Antarctic permafrost degassing in Taylor Valley by extensive soil gas investigation.

Ongoing studies conducted in northern polar regions reveal that permafrost stability plays a key role in the modern carbon cycle as it potentially stores considerable quantities of greenhouse gases. Rapid and recent warming of the Arctic permafrost is resulting in significant greenhouse gas emissions, both from physical and microbial processes. The potential impact of greenhouse gas release from the Antarctic region has not, to date, been investigated. In Antarctica, the McMurdo Dry Valleys comprise 10 % of the ice-free soil surface areas in Antarctica and like the northern polar regions are also warming albeit at a slower rate. The work presented herein examines a comprehensive sample suite of soil gas (e.g., CO2, CH4 and He) concentrations and CO2 flux measurements conducted in Taylor Valley during austral summer 2019/2020. Analytical results reveal the presence of significant concentrations of CO2, CH4 and He (up to 3.44 vol%, 18,447 ppmv and 6.49 ppmv, respectively) at the base of the active layer. When compared with the few previously obtained measurements, we observe increased CO2 flux rates (estimated CO2 emissions in the study area of 21.6 km2 ≈ 15 tons day-1). We suggest that the gas source is connected with the deep brines migrating from inland (potentially from beneath the Antarctic Ice Sheet) towards the coast beneath the permafrost layer. These data provide a baseline for future investigations aimed at monitoring the changing rate of greenhouse gas emissions from Antarctic permafrost, and the potential origin of gases, as the southern polar region warms.

Key

Detection of nuclear-decay γ rays provides a sensitive thermometer of nova nucleosynthesis. The most intense γ-ray flux is thought to be annihilation radiation from the ß^{+} decay of ^{18}F, which is destroyed prior to decay by the ^{18}F(p,α)^{15}O reaction. Estimates of ^{18}F production had been uncertain, however, because key near-threshold levels in the compound nucleus, ^{19}Ne, had yet to be identified. We report the first measurement of the ^{19}F(^{3}He,tγ)^{19}Ne reaction, in which the placement of two long-sought 3/2^{+} levels is suggested via triton-γ-γ coincidences. The precise determination of their resonance energies reduces the upper limit of the rate by a factor of 1.5-17 at nova temperatures and reduces the average uncertainty on the nova detection probability by a factor of 2.1.

Return of warm conditions in the southeastern Bering Sea: Physics to fluorescence.

From 2007 to 2013, the southeastern Bering Sea was dominated by extensive sea ice and below-average ocean temperatures. In 2014 there was a shift to reduced sea ice on the southern shelf and above-average ocean temperatures. These conditions continued in 2015 and 2016. During these three years, the spring bloom at mooring site M4 (57.9°N, 168.9°W) occurred primarily in May, which is typical of years without sea ice. At mooring site M2 (56.9°N, 164.1°W) the spring bloom occurred earlier especially in 2016. Higher chlorophyll fluorescence was observed at M4 than at M2. In addition, these three warm years continued the pattern near St. Matthew Island of high concentrations (>1 µM) of nitrite occurring during summer in warm years. Historically, the dominant parameters controlling sea-ice extent are winds and air temperature, with the persistence of frigid, northerly winds in winter and spring resulting in extensive ice. After mid-March 2014 and 2016 there were no cold northerly or northeasterly winds. Cold northerly winds persisted into mid-April in 2015, but did not result in extensive sea ice south of 58°N. The apparent mechanism that helped limit ice on the southeastern shelf was the strong advection of warm water from the Gulf of Alaska through Unimak Pass. This pattern has been uncommon, occurring in only one other year (2003) in a 37-year record of estimated transport through Unimak Pass. During years with no sea ice on the southern shelf (e.g. 2001-2005, 2014-2016), the depth-averaged temperature there was correlated to the previous summers ocean temperature.

A non-destructive sampling protocol for field studies of seed dispersal by fishes.

