Atlantic Ocean circulation at the Last Glacial Maximum : inferences from data and models

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2012This thesis focuses on ocean circulation and atmospheric forcing in the Atlantic Ocean at the Last Glacial Maximum (LGM, 18-21 thousand years before present). Relative to the pre-industrial climate, LGM atmospheric CO2 concentrations were about 90 ppm lower, ice sheets were much more extensive, and many regions experienced significantly colder temperatures. In this thesis a novel approach to dynamical reconstruction is applied to make estimates of LGM Atlantic Ocean state that are consistent with these proxy records and with known ocean dynamics. Ocean dynamics are described with the MIT General Circulation Model in an Atlantic configuration extending from 35°S to 75°N at 1° resolution. Six LGM proxy types are used to constrain the model: four compilations of near sea surface temperatures from the MARGO project, as well as benthic isotope records of δ18O and δ13C compiled byMarchal and Curry; 629 individual proxy records are used. To improve the fit of the model to the data, a least-squares fit is computed using an algorithm based on the model adjoint (the Lagrange multiplier methodology). The adjoint is used to compute improvements to uncertain initial and boundary conditions (the control variables). As compared to previous model-data syntheses of LGM ocean state, this thesis uses a significantly more realistic model of oceanic physics, and is the first to incorporate such a large number and diversity of proxy records. A major finding is that it is possible to find an ocean state that is consistent with all six LGM proxy compilations and with known ocean dynamics, given reasonable uncertainty estimates. Only relatively modest shifts from modern atmospheric forcing are required to fit the LGM data. The estimates presented herein successfully reproduce regional shifts in conditions at the LGM that have been inferred from proxy records, but which have not been captured in the best available LGM coupled model simulations. In addition, LGM benthic δ18O and δ13C records are shown to be consistent with a shallow but robust Atlantic meridional overturning cell, although other circulations cannot be excluded.Primary support was provided by a National Defense Science and Engineering Graduate Fellowship and two National Science Foundation awards: Award #OCE-0645936: “Beyond the Instrumental Record: the Case of Circulation at the Last Glacial Maximum” and Award #OCE-1060735: “Collaborative Research: Beyond the Instrumental Record - the Ocean Circulation at the Last Glacial Maximum and the de-Glacial Sequence”. Important secondary support came from the National Ocean Partnership Program and the National Aeronautics and Space Administration via the ECCO effort at MIT

DIET : new developments and recent results

Among existing grid middleware approaches, one simple, powerful, and flexibleapproach consists of using servers available in different administrative domainsthrough the classic client-server or Remote Procedure Call (RPC) paradigm.Network Enabled Servers (NES) implement this model also called GridRPC.Clients submit computation requests to a scheduler whose goal is to find aserver available on the grid. The aim of this paper is to give an overview of anNES middleware developed in the GRAAL team called DIET and to describerecent developments. DIET (Distributed Interactive Engineering Toolbox) is ahierarchical set of components used for the development of applications basedon computational servers on the grid.Parmi les intergiciels de grilles existants, une approche simple, flexible et performante consiste a utiliser des serveurs disponibles dans des domaines administratifs différents à travers le paradigme classique de l’appel de procédure àdistance (RPC). Les environnements de ce type, connus sous le terme de Network Enabled Servers, implémentent ce modèle appelé GridRPC. Des clientssoumettent des requêtes de calcul à un ordonnanceur dont le but consiste àtrouver un serveur disponible sur la grille.Le but de cet article est de donner un tour d’horizon d’un intergiciel développédans le projet GRAAL appelé DIET 1. DIET (Distributed Interactive Engineering Toolbox) est un ensemble hiérarchique de composants utilisés pour ledéveloppement d’applications basées sur des serveurs de calcul sur la grille

A Modular Framework for Adaptive Scheduling in Grid Application

To achieve improved performance, application schedulers are typically designed to satisfy the resource requirements of specific applications. Consequently, application characteristics and models are often embedded in the scheduler itself. Results have shown that this strategy is effective for achieving improved application performance. However, application-specific schedulers may not be easily retargeted for other applications. In this thesis, we propose a modular application scheduler design that employs detailed application performance models and mapping strategies that promote application performance, but does not embed such components within the scheduler itself. Our scheduler is both environment-sensitive and configurable. To ensure that schedules are properly targeted for conditions of the target execution environment at run-time, the scheduler can incorporate dynamic resource availability in scheduling decisions. The scheduler also supports a set of configurable scheduling policies that are easily tuned to control scheduler behavior. We implement a prototype scheduler and use the class of iterative, mesh-based applications to test the prototype. We implement two test applications, Jacobi and the Game of Life, and develop performance models and mapping strategies for each application. We present experimental results we obtained by applying our scheduling methodology to Jacobi and the Game of Life in Computational Grid environments. Our testbeds included up to 20 machines organized in 4 clusters at 3 geographically distributed sites. In these experiments, our approach consistently outperforms conventional scheduling approaches.Pre-2018 CSE ID: CS2002-069

Adaptive window scheduling for a hierarchical agent system

International audienceDIET (distributed interactive engineering toolbox) is a toolbox for the construction of network enabled server (NES) systems. For most NES systems, as for most grid middleware systems, the scheduling system is centralized and can suffer from poor scalability. DIET provides an alternative: low-latency, scalable scheduling services based on a distributed hierarchy of scheduling agents. However, the online scheduling model used currently in DIET can overload interactive servers in high-load conditions and does not allow adaption to task or data dependencies. In this article we consider an alternative model based on active management of the flow of requests throughout the system. We have added support for (1) limiting the number of concurrent requests on interactive servers, (2) server and agent-level queues, and (3) window-based scheduling algorithms whereby the request release rate to servers can be controlled and some re-arrangement of request to host mappings is possible. We present experiments demonstrating that these approaches can improve performance and that the overheads introduced are not significantly different from those of the standard DIET approac

