The samples in this study were collected from the drilling cores W-2 and S-4 obtained from the slope-stability monitoring project inside the campus of NSYSU. The Sheng-Li (SL) core was drilled for groundwater monitoring project in the northern of Kaohsiung city. The mudstone sections in these three cores were sampled to reconstruct the sedimental history of the southwestern Taiwan. This study mainly contains 3 parts: firstly we dated the downcore records based on nannobiostratigraphy. Secondly, we analyzed the benthic foraminiferal assemblages in sedimentary sequences. Finally we chose specific benthic species and analyzed the shell trace metals, especially Mg/Ca and Sr/Ca ratio with an ICP-MS. Overall the mudstone sections analyzed in this study fall in the biostratigraphic range of small Gephyrocapsa Subchron, which spreads within 1242ka~1031ka according to the previous report. The age range in W-2 was further constrained within 1186ka~1065ka based on the oxygen isotope stratigraphy (Tseng, 2004). There are four dominant benthic species, including Bulimina spp., Uvigerina spp., Brizalina tainanesis and Siphogenerina raphanus in Cores W-2 and S-4. There are five dominant benthic species, including Brizalina spp., Pseudorotalia spp., Siphogenerina raphanus, Amphicoryna scalaris and Brizalina alata in Core SL. The benthic foraminiferal shell Mg/Ca ratios obtained from Core W-2 indicate the bottom water temperature are between 6 - 12¢J, which reflects the paleo water depth had varied between 300 - 700m. It also indicates that strata were uplifted and the deposition depth become shallow.

The Antarctic plays an important role in the global climate system. On the one hand, the Antarctic Ice Sheet is the largest freshwater reservoir on Earth. On the other hand, a major proportion of the global bottom-water formation takes place in Antarctic shelf regions, forcing the global thermohaline circulation. The main goal of this dissertation is to provide new insights into the dynamics and stability of the EAIS during the Quaternary. Additionally, variations in the activity of bottom-water formation and their causes are investigated. The dissertation is a German contribution to the International Polar Year 2007/ 2008 and was funded by the ‘Deutsche Forschungsgesellschaft’ (DFG) within the scope of priority program 1158 ‘Antarctic research with comparative studies in Arctic ice regions’. During RV Polarstern expedition ANT-XXIII/9, glaciomarine sediments were recovered from the Prydz Bay-Kerguelen region. Prydz Bay is a key region for the study of East EAIS dynamics, as 16% of the EAIS are drained through the Lambert Glacier into the bay. Thereby, the glacier transports sediment into Prydz Bay which is then further distributed by calving icebergs or by current transport. The scientific approach of this dissertation is the reconstruction of past glaciomarine environments to infer on the response of the Lambert Glacier-Amery Ice Shelf system to climate shifts during the Quaternary. To characterize the depositional setting, sedimentological methods are used and statistical analyses are applied. Mineralogical and (bio)geochemical methods provide a means to reconstruct sediment provenances and to provide evidence on changes in the primary production in the surface water column. Age-depth models were constructed based on palaeomagnetic and palaeointensity measurements, diatom stratigraphy and radiocarbon dating. Sea-bed surface sediments in the investigation area show distinct variations in terms of their clay minerals and heavy-mineral assemblages. Considerable differences in the mineralogical composition of surface sediments are determined on the continental shelf. Clay minerals as well as heavy minerals provide useful parameters to differentiate between sediments