Decrease In PCO2 Research Articles

Lesions in the cerebellar fastigial nucleus have a small effect on the hyperpnea needed to meet the gas exchange requirements of submaximal exercise

The purpose of this study was to test the hypothesis that an intact cerebellar fastigial nucleus (CFN) is necessary for the hyperpnea to meet the gas exchange needs of submaximal exercise. Bilateral stainless steel microtubules were implanted in the cerebellum inside (n = 12) or outside (n = 2) the CFN for injection (0.5 to 10 microl) of the neurotoxin ibotenic acid. All goats had difficulty maintaining normal posture and walking for up to 1 mo after the implantation of the microtubules and again for hours or days after the neurotoxin was injected. Postmortem histology indicated there were 55% fewer living neurons (P < 0.001, n = 9, 3,720 +/- 553 vs. 1,670 +/- 192) in the CFN of the experimental goats compared with a control group of goats. As is typical for goats before implantation of the microtubules, the decrease in arterial Pco(2) from rest during mild and moderate treadmill exercise was 2.0 +/- 0.39 and 3.5 +/- 0.45 Torr, respectively. Implantation of the microtubules did not significantly change this exercise hyperventilation. However, neurotoxic lesioning with 10 mul ibotenic acid significantly (P < 0.05) attenuated the decrease in arterial Pco(2) by 1.3 and 2.8 Torr at the first and second workload, respectively. The modest attenuation of the exercise hypocapnia at both workloads in CFN-lesioned goats suggests that the CFN is part of the control system that enables the ventilatory response to meet the gas exchange requirements of submaximal exercise.

Temporal patterns of carbon dioxide in relation to hydrological conditions and primary production in the northeastern shelf of the Gulf of Cadiz (SW Spain)

Abstract The variations of the partial pressure of CO2 (pCO2) in surface seawaters of the northeastern shelf of the Gulf of Cadiz were studied during a 12-month period (March 2003–March 2004) in relation to hydrological conditions, chlorophyll concentrations, and primary production (PP). Monthly air–sea CO2 fluxes also were calculated. In spring, during the period of complete mixing of the water column, nutrients mainly brought to surface waters by the river discharge allowed a phytoplankton bloom to develop. PP rates estimated by remote sensing showed the highest values between March and May 2003, occurring concomitantly with the lowest values of surface pCO2. The undersaturation registered with respect to atmospheric pCO2 led the area to behave as a net sink for CO2. In late summer, water stratification, wind relaxation, and the absence of river discharge resulted in decreased chlorophyll concentrations, which were accompanied by a reduction in the productivity of the shelf. A marked increase in surface pCO2 took place, also in response to higher water temperatures and the flux reversed towards the atmosphere. As autumn progressed, nutrient concentrations rose as a consequence of fluvial inputs, which in conjunction with a complete mixing in the water column favored the appearance of a second, but less intense, phytoplankton bloom. PP increased with respect to summer and a decrease in surface pCO2 was observed. The undersaturation and the modulating influence of the wind resulted in a net capture of atmospheric CO2. Although chlorophyll concentration decreased during winter in response to the reduction in the incident irradiance, the air–sea CO2 flux remained directed towards the ocean. These preliminary results strongly suggest that, on annual basis, the northeastern shelf of the Gulf of Cadiz behaves as a net sink for atmospheric CO2.

Role of heterotrophic dinoflagellate Gyrodinium sp. in the fate of an iron induced diatom bloom

Iron enrichment to high‐nutrient low‐chlorophyll (HNLC) regions is being considered as a possible way of atmospheric CO2 sequestration to the deep sea. Mesoscale iron‐enrichment to the HNLC subarctic Pacific induced a massive diatom bloom and led to a large decrease in pCO2. In response to the diatom bloom, the heterotrophic dinoflagellate Gyrodinium sp. increased and phagotrophically fed on the diatoms up to 12 times their length. Mathematical simulations show the carbon fixed by diatoms is mostly respired by Gyrodinium sp. in the sea surface. The emergence of initially rare species and their key biogeochemical roles were unexpected due to our limited understanding of food‐web components. This indicates that the prediction of ecosystem responses to natural or anthropogenic perturbation remains a challenging issue. Effective carbon sequestration as a geoengineering technique may not be accomplished by purposeful iron‐enrichment, at least in the western subarctic Pacific where rapid‐growth diatom grazers stand by.

