During the summer of 2018, a widespread drought developed over Northern and Central Europe. The increase in temperature and the reduction of soil moisture have influenced carbon dioxide (CO 2) ...exchange between the atmosphere and terrestrial ecosystems in various ways, such as a reduction of photosynthesis, changes in ecosystem respiration, or allowing more frequent fires. In this study, we characterize the resulting perturbation of the atmospheric CO 2 seasonal cycles. 2018 has a good coverage of European regions affected by drought, allowing the investigation of how ecosystem flux anomalies impacted spatial CO 2 gradients between stations. This density of stations is unprecedented compared to previous drought events in 2003 and 2015, particularly thanks to the deployment of the Integrated Carbon Observation System (ICOS) network of atmospheric greenhouse gas monitoring stations in recent years. Seasonal CO 2 cycles from 48 European stations were available for 2017 and 2018. Earlier data were retrieved for comparison from international databases or national networks. Here, we show that the usual summer minimum in CO 2 due to the surface carbon uptake was reduced by 1.4 ppm in 2018 for the 10 stations located in the area most affected by the temperature anomaly, mostly in Northern Europe. Notwithstanding, the CO 2 transition phases before and after July were slower in 2018 compared to 2017, suggesting an extension of the growing season, with either continued CO 2 uptake by photosynthesis and/or a reduction in respiration driven by the depletion of substrate for respiration inherited from the previous months due to the drought. For stations with sufficiently long time series, the CO 2 anomaly observed in 2018 was compared to previous European droughts in 2003 and 2015. Considering the areas most affected by the temperature anomalies, we found a higher CO 2 anomaly in 2003 (+3 ppm averaged over 4 sites), and a smaller anomaly in 2015 (+1 ppm averaged over 11 sites) compared to 2018. This article is part of the theme issue 'Impacts of the 2018 severe drought and heatwave in Europe: from site to continental scale'.
We present a statistical framework to identify regional signals in
station-based CO2 time series with minimal local influence. A
curve-fitting function is first applied to the detrended time series ...to
derive a harmonic describing the annual CO2 cycle. We then combine a
polynomial fit to the data with a short-term residual filter to estimate the smoothed cycle and define a seasonally adjusted noise component, equal to 2 standard deviations of the smoothed cycle about the annual cycle. Spikes in the smoothed daily data which surpass this ±2σ threshold are classified as anomalies. Examining patterns of anomalous behavior across multiple sites allows us to quantify the impacts of synoptic-scale atmospheric transport events and better understand the regional carbon cycling implications of extreme seasonal occurrences such as droughts.
During the summer of 2018, a widespread drought developed over Northern and Central Europe. The increase in temperature and the reduction of soil moisture have influenced carbon dioxide (CO
) ...exchange between the atmosphere and terrestrial ecosystems in various ways, such as a reduction of photosynthesis, changes in ecosystem respiration, or allowing more frequent fires. In this study, we characterize the resulting perturbation of the atmospheric CO
seasonal cycles. 2018 has a good coverage of European regions affected by drought, allowing the investigation of how ecosystem flux anomalies impacted spatial CO
gradients between stations. This density of stations is unprecedented compared to previous drought events in 2003 and 2015, particularly thanks to the deployment of the Integrated Carbon Observation System (ICOS) network of atmospheric greenhouse gas monitoring stations in recent years. Seasonal CO
cycles from 48 European stations were available for 2017 and 2018. Earlier data were retrieved for comparison from international databases or national networks. Here, we show that the usual summer minimum in CO
due to the surface carbon uptake was reduced by 1.4 ppm in 2018 for the 10 stations located in the area most affected by the temperature anomaly, mostly in Northern Europe. Notwithstanding, the CO
transition phases before and after July were slower in 2018 compared to 2017, suggesting an extension of the growing season, with either continued CO
uptake by photosynthesis and/or a reduction in respiration driven by the depletion of substrate for respiration inherited from the previous months due to the drought. For stations with sufficiently long time series, the CO
anomaly observed in 2018 was compared to previous European droughts in 2003 and 2015. Considering the areas most affected by the temperature anomalies, we found a higher CO
anomaly in 2003 (+3 ppm averaged over 4 sites), and a smaller anomaly in 2015 (+1 ppm averaged over 11 sites) compared to 2018. This article is part of the theme issue 'Impacts of the 2018 severe drought and heatwave in Europe: from site to continental scale'.
