scholarly journals Glacial cycles and solar insolation: the role of orbital, seasonal, and spatial variations

2010 ◽  
Vol 6 (6) ◽  
pp. 2557-2591 ◽  
Author(s):  
R. K. Kaufmann ◽  
K. Juselius
Keyword(s):  
Late Quaternary ◽  
Explanatory Power ◽  
Spatial Variations ◽  
Glacial Cycles ◽  
Solar Insolation ◽  
Vector Autoregressive ◽  
Ice Volume ◽  
Seasonal And Spatial Variations ◽  
Summer Time

Abstract. We use a statistical model, the cointegrated vector autoregressive model, to evaluate the relative roles that orbital, seasonal, and spatial variations in solar insolation play in glacial cycles during the late Quaternary (390kyr – present). To do so, we estimate models of varying complexity and compare the accuracy of their in-sample simulations. Results indicate that variations in solar insolation associated with changes in Earth's orbit have the greatest explanatory power and that obliquity, precession, and eccentricity are needed to generate an accurate simulation of glacial cycles. Seasonal variations in insolation play a lesser role, while cumulative summer-time insolation has little explanatory power. Finally, solar insolation in the Northern Hemisphere generates the more accurate in-sample simulation of surface temperature while ice volume is simulated most accurately by solar insolation in the Southern Hemisphere.

scholarly journals Glacial cycles: exogenous orbital changes vs. endogenous climate dynamics

2010 ◽  
Vol 6 (2) ◽  
pp. 585-626 ◽  
Author(s):  
R. K. Kaufmann ◽  
K. Juselius
Keyword(s):  
Statistical Models ◽  
Late Quaternary ◽  
Climate Dynamics ◽  
Threshold Effects ◽  
Climate Variables ◽  
Vector Autoregressive Model ◽  
Glacial Cycles ◽  
Solar Insolation ◽  
Vector Autoregressive ◽  
Do So

Abstract. We use a statistical model, the cointegrated vector autoregressive model, to assess the degree to which variations in Earth's orbit and endogenous climate dynamics can be used to simulate glacial cycles during the late Quaternary (390 kyr–present). To do so, we estimate models of varying complexity and compare the accuracy of their in-sample simulations. Results indicate that strong statistical associations between endogenous climate variables are not enough for statistical models to reproduce glacial cycles. Rather, changes in solar insolation associated with changes in Earth's orbit are needed to simulate glacial cycles accurately. Also, results suggest that non-linear dynamics, threshold effects, and/or free oscillations may not play an overriding role in glacial cycles.

scholarly journals The role of orbital forcing, carbon dioxide and regolith in 100 kyr glacial cycles

2011 ◽  
Vol 7 (4) ◽  
pp. 2391-2411 ◽  
Author(s):  
A. Ganopolski ◽  
R. Calov
Keyword(s):  
Nonlinear Response ◽  
Co2 Concentration ◽  
Orbital Forcing ◽  
Orbital Eccentricity ◽  
Glacial Cycles ◽  
Strongly Nonlinear ◽  
Ice Volume ◽  
The North ◽  
Continental Area

Abstract. The origin of the 100 kyr cyclicity which dominates ice volume variations and other climate records over the past million years remains debatable. Here, using a comprehensive Earth system model of intermediate complexity, we demonstrate that both strong 100 kyr periodicity in the ice volume variations and the timing of glacial terminations during past 800 kyr can be successfully simulated as the direct, strongly nonlinear response of the climate-cryosphere system to the orbital forcing alone, if the atmospheric CO2 concentration stays below its typical interglacial value. The existence of long glacial cycles is primarily attributed to the North American ice sheet and requires presence of a large continental area with exposed rocks. We show that the sharp peak in the power spectrum of ice volume at 100 kyr period results from the long glacial cycles being synchronized with the Earth's orbital eccentricity. Although 100 kyr cyclicity can be simulated with a constant CO2 concentration, temporal variability in the CO2 concentration plays an important role in the amplification of the 100 kyr cycles.

scholarly journals The role of orbital forcing, carbon dioxide and regolith in 100 kyr glacial cycles