Comparison of Pycnogenol® and Daflon® in Treating Chronic Venous Insufficiency: A Prospective, Controlled Study

The aim of this study was to investigate the clinical efficacy of oral Pycnogenol (Horphag Research Ltd., UK) in patients with severe chronic venous insufficiency (CVI) in comparison to the combination of diosmin and hesperidin (Daflon, Servier, France). A group of 86 patients with severe chronic venous insufficiency (CVI), venous hypertension, ankle swelling) and previous history of venous ulcerations received either oral Pycnogenol (capsules) 150 mg or 300 mg daily for 8 weeks or Daflon, 1,000 mg/day. All patients completed the study without dropouts. At the end of the study, microcirculatory results indicated: a progressive decrease of skin flux at rest (RF); a significant decrease in capillary filtration (RAS); an improvement in the symptomatic venous score (ASLS); a reduction in edema; a significant improvement (increase) in pO(2) and a decrease in pCO(2) in the Pycnogenol group. A significant level of improvement was reached after 4 weeks of treatment in most patients (p < .05) of the Pycnogenol group while clinical improvement was significant only in 6 subjects in the Daflon group. The positive effects of treatment with Pycnogenol after 8 weeks were significantly larger in comparison with the Daflon group. In conclusion, this study confirms the fast clinical efficacy of Pycnogenol in patients with chronic venous insufficiency and venous microangiopathy and its superiority-considering the evaluated parameters-to the combination of diosmin and hesperidin.

Bicarbonate Reduces Serum Prolactin Increase Induced by Exercise to Exhaustion

The aim of the study was to examine the effect of acid-base status on serum prolactin (PRL) concentration postexercise. Seven male recreational athletes participated in two experimental trials separated by 1 wk. In the respective trial, subjects received either a placebo infusion (normal isotonic saline) or an alkali infusion (isotonic sodium bicarbonate) before and during exercise. Venous and capillary blood samples were drawn at rest, immediately after a 10-min warm-up period, and after a maximal ramp test on a cycle ergometer, as well as at 3, 6, 10, and 15 min postexercise. Power output, HR, capillary blood lactate concentration, carbon dioxide pressure (PCO2), and partial oxygen pressure (PO2) did not differ between trials at any point in time. Capillary PO2 did not change from resting values, but a significant increase (P < 0.05) was found from the end of warm-up to 3 min of the recovery period. Exercise induced a significant (P < 0.01) decrease in capillary blood bicarbonate concentration (HCO3-), pH, base excess (BE), and PCO2 at exhaustion and during the recovery period. Significantly higher HCO3-, pH, and BE were found during bicarbonate infusion and postexercise in comparison with the placebo trial. Serum PRL concentration was significantly increased 3 min postexercise until the end of the placebo trial, whereas after bicarbonate infusion, serum PRL concentration did not change from values at rest. Significant (P < 0.01) differences between trials in serum PRL concentration were found 10 and 15 min postexercise. The present study suggests that acidosis is a stimulus for exercise-induced PRL secretion.

Shear stress-induced pH increase in plasma is mediated by a decrease in PCO2: The increase in pH enhances shear stress-induced P-selectin expression in platelets

To investigate shear stress-induced platelet activation, the cone-plate viscometer or the Couette rotational viscometer has been widely used. In a previous report, it was shown that shearing platelet-rich plasma using a Couette rotational viscometer could lead to an increase in pH by CO2 release. However, any clear mechanism has not been provided. In this study, we examined whether shearing cell free plasma only using a cone-plate viscometer can also induce pH increase and studied the underlying mechanism of shear-induced pH increase by directly measuring total CO2 (TCO2) and CO2 tension (PCO2). When human plasma was sheared using a cone-plate viscometer, the pH of the human plasma increased time- and shear rate-dependently. Although TCO2 of human plasma was not affected, PCO2 was decreased by shearing, indicating that the decreased PCO2 is associated with a pH increase of plasma. In addition, the pH of bicarbonate-containing suspension buffer was also shown to be increased by shearing; suggesting that the platelet studies using suspension buffers containing bicarbonate could be affected similarly. The effects of pH changes on shear stress-induced platelet activation were also investigated in the same in vitro systems. While shear stress-induced platelet aggregation was not affected by the pH changes, P-selectin expression was significantly increased in accordance with the pH increase. In conclusion, shear stress using a cone-plate viscometer induces pH increase in plasma or bicarbonate-containing suspension buffer through a PCO2 decrease and the pH changes alone can contribute to platelet activation by enhancing shear stress-induced P-selectin expression.

