Oceanic control of the sea ice edge and multiple equilibria in the climate system

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2010.Cataloged from PDF version of thesis.Includes bibliographical references (p. 215-227).I study fundamental mechanisms of atmosphere-ocean-sea ice interaction. Hierarchies of idealized models are invoked to argue that multiple equilibria and abrupt change are robust features of the climate system. The main finding is that meridional structure in poleward oceanic energy transport, which is set by the wind forcing, gives rise to preferred latitudes for the sea ice edge, including a stable large ice cap extending into mid-latitudes. I review multiple equilibria in energy balance models (EBMs), and extend the EBM to include explicit ocean heat transport (OHT) and insulating sea ice. I derive a method for simultaneously satisfying global energy and angular momentum budgets through a diffusive closure for potential vorticity, enabling a prediction of the basic shape of the surface wind stress. An idealized model of wind-driven gyres links this stress to OHT, and gives significant structure on sub-hemispheric scales in agreement with observations. This model predicts a stable large ice cap solution not found in the classic EBM, made possible by convergence of OHT in mid-latitudes. Analogous multiple equilibria are found in coupled atmosphere-ocean-sea ice general circulation model (GCM) simulations with idealized geometry (a pure aquaplanet and a "ridgeworld" with a global-scale ocean basin). Despite differing ocean dynamics, both configurations support similar equilibria: an ice-free climate, a cold climate with mid-latitude sea ice edge, and a completely ice-covered Snowball state. Multiple states persist despite a seasonal cycle and vigorous internal variability. Simulations with slowly-evolving thermal forcing show that some transitions between the ice-free and large ice cap states are abrupt. Multiple equilibria are explored in uncoupled simulations with prescribed OHT. The large ice cap is stabilized by wind-driven convergence of OHT at the poleward edge of the subtropical thermocline. The size of the large ice cap is sensitive to the meridional and seasonal distribution of OHT convergence. The ice-free state persists in the absence of high-latitude OHT. Mid-latitude convergence of OHT warms the poles by driving increased atmospheric heat transport to the poles. This effect is captured in a simple diffusive EBM. I discuss the significance of these findings for understanding the paleoclimate record.by Brian E. J. Rose.Ph.D

Starbursts versus Truncated Star Formation in Nearby Clusters of Galaxies

We present long-slit spectroscopy, B and R bandpass imaging, and 21 cm observations of a sample of early-type galaxies in nearby clusters which are known to be either in a star-forming phase or to have had star formation which recently terminated. From the long-slit spectra, obtained with the Blanco 4-m telescope, we find that emission lines in the star-forming cluster galaxies are significantly more centrally concentrated than in a sample of field galaxies. The broadband imaging reveals that two currently star-forming early-type galaxies in the Pegasus I cluster have blue nuclei, again indicating that recent star formation has been concentrated. In contrast, the two galaxies for which star formation has already ended show no central color gradient. The Pegasus I galaxy with the most evident signs of ongoing star formation (NGC7648), exhibits signatures of a tidal encounter. Neutral hydrogen observations of that galaxy with the Arecibo radiotelescope reveal the presence of ~4 x 10^8 solar masses of HI. Arecibo observations of other current or recent star-forming early-type galaxies in Pegasus I indicate smaller amounts of gas in one of them, and only upper limits in others.Comment: to be published in Astronomical Journa

Clinical stakeholders' opinions on the use of selective decontamination of the digestive tract in critically ill patients in intensive care units : an international Delphi study

Peer reviewedPublisher PD

Multicentric Castleman's disease: a case report

Castleman's disease is a clinicopathological entity associated with lymphoproliferation. We report a case of a 71 year old gentleman who was initially clinically suspected to have lymphoma (owing to clinical features at presentation), but was later histologically confirmed to have Castleman's disease. This case report underlines the importance of definitive histological diagnosis in patients with lympadenopathic presentation associated with systemic symptoms and the distinctiveness of multicentric Castleman's disease from malignant lymphoma. In this report we also attempt to provide new insight (through the review of medical literature) into the clinical features, pathogenesis, diagnosis and treatment of this rare and relatively benign disorder

The dependence of transient climate sensitivity and radiative feedbacks on the spatial pattern of ocean heat uptake

The effect of ocean heat uptake (OHU) on transient global warming is studied in a multimodel framework. Simple heat sinks are prescribed in shallow aquaplanet ocean mixed layers underlying atmospheric general circulation models independently and combined with CO_2 forcing. Sinks are localized to either tropical or high latitudes, representing distinct modes of OHU found in coupled simulations. Tropical OHU produces modest cooling at all latitudes, offsetting only a fraction of CO_2 warming. High-latitude OHU produces three times more global mean cooling in a strongly polar-amplified pattern. Global sensitivities in each scenario are set primarily by large differences in local shortwave cloud feedbacks, robust across models. Differences in atmospheric energy transport set the pattern of temperature change. Results imply that global and regional warming rates depend sensitively on regional ocean processes setting the OHU pattern, and that equilibrium climate sensitivity cannot be reliably estimated from transient observations

A comparison of postrelease survival parameters between single and mass stranded delphinids from Cape Cod, Massachusetts, U.S.A.

