The aim of this dissertation was to understand lithogenic suspended sediment transport mechanisms and distribution in two river-influenced margins: The Cariaco Basin, Venezuela, and the Amazon Shelf, Brazil. Lithogenic sediment input in the Cariaco Basin is controlled by small mountainous rivers (SMR), while in the Amazon Shelf it is dominated by the Amazon River, the largest river in the world in terms of freshwater discharge (~20% of global riverine discharge). Optical transmissometer measurements were coupled with particulate organic matter (POM) observations to understand changes in the geochemical composition of suspended sediment and spatial/temporal distributions over the two regions of interest. In the Cariaco Basin sampling was conducted during the rainy seasons of September 2003, 2006 and 2008, and during the upwelling period (dry season) of 2009. Our results suggest that bottom nepheloid layers (BNL) originating at the mouth of the SMR discharging into the Cariaco Basin are a major delivery mechanism of terrigenous sediments to the basin's interior year-round. Intermediate nepheloid layers (INL) were also observed near the shelf break (~100m) and appear to effectively carry terrigenous material laterally from the shelf to deep waters, thereby providing a plausible supply mechanism of the terrestrial material observed in sediment traps, deployed >70 km offshore as part of the CARIACO Ocean Time-Series. These findings highlight the importance of small, local rivers in the Cariaco Basin as sources of terrestrial material. Indeed, the low isotopic composition of particulate organic carbon (δ13Corg, ~-30 - -24 ‰) carried by the BNL suggests that this material was continentally derived. BNL δ13Corg also changed with season, indicating that the geochemical composition of BNL reflects particle source. These nepheloid layers contained relatively low POM concentrations (average of 10%), agreeing well with published data, yet the fine sediment of the BNL may serve as mineral ballast, enhancing the sinking velocities of POC and thus increasing the efficiency of the biological pump in Cariaco. We suggest that during the transition between the upwelling and rainy season BNL deliver sediment to the deep Cariaco Basin in pulses. During upwelling, BNL are retained on the inner shelf by onshore Ekman transport associated with upwelling. The nepheloid layers are later released as the upwelling subsides; this, coupled with high river discharge rates, may explain the seasonal pulse of sediment observed at the end of the upwelling period (May) in the sediment trap array. The SMR in Cariaco also have the capacity to deliver large amounts of sediment to the Cariaco Basin during episodic events, such as earthquakes and floods. During September 2008 a sediment density flow was observed in the eastern Cariaco Basin, likely triggered by a magnitude 5.2 earthquake that occurred on August 11, 2008 off the city of Cumaná. Elevated suspended sediments near the bottom were observed at the mouth of the Manzanares Canyon (> 90 g m-2, over a depth of 165 m) and decreased to ~11 g m-2 (over a depth of 40 m) 42 Km away from the canyon's mouth at the CARIACO Ocean Time-Series site (10.5° N, 64.67° W). The sediment flux associated with this single event was ~ 10% of the total annual sediment flux that typically reaches the Cariaco Basin deep seafloor. Average carbon to nitrogen atomic ratios (C/N) as well as C and N isotopic composition confirm that most of the organic matter transferred by the sediment flow was of continental origin (C/N ratios of ~19.3, δ13C of -27.04 ‰, and δ15N of 6.83 ‰). The Manzanares River mouth is located at the head of the canyon, and likely supplies most of the fine grained sediments and fresh organic carbon that accumulate in the upper part of the canyon. This suggests that the canyon is an active depositional center, and its proximity to the Manzanares River and Cariaco Basin is critical for sediment supply offshore, which in turn can have a significant impact on the