Cerebral blood flow during orthostasis: role of arterial CO2

Reductions in end-tidal Pco(2) (Pet(CO(2))) during upright posture have been suggested to be the result of hyperventilation and the cause of decreases in cerebral blood flow (CBF). The goal of this study was to determine whether decreases in Pet(CO(2)) reflected decreases in arterial Pco(2) (Pa(CO(2))) and their relation to increases in alveolar ventilation (Va) and decreases in CBF. Fifteen healthy subjects (10 women and 5 men) were subjected to a 10-min head-up tilt (HUT) protocol. Pa(CO(2)), Va, and cerebral flow velocity (CFV) in the middle and anterior cerebral arteries were examined. In 12 subjects who completed the protocol, reductions in Pet(CO(2)) and Pa(CO(2)) (-1.7 +/- 0.5 and -1.1 +/- 0.4 mmHg, P < 0.05) during minute 1 of HUT were associated with a significant increase in Va (+0.7 +/- 0.3 l/min, P < 0.05). However, further decreases in Pa(CO(2)) (-0.5 +/- 0.5 mmHg, P < 0.05), from minute 1 to the last minute of HUT, occurred even though Va did not change significantly (-0.2 +/- 0.3 l/min, P = not significant). Similarly, CFV in the middle and anterior cerebral arteries decreased (-7 +/- 2 and -8 +/- 2%, P < 0.05) from minute 1 to the last minute of HUT, despite minimal changes in Pa(CO(2)). These data suggest that decreases in Pet(CO(2)) and Pa(CO(2)) during upright posture are not solely due to increased Va but could be due to ventilation-perfusion mismatch or a redistribution of CO(2) stores. Furthermore, the reduction in Pa(CO(2)) did not fully explain the decrease in CFV throughout HUT. These data suggest that factors in addition to a reduction in Pa(CO(2)) play a role in the CBF response to orthostatic stress.

The Upper Valanginian (Early Cretaceous) positive carbon–isotope event recorded in terrestrial plants

Our understanding of the ancient ocean-atmosphere system has focused on oceanic proxies. However, the study of terrestrial proxies is equally necessary to constrain our understanding of ancient climates and linkages between the terrestrial and oceanic carbon reservoirs. We have analyzed carbon‐isotope ratios from fossil plant material through the Valanginian and Lower Hauterivian from a shallow-marine, ammonite-constrained succession in the Crimean Peninsula of the southern Ukraine in order to determine if the Upper Valanginian positive carbon‐isotope excursion is expressed in the atmosphere. d 13 Cplant values fluctuate around ! 23x to ! 22x for the Valanginian‐Hauterivian, except during the Upper Valanginian where d 13 Cplant values record a positive excursion to ~! 18x. Based upon ammonite biostratigraphy from Crimea, and in conjunction with a composite Tethyan marine d 13 Ccarb curve, several conclusions can be drawn: (1) the d 13 Cplant record indicates that the atmospheric carbon reservoir was affected; (2) the defined ammonite correlations between Europe and Crimea are synchronous; and (3) a change in photosynthetic carbon‐isotope fractionation, caused by a decrease in atmospheric pCO2, occurred during the Upper Valanginian positive d 13 C excursion. Our new data, combined with other paleoenvironmental and paleoclimatic information, indicate that the Upper Valanginian was a cool period (icehouse) and highlights that the Cretaceous period was interrupted by periods of cooling and was not an equable climate as previously thought. D 2005 Elsevier B.V. All rights reserved.

