| 1. |
- Bornmalm, Lennart, 1956, et al.
(författare)
-
Quantification of past environmental and biological processes by analysis of physical properties of fossils and fossil assemblages
- 2013
-
Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier BV. - 0031-0182. ; 391
-
Tidskriftsartikel (refereegranskat)abstract
- During the last four decades, reconstructions of past environments and biological processes based on fossil data have reached a remarkably high level of mathematical sophistication and statistical rigour. This development proceeded hand in hand with the increase in computing capacity and enabled researchers to extract new patterns from complex data, characterise uncertainty and formulate and test process-based hypotheses. From analysis of morphological evolution to reconstructions of past temperatures, between foraminifera and corals, climatological data, isotopes and assemblage counts, this field has been closely linked with the work of Professor Björn A. Malmgren, who has been one of the most prominent and innovative researchers in the field, applying cutting-edge mathematical techniques to Earth-science problems in a visionary manner that inspired several generations, and to whom this special issue is dedicated. Among the multitude of possibilities to analyse fossil data, applications in the field of paleoproxies are most numerous and most prominent. In this context, measurable properties of fossils are used as indirect representations of the state of the ambient environment acting on the organism that delivered the fossil and of the state of the environment to which the fossil has been exposed after the death of the organism. Two fundamental approaches to fossil proxies exist. The state of the environment can be reconstructed either from the chemical composition of the material of the fossil or from the physical properties of the fossil. The former is more prominent and has been the topic of many recent reviews, whereas the latter is conceptually more complex and less commonly used. The difference stems from the way in which the environmental signal is reflected in the proxy parameter. In geochemical proxies, passive incorporation or kinetic fractionation allows a more direct mechanistic interpretation of the signal, even though biological overprint is often present. Physical properties of fossils comprise characteristics of individual specimens, analysed by means of biometry (see Moller et al. and Quillévéré et al., in this issue), and properties of fossil assemblages, analysed by multivariate techniques (see Seidenkrantz et al. and Hernandez-Almeida et al., in this issue). Unlike geochemical proxies, these parameters are chiefly the result of biological processes such as individual growth, biomineralisation and population dynamics, which are inherently more difficult to link to environmental variables. This issue is dedicated to the interesting and somewhat overlooked field of proxies based on physical properties of fossils. It presents a selection of studies covering the main facets of quantitative analyses of fossil physical properties: morphometry and assemblage structure. It combines evaluation of uncertainty with proxy development and application for the understanding of past environmental processes. Although the concepts and approaches are equally applicable to any type of fossils, the examples in this issue all refer to microfossils. Due to their high abundance in small samples, microfossils have always been most amenable to quantitative treatment and they have also been the main object of study by Björn Malmgren. The difficulty to link shape and abundance of fossils to specific environmental variables results in a conceptually complex layer of uncertainty surrounding quantitative reconstructions based on physical properties of fossils. This complexity has multiple sources, beginning with the fidelity of taxonomic concepts, reflecting our ability to correctly identify biologically meaningful and ecologically homogenous taxa from morphological properties of fossils alone. This specific issue and its consequences are covered in contributions by Quillévéré et al. and Morard et al. in this issue. Collectively, this issue aims to reaffirm the central role that quantitative methods continue to play in analyses of fossil properties across an unexpectedly broad range of fields and to highlight the potential of this approach when sources of uncertainty are considered.
|
|
| 2. |
- Bornmalm, Lennart, 1956, et al.
(författare)
-
Quantitative analysis of fossil data in the development and application of paleoproxies.
- 2013
-
Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - 0031-0182. ; 391:Part A, s. 1-82
-
Tidskriftsartikel (refereegranskat)abstract
- During the last four decades, reconstructions of past environments and biological processes based on fossil data have reached a remarkably high level of mathematical sophistication and statistical rigour. This development proceeded hand in hand with the increase in computing capacity and enabled researchers to extract new patterns from complex data, characterise uncertainty and formulate and test process-based hypotheses. From analysis of morphological evolution to reconstructions of past temperatures, between foraminifera and corals, climatological data, isotopes and assemblage counts, this field has been closely linked with the work of Professor Björn A. Malmgren, who has been one of the most prominent and innovative researchers in the field, applying cuttingedge mathematical techniques to Earth-science problems in a visionary manner that inspired several generations, and to whom this special issue is dedicated. Among the multitude of possibilities to analyse fossil data, applications in the field of paleoproxies are most numerous and most prominent. In this context, measurable properties of fossils are used as indirect representations of the state of the ambient environment acting on the organism that delivered the fossil and of the state of the environment to which the fossil has been exposed after the death of the organism. Two fundamental approaches to fossil proxies exist. The state of the environment can be reconstructed either from the chemical composition of the material of the fossil or from the physical properties of the fossil. The former is more prominent and has been the topic of many recent reviews, whereas the latter is conceptually more complex and less commonly used. The difference stems from the way in which the environmental signal is reflected in the proxy parameter. In geochemical proxies, passive incorporation or kinetic fractionation allows a more direct mechanistic interpretation of the signal, even though biological overprint is often present. Physical properties of fossils comprise characteristics of individual specimens, analysed by means of biometry (see Moller et al. and Quillévéré et al., in this issue), and properties of fossil assemblages, analysed by multivariate techniques (see Seidenkrantz et al. and Hernandez-Almeida et al., in this issue). Unlike geochemical proxies, these parameters are chiefly the result of biological processes such as individual growth, biomineralisation and population dynamics, which are inherently more difficult to link to environmental variables. This issue is dedicated to the interesting and somewhat overlooked field of proxies based on physical properties of fossils. It presents a selection of studies covering the main facets of quantitative analyses of fossil physical properties: morphometry and assemblage structure. It combines evaluation of uncertainty with proxy development and application for the understanding of past environmental processes. Although the concepts and approaches are equally applicable to any type of fossils, the examples in this issue all refer to microfossils. Due to their high abundance in small samples, microfossils have always been most amenable to quantitative treatment and they have also been the main object of study by Björn Malmgren. The difficulty to link shape and abundance of fossils to specific environmental variables results in a conceptually complex layer of uncertainty surrounding quantitative reconstructions based on physical properties of fossils. This complexity has multiple sources, beginning with the fidelity of taxonomic concepts, reflecting our ability to correctly identify biologically meaningful and ecologically homogenous taxa from morphological properties of fossils alone. This specific issue and its consequences are covered in contributions by Quillévéré et al. and Morard et al. in this issue. Collectively, this issue aims to reaffirm the central role that quantitative methods continue to play in analyses of fossil properties across an unexpectedly broad range of fields and to highlight the potential of this approach when sources of uncertainty are considered.