long-term sequestration of carbon into the deep basin. The nutrient and sediment biogeochemistry of the outer Amazon Shelf was studied in February-March 2010 to replicate observations made by the AmasSeds study in 1989-1991. These transects roughly corresponded to the AmasSeds Open Shelf (OS) and River Mouth (RM) transects. Onshore winds (~6 m s-1) contained the Amazon plume within ~120 Km of the coast; the plume was visible only in the mid-shelf stations located closest to the coast in the OS transect. Within the river plume, surface dissolved inorganic nutrient concentrations were near zero, except for silicates (4-6 μM). Coupled with oxygen supersaturation (AOU < 1), this suggested complete biological uptake of the major dissolved inorganic nutrients (N, P). Dissolved organic carbon (DOC) was also highest within the plume (average of 116 μM), decreasing to ~73 μM in oceanic waters. Total suspended solids (TSS) in surface waters within the plume were ~1-1.5 mg l-1, decreasing to ~0.2-0.3 mg l-1 in all other sampled stations both over the shelf and in deeper waters. TSS were highest within BNL (22-33 mg l-1) observed over the inner shelf; BNL were not observed outside the area of the Amazon plume. Suspended particulate organic carbon (POCsusp) showed a depleted δ13C isotopic signal (~-25 ‰ to -28 ‰) in surface and bottom waters, suggesting terrestrial provenance. Within the BNL, %POC was low (0.6-0.9%, as compared to 7-18% in surface waters), showing extensive and rapid decomposition of organic matter over the shelf. Atomic C/N ratios in particulate organic matter both in surface waters and within BNL were relatively close to Redfield's (8-14) and relatively stable over the area sampled. Particulate atomic organic carbon vs. particulate organic phosphorous (POC/POP) ratios were also low within the BNL (~110) and increased offshore (>500), suggesting a direct input of particulate P from the Amazon River or from reworked surface sediments. The fraction of POC in surface sediments was also low (0.73 ±; 0.56%; N = 5) and relatively uniform across the region sampled. We estimated instantaneous fluxes of 38.7 metric tons TSS s-1, 0.24 metric tons POC s-1 and 6.42 x 10-3 metric tons POP s-1 northwestward over an area extending between ~50 Km and 120 Km offshore. Our TSS estimates are 30% lower than those calculated by Nittrouer et al. (1986) during peak discharge of the Amazon. We also calculated that some 1.50 Tg yr-1 of DOC were being flushed northwestward along the outer shelf annually, which represent ~6% of the total DOC transported by the Amazon. By analyzing these two geographical settings it was possible to compare and contrast transport mechanisms of continentally-derived material and establish the relative importance of each mechanism in their different environment. There is still much to be understood regarding BNL in the Cariaco Basin, such as their role within the Manzanares Submarine Canyon with regards to sediment contribution and deposition. Additionally, during the last 30 years, anthropogenic influences on the small rivers around the Basin have significantly altered the drainage and sediment loads, yet reliable data to quantify the level of influence and change over time are not available. We need a better understanding of the natural variability of these small, tropical fluvial systems, trends and impact of episodic events, to better interpret the climate record stored at the bottom of the basin and predict future ecosystem changes in the region. In the Amazon Shelf, more accurate estimates of DOC, POC and POP fluxes northwestward are warranted. The magnitude of the Amazon River discharge dampens changes that have occurred in the last 20 years within the Amazon Basin, suggesting that historic Amazon Shelf sediment and carbon estimates are still valid. The data presented here adds to the growing body of literature that highlights the significance of river-influenced continental margins as sites of organic carbon deposition, remineralization export and sequestration.

