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- Beerling, D. J., et al.
(författare)
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Leaf metabolic and morphological responses of dwarf willow (Salix herbacea) in the sub-arctic to the past 9000 years of global environmental change
- 2000
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Ingår i: New Phytologist. - : Wiley. - 0028-646X .- 1469-8137. ; 145:2, s. 257-269
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Tidskriftsartikel (refereegranskat)abstract
- Ice-core records of the concentration of atmospheric CO2 and its stable isotope ratio (δ13C(a)) have shown that the global C cycle has not remained in steady-state over the past 11000 yr, implying a possible change in vegetation activity over this period. Here we evaluated the ecophysiological responses of the dwarf willow (Salix herbacea) over the past 9000 yr by measuring the stable carbon isotope composition and stomatal characters of a unique, well dated, high-latitude (68°N) sub-fossil leaf sequence. After correction for corresponding changes in δ13C(a), 9000-yr record of variations in the ratio of intercellular (c(j)) to atmospheric (c(a)) CO2 concentration was established. Intercellular: atmospheric CO2 concentration ratios provide a time-integrated indicator of the set-point of leaf gas exchange, and the historical variations revealed in this record have been interpreted as an impact of environmental changes on leaf gas exchange. The sequence shows a progressive fall in c(i)/c(a) 9000-3000 yr BP as well as the climatic effects of the Medieval Warm Period, the Little Ice Age and the post-industrial CO2 rise. Leaf stomatal index (proportion of epidermal cells as stomata), but not stomatal density, was significantly (P <0.01) correlated with Holocene atmospheric CO2 variations. A process-based interpretation of the changes in c(i)/c(a) was made using two different coupled photosynthesis-stomatal conductance models. Calculated in this way, S. herbacea photosynthetic rates were relatively stable throughout the Holocene whilst stomatal conductance progressively declined. Both, however, showed the marked effects of the Medieval Warm Period and the Little Ice Age. Overall, the results demonstrate that S. herbacea leaf metabolism, like the global C cycle, has not remained in steady state during the Holocene but has responded to changes in atmospheric CO2 concentration and short-term climatic oscillations.
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| 2. |
- John Lowe, J., et al.
(författare)
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Inter-regional correlation of palaeoclimatic records for the last Glacial-Interglacial Transition : A protocol for improved precision recommended by the INTIMATE project group
- 2001
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Ingår i: Quaternary Science Reviews. - 0277-3791. ; 20:11, s. 1175-1187
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Tidskriftsartikel (refereegranskat)abstract
- The remit of the INTIMATE project of the INQUA Palaeoclimate Commission is to synthesise marine, terrestrial and ice-core data for the North Atlantic region during the Last Glacial-Interglacial Transition (LGIT: ca 13-1014C kyr BP; ca 15-11.5 ice-core kyr BP). A major problem, however, is the difficulty of effecting correlations at a temporal resolution that are adequate for defining 'leads' and 'lags' between the polar ice, terrestrial, marine, and atmospheric realms. The limitations of the dating and correlation methods currently employed are summarised, and new quality assurance protocols are proposed. These include recommendations on the contextual information that should accompany radiocarbon dates, procedures for radiocarbon calibration, the use of an event-stratigraphic approach in inter-regional correlations, and the more widespread use of time-parallel marker horizons (based on tephra layers, oxygen isotope stratigraphy, palaeomagnetic stratigraphy, and radiocarbon 'wiggle-matching') to underpin the geochronology and correlation of events during the LGIT. These protocols will be adopted by the INTIMATE project in future international, collaborative research and are recommended to other groups working on this important time period.
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| 6. |
- Forkman, Peter, 1959, et al.