which originated from erosion of crystalline rocks and sediments originating from Permo-Triassic deposits. Consequently, mineralogical parameters can be used to reconstruct the provenance of current-transported and ice-rafted material. The investigated sediment cores cover the time intervals of the last 1.4 Ma (continental slope) and the last 12.8 cal. ka BP (MacRobertson shelf). The sediment deposits were mainly influenced by glacial and oceanographic processes and further by biological activity (continental shelf), meltwater input and possibly gravitational transport. Sediments from the continental slope document two major deglacial events: the first deglaciation is associated with the mid-Pleistocene warming recognized around the Antarctic. In Prydz Bay, the Lambert Glacier-Amery Ice Shelf retreated far to the south and high biogenic productivity commenced or biogenic remains were better preserved due to increased sedimentation rates. Thereafter, stable glacial conditions continued until 400 - 500 ka BP. Calving of icebergs was restricted to the western part of the Lambert Glacier. The deeper bathymetry in this area allows for floating ice shelf even during times of decreased sea-level. Between 400 - 500 ka BP and the last interglacial (marine isotope stage 5) the glacier was more dynamic. During or shortly after the last interglacial the LAIS retreated again due to sea-level rise of 6 - 9 m. Both deglacial events correlate with a reduction in the thickness of ice masses in the Prince Charles Mountains. It indicates that a disintegration of the Amery Ice Shelf possibly led to increased drainage of ice masses from the Prydz Bay hinterland. A new end-member modelling algorithm was successfully applied on sediments from the MacRobertson shelf used to unmix the sand grain size fractions sorted by current activity and ice transport, respectively. Ice retreat on MacRobertson Shelf commenced 12.8 cal. ka BP and ended around 5.5 cal. ka BP. During the Holocene, strong fluctuations of the bottomwater activity were observed, probably related to variations of sea-ice formation in the Cape Darnley polynya. Increased activity of bottom-water flow was reconstructed at transitions from warm to cool conditions, whereas bottom-water activity receded during the mid- Holocene climate optimum. It can be concluded that the Lambert Glacier-Amery Ice Shelf system was relatively stable in terms of climate variations during the Quaternary. In contrast, bottom-water formation due to polynya activity was very sensitive to changes in atmospheric forcing and should gain more attention in future research. / Die Antarktis spielt im globalen Umweltsystem eine tragende Rolle. Mit ihrem mächtigen Eispanzer ist sie nicht nur der größte Süsswasserspeicher auf der Erde, in ihren Schelfregionen wird auch ein Großteil der globalen Bodenwassermassen gebildet, welche die globale thermohaline Zirkulation antreiben. Hauptziel dieser Arbeit, welche einen deutschen Beitrag zum Internationalen Polarjahr 2007/ 2008 liefert, war es, neue Erkenntnisse hinsichtlich der Stabilität des Ostantarktischen Eisschildes während des Quartärs zu liefern. Weiterhin sollten Aussagen über Variationen in der Bildung von Antarktischem Bodenwasser und deren Ursachen getroffen werden. Dazu wurde im Rahmen der ‚Polarstern‘ Expedition ANT-XXIII/9 eine Beprobung glaziomariner Sedimente zwischen Prydz Bucht und Kerguelen Plateau durchgeführt. Diese Region eignet sich zur Untersuchung der Ostantarktischen Eisdynamik besonders gut, da hier der Lambert Gletscher, etwa 16% des Ostantarktischen Eispanzers drainiert. Er transportiert dabei Sediment nach Norden, das schließlich die Prydz Bucht erreicht und durch direkten Transport über kalbende Eisberge oder durch Umlagerung und Verteilung mithilfe von Meeresströmungen weiter