Fundação Carlos Chagas Filho de Amparo a Pesquisa do Estado do Rio de Janeiro / A pesquisa aqui apresentada amostrou a plataforma continental e talude superior entre Ubatuba (SP) e o cabo Búzios (RJ), em dois projetos de escala local e de meso-escala. A campanha entre Ubatuba e o cabo Frio foi realizada no âmbito do projeto Oceano-Rio: levantamentos oceanográficos integrados ao largo do Estado do Rio de Janeiro, realizado em colaboração com o Ministério de Ciência e Tecnologia (MCT) e com a cooperação da Marinha do Brasil (MB), a bordo do Navio Hidro-oceanográfico Cruzeiro do Sul. Dos dados coletados nesta campanha oceanográfica, foram analisados os dados de CTD, concentração de oxigênio dissolvido, fluorescência, transmissividade, atenuação, retro-espalhamento além de amostras de água para a determinação direta da concentração de material particulado em suspensão (MPS). No experimento de menor escala, entre o cabo Frio e o cabo Búzios, além destes dados, foi realizado um fundeio entre 02 e 30 de julho de 2011, que amostrou a intensidade do eco, as correntes e as ondas. As análises realizadas permitiram observar uma grande abrangência da massa dágua característica da Ressurgência sobre a plataforma continental entre Ubatuba (SP) e cabo Búzios (RJ), inclusive em regiões muito rasas. A ressurgência nem sempre ocorreu associada aos ventos NE, sugerindo que a ocorrência de vórtices tem grande influência sobre o Sistema de Ressurgência de Cabo Frio. O padrão de distribuição de MPS na região é muito influenciado pela ressuspensão dos sedimentos de fundo (aumentada durante as tempestades, quando a coluna dágua passa a apresentar maiores concentrações de MPS), produção fitoplanctônica e aporte das baías costeiras. Outros processos que parecem influenciar este padrão são os vórtices e as ondas internas no talude. A complexidade da interação destas diferentes fontes de MPS e processos associados à sua distribuição ficou evidenciada no processo de conversão dos sinais óticos do transmissômetro e nefelômetro em concentração de MPS. Apesar desta dificuldade associada à grande variabilidade das características do MPS, as análises dos testes de conversão do sinal ótico em concentração de MPS permitem concluir que as melhores conversões podem ser obtidas após a inspeção visual das concentrações de MPS medidos (filtração) e remoção das amostras que não seguem a tendência geral esperada de dispersão sinal ótico versus concentração de MPS. / The research presented here sampled the continental shelf and upper slope from Ubatuba (SP) to Búzios cape (RJ) on two projects at local and meso-scale. The cruise between Cape Frio and Ubatuba was performed under the project Oceano-Rio: levantamentos oceanográficos integrados ao largo do Estado do Rio de Janeiro, conducted in collaboration with the Ministry of Science and Technology (MCT) and the Brazilian Navy aboard the Cruzeiro do Sul Hydro-Oceanographic vessel. Of oceanographic data collected in this campaign, we analyzed data from CTD, dissolved oxygen, fluorescence, transmissivity, attenuation, back-scattering as well as water samples for the direct determination of the concentration of suspended particulate matter (SPM). In the experiment between Cabo Frio and Búzios capes, in addition to these data, an Acoustic Doppler Current Profiler (ADCP) was positioned near the bottom and collected data from the echo intensity, currents and waves, between 02 and 30 July 2011. The analysis allowed to observe a wide range of water mass characteristic of upwelling on the continental shelf from Ubatuba (SP) to Búzios cape (RJ), even in very shallow regions. The resurgence was not always associated with the NE winds, suggesting that the occurrence of vortices has a great influence on the Upwelling System of Cabo Frio. The distribution pattern of SPM in the region is strongly influenced by resuspension of bottom sediments (enhanced during storms, when the water column begins to show higher concentrations of SPM), phytoplankton production and supply of coastal bays. Other processes that seem to influence this pattern are the vortices and internal waves on the slope. The complexity of the interaction of these different sources of MPS and processes associated with its distribution was evident in the process of converting the optical signals (transmissivity, attenuation and back-scattering) at a concentration of SPM. Despite this difficulty associated with the high variability of the characteristics of the SPM, the analysis of several tests that were carried out to convert optical signals into concentrations of SPM revealed that significantly improved results may be achieved after visual inspection of the directly determined values (through filtration of water samples) and removal of samples that do not follow the expected trend in regressions of the optical signals against concentrations.

