Abstracts on Global Climate Change

Jan 2004

Electrodynamic structure of charged dust clouds in the earth’s middle atmosphere

Scales, WA Ganguli, G


Noctilucent clouds (NLCs) and polar mesospheric summer echoes (PMSEs) are two phenomena at the forefront of near-earth space science. NLCs are high-altitude clouds in the earth’s mesosphere that are formed from visible aerosol particles. The occurrence rate of NLCs over time is believed to have profound implications on global climate change. NLCs are often associated with PMSEs which are strong 50 MHz-1.3 GHz radar echoes from mesospheric electron irregularities. Therefore, PMSEs may be an important remote-sensing diagnostic for the evolution of NLCs and the earth’s middle atmosphere in general. The electron irregularities that produce PMSEs are generally believed to result from charging of electrons onto subvisible aerosol irregularities, the source of which is currently a debated issue. Neutral air turbulence has long been considered a primary source of the irregularities. However, there are clearly fundamental characteristics of the irregularities in past and recent observations that cannot be explained by neutral air turbulence and most probably involve plasma processes. This work considers the latter mechanism and the possibility of production of aerosol irregularities in the boundary region between the charged aerosol layer and the background mesospheric plasma. First a model for investigating the electrodynamics of this boundary layer is described. This model indicates that plasma flows are expected to exist in the electrodynamic equilibrium. An initial assessment of the possible role of these plasma flows in producing irregularities that may ultimately result in PMSEs is provided.

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Critically pressured free-gas reservoirs below gas-hydrate provinces

Hornbach, MJ Saffer, DM Holbrook, WS

NATURE 427:6970 142-144

Palaeoceanographic data have been used to suggest that methane hydrates play a significant role in global climate change. The mechanism by which methane is released during periods of global warming is, however, poorly understood(1). In particular, the size and role of the free-gas zone below gas-hydrate provinces remain relatively unconstrained, largely because the base of the free-gas zone is not a phase boundary and has thus defied systematic description. Here we evaluate the possibility that the maximum thickness of an interconnected free-gas zone is mechanically regulated by valving caused by fault slip in overlying sediments(2). Our results suggest that a critical gas column exists below most hydrate provinces in basin settings, implying that these provinces are poised for mechanical failure and are therefore highly sensitive to changes in ambient conditions(3). We estimate that the global free-gas reservoir may contain from one-sixth to two-thirds of the total methane trapped in hydrate(4). If gas accumulations are critically thick along passive continental slopes, we calculate that a 5 degreesC temperature increase at the sea floor could result in a release of similar to2,000 Gt of methane from the free-gas zone, offering a mechanism for rapid methane release during global warming events.

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Could CO2-induced land-cover feedbacks alter near-shore upwelling regimes?

Diffenbaugh, NS Snyder, MA Sloan, LC


The response of marine and terrestrial environments to global changes in atmospheric carbon dioxide (CO2) concentrations will likely be governed by both responses to direct environmental forcing and responses to Earth-system feedbacks induced by that forcing. it has been proposed that anthropogenic greenhouse forcing will intensify coastal upwelling in eastern boundary current regions [Bakun, A. (1990) Science 247, 198-201]. Focusing on the California Current, we show that biophysical land-cover-atmosphere feedbacks induced by CO2 radiative forcing enhance the radiative effects Of CO2 on land-sea thermal contrast, resulting in changes in eastern boundary current total seasonal upwelling and upwelling seasonality. Specifically, relative to CO2 radiative forcing, land-cover-atmosphere feedbacks lead to a stronger increase in peak- and late-season near-shore upwelling in the northern limb of the California Current and a stronger decrease in peak- and late-season near-shore upwelling in the southern limb. Such changes will impact both marine and terrestrial communities [Bakun, A. (1990) Science 247,198-201; Soto, C. G. (2001) Rev. Fish Biol. Fish. 11, 181-195; and Agostini, V. N. & Bakun, A. (2002) Fish. Oceanogr. 11, 129-142], and these and other Earth-system feedbacks should be expected to play a substantial role in shaping the response of eastern boundary current regions to CO2 radiative forcing.