MONITORING SKELETAL MUSCLE AND SUBCUTANEOUS TISSUE ACID-BASE STATUS AND OXYGENATION DURING HEMORRHAGIC SHOCK AND RESUSCITATION

Gastric tonometry correlates with the severity of blood loss during shock. However, tonometry is cumbersome, has a slow response time, and is not practical to apply in the acute resuscitation setting. We hypothesized that subcutaneous tissue (SC) and skeletal muscle (SM) pH, pCO2, and pO2 changes are comparable with changes seen in bowel tonometry during shock and resuscitation. Thirteen male mini-swine (25-35 kg; n = 4 control, n = 9 shock) underwent laparotomy and jejunal tonometry. A multisensor probe (Diametrics Medical, Roseville, MN) was placed in the carotid artery, the chest SC, and the adductor muscle of the leg (SM). PaCO2 was maintained between 40 and 45 mmHg. Shocked animals were hemorrhaged and kept at mean arterial pressure of 40 mmHg. Animals were bled until a reinfusion of >10% of the total shed blood was needed to maintain the mean arterial pressure at 40 mmHg. Animals were resuscitated with shed blood plus 2x shed volume in lactated Ringer's solution (20 min) and were observed for 3 h. The average blood loss was 47.2% +/- 8.7% of calculated blood volume. During the hemorrhagic phase, SM and SC displayed tissue acidosis (r2 = 0.951), tissue hypercapnea (r2 = 0.931), and tissue hypoxia (r2 = 0.748). Overall, pH displayed the best correlation between SM and SC during shock and resuscitation. PCO2 in the jejunum (tonometry), SM, and SC increased during decompensation. However, during resuscitation as tonometric pCO2 normalized, only SC pCO2 decreased to its baseline value, whereas the SM pCO2 decrease tended to lag behind. Bland-Altman analyses demonstrated that the variability of the tissue pH changes in SM and SC are predictable according to the phases of hemorrhage and resuscitation. Changes in tissue pH correlated during bleeding and during resuscitation among SC and SM, and these changes followed the trends in gut tonometry as well. Continuous pCO2 and pO2 monitoring in the SM and SC tissues had significant correlations during the induction of shock only. SM and SC continuous pH and pCO2 monitoring reflect bowel pCO2 values during hemorrhagic shock. The response of these indicators as potential surrogates of impaired tissue metabolism varies among tissues and according to the phases of hemorrhage or resuscitation.

Effect of addition of sodium dodecyl sulfite on physical properties of wheat gluten films

Films were made from the wheat glutens treated with 5%, 10%, 15%, 20%, 25% and 30% (wt% of gluten) of sodium dodecyl sulfite (SDS) in order to improve the properties of the films. Glycerol was used as a plasticizer. An addition of SDS in wheat glutens prior to forming films significantly increased the elongation at break (E) (P<0.05) and reduced notably the water vapor permeability (WVP) (P<0.05). In contrast, a decrease in the tensile strength (TS) of the films from gluten containing-SDS was found. Moreover, a significant decrease in Po2 and Pco2 of films from gluten treated with SDS was noticed. Although SDS-treated gluten film was slightly more yellow and darker than control one, it was not visually detrimental. It is indicated that the treatment with SDS prior to forming films greatly enhances the mechanical properties of wheat gluten films. The obivous improvement in water vapor permeability and extensibility of gluten films means that the use of SDS is a potential choice for improving properties of gluten filsm. The edible film was used to preserve tomatoes. The experimental results show that the shelf life of tomatoes coated with the edible film is extended, and the nutritional quality is kept well.

CO adsorption and correlation between CO surface coverage and activity/selectivity of preferential CO oxidation over supported Ag catalyst: an in situ FTIR study

In situ IR measurements for CO adsorption and preferential CO oxidation in H2-rich gases over Ag/SiO2 catalysts are presented in this paper. CO adsorbed on the Ag/SiO2 pretreated with oxygen shows a band centered around 2169 cm−1, which is assigned to CO linearly bonded to Ag+ sites. The amount of adsorbed CO on the silver particles (manifested by an IR band at 2169 cm−1) depends strongly on the CO partial pressure and the temperature. The steady-state coverage on the Ag surface is shown to be significantly below saturation, and the oxidation of CO with surface oxygen species is probably via a non-competitive Langmuir–Hinshelwood mechanism on the silver catalyst which occurs in the high-rate branch on a surface covered with CO below saturation. A low reactant concentration on the Ag surface indicates that the reaction order with respect to Pco is positive, and the selectivity towards CO2 decreases with the decrease of Pco. On the other hand, the decrease of the selectivity with the reaction temperature also reflects the higher apparent activation energy for H2 oxidation than that for CO oxidation.