This paper presents a standardized protocol for the non-lethal capture of fishes, sampling of stomach contents and quantification of seed dispersal efficiency by frugivorous fishes. Neotropical pacu Piaractus mesopotamicus individuals were collected with fruit-baited hooks. The diets of 110 fish were sampled using a lavage method, which retrieved >90% of stomach contents of both juveniles and adults and allowed individuals to recover within 5 min of treatment. The proportional volume of six food categories was similar for stomachs and whole digestive tracts retrieved by dissection. Fruit pulp was proportionally lower in the stomach. The abundance and species richness of intact seeds increased with fish size independent of whether only stomachs or whole digestive tracts were analysed. The analysis of stomach contents accounted for 62·5% of the total species richness of seeds dispersed by P. mesopotamicus and 96% of common seeds (seed species retrieved from more than one fish). Germination trials revealed that seed viability was similar for seeds collected from the stomach via lavage and seeds that passed through the entire digestive tract. Therefore, stomach contents provide an unbiased representation of the dietary patterns and seed dispersal of frugivorous fishes.

Spatial and temporal patterns in summer ichthyoplankton assemblages on the eastern Bering Sea shelf 1996-2007.

Larval and early juvenile fishes were sampled from the eastern Bering Sea (EBS) shelf from 2001 to 2005, and in 2007. Data from these collections were used to examine spatial and temporal patterns in species assemblage structure and abundance. The years 2001-2005 were unusual because the EBS water temperature was 'warm' compared with the long-term mean temperature. In contrast, 2007 was a 'cold' year. The abundance of the five most numerous taxa at 12 stations common to all years sampled (1996-2005, 2007) were significantly different among years. Larval and early juvenile stage Theragra chalcogramma (walleye pollock), a commercially important gadid, were by far the most abundant fish in all years. Bottom depth alone best explained assemblage structure in most years, but in others, bottom depth and water column temperature combined and percent sea-ice coverage were most important. Abundance of T. chalcogramma larvae increases with water column temperature until 5°C and then becomes level. Higher abundances of Gadus macrocephalus (Pacific cod) larvae occur in years with the greatest percent sea-ice cover as indicated by GAM analysis. Larvae of Lepidopsetta polyxystra (northern rock sole) increase in abundance with increasing maximum wind speed, but decrease at a later date during the last winter storm. The data are consistent with the hypothesis that oceanographic conditions, specifically water temperature and sea-ice coverage, affect the spatial and temporal pattern of larval abundances. In general, ichthyoplankton species assemblages can be important early indicators of environmental change in the Bering Sea and potentially other subarctic seas as well.

The evolution of quantitative traits in complex environments.

Species inhabit complex environments and respond to selection imposed by numerous abiotic and biotic conditions that vary in both space and time. Environmental heterogeneity strongly influences trait evolution and patterns of adaptive population differentiation. For example, heterogeneity can favor local adaptation, or can promote the evolution of plastic genotypes that alter their phenotypes based on the conditions they encounter. Different abiotic and biotic agents of selection can act synergistically to either accelerate or constrain trait evolution. The environmental context has profound effects on quantitative genetic parameters. For instance, heritabilities measured in controlled conditions often exceed those measured in the field; thus, laboratory experiments could overestimate the potential for a population to respond to selection. Nevertheless, most studies of the genetic basis of ecologically relevant traits are conducted in simplified laboratory environments, which do not reflect the complexity of nature. Here, we advocate for manipulative field experiments in the native ranges of plant species that differ in mating system, life-history strategy and growth form. Field studies are vital to evaluate the roles of disparate agents of selection, to elucidate the targets of selection and to develop a nuanced perspective on the evolution of quantitative traits. Quantitative genetics field studies will also shed light on the potential for natural populations to adapt to novel climates in highly fragmented landscapes. Drawing from our experience with the ecological model system Boechera (Brassicaceae), we discuss advancements possible through dedicated field studies, highlight future research directions and examine the challenges associated with field studies.

Effects of pneumoperitoneum on intraoperative pulmonary mechanics and gas exchange during laparoscopic gastric bypass.