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Observations on permafrost ground thermal regimes from Antarctica and the Italian Alps, and their relevance to global climate change

Guglielmin, M


Active-layer monitoring and the permafrost thermal regime are key indicators of climate change. The results of 3 years (1997-1999) of active-layer monitoring at one high-mountain site (La Foppa, 46degrees28’ 42” N; 10degrees11’ 18” E, 2670 m a.s.l.) and at one Antarctic site (Boulder Clay, 74degrees44’ 45” S; 164degrees01’ 17” E, 205 m a.s.l) are presented. The initial analysis of a thermal profile in a borehole (100.3 m deep) within mountain permafrost at Stelvio (3000 m a.s.l., 46degrees30’ 59”N; 10degrees28’ 35” E) is also presented. At the alpine site, the active-layer thickness variations (between 193 and 229 cm) relate to both the snow cover and to the air temperature changes. By contrast, at the Antarctic site, there is a strong direct linkage only between air temperature fluctuations and active-layer variations. At the alpine (La Foppa) site, the relationship between climate and active-layer thickness is complicated by thermal offset that is almost negligible at both the Stelvio and Antarctic sites. The permafrost temperature profile at Stelvio site contains a climate signal suitable for paleoclimate reconstruction. The permafrost at this site has a mean annual ground surface temperature (MAGST) of - 1.9degreesC (during 1998/1999), an active layer of about 2.5 in thick and a total thickness of - 200 m. Analysis of the MAGST history, obtained by applying a simple heat conduction one-dimensional model, revealed the occurrence of a cold period from 1820 to 1940 followed by a warming period until 1978. Since the beginning of the 1980s, temperature dropped (less than 2degreesC) until the middle 1990s, when a new period of warming started. All these climatic changes fit well with the glacial fluctuations in the area and with other paleoclimatic information derived from different proxy data. (C) 2003 Elsevier B.V. All rights reserved.

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Elevational dependence of projected hydrologic changes in the San Francisco Estuary and watershed

Knowles, N Cayan, DR

CLIMATIC CHANGE 62:1-3 319-336

California’s primary hydrologic system, the San Francisco Estuary and its upstream watershed, is vulnerable to the regional hydrologic consequences of projected global climate change. Previous work has shown that a projected warming would result in a reduction of snowpack storage leading to higher winter and lower spring-summer streamflows and increased spring-summer salinities in the estuary. The present work shows that these hydrologic changes exhibit a strong dependence on elevation, with the greatest loss of snowpack volume in the 1300 - 2700 m elevation range. Exploiting hydrologic and estuarine modeling capabilities to trace water as it moves through the system reveals that the shift of water in mid-elevations of the Sacramento river basin from snowmelt to rainfall runoff is the dominant cause of projected changes in estuarine inflows and salinity. Additionally, although spring-summer losses of estuarine inflows are balanced by winter gains, the losses have a stronger influence on salinity since longer spring-summer residence times allow the inflow changes to accumulate in the estuary. The changes in inflows sourced in the Sacramento River basin in approximately the 1300 - 2200 m elevation range thereby lead to a net increase in estuarine salinity under the projected warming. Such changes would impact ecosystems throughout the watershed and threaten to contaminate much of California’s freshwater supply.

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Impact of soil warming and shading on colonization and community structure of arbuscular mycorrhizal fungi in roots of a native grassland community

Heinemeyer, A Ridgway, KP Edwards, EJ Benham, DG Young, JPW Fitter, AH


Arbuscular mycorrhizal (AM) fungi have a major influence on the structure, responses and below-ground C allocation of plant communities. Our lack of understanding of the response of AM fungi to factors such as light and temperature is an obstacle to accurate prediction of the impact of global climate change on ecosystem functioning. In order to investigate this response, we divided a grassland site into 24 plots, each either unshaded or partly shaded with soil either unheated or heated by 3degreesC at 2 cm depth. In both short-term studies in spring and autumn, and in a 1-year-long study, we measured root length colonization (LRC) by AM and non-AM fungi. For selected root samples, DNA sequences were amplified by PCR with fungal-specific primers for part of the small sub-unit (SSU) rRNA gene. In spring, the total LRC increased over 6 weeks from 12% to 25%. Shading significantly reduced AM but increased non-AM fungal colonization, while soil warming had no effect. In the year-long study, colonization by AM fungi peaked in summer, whereas non-AM colonization peaked in autumn, when there was an additive effect of shading and soil warming that reduced AM but increased non-AM fungi. Stepwise regression revealed that light received within the 7 days prior to sampling was the most significant factor in determining AM LRC and that mean temperature was the most important influence on non-AM LRC. Loglinear analysis confirmed that there were no seasonal or treatment effects on the host plant community. Ten AM fungal sequence types were identified that clustered into two families of the Glomales, Glomaceae and Gigasporaceae. Three other sequence types were of non-AM fungi, all Ascomycotina. AM sequence types showed seasonal variation and shading impacts: loglinear regression analysis revealed changes in the AM fungal community with time, and a reduction of one Glomus sp. under shade, which corresponded to a decrease in the abundance of Trifolium repens. We suggest that further research investigating any impacts of climate change on ecosystem functioning must not only incorporate their natural AM fungal communities but should also focus on niche separation and community dynamics of AM fungi.

