Shallow upper mantle rheology and secular ice sheet fluctuations

n/

Mediterranean sapropels: a mere geological problem or a resource for the study of a changing planet?

Sapropels are sediments rich in organic carbon occurring cyclically in the Mediterranean marine records and whose origin has been matter of great debate during the last decades. While the first sapropels were found in eastern Mediterranean sediments from the Miocene period, in this paper we focus on the layers that were subsequently found in sediment cores of Pliocene to Quaternary age from the eastern Mediterranean mostly. Since the very beginning of the history of studies on sapropels, authors inferred that those lev- els, being interbedded as dark layers in more or less normal light “open marine” sediments, formed during short-lived but catastrophic alterations in Mediterranean oceanographic conditions, probably linked to broader climate changes. In this paper, the main hypotheses regarding the origin of those sediments are described and we highlight the importance of sapropel records for the study of climatic and oceanographic variability in the Mediterranean area in the context of global climate change

Impact of global SST gradients on the Mediterranean runoff changes across the Plio-Pleistocene transition

This work explores the impact of the development of global meridional and zonal sea surfacetemperature (SST) gradients on the Mediterranean runoff variability during the Plio-Pleistocene transition,about 3 Ma. Results show that total annual mean Pliocene Mediterranean runoff is about 40% larger thanduring the preindustrial period due to more increased extratropical specific humidity. As a consequenceof a weakened and extended Hadley cell, the Pliocene northwest Africa hydrological network producesa discharge 30 times larger than today. Our results support the conclusion that during the Pliocene, theMediterranean water deficit was reduced relative to today due to a larger river discharge. By means ofa stand-alone atmospheric general circulation model, we simulate the separate impact of extratropicaland equatorial SST cooling on the Mediterranean runoff. While cooling the equatorial SST does not implysignificant changes to the Pliocene Mediterranean hydrological budget, the extratropical SST coolingincreases the water deficit due to a decrease in precipitation and runoff. Consequently, river dischargefrom this area reduces to preindustrial levels. The main teleconnections acting upon the Mediterraneanarea today, i.e., the North Atlantic Oscillation during winter and the “monsoon-desert” mechanism duringsummer already have a large influence on the climate of our Pliocene simulations. Finally, our results alsosuggest that in a climate state significantly warmer than today, changes of the Hadley circulation couldpotentially lead to increased water resources in northwest Africa

Impact of Orbital Parameters and Greenhouse Gas on the Climate of MIS 7 and MIS 5 Glacial Inceptions

This work explores the impact of orbital parameters and greenhouse gas concentrations on the climate of marine isotope stage (MIS) 7 glacial inception and compares it to that of MIS 5. The authors use a coupled atmosphere-ocean general circulation model to simulate the mean climate state of six time slices at 115, 122, 125, 229, 236, and 239 kyr, representative of a climate evolution from interglacial to glacial inception conditions. The simulations are designed to separate the effects of orbital parameters from those of greenhouse gas (GHG). Their results show that, in all the time slices considered, MIS 7 boreal lands mean annual climate is colder than the MIS 5 one. This difference is explained at 70% by the impact of the MIS 7 GHG. While the impact of GHG over Northern Hemisphere is homogeneous, the difference in temperature between MIS 7 and MIS 5 due to orbital parameters differs regionally and is linked with the Arctic Oscillation. The perennial snow cover is larger in all the MIS 7 experiments compared to MIS 5, as a result of MIS 7 orbital parameters, strengthened by GHG. At regional scale, Eurasia exhibits the strongest response to MIS 7 cold climate with a perennial snow area 3 times larger than in MIS 5 experiments. This suggests that MIS 7 glacial inception is more favorable over this area than over North America. Furthermore, at 239 kyr, the perennial snow covers an area equivalent to that of MIS 5 glacial inception (115 kyr). The authors suggest that MIS 7 glacial inception is more extensive than MIS 5 glacial inception over the high latitudes

Influence of speed of sample processing on placental energetics and signalling pathways: implications for tissue collection.

INTRODUCTION: The placenta is metabolically highly active due to extensive endocrine and active transport functions. Hence, placental tissues soon become ischaemic after separation from the maternal blood supply. Ischaemia rapidly depletes intracellular ATP, and leads to activation of stress-response pathways aimed at reducing metabolic demands and conserving energy resources for vital functions. Therefore, this study aimed to elucidate the effects of ischaemia ex vivo as may occur during tissue collection on phosphorylation of placental proteins and kinases involved in growth and cell survival, and on mitochondrial complexes. METHODS: Eight term placentas obtained from normotensive non-laboured elective caesarean sections were kept at room-temperature and sampled at 10, 20, 30 and 45 min after delivery. Samples were analyzed by Western blotting. RESULTS: Between 10 and 45 min the survival signalling pathway intermediates, P-AKT, P-GSK3α and β, P-4E-BP1 and P-p70S6K were reduced by 30-65%. Stress signalling intermediates, P-eIF2α increased almost 3 fold after 45 min. However, other endoplasmic reticulum stress markers and the Heat Shock Proteins, HSP27, HSP70 and HSP90, did not change. Phosphorylation of AMPK, an energy sensor, was elevated 2 fold after 45 min. Contemporaneously, there was an ∼25% reduction in mitochondrial complex IV subunit I. DISCUSSION AND CONCLUSIONS: These results suggest that for placental signalling studies, samples should be taken and processed within 10 min of caesarean delivery to minimize the impact of ischaemia on protein phosphorylation

