The aim of this research was to gain a better understanding of the ecology and life history of the deepwater notothenid, Dissostichus eleginoides, on the Patagonian Shelf. Archival tagging revealed strong site fidelity of adult toothfish with the majority of fish remaining within 50km of release. Furthermore depth data revealed three behavioural patterns showing feeding, seasonal and spawning activities. The trophic ecology of five notothenioids was studied, examining resource utilisation and niche separation on the Falkland’s shelf. Spatial, ontogenic and seasonal variations in the parasite fauna for juvenile D. eleginoides are described and potential species for use as biological tags to study toothfish population structure are suggested. Validated age readings gave maximum estimated ages of 35 (L = 214.3cm) and 26 years (L = 126.3cm) for females and males respectively and reasons for this sexual dimorphism are discussed. Comparisons of otolith transition zones and growth rates from different regions shows toothfish have adapted their life history traits dependant on their environmental and hydrological surroundings, with populations in warmer areas growing quicker than those in cooler waters. Reproduction in toothfish is discontinuous and group synchronous and final spawning was found to occur in batches. Toothfish predominantly spawn only in one region around the Falklands, on the Burdwood Bank, mainly during July/August. Evidence of skipped spawning was identified indicating that not all fish spawn annually and this aspect is discussed in terms of body condition, periodic strong recruitment and the lack of large scale migrations of adult toothfish. Toothfish around the Falklands have a higher fecundity compared to other regions, a potential adaption to living north of the polar front. This new information on age, growth, reproduction and movements of toothfish, combined with its role in the Patagonian shelf and slope ecosystems, is vital for accurate stock assessment and hence sustainable fisheries management.

In this MSc thesis I determine if wind-generated bubbles elevated measurements of above-water normalized water-leaving radiance (nLw) and subsequent remote sensing estimates of particulate inorganic carbon (PIC) in a coccolithophore bloom on the Patagonian Shelf. Although no measurements were made of bubbles, shipboard wind speed was used as a proxy for bubble backscattering. An empirical orthogonal function (EOF) analysis was performed on nLw. The first EOF accounted for 95% of the variance, and was attributed to changes in spectral amplitude. Scores of the first EOF were positively correlated with flow-through PIC backscattering (bb′) > 5x10-4 m-1, indicating that above this threshold PIC was an optically active seawater constituent. There was only evidence for a bubble elevation of nLw at values of bb′ < 5x10-4 m-1 and wind speeds > 12.5 m s-1. There was no evidence for a bubble elevation of PIC estimated using the two-band PIC algorithm.

Patagonian toothfish (Dissostichus eleginoides) or "Chilean sea bass" support a valuable and controversial fishery, but the life history is little known and longevity estimates range from ~20 to more than 40 or 50 yr. In this study, lead-radium dating provided validated age estimates from juveniles to older adults, supporting the use of otoliths as accurate indicators of age. The oldest age groups were near 30 yr, which provided support for age estimates exceeding 40 or 50 yr from grow zone counts in otolith sections. Hence, scale reading, which rarely exceeds 20 years, has the potential for age underestimation. Lead-radium dating revealed what may be minor differences in age interpretation between two facilities and findings may provide an age-validated opportunity for the CCAMLR Otolith Network to reassess otolith interpretations. Orange roughy (Hoplostethus atlanticus) support a major deep-sea fishery and stock assessments often depend on age analyses, but lifespan estimates range from ~20 to over 100 yr and validation of growth zone counts remained unresolved. An early application of lead-radium dating supported centenarian ages, but the findings were met with disbelief and some studies have attempted to discredit the technique and the long lifespan. In this study, an improved lead-radium dating technique used smaller samples than previously possible and circumvented assumptions that were previously necessary. Lead-radium dating of otolith cores, the first few years of growth, provided ratios that correlated well with the ingrowth curve. This provided robust support for age estimates from otolith thin sections. Use of radiometric ages as independent age estimates indicated the fish in the oldest group were at least 93 yr. Lead-radium dating has validated a centenarian lifespan for orange roughy. To date, radium-226 has been measured in otoliths of 39 fish species ranging from the northern Pacific and Atlantic Oceans to the Southern Ocean. In total, 367 reliable radium-226 measurements were made in 36 studies since the first lead-radium dating study on fish in 1982. The activity of radium-226 measurements ranged over 3 orders of magnitude (<0.001 to >1.0 dpm.g⁻¹). An analysis revealed ontogenetic differences in radium-226 uptake that may be attributed to changes in habitat or diet. Radiometric age from otolith core studies was used to describe a radium-226 uptake time-series for some species, which revealed interesting patterns over long periods. This synopsis provides information on the uptake of radium-226 to otoliths from an environmental perspective, which can be used as a basis for future studies.