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Long-term changes within the invertebrate and fish communities of the Upper Rhone River: effects of climatic factors

Daufresne, M Roger, MC Capra, H Lamouroux, N


There is increasing evidence that the global climate change is already having measurable biological impacts. However, no study (based on actual data) has assessed the influence of the global warming on communities in rivers. We analyzed long-term series of fish (1979-1999) and invertebrate (1980-1999) data from the Upper Rhone River at Bugey to test the influence of climatic warming on both communities. Between the periods of 1979-1981 and 1997-1999, the average water temperature of the Upper Rhone River at Bugey has increased by about 1.5degreesC due to atmospheric warming. In the same period, several dams have been built from 12.5 to 85 km upstream of our study segment and a nuclear power plant has been built on it. Changes in the community structure were summarized using multivariate analysis. The variability of fish abundance was correlated with discharge and temperature during the reproduction period (April-June): low flows and high temperatures coincided with high fish abundance. Beyond abundance patterns, southern, thermophilic fish species (e.g. chub, and barbel) as well as downstream, thermophilic invertebrate taxa (e.g. Athricops, Potamopyrgus) progressively replaced northern, cold-water fish species (e.g. dace) and upstream, cold-water invertebrate taxa (e.g. Chloroperla, Protoneumura). These patterns were significantly correlated with thermal variables, suggesting that shifts were the consequences of climatic warming. All analyses were carried out using statistics appropriate for autocorrelated time series. Our results were consistent with previous studies dealing with relationships between fish or invertebrates and water temperature, and with predictions of the impact of climatic change on freshwater communities. The potential confounding factors (i.e. dams and the nuclear power plant) did not seem to influence the observed trends.

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An inventory-based carbon budget for forest and woodland ecosystems of Turkey

Evrendilek, F


Environmental monitoring of national-level comparisons of CO2 emissions is needed to quantify sources and sinks of carbon ( C) in national ecosystems. In this study, a national forest inventory database was used to estimate the past and current pools and fluxes of C in deciduous and coniferous forest and woodland ecosystems (20.7 x 10(6) ha) of Turkey. Growing C stock was 12.63 t C ha(-1) in 1960 and 16.55 t C ha(-1) in 1995. Total C store in the whole live woody biomass was estimated at 22.77 t C ha(-1) in 1996. The total flux of C from the atmosphere into the forest and woodland ecosystems driven by primary productivity was about 1.46 t C ha(-1) (or 30.2 Mt C) in 1996. The estimated net release of C from the forest and woodland ecosystems of Turkey to the atmosphere was about 1.34 t C ha(-1) ( or 21.5 Mt C) in 1996. When C released was taken into account, net ecosystem sequestration (NES) resulted in 0.12 t C ha(-1) per year. Such analytical tools as national forest C budgets are needed to improve our preventive and mitigative strategies for dealing with global climate change.

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Comparison of the Holocene and Eemian palaeoenvironments in the South Icelandic Basin: dinoflagellate cysts as proxies for the North Atlantic surface circulation

Eynaud, F Turon, JL Duprat, J


A precise assessment of the hydrological changes in the northern Atlantic Ocean throughout the last climatic cycle stands as one of the key priorities for understanding the mechanisms of global climate change. A high resolution micropalaeontological study of a sediment core (MD95-2015) retrieved from the South Icelandic Basin, allows us to infer patterns of North Atlantic surface hydrological changes during the present (Holocene) and the ultimate (Marine Isotopic Stage 5) Interglacial periods. The downcore distribution of organic-walled dinoflagellate cysts (dinocysts) is used, in conjunction with additional proxies (sediment magnetic susceptibility, CaCO3, stables isotopes and planktic foraminifer assemblages) to identify climatic instabilities of various amplitudes. These events are mostly characterised by prominent changes in relative abundance of the dinocysts Spiniferites mirabilis and Operculodinium centrocarpum, whose maximum values are thought to trace sea-surface temperature peaks at the core site. Two hypsithermal periods are identified on this basis, between 126 and 120 kyr BP and from 9.2 to 5.7 cal kyr BP (similar to8-5 C-14 kyr BP), respectively. Some discrepancies between the micropalaeontological tracers used are discussed here in the light of their qualitative and quantitative (transfer functions) ecological interpretation. (C) 2003 Elsevier B.V. All rights reserved.