BACKGROUND: Hypercarbia and elevated intraabdominal pressure resulting from carbon dioxide (CO2) pneumoperitoneum can adversely affect respiratory mechanics. This study examined the changes in mechanical ventilation, CO2 homeostasis, and pulmonary gas exchange in morbidly obese patients undergoing a laparoscopic or open gastric bypass (GBP) procedure. METHODS: In this study, 58 patients with a body mass index (BMI) of 40 to 60 kg/m2 were randomly allocated to laparoscopic ( n = 31) or open ( n = 27) GBP. Minute ventilation was adjusted to maintain a low normal arterial partial pressure of CO2 (PaCO2), low normal end-tidal partial pressure of CO2 (ETCO2), and low airway pressure. Respiratory compliance, ETCO2, peak inspiratory pressure (PIP), total exhaled CO2 per minute (VCO2), and pulse oximetry (SO2) were measured at 30-min intervals. The acid-base balance was determined by arterial blood gas analysis at 1-h intervals. The pulmonary gas exchange was evaluated by calculation of the alveolar dead space-to-tidal volume ratio (V(Dalv)/V(T)) and alveolar-arterial oxygen gradient (PAO2-PaO2). RESULTS: The two groups were similar in age, gender, and BMI. As compared with open GBP, laparoscopic GBP resulted in higher ETCO2, PIP, and VCO2, and a lower respiratory compliance. Arterial blood gas analysis demonstrated higher PaCO2 and lower pH during laparoscopic GBP than during open GBP ( p < 0.05). The V(Dalv)/V(T) ratio and PAO2-PaO2 gradient did not change significantly during laparoscopic GBP. Intraoperative oxygen desaturation (SO2 < 90%) did not develop in any of the patients in either group. CONCLUSIONS: Laparoscopic GBP alters intraoperative pulmonary mechanics and acid-base balance but does not significantly affect pulmonary oxygen exchange. Changes in pulmonary mechanics are well tolerated in morbidly obese patients when proper ventilator adjustments are maintained.

Multiinstitutional experience with the management of superior mesenteric artery injuries.

BACKGROUND: Superior mesenteric artery (SMA) injuries are rare and often lethal injuries incurring very high morbidity and mortality. The purposes of this study are to review a multiinstitutional experience with these injuries; to analyze Fullen's classification based on anatomic zone and ischemia grade for its predictive value; to correlate the American Association for the Surgery of Trauma-Organ Injury Scale (AAST-OIS) for abdominal vascular injury with mortality; and to identify independent risk factors predictive of mortality, describing current trends for the management of this injury in America. DESIGN: We performed a retrospective multiinstitutional study of patients sustaining SMA injuries involving 34 trauma centers in the US over 10 years. Outcomes variables, both continuous and dichotomous, were analyzed initially with univariate methods. For the subsequent multivariate analysis, stepwise logistic regression was used to identify a set of risk factors significantly associated with mortality. RESULTS: There were 250 patients enrolled, with a mean Revised Trauma Score (RTS) of 6.44 and a mean Injury Severity Score (ISS) of 25. Surgical management consisted of ligation in 175 of 244 patients (72%), primary [corrected] repair in 53 of 244 patients (22%), autogenous grafts were used in 10 of 244 (4%), and prosthetic grafts of PTFE in 6 of 244 patients (2%). Overall mortality was 97 of 250 patients (39%). Mortality versus Fullen's zones: zone I, 39 of 51 (76.5%); zone II, 15 of 34 (44.1%); zone III, 11 of 40 (27.5%); and zone IV, 25 of 108 (23.1%). Mortality versus Fullen's ischemia grade: grade 1, 22 of 34 (64.7%). Mortality versus AAST-OIS for abdominal vascular injury: grade I, 9 of 55 (16.4%); grade II, 13 of 51 (25.5%); grade III, 8 of 20 (40%); grade IV, 37 of 69 (53.6%); and grade V, 17 of 19 (89.5%). Logistic regression analysis identified as independent risk factors for mortality the following: transfusion of greater than 10 units of packed RBCs, intraoperative acidosis, dysrhythmias, injury to Fullen's zone I or II, and multisystem organ failure. CONCLUSION: SMA injuries are highly lethal. Fullen's anatomic zones, ischemia grade, and AAST-OIS abdominal vascular injuries correlate well with mortality. Injuries to Fullen's zones I and II, Fullen's maximal ischemia grade, and AAST-OIS injury grades IV and V, high-intraoperative transfusion requirements, and presence of acidosis and disrhythmias are significant predictors of mortality. All of these predictive factors for mortality must be taken into account in the surgical management of these injuries.