La marge sud-chilienne constitue la seule masse continentale de l’hémisphère sud qui intercepte l’intégralité de la ceinture des vents d’ouest (SWW), en interaction avec la circulation océanique. Elle occupe donc une position stratégique pour les reconstructions paléoclimatiques et a fait l’objet d’une attention croissante ces dernières décennies. Dans le contexte des hautes latitudes sud de la marge chilienne, les objectifs de cette thèse se sont portés sur (1) l’établissement d’une chronostratigraphie précise basée sur des datations radiocarbone et la téphrochronologie et (2) sur la reconstruction de la dynamique de la calotte nord-Patagonienne en lien direct avec le régime des précipitations, les températures et/ou la dynamique interne des glaciers sur les derniers 22 ka BP à partir de l’étude d’un enregistrement marin à ultra haute résolution et à fort taux de sédimentation, collecté au large de la péninsule de Taitao (~46°S). Basé sur un modèle d’âge robuste par des datations radiocarbone associées à une étude téphrochronologique, l’enregistrement marin MD07-3088 permet une couverture temporelle large depuis le dernier maximum glaciaire, la déglaciation et l’Holocène. Plusieurs traceurs (minéralogie des argiles, granulométrie, géochimie inorganique) ont été utilisés afin de retracer la variabilité des sources et les fluctuations de la calotte nord patagonienne. Couplée aux paléoreconstructions des températures des eaux de surface et de la variabilité des proportions polliniques, cette étude a permis de retracer les variations dans le régime des précipitations et les interconnections entre les réservoirs océaniques et atmosphériques. Les résultats ont montré qu’au cours du DMG (22-18 ka BP), les températures globalement plus froides semblent contrôler les apports terrigènes en provenance de la chaine côtière proximale et la dynamique des glaciers. Lors de la déglaciation (18-11,5 ka BP), les conditions globalement plus chaudes marquent un changement radical dans la source des apports détritiques, avec une dominance de la cordillère andéenne distale. Cet intervalle est ponctué par 3 évènements de refroidissement, dont l’ACR (14,3-12,7 ka BP) pendant lesquels un regain de l’activité glaciaire est enregistré. Au cours de cet intervalle, l’expansion des tourbières Magellanes suggère des conditions climatiques plus froides et très humides résultant de la migration progressive vers le nord des Westerlies. L’Holocène Inférieur (11,5-8 ka BP) se caractérise par des conditions similaires à celles de la déglaciation avec la présence d’un événement plus grossier témoignant soit de l’influence de la légère baisse des températures (~2°C), soit d’un rôle plus important de la dynamique interne des glaciers. L’Holocène Moyen (8-3 ka BP) est illustré par la mise en place de la phase de Néoglaciation qui se traduit par un déplacement vers le nord de la cellule des vents d’ouest caractérisé par des forts apports de précipitations dans notre zone d’étude bien que peu de variations soient enregistrées dans les estimations des SST. Enfin, la faible variation des SST et la légère augmentation des précipitations enregistrées au cours de l’Holocène Inférieur (3 ka BP à l’actuel) témoignent d’un retour de la cellule des vents à une position similaire à l’actuel. / The south-chilean margin is the one continental mass to intercept the entire Westerly Winds cell (SWW), closely linked to the oceanic circulation. It constitutes a strategic area for paleoclimatic reconstructions and represents a peculiar interest since the last decades. In the southern high latitude chilean margin setting, the main objectives of this thesis were focused on (1) the establishment of a precise chronology based on radiocarbon dates and tephrochronology and (2) to restore the north-Patagonian icefield dynamic strongly linked to the rainfall features, temperatures and/or internal glaciers dynamic over the last 22 ka BP from a High-resolution and High sedimentation rate deep-sea core collected offshore the Taitao peninsula (~46°S). Based on robust age model by radiocarbon dates and tephrochronology study, the marine record MD07-3088 