|
|
| 3. |
- Fischer, Hubertus, et al.
(författare)
-
Palaeoclimate constraints on the impact of 2 °C anthropogenic warming and beyond
- 2018
-
Ingår i: Nature Geoscience. - : Springer Science and Business Media LLC. - 1752-0894 .- 1752-0908. ; 11:7, s. 474-485
-
Tidskriftsartikel (refereegranskat)abstract
- Over the past 3.5 million years, there have been several intervals when climate conditions were warmer than during the pre-industrial Holocene. Although past intervals of warming were forced differently than future anthropogenic change, such periods can provide insights into potential future climate impacts and ecosystem feedbacks, especially over centennial-to-millennial timescales that are often not covered by climate model simulations. Our observation-based synthesis of the understanding of past intervals with temperatures within the range of projected future warming suggests that there is a low risk of runaway greenhouse gas feedbacks for global warming of no more than 2 °C. However, substantial regional environmental impacts can occur. A global average warming of 1–2 °C with strong polar amplification has, in the past, been accompanied by significant shifts in climate zones and the spatial distribution of land and ocean ecosystems. Sustained warming at this level has also led to substantial reductions of the Greenland and Antarctic ice sheets, with sea-level increases of at least several metres on millennial timescales. Comparison of palaeo observations with climate model results suggests that, due to the lack of certain feedback processes, model-based climate projections may underestimate long-term warming in response to future radiative forcing by as much as a factor of two, and thus may also underestimate centennial-to-millennial-scale sea-level rise.
|
|
| 4. |
- Korotov, Sergey, et al.
(författare)
-
On degenerating finite element tetrahedral partitions
- 2022
-
Ingår i: Numerische Mathematik. - : SPRINGER HEIDELBERG. - 0029-599X .- 0945-3245. ; 152:2, s. 307-329
-
Tidskriftsartikel (refereegranskat)abstract
- Degenerating tetrahedral partitions show up quite often in modern finite element analysis. Actually the commonly used maximum angle condition allows some types of element degeneracies. Also, mesh generators and various adaptive procedures may easily produce degenerating mesh elements. Finally, complicated forms of computational domains (e.g. along with a priori known solution layers, etc) may demand the usage of elements of various degenerating shapes. In this paper, we show that the maximum angle condition presents a threshold property in interpolation theory, as the interpolation error may grow (or at least does not decay) if this condition is violated (which does not necessarily imply that FEM error grows). We also demonstrate that the popular red refinements, if done inappropriately, may lead to degenerating partitions which break the maximum angle condition. Finally, we prove that not all tetrahedral elements from a family of tetrahedral partitions are badly shaped when the discretization parameter tends to zero.
|
|
| 5. |
- Schiebel, Ralf, et al.
(författare)
-
Advances in planktonic foraminifer research : New perspectives for paleoceanography
- 2018
-
Ingår i: Revue de Micropaleontologie. - : Elsevier BV. - 0035-1598 .- 1873-4413. ; 61:3-4, s. 113-138
-
Forskningsöversikt (refereegranskat)abstract
- Planktonic foraminifer tests are major archives of environmental change and provide a multitude of proxies in paleoceanography and paleoclimatology. The application of such proxies is contingent upon a collaborative effort to better understand how the living organisms record the properties of their environment and how the resulting signals are recorded in marine sediments. In this contribution, we provide a review of the rapidly developing sub-fields of research, where new advances have been made possibleby technological developments, and by cross-disciplinary work of the scientific community. Following brief historical overviews of the sub-fields, we discuss the latest advances in planktonic foraminifer research and highlight the resulting new perspectives in ocean and climate research. Natural classification based on consistent species concepts forms the basis for analysis of any foraminifer-derived proxy. New approaches in taxonomy and phylogeny of Cenozoic planktonic foraminifers (Section 2) are presented, highlighting new perspectives on sensitivity and response of planktonic foraminifers to the changing climate and environment (Section 4). Calibration of foraminifer-specific data and environmental parameters is improving along with the technical development of probes and the access to samples from the natural environment (Section 3), enhancing our understanding of the ever-changing climate and ocean system. Comprehension of sedimentation and flux dynamics facilitates maximum gain of information from fossil assemblages (Section 5). Subtle changes in the physical (e.g., temperature), chemical (e.g., pH), and biological (e.g., food) conditions of ambient seawater affect the abundance of species and composition of assemblages as well as the chemical composition of the foraminifer shell and provide increasingly-detailed proxy data on paleoenvironments (Section 6).
|
|
| 6. |
|
|
