Planktonic organisms form the base of the marine food web and may be impacted by environmental change in many ways. The interactive effects of multiple, simultaneous climate-driven changes on these organisms are not well understood. This dissertation examined the impacts of ocean acidification in combination with other environmental stressors on marine plankton and determined spatial patterns of one of these potential interactive drivers. Chapter 2 investigated the synergistic effects of ocean acidification and hypoxia on the harmful dinoflagellate Amphidinium carterae. Findings indicated that empirical studies may be crucial to accurately predict organismal responses to multi-stressors. Results also suggested that photorespiration may serve a previously unrecognized role in dinoflagellate metabolism. Chapter 3 examined the combined effects of ocean acidification and lithogenic trace metals on the growth of another harmful dinoflagellate, Cochlodinium polykrikoides. Results indicated that high suspended sediment loads may deliver toxic concentrations of trace elements to marine phytoplankton in acidified coastal ecosystems. Chapter 4 examined the interactive effects of ocean acidification and bacteria on the severity and extent of dissolution in the shells of larval gastropods and the adult pteropod Limacina helicina. Research findings indicated that microbial communities on the shell surfaces of some planktonic molluscs may mediate certain types of shell dissolution in acidified, upwelled waters. Chapter 5 explored the use of thorium isotope fluxes as a proxy for dust and lithogenic iron in the Indian Ocean. Results suggested that the gradient of dust fluxes in the region could impose thresholds for biological productivity. Together, these interdisciplinary studies demonstrate coupled biological and chemical changes in marine ecosystems as a result of increased anthropogenic environmental change.

O presente estudo objetiva avaliar os mecanismos de transferência de carbono entre os compartimentos atmosfera, vegetação, solo e igarapé em uma microbacia da Amazônia Ocidental. Dois igarapés drenandos, respectivamente, 2927 e 66,73 ha de floresta de terra firme, foram monitorados durante um ano. A área de estudo se encontra na zona de amortecimento de uma Unidade de Conservação de Uso Sustentável denominada Floresta Estadual do Amapá (FLOTA/AP), na região central do estado de mesmo nome. Foram coletadas as águas da chuva, da precipitação interna da floresta, do escoamento de água pelo tronco, do escoamento superficial pelo solo, da solução do solo, da água subterrânea e da água do igarapé. Os solos também foram investigados em relação a suas características físico-químicas. Para calcular a entrada e saída de C do sistema, foram determinadas as concentrações do carbono orgânico e inorgânico dissolvido (COD e CID, respectivamente) na água da chuva e do igarapé, em 16 eventos de chuva. As concentrações médias de COD na água da chuva foram de 1,6± 1,52 mg L-1, resultando em um aporte de 11,43 Kg C ha-1 ano-1. Na precipitação interna os valores médios observados foram de 9,1 ± 5,99 mg L-1, o que corresponde a um fluxo de 100,71 Kg C ha-1 ano-1. No escoamento do tronco, os valores médios observados foram de 17,4 ± 8,03 mg L-1 e no escoamento superficial do solo de 14,2 ± 6,4 mg L-1. Nos compartimentos amostrados abaixo do solo, solução do solo e água do lençol, as concentrações de COD foram relativamente mais baixas. A saída de COD pelo igarapé, os fluxos foram de 0,45 Kg C ha-1 ano-1. Em relação às concentrações de CID, o aporte pela água da chuva foi de 3,66 Kg C ha-1 ano-1, passando a 10,10 Kg C ha-1 ano-1 na precipitação interna e com uma saída pelo igarapé de 0,07 Kg C ha-1 ano-1. Os resultados mostram grande variabilidade espaço-temporal e retenção de C pelo sistema, seja na fase orgânica (COD) ou inorgânica (CID), demonstrando a importância destes processos para a compreensão do funcionamento destes ecossistemas. / This study aims to evaluate carbon transfer mechanisms between the atmosphere, vegetation, soil and stream in a microbasin of eastern Amazon. Two streams, draining respectively 2917 and 66.73 ha of \"terra firme\" forests were monitored during one year. The study area is located in a Conservation Unit named Amapá State Forest (FLOTA/AP), in the central region of the Amapá State. We sample rain water, throughfall, stemflow, soil surface flow, soil solution, groundwater and stream water. Physico-chemical characteristics of soils were also evaluated. To calculate inputs and outputs of C in this system, we determined the concentrations of dissolved organic and inorganic carbon (DOC and DIC, respectively) in rain and stream water during 16 rain events. Average concentrations of DOC in rain water were 1.6± 1.52 mg L-1, resulting in an input of 11.43 Kg C ha-1 year-1. Throughfall had average concentrations of 9.1 ± 5.99 mg L-1, which increased inputs to 100.71 Kg C ha-1 year-1. Stemflow had average concentrations of 17.4 ± 8.03 mg L-1 while those of soil surface flow were 14.2 ± 6.4 mg L-1. Bellow ground DOC concentrations were relatively lower. The export of DOC in stream water was 0.45 Kg C ha-1 year-1. In relation to DIC, the input from rain water was 3.66 Kg C ha-1 year-1, increasing to 10.10 Kg C ha-1 year-1 in throughfall and exiting the micro basin through the stream with a flux of 0.07 Kg C ha-1 year-1. The results show large spatiotemporal variations and C retention within the system, either in the organic (DOC) or inorganic (DIC) phases, showing the importance of these processes for the comprehension of the functioning of these ecosystems.