verfrachtet wird. Der wissenschaftliche Ansatz dieser Arbeit besteht darin, über die Verteilung dieser Sedimente in Raum und Zeit, d.h. über Variationen des glaziomarinen Paläoregimes, die Reaktion des Lambert Gletschers und des vorgelagerten Amery Schelfeises auf Klimaschwankungen während des Quartärs zu rekonstruieren. Dabei werden sowohl sedimentologische Methoden unter Einbeziehung neuer statistischer Möglichkeiten angewandt, um Sedimentationsprozesse zu charakterisieren, als auch mineralogische und (bio)geochemische Parameter verwendet, um Aussagen über die Herkunft der Sedimente und Änderungen in der Produktivität im Oberflächenwasser treffen zu können. Die Altersbestimmung der Sedimentkerne erfolgte mittels Paläomagnetik, Paläointensitäten, Biostratigraphie und Radiokarbondatierungen. Die Oberflächensedimente im Untersuchungsgebiet zeigen deutliche Unterschiede sowohl hinsichtlich ihrer Tonmineral- als auch Schwermineralzusammensetzung. Beide mineralogischen Parameter zeigen die größten Differerenzen auf dem Schelf. Dort lassen sich deutlich Sedimente der Prydz Bucht von Sedimenten des MacRobertson Shelfes differenzieren. Sie stellen daher ein gutes Hilfsmittel dar, um sowohl die Herkunft von eis- als auch strömungstransportiertem Material zu rekonstruieren. Die untersuchten Sedimentkerne decken den Zeitraum der letzten 1,4 Millionen Jahre (Kontinentalhang) bzw. der letzten 12,8 tausend kal. Jahre v. H. ab (MacRobertson Schelf). Die abgelagerten Sedimente wurden i. W. durch glaziale und ozeanographische Einflüsse geprägt, aber auch durch Bioproduktion (Schelf) bzw. durch Schmelzwassereinträge und möglicherweise gravitative Prozesse (Kontinentalhang). In den Sedimenten des Kontinentalhangs sind zwei starke Enteisungsereignisse überliefert: Das erste Ereignis steht mit dem mittelpleistozänen Klimaoptimum in Verbindung, das auch in anderen antarktischen Regionen nachgewiesen wurde. Es führte in der Prydz Bucht zu einem weitreichenden Rückzug des Lambert Gletscher-Amery Schelfeises (LAIS) und gleichzeitig zu einer hohen Primärproduktion. Danach herrschten bis etwa 400 - 500 tausend Jahre v. H. stabile glaziale Bedingungen. Kalbung von Eisbergen war wahrscheinlich auf den westlichen Teil des Lambert Gletschers begrenzt, wo eine tiefere Bathymetrie auch bei niedrigerem globalen Meeresspiegel noch Aufschwimmen des Gletschereises erlaubt. Zwischen 400 - 500 tausend Jahren v. H. und vermutlich dem letzten Interglazial wurde der Gletscher schließlich wieder dynamischer, um mit oder kurz nach dem letzten Interglazial (Meeresspiegel etwa 6 - 9 m höher) eine weitere Phase deutlichen Rückzuges zu durchlaufen. Beide Ereignisse lassen sich mit Phasen der Eisreduktion in den Prinz Charles Bergen korrelieren, d.h. der Rückzug des Lambert Gletschers hatte möglicherweise ein erhöhtes Nachfließen von Eismassen aus dem Hinterland zur Folge. An den Sedimenten des Schelfkernes wurde ein neu entwickeltes Verfahren der Endmember-Modellierung erfolgreich getestet. Der Eisrückzug auf dem MacRobertson Schelf begann etwa 12,8 tausend kal. Jahre v. H. und war gegen 5,5 tausend kal. Jahre v. H. abgeschlossen. Während des Holozäns kam es zu starken Schwankungen in der Bodenwasseraktivität, die höchst wahrscheinlich mit der Neubildungsrate von Meereis in der Kap Darnley Polynia in Zusammenhang stehen. Besonders auffallend war eine erhöhte Bodenwasseraktivität am Übergang von Warm- zu Kaltphasen bzw. ihr extremer Rückgang während des Mittel-Holozänen Klimaoptimums. Insgesamt zeigen die Ergebnisse der Arbeit, dass sich das LAIS während des Quartärs relativ stabil gegenüber Klimaveränderungen verhalten hat. Die Bodenwasserproduktion in Polynien dagegen reagierte sehr empfindlich auf relative geringe atmosphärische Veränderungen und bedarf in Zukunft verstärkter Aufmerksamkeit.

