Este trabalho apresenta uma investigação da interação entre o gelo marinho Antártico e o setor austral e sudoeste do Atlântico Sul. Para realizar este estudo foram utilizados dados de satélite da concentração do gelo marinho e o modelo numérico acoplado do NCAR (Nacional Center for Atmospheric Research) o CCSM3 (Community Climate System Model) versão 3. O CCSM3 foi integrado por 150 anos em 3 diferentes simulações. Estas foram forçadas com as climatologias prescritas da concentração de gelo máximo (MAX), mínimo (MIN) e médio (controle) com o objetivo de avaliar o impacto das mudanças do gelo marinho Antártico no Mar de Weddell e na região da Confluência Brasil-Malvinas (CBM). Este estudo enfatiza a interação das escalas de tempo anual, interanual a decadal. A metodologia empregada nesta pesquisa inclue as análises de correlação e espectral, bem como as técnicas estatísticas de funções ortogonais empíricas (EOF) e decomposição de valores singulares (SVD). O comportamento climático das variáveis oceânicas apresentou sensibilidade às diferentes concentrações de gelo marinho Antártico. A variabilidade das anomalias de TSM e SSM mostraram para o experimento MIN padrões espaciais que caracterizam um regime frio do Giro de Weddell, associado a menor intrusão da CDW. A resposta da variabilidade da temperatura, entre os cenários de gelo MAX e MIN, para a região da CBM sugere que menores concentrações de gelo marinho Antártico intensificam as anomalias de TSM desta região, com periodicidade interanual de 2-3 anos e decadal de 25 anos. A circulação oceânica, em ambas as regiões analisadas, associada a fase positiva da SAM se intensifica devido a influência das menores concentrações de gelo marinho. / In this work the interaction between Antarctic sea-ice and the South Atlantic ocean (austral and southwestern sectors) is investigated. To accomplish this satellite-observed sea-ice concentration (SIC) and a coupled model from NCAR-CCSM3 (National Center for Atmospheric Research - Community Climate System Model version 3) were employed. Three 150-year simulations, one each with the maximum (MAX), minimum (MIN) and average (control) SIC prescribed climatologies, were used to drive the CCSM3 run. The goal of the research is to evaluate the Weddell Sea and Brazil-Malvinas confluence (BMC) response to observed extremes in Antarctic sea-ice. This study focuses on annual, interannual and decadal timescales. The applied methodology uses correlation and spectrum analyses, as well as Empirical Orthogonal Functions (EOF) and Singular Value Decomposition (SVD). The annual mean behavior of oceanic variables showed sensibility to Antarctic sea-ice changes. The variability of SST and SSS anomalies showed for the sea-ice MIN experiment a spatial pattern that characterizes the cold regime of the Weddell Gyre, associate with low CDW intrusion. The response of the temperature variability, between sea-ice MAX and MIN scenarios, for the BMC region suggests that less Antarctic sea-ice produces a SST anomaly intensification in this region with a interannual cycle of the 2-3year and decadal cycle of the 25-year. The oceanic circulation in both study regions, related to positive SAM events, showed a intensification to less SIC influence.

Early 1990s to late 2000s freshening (ΔS ≈ -0.001–0.002) and warming (Δθ ≈ 0.02°C–0.035°C) of bottom waters was detected in the southern Pacific Ocean, and Ross Sea source waters progressively freshened during the past four decades. This study investigates potential freshwater anomaly sources and quantifies their effect. Glacial melt water inputs to the GCT increased by 1.3 km^3 per decade (1976– 2007), more rapidly so after 2000 (6.8 km^3 per decade), freshening local Shelf Water by 0.0004 per decade. Lighter basal melt inputs to the LAT started in 1994 and also picked up after 2000 to 14.9 km^3 per decade, lowering the local Antarctic Surface Water salinity by -0.017 per decade. Upstream in the Amundsen Sea surface water freshened by -0.03 per decade (1994–2007) mostly (50%) from larger melt water inputs from the Pine Island (17.7 km^3 per decade) and Dotson (14.8 km^3 per decade) glaciers. Two decades of steady (1978-2000) strengthening of sea ice productivity (200 km^3 per decade) within the Ross Sea Polynya suddenly reversed to weakening (-98.6 km^3 per decade) and resulted in Shelf Water freshening (-0.02 per decade) thereafter. To fully account for the observed variability in Ross Sea waters, the progressive (1992- 2011) adjustment of the density field and induced advective contributions are estimated based on a simplified three-layer stratification. Eastern (western) inflow (outflow) of light surface (dense shelf) water increased by 28% (15%) to 1.11 Sv (1.01 Sv) by 2011; whereas a sluggish intermediate inflow (0.02 Sv) of Modified Circumpolar Deep Water turned into outflow after 2007, thus contributing 0.09 Sv by 2011 to the ventilation of deep waters farther offshore. The estimated evolution of overturning and advective salt fluxes in the Ross Sea yield overall freshening of water masses similar to those derived from observations. Volumetric mean salinities declined at -0.07 per decade for Antarctic Surface Water, -0.05 per decade for Modified Circumpolar Water, and -0.03 per decade for Shelf Water. Outflow intensification of Shelf Water mixtures is also consistent with bottom water property changes (freshening and warming) measured farther downstream in the southern Pacific Ocean.

