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Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Sciences, 1980. / Microfiche copy available in Archives and Science. / Vita. / Bibliography : leaves 227-236. / by Mary Josephine Richardson. / Ph.D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Sciences, 1980. / Microfiche copy available in Archives and Science. / Bibliography: leaves 92-98. / by Eric Arthur D'Asaro. / Ph.D.

The International Civil Aviation Organization (ICAO) proposed to introduce new operational strategies across the North Atlantic (NAT) airspace. This includes Minimum Navigation Performance Specifications (MNPS) airspace to increase the capacity and efficiency of the North Atlantic Organized Track System (NAT OTS). A numerical integration and simulation model called North Atlantic Simulation and Modeling (NATSAM) is developed to study the effects of these new strategies on NAT system performance. The model is capable of investigating the effects of implementing different operational policies and strategies proposed by ICAO such as Reduced Lateral Separation Minimum (RLatSM), NAT Region Data link mandate (DLM), Reduced Longitudinal Separation Minimum (RLongSM), cruise-climb profiles, variable Mach number profiles, step-climbs and other operational concepts to be studied by the ICAO. NATSAM models the individual flight performance using the Base of Aircraft Data (BADA) 3.9 model to calculate the flight profiles and fuel burn. The model employs simple heuristics to execute flight track assignment in the organized track system for each scenario. Detailed outputs and also aggregated outputs are provided by the model from which various key performance indicators (KPI) can be derived to assess the performance of the system. / Master of Science

This thesis presents a performance assessment of flight operations in the North Atlantic Organized Track System (OTS) using the Global Oceanic Model. The main contributions of the study are: a) improvements to the logic of the Global Oceanic Model; b) prediction of benefits among various aircraft separation minima and operational policies to assign flights to tracks in the OTS system; and c) forecast of OTS traffic over North Atlantic from 2020 to 2040. The preliminary results show that a concept of operation with longitudinal separation minima of 15 nm and information of the flight cost matrix provides average fuel savings of 93 kilograms per flight using 2020 traffic. The fuel savings increase to 170 kilograms per flight using traffic levels expected in the year 2040. A new operational track assignment routine is developed and it could save around 40 kilograms per flight compared with the current concept of operations. The study results show a shortage of capacity of the Organized Track System in the future. The analysis shows that the OTS configuration used today and in 2020 is unable to accommodate the traffic projected in 2040. The analysis concludes that more tracks will be needed to maintain an acceptable level of service. / MS

Atlantic Meridional Overturning Circulation (AMOC) is a vital process that transfers heat and nutrients throughout the world's oceans, helping to regulate global climate and support marine ecosystems. The timing and nature of the shift to modern AMOC, and especially to deep-water formation in the North Atlantic, has been a topic of ongoing study, with the Eocene-Oligocene Transition (EOT, ~34 Ma) as a potential focal point of this shift. However, the role played by abrupt EOT cooling and Antarctic glaciation in North Atlantic circulation remains unclear. Improved constraints on Paleogene circulation will provide insight into the sensitivity of AMOC to perturbations in global climate, which is particularly relevant in light of contemporary climate change. To examine deep North Atlantic circulation response to the EOT we obtained grain-size data from the terrigenous fraction of the mud-dominated sediments of the Southeast Newfoundland Ridge contourite drift complex at IODP Site U1411, which is interpreted to have formed under the influence of the Deep Western Boundary Current. We analyzed 195 samples that span 150 m of stratigraphy from 36-26 Ma. The main objective was to use the 'sortable silt' fraction (10-63 µm) to generate a record of relative change in bottom-current intensity. These data are complemented with a record of the abundance and size of lithogenic sand (>63 µm). Here we present the first physical proxy record of abyssal current intensity in the North Atlantic, from late Eocene to mid Oligocene. Invigoration of North Atlantic deep circulation occurred gradually (over Myr timescales), with no significant changes linked temporally to the EOT. We infer that deep circulation in the North Atlantic was not sensitive to the abrupt global cooling and Antarctic glaciation associated with the EOT. Rather, our data suggest that changes in North Atlantic circulation were likely governed by longer-term processes related to the opening of key tectonic gateways, such as the Greenland-Scotland Ridge in the North Atlantic, and the Drake and Tasman Passages in the Southern Ocean. Additionally, we identify a significant mid-Oligocene invigoration of North Atlantic abyssal circulation, which climaxes around 27.9 Ma, and is coeval with a decrease in atmospheric CO2. / Master of Science