Practical utility of the D-dimer assay for excluding thromboembolism in severely injured trauma patients.

BACKGROUND: We have advocated the use of a D-dimer assay to exclude the diagnosis of pulmonary embolism (PE) and deep venous thrombosis (DVT) in surgical and trauma patients suspected of having these diagnoses. Injury is known to increase D-dimer levels independent of thromboembolism. The purpose of this study was to assess the period after injury over which the D-dimer assay remains positive because of injury exclusive of thromboembolism. METHODS: We prospectively sampled the plasma of severely injured patients for D-dimer using an enzyme-linked immunosorbent assay method at admission; at hours 8, 16, 24, and 48; and at days 3, 4, 5, and 6. Patients were then screened for DVT with a routine duplex Doppler at day 7. Patients were followed for PE, adult respiratory distress syndrome, and disseminated intravascular coagulation. RESULTS: One hundred fifty-four patients (mean Injury Severity Score of 23) underwent a total of 1,230 D-dimer assays. Twenty-six (17%) had thromboembolism. Nine (6%) patients developed DVT, 2 (1%) developed PE, 13 (8%) developed disseminated intravascular coagulation, and 11 (7%) developed severe adult respiratory distress syndrome. None of the trauma patients with thromboembolism had a (false) negative D-dimer at or after the time of their thromboembolic complication. True-negative D-dimer results as a function of time from injury are: 0 hours, 18%; 8 hours, 16%; 16 hours, 17%; 24 hours, 22%; 48 hours, 37%; day 3, 34%; day 4, 32%; day 5, 30%; and day 6, 30%. The negative predictive value of the assay was 100%. D-dimer levels were significantly higher in those who developed a thromboembolic complication than in those who did not (independent of Injury Severity Score). CONCLUSION: These data serve to validate D-dimer as a means of excluding thromboembolism, specifically in patients with severe injury (100% negative predictive value). Before 48 hours after injury, however, the vast majority of these patients without thromboembolism had positive D-dimer assays. Because of the high false-positive rate early after severe injury, the D-dimer assay may be of little value before postinjury hour 48.

Surgical treatment of atrial fibrillation using radiofrequency energy.

BACKGROUND: The Maze III procedure for atrial fibrillation (AF) is effective but has not been used widely due to its complexity, bleeding risk, and added operative time. Surgical radiofrequency ablation may simplify the procedure and make intraoperative correction of AF more accessible and widely performed. METHODS: Endocardial pulmonary venous isolation was performed on 48 patients with AF undergoing concurrent operation using temperature-controlled radiofrequency energy delivered through a hand-held flexible probe. Additional right-sided lesions were made at the surgeon's discretion. RESULTS: Forty-two patients were appropriate for analysis (6 died). These patients had an AF duration of 4.8 +/- 6.4 years. At a mean follow-up of 138 +/- 96 days, 34 patients were in sinus rhythm. We were unable to demonstrate a difference in outcome based on AF duration, left atrial size, or addition of right-sided lesions. CONCLUSIONS: Radiofrequency atrial ablation was effective in 81% of patients with AF at restoring sinus rhythm at an average follow-up of 4 months. This procedure is simple to perform and should broaden the number of patients that receive an AF treatment procedure during concurrent cardiac operation.

Evaluation of intra-abdominal pressure after laparoscopic and open gastric bypass.

BACKGROUND: Increased intra-abdominal pressure (IAP) postoperatively can adversely affect cardiovascular, pulmonary, and renal function. In this prospective, randomized trial, we compared the IAP in morbidly obese patients after laparoscopic and open gastric bypass (GBP) surgery. METHODS: 64 patients with a body mass index of 40 to 60 kg/m2 were randomized to undergo laparoscopic or open GBP. IAPs were obtained at baseline (after induction of anesthesia), immediately after the operation, and on post-operative day (POD) 1, 2, and 3. Intraoperative and postoperative fluid requirements, urine output, and creatinine clearance were recorded. RESULTS: Demographics of the two groups were similar. IAP increased from baseline immediately after laparoscopic and open GBP (p < 0.05). IAP returned to baseline by POD 2 after laparoscopic GBP but remained elevated through POD 3 after open GBP. In fact, IAP was lower after laparoscopic GBP than after open GBP on POD 1, 2 and 3 (p < 0.05). The amount of intraoperative IV fluid was similar between groups, but laparoscopic GBP required less IV fluid and facilitated higher urine output postoperatively than open GBP. There was no significant difference in creatinine clearance between groups. CONCLUSIONS: Laparoscopic GBP resulted in significantly lower IAP, less postoperative fluid required, and greater postoperative urine output than open GBP.