Recent work has described how gas exchange can occur through sea ice. First, carbon fluxes over sea ice surfaces have been measured. Second, sea ice brine has an elevated capacity over seawater to absorb CO2(g) due to its cold temperature and chemical equilibrium promoting carbon phase changes. Sea ice pCO2 profiles were collected using a new method of remotely sampling gas in situ via diffusive membranes placed within growing sea ice. Gas analysis was complimented by measurements of local meteorology and ice chemistry. The work was part of the CASES 2004 project. The observed elevation in sea ice pCO2 coupled with the mobility of the brine points to the role that brine plays in Arctic carbon transport. The gas transport links the Arctic atmosphere and ocean and indicates that a thinning and receding ice cover may not result in creating a negative feedback to the increasing atmospheric CO2(g) concentration. / October 2008

This work aims to increase our understanding of the nature of large scale features of sea ice from a dynamics point of view.Sea ice plays an important part in the exchange of heat and humidity between sea and air and thus is an important component of the climate system. Its physical presence also directly impacts the various forms of life such as diatoms, polar bears and humans alike.The dynamics of sea ice affect both weather and climate, through the large scale drift in the Arctic from the Siberian coast towards Fram Strait, through creation of cracks in the ice called leads or polynyas, and through ridging and other mechanical deformations of ice floes.In this work, we have focused on modelling of ridged ice for a number of reasons. Direct observations of the internal ice state is very difficult to perform and in general, observations of sea ice are either sparse or of limited information density. Ridged ice can be seen as the memory of high ice stress events, giving us a view on these highly dynamic events. Ridging is of major importance for the ice thickness distribution, as the thickest ice can only be formed through mechanical processes. Further, ridged ice is of direct interest for anyone conducting shipping through seasonal or perennial ice covered seas as it can form impenetrable barriers or in extreme even cases crush a ship caught within the ice pack. To this end, a multi-category sea ice model, the HELsinki Multi category Ice model (HELMI), was implemented into the Rossby Centre Ocean model (RCO). HELMI has explicit formulations for ridged and rafted ice, as well as sub-grid scale ice thickness distribution (a feature shared with other multi category models) and an ice strength based on energetics. These features give RCO better representation of sub-grid scale physics and gives us the possibility to study the deformed ice in detail. In paper I we look at the change in behaviour in the Arctic as the ice becomes more mobile, leading to a slight increase in modelled ridged ice volume in the central Arctic, despite a general trend of a decreasing ice cover.Paper II takes us to the Baltic Sea and the possibilities of modelling ridge ice concentration with a statistical model.In Paper III we investigate how the diminishing ice cover in future scenarios affects the biological activity in the Baltic Sea.Finally Paper IV investigates how the ice stress and the internal ice force can be interpreted in terms of ice compression on the ship scale. / <p>At the time of the doctoral defence the following paper was unpublished and had a status as follows: Paper 4: Manuscript</p>

Recent work has described how gas exchange can occur through sea ice. First, carbon fluxes over sea ice surfaces have been measured. Second, sea ice brine has an elevated capacity over seawater to absorb CO2(g) due to its cold temperature and chemical equilibrium promoting carbon phase changes. Sea ice pCO2 profiles were collected using a new method of remotely sampling gas in situ via diffusive membranes placed within growing sea ice. Gas analysis was complimented by measurements of local meteorology and ice chemistry. The work was part of the CASES 2004 project. The observed elevation in sea ice pCO2 coupled with the mobility of the brine points to the role that brine plays in Arctic carbon transport. The gas transport links the Arctic atmosphere and ocean and indicates that a thinning and receding ice cover may not result in creating a negative feedback to the increasing atmospheric CO2(g) concentration.

No description available.