2011 ◽  
Vol 7 (4) ◽  
pp. 1415-1425 ◽  
Author(s):  
A. Ganopolski ◽  
R. Calov
Keyword(s):  
Co2 Concentration ◽  
Orbital Forcing ◽  
Orbital Eccentricity ◽  
Glacial Cycles ◽  
Strongly Nonlinear ◽  
Ice Volume ◽  
The North ◽  
Nonlinear Responses ◽  
Continental Area

Abstract. The origin of the 100 kyr cyclicity, which dominates ice volume variations and other climate records over the past million years, remains debatable. Here, using a comprehensive Earth system model of intermediate complexity, we demonstrate that both strong 100 kyr periodicity in the ice volume variations and the timing of glacial terminations during past 800 kyr can be successfully simulated as direct, strongly nonlinear responses of the climate-cryosphere system to orbital forcing alone, if the atmospheric CO2 concentration stays below its typical interglacial value. The existence of long glacial cycles is primarily attributed to the North American ice sheet and requires the presence of a large continental area with exposed rocks. We show that the sharp, 100 kyr peak in the power spectrum of ice volume results from the long glacial cycles being synchronized with the Earth's orbital eccentricity. Although 100 kyr cyclicity can be simulated with a constant CO2 concentration, temporal variability in the CO2 concentration plays an important role in the amplification of the 100 kyr cycles.

Glaciation cycle models and their pullback attractors

2021 ◽  
Author(s):  
Keno Riechers ◽  
Niklas Boers ◽  
Michael Ghil ◽  
Takahito Mitsui
Keyword(s):  
Explanatory Power ◽  
Power Spectra ◽  
Climate System ◽  
Sustained Oscillation ◽  
Orbital Forcing ◽  
Pullback Attractors ◽  
Glacial Cycles ◽  
Ice Volume ◽  
The Earth ◽  
Dynamic Stochastic

<p><span>The Pleistocene climate was dominated by alternating retreat and regrowth of massive ice sheets accompanied by large variations in the global mean temperature and sea level. Partial agreement between the power spectra of global ice volume proxies and high-latitude summer insolation provides evidence that quasi-periodic changes in the earth’s orbital configuration affect the timing of glaciations and deglaciations. It remains, however, a topic of active debate whether the main cause of glacial cycles is an internal self-sustained oscillation of the climate system that merely phased locked, more or less, to orbital forcing or whether glacial cycles could not exist at all in the absence of orbital forcing. Furthermore, it is unclear whether past ice volume records should be regarded as the result of a purely deterministic process or as a randomly selected trajectory of a stochastic process. To study plausible paths of the earth’s climate system given the orbital forcing, we compute the pullback attractors of several conceptual Pleistocene models. The results are confronted with the power spectra, as well as the time series of proxy records and conclusions will be drawn about the role of internal vs. forced variability and the possible contribution of stochastic processes to the mix of causes. We argue, moreover, that the explanatory power of either a deterministically chaotic or a dynamic-stochastic model cannot be assessed by comparing the model output to observations in the time domain alone.</span></p>

Contribution of large bacteria to bacterial biomass in a deep freshwater lake (Lake Biwa, Japan)

2020 ◽  
Vol 85 ◽  
pp. 131-139
Author(s):  
S Shen ◽  
Y Shimizu
Keyword(s):  
Cell Volume ◽  
Bacterial Cell ◽  
Lake Biwa ◽  
Bacterial Biomass ◽  
Spatial Variations ◽  
Freshwater Lake ◽  
Heterotrophic Nanoflagellates ◽  
Bacterial Productivity ◽  
Transmission Electron ◽  
Seasonal And Spatial Variations