Fundação Carlos Chagas Filho de Amparo a Pesquisa do Estado do Rio de Janeiro / A pesquisa aqui apresentada amostrou a plataforma continental e talude superior entre Ubatuba (SP) e o cabo Búzios (RJ), em dois projetos de escala local e de meso-escala. A campanha entre Ubatuba e o cabo Frio foi realizada no âmbito do projeto Oceano-Rio: levantamentos oceanográficos integrados ao largo do Estado do Rio de Janeiro, realizado em colaboração com o Ministério de Ciência e Tecnologia (MCT) e com a cooperação da Marinha do Brasil (MB), a bordo do Navio Hidro-oceanográfico Cruzeiro do Sul. Dos dados coletados nesta campanha oceanográfica, foram analisados os dados de CTD, concentração de oxigênio dissolvido, fluorescência, transmissividade, atenuação, retro-espalhamento além de amostras de água para a determinação direta da concentração de material particulado em suspensão (MPS). No experimento de menor escala, entre o cabo Frio e o cabo Búzios, além destes dados, foi realizado um fundeio entre 02 e 30 de julho de 2011, que amostrou a intensidade do eco, as correntes e as ondas. As análises realizadas permitiram observar uma grande abrangência da massa dágua característica da Ressurgência sobre a plataforma continental entre Ubatuba (SP) e cabo Búzios (RJ), inclusive em regiões muito rasas. A ressurgência nem sempre ocorreu associada aos ventos NE, sugerindo que a ocorrência de vórtices tem grande influência sobre o Sistema de Ressurgência de Cabo Frio. O padrão de distribuição de MPS na região é muito influenciado pela ressuspensão dos sedimentos de fundo (aumentada durante as tempestades, quando a coluna dágua passa a apresentar maiores concentrações de MPS), produção fitoplanctônica e aporte das baías costeiras. Outros processos que parecem influenciar este padrão são os vórtices e as ondas internas no talude. A complexidade da interação destas diferentes fontes de MPS e processos associados à sua distribuição ficou evidenciada no processo de conversão dos sinais óticos do transmissômetro e nefelômetro em concentração de MPS. Apesar desta dificuldade associada à grande variabilidade das características do MPS, as análises dos testes de conversão do sinal ótico em concentração de MPS permitem concluir que as melhores conversões podem ser obtidas após a inspeção visual das concentrações de MPS medidos (filtração) e remoção das amostras que não seguem a tendência geral esperada de dispersão sinal ótico versus concentração de MPS. / The research presented here sampled the continental shelf and upper slope from Ubatuba (SP) to Búzios cape (RJ) on two projects at local and meso-scale. The cruise between Cape Frio and Ubatuba was performed under the project Oceano-Rio: levantamentos oceanográficos integrados ao largo do Estado do Rio de Janeiro, conducted in collaboration with the Ministry of Science and Technology (MCT) and the Brazilian Navy aboard the Cruzeiro do Sul Hydro-Oceanographic vessel. Of oceanographic data collected in this campaign, we analyzed data from CTD, dissolved oxygen, fluorescence, transmissivity, attenuation, back-scattering as well as water samples for the direct determination of the concentration of suspended particulate matter (SPM). In the experiment between Cabo Frio and Búzios capes, in addition to these data, an Acoustic Doppler Current Profiler (ADCP) was positioned near the bottom and collected data from the echo intensity, currents and waves, between 02 and 30 July 2011. The analysis allowed to observe a wide range of water mass characteristic of upwelling on the continental shelf from Ubatuba (SP) to Búzios cape (RJ), even in very shallow regions. The resurgence was not always associated with the NE winds, suggesting that the occurrence of vortices has a great influence on the Upwelling System of Cabo Frio. The distribution pattern of SPM in the region is strongly influenced by resuspension of bottom sediments (enhanced during storms, when the water column begins to show higher concentrations of SPM), phytoplankton production and supply of coastal bays. Other processes that seem to influence this pattern are the vortices and internal waves on the slope. The complexity of the interaction of these different sources of MPS and processes associated with its distribution was evident in the process of converting the optical signals (transmissivity, attenuation and back-scattering) at a concentration of SPM. Despite this difficulty associated with the high variability of the characteristics of the SPM, the analysis of several tests that were carried out to convert optical signals into concentrations of SPM revealed that significantly improved results may be achieved after visual inspection of the directly determined values (through filtration of water samples) and removal of samples that do not follow the expected trend in regressions of the optical signals against concentrations.