This thesis investigates how benthic fluxes of phosphorus (P), nitrogen (N), and silicon (Si) change upon oxygenation of anoxic soft bottoms in the brackish, eutrophicated Baltic Sea. Direct measurements in situ by benthic landers demonstrated that fluxes of dissolved inorganic P (DIP) from anoxic bottom sediments in the Eastern Gotland Basin are higher than previously thought (Paper I). It is argued that the benthic DIP flux has a much larger influence on the DIP inventory in the Baltic proper than the external sources. Similarly, benthic fluxes of DIP and dissolved inorganic N (DIN) from anoxic sediment in the coastal Kanholmsfjärden Basin, Stockholm archipelago, were sufficiently high to renew the pools of these nutrients below the upper mixed layer in roughly one year (Paper II). A natural inflow of oxygen rich water into the deep, and previously long-term anoxic part of Kanholmsfjärden Basin, increased the P content in the sediment by 65% and lowered DIP and dissolved silica (DSi) concentrations in the pore water. These changes, as well as the large increases in benthic effluxes of these solutes following de-oxygenation of the bottom water, suggest that they are influenced similarly by changing oxygen conditions. Experimental results in papers III and IV show that common benthic macrofauna species in the Baltic Sea can stimulate benthic release of DIN and DSi, as well as dissolved organic and particulate bound nutrients. Thus, if benthic oxygen conditions would improve in the Baltic, initial effects on benthic–pelagic nutrient coupling will change due to animal colonisation of currently azoic soft bottoms. A new box corer was designed (Paper V) which can be used to obtain highly needed virtually undisturbed samples from soft bottom sediments – if lowered slowly and straight into the bottom strata – as demonstrated by in situ videography and turbidimetry. The commonly used USNEL box corer caused severe biasing during sediment collection. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 4: Manuscript. Paper 5: Manuscript.</p> / Baltic oxygenation project

Multi-proxy approach for the reconstruction of paleo-redox conditions is attempted on a radiocarbon (C-14) dated sediment core near the equatorial Indian Ocean. Based on the behavior and distribution of redox sensitive and productivity proxies, study demonstrates prevalence of anoxic bottom water conditions during LGM due to poorly ventilated bottom waters augmented by high surface productivity resulting in better preservation of organic carbon (OC). During early Holocene, the equatorial Indian Ocean witnessed high sedimentation rates resulting in high organic carbon (OC) with depleted redox sensitive elements thereby causing better preservation of OC. The study underscores poor bottom water ventilation during LGM and preservation of OC as a result of high sedimentation rate in early Holocene.

The upper ocean mediates the transfer of heat and carbon between the atmosphere and ocean interior. The study of this dynamic environment, made possible in part by long-term time series gathered from oceanographic moorings, is therefore crucial to our understanding of Earth’s climate. In this thesis, we use moored datasets from the Southeast Pacific and Southern Oceans to explore two upper-ocean processes relevant to the transfer and eventual sequestration of atmospheric heat and carbon into the deep ocean: wind-, wave-, and buoyancy-forced turbulence and the release of brine in Antarctic polynyas that drives the formation of Antarctic Bottom Water (AABW). In Chapter 1, we use measurements of turbulence kinetic energy (TKE) dissipation rate (ε) collected at 8.4 m depth on the long-established Stratus Mooring in the Southeast Pacific (20° S, 85° W) to assess the applicability of Monin-Obukhov similarity theory (MOST), Law of the Wall (LOW), and other boundary layer similarity scalings to turbulence in the upper ocean. TKE facilitates the mixing of heat, momentum, and solutes within and between the ocean and atmosphere and is generated in the upper ocean primarily by wind, waves, and buoyancy fluxes. Its production can generally be assumed to equal its dissipation, and measurements of ε therefore serve as a means for quantifying turbulence in a system. We present 9 months of ε measurements, a remarkably long time series made possible by the use of a moored pulse-coherent Acoustic Doppler Current Profiler (ADCP), a new methodology for measuring ε that uniquely allows for concurrent surface flux and wave measurements across an extensive length of time and range of conditions. We find that turbulence regimes are quantified similarly using the classic Obukhov length scale (L_M=(u_*³)/(κ𝐵ₒ), where u_* is ocean-side friction velocity, κ is the von Kármán constant, and B_0 is surface buoyancy flux) and the newer Langmuir stability length scale (L_L=(〖u_s u〗_*²)/B_0 , where u_s is surface Stokes drift velocity), suggesting that u_* implicitly captures the influence of Langmuir turbulence at this site. This is consistent with the strong correlation observed between u_s and u_*, likely promoted by the steady southeast trade winds, and suggests that classic wind and buoyancy-based boundary layer scalings sufficiently describe turbulence in this this region. Accordingly, we find the LOW (ε=(u_*³)/κz, where z is instrument