No / he two archipelagos of Orkney and Shetland, which form the Northern Isles of Britain, are an active focus of archaeological research. The rich Neolithic heritage of Orkney has been acknowledged by the granting of World Heritage status. Although set in both a biogeographically peripheral position and within what may be considered to be marginal landscapes, these North Atlantic islands have a large number of settlement sites with long occupational sequences, often stretching from the Neolithic to the Late Iron Age or into the Norse period. The mixed paleoeconomic strategy presented by three of these settlements—Tofts Ness, Sanday, Orkney (excavated 1985–1988); the Iron Age sequences at Old Scatness, Shetland (excavated 1995–2006); and Late Neolithic and Bronze Age cultivated middens from Jarlshof, Shetland (investigated in 2004)—provide the core of the evidence discussed within this paper (the radiocarbon chronologies for the key sequences from these three sites are provided as Appendix 1). The role of the prehistoric paleoeconomy is argued to be of central importance in the longevity of these settlements. In particular, barley production is evidenced on all three sites by the plant macrofossils and by the human investment in the creation and management of manured soils, providing an infield area around the settlement. This paper focuses on the identification of these anthropogenic soils in the archaeological record. The investment in and management of these arable soils provides clear evidence for resource creation on all three sites. It is argued that these soils were a crucial resource that was necessary to support intensive barley cultivation. The intensive management implied by the presence of these soils is seen as a catalyst for sedentary living and sustainability within a marginal landscape. The evidence also demonstrates the continuity of agricultural practice from the Neolithic to the Iron Age together with the social dynamics that such a practice generates. This paper is in two parts: the first section examines in detail the evidence for the presence of anthropogenic soils and the mixed economic strategies for the Neolithic and Early Bronze Age presented by the evidence from Tofts Ness and Jarlshof. The evidence for the continuity of this intensive strategy of soil management is seen from the later evidence of the Bronze Age and Early Iron Age at Tofts Ness and the Middle Iron Age evidence at Old Scatness. The second part of the paper examines the importance of these soils as an inherited resource within the Neolithic and Early Bronze Age paleoeconomic system. Two models are presented. The first examines the cyclic importance of human creation and maintenance of small arable plots to high barley production yields and therefore to site viability, and the effect this has within a mixed resource system in providing settlement viability through time. The second explores the theoretical land and seascape that would provide this mixed resource base.

La circulation méridienne de retournement (MOC) de l’Atlantique Nord est une composante clé du système climatique global, via son rôle dans la redistribution de chaleur, d’eau douce et de propriétés chimiques entre hautes et basses latitudes. Aux moyennes et hautes latitudes, le Courant Nord-Atlantique(NAC) forme la branche haute de la MOC. Il s’écoule vers le nord-est à la frontière des gyres subpolaire et subtropical, et se divise en deux branches principales dans l’est du gyre subpolaire : une branche nord qui recircule vers l’ouest dans le gyre subpolaire et une branche sud qui alimente les mers Nordiques.Une simulation réaliste haute résolution (ORCA025-G70, 1/4°) est combinée à un outil d’analyse Lagrangienne pour étudier la variabilité de la MOC (1965-2004) à travers la section A25-Ovide qui joint le Portugal au Groenland. Deux cellules de retournement vertical sont identifiées : une cellule subtropicale connectant les hautes et basses latitudes et une cellule interne aux régions subpolaires. La variabilité décennale de la MOC est associée à des changements synchronisés des apports subtropical et subpolaire dans la NAC. Ce dernier subit d’importantes restructurations horizontales caractérisées par la variabilité opposée de ses deux branches. Ces modifications de la distribution horizontale du transport sont principalement régies par la variabilité de l’afflux subtropical.Les