Modeling transport and fate of riverine dissolved organic carbon in the Arctic Ocean

Author Posting. © American Geophysical Union, 2009. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 23 (2009): GB4006, doi:10.1029/2008GB003396.The spatial distribution and fate of riverine dissolved organic carbon (DOC) in the Arctic may be significant for the regional carbon cycle but are difficult to fully characterize using the sparse observations alone. Numerical models of the circulation and biogeochemical cycles of the region can help to interpret and extrapolate the data and may ultimately be applied in global change sensitivity studies. Here we develop and explore a regional, three-dimensional model of the Arctic Ocean in which, for the first time, we explicitly represent the sources of riverine DOC with seasonal discharge based on climatological field estimates. Through a suite of numerical experiments, we explore the distribution of DOC-like tracers with realistic riverine sources and a simple linear decay to represent remineralization through microbial degradation. The model reproduces the slope of the DOC-salinity relationship observed in the eastern and western Arctic basins when the DOC tracer lifetime is about 10 years, consistent with published inferences from field data. The new empirical parameterization of riverine DOC and the regional circulation and biogeochemical model provide new tools for application in both regional and global change studies.I.M.M. and M.J.F. are grateful to National Science Foundation for financial support

Asteroids and Comets

Asteroids and comets are remnants from the era of Solar System formation over 4.5 billion years ago, and therefore allow us to address two fundamental questions in astronomy: what was the nature of our protoplanetary disk, and how did the process of planetary accretion occur? The objects we see today have suffered many geophysically-relevant processes in the intervening eons that have altered their surfaces, interiors, and compositions. In this chapter we review our understanding of the origins and evolution of these bodies, discuss the wealth of science returned from spacecraft missions, and motivate important questions to be addressed in the future.Comment: 84 pages, 27 figures. To be published in Treatise on Geophysics, 2nd edition (G. Schubert, Editor-in-Chief), Volume 10 (T. Spohn, Editor

Progressive Independence in Clinical Training: A Tradition Worth Defending?

BACKGROUND: Progressive independence is a traditional premise of clinical training. Recently, issues such as managed care, work hours limitation, and patient safety have begun to impact the degree of autonomy afforded to clinical trainees. This article reviews empirical evidence and theory pertaining to the role of progressive autonomy in clinical learning. METHOD: A computerized literature search was performed using Medline, PsycINFO, Social Sciences Citation Index, and Educational Resources Information Center. This article presents a synthetic review of relevant empirical and theoretical concepts from the domains of medicine, psychology, education, kinesiology, and sociology. RESULTS: The clinical psychology and medical education literatures provide evidence that clinical trainees act more independently as their training progresses, but have not yet evaluated the educational efficacy of providing progressive independence, or the consequences of failing to do so. The expertise and motor learning literatures provide some theoretical evidence (as yet untested in complex clinical environments) that the provision of too much guidance or feedback to trainees could be educationally detrimental in the long term. The sociology literature provides insight into the cultural values underlying the behavior of clinical teachers and trainees relating to issues of supervision and independence. CONCLUSIONS: There is limited empirical support for the current model of progressive independence in clinical learning; however, diverse theoretical perspectives raise concern about the potential educational consequences of eroding progressive independence. These perspectives could inform future research programs that would create a creative and effective response to the social and economic forces impacting clinical education