Abstracts on Global Climate Change

Jul 2004

Diurnal temperature range as an index of global climate change during the twentieth century

Braganza, K Karoly, DJ Arblaster, JM


The usefulness of global-average diurnal temperature range (DTR) as an index of climate change and variability is evaluated using observations and climate model simulations representing unforced climate variability and anthropogenic climate change. On decadal timescales, modelled and observed intrinsic variability of DTR compare well and are independent of variations in global mean temperature. Observed reductions in DTR over the last century are large and unlikely to be due to natural variability alone. Comparison of observed and anthropogenic-forced model changes in DTR over the last 50 years show much less reduction in DTR in the model simulations due to greater warming of maximum temperatures in the models than observed. This difference is likely attributed to increases in cloud cover that are observed over the same period and are absent in model simulations.

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Seasonal thermal signatures of heat transfer by water exchange in an underground vault

Perrier, F Morat, P Yoshino, T Sano, O Utada, H Gensane, O Le Mouel, JL


The temperature of a 10-point vertical profile at the rock-atmosphere interface has been monitored since 2000 September in an underground vault at Aburatsubo, Japan, where resistivity variations have been reported in association with earthquakes. The non-ventilated vault is characterized by an annual temperature variation of about 1.2degreesC peak to peak, compatible with thermal diffusion in the surrounding tuff rock, and by a long-term temperature increase of about 0.1degreesC per year, possibly due to a local or global climate change. Owing to a careful relative calibration of the 10 thermistors used in this experiment, these data establish that the ceiling temperature is higher than the floor temperature by 0.04 to 0.28degreesC. Transient temperature variations are observed in association with human presence or with typhoons, with a characteristic spatial pattern revealing structural heterogeneity. Variations with periods ranging from 1 day to 1 week, with an amplitude two time larger and a phase advance on the floor with respect to the ceiling, are observed from November to May. Variations with periods larger than 1 week, with an amplitude two times smaller and a phase lag on the floor with respect to the ceiling, are observed from June to October. These cycles are linked to the sign of the seasonal heat flux. We propose an interpretation in which heat transfer in the cavity is dominated by diffusion of water vapour from June to October (heat flux downwards, summer regime) and by convective water transport from November to May (heat flux upwards, winter regime). The water flow inferred from this model can be used to predict the water saturation of the rock as a function of time. Because of a permanent radiative heat flux from top to bottom, the upward water flow in the winter regime is larger than the downward water flow in the summer regime, resulting in a slow depletion of water from the rock below the cavity. This unbalanced water flow could contribute to an observed steady secular increase of rock resistivity, and possibly also to the long-term temperature increase of 0.1degreesC per year. It is important to understand these processes in the context of underground geophysical observatories, underground waste storage and contaminant transport, as well as for the preservation of cultural items such as cave paintings.

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Reconstructing the Pleistocene geography of the Aphelocoma jays (Corvidae)

Peterson, AT Martinez-Meyer, E Gonzalez-Salazar, C


Understanding historical distributions of species and evolving lineages has been a topic of considerable interest, yet methods used to date have not provided detailed, quantitative distributional hypotheses. Here, we present a technique based on models of species’ ecological niches and Pleistocene climate reconstructions that provides such hypotheses, providing the example of reconstructions for the Aphelocoma jays. We demonstrate in general a greater degree than expected of stability in jay species’ distributional areas back through at least the most recent glaciation event, and that existing patterns of genetic differentiation may date to before the Late Pleistocene glaciations. More generally, the method offers the potential for reconstructing historical distributions of species or lineages, and providing a detailed geographic framework for addressing many biogeographic and systematic questions.

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Scale-dependent climate signals drive breeding phenology of three seabird species

Frederiksen, M Harris, MP Daunt, F Rothery, P Wanless, S


Breeding at the right time is essential for animals in seasonal climates in order to ensure that the energy demands of reproduction, particularly the nutritional requirements of growing young, coincide with peak food availability. Global climate change is likely to cause shifts in the timing of peak food availability, and in order to adapt successfully to current and future climate change, animals need to be able to adjust the time at which they initiate breeding. Many animals use environmental cues available before the breeding season to predict the seasonal peak in food availability and adjust their phenology accordingly. We tested the hypothesis that regulation of breeding onset should reflect the scale at which organisms perceive their environment by comparing phenology of three seabird species at a North Sea colony. As predicted, the phenology of two dispersive species, black-legged kittiwake (Rissa tridactyla) and common guillemot (Uria aalge), correlated with a large-scale environmental cue (the North Atlantic Oscillation), whereas a resident species, European shag (Phalacrocorax aristotelis), was more affected by local conditions (sea surface temperature) around the colony. Annual mean breeding success was lower in late years for European shags, but not for the other two species. Since correlations among climate patterns at different scales are likely to change in the future, these findings have important implications for how migratory animals can respond to future climate change.

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Cadmium effects on mitochondrial function are enhanced by elevated temperatures in a marine poikilotherm, Crassostrea virginica Gmelin (Bivalvia : Ostreidae)

