Glacial Ice Age Shapes Microbiome Composition in a Receding Southern European Glacier

Glaciers and their microbiomes are exceptional witnesses of the environmental conditions from remote times. Climate change is threatening mountain glaciers, and especially those found in southern Europe, such as the Monte Perdido Glacier (northern Spain, Central Pyrenees). This study focuses on the reconstruction of the history of microbial communities over time. The microorganisms that inhabit the Monte Perdido Glacier were identified using high-throughput sequencing, and the microbial communities were compared along an altitudinal transect covering most of the preserved ice sequence in the glacier. The results showed that the glacial ice age gradient did shape the diversity of microbial populations, which presented large differences throughout the last 2000 years. Variations in microbial community diversity were influenced by glacial conditions over time (nutrient concentration, chemical composition, and ice age). Some groups were exclusively identified in the oldest samples as the bacterial phyla Fusobacteria and Calditrichaeota, or the eukaryotic class Rhodophyceae. Among groups only found in modern samples, the green sulfur bacteria (phylum Chlorobi) stood out, as well as the bacterial phylum Gemmatimonadetes and the eukaryotic class Tubulinea. A patent impact of human contamination was also observed on the glacier microbiome. The oldest samples, corresponding to the Roman Empire times, were influenced by the beginning of mining exploitation in the Pyrenean area, with the presence of metal-tolerant microorganisms. The most recent samples comprise 600-year-old ancient ice in which current communities are living.

Does a difference in ice sheets between Marine Isotope Stages 3 and 5a affect the duration of stadials? Implications from hosing experiments

Glacial periods undergo frequent climate shifts between warm interstadials and cold stadials on a millennial timescale. Recent studies show that the duration of these climate modes varies with the background climate; a colder background climate and lower CO2 generally result in a shorter interstadial and a longer stadial through its impact on the Atlantic Meridional Overturning Circulation (AMOC). However, the duration of stadials is shorter during Marine Isotope Stage 3 (MIS3) than during MIS5, despite the colder climate in MIS3, suggesting potential control from other climate factors on the duration of stadials. In this study, we investigate the role of glacial ice sheets. For this purpose, freshwater hosing experiments are conducted with an atmosphere–ocean general circulation model under MIS5a and MIS3 boundary conditions, as well as MIS3 boundary conditions with MIS5a ice sheets. The impact of ice sheet differences on the duration of the stadials is evaluated by comparing recovery times of the AMOC after the freshwater forcing is stopped. These experiments show a slightly shorter recovery time of the AMOC during MIS3 compared with MIS5a, which is consistent with ice core data. We find that larger glacial ice sheets in MIS3 shorten the recovery time. Sensitivity experiments show that stronger surface winds over the North Atlantic shorten the recovery time by increasing the surface salinity and decreasing the sea ice amount in the deepwater formation region, which sets favorable conditions for oceanic convection. In contrast, we also find that surface cooling by larger ice sheets tends to increase the recovery time of the AMOC by increasing the sea ice thickness over the deepwater formation region. Thus, this study suggests that the larger ice sheet during MIS3 compared with MIS5a could have contributed to the shortening of stadials in MIS3, despite the climate being colder than that of MIS5a, because surface wind plays a larger role.

Viscosity in Matter, Life and Sociality: The Case of Glacial Ice

A tension between solidity and fluidity tends to divide the sciences and the humanities along lines that define what is hard and soft in knowledge. This divide relates to similar dichotomies, between exteriority and interiority, material and spiritual, homogeneity and heterogeneity, matter and form, all of which have been partially mapped in Western thinking onto a traditional separation between earth and sky. Yet particular forms of knowledge sit uneasily within these tensions, a paradigmatic example of which is an understanding of solids as ‘viscous fluids’. This article explores the concept of viscosity, attending to how it has impacted on understandings of matter, as well as broader social and cultural issues. It does so, particularly, by looking into the scientific study of ice, a material that has historically been regarded as solidfluid, to argue that life and sociality remain possible only in so far as matter that is viscid allows solid and fluid states to mingle.

Introduction to the Principles of δ18O, δ13C, and 87Sr/86Sr in the Palaeosciences.

The stable isotopes of oxygen (O), carbon (C), strontium (Sr), hydrogen (H), and nitrogen (N) have all been utilised for great effect in palaeoclimate, palaeoecological and palaeobiological studies. Of these, O and C have been by far the most important and, in many types of study, their use has become routine in universities and research institutions around the world. Stable isotopes provide quantitative data about palaeotemperatures, metabolic rates, food webs, palaeosalinity, palaeoprecipitation and evaporation rates as well as glacial ice volumes, production and burial of organic carbon, and other processes related to palaeoclimatic/biological/ecological change. Except for Sr, all the previously mentioned isotopes (O, C, H, and N) directly record paleoclimatic, biological and palaeoecological processes. Conversely, Sr reflects the composition of rocks at the Earth's surface, and its values reflect on the climate indirectly as it is a proxy for global weathering rates and seafloor spreading. This review will only be focusing on three isotopes commonly deployed by palaeo-researchers: carbon, oxygen, and strontium.