© The Author(s), 2015. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Marine Mammal Science 32 (2016): 161–180, doi:10.1111/mms.12255.The viability of healthy single stranded dolphins as immediate release candidates has received little attention. Responders have been reluctant to release lone delphinids due to their social needs, even when they pass the same health evaluations as mass stranded animals. This study tracked postrelease success of 34 relocated and released satellite tagged delphinids from single and mass strandings. Three postrelease survival parameters (transmission duration, swim speed, and daily distance) were examined to evaluate whether they differed among single stranded/single released (SS/SR), mass stranded/single released (MS/SR), or mass stranded/mass released (MS/MR) dolphin groups. Comparisons were also made between healthy and borderline release candidates. Satellite tags transmitted for a mean of 21.2 d (SD = 19.2, range = 1–79), daily distance traveled was 42.0 km/d (11.25, 20.96–70.72), and swim speed was 4.3 km/h (1.1, 2.15–8.54). Postrelease parameters did not differ between health status groups, however, SS/SR dolphins transmitted for a shorter mean duration than MS/MR and MS/SR groups. Postrelease vessel-based surveys confirmed conspecific group location for two healthy, MS/SR dolphins. Overall, these results support the potential to release healthy stranded single delphinids; however, further refinement of health assessment protocols for these challenging cases is needed.National Oceanic and Atmospheric Administration's National Marine Fisheries Service (NOAA NMFS); John H. Prescott Marine Mammal Rescue Assistance Program Grant Numbers: NA11NMF4390078, NA11NMF4390079, NA11NMF439009

Selective decontamination of the digestive tract in critically ill patients treated in intensive care units: a mixed-methods feasibility study (the SuDDICU study)

Background: Hospital-acquired infections (HAIs) are a major cause of morbidity and mortality. Critically ill patients in intensive care units (ICUs) are particularly susceptible to these infections. One intervention that has gained much attention in reducing HAIs is selective decontamination of the digestive tract (SDD). SDD involves the application of topical non-absorbable antibiotics to the oropharynx and stomach and a short course of intravenous (i.v.) antibiotics. SDD may reduce infections and improve mortality, but has not been widely adopted in the UK or internationally. Hence, there is a need to identify the reasons for low uptake and whether or not further clinical research is needed before wider implementation would be considered appropriate. Objectives: The project objectives were to (1) identify and describe the SDD intervention, (2) identify views about the evidence base, (3) identify acceptability of further research and (4) identify feasibility of further randomised controlled trials (RCTs). Design : A four-stage approach involving (1) case studies of two ICUs in which SDD is delivered including observations, interviews and documentary analysis, (2) a three-round Delphi study for in-depth investigation of clinicians' views, including semi-structured interviews and two iterations of questionnaires with structured feedback, (3) a nationwide online survey of consultants in intensive care medicine and clinical microbiology and (4) semistructured interviews with international clinical triallists to identify the feasibility of further research. Setting : Case studies were set in two UK ICUs. Other stages of this research were conducted by telephone and online with NHS staff working in ICUs. Participants : (1) Staff involved in SDD adoption or delivery in two UK ICUs, (2) ICU experts (intensive care consultants, clinical microbiologists, hospital pharmacists and ICU clinical leads), (3) all intensive care consultants and clinical microbiologists in the UK with responsibility for patients in ICUs were invited and (4) international triallists, selected from their research profiles in intensive care, clinical trials and/or implementation trials. Interventions : SDD involves the application of topical non-absorbable antibiotics to the oropharynx and stomach and a short course of i.v. antibiotics. Main outcome measures: Levels of support for, or opposition to, SDD in UK ICUs; views about the SDD evidence base and about barriers to implementation; and feasibility of further SDD research (e.g. likely participation rates). Results : (1) The two case studies identified complexity in the interplay of clinical and behavioural components of SDD, involving multiple staff. However, from the perspective of individual staff, delivery of SDD was regarded as simple and straightforward. (2) The Delphi study (n = 42) identified (a) specific barriers to SDD implementation, (b) uncertainty about the evidence base and (c) bimodal distributions for key variables, e.g. support for, or opposition to, SDD. (3) The national survey (n = 468) identified uncertainty about the effect of SDD on antimicrobial resistance, infection rates, mortality and cost-effectiveness. Most participants would participate in further SDD research. (4) The triallist interviews (n = 10) focused largely on the substantial challenges of conducting a large, multinational clinical effectiveness trial. Conclusions : There was considerable uncertainty about possible benefits and harms of SDD. Further large-scale clinical effectiveness trials of SDD in ICUs may be required to address these uncertainties, especially relating to antimicrobial resistance. There was a general willingness to participate in a future effectiveness RCT of SDD. However, support was not unanimous. Future research should address the barriers to acceptance and participation in any trial. There was some, but a low level of, interest in adoption of SDD, or studies to encourage implementation of SDD into practice