Life-Threatening Asthma in Children: Treatment With Sodium Bicarbonate Reduces Pco2

To assess the effect of administration of sodium bicarbonate on carbon dioxide levels in children with life-threatening asthma (LTA) and to evaluate the clinical effect of this treatment.Retrospective study.A pediatric ICU (PICU) of a tertiary care university hospital.Seventeen children with LTA who received sodium bicarbonate.In January 1999, a new protocol for the treatment of LTA was initiated in our institution, incorporating the use of IV sodium bicarbonate in acidotic patients (pH < 7.15) with refractory status asthmaticus. Since January 1999, sodium bicarbonate was administered to 17 patients; 5 patients received two or three doses of sodium bicarbonate. In three patients, sodium bicarbonate was administered after intubation. Intubation and mechanical ventilation were performed in five patients before admission to the PICU, and in one patient during admission. There was a significant decrease of Pco(2) after sodium bicarbonate infusion (p = 0.007). An improvement of respiratory distress in all but one patient was seen as well.Administration of sodium bicarbonate in 17 children with LTA was associated with a significant decrease in Pco(2) and an improvement of respiratory distress. The possible benefits of sodium bicarbonate in LTA deserve further study in a controlled, prospective design.

Response of retinal blood flow to systemic hyperoxia in smokers and nonsmokers

We investigated the influence of chronic smoking on ocular vascular reactivity during breathing of 100% oxygen. Retinal vascular reactivity was tested during inhalation of 100% oxygen over 10 min. The observer-masked two-cohort study was performed in 24 healthy male volunteers (12 smokers and 12 nonsmokers) using the Zeiss Retinal Vessel Analyzer and laser Doppler velocimetry. From these parameters retinal blood flow was calculated. Hyperoxia significantly decreased arterial (smokers: p<0.001 vs baseline; nonsmokers: p=0.003 vs baseline) and venous (smokers: p<0.001 vs baseline; nonsmokers: p<0.001 vs baseline) diameters. This decrease was significantly more pronounced in smokers (arterial diameter: p<0.001, venous diameter: p=0.003). Hyperoxia decreased venous blood flow velocity (smokers: p=0.02 vs baseline; nonsmokers: p<0.001 vs baseline) to a comparable degree (p=0.51). The two groups showed a comparable decrease in retinal blood flow during hyperoxia (smokers: p<0.001 vs baseline; nonsmokers: p<0.001 vs baseline; p=0.76 between groups). The decrease of PCO(2) during inhalation of 100% oxygen was significantly more pronounced in smokers than in nonsmokers (p=0.038). The present study indicates an abnormal retinal vascular response to hyperoxia in smokers. Further studies are needed to identify possible neural or humoral factors involved in this shifted vasoconstrictory status in smokers.

Ventilatory acclimatization in response to very small changes in Po2 in humans

Ventilatory acclimatization to hypoxia (VAH) consists of a progressive increase in ventilation and decrease in end-tidal Pco(2) (Pet(CO(2))). Underlying VAH, there are also increases in the acute ventilatory sensitivities to hypoxia and hypercapnia. To investigate whether these changes could be induced with very mild alterations in end-tidal Po(2) (Pet(O(2))), two 5-day exposures were compared: 1) mild hypoxia, with Pet(O(2)) held at 10 Torr below the subject's normal value; and 2) mild hyperoxia, with Pet(O(2)) held at 10 Torr above the subject's normal value. During both exposures, Pet(CO(2)) was uncontrolled. For each exposure, the entire protocol required measurements on 13 consecutive mornings: 3 mornings before the hypoxic or hyperoxic exposure, 5 mornings during the exposure, and 5 mornings postexposure. After the subjects breathed room air for at least 30 min, measurements were made of Pet(CO(2)), Pet(O(2)), and the acute ventilatory sensitivities to hypoxia and hypercapnia. Ten subjects completed both protocols. There was a significant increase in the acute ventilatory sensitivity to hypoxia (Gp) after exposure to mild hypoxia, and a significant decrease in Gp after exposure to mild hyperoxia (P < 0.05, repeated-measures ANOVA). No other variables were affected by mild hypoxia or hyperoxia. The results, when combined with those from other studies, suggest that Gp varies linearly with Pet(O(2)), with a sensitivity of 3.5%/Torr (SE 1.0). This sensitivity is sufficient to suggest that Gp is continuously varying in response to normal physiological fluctuations in Pet(O(2)). We conclude that at least some of the mechanisms underlying VAH may have a physiological role at sea level.