depth) and surface buoyancy scaling (ε=B_0, where B_0 is destabilizing surface buoyancy flux) used in classic turbulence scaling studies, such as Lombardo and Gregg (1989), to describe our measurements well, and a newer scaling for Langmuir turbulence scaling based on u_s and u_* to scale ε well at times but to be overall less consistent than (u_*³)/κz. The performance of MOST relationships from prior studies in a variety of aquatic and atmospheric settings are also examined, and we find them to largely agree with our data in conditions where both convection and wind-driven current shear act as significant sources of TKE (-1<z/L_M <0). The apparent redundancy of Langmuir turbulence scaling and the sufficiency of LOW and MOST observed in this study may help inform the development of general circulation models (GCMs), which rely on boundary layer scaling to parametrize turbulent mixing in the upper ocean. In Chapters 2 and 3, we focus on the Terra Nova Bay Polynya in the western Ross Sea of Antarctica, where High Salinity Shelf Water (HSSW) forms as a result of the cooling and salinification of the surface ocean by an intense katabatic wind regime and its associated ice production. HSSW is a precursor to AABW, a vital water mass that feeds the bottom limb of the meridional overturning circulation (MOC) and facilitates the sequestration of atmospheric heat and carbon into the abyss. A decades-long freshening trend in the salinity of Ross Sea HSSW resulting from increased glacial meltwater fluxes, and more recently, its abrupt reversal associated with the occurrence of a climate anomaly, have highlighted the complexity of this system and its sensitivity to changes in climate. Because the density of HSSW has a direct impact on the density of downstream AABW, and therefore the strength of the MOC, it is imperative to better understand the variability and mechanisms of HSSW formation. However, inhospitable wintertime conditions in this region severely restrict the collection of in-situ data in the presence of active brine rejection and HSSW formation. Here, we present an unprecedented set of upper-ocean salinity, temperature, turbulence, current velocity, and acoustic surface tracking time series collected from a mooring in Terra Nova Bay during austral winter 2017. One poorly constrained aspect of HSSW in Terra Nova Bay is its rate of production, and in Chapter 2 we endeavor to produce the first production rate estimates to be based on in-situ salinity data. We find an average production rate of ~0.6 Sverdrups (10⁶ m³ s⁻¹), which allows us to improve on and validate an existing approach for estimating rates using parametrized net surface heat fluxes out of the polynya. We use this approach to examine interannual variability in production across the decade and find estimates of HSSW production in Terra Nova Bay to be largely increasing from 2015 onward. As higher production rates of Terra Nova Bay HSSW, the saltiest variety of HSSW across Antarctica, could increase the salinity of downstream AABW, this apparent increase may have played a previously unrecognized role in the recently observed recovery of AABW salinity in this region. In Chapter 3, we examine a number of interconnected processes surrounding HSSW formation, including the coupling of salinity to winds, the breakdown of summer stratification that primes the water column for HSSW formation in the winter, wind-driven turbulence that facilitates the breakdown of stratification and mixing of HSSW to depth, and potential circulation pathways for HSSW formed at the mooring site. We find that salinity at the shallowest depth on the mooring line, 47 m, couples strongly to wind speeds measured at the nearby Automatic Weather Station (AWS) Manuela from April onward, demonstrating the dependence of polynya formation, ice production, and brine rejection on winds at the mooring site. Salinity at the deepest depth on the mooring line, 360 m, couples to salinity at 47 m beginning in June, following the progressive breakdown of lingering summertime water column stratification that previous studies have established as a prerequisite for HSSW formation in the winter. We incorporate concepts from Chapter 1 to explore the scaling of turbulence in a polynya environment, finding that daily-averages of ε are sufficiently approximated according to the classic LOW scaling, despite visible evidence of Langmuir circulation in the polynya. To the best of our knowledge, this represents the first examination of turbulence scaling using in-situ time series measurements in an Antarctic polynya, an environment that connects the turbulent mixing of heat and solutes in the upper ocean to the properties of the deepest layer of the ocean. Lastly, we infer from current velocities and a late-winter coupling of salinity measured at our mooring to that measured by a second mooring within the Drygalski Basin that HSSW may travel one of two pathways following its formation at our mooring site: Directly southeastward into the Drygalski Basin or northeastward along with the cyclonic gyre of Terra Nova Bay. More mooring deployments across space and time within the bay are needed in order to further elucidate the variability and mechanisms surrounding HSSW formation, critical foci of study in the context of a rapidly changing Antarctic environment.