allows a large time-span since the Last Glacial Maximum, the deglaciation and the Holocene. Several proxies (clay mineralogy, grain-size and inorganic geochemistry) were used to restore the variability in continental source inputs and north-patagonian icefield fluctuations. Coupled to SST estimations and palynological dataset, this study allows to reconstruct rainfall changes and interconnections between oceanic and atmospheric features. Results show that during the LGM (22-18 ka BP), the globally colder temperatures play a major role in the detrital supplies from Coastal Range and glacier dynamic. During the deglaciation (18-11,5 ka BP), warmer conditions mark a drastic change in the terrigenous source with a dominance of Andean Cordillera influence. This interval is punctuated by 3 colder events, in particularly the ACR event (14,3-12,7 ka BP) during which a renewed glacial activity is recorded as shown by the expansion of Magellanes moorlands, typical of colder and more humid climate as a result of the northward migration of the Westerly Winds. The Early Holocene (11,5-8 ka BP) is marked by climatic conditions similar to those of the deglaciation with only the presence of one colder event resulting either by slightly temperatures decreasing (~2°C) or the internal glacier dynamic contribution. The Middle Holocene (8-3 ka BP) is illustrated by the settlement of the Neoglaciation phase resulting from the northward displacement of the SWW cell favouring more intense rainfalls in the study site even Tough any significant temperature variations are observed. Finally, the low SST variability and the slight increase of rainfalls recorded during the Upper Holocene (3 ka BP to present) give clues about the return of the SWW to modern location.

The southern Patagonian Andes record the Late Cretaceous closure and inversion of the Late Jurassic – Early Cretaceous Rocas Verdes marginal basin, subsequent development of the Patagonian retroarc fold-thrust belt and the Neogene to present tectonic superposition of a left-lateral strike-slip plate margin defined by the Magallanes- Fagnano fault zone. In this dissertation, I present new geologic maps, cross sections and detailed macro- and microscopic structural analyses that describe the geometry and kinematic evolution of the fold-thrust belt and superposed strike-slip deformation over ~200 km along-strike between 53° and 55° S latitude. Results are discussed in the context of the regional tectonic development of the southernmost Andes and are relevant to the understanding of important tectonic processes including the development of a retroarc fold-thrust belt, the formation of a basal décollement below and toward the hinterland of a fold-thrust belt and the spatial distribution of deformation along a strike-slip plate margin. New maps and balanced cross-sections of the Patagonian fold-thrust belt show that it developed during two main phases of Late Cretaceous to Paleogene shortening that were partly controlled by the antecedent geology and mechanical stratigraphy of the Rocas Verdes basin. During the Late Cretaceous, a thin-skinned thrust belt developed above a décollement that formed first in relatively weak shale deposits of the Rocas Verdes basin and later deepened to <1 km below the basement-cover contact. Ramps that cut mechanically rigid volcanic rocks of the marginal basin link the two décollements. Basement-involved reverse faults that cut the early décollements and probably reactivate Jurassic normal faults reflect Paleogene shortening. Shortening estimates increase northwest to southeast from 26 to 37% over 100 km along-strike and are consistent with regional models of the fold-thrust belt. Structural data, kinematic analyses, and microstructural observations from the lower décollement show that it is defined by transposition of several generations of northeast-vergent noncylindrical folds, shear bands, and a quartz stretching lineation that are kinematically compatible with first-generation structures of the fold-thrust belt. Quartz microstructural data from the décollement are consistent with deformation temperatures that