(författare)
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The 22 GHz radio-aeronomy receiver at Onsala Space Observatory
- 2003
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Ingår i: Journal of Quantitative Spectroscopy and Radiative Transfer. - 0022-4073. ; 77:1, s. 23-42
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Tidskriftsartikel (refereegranskat)abstract
- We present a radiometer system for regular long-term measurements of water vapour in the middle atmosphere. To be able to do continuous and long-term measurements a simple, robust, reliable and automatic system is needed. Our system therefore is based on a stable, uncooled, HEMT amplifier frontend and on a digital spectrometer backend. In order to minimise reflections in the frontend transmission line, which distort the signal due to standing waves, we have designed a corrugated receiver horn, which combines good characteristics (low return loss and sidelobes) and narrow beamwidth to simplify the receiver optics. In order to make the radiometer system as simple as possible, we use the sky as the calibration cold load. This is possible since we use the observed brightness temperatures of an already existing broadband dual-channel 21.0/31.4-GHz radiometer, at the observation site, to estimate the brightness temperature of the sky at . However, we have developed a calibration method, which makes it possible to estimate the sky brightness temperature even if we cannot use the dual-channel radiometer. Despite new measurements, which became available in recent years, the determination of middle atmospheric water vapour distribution still remains a challenge due to the fact that there is a large dispersion among the different measurement methods and data sets, which are obtained on a sparse and sporadic basis. This is the reason why several instruments similar to ours currently are developed in Europe.
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| 7. |
- Buckland, Philip I., et al.
(författare)
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How can a database full of Bugs help reconstruct the climate?
- 2002
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Ingår i: Archaeological Informatics - Pushing the Envelope - CAA 2001 - Computer Applications and Quantitative Methods in Archaeology. - : British Archaeological Reports. ; , s. 453-461
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The BUGS Insect Ecology Package was originally constructed (using Dbase and Clipper) to compile Coleoptera (beetle) habitat and distribution data from a myriad of sources into one, easy to use, and publicly available database. Its primary users were researchers and teachers within the palaeoentomology field. The present system, five versions and many revisions later, is built in MS Access 2000, and covers some 5300 species, 2000 references, and 240 sites (archaeological and Quaternary), and is of value to archaeologists, ecologists, and conservationists alike.BUGS is essentially a relational database management system constructed around three components:- the species data (modern ecology and distribution)- the bibliography- the site data with species listsIts implementation in several institutions has greatly accelerated the efficiency with which palaeoentomological investigations can be carried out, and greatly improved the teaching of the subject.Palaeoenvironmental reconstructions are performed by the superimposition of the ecology and distribution of modern insect populations over fossil assemblages. At the moment, this is essentially performed semi-quantitatively by cross-reference of the data (which BUGS collates for a species list and then exports as an RTF file to any word processing package). BUGS contains a wealth of ecological data which can be employed in the interpretation of archaeological sites and contexts. In natural deposits, away from the artificial heat islands created by human activity, insect distributions are essentially constrained by climatic parameters. Tim Atkinson (UEA) and Dave Perry (formerly at Birmingham University) digitally encoded the temperature range data for over 400 species into a program for the calculation of palaeoclimates through the MCR (Mutual Climatic Range) method, and this has been extensively used in the modelling of Quaternary climates from beetle remains. The aim of our present phase of BUGS development is to implement MCR functionality into the BUGS database system. From this point it should be possible to move on to other ecological variables such as habitat and vegetation types, and increase the precision of modern climatic data, thus enhancing the value of insects in archaeological interpretation and the modelling of past climates.
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| 8. |
- Majoran, Stefan, et al.
(författare)
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The effect of temperature on shell size and growth rate in Krithe praetexta praetexta (Sars)
- 2000
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Ingår i: Hydrobiologia. - 0018-8158. ; 419, s. 141-148
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Tidskriftsartikel (refereegranskat)abstract
- The effect of temperature on growth rate, shell size and shell shape in Krithe praetexta praetexta (Sars) was studied in four thermocultures. From July 1995 to June 1996, the cultures were kept in a continuously flowing open system pumping water from the intermediate watermass of the Gullmarn fjord, west coast of Sweden. Three cultures were kept at constant temperatures of 5, 10 and 14 °C, respectively. The fourth (reference) culture largely followed the natural variation in temperature. At the termination of the experiment, all living ostracods from a 125 μm sieve were sampled from the cultures. Population age structures were analysed for the various thermocultures of K. praetexta praetexta. These were more shifted towards later ontogenetic stages with higher temperature, i.e. the ontogenetic development was more rapid in the warmer cultures. An alternative explanation is due to diapause causing cohorts to accumulate in some ontogenetic stages only when the temperature is constant. The differences in shell size of K. praetexta praetexta among the thermoconstant cultures were not statistically significant.
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