Injury surveillance in construction: injuries to laborers.

Construction is one of the largest industries in the United States, employing over 7.5 million people. It accounts for 3 times as many accidents as might be expected on a per capita basis. Laborers represent one of 15 job classifications participating in this industry. They have a higher risk of death or injury from a number of causes than do other construction workers.

Whole blood D-dimer assay: an effective noninvasive method to rule out pulmonary embolism.

BACKGROUND: The whole blood D-dimer assay has gained recognition as a noninvasive test to rule out pulmonary embolism (PE) in medical patients. METHODS: We performed a whole blood D-dimer assay in medical and surgical patients undergoing either pulmonary angiogram or pulmonary ventilation perfusion scan for suspected PE or duplex Doppler or venogram for suspected deep venous thrombosis (DVT). RESULTS: A total of 483 patients were enrolled; 16 were excluded because of an equivocal pulmonary ventilation perfusion scan. The 467 remaining patients had a mean age of 56 +/- 27 years. There were 258 women and 209 men. A total of 353 patients were admitted to a medical service and 114 to surgery/ trauma. A total of 82 patients (18%) developed thromboembolism: 20 had PE, and 62 had DVT. CONCLUSION: No surgical patient with PE or DVT (n = 27) had a negative D-dimer. A negative D-dimer result in a stable surgical patient should be considered conclusive evidence to rule out thromboembolism and, thus, negate the need for further diagnostic studies. In our surgical patients suspected of DVT or PE, had D-dimer been used, one third of the patients would have avoided an expensive or invasive diagnostic test.

Injury and employment patterns among Hispanic construction workers.

This article describes non-fatal injuries among Hispanic construction workers treated at an emergency department from 1990 to 1998. Medical and interview data were analyzed to evaluate and explain the workers' apparently inflated risk of injury. The majority of the injured Hispanic workers were employed in the less-skilled trades. Compared with other injured workers, Hispanics had a higher proportion of serious injuries and were disadvantaged in terms of training and union status. With the exception of union status, these differences largely disappeared after controlling for trade. The physical, financial, and emotional consequences were more apparent 1 year later for injured Hispanics, even after controlling for trade. These observations suggest that minority status is a predictor of trade and that trade is a predictor of injury risk. In addition to reducing injury hazards, interventions should address the limited employment and union membership options that are available to minority workers in the construction industry.

Increased use of prophylactic vena cava filters in trauma patients failed to decrease overall incidence of pulmonary embolism.

BACKGROUND: Recent studies have reported that placement of vena cava filters (VCFs) early after injury may decrease the incidence of pulmonary embolism (PE) in high-risk trauma patients. STUDY DESIGN: This was a retrospective review of all trauma patients with placement of VCFs admitted to a single level-1 trauma center between 1989 and 1997. Two cohorts corresponding to years of high or low prophylactic VCF use (PVCF) were compared. RESULTS: Records were reviewed for 299 trauma patients identified as having had placement of a VCE Two hundred forty-eight filters were placed before the diagnosis of PE. During years of low PVCF use, the overall PE incidence was 0.31%; during years of high PVCF use, the incidence of PE was higher at 0.48% (p = 0.045, chi-square). CONCLUSIONS: Increased use of PVCFs failed to decrease the overall rate of PE in our trauma patient population.

Bedside noninvasive detection of acute pulmonary embolism in critically ill surgical patients.