Despite the importance of bacterial cell volume in microbial ecology in aquatic environments, literature regarding the effects of seasonal and spatial variations on bacterial cell volume remains scarce. We used transmission electron microscopy to examine seasonal and spatial variations in bacterial cell size for 18 mo in 2 layers (epilimnion 0.5 m and hypolimnion 60 m) of Lake Biwa, Japan, a large and deep freshwater lake. During the stratified period, we found that the bacterial cell volume in the hypolimnion ranged from 0.017 to 0.12 µm3 (median), whereas that in the epilimnion was less variable (0.016 to 0.033 µm3, median) and much lower than that in the hypolimnion. Additionally, in the hypolimnion, cell volume during the stratified period was greater than that during the mixing period (up to 5.7-fold). These differences in cell volume resulted in comparable bacterial biomass in the hypolimnion and epilimnion, despite the fact that there was lower bacterial abundance in the hypolimnion than in the epilimnion. We also found that the biomass of larger bacteria, which are not likely to be grazed by heterotrophic nanoflagellates, increased in the hypolimnion during the stratified period. Our data suggest that estimation of carbon flux (e.g. bacterial productivity) needs to be interpreted cautiously when cell volume is used as a constant parametric value. In deep freshwater lakes, a difference in cell volume with seasonal and spatial variation may largely affect estimations.

Science and Dialectics in the Philosophies of Deleuze, Bachelard and DeLanda

Paragraph ◽  
2006 ◽  
Vol 29 (2) ◽  
pp. 98-114 ◽  
Author(s):  
James Williams
Keyword(s):  
Gilles Deleuze ◽  
Explanatory Power ◽  
Scientific Theories ◽  
Gaston Bachelard ◽  
Contemporary Science

This article charts differences between Gilles Deleuze's and Gaston Bachelard's philosophies of science in order to reflect on different readings of the role of science in Deleuze's philosophy, in particular in relation to Manuel DeLanda's interpretation of Deleuze's work. The questions considered are: Why do Gilles Deleuze and Gaston Bachelard develop radically different philosophical dialectics in relation to science? What is the significance of this difference for current approaches to Deleuze and science, most notably as developed by Manuel DeLanda? It is argued that, despite its great explanatory power, DeLanda's association of Deleuze with a particular set of contemporary scientific theories does not allow for the ontological openness and for the metaphysical sources of Deleuze's work. The argument turns on whether terms such as ‘intensity’ can be given predominantly scientific definitions or whether metaphysical definitions are more consistent with a sceptical relation of philosophy to contemporary science.

Language Ideology and Second Language Learning

2008 ◽  
Vol 155 ◽  
pp. 95-115 ◽  
Author(s):  
Theresa McGarry
Keyword(s):  
Second Language ◽  
Second Language Acquisition ◽  
Language Acquisition ◽  
Language Learning ◽  
Language Ideology ◽  
Second Language Learning ◽  
Classroom Practices ◽  
Explanatory Power

AbstractThe increasing recognition of the concept language ideology and the corresponding increasing use of the term have not yet been matched by applications in the field of second language acquisition. However, applications of the concept in analysis of actual classroom practices have shown it to have considerable explanatory power. Greater consideration of language ideology in SLA is necessary not only to achieve greater understanding of the role of ideology in various areas but also to show connections between these areas that may yield important generalizations and to impel the application of the concept in areas where it has been neglected by highlighting its uneven treatment.

VAR INTERPRETATIONS OF HAAVELMO’S MARKET MODEL OF CAPITAL AND INVESTMENT

2014 ◽  
Vol 31 (2) ◽  
pp. 195-212
Author(s):  
Erik Biørn
Keyword(s):  
Rational Expectations ◽  
Joint Effect ◽  
Simultaneous Equation ◽  
Market Model ◽  
Equation Modeling ◽  
Vector Autoregressive ◽  
Investment Theory ◽  
The Interest Rate ◽  
Geometric Decay

In the paper attempts are made to integrate two parts of Trygve Haavelmo’s work: investment theory and dynamic econometric models of interrelated markets. Specifically, the duality in the representation of the capital service price and the capital quantity in relation to the investment price and quantity are brought to the forefront and confronted with elements from simultaneous equation modeling of vector autoregressive systems containing exogenous variables (VARX), using linear four-equation models. The role of the interest rate and the modeling of the expectation element in the capital service price and the capital’s retirement pattern, and their joint effect on the model’s investment quantity and price dynamics are discussed. Stability conditions are illustrated by examples. Extensions relaxing geometric decay and ways of accounting for forward-looking behavior, including rational expectations, are outlined. Some remarks on the theory-data confrontation of this kind of model are given.

Sign in / Sign up

Export Citation Format

Share Document