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.

Here we investigate sedimentological responses to past climate change in shallow to deep marine depositional environments. Our primary study spans from the Late Pliocene to the Pleistocene (3.3 to 0.7 Ma), and features results from two International Ocean Discovery Program (IODP) Sites U1525 and U1524. Each of these sites is discussed in separate chapters here (Chapters 1 and 2). This interval experienced the change from the warming of the Late Pliocene, known as the Mid-Piacenzian Warming Period, to the Pleistocene cooling. This shift significantly impacted the expansion of the West Antarctic Ice Sheet, sea ice/polynya formation, and, notably, the genesis of Antarctic Bottom Water (AABW), a crucial component of the global thermohaline circulation. In Chapter 1, we propose that turbidite currents, arising from the formation of dense shelf water (DSW) in the Ross Sea (a precursor to AABW), leave a distinct record in the levees of Hillary Canyon. This canyon acts as a conduit, channeling DSW into the deep ocean and contributing to AABW production. By analyzing turbidite beds based on their frequency, thickness, and grain size, we gain insights into the historical occurrence and magnitude of these currents. Furthermore, we explore the influence of factors such as shelf availability and sea ice/polynya formation within the broader climate context of AABW formation. Chapter 2 shifts its focus to the sedimentological variability from shelf-to-slope along Hillary Canyon. This chapter examines the turbidite record associated with AABW formation within the shared timeframe (2.1 to 0.7 million years ago) between IODP Sites U1524 and U1525, and the impact of along slope currents and other processes in the sedimentary deposition and transport. The second study interval (Chapter 3), focuses on the regional sedimentological response proximal to a hydrothermal vent complex associated with the Paleocene-Eocene Thermal Maximum (PETM; ca. 56 Ma), a global warming event during which thousands of Gt C was released into the ocean-atmosphere on Kyr timescales. IODP Site U1568, strategically located near the hydrothermal vent complex and part of a broader drilling transect in the Modgunn Arch, North Atlantic, is the main study subject. This site's proximity to the vent complex offers a distinctive environment for refining our understanding of stratigraphy and sedimentology within the PETM. We achieve this through a comprehensive analysis of grain size and composition, coupled with a comparison to XRF data. Our findings show that the timing between the onset of the PETM and the response of the sedimentary system to the warming, reflected in the grain size coarsening after the start of the PETM, is not synchronous. Notably, the transition from a marine to a more terrestrial composition predates this shift in grain size, aligning with the PETM onset instead. / Doctor of Philosophy / Deep-marine core records are invaluable sources of sedimentological information that provide insights into the ocean's response to past climates. These cores, extracted from the deep-ocean floor, contain layers of sediment that accumulate over time because of the different processes that occur in the ocean. Analyzing these sediments, by looking at their physical characteristics like how frequently are they deposited, the thickness of the layers, their grain size, and their composition helps to reconstruct past environmental conditions and understand how the oceans have responded to climatic changes. This dissertation focuses on studying the record of two main processes. The first one is the sedimentary record left behind by the formation of Antarctic Bottom Water (AABW), one of the coldest (-1°C), deepest (> 2000 meters below sea level), and densest water masses in the ocean. AABW is a key component of the global ocean circulation system, often referred to as the "global conveyor belt" or the thermohaline circulation. This circulation pattern plays a crucial role in redistributing heat, salt, and nutrients around the world's oceans. AABW is formed near Antarctica through a process that begins with the cooling and sinking of surface waters near the continent. As these waters sink, they become denser and eventually form AABW, filling the deep ocean basins around Antarctica. The dense water flows from the surface to the bottom of the ocean forming turbidity currents. These turbidity currents, dense plumes of water and sediments, flow