To determine the maximum carbon dioxide (CO2) emissions consistent with a given global warming threshold, the scientific community must robustly quantify what proportion of human emitted CO2 will be taken up by the terrestrial and marine carbon reservoirs. The North Atlantic Ocean is a region of intense uptake of atmospheric CO2. To assess how the North Atlantic CO2 sink has evolved over the past decades and understand the mechanisms involved in that uptake, observations and models are used. To appreciate the strengths and limitations of observation-based and modelled products, I explore the sources of uncertain- ties of two widely-used biogeochemical observational products (GLODAP and SOCAT), and carefully evaluate the latest generation of Earth System Models (ESMs) (i.e. the CMIP5 models) against these data. The lack of robust uncertainties on observation-based estimates of the North Atlantic CO2 uptake has so far limited the community’s ability to use observed trends to evaluate CO2 uptake behaviour simulated by the models. Here, by making use of the strengths of observation-based and modelled products, a novel gap-filling and uncertainty assessment method is developed to (1) robustly quantify the recent change in the basin-wide North Atlantic CO2 sink, and (2) evaluate simulations of the recent uptake in ESMs. Through the assessment of robust interpolation uncertainties on the annually-varying North Atlantic CO2 uptake and on the resulting trends over the period 1992-2014, I find that (1) the North Atlantic CO2 uptake increased at a rate of 0.081 ± 0.012 PgC/yr/decade from 1992- 2014, corresponding to an additional uptake of 2.2 PgC over this interval relative the flux in the 1992, and (2) state-of-the-art ESMs are consistently biased to lower trend values, with a mean that is about three times smaller than the observation-based trend, equating to an additional uptake of only 0.72 ± 0.40 PgC over the period 1992-2014. I further show that the inability of these models to capture the observed increase in CO2 uptake is due primarily to biases in modelled ocean biogeochemistry, which I explore through comparison with observations. Our current understanding of the ocean carbon-cycle, as synthesised by ESMs, cannot explain the recent behaviour of the North Atlantic CO2 sink. Current projections may therefore underestimate the contribution of the North Atlantic to mitigating increasing future atmospheric CO2 concentrations.