variations du transport de chaleur à travers A25-Ovide sont la cause principale de la variabilité du contenu de chaleur observée dans l’est du gyre subpolaire (1965-2004). La variabilité du transport de chaleur résulte d’un déséquilibre entre des changements opposés de ses composantes « vitesse » et « température ». Les anomalies de vitesse et température sont en partie reflétées dans des déplacements verticaux d’isopycnes, potentiellement associés à la proportion changeante de masses d’eau subtropicales et subpolaires transportées par la branche nord du NAC.Enfin, une circulation surface-fond moyenne calculée depuis des mesures hydrographiques répétées et des mesures altimétriques indique une contribution mineure de la mer du Labrador pour la MOC global. Cependant, l’intensité du retournement diapycnal à AR7W a presque diminué de moitié entres les 1990’s et les 2000’s, confirmant l’importance de la région pour la variabilité basse-fréquence de la MOC. / The meridional Overturning Circulation (MOC) of the North Atlantic ocean is a key component of the global climate system, through its role in redistributing heat, freshwater end chemical properties between low and high latitude regions. In mid-high latitude regions, the North Atlantic Current (NAC) forms the upper limb of the MOC. It flows northeastward at the subtropical/subpolar boundary, and splits into two main branches in the eastern subpolar gyre: a northern branch that recirculates within the subpolar region and a southern branch that feed the Nordic Seas.A realistic eddy-permitting simulation (ORCA025-G70, 1/4°) is combined with a Lagrangian analysis tool (ARIANE) to investigate the MOC variability (1965-2004) across the A25-Ovide line, which joins Greenland to Portugal. Two vertical overturning cells are identified: a subtropical cell connecting low and high latitudes (12Sv) and a cell internal to the subpolar gyre (4Sv). The decadal MOC variability is associated with synchronized transport changes of the subtropical and subpolar inflow within the NAC. The latter undergoes important horizontal restructuring with opposed transport changes of its northern and southern branches. Those horizontal transport changes are largely induced by the horizontal variability of the subtropical inflow.Changes in oceanic heat transport across A25-Ovide are largely responsible for the observed heat content changes in the eastern subpolar gyre (1965-2004). Heat transport variability at A25-Ovide results from an imbalance between opposed changes in its velocity and temperature components. Both temperature and velocity anomalies are partly reflected in large scale heaves of isopycnals, and potentially relate to the varying proportion of warm subtropical waters and cold subpolar waters advected within the northern NAC branch.A 2000’s mean full-depth circulation computed along the merged AR7W/A25-Ovide line from repeated hydrographic profile and altimetry data indicates a minor contribution of the Labrador Sea to the basin wide mean MOC. However, the strength of the diapycnal overturning at AR7W has almost halved between the 1990’s and the 2000’s, confirming the importance of the region for the low-frequency MOC Variability.

Le but de cette thèse est d’analyser les impacts de la variabilité atmosphérique grande échelle sur la circulation océanique. Ceci a déjà fait l’objet de nombreuses publications, dans lesquelles la variabilité atmosphérique est analysée en termes de modes de variabilité, déterminés par analyse en composantes principales (EOF en anglais) des anomalies de pression de surface. Ces modes sont l’Oscillation Nord-Atlantic (NAO), le Pattern Est-Atlantique (EAP) et le Pattern Scandinave (SCAN). La décomposition en EOF implique que les modes sont orthogonaux et symétriques. Cette dernière hypothèse a été montrée comme étant invalide pour la NAO. Par conséquent, un nouveau concept est proposé dans cette étude pour estimer la variabilité atmosphérique, celui des régimes de temps. Ces derniers sont des structures spatiales de grande échelle, récurrents et quasi-Stationnaires qui permettent de capturer la variabilité des forçages atmosphériques. De plus, ils permettent de séparer les patterns spatiaux des deux phases de la NAO. Ces régimes de temps sont donc une alternative prometteuse pour l’analyse de la variabilité océanique forcée par l’atmosphère. A partir d’observation et de modèles numériques (réalistes ou idéalisés), nous avons montré que les régimes Atlantic Ridge (AR), NAO− et NAO+ induisent une réponse rapide (échelles mensuelles à interannuelles) des gyres subtropical et subpolaire (via un mécanisme de Sverdrup topographique) et de la cellule de retournement (MOC, ajustement aux anomalies de transport d’Ekman). Aux échelles décennales, le gyre subpolaire s’intensifie lors de conditions NAO+ et BLK persistantes via un ajustement barocline aux flux