down submarine conduits, such as Hillary Canyon in the Ross Sea, Antarctica, leaving a sedimentary record in the levees or flanks, called turbidites. The turbidite sequences in sediment cores can reveal information about the frequency and magnitude of these currents, providing insights into the sediment transport processes in deep-marine settings, and for this work, the history of the AABW formation over the last 3.3 Ma. This study will help to understand what are the main controls for AABW formation across different climates in the past, and how we project this into the future climate scenarios. In the second part of the study (Chapter 3), we look at the sedimentary record of a warming event that happened around 56 million years ago. This event, known as the Paleocene-Eocene Thermal Maximum (PETM), involved a significant amount of carbon being released into the air and oceans over thousands of years (150,000 to 200,000). Our focus is IODP Site U1568, located near a submarine hydrothermal vent, and part of a larger drilling transect in the North Atlantic's Modgunn Arch. The vent's unique location provides a crucial perspective for understanding how the system responded to the warming during the Paleocene-Eocene Thermal Maximum (PETM). This warming event was triggered by the release of carbon into the atmosphere, with the vent serving as one of the conduits for this release. To understand this, we studied the grain size and content of the sediment, and compared that with XRF data. Changes in grain size serve as indicators of shifts in the energy of the environment – coarser grains signify a more energetic system. Warmer weather, for instance, can increase precipitation, leading to more erosion and sediment influx into the basin. This influx also brings in more materials from the land, as evidenced by the presence of microfossils and plant fragments. Our discoveries indicate that the sedimentary system responded gradually to the PETM, as reflected in the coarsening of grain size after the PETM's onset. Notably, the transition from a marine to a more terrestrial composition occurred before the change in grain size, aligning more closely with the initiation of the PETM itself.

A complexa interação que ocorre entre os processos oceânicos e atmosféricos no Oceano Austral afeta a circulação oceânica global em diferentes camadas. O Mar de Weddell e o Mar de Ross possuem reconhecida importância na formação da Água de Fundo Antártica (AABW). O objetivo principal deste trabalho é caracterizar as massas de água dos Mares de Weddell e Ross, através dos dados mais recentes de reanálise oceânica SODA (Simple Ocean Data Assimilation). Através da técnica de separação de massas de água Análise Multiparamétrica Ótima (AMO) foi possível a identificação de 3 principais massas de água no Mar de Ross: Água Profunda Circumpolar Superior (UCDW), Água Profunda Circumpolar Inferior (LCDW) e Água de Plataforma de Baixa Salinidade (LSSW). A UCDW foi a que apresentou a maior variabilidade, não atingindo a Plataforma de gelo do MR durante os anos de 1950-1974. No Mar de Weddell foi possível a identificação das seguintes massas de água: Água Profunda Cálida (WDW), Água Profunda do Mar de Weddell (WSDW) e Água de Fundo do Mar de Weddell (WSBW). A WDW atingiu valores >70% à 800m. A WSDW possui em seu núcleo valores > 90% entre 2000 e 3500m. A WSBW, apresenta ~100% em profundidades > 4000m. / The complex interaction that occurs between the oceanic and atmospheric processes in the Southern Ocean affects global ocean circulation in different layers. The Weddell and Ross Seas have recognized importance in the formation of Antarctic Bottom Water (AABW). This work aims to characterize the water masses of the Weddell and Ross Seas, using the latest ocean data reanalysis SODA (Simple Ocean Data Assimilation). Through the water masses separation technique, Optimum Multiparameter Analysis (OMP), it was possible to identify three main water masses in Ross Sea: Upper Circumpolar Deep Water (UCDW), Lower Circumpolar Deep Water (LCDW) and Low Salinity Shelf Water (LSSW). UCDW showed the greatest variability, not reaching the Ross Sea Ice Shelf during the years 1950-1974. It was possible to identify the following water masses in Weddell Sea: Warm Deep Water (WDW), Weddell Sea Deep Water (WSDW) and Weddell Sea Bottom Water (WSBW). WDW reached values up to 70% in 800m. WSDW has in its core values > 90% between 2000 and 3500m. WSBW presents a contribution up to 100% at depths > 4000m.

