystem differentiated insulation by snow on the soil thermal regime and on the terrestrial soil carbon distribution in the pan-Arctic area. This is done by means of a sensitivity study performed with the land surface model ORCHIDEE, which furthermore provides a first quantification of this effect. Based on field campaigns reporting higher thermal conductivities and densities for the tundra snowpack than for taiga snow, two distributions of near-equilibrium soil carbon stocks are computed, one relying on uniform snow thermal properties and the other using ecosystem-differentiated snow thermal properties. Those modeled distributions strongly depend on soil temperature through decomposition processes. Considering higher insulation by snow in taiga areas induces warmer soil temperatures by up to 12 K in winter at 50 cm depth. This warmer soil signal persists over summer with a temperature difference of up to 4 K at 50 cm depth, especially in areas exhibiting a thick, enduring snow cover. These thermal changes have implications on the modeled soil carbon stocks, which are reduced by 8% in the pan-Arctic continental area when the vegetation-induced variations of snow thermal properties are accounted for. This is the result of diverse and spatially heterogeneous ecosystem processes: where higher soil temperatures lift nitrogen limitation on plant productivity, tree plant functional types thrive whereas light limitation and enhanced water stress are the new constrains on lower vegetation, resulting in a reduced net productivity at the pan-Arctic scale. Concomitantly, higher soil temperatures yield increased respiration rates (+22% over the study area) and result in reduced permafrost extent and deeper active layers which expose greater volumes of soil to microbial decomposition. The three effects combine to produce lower soil carbon stocks in the pan-Arctic terrestrial area. Our study highlights the role of snow in combination with vegetation in shaping the distribution of soil carbon and permafrost at high latitudes.

Abstract: We demonstrate a clear relation between the vigor of an explosive eruption and inferred pressure change in a magma chamber feeding the eruption, based on near-field records of continuous GPS and ground tilt observations. The explosive phreatomagmatic VEI4 eruption of the subglacial Grímsvötn volcano in Iceland, 21-28 May 2011, produced initial plume reaching about 20 km height. Magma feeding the eruption drained from a shallow magma chamber under the Grímsvötn caldera. A continuous GPS site on the caldera rim sampling data at 5 Hz has allowed the reconstruction of the history of the pressure drop in this magma chamber. The pressure drop started at a fast rate about an hour prior to the eruption while a feeder dike formed. The pressure drop continued throughout the eruption, but decayed exponentially. These observations are compared to measurements of plume height, based on C-band radar located 257 km from the volcano and a mobile X-band weather radar placed at 75 km distance from the volcano after the eruption began. The radar further away has height resolution steps of 5 km at the location of Grímsvötn above 10 km elevation, and the one closer has resolution steps of 2-3 km. The measurements reveal plume heights often above 15 km between 19:21 on 21 May and 17:35 on 22 May (local time same as GMT). Peak elevation values of about 20-25 km for about 30 minute intervals were observed a few times between 21:25 on 21 May and 06:40 on 22 May. The initial strong plume was followed by pulsating but generally declining activity. After 04:55 UTC on 23 May the measurements indicate a fluctuating plume mainly below 10 km. In order to generate a continuous curve of plume elevation we average all available plume elevation information for each hour. The resulting plume height was then related to magma flow rate using an empirical formula from Larry Mastin et al. (2009). Integrating these flow rates yields an estimate of accumulated volume of eruptive products calculated as dry rock equivalent (DRE). Despite large uncertainties on the inferred magma flow rate, the shape of the curve of inferred accumulated DRE has is the same as the pressure drop curve. For this eruption, we see a clear link between the strength of an eruption plume and pressure change in the feeding magma chamber, measured by high rate ground deformation studies. Hence we can conclude that magma flow inferred from plume height correlates with the pressure change, which demonstrates the importance of real time high rate geodesy to foresee both onset and evolution of explosive eruptions and their plumes. The inferred volume change of the underlying magma chamber, modeled as a Mogi source, is about 5-8 times smaller than the suggested DRE volume from the integration of plume height, which we relate to the effects of magma compressibility.

Abstract: We construct a new seismic model for central and West Antarctica by jointly inverting Rayleigh wave phase and group velocities along with P wave receiver functions. Ambient noise tomography exploiting data from more than 200 seismic stations deployed over the past 18 years is used to construct Rayleigh wave phase and group velocity dispersion maps. Comparison between the ambient noise phase velocity maps with those constructed using teleseismic earthquakes confirms the accuracy of both results. These maps, together with P receiver function waveforms, are used to construct a new 3-D shear velocity (Vs) model for the crust and uppermost mantle using a Bayesian Monte Carlo algorithm. The new 3-D seismic model shows the dichotomy of the tectonically active West Antarctica (WANT) and the stable and ancient East Antarctica (EANT). In WANT, the model exhibits a slow uppermost mantle along the Transantarctic Mountains (TAMs) front, interpreted as the thermal effect from Cenozoic rifting. Beneath the southern TAMs, the slow uppermost mantle extends horizontally beneath the traditionally recognized EANT, hypothesized to be associated with lithospheric delamination. Thin crust and lithosphere observed along the Amundsen Sea coast and extending into the interior suggest involvement of these areas in Cenozoic rifting. EANT, with its relatively thick and cold crust and lithosphere marked by high Vs, displays a slower Vs anomaly beneath the Gamburtsev Subglacial Mountains in the uppermost mantle, which we hypothesize may be the signature of a compositionally anomalous body, perhaps remnant from a continental collision.