In situ pCO2 and O2 measurements in a lake during turnover and stratification: Observations and modeling

Sensors for the partial pressure of CO2 (pCO2) and dissolved O2 (DO) were deployed near the surface and bottom of a freshwater lake (Placid Lake, Montana) during the period from ice cover to seasonal stratification. Sources of variability were examined using one‐dimensional physical and biogeochemical models. Model predictions for pCO2 and DO were compared to further constrain model parameters. A number of transient processes were documented that have not been well characterized in previous studies. The models made it possible to link these short‐term events to specific forcings. We found that (1) 11 d of the 13‐d turnover period occurred under ice through lightdriven convective mixing, (2) phytoplankton biomass increased to its highest seasonal level under ice, (3) weak stratification set up immediately after ice‐out, causing bottom water pCO2 and DO to diverge from surface levels, (4) subsequent diel convective mixing brought bottom pCO2 and DO back toward surface levels, and (5) before stable stratification, vertical entrainment of CO2‐rich water, net production, and air‐water exchange drove 100‐200 µatm daily changes in pCO2, but, because of their counterbalancing effects, surface pCO2 remained &gt;1,000 µatm for nearly 1 month after ice‐out. Upon stable stratification, net production and air‐water exchange overcame pCO2 gains from mixing and heating and reduced pCO2 to near atmospheric levels within 20 d. Net production and gas exchange accounted for ~75% and 25%, respectively, of the decrease in surface pCO2 observed after ice‐out. Diel convection was the dominant mixing process both under ice and after ice‐out and may be an important underrepresented mechanism for CO2 and DO exchange between surface and bottom water.

An Ecosystem Model Coupled with Nitrogen-Silicon-Carbon Cycles Applied to Station A7 in the Northwestern Pacific

A model based on that of Kishi et al. (2001) has been extended to 15 compartments including silicon and carbon cycles. This model was applied to Station A7 off Hokkaido, Japan, in the Northwestern Pacific. The model successfully simulated the observations of: 1. a spring bloom of diatoms; 2. large seasonal variations of nitrate and silicate concentrations in the surface water; and 3. large inter-annual variations in chlorophyll-a. It also reproduced the observed features of the seasonal variations of carbon dioxide partial pressure (pCO2)—a peak in pCO2 in winter resulting from deep winter convection, a rapid decrease in pCO2 as a result of the spring bloom, and an almost constant pCO2 from summer through fall (when the effect of increasing temperature cancels the effect of biological production). A comparison of cases with and without silicate limitation shows that including silicate limitation in the model results in: 1. decreased production by diatoms during summer; and 2. a transition in the dominant phytoplankton species, from diatoms to other species that do not take up silicate. Both of these phenomena are observed at Station A7, and our results support the hypothesis that they are caused by silicate limitation of diatom growth.

Brief Communication: EFFECTS OF QI-TRAINING (QIGONG) ON FOREARM BLOOD GAS CONCENTRATIONS

Using an ABA' design, the authors investigated the effects of Qi training on blood gas concentrations with a 20 min control rest period (A), 1 h of Qi-training (B), and a 20-min rest period (A'). The blood partial pressures of oxygen (PO2) and carbon dioxide (PCO2), and oxygen content, oxygen saturation, and pH were significantly altered. The mean PO2 value increased significantly during Qi training by 14 mmHg (about 24%, p < .01) compared with control A. During Qi-training, the mean decrease in PCO2 was 3 mmHg (about 10%). These results suggest that the practical application of Qi-training may exert a positive regulatory function on physiological status.