This thesis considers the use of two U-series nuclides – 231 Pa and 230 Th – as proxies for studying ocean circulation. A total of six water-column profiles of 231 Pa, 230 Th, and 232 Th have been measured from two regions of the southwestern Indian Ocean: the Madagascar and Mascarene Basins; and the southeastern continental margin of South Africa. Measurement by MC-ICP-MS of 10 litre water samples is possible for samples with as little as 4 and 2 fg of 231 Pa and 230 Th and yields typical uncertainties of 6% and 14% respectively. These profiles show that the scavenging and advection histories of water masses can affect their 231 Pa concentration, with distinct variations superimposed on a general increase in concentration with depth due to reversible scavenging. A 1D particle scavenging model is used to show that sedimentary (231 Paxs /230 Thxs )0 is most representative of the (231 Pa/230 Th) of the bottom most water mass at any one locality, although in turn this water mass (231 Pa/230 Th) will be dependent not only on its advection and scavenging history but also the 231 Pa and 230 Th concentrations of the overlying water masses during advection. Acknowledgment that sedimentary (231 Paxs /230 Thxs )0 is “set” by the bottommost water mass is important for interpretation of scenarios where changes in depth of circulation, as well as circulation strength, may have occurred. A record of sedimentary (231 Paxs /230 Thxs )0 has been recovered from a 6 m Kasten core from the Mascarene Basin covering the past 140 ka, in order to reconstruct flow of AABW into the basin. The (231 Paxs /230 Thxs )0 measured is below the production ration of 0.093 and shows no significant variation. This indicates that (231 Paxs /230 Thxs )0 is sensitive to changes in particle productivity and circulation at this location and that there has been little or no change in either environmental variable over the last full interglacial-glacial cycle. This finding is in contrast to other ocean basins, particularly the North Atlantic, where large changes in circulation are observed.

The health of the Baltic Sea is negatively affected by hazardous substances such as metals and persistent organic pollutants (POPs), which include legacy pollutants that were banned decades ago, but still circulate in the ecosystem. Elevated levels of legacy pollutants, identified by HELCOM as key hazardous substances, have been found in accumulations of fibrous sediments, so-called fiberbanks and fiber-rich sediments, which derive from old pulp mills along the Swedish north coast. The fiberbanks are deposited in shallow water and bathymetrical models show evidence of their erosion, potentially caused by propeller wash, submarine landslides and gas ebullition. This thesis addresses the potential dispersal of key substances from three fiberbank sites located in a non-tidal Swedish estuary, in which metals and POPs are present in concentrations that may pose a risk for benthic organisms. Metals and POPs are partitioned to organic material and, as expected, show the highest partitioning coefficients (KD) in fiberbanks that have higher TOC levels compared to adjacent areas with fiber-rich sediments (natural clay sediments mixed up with fibers) or relatively unaffected postglacial clays. However, many analytes were found to be present in quantifiable concentrations in pore water, which indicates diffusion of substances from the solid phase to the aqueous phase. To assess the dispersive influence of an abrupt erosional event on dispersion, metals were measured in undisturbed bottom water and in bottom water disturbed by artificial re-suspension of fibrous sediments. The bioavailable, dissolved fraction of metals decreased in bottom water after re-suspension, probably due to the particle concentration effect. In contrast, the total concentrations of metals and number of quantifiable metals increased with particle concentration caused by re-suspension. At one station, the total concentration of chromium (Cr) was elevated to a level where it may lower the ecological status of the water body during periods of substantial erosion (e.g. spring floods or submarine landslides). Analyses of disturbed bottom water revealed, however, that minerogenic particles were preferentially re-suspended compared to organic. This suggests that physical erosion and re-suspension of fiberbank sediments might have a larger effect on dispersal of metals than on POPs. / TREASURE