HYPOTHESIS: We hypothesized that late pulmonary dead space fraction (Fd(late)) would be a useful tool to screen for pulmonary embolism (PE) in a group of surgical patients, including patients who required mechanical ventilation and patients with adult respiratory distress syndrome. DESIGN: We prospectively calculated Fd(late) in patients with suspected PE who underwent pulmonary angiography. SETTING: University-based, level I trauma center. MAIN OUTCOME MEASURE: Ability of Fd(late) to identify patients with PE. RESULTS: Twelve patients had 14 angiograms for suspected PE. The Fd(late) was 0.12 or above in all 5 patients who had PE; 4 required mechanical ventilation. The Fd(late) values were below 0.12 in 8 of 9 patients without PE. Four patients had adult respiratory distress syndrome. The Fd(late) had 100% sensitivity and 89% specificity for the detection of PE. CONCLUSIONS: The Fd(late) is a valuable tool for bedside screening of PE in surgical patients. We were able to accurately detect all PEs.

Field triage of the pulseless trauma patient.

HYPOTHESIS: Trauma patients who are pulseless at the scene of injury and whose electrical cardiac activity is less than 40 beats/min cannot be revived. DESIGN: Retrospective review. SETTING: University hospital, level I trauma center. PATIENTS: Pulseless trauma patients who had cardiopulmonary resuscitation at the scene, en route, or in the emergency department and presented between January 1, 1991, and July 1, 1996. MAIN OUTCOME MEASURE: Survival after traumatic cardiopulmonary arrest. RESULTS: Sixteen thousand seven hundred twenty-four trauma patients were admitted. The study cohort comprised 604 victims of traumatic cardiopulmonary arrest, 304 as a result of blunt injury and 300 as a result of penetrating injury. Transport time for the study patients was 11+/-6.1 minutes (mean +/- SD). Cardiopulmonary resuscitation was performed on them for 22+/-11 minutes. Three hundred four patients (50%) had resuscitative thoracotomy in the emergency department; 160 patients were taken to the operating room for further resuscitation and treatment of their injuries. Sixteen patients (2.6%) survived to discharge from the hospital; 7 had severe neurologic disabilities. No patient (0/212) with electrical asystole survived. Five of 134 patients with an initial electrical heart rate between 1 and 39 beats/min survived long enough to reach the intensive care unit but died within 48 hours (4 died within 24 hours). No patient survived to leave the hospital if the initial electrical heart rate was less than 40 beats/min. All 16 survivors had an initial heart rate of 40 beats/min or greater. CONCLUSION: Trauma victims who are pulseless and have asystole or agonal electrical cardiac activity (heart rate <40 beats/min) should be pronounced dead at the scene of injury.

Impairment of cardiac performance by laparoscopy in patients receiving positive end-expiratory pressure.

BACKGROUND: The cardiopulmonary effects of the combination of abdominal and thoracic pressures in humans have not been well delineated. OBJECTIVE: To study the cardiopulmonary effects of 15 mm Hg of intra-abdominal pressure in the presence and absence of 10 cm H20 of positive end-expiratory pressure (PEEP). DESIGN: Prospective. SETTING: University hospital. METHODS: Nine patients undergoing laparoscopic cholecystectomy had pulmonary compliance, cardiac output, exhaled carbon dioxide, and preload (left ventricular end-diastolic volume) determined at 4 points while undergoing ventilation with (1) no PEEP before pneumoperitoneum; (2) 10 cm H20 of PEEP and no pneumoperitoneum; (3) no PEEP and 15 mm Hg of pneumoperitoneum; and (4) 10 cm H20 of PEEP and 15 mm Hg of pneumoperitoneum. Preload and cardiac output were determined by means of transesophageal echocardiography. Pulmonary compliance and exhaled carbon dioxide were determined by an attachment to the end of the endotracheal tube. MAIN OUTCOME MEASURES: Preload, cardiac output, exhaled carbon dioxide, and pulmonary compliance. RESULTS: There was no significant change from baseline in preload, cardiac output, or pulmonary compliance when either PEEP or pneumoperitoneum was applied separately. However, there was a significant decrease in preload (P<.01), cardiac output (P = .01), and exhaled carbon dioxide (P =.04) when PEEP and pneumoperitoneum were applied together. Pulmonary compliance was not significantly affected at any of these points. CONCLUSIONS: There was a significant reduction in preload and cardiac output when there was intra-abdominal pressure of 15 mm Hg in the presence of 10 cm H20 of PEEP. This combination of pressures may pose a contraindication to laparoscopic surgery.