An assessment of aerosol‐cloud interactions in marine stratus clouds based on surface remote sensing

An assessment of aerosol-cloud interactions (ACI) from ground-based remote sensing under coastal stratiform clouds is presented. The assessment utilizes a long-term, high temporal resolution data set from the Atmospheric Radiation Measurement (ARM) Program deployment at Pt. Reyes, California, United States, in 2005 to provide statistically robust measures of ACI and to characterize the variability of the measures based on variability in environmental conditions and observational approaches. The average ACIN (= dlnNd/dlna, the change in cloud drop number concentration with aerosol concentration) is 0.48, within a physically plausible range of 0–1.0. Values vary between 0.18 and 0.69 with dependence on (1) the assumption of constant cloud liquid water path (LWP), (2) the relative value of cloud LWP, (3) methods for retrieving Nd, (4) aerosol size distribution, (5) updraft velocity, and (6) the scale and resolution of observations. The sensitivity of the local, diurnally averaged radiative forcing to this variability in ACIN values, assuming an aerosol perturbation of 500 c-3 relative to a background concentration of 100 cm-3, ranges betwee-4 and -9 W -2. Further characterization of ACI and its variability is required to reduce uncertainties in global radiative forcing estimates

Top predators in relation to bathymetry, ice and krill during austral winter in Marguerite Bay, Antarctica

Author Posting. © Elsevier B.V., 2007. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part II: Topical Studies in Oceanography 55 (2008): 485-499, doi:10.1016/j.dsr2.2007.11.006.A key hypothesis guiding the U.S. Southern Ocean Global Ocean Ecosystems Dynamics (U.S. SO GLOBEC) program is that deep across-shelf troughs facilitate the transport of warm and nutrient-rich waters onto the continental shelf of the Western Antarctic Peninsula, resulting in enhanced winter production and prey availability to top predators. We tested aspects of this hypothesis during austral winter by assessing the distribution of the resident pack-ice top predators in relation to these deep across-shelf troughs and by investigating associations between top predators and their prey. Surveys were conducted July-August 2001 and August-September 2002 in Marguerite Bay, Antarctica, with a focus on the main across-shelf trough in the bay, Marguerite Trough. The common pack-ice seabird species were snow petrel (Pagodroma nivea, 1.2 individuals km-2), Antarctic petrel (Thalassoica antarctica, 0.3 individuals km-2), and Adélie penguin (Pygoscelis adeliae, 0.5 individuals km-2). The most common pack-ice pinniped was crabeater seal (Lobodon carcinophagus). During both winters, snow and Antarctic petrels were associated with low sea ice concentrations independent of Marguerite Trough, while Adélie penguins occurred in association with this trough. Krill concentrations, both shallow and deep, were also associated with Adélie penguin and snow petrel distributions. During both winters, crabeater seal occurrence was associated with deep krill concentrations and with regions of lower chlorophyll concentration. The area of lower chlorophyll concentrations occurred in an area with complex bathymetry close to land and heavy ice concentrations. Complex or unusual bathymetry via its influence on physical and biological processes appears to be one of the keys to understanding how top predators survive during the winter in this Antarctic region.This material is based upon work supported by the National Science Foundation under Grants No. OPP-9910096 (to C. Ribic), OPP-9910307 (to P. Wiebe), OPP-9632763, OPP-0120525, OPP-0217282 and OPP-0224727 (to W. Fraser), and a Fulbright Scholarship and Office of Naval Research Grant N00014-03-0212 (to G. Lawson)

Neutralization of tumor necrosis factor-alpha reverses insulin resistance in skeletal muscle but not adipose tissue

We examined the possible role of tumor necrosis factor-alpha (TNF-alpha) as a mediator of insulin resistance in maturing male Sprague-Dawley rats. Rats were treated either with goat anti-murine TNF-alpha IgG (anti-TNF-alpha) or goat nonimmune IgG (NI) for 7 days. Vascular catheters were implanted, and rats were fasted overnight before hyperinsulinemic euglycemic clamp (HUC) studies were performed. TNF-alpha neutralization increased the rate of glucose infusion required to maintain euglycemia by 68%. Insulin-stimulated glucose transport into individual tissues was measured after bolus administration of 2-deoxy-[(14)C]glucose during HUC. Anti-TNF-alpha administration increased glucose transport in muscles composed predominantly of fast-twitch fibers: white gastrocnemius muscle (68% increase) and tibialis anterior muscle (64% increase). There were nonsignificant trends for increased glucose transport in the slow-twitch soleus muscle and in the mixed-fiber red gastrocnemius muscle. Glucose transport was unchanged in visceral and subcutaneous fat. Anti-TNF treatment did not alter body weight, muscle mass, or fat mass. Anti-TNF-alpha did not alter the distribution of the 17-kDa and 26-kDa forms of TNF-alpha in either muscle or fat. However, anti-TNF-alpha treatment caused an approximately 50% reduction in the secretion of TNF-alpha bioactivity in vitro by explants of visceral and subcutaneous fat. We conclude that TNF-alpha neutralization reversed insulin resistance substantially in fast-twitch muscle and may have done so in other muscles, while having little effect in fat. TNF-alpha neutralization was accompanied by reduced TNF-alpha bioactivity without tissue depletion of TNF-alpha protein.Journal ArticleFinal article publishe