676 research outputs found
Sea-level rise in the Mediterranean Sea by 2050: Roles of terrestrial ice melt, steric effects and glacial isostatic adjustment
No full textTo assess the regional pattern of future low-frequency sea-level variations in the Mediterranean Sea, we combine the terrestrial ice melt, the glacio-isostatic and the steric sea-level components. The first is obtained from global scenarios for the future mass balance of the Greenland and Antarctica ice sheets, glaciers and ice caps. The second is based on modeling, using different assumptions about the Earth's rheology and the chronology of deglaciation since the Last Glacial Maximum. The third is obtained from published simulations based on regional atmosphere–ocean coupled models. From a minimum and a maximum scenario by 2040–2050, we find that the total, basin averaged sea-level rise will be 9.8 and 25.6 cm. The terrestrial ice melt component will exceed the steric contribution, which however will show the strongest regional imprint. Glacial isostatic adjustment will have comparatively minor effects. According to our estimates, at the Mediterranean Sea tide gauges, the rate of sea-level change will increase, by 2050, by a factor of ~ 1–6 relative to the observed long-term rates
Linear and non-linear sea-level variations in the Adriatic Sea from tide gauge records (1872-2012)
No full textWe have analyzed tide gauge data from the Adriatic Sea in order to assess
the secular sea-level trend, its acceleration and the existence of
possible cyclic variation. Analyzing the sea-level stack of all Adriatic
tide gauges, we have obtained a trend of (1.25±0.04) mm yr-1, in agreement
with that observed for the last century in the Mediterranean Sea,
and an acceleration that is negligibile compared to the average global
values. By means of the Ensemble Empirical Mode Decomposition technique,
we have evidenced an energetic oscillation with a period of ∼20
years that we relate with the recurrence of opposite phases in the Atlantic
Multi–decadal Oscillation and North Atlantic Oscillation indices.
We suggest that anomalously high sea-level values observed at
all the Adriatic tide gauges during 2010 and 2011 can be explained by
the rising phase of this 20 years cycl
Extent and dynamic evolution of the lost land aquaterra since the Last Glacial Maximum
No full textWe study the evolution of a recently recognised global geographical feature, named aquaterra, enclosing those lands that in previous glacial cycles have been repeatedly exposed and flooded. So far, the geography of aquaterra has been studied as a first approximation neglecting the isostatic effects and assuming globally uniform (i.e. eustatic) sea-level variations. Focussing on the last deglaciation and considering both global and regional aspects, we show that isostatic effects related with mantle dynamics have indeed played a significant role in the evolution of aquaterra. Our analysis is based upon paleogeographic reconstructions in the framework of well-established Glacial Isostatic Adjustment theories
Mario De Micheli fra 'le parole e le cose'
No full textStudio specifico sull'attività del critico d'arte Mario De Micheli relativamente al suo periodo giovanile, dagli anni Quaranta ai Settanta del Novecento, ricostruito attraverso la consultazione del suo archivio privato in provincia di Milano. Ne è emersa una figura, alla luce di scritti e testimonianze di contatti con artisti del secondo dopoguerra, particolarmente significativa: dal suo ruolo nell'ambito del movimento di 'Corrente' alla promozione del concetto di "realismo dialettico", in dissonanza con quello filo-sovietico di "realismo socialista"
The Bering Transitory Archipelago: stepping stones for the first Americans
No full textRetrospective sea-level mapping advances a promising geographic solution to the longstanding mystery about when, where, and how the first Americans crossed over from Asia. A paleotopographic reconstruction accounting for Glacial Isostatic Adjustment digitally explores an archipelago about 1400 km long that likely existed from >30,000 BP to 8000 BP. Here the authors examine this Bering Transitory Archipelago in regard to established hypotheses—Clovis-first, Ice-free (deglaciation) Corridor, Kelp Highway, and Beringian Standstill hypotheses—and a new Stepping-Stones hypothesis. Scores of islands at that time would meet all requirements previously proposed for a viable hypothesis: a source population in Asia, a pathway with abundant sustenance, settlements in North America soon after but not before, and an isolated sanctuary where Beringians could have become genetically distinct
Global Choke Points May Link Sea Level And Human Settlement At The Last Glacial Maximum
No full textGlobal choke points are preeminent nodes in geographic networks and geopolitical touchpoints subject to control by nations. They appear today as recurring theaters of conflict worldwide and also in archaeological investigations delving thousands of years back in time. How different were today’s global choke points at the Last Glacial Maximum (LGM) ~ 20,000 years ago? For the first time, we map nine of them to visualize their conditions at LGM. The global feature aquaterra—all lands inundated and exposed repeatedly during the Late Pleistocene ice ages—initially was mapped as first approximations of sea level. Here we refine its boundaries using Glacial Isostatic Adjustment (GIA) models to account for the Earth’s deformation and horizontal migrations of shorelines in response to glacial melting. We found three choke points sufficiently open to navigation, but six others presented substantially greater barriers than today. Implications include strategic insights on where to search for submerged evidence of human settlement