Modeling Northern Hemisphere ice-sheet distribution during MIS 5 and MIS 7 glacial inceptions

The present manuscript compares Marine Iso- tope Stage 5 (MIS 5, 125–115 kyr BP) and MIS 7 (236– 229 kyr BP) with the aim to investigate the origin of the difference in ice-sheet growth over the Northern Hemi- sphere high latitudes between these last two inceptions. Our approach combines a low resolution coupled atmosphere– ocean–sea-ice general circulation model and a 3-D thermo- mechanical ice-sheet model to simulate the state of the ice sheets associated with the inception climate states of MIS 5 and MIS 7. Our results show that external forcing (orbitals and GHG) and sea-ice albedo feedbacks are the main fac- tors responsible for the difference in the land-ice initial state between MIS 5 and MIS 7 and that our cold climate model bias impacts more during a cold inception, such as MIS 7, than during a warm inception, such as MIS 5. In addition, if proper ice-elevation and albedo feedbacks are not taken into consideration, the evolution towards glacial inception is hardly simulated, especially for MIS 7. Finally, results high- light that while simulated ice volumes for MIS 5 glacial in- ception almost fit with paleo-reconstructions, the lack of pre- cipitation over high latitudes, identified as a bias of our cli- mate model, does not allow for a proper simulation of MIS 7 glacial inception

SmartIX: A database indexing agent based on reinforcement learning

Configuring databases for efficient querying is a complex task, often carried out by a database administrator. Solving the problem of building indexes that truly optimize database access requires a substantial amount of database and domain knowledge, the lack of which often results in wasted space and memory for irrelevant indexes, possibly jeopardizing database performance for querying and certainly degrading performance for updating. In this paper, we develop the SMARTIX architecture to solve the problem of automatically indexing a database by using reinforcement learning to optimize queries by indexing data throughout the lifetime of a database. We train and evaluate SMARTIX performance using TPC-H, a standard, and scalable database benchmark. Our empirical evaluation shows that SMARTIX converges to indexing configurations with superior performance compared to standard baselines we define and other reinforcement learning methods used in related work

Suppression of Mitochondrial Electron Transport Chain Function in the Hypoxic Human Placenta: A Role for miRNA-210 and Protein Synthesis Inhibition

Fetal growth is critically dependent on energy metabolism in the placenta, which drives active exchange of nutrients. Placental oxygen levels are therefore vital, and chronic hypoxia during pregnancy impairs fetal growth. Here we tested the hypothesis that placental hypoxia alters mitochondrial electron transport chain (ETS) function, and sought to identify underlying mechanisms. We cultured human placental cells under different oxygen concentrations. Mitochondrial respiration was measured, alongside levels of ETS complexes. Additionally, we studied placentas from sea-level and high-altitude pregnancies. After 4 d at 1% O2 (1.01 KPa), complex I-supported respiration was 57% and 37% lower, in trophoblast-like JEG3 cells and fibroblasts, respectively, compared with controls cultured at 21% O2 (21.24 KPa); complex IV-supported respiration was 22% and 30% lower. Correspondingly, complex I levels were 45% lower in placentas from high-altitude pregnancies than those from sea-level pregnancies. Expression of HIF-responsive microRNA-210 was increased in hypoxic fibroblasts and high-altitude placentas, whilst expression of its targets, iron-sulfur cluster scaffold (ISCU) and cytochrome c oxidase assembly protein (COX10), decreased. Moreover, protein synthesis inhibition, a feature of the high-altitude placenta, also suppressed ETS complex protein levels. Our results demonstrate that mitochondrial function is altered in hypoxic human placentas, with specific suppression of complexes I and IV compromising energy metabolism and potentially contributing to impaired fetal growth. \ua9 2013 Colleoni et al

Coastal permafrost was massively eroded during the Bølling-Allerød warm period

The Bølling-Allerød interstadial (14,700–12,900 years before present), during the last deglaciation, was characterized by rapid warming and sea level rise. Yet, the response of the Arctic terrestrial cryosphere during this abrupt climate change remains thus far elusive. Here we present a multi-proxy analysis of a sediment record from the northern Svalbard continental margin, an area strongly influenced by sea ice export from the Arctic, to elucidate sea level - permafrost erosion connections. We show that permafrost-derived material rich in biospheric carbon became the dominant source of sediments at the onset of the Bølling-Allerød, despite the lack of direct connections with permafrost deposits. Our results suggest that the abrupt temperature and sea level rise triggered massive erosion of coastal ice-rich Yedoma permafrost, possibly from Siberian and Alaskan coasts, followed by long-range sea ice transport towards the Fram Strait and the Arctic Ocean gateway. Overall, we show how coastal permafrost is susceptible to large-scale remobilization in a scenario of rapid climate variability