We obtained likelihoods in the lower mantle for long-wavelength models of bulk sound and shear wave speed, density, and boundary topography, compatible with gravity constraints, from normal mode ...splitting functions and surface wave data. Taking into account the large uncertainties in Earth's thermodynamic reference state and the published range of mineral physics data, we converted the tomographic likelihoods into probability density functions for temperature, perovskite, and iron variations. Temperature and composition can be separated, showing that chemical variations contribute to the overall buoyancy and are dominant in the lower 1000 kilometers of the mantle.
We use a neighborhood algorithm to explore the fit to long period seismic data of a wide variety of long wavelength mantle models. This approach to the global tomographic inverse problem yields ...probability distributions for seismic velocities, density, and related properties as functions of depth. Such distributions can be robust even when individual models are not, and allow us to test several assumptions about the Earth that have long been enforced a priori in inversions. In particular, we are able to test the paradigm of deep mantle heterogeneity that is dominantly thermal in origin, producing velocity and density perturbations that are well correlated and have relative amplitudes given by delta ln rho / delta lnv sub s < 0.5. Our distributions show that such relationships are unlikely, and even though the results are consistent with recent best fitting models from damped seismic inversions, they demonstrate that many specific properties of such models are not robust. The data clearly favor density perturbations that are poorly or negatively correlated with velocity heterogeneity and have amplitudes several times larger (yielding delta ln rho / delta lnv sub s > 1.0) than damped inversions allow. These characteristics are most pronounced in the upper mantle transition zone and the base of the lower mantle, suggesting layered convection. The negative density- velocity correlations favored at these depths imply dominantly chemical heterogeneity, while the likelihood of relatively high amplitude density variations suggests that variable iron content is an important component of this heterogeneity. These results, which we show to be consistent with independent gravity constraints, represent a profound change in the interpretation of seismic constraints. In addition, the distributions show that even though best fitting density models from recent inversions or our sampling are consistent with the data, most specific properties of such models are not robust. This implies that it is more appropriate to use seismic model distributions, rather than individual models, to make geodynamic and geochemical inferences.
We present the results of generalized spectral fitting (GSF) regressions which estimate normal mode structure coefficients for the observable spheroidal and toroidal free oscillation multiplets below ...3 mHz. The size, accuracy, and precision of our new catalogue of modal constraints make it a powerful new tool for assessing and refining three‐dimensional Earth models. The estimates include more than 3100 coefficients for 90 multiplets and 25 pairs of coupled multiplets, including several deep mantle overtones previously obscured by fundamental modes. The coefficients constrain mantle structures of both even and odd spherical harmonic degrees, through degree 12 in some cases. Improvements in accuracy and precision have been achieved with three innovations: the development of GSF, an enhancement of the established spectral fitting technique which incorporates both Coriolis and structural coupling between multiplets; the application of GSF to an edited, high signal‐to‐noise and geographically diverse data set of more than 4500 seismograms from 33 high moment earthquakes; and the assignment of coefficient uncertainties using a Monte Carlo method to simulate the effects of seismic noise, theoretical errors, and coefficient covariances. The results of GSF are assessed by examining the internal consistency of estimated coefficients and through comparisons with recent mantle models. The new catalogue of structure coefficients and uncertainties is available as an electronic supplement to this paper and through the University of Colorado internet site.
Error bars for the global seismic Q profile Resovsky, Joseph; Trampert, Jeannot; Van der Hilst, R.D.
Earth and planetary science letters,
02/2005, Letnik:
230, Številka:
3
Journal Article
Recenzirano
Odprti dostop
The radial attenuation profile of the Earth is needed to account for dispersion effects when interpreting seismic velocities and can provide important constraints on composition. To date, most radial
...Q models have been produced using traditional damped inversions of free oscillation and surface wave data. Because such inversions can severely underestimate the model uncertainties that are needed to guide mineralogical and dynamic interpretation, and because the quality of data has continued to improve, we revisit this seismic inverse problem using a model space search approach already proven effective with similar data. We do, indeed, observe model uncertainties at least an order of magnitude greater than earlier estimates. At the same time, we find that
Q is determined well enough to confirm that the data favor several important features previously disputed because of questions of consistency. These include shear attenuation that drops significantly in the lower third of the lower mantle and bulk attenuation that is negligible in the inner core but stronger in the outer core and lower mantle than suggested by most models.