Experiences with hierarchical request flow management for Network-Enabled Server Environments

DIET (Distributed Interactive Engineering Toolbox) is a toolbox for the construction of Network Enabled Server systems. Client requests for computational services are automatically matched with available resources by a distributed hierarchy of scheduling agents. Traditionally NES systems have used a centralized agent for performance prediction and resource information management; in DIET, these services are distributed by providing them at the DIET server level. DIET has traditionally offered an online scheduling model whereby all requests are scheduled immediately or refused. This approach can overload interactive servers in high-load conditions and does not allow adaptation of the schedule to task or data dependencies. In this article we consider an alternative model based on active management of the flow of requests throughout the system. We have added support for (1) limiting the number of concurrent requests on interactive servers, (2) server and agent-level queues, and (3) window-based scheduling algorithms whereby the request release rate to servers can be controlled and some re-arrangement of request to host mappings is possible. We present experiments demonstrating that these approaches can improve performance and that the overheads introduced are not significantly different from those of the standard DIET approach.DIET (Distributed Interactive Engineering Toolbox) est une boîte à outils pour la création de systèmes type NES (Network Enabled Server). L’environnement proposé est capable de déterminer le serveur approprié en tenant compte de la requête de calcul. Ce service est fourni par une hiérarchie d’agents distribués. Typiquement, les systèmes NES prédisent les performances et gèrent l’information sur les ressources disponibles à partir d’un agent centralisé. Dans DIET, ces services sont distribués au niveau des serveurs DIET. Actuellement, DIET utilise un modèle d’ordonnancement «on-line» où toutes les requêtes sont soit ordonnancées soit refusées immédiatement. Avec ce modèle, les serveurs interactifs peuvent devenir surchargés et il est impossible d’échanger le placement des tâches pour prendre en compte les dépendances entre les tâches ou sur les données. Dans cet article, nous présentons un modèle alternatif basé sur la gestion actif du mouvement des tâches au travers du système. Nous avons ajouté la capacité de (1) limiter le nombre de requêtes actives sur un serveur en même temps, (2) garder les requêtes dans une file d’attente au niveau des serveurs et des agents, et (3) ordonnancer les tâches dans une fenêtre de temps, ce qui permet de contrôler le flux des tâches vers les serveurs et rend possible le redistribution du placement des tâches. Nous présentons des expériences qui montrent que ces apports peuvent ameliorer les performances de DIET et que les coûts ajoutés sont proche de celle de l’approche DIET actuel

GoDIET: Un outil pour le déploiement de DIET

In this article, we address the automatic configuration, launch, and management of a distributed middleware platform for the Grid of type Application Service Provider (ASP) called Distributed Interactive Engineering Toolbox (DIET). The difficulty of this task is due to the architecture of DIET, which is distributed and hierarchical. The need for an automated tool for these tasks is reinforced by the diversity and number of components for the DIET middleware. In this article, we present GoDIET, a new tool created to satisfy these needs, though the solutions presented are valid for any distributed, hierarchical environment. The principles underlying GoDIET will be detailed by example with the configuration and launch of DIET and LogService, an external service for the management of traces for distributed software components. We then present a series of experiments that permit the evaluation of the performance and efficacity of GoDIET. We also evaluate the robustness of the DIET platform for a large number of servers

GoDIET: a tool for managing distributed hierarchies of DIET agents and servers

The Distributed Interactive Engineering Toolbox (DIET) is an Application Service Provider (ASP) platform providing remote execution of computational problems on distributed, heterogeneous resources. Traditional ASP toolkits are based on a single, centralized scheduling agent coordinating computation requests from clients with service offerings from servers. DIET is based on a hierarchy of agents that collaborate to perform scheduling decisions; we are exploring the benefits of hierarchical agent architectures for scalability and adaptation to heterogeneous network performance. This paper describes GoDIET, a new tool for the configuration, launch, and management of DIET on computational grids. Users of GoDIET write an XML file describing their available compute and storage resources and the desired overlay of DIET agents and servers onto those resources. GoDIET automatically generates and stages all necessary configuration files, launches agents and servers in appropriate hierarchical order, reports feedback on the status of running components, and allows shutdown of all launched software. We present a series of experiments that permit the evaluation of the performance of GoDIET for several launch and management approaches. We also evaluate the robustness of the DIET platform for a large number of servers.Dans cet article, nous exposons les travaux menés autour de la configuration, du lancement et de la gestion de DIET, un intergiciel de type ASP (Application Service Provider) pour la grille. La difficulté de cette tâche repose sur l’architecture de DIET qui est distribuée et hiérarchique. Le besoin de disposer de ce type d’outil est renforcé par la diversité et le nombre des éléments de cet intergiciel. Dans cet article, nous présenterons GoDIET,un nouvel outil adapté aux contraintes de DIET, cependant les concepts mis en œuvre restent valides pour tout environnement distribué et hiérarchique. Le principe de fonctionnement de GoDIET sera détaillé au travers de son utilisation pour la gestion de DIET et du LogService, un service externe pour la gestion de traces d’ éléments distribués. Enfin, nous présentons une série d’expérimentations qui permettent d’ évaluer la performance et l’efficacité de GoDIET. Dans cette même série d’expériences la robustesse de la plate-forme DIET sur un grand nombre de serveurs sera également étudiée