Global change in the Late Devonian: modelling the Frasnian–Famennian short-term carbon isotope excursions

A model of the global biogeochemical cycles coupled to a energy-balance climate model (the COMBINE model) is used to identify the causes of two large δ 13C value excursions across the Frasnian–Famennian (F-F) boundary. We test a scenario that links the sea-level rise to stratification of the Proto-Tethys ocean through the formation of warm saline deep waters in extended epicontinental seas. Even though this scenario can produce dysoxia below 100 m depth, it fails to increase the global burial flux of organic carbon and thus seawater δ 13C values, since stratification of the ocean leads to decreased productivity in surface waters. Several scenarios postulating a continental origin of the perturbations in the Late Devonian biogeochemical cycles are then tested. We found that weathering of platform carbonates exposed during the Early Famennian sea-level fall can account for a maximum positive shift in δ 13C value of +0.7‰ at the end of the sea-level fall episode. Another +1.0‰ increase in δ 13C might originate from rapid spreading of vascular land plants near the F-F boundary, postulating that higher plants globally increased the weatherability of continental surface, and that colonized continental area increased by 30% across the F-F boundary. Finally, the δ 13C excursion observed at the base of Upper rhenana Zone and the rapid increase of the carbon isotope ratios at the F-F boundary require an increase of phosphorus delivery to the ocean by 40%, coeval with the sea-level rises. Once the calculated δ 13C values are in agreement with the measured data, the COMBINE model calculates a decrease in atmospheric pCO 2 from pre-perturbation 2925 ppmv in the Lower rhenana conodont Zone to 1560 ppmv in the Upper triangularis Zone. This decrease in pCO 2 is due to the increase in burial of organic matter during the Kellwasser events, and increased continental weatherability triggered by the spreading of continental vascular plants. These changes occur within 4 million years. The corresponding global climatic cooling reaches 4.4°C at the pole, and 2.1°C at the equator.

Carbon isotopes across the Eocene‐Oligocene boundary sequence of Kutch, western India: Implications to oceanic productivity and pCO2 change

Analyses of foraminiferal δ18O (δ18Ocarb), δ13C (δ13Ccarb) and bulk organic matter (δ13Corg) across a tropical Eocene/Oligocene boundary (EOB) section from Kutch basin, western India show that the ocean cooling (at least ∼3°C) is coincident with a rapid enrichment (∼3‰) in δ13Corg but depletion (∼1.5‰) in δ13Ccarb. The decrease in pCO2 in ocean‐atmosphere system across the boundary, possibly resulting from enhanced silicate weathering in rising Himalayas and accompanied organic carbon burial in ocean, caused the cooling and δ13Corg enrichment. The end‐Eocene climatic stress decreased the oceanic productivity (and δ13Ccarb) eventually causing extinction of larger benthic foraminiferal community. The data suggest a critical role of tropical ocean and direct forcing of CO2 on global climate change at least for this crucial Cenozoic transition.

Model sensitivity in the effect of Antarctic sea ice and stratification on atmospheric pCO2

Several recent papers have demonstrated a decrease in atmospheric pCO2 resulting from barriers to communication between the deep sea and the atmosphere in the Southern Ocean. Stephens and Keeling [2000] decreased pCO2 by increasing Antarctic sea ice in a seven‐box model of the world ocean, and Toggweiler [1999] showed a similar response to Southern Ocean stratification. In box models the pCO2 of the atmosphere is controlled by the region of the surface ocean that fills the deep sea [Archer et al., 2000a]. By severing the Southern Ocean link between the deep sea and the atmosphere, atmospheric pCO2 in these models is controlled elsewhere and typically declines, although the models range widely in their responses. “Continuum models,” such as three‐dimensional (3‐D) and 2‐D general circulation models, control pCO2 in a more distributed way and do not exhibit box model sensitivity to high‐latitude sea ice or presumably stratification. There is still uncertainty about the high‐latitude sensitivity of the real ocean. Until these model sensitivities can be resolved, glacial pCO2 hypotheses and interpretations based on Southern Ocean barrier mechanisms (see above mentioned references plus Elderfield and Rickaby [2000], Francois et al. [1998], Gildor and Tziperman [2001], Sigman and Boyle [2000], and Watson et al. [2000]) are walking on thin ice.