Search results for "HEE"

2017

Information about past volcanic impact on climate is mostly derived from historic documentary data and sulfate depositions in polar ice sheets. Although these archives have provided important insights into the Earth's volcanic eruption history, the climate forcing and exact dating of many events is still vague. Here we apply a new method of break detection to the first millennium-length maximum latewood density reconstruction of Northern Hemisphere summer temperatures to develop an alternative record of large volcanic eruptions. The analysis returns fourteen outstanding cooling events, all of which agree well with recently developed volcanic forcing records from high-resolution bipolar ice …

Reorganization of the North Atlantic Oscillation during early Holocene deglaciation

2016

Laurentide ice-sheet retreat continued into the mid-Holocene. Speleothem-based precipitation records suggest the cessation of melt led to the establishment of the present precipitation patterns associated with the North Atlantic Oscillation. The North Atlantic Oscillation is the dominant atmospheric pressure mode in the North Atlantic region and affects winter temperature and precipitation in the Mediterranean, northwest Europe, Greenland, and Asia1. The index1 that describes the sea-level pressure difference between Iceland and the Azores is correlated with a dipole precipitation pattern over northwest Europe and northwest Africa. How the North Atlantic Oscillation will develop as the Gree…

A mechanism for brief glacial episodes in the Mesozoic greenhouse

2011

[1] The Mesozoic, perhaps the longest period of warmth during the Phanerozoic Earth history, has been repeatedly affected by short-lived cold interludes lasting about one million years. While the origin of these cold snaps has been classically attributed to a temporary atmospheric CO2 drawdown, quantified mechanisms explaining these instabilities of the carbon cycle are still lacking. Based on a climate carbon cycle model, we show that the general demise of carbonate platforms accompanying these short-lived cold interludes is a powerful mechanism capable of generating a fast atmospheric CO2 decrease and a moderate sea level drop associated with ice sheet buildup. The temporary nature of the…

Impact of Holocene climate variability on lacustrine records and human settlements in South Greenland

2015

Due to its sensitivity to climate changes, south Greenland is a particularly suitable area to study past global climate changes and their influence on locale Human settlements. A paleohydrological investigation was therefore carried out on two river-fed lakes: Lake Qallimiut and Little Kangerluluup, both located close to the Labrador Sea in the historic farming center of Greenland. Two sediment cores (QAL-2011 and LKG-2011), spanning the last four millennia, were retrieved and showed similar thin laminae, described by high magnetic susceptibility and density, high titanium and TOC / TN atomic ratio, and coarse grain size. They are also characterized either by inverse grading followed by nor…

Pleistocene Glaciations in Latvia

2011

Abstract During the Pleistocene the territory of Latvia was repeatedly overridden by Scandinavian ice sheets, at least from the Elsterian onwards. Extent limit of all glaciations was located far outside of Latvia. Due to vigorous erosion by subsequent glaciations the Pleistocene record is incomplete. Radiocarbon, cosmogenic nuclide and radiation exposure dating methods have been mainly used only for age determination of the upper part of the Pleistocene sequence. Decay of the Late Weichselian glaciation in Latvia is marked by five major ice-marginal zones

Tectono-Magmatic Evolution, Age and Emplacement of the Agardagh Tes-Chem Ophiolite in Tuva, Central Asia: Crustal Growth by Island arc Accretion

2004

Publisher Summary The Agardagh Tes–Chem ophiolite in Tuva, Central Asia, is part of the Central Asian Mobile Belt which formed during subduction–accretion processes lasting from the early Neoproterozoic to the late Palaeozoic. The Agardagh Tes–Chem ophiolite marks the northwestern border of the Tuva–Mongolian Massif (TMM), which comprises several intrusive and metamorphic complexes. These complexes consist of metatonalites, gneisses, migmatites, amphibolites, marbles, quartzites, low-grade metasedimentary rocks and minor ultramafic lenses, and radiometric ages range between 536 and 464 Ma. Field observations suggest that the southwestern part of the Tes–Chem unit represents the lower to int…

Ice age at the Middle–Late Jurassic transition?

2003

A detailed record of sea surface temperatures in the Northern Hemisphere based on migration of marine invertebrate fauna (ammonites) and isotopic thermometry (δ18O values of shark tooth enamel) indicates a severe cooling at the Middle–Late Jurassic transition (MLJT), about 160 Ma ago. The magnitude of refrigeration (1–3°C for lower middle latitudes) and its coincidence in time with an abrupt global-scale fall of sea level documented through sequence stratigraphy are both suggestive of continental ice formation at this time. Ice sheets may have developed over the high-latitude mountainous regions of Far-East Russia. The drastic cooling just post-dated the Middle–Late Callovian widespread dep…

Experimental deformation of deuterated ice in 3D and 2D: identification of grain-scale processes

2015

Major polar ice sheets and ice caps experience cycles of variable flow during different glacial periods and as a response to past warming. The rate and localisation of deformation inside an ice body controls the evolution of ice microstructure and crystallographic fabric. This is critical for interpreting proxy signals for climate change, with deformation overprinting and disrupting stratigraphy deep under ice caps due to the nature of the flow. The final crystallographic fabric in polar ice sheets provides a record of deformation history, which in turn controls the flow properties of ice during further deformation and affects geophysical sensing of ice sheets. For example, identification o…

Exploring 2040 : Global Trends and International Policies Setting Frames for the Finnish Wood-Based Economy

2022

Global trends influence the approaches and mindset for using natural resources and technological capacities. Participatory scenario methods have proven useful in long-term foresight. However, country-level foresight studies often ignore the broader trends affecting international markets and setting frames for economic development. This study envisions which global trends could occur and how the resulting European policies might affect the Finnish forest sector’s development in 2040. We applied a Futures Wheel approach, where stakeholder groups consisting of policy-, economic- and social sustainability-, technology-, and climate sustainability -experts in the field of forestry and interlinki…

Tavoiteristiriita ja kiinteys : tapaus- ja seurantatutkimus yhdestä naisten SM-tason ringettejoukkueesta

2015

Joukkuetavoitteita tutkittaessa lähtökohtana on ollut, että kaikki pelaajat mieltävät yhteisen tavoitteen samalla tavalla. Yhdessä tutkimuksessa kuitenkin havaittiin että useassa joukkueessa vallitsi erilaisia käsityksiä yhteisestä tavoitteesta, joten ilmiö saattaa olla oletettua yleisempi. Tässä tutkimuksessa tarkastellaan yhtä naisten SM-sarjassa pelannutta ringettejoukkuetta, jossa vallitsi pelaajien kesken ristiriitainen käsitys tulostavoitteesta koko kauden ajan. Tämän määrällistä ja laadullista aineistoa sisältävän tapaus- ja seurantatutkimuksen tarkoituksena on kuvata ja ymmärtää pelaajien ristiriitaisia käsityksiä yhteisestä tavoitteesta. Joukkueen pelaajat (N=20) vastasivat kolmeen…