[1] Measurements of atmospheric O 2 /N 2 ratios and CO 2 concentrations can be combined into a tracer known as atmospheric potential oxygen (APO % O 2 /N 2 + CO 2 ) that is conservative with respect to terrestrial biological activity. Consequently, APO reflects primarily ocean biogeochemistry and atmospheric circulation. Building on the work of Stephens et al. (1998), we present a set of APO observations for the years 1996-2003 with unprecedented spatial coverage. Combining data from the Princeton and Scripps air sampling programs, the data set includes new observations collected from ships in the low-latitude Pacific. The data show a smaller interhemispheric APO gradient than was observed in past studies, and different structure within the hemispheres. These differences appear to be due primarily to real changes in the APO field over time. The data also show a significant maximum in APO near the equator. Following the approach of Gruber et al. (2001), we compare these observations with predictions of APO generated from ocean O 2 and CO 2 flux fields and forward models of atmospheric transport. Our model predictions differ from those of earlier modeling studies, reflecting primarily the choice of atmospheric transport model (TM3 in this study). The model predictions show generally good agreement with the observations, matching the size of the interhemispheric gradient, the approximate amplitude and extent of the equatorial maximum, and the amplitude and phasing of the seasonal APO cycle at most stations. Room for improvement remains. The agreement in the interhemispheric gradient appears to be coincidental; over the last decade, the true APO gradient has evolved to a value that is consistent with our time-independent model. In addition, the equatorial maximum is somewhat more pronounced in the data than the model. This may be due to overly vigorous model transport, or insufficient spatial resolution in the air-sea fluxes used in our modeling effort. Finally, the seasonal cycles predicted by the model of atmospheric transport show evidence of an excessive seasonal rectifier in the Aleutian Islands and smaller problems elsewhere.

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Hospital clowning is a programme in healthcare facilities involving visits from specially trained actors. In the paediatric intensive care unit (PICU), clowning may appear inappropriate and less intuitive. The patient could appear too ill and/or sedated, the environment too crowded or chaotic and the parents too stressed. Relying on our experience with professionally trained clowns both in France and Canada, the purpose of this article is to offer a model for hospital clowning and to suggest standards of practice for the implementation of clowning in PICUs. In this work, we provide a framework for the implementation of clown care in the PICU, to overcome the challenges related to the complex technical environment, the patient's critical illness and the high parental stress levels. Regardless of the specifics of the PICU, our experience suggests that professional clown activity is feasible, safe and can offer multiple benefits to the child, his/her parents and to hospital personnel. Due to the specific challenges in the PICU, clowns must be educated and prepared to work in this highly specialised environment. We stress that prior to clowning in a PICU, professional performers must be highly trained, experienced, abide by a code of ethics and be fully accepted by the treating healthcare team.

We suggested that medical clowning in the PICU is well accepted by parents, regardless of severity of their child's condition. This study supports the adoption of medical clowning in PICUs as a patient- and family-centred care practice.

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