Recent work has described how gas exchange can occur through sea ice. First, carbon fluxes over sea ice surfaces have been measured. Second, sea ice brine has an elevated capacity over seawater to absorb CO2(g) due to its cold temperature and chemical equilibrium promoting carbon phase changes. Sea ice pCO2 profiles were collected using a new method of remotely sampling gas in situ via diffusive membranes placed within growing sea ice. Gas analysis was complimented by measurements of local meteorology and ice chemistry. The work was part of the CASES 2004 project. The observed elevation in sea ice pCO2 coupled with the mobility of the brine points to the role that brine plays in Arctic carbon transport. The gas transport links the Arctic atmosphere and ocean and indicates that a thinning and receding ice cover may not result in creating a negative feedback to the increasing atmospheric CO2(g) concentration.

Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro / Recentes observações satelitais têm demonstrado um aumento na extensão total do gelo marinho Antártico e redução do gelo marinho no Ártico. Apesar destas constatações, no Oceano Sul análises regionais apontam tendências negativas nos mares de Bellingshausen-Amundsen e positivas no mar de Ross, enquanto que para o Ártico ocorrer uma redução uniforme do gelo marinho. Neste estudo, foi realizada uma análise multivariada para identificar as mudanças na extensão do gelo marinho Antártico e Ártico em resposta à variabilidade de um conjunto de forçantes/parâmetros/índices climáticos de reconhecida importância em escala global. Especificamente, as associações entre o gelo marinho e os parâmetros e forçantes climáticos foram examinadas através da correlação linear e da análise de agrupamento. Diferentes respostas em diferentes setores foram examinadas e discutidas. Os resultados indicam que a variabilidade do gelo marinho Antártico e Ártico é um fenômeno multivariado e que a extensão de gelo marinho mínima, média e máxima podem apresentar diferentes padrões espaciais e responderem a diferentes conjuntos de parâmetros e forçantes climáticos. Foi identificado um significativo impacto de forçantes/parâmetros/índices climáticos sobre o gelo marinho no Oeste Antártico. No hemisfério Norte o aumento da temperatura média global e do CO2 atmosférico são os principais responsáveis pela redução na extensão do gelo marinho. / Recent satellite observations have shown an increase in the total extent of Antarctic sea ice and a reduction of sea ice in the Arctic. Despite these findings, regional analyses in the Southern Ocean indicates negative trends in the Bellingshausen-Amundsen Sea and positive trends in the Ross Sea, while in the Arctic seems to occur a uniform reduction of sea ice. In this study, mutivariate analysis was performed to identify changes in Antarctic sea ice in response to changes in a set of climate forcings/parameters/indices. More specifically, the relationships between sea ice and climate forcings and parameters were examined by linear correlation and cluster analysis. Different responses in different sectors were examined and discussed. The findings indicate that Antarctic sea ice variability is a multivariate phenomenon and that the minimum, maximum, and mean sea ice extent depicts different spatial pattern and may respond to a different set of climate forcings/parameters/indices. A significant impact of climate forcings/parameters/indices occurs over western Antarctic. In the northern hemisphere the increase in global mean temperature and atmospheric CO2 seems to be the major responsible for the reduction in sea ice extent.