The De Long Trough: defining the mineralogical signature of the East Siberian Ice Sheet

The Arctic's glacial history has classically been interpreted from marine records in terms of the fluctuations of the Eurasian and North American ice sheets. However, the existence, size, and timing of the East Siberian Ice Sheet (ESIS) remains highly uncertain. A recently discovered glacially scoured cross-shelf trough extending to the edge of the continental shelf north of the De Long Islands has provided additional evidence that glacial ice existed on parts of the East Siberian Sea (ESS) during previous glacial periods (MIS 6 and 4). This study concentrates on defining the mineralogical signature and dynamics of the ESIS. Sediment materials from the East Siberian shelf and slope were collected during the 2014 SWERUS-C3 expedition. The cores studied are 20-GC1 from the East Siberian shelf, 23-GC1 and 24-GC1 from the De Long Trough (DLT), and 29-GC1 from the southern Lomonosov Ridge (LR). Heavy mineral assemblages were used to identify prominent parent rocks in hinterland and other sediment source areas. The parent rocks areas include major eastern Siberian geological provinces such as the Omolon massif, the Chukotka Fold Belt, the Verkhoyansk Fold Belt, and possibly the Okhotsk–Chukotka Volcanic Belt. The primary riverine sources for the ESS sediments are the Indigirka and Kolyma rivers, which material then was glacially eroded and re-deposited in the DLT. The higher abundances of hornblendes in the heavy mineral assemblages may indicate ESS paleovalley of the Indigirka river as a major pathway of sediments, while the Kolyma river paleovalley pathway relates to a higher share of pyroxenes and epidote. Mineralogical signature in the DLT diamicts, consisting predominantly of amphiboles and pyroxenes with minor content of garnet and epidote, show clear delivery from the eastern sector of the ESIS. Although the physical properties of the DLT basal diamict closely resemble a pervasive diamict unit recovered across the southern LR, their source material is slightly different according to their heavy mineral content. Assemblages with elevated amphibole and garnet content, along with higher titanite and ilmenite content from core 29-GC1 from the southern LR emphasise the Verkhoyansk Fold Belt as a possible source. This suggests that glacial ice not only grew out from the East Siberian shelf, but also from the New Siberian Islands and westerly sources due to the dynamics in the ice flow and deposition. An increase in the iron oxides in the sediments overlying the diamicts relates to the deglaciation cycle of the ESIS when the central plateau, or at least the shoreline and river discharge region, were possibly free from ice, and the reworking as well as enrichment of iron oxides was possible. This indicates sea-ice rather than iceberg transport for the present distal shelf sediments.

Greenland Ice Sheet runoff reduced by meltwater refreezing in bare ice

The Greenland Ice Sheet’s contribution to global sea-level rise is accelerating1 due to increased melting of its bare-ice ablation zone2–6, but there is growing evidence that climate models overestimate runoff from this critical area of the ice sheet7–12. Current climate models assume all bare ice runoff escapes to the ocean, unlike snow covered areas where some fraction of runoff is retained and/or refrozen in porous firn13–15. Here we use in situ measurements and numerical modeling to reveal extensive retention and refreezing of liquid meltwater in bare glacial ice, explaining chronic runoff overestimation by climate models. From 2009–2018, refreezing of liquid meltwater in bare, porous glacial ice reduced meltwater runoff by 11–23 Gt a-1 in southwest Greenland alone, equivalent to 10–20% of annual meltwater production. This mass retention is commensurate with current estimates of climate model ice sheet meltwater runoff uncertainty, and may represent an overlooked buffer on projected runoff increases for the coming century16. Inclusion of bare-ice retention and refreezing processes in climate models therefore has immediate potential to improve forecasts of ice sheet runoff and its contribution to global sea-level rise.

Geophysical constraints on the properties of a subglacial lake in northwest Greenland

In this study, we report the results of an active-source seismology and ground-penetrating radar survey performed in northwestern Greenland at a site where the presence of a subglacial lake beneath the accumulation area has previously been proposed. Both seismic and radar results show a flat reflector approximately 830–845 m below the surface, with a seismic reflection coefficient of −0.43 ± 0.17, which is consistent with the acoustic impedance contrast between a layer of water and glacial ice. Additionally, in the seismic data we observe an intermittent lake bottom reflection arriving between 14–20 ms after the lake top reflection, corresponding to a lake depth of approximately 10–15 m. A strong coda following the lake top and lake bottom reflections is consistent with a package of lake bottom sediments although its thickness and material properties are uncertain. Finally, we use these results to conduct a first-order assessment of the lake origins using a one-dimensional thermal model and hydropotential modeling based on published surface and bed topography. Using these analyses, we narrow the lake origin hypotheses to either anomalously high geothermal flux or hypersalinity due to local ancient evaporite. Because the origins are still unclear, this site provides an intriguing opportunity for the first in situ sampling of a subglacial lake in Greenland, which could better constrain mechanisms of subglacial lake formation, evolution, and relative importance to glacial hydrology.