Le but de cette étude est de retracer l’évolution de l’hydrologie dans la partie occidentale de l’Océan Pacifique subtropical en utilisant le proxy εNd analysé sur les foraminifères et sur les oxydes de ferromanganèse authigéniques dans les sédiments. Ceux-ci proviennent de carottes sédimentaires prélevées au nord de la Mer de Chine du Sud (MCS). Avant d’utiliser l’εNd dans les sédiments profonds de la MCS, 16 profils d’eau de mer, collectés au nord de la MCS et dans le Mer des Philippines, ont été analysés afin d’établir la distribution d’εNd des masses d’eau dans l’ouest du Pacifique tropical et dans la MCS, qui jusqu’à aujourd’hui n’était pas documentée. Les valeurs d’εNd des masses d’eau profondes et intermédiaires varient de -2,7 à -4,4 et augmentent légèrement avec la profondeur. Dans la mer des Philippines, les valeurs d’εNd de l’eau intermédiaire du Pacifique Nord (North Pacific Intermediate Water, NPIW) atteint -2.7±0.4 à moyenne profondeur (500 à 1400m). En-dessous de de 1800m, l’eau profonde Pacifique (Pacific Deep Water, PDW) est caractérisée par du Nd moins radiogénique (-4.1±0.5), indiquant l’intrusion de masses d’eau australes. Pour la plupart des stations du nord de la MCS, les masses d’eau en-dessous de 1500m (PDW) affichent des valeurs d’εNd homogènes (~ -4.1), similaires à celles de la PDW dans la Mer des Philippines. Les valeurs d'εNd pour l'eau intermédiaire de la mer de Chine du Sud (South China Sea Intermediate Water, SCSIW, 500-1500m) varient entre -3.0 et -3.9 dû au mélange vertical de la NPIW avec la PDW. Les valeurs d'εNd de l'eau de mer dans la MCS (-5.3 à -7.0) affichent des modifications locales dans des zones où l'eau s'écoule au-dessus de systèmes de dépôt sédimentaire. Ceci implique que "l'échange à la marge" avec des sédiments non radiogéniques (autour de -11) peut se produire dans le temps et dans l'espace sans modifier la composition isotopique du Nd de la PDW dans le Nord de la MCS. Dans un second temps, l’εNd extrait des foraminifères planctoniques G. ruber a été étudié sur la carotte MD05-2904, collectée à 2000m de profondeur sur la marge nord-ouest de la MCS. Cette étude a été conduite dans le but de retracer les variations hydrologiques depuis le Dernier Maximum Glaciaire (DMG) dans la partie occidentale du Pacifique Nord subtropical. Les enregistrements d'εNd ainsi obtenus couvrent les derniers 25 000 ans. Ils affichent une large gamme de valeurs de -4±0.2 à -6.7±0.3, suggérant d'importants changements dans la contribution de la NPDW (εNd=-4) et de la UCDW (Upper circumpolar Deep Water, εNd -6 to -8) dans la zone étudiée. Durant la déglaciation, les enregistrements d'εNd indiquent une diminution des excursions négatives de l'εNd impliquant une plus forte proportion de SSW (Southern-sourced Water) entre 17 et 15 ka BP ainsi qu'entre 10 et 8 ka BP. Ces intervalles de temps sont contemporains de l’évènement Heinrich 1 (HS1) et de l’Holocène inférieur. Les shifts négatifs centrés sur le HS1 coïncident avec un phénomène d'upwelling renforcé dans l'océan austral, associé à un déplacement vers le pôle des vents d'ouest. Ceci implique une augmentation de la formation de la SSW qui se propage dans l'Ouest du Pacifique subtropical. L'excursion négative de l'εNd durant l’Holocène inferieur (~10-8 cal ka BP) indique une plus grande proportion de SSW qui pourrait être associée avec une plus forte production de SSW, comme observé récemment dans l'atlantique