Methane is a potent greenhouse gas commonly supersaturated in the oxic surfaces waters of oceans and lakes, yet canonical microbial methanogens are obligate anaerobes. One proposed methane production pathway involves microbial degradation of methylphosphonate (MPn), which can proceed in the presence of oxygen. Directly tracing dissolved methane to its source in oxic waters, however, remains a challenge. To address this knowledge gap, we quantified the carbon isotopic fractionation between substrate MPn and product methane (1.3‰) in lab experiments, which was 1 to 2 orders of magnitude smaller than canonical pathways of microbial methanogenesis (20 to 100‰). Together, these results indicated that microbial catabolism of MPn is a source of methane in surface oceans and lake waters, but to differentiate sources of MPn in nature a further accounting of all sources is necessary. Methane from this pathway must be considered in constraining the marine carbon cycle and methane budget.

Aim Active travel is advised to help meet recommended weekly physical activity levels. However limited research has examined active travel associations with health indicators. The aim of this study is to investigate active commuting associations with BMI and self-rated health (SRH) using data from the Healthy Ireland Survey. Subjects and methods Cross-sectional analysis of data was conducted from a nationally representative study of the Irish population. Participants who worked or attended education (n = 4038) provided information regarding their most common travel mode to work or education and demographic, lifestyle and health characteristics during an interview. Following comparative analysis, multivariable logistic regression was used to investigate associations between active commuting modes and overweight, obesity and SRH. Results Active commuting was associated with decreased likelihood of obesity (AOR 0.69, 95% CI = 0.52, 0.90) relative to non-active commuting. Examination of active commuting mode revealed further reduced obesity risk among cyclists (AOR 0.23, 95% CI = 0.09, 0.56) relative to non-cyclists and among those actively travelling ≥3 km (AOR 0.54, 95% CI = 0.30, 0.98). No associations between active commuting and overweight or SRH were observed. Conclusion Our findings, which indicate an inverse association between active commuting and obesity, represent a significant contribution to the evidence base supporting promotion of active travel for obesity prevention.