Anomalous secular sea-level acceleration in the Baltic Sea caused by isostatic adjustment
No full textObservations from the global array of tide gauges show that global sea-level has been rising at an average rate of 1.5-2 mm/yr during the last ~150 years [Douglas 1991, Spada and Galassi 2012]. Although a global sea-level acceleration was initially ruled out [Douglas 1992], subsequent studies [Douglas 1997, Church and White 2006, Jevrejeva et al. 2008, Church and White 2011] have coherently proposed values of ~1 mm/year/century [Olivieri and Spada 2013]. More complex non-linear trends and abrupt sea-level variations have now also been recognized. Globally, these could manifest a regime shift between the late Holocene and the current rhythms of sea-level rise [Gehrels and Woodworth 2013], while locally they result from ocean circulation anomalies, steric effects and wind stress [Bromirski et al. 2011, Merrifield 2011]. Although isostatic readjustment affects the local rates of secular sea-level change [Milne and Mitrovica 1998, Peltier 2004], a possible impact on regional acceleration has been so far discounted [Douglas 1992, Jevrejeva et al. 2008, Woodworth et al. 2009] since the process evolves on a millennium time scale [Turcotte and Schubert 2002]. Here we report a previously unnoticed anomaly in the long-term sea-level acceleration of the Baltic Sea tide gauge records, and we explain it by the classical post-glacial rebound theory and numerical modeling of glacial isostasy. Contrary to previous assumptions, our findings demonstrate that isostatic compensation plays a role in the regional secular sea-level acceleration.</p
Modeling sea level changes and geodetic variations by glacial isostasy: the improved SELEN code
No full textWe describe the basic features of SELEN, an open source Fortran 90 program
for the numerical solution of the so-called "Sea Level Equation" for a
spherical, layered, non-rotating Earth with Maxwell viscoelastic rheology. The
Sea Level Equation was introduced in the 70s to model the sea level variations
in response to the melting of late-Pleistocene ice-sheets, but it can be also
employed for predictions of geodetic quantities such as vertical and horizontal
surface displacements and gravity variations on a global and a regional scale.
SELEN (acronym of SEa Level EquatioN solver) is particularly oriented to
scientists at their first approach to the glacial isostatic adjustment problem
and, according to our experience, it can be successfully used in teaching. The
current release (2.9) considerably improves the previous versions of the code
in terms of computational efficiency, portability and versatility. In this
paper we describe the essentials of the theory behind the Sea Level Equation,
the purposes of SELEN and its implementation, and we provide practical
guidelines for the use of the program. Various examples showing how SELEN can
be configured to solve geodynamical problems involving past and present sea
level changes and current geodetic variations are also presented and discussed
Modeling sea level changes and geodetic variations by glacial isostasy: the improved SELEN code
No full textWe describe the basic features of SELEN, an open source Fortran 90 program
for the numerical solution of the so-called "Sea Level Equation" for a
spherical, layered, non-rotating Earth with Maxwell viscoelastic rheology. The
Sea Level Equation was introduced in the 70s to model the sea level variations
in response to the melting of late-Pleistocene ice-sheets, but it can be also
employed for predictions of geodetic quantities such as vertical and horizontal
surface displacements and gravity variations on a global and a regional scale.
SELEN (acronym of SEa Level EquatioN solver) is particularly oriented to
scientists at their first approach to the glacial isostatic adjustment problem
and, according to our experience, it can be successfully used in teaching. The
current release (2.9) considerably improves the previous versions of the code
in terms of computational efficiency, portability and versatility. In this
paper we describe the essentials of the theory behind the Sea Level Equation,
the purposes of SELEN and its implementation, and we provide practical
guidelines for the use of the program. Various examples showing how SELEN can
be configured to solve geodynamical problems involving past and present sea
level changes and current geodetic variations are also presented and discussed
Tide gauge observations in Antarctica (1958–2014) and recent ice loss
No full textSeveral historical sea level time series from Antarctic tide gauges, available from the Permanent Service for Mean Sea Level, are analysed. Two sea level curves, obtained by averaging data from the Antarctic Peninsula and West Antarctica, for 1958–2014, show trends of (2.0±0.1) and (1.8 ± 0.2) mm yr-1, respectively. By empirical mode decomposition, cyclic and non-cyclic components of sea level change were separated. A periodicity of 4–5 years was confirmed and attributed to the effects of the Antarctic Circumpolar Wave. The non-cyclic components were found to show a ‘levelling off’ of ≈ 1 mm yr-1 since c. 2000, which cannot be attributed to the isostatic response to Holocene ice melting. Using assessed mass balance data from the West Antarctic Ice Sheet and the Antarctic Peninsula, we studied the response to current ice loss in the region and found that the levelling off could be partly explained by accelerated melting during the last approximately two decades. This may represent the first evidence of sea level fingerprints of glacial melting in Antarctica
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