decrease from ~500-650° C to ~400-550° C over ~75 km in the transport direction, indicating that the décollement dipped shallowly (~6°) toward the hinterland. The décollement decoupled the underthrust continental margin from the fold- thrust belt and exemplifies the kinematic relationship between shortening that occurs coevally in a retroarc fold thrust-belt and its polydeformed metamorphic ‘basement’. Fault kinematic data and crosscutting relationships show kinematic and temporal relationships between populations of thrust, strike-slip and normal faults that occur in the study area. Thrust faults form an internally compatible population that shows subhorizontal northeast-trending shortening of the fold-thrust belt and is kinematically distinct from populations of normal and strike-slip faults. Both strike-slip and normal faults crosscut the fold-thrust belt, are localized near segments of the Magallanes- Fagnano fault zone, have mutually compatible kinematic axes and are interpreted to be coeval. Strike-slip faults form Riedel and P-shear geometries that are compatible with left-lateral slip on the Magallanes-Fagnano fault-zone. Strike-slip and normal faults occur in a releasing step-over between two overlapping left-lateral, left-stepping segments of the Magallanes fault zone and record a tectonic event defined by sinistral transtension that probably reflects changing plate dynamics associated with the opening of the Drake Passage during the Early Miocene. / text

Le plan de thèse comprend les objectifs spécifiques suivants: D'après les observations de terrain, la carte géologique structurale sera obtenue en couvrant la zone géoréférencée entre le lac Buenos Aires et la rivière Mayer dans le sud des Andes de la Patagonie, province de Santa Cruz. L'analyse de la provenance a été faite par des études pétrographiques en grès à cinq coupes stratigraphiques représentatives des séquences considérées appartenant au Crétacé inférieur et au Miocène dans le secteur nord du bassin Austral. D'autres études préliminaires de diffraction des rayons X à un profil (appelé Veranada de Gómez). Aussi, deux unités lithostratigraphiques ont été datées et étudiées par provenance des zircons détritiques. Il est prévu de déterminer pour la zone d'étude, le début de l'avant-pays d'étape, et une estimation est obtenue l'âge de l'exhumation des régions d'origine, et donc une approche semi-quantitative à la fois de l'apparition du soulèvement, comme modèles de dispersion des sédiments. L'analyse complète de ces données donnera la structure générale de la dispersion paléogéographique et des sédiments de la bordure nord du Bassin du Sud pour s'harmoniser avec le patron du secteur sud, qui a alimenté la zone d'étude. De plus, une déformation fragile sera étudiée en analysant les failles striaes pour caractériser les déformations dans la zone. / The thesis plan includes the following specific objectives: According to field observations structural geological map will be obtained georeferenced area covering between the lake Buenos Aires and Mayer River in the Southern Andes Patagonian, Santa Cruz province. Provenance analysis were done by petrographic studies in sandstones at five stratigraphic sections representative of the sequences considered belonging to the Lower Cretaceous and Miocene in the northern sector of the Austral basin. Further X-ray diffraction preliminary studies at one profile (called Veranada de Gómez). Also, two lithostratigraphic units were dated and study by detrital zircons provenance. It is expected to determine for the study area, the beginning of the stage foreland, and an estimate is obtained the age of the exhumation of the regions of origin, and thus a semi-quantitative approach at a time the age of onset of uplift, as sediment dispersion models. The comprehensive analysis of these data will give the general pattern of palaeogeographic dispersal and sediments of the northern edge of Southern Basin to mesh with the southern sector pattern, which fed the study area. Moreover fragile deformation will be studied by analyzing faults striaes to characterize the deformation events in the area.