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The value of museum collections for research and society

Suarez, AV Tsutsui, ND

BIOSCIENCE 54:1 66-74

Many museums and academic institutions maintain first-rate collections of biological materials, ranging from preserved whole organisms to DNA libraries and cell lines. These biological collections make innumerable contributions to science and society in areas as divergent as homeland security, public health and safety, monitoring of environmental change, and traditional taxonomy and systematics. Moreover, these collections save governments and taxpayers many millions of dollars each year by effectively guiding government spending, preventing catastrophic events in public health and safety, eliminating redundancy, and securing natural and agricultural resources. However, these contributions are widely underappreciated by the public and by policymakers, resulting in insufficient financial support for maintenance and improvement of biological collections.

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N2O exchange within a soil and atmosphere profile in alpine grasslands on the Qinghai-Xizang Plateau

Pei, ZY Ouyang, H Zhou, CP Xu, XL


Knowledge of nitrous oxide (N2O) exchanges through soils and atmosphere in various ecosystems has been of great importance in global climate change studies. However, the relative magnitude of surface and subsurface N2O production sources from the alpine grassland ecosystem is unclear. In the present study, the N2O concentration profile from 1.5 m in depth in soil to 32 m in height in air was measured from July 2000 to July 2001 in alpine grassland located in the permafrost area of the Qinghai-Xizang Plateau, which revealed that N2O concentrations had a distinct variation pattern both in air and in soil during the study period. Mean N2O concentrations in the atmosphere were significantly lower than those in the soil, which induced the N2O emission from the alpine steppe soil into the atmosphere. Mean flux of N2O in this alpine grassland experiment site was 0.05x10(-4) mumol(.)m(-2.)s(-1). But the variation in N2O emissions did not show any clear trends over the whole-year experiment in our study site. The highest N2O concentration was found at the depth of 1.5 m in the soil while the lowest N2O concentration occurred at the height of 8 m in the atmosphere. Mean N2O concentrations in the soil increased significantly with depth. This was the influence of increasing soil moistures, which induced the increasing denitrification potential with depth. The mean N2O concentrations at different heights in the air remained a more steady state because of the atmospheric negotiability. Seasonal variations of N2O concentrations showed significant correlations between the neighbor layers both in the soil and in the atmosphere. The seasonal variations of N2O concentrations at all horizons in the soil showed very clear patterns, with the highest concentrations occurring from the onset of frost to the freeze-thaw period and lowest concentrations occurring during the spring and the summer. Further analyses showed that the seasonal variations of N2O concentrations in the soil were hardly explained by soil temperatures at any depth. Temporally, atmospheric N2O concentrations at all heights exhibited almost the same seasonal pattern with the soil N2O variations, while soil is believed to be the predominant natural source of atmospheric N2O near the earth surface in this alpine grassland area. Also, a significant correlation was found between N2O emissions and soil N2O concentrations at 0.2 m in depth during the study period. This implied the variation of N2O concentrations in the soil surface horizon was the most direct driving force of N2O exchanges between the soil and the atmosphere. Soil atmospheric N2O at surface layers is the main source of N2O emissions from the soil surface to the atmosphere. Soil N2O concentrations at deeper layers were all significantly higher than those at surface layers, which indicated that N2O was diffused from the deeper layers to the surface layers in the soil, and finally was emitted to the atmosphere.

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Changes in latitudes, changes in aptitudes: Nucella canaliculata (Mollusca : Gastropoda) is more stressed at its range edge

Sorte, CJB Hofmann, GE


A paradigm in biogeography is that organisms have ‘abundant center’ distributions, with abundances peaking at the range center and declining towards the range boundaries. One explanation for this pattern is that abundances are associated with organisms’ physiological stress levels and performances, with organisms experiencing more stress at the range edges. Here we explored whether the intertidal dogwhelk Nucella canaliculata was distributed in an ‘abundant center’ pattern. We addressed the role of stress in setting the species’ range limits. We determined dogwhelk abundances at range-center and range-edge sites and measured physiological stress levels by quantifying the 70 kDa heat-shock protein as a biochemical stress index. N. canaliculata was less abundant and more stressed at its southern range edge than at the range center, suggesting that populations at the range edge may be most impacted by global climate change.

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