Sud, et/ou avec une possible réduction de la NPIW. Nos données suggèrent que le schéma de circulation actuel dans la partie occidental du Pacifique subtropical s'est mis en place il y a 4600 ans. / The aim of this study is to reconstruct the evolution of the hydrology of the western subtropical North Pacific Ocean by using εNd proxy analysed on foraminifera and dispersed authigenic ferromanganese oxide precipitates in sediments from deep-sea cores collected in the northern SCS. Before using the εNd proxy on deep sea sediments of the SCS, Nd of 16 seawater profiles collected in the northern South China Sea (SCS) and the Philippine Sea were investigated to establish the εNd distribution of water masses along the tropical western Pacific and the SCS that, until now have not been documented. εNd values for mid- and deep-water masses of the Philippine Sea and the SCS range from -2.7 to -4.4 and generally increase slightly with water depth. In the Philippine Sea, εNd values for the North Pacific Intermediate Water (NPIW) reach- 2.7±0.4 at mid-depths (500 to 1400 m). Below ~1800 m, the Pacific Deep Water (PDW) is characterized by less radiogenic Nd (-4.1±0.5) indicating the instrusion of southern sourced water masses. For most of the stations in the Northern SCS, water masses below 1500m (PDW) display homogenous εNd values (~ -4.1) similar to those of the PDW in the Philippine Sea. εNd values for the South China Sea Intermediate Water (SCSIW, 500-1500m) vary from -3.0 to -3.9 as a result of the vertical mixing of the NPIW with the PDW in the SCS. Seawater εNd values for the SCS (~5.3 to -7.0) display local modification in areas where the water lies above sediment drift deposit systems. This implies that “boundary exchange” with unradiogenic sediments (around~11) may occur temporally and spatially and does not modify he Nd isotopic composition of the PDW in the Northern SCS. In a second step, seawater εNd extracted from cleaned planktonic foraminifera G. ruber has been investigated on core MD05-2904, collected at a deph of 2000m on the north-western margin of the SCS. This study was undertaken in order to reconstruct hydrological variations since the LGM in the western subtropical North Pacific. The εNd records obtained from foraminifera spanning the past 25kyr. Display a wide range of values, ranging from -4±0.2 to -6.7±0.3, suggesting important changes in the contribution of the NPDW (εNd=-4) and the UCDW (εNd -6 to -8) in the subtropical western Pacific. During the period of deglaciation, εNd records indicate a relative decrease in the negative excursions of the εNd implying a higher proportion of SSW during the time intervals 17-15 cal kyr BP and 10-8 cal kyr BP; these intervals are coeval with the HS1 and early Holocene. The negative shifts centered on the HS1coincide with an enhanced upwelling in the Southern Ocean, associated with a polewards shift of the southern westerlies, inducing an enhanced formation of the SSW that propagates to the subtropical western Pacific. The negative excursion of the εNd during the Early Holocene (~10-8 cal kyr BP) indicates a higher relative proportion of SSW that could be associate with higher production of the SSW, as has been recently observed in the South Atlantic, and/or with a possible reduction of the NPIW. Our data suggest that the present modern circulation pattern in the western subtropical Pacific Ocean was fully established after 4.6 cal kyr BP.