Sokolova, IM


Marine intertidal mollusks, such as oysters, are exposed to multiple stressors in estuaries, including varying environmental temperature and levels of trace metals, which may interactively affect their physiology. In order to understand the combined effects of cadmium and elevated temperature on mitochondrial bioenergetics of marine mollusks, respiration rates and mitochondrial volume changes were studied in response to different cadmium levels (0-1000 mumol l(-1)) and temperatures (15, 25 and 35degreesC) in isolated mitochondria from the eastern oyster Crassostrea virginica acclimated at 15degreesC. It was found that both cadmium and temperature significantly affect mitochondrial function in oysters. Elevated temperature had a rate-enhancing effect on state 3 (ADP-timulated) and states 4 and 4+ (representative of proton leak) respiration, and the rate of temperature-dependent increase was higher for states 4 and 4+ than for state 3 respiration. Exposure of oyster mitochondria to 35degreesC resulted in a decreased respiratory control and phosphorylation efficiency (P/O ratio) compared to that of the-acclimation temperature (15degreesC), while an intermediate temperature (25degreesC) had no effect. Cadmium exposure did not lead to a significant volume change in oyster mitochondria in vitro. Low levels of cadmium (1-5 mumol l(-1)) stimulated the rate of proton leak in oyster mitochondria, while not affecting ADP-stimulated state 3 respiration. In contrast, higher cadmium levels (10-50 mumol l(-1)) had little or no effect on proton leak, but significantly inhibited state 3 respiration by 40-80% of the control rates. Elevated temperature increased sensitivity of oyster mitochondria to cadmium leading to an early inhibition of ADP-stimulated respiration and an onset of complete mitochondrial uncoupling at progressively lower cadmium concentrations with increasing temperature. Enhancement of cadmium effects by elevated temperatures suggests that oyster populations subjected to elevated temperatures due to seasonal warming or global climate change may become more susceptible to trace metal pollution, and vice versa.

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Phasing of deglacial warming and laurentide ice sheet meltwater in the Gulf of Mexico

Flower, BP Hastings, DW Hill, HW Quinn, TM

GEOLOGY 32:7 597-600

Evidence is emerging that the tropical climate system played a major role in global climate change during the last deglaciation. However, existing studies show that deglacial warming was asynchronous across the tropical band, complicating the identification of causal mechanisms. The Orca Basin in the northern Gulf of Mexico is ideally located to record subtropical Atlantic sea-surface temperature (SST) warming in relation to mellwater input from the Laurentide Ice Sheet. Paired delta(18)O and Mg/Ca data on the planktonic foraminifer Globigerinoides ruber from core EN32-PC6 are used to separate deglacial changes in SST and delta(18)O of seawater. SST as calculated from Mg/Ca data increased by >3 degreesC from ca. 17.2 to 15.5 ka in association with Heinrich event I and was not in phase with Greenland air temperature. Subtracting temperature effects from delta(18)O values in G. ruber reveals two excursions representing Laurentide meltwater input to the Gulf of Mexico, one of >1.5parts per thousand from ca. 16.1 to 15.6 ka and a second major spike of >2.5parts per thousand from ca. 15.2 to 13.0 ka that encompassed meltwater pulse 1A and peaked ca. 13.8 ka during the Bolling-Allerod. Conversion to salinity through the use of a Laurentide meltwater end member of -25parts per thousand indicates that near-surface salinity decreased by 2parts per thousand-4parts per thousand during these spikes. These results suggest that Gulf of Mexico SST warming preceded peak Laurentide Ice Sheet decay and the Bolling-Allerod interval by >2 k.y. and that heat was retained in the subtropical Atlantic during Heinrich event 1, consistent with modulation of deglaciall climate by thermohaline circulation.

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Dating the earliest lowland glaciation of eastern England: a pre-MIS 12 early Middle Pleistocene Happisburgh glaciation

Lee, JR Rose, J Hamblin, RJO Moorlock, BSP


This paper outlines the evidence for the Happisburgh Glaciation-the first Middle Pleistocene glaciation of lowland eastern England and the adjacent margins of the North Sea Basin. We propose that this glaciation occurred during a pre-Elsterian/Anglian (MIS 12) cold stage based on evidence of clasts of till, erratics and heavy minerals from the third youngest terrace of the ‘pre-glacial’ Bytham River in southern Norfolk. The heavy minerals show a progressive increase in glacially sourced materials from the bottom to the top of the Bytham River third terrace sediments. The till clasts are correlated with the extensive deposits of the Happisburgh Formation on the basis of their colour, heavy minerals and particle size properties. Thus, the Happisburgh Glaciation occurred during the accumulation of the Bytham River terrace deposits and prior to MIS 12, when the Bytham River system was destroyed by the Anglian glaciation. In the absence of any geochronology or robust biostratigraphy, the age of the Happisburgh Glaciation is estimated by the synchronisation of the pattern of large-scale river activity with patterns of Milankovitch-forced global climate change. On this basis, and assuming the British Ice Sheet acted in phase with global patterns of ice volume, the Happisburgh Glaciation is considered to have occurred during MIS 16 and be equivalent of the Don Glaciation of eastern Europe. (C) 2004 NERC. Published by Elsevier Ltd. All rights reserved.

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Tedlar bag sampling technique for vertical profiling of carbon dioxide through the atmospheric boundary layer with high precision and accuracy

Schulz, K Jensen, ML Balsley, BB Davis, K Birks, JW


Carbon dioxide is the most important greenhouse gas other than water vapor, and its modulation by the biosphere is of fundamental importance to our understanding of global climate change. We have developed a new technique for vertical profiling of CO2 and meteorological parameters through the atmospheric boundary layer and well into the free troposphere. Vertical profiling of CO2 mixing ratios allows estimates of landscape-scale fluxes characteristic of similar to100 km(2) of an ecosystem. The method makes use of a powered parachute as a platform and a new Tedlar bag air sampling technique. Air samples are returned to the ground where measurements of CO2 mixing ratios are made with high precision (less than or equal to0.1%) and accuracy (less than or equal to0.1%) using a conventional nondispersive infrared analyzer. Laboratory studies are described that characterize the accuracy and precision of the bag sampling technique and that measure the diffusion coefficient of CO2 through the Tedlar bag wall. The technique has been applied in field studies in the proximity of two AmeriFlux sites, and results are compared with tower measurements of CO2.

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