O sistema atmosfera-gelo marinho é complexo e fortemente acoplado. Em uma região de transição entre a cobertura de gelo marinho e o mar aberto a interação entre esse sistema é particularmente intensa, sendo significativa o suficiente para influenciar a circulação atmosférica de grande escala e a distribuição de gelo marinho. Assim, o objetivo principal deste trabalho foi analisar as interações entre os ciclones extratropicais e a variabilidade extrema do gelo marinho nos setores dos mares de Bellingshausen-Amundsen (MBA) e do mar de Weddell (MW), no período de verão e inverno austral entre 1989 e 2007. Foram utilizados dados de extensão de gelo marinho do NSIDC/NASA; campos atmosféricos da superfície até os altos níveis da troposfera das reanálises do ERA-Interim (ECMWF); composição de imagens de satélite do canal infravermelho do SSEC; Índice de Niño Oceânico do CPC/NOAA. As anomalias de alta frequência (período de 2-10 dias) e interanual (período maior que 370 dias) foram obtidas aplicando-se a transformada rápida de Fourier nas séries temporais (1989-2007). Os extremos de gelo marinho foram obtidos através do primeiro e terceiro quartil da distribuição dos dados. As características da circulação atmosférica de alta frequência e interanual associadas aos eventos extremos negativos (ENGM) e positivos (EPGM) de gelo marinho, na mesma escala de tempo, foram obtidas através de composições defasadas das anomalias dos campos atmosféricos. Para evidenciar e exemplificar os padrões encontrados nas composições de alta frequência apresenta-se uma análise sinótica de estudo de casos para o setor dos MBA durante o inverno austral, em eventos ENGM e EPGM, separando os casos em fases distintas do fenômeno tropical El Niño. Foi utilizada a estatística de ciclones do Automatic Cyclone Tracking, da Universidade de Melbourne, para analisar a ocorrência de ciclones associados aos períodos de mínima e máxima extensão de gelo marinho na escala interanual. Os resultados mostram que no verão e inverno austral, os eventos ENGM de alta frequência no setor dos MBA e do MW estão associados com as anomalias dos campos atmosféricos, na mesma escala temporal, que se assemelham a um trem de ondas ocorrido a partir de três dias anteriores ao evento extremo. A anomalia ciclônica no oeste e a anomalia anticiclônica no leste do setor resultam em uma anomalia de ventos de norte e, consequentemente, a anomalias positivas de temperatura do ar. Essa configuração anômala contribui para os eventos ENGM através do derretimento do gelo marinho e do seu próprio transporte em direção às latitudes maiores pelos ventos de norte anômalos. As anomalias de alta frequência dos campos atmosféricos em todos os casos (composições defasadas) de eventos EPGM apresentam fases opostas em relação aos eventos ENGM. Portanto, fases distintas do trem de ondas induzem na modulação de extremos de gelo marinho opostos. Em relação às análises sinóticas dos eventos ENGM e EPGM em fases distintas do fenômeno El Niño, verificou-se que em períodos de El Niño há uma intensificação do jato subtropical e um enfraquecimento do jato polar no Pacífico Sul. Há uma menor atuação dos ciclones extratropicais, predominando o sistema de cristas e cavados. Na fase de La Niña há um reforço do jato polar e uma intensa atividade ciclônica sobre os MBA. No evento ENGM (EPGM) há uma associação entre os ventos de norte (de sul) com a vanguarda (retaguarda) dos sistemas ciclônicos em superfície. Na fase Neutra verificou-se uma intensificação do jato polar e uma atuação do sistema de cristas/cavados e de sistemas ciclônicos em superfície. Na análise da influência da circulação atmosférica interanual na variabilidade extrema do gelo marinho, na mesma escala de tempo, observou-se que a fase quente (fria) do ENSO provavelmente está associada com eventos ENGM (EPGM) nos MBA e com eventos EPGM (ENGM) no MW. Sobre a influência da variabilidade interanual da extensão do gelo marinho na atividade ciclônica, nas composições de anomalias interanuais de PNMM em relação aos eventos ENGM nos MBA (lag = 0) no verão, há um predomínio de anomalias positivas de pressão ao nível médio do mar (PNMM) sobre grande parte do Oceano Austral, o que contribuiria para uma menor profundidade e raio dos sistemas em superfície. Já em relação aos eventos ENGM no MW, verifica-se que no lag = 0 há um predomínio de anomalias negativas de PNMM no Oceano Austral, o que contribuiria para um aumento da profundidade e raio dos ciclones. / The sea ice-atmosphere system is complex and tightly coupled. In a transition region between the coverage of sea ice and open ocean the interaction between this system is particularly intense, being significant enough to influence large-scale atmospheric circulation and sea ice distribution. Thus, the main objective of this study was to analyze the interactions between extratropical cyclones and extreme variability of sea ice in the sectors of the Bellingshausen-Amundsen Seas (BAS) and the Weddell Sea (WS), in the period of austral summer and winter between 1989 and 2007. We used sea ice extent data from NSIDC/NASA; atmospheric fields (surface to higher tropospheric levels) from ERA-Interim reanalysis; SSEC IR satellite image composition; and the Oceanic Niño Index CPC/NOAA. Anomalies of high-frequency (2-10 days) and interannual (longer than 370 days) were obtained by applying a fast Fourier transform in the time series (1989-2007). The extremes of sea ice were obtained from the first and third quartile of the data distribution. The characteristics of high-frequency atmospheric circulation and interannual associated with negative (NESI) and positive (PESI) extreme events of sea ice at the same time scale, were obtained from the lagged composites of the anomalies of atmospheric fields. To highlight and illustrate the patterns found in the composites of high frequency presents a synoptic analysis of case studies for the sector of the BAS during the austral winter at NESI and PESI events, separating the cases in different stages of the tropical El Niño phenomenon. Was used a statistical cyclone of Automatic Cyclone Tracking, from University of Melbourne, to analyze the occurrence of cyclones associated with periods of minimum and maximum extent of sea ice in the interannual scale. The results show that in the austral summer and winter, the NESI events of high frequency in the sector of the BAS and the WS are associated with the anomalies of atmospheric fields in the same timescale that resemble a wave train occurring from three days before the extreme event. The cyclonic anomaly in the west and anticyclonic anomaly in the east sector result in an anomaly of north winds and, consequently, the positive anomalies of air temperature. This anomalous configuration contributes for events NESI by sea ice melting and its own transport to higher latitudes by anomalous north winds. Synoptic atmospheric fields anomalies, in all PESI event cases are in opposite phases to NESI events. Therefore, different phases of the circumpolar wave train induce modulation of concurrent sea ice extremes. Regarding the synoptic analysis of events NESI and PESI in different phases of El Niño, it was found that during periods of El Niño it has a strengthening of the subtropical jet and a weakening of the polar jet in the South Pacific. There is less activity of extratropical cyclones, and the predominant system of ridge and troughs. In the La Niña case studies, has a strengthening of the polar jet and an intense cyclonic activity over the BAS. In the NESI (PESI) event there is an association between the north (south) winds at the vanguard (rear) of the cyclone systems at surface. In the Neutral phase case studies, there is an intensification of the polar jet and performance of the system of ridge/troughs and cyclonic systems at surface. In the analysis of the influence of interannual atmospheric circulation on extreme variability of sea ice, at the same time scale, it was observed that the warm (cold) phase of ENSO are probably associated with NESI (PESI) events at BAS and with PESI (NESI) events in the WS. On the influence of interannual variability of sea ice extent in the cyclonic activity, in the composites of interannual anomalies of mean sea level pressure (MSLP) in relation to NESI events in the BAS (lag = 0) in the summer, there is a predominance of positive anomalies of MSLP over much of the Southern Ocean, which would contribute to a lower depth and radius of the surface systems. In relation to NESI events in WS, it appears that in the lag = 0 there is a predominance of negative anomalies of MSLP in the Southern Ocean, which would contribute to an increase in depth and radius cyclones.