de flottabilité et s’affaiblit pour AR via un ajustement barocline aux anomalies de rotationnel de vent. Ce dernier mécanisme explique aussi l’augmentation du gyre subtropical pour une NAO+ persistante et son affaiblissement pour un AR persistant. La réponse des gyres pour des conditions de NAO− persistantes est un déplacement vers le sud des gyres (l’intergyre gyre). L’intensité de la MOC est augmentée pour des conditions de NAO+ et BLK persistantes, dû à l’augmentation de la formation d’eau dense en mer du Labrador, et inversement pour NAO− et AR. Finalement, des bilans de contenu de chaleur dans la gyre subpolaire et les mers nordiques ont été effectués dans quatre modèles océaniques globaux. Les moyennes d’hiver de convergence océanique de chaleur dans la partie ouest de la gyre subpolaire sont positivement corrélées aux occurrences d’hiver de NAO−, ce qui est dû à la présence de l’intergyre, tandis que cette convergence est négativement corrélée aux occurrences d’AR, ce qui est dû à la réduction des deux gyres qui lui est associée. Les flux de chaleur vers l’océan dans la gyre subpolaire sont négativement corrélés aux occurrences d’hiver de la NAO+ et inversement pour la NAO−. Dans les mers Nordiques, ils sont positivement corrélés aux occurrences de BLK et, dans une moindre mesure, aux occurrences de AR. De plus, nous suggérons que la variabilité du contenu de chaleur dans la partie ouest du gyre subpolaire est la réponse décalée (lag de 6 ans) à l’intégration temporelle du forçage lié au régime NAO+, due à la combinaison de la réponse en phase (0-Lag) des flux de chaleur et à la réponse décalée (lag de 3 ans) de la convergence de chaleur. / The aim of the PhD is to investigate the impacts of the large-Scale atmospheric variability on the North- Atlantic ocean circulation. This question has already been addressed in a large number of studies, in which the atmospheric variability is decomposed into modes of variability, determined by decomposing sea-Level pressure anomalies into Empirical Orthogonal Function (EOFs). These modes of variability are the North-Atlantic Oscillation (NAO), the East-Atlantic Pattern (EAP) and the Scandinavian Pattern (SCAN). EOF decomposition assumes that the modes are orthogonal and symmetric. The latter assumption, however, has been shown to be inadequate for the NAO. Hence, a different framework is used in this study to assess the atmospheric variability, the so-Called weather regimes. These are large-Scale, recurrent and quasi-Stationary atmospheric patterns that have been shown to capture well the interannual and decadal variability of atmospheric forcing to the ocean. Furthermore, they allow to separate the spatial patterns of the positive and negative NAO phases. Hence, these weather regimes are a promising alternative to modes of variability in the study of the ocean response to atmospheric variability. Using observations and numerical models (realistic or in idealised settings), we have shown that the Atlantic Ridge (AR), NAO− and NAO+ regimes drive a fast (monthly to interannual) wind-Driven response of the subtropical and subpolar gyres (topographic Sverdrup balance) and of the meridional overturning circulation (MOC, driven by Ekman transport anomalies). At decadal timescales, the subpolar gyre strengthens for persistent NAO+ and Scandinavian Blocking (BLK) conditions via baroclinic adjustment to buoyancy fluxes and slackens for persistent AR conditions via baroclinic adjustment to wind-Stress curl anomalies. The latter mechanism also accounts for the strengthening of the subtropical gyre for persistent NAO+ conditions and its weakening for persistent AR conditions. The gyres response to persistent NAO− conditions reflects the southward shift of the gyre system (the intergyre gyre). The MOC spins-Up for persistent NAO+ and BLK conditions via increased deep water formation in the Labrador Sea, and conversely for the NAO− and AR regimes. Last, heat budget calculations in the subpolar gyre and the Nordic Seas have been performed using four global ocean hindcasts. The winter averaged heat convergence in the western subpolar gyre is positively correlated with the NAO− winter occurrences, which is due to the intergyregyre circulation, while it is negatively correlated with AR winter occurrences, because of the wind-Driven reduction of both gyres. Downward surface heat flux anomalies are negatively correlated with NAO+ occurrences, and conversely for the NAO−. In the Nordic Seas, they are positively correlated with BLK and to a lesser extent AR occurrences. Furthermore, we suggest that the heat content variability in the western subpolar gyre is the signature of the delayed response (6-Year lag) to the time-Integrated NAO+ forcing, due to the combination of the immediate (0-Lag) response of surface heat flux and the lagged (3 year lag) response of ocean heat convergence.