Abstract Objectives Affective dysregulation is a core feature of bipolar disorder (BD). Abnormalities in neural circuits underlying affect regulation have been observed in BD, specifically in the ...structure and function of the amygdala and orbital frontal cortex (OFC). Fear extinction is an automatic affect regulatory process relying on neural circuits that are abnormal in BD. Thus, fear extinction might be useful in probing automatic affect regulation deficits in BD. We tested the hypothesis that BD is associated with reduced ability to extinguish fear responses. Methods We examined fear conditioning, extinction, and extinction memory recall in a sample of stable, euthymic participants with BD ( n =19) vs. healthy comparison participants ( n =32). A limited number of subjects (BD: n =12; healthy comparison: n =11) underwent structural MRI scanning to examine cortical size associations with extinction recall. Results Both healthy comparison and BD participants were successful in acquiring a fear response, but BD participants responded with greater startle to both threat and safety cues. Both groups showed significant extinction. The BD group showed superior extinction recall. Extinction recall was associated with right rostral middle frontal cortex thickness across groups, whereas right OFC surface area was associated with recall only in healthy comparisons. Limitations Limitations include use of a stable, highly screened sample and a relatively small number of participants available for MRI analysis. Conclusions Increased fear reactivity may be related to a “trait” disruption in BD patients similar to that previously described in anxiety disorders. This task may be useful for probing automatic affect regulatory processes in BD, and understanding treatment response.
Normal mode structure coefficients provide important constraints on the long‐wavelength component of 3‐D mantle density (ρ) structure, but inversions for independent models of υs, υp, and ρ using ...normal mode data alone are ill‐posed even at long wavelengths. Ill‐posed inversions typically are regularized by imposing a priori assumptions on the set of estimated models, but such regularization can introduce important uncertainties in the models. We characterize these uncertainties for ρ models estimated from current normal mode data using a set of 512 different “regularization schemes”. These schemes sample a variety of plausible a priori assumptions about the nature and distribution of mantle heterogeneity by specifying allowable υs, υp, ρ, and boundary topography structures. The estimated ρ models are fairly robust with respect to prior constraints on υs, υp, and topography. However, the character and amplitude of the estimated ρ models depend strongly on how ρ is allowed to decorrelate from υs, and we display several models in which ρ and υs, decorrelate in very different depth intervals. Because these models all result from plausible prior constraints and fit the data equally and acceptably well, inversions of current normal mode data cannot robustly locate the decorrelation of ρ from υs. It remains possible that reliable ρ models may be obtained in the future as more normal mode measurements are introduced to break the strong tradeoffs between upper and lower mantle ρ structures that characterize current inversions.
We present inversions for a new three‐dimensional mantle υs model, MM2_L12D8, using a recently compiled catalogue of ∼2300 normal mode structure coefficients for 90 multiplets below 3 mHz. These ...inversions demonstrate the capabilities and limitations of existing normal mode data and reveal new images of structures in the midmantle (900–1800 km depth), which is poorly resolved by surface wave and body wave data. Our inversions are distinguished both by efforts to maintain consistency with a variety of seismic models, and hence data sets, and by attempts to characterize the sensitivity of our model to the choice of damping, to unspecified structures, and to data errors. We find that sensitivity to damping is the dominant source of model uncertainty, but MM2_L12D8 proves to be a robust model of υs with amplitude uncertainties less than 35% for most depths and degrees. Other characteristics of MM2_L12D8 include χ2 misfit to normal mode structure coefficients which is 58% smaller than that of the best existing models, greater similarity to existing models than they have to each other, perturbations relative to existing υs models that are largest in the midmantle, and amplitudes that are most consistent with existing models that employ global, rather than local, basis functions. MM2_L12D8 also displays definite images of “slabs” and “plumes” in the midmantle and a spectrum of heterogeneity that is more continuous with depth than in most other models. These characteristics suggest that the midmantle participates in a very long wavelength pattern of circulation that involves at least the whole lower mantle. Inversions for υp and ρ heterogeneities decorrelated from υs structure demonstrate that there is a significant signal from such structures in the normal mode data, but υp and ρ models are much more sensitive to damping than are υs models. The normal mode catalogue must be expanded before normal mode models of υp and ρ approach the reliability of the υs structures in MM2_L12D8. (This model, together with our catalogue of structure coefficients, is available at web site phys‐geophys.colorado.edu/geophysics/nm.dir.).
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