Arctic sea ice is rapidly declining in extent, thickness, volume and age, with the majority of the decline in extent observed at the end of the melt season. Advanced melt is a thermodynamic regime and is characterized by the formation of melt ponds on the sea ice surface, which have a lower surface albedo (0.2-0.4) than the surrounding ice (0.5-0.7) allowing more shortwave radiation to enter the system. The loss of multiyear ice (MYI) may have a profound impact on the energy balance of the system because melt ponds on first-year ice (FYI) comprise up to 70% of the ice surface during advanced melt, compared to 40% on MYI. Despite the importance of advanced melt to the ocean-sea ice-atmosphere system, advanced melt and the extent to which winter conditions influence it remain poorly understood due to the highly dynamic nature of melt pond formation and evolution, and a lack of reliable observations during this time. In order to establish quantitative links between winter and subsequent advanced melt conditions, and assess the effects of scale and choice of aggregation features on the relationships, three data aggregation approaches at varied spatial scales were used to compare high resolution satellite GeoEye-1 optical images of melt pond covered sea ice to winter airborne laser scanner surface roughness and electromagnetic induction sea ice thickness measurements. The findings indicate that winter sea ice thickness has a strong association with melt pond fraction (fp) for FYI and MYI. FYI winter surface roughness is correlated with fp, whereas for MYI no association with fp was found. Satellite-borne synthetic aperture radar (SAR) data are heavily relied upon for sea ice observation; however, during advanced melt the reliability of observations is reduced. In preparation for the upcoming launch of the RADARSAT Constellation Mission (RCM), the Kolmogorov-Smirnov (KS) statistical test was used to assess the ability of simulated RCM parameters and grey level co-occurrence matrix (GLCM) derived texture features to discriminate between major ice types during winter and advanced melt, with a focus on advanced melt. RCM parameters with highest discrimination ability in conjunction with optimal GLCM texture features were used as input parameters for Support Vector Machine (SVM) supervised classifications. The results indicate that steep incidence angle RCM parameters show promise for distinguishing between FYI and MYI during advanced melt with an overall classification accuracy of 77.06%. The addition of GLCM texture parameters improved accuracy to 85.91%. This thesis provides valuable contributions to the growing body of literature on fp parameterization and SAR ice type discrimination during advanced melt. / Graduate / 2019-03-21