This thesis addresses time-series analyses of microbial (i.e. marine heterotrophic bacteria and phytoplankton) and microbially relevant ecosystem variables at two ocean time series stations - Palmer Station in the coastal Western Antarctic Peninsula (WAP) and the Bermuda Atlantic Time-series Study (BATS) site in the Sargasso Sea. Using a diverse spectrum of statistical analyses and models, the aim of this thesis is to gain the better insight into 1) variability of microbial and ecosystem processes across varying time scales, from seasonal to interdecadal, and 2) how each process is influenced by variability of surrounding local physical forcing factors as well as regional and global-scale climate variability along the study region. Chapter 1 provides an introduction to the two study sites as well as a brief history of the ocean time-series programs there. Chapter 2 deals with phytoplankton and nutrient drawdown variability over an interdecadal (1993-2013) period using seasonal time-series variables collected at Palmer Station during full 6-months of Austral growing seasons (October-March). Specifically, the linkage between large-scale climate modes relevant to the WAP area and phytoplankton and nutrient patterns is explored to establish the underlying mechanisms of the observed ecosystem variability, which is ultimately triggered by climate conditions via mediatory physical forcing factors. Chapter 3 addresses a decadal (2002-2014) variability of heterotrophic bacterial variables collected at Palmer Station in Antarctica. This Chapter 3 provides an insight into why bacterial activity was shown to be restricted in this very productive ecosystem from diverse aspects gained using different statistical approaches. Furthermore, the linkage between bacterial properties and surrounding environmental conditions is explored. Finally, Chapter 4 concerns an event-scale phenomenon - the frequency of winter storms - and its impact on bacterial dynamics and ecological processes at the BATS site. Using a previously developed storm tracking algorithm, this study benefits from establishing a mechanistic connection between storm forcing and bacterial processes via storm-induced variability of physical environments - the extent of wind-mixing and entrainment of cold water into the upper mixed-layer. The finding of Chapter 4 is novel in the aspect that prevalent negative North Atlantic Oscillation (NAO) conditions, which lead to frequent arrivals of winter storms over the BATS region, in part, explain a significant decreasing bacterial trend over the past 24-year period. Overall, my thesis, in conjunction with work performed by fellow microbial oceanographers, aims to provide evidence of microbial responses to physical forcings across varying time scales in the strongly coupled climate-biogeochemical systems at two contrasting ocean sites based on a variety of statistical approaches.

One central goal in ecology is to understand how biodiversity, and key organismal traits, interact with ecosystem properties and processes, and ultimately to understand and predict how these interactions will be affected by rapid environmental change. Thus, global change experiments and observational gradients in diversity provide the opportunity to examine and test hypotheses about how organismal traits, multiple dimensions of biodiversity, and ecosystem function will respond to environmental change. In Arctic tundra, increased nitrogen (N) and phosphorus (P) availability accompanying rapid warming is thought to significantly alter plant community composition and ecosystem function. The following four chapters examine hypotheses about the responses of species’ traits, multiple dimensions of biodiversity, and ecosystem function to the effects Arctic warming. Chapter 1 examines plant community composition and the capacity for ecosystem function (net ecosystem exchange, ecosystem respiration, and gross primary production) across a gradient of experimental N and P addition expected to more closely approximate warming-induced fertilization, demonstrating declines in plant diversity and an increase in the capacity for ecosystem carbon uptake at the highest level of fertilization. Chapter 2 examines a set of physiological and functional leaf traits across the same N and P gradient in order to evaluate the possible physiological mechanisms underlying community and ecosystem responses, highlighting the effects of increasing nutrient availability for deciduous shrub species. Chapter 3 found that single-dose, long-term nutrient addition (i.e., > 20 years) led to significant declines in multiple dimensions of diversity (taxonomic, functional and phylogenetic), and that these effects persist through time, increasing for dimensions that capture organismal traits (functional and phylogenetic). Finally, Chapter 4 examined the relationship between multidimensional diversity and ecosystem function across a natural gradient of diversity, and found that taxonomic diversity and functional diversity were significantly and positively related to whole ecosystem productivity, and, conversely, functional evenness and dispersion were significantly and negatively related to ecosystem productivity. Cumulatively, these four chapters advance our understanding of the connections between communities and ecosystems in a rapidly changing ecosystem.

abstract: Migrations, past and present, fundamentally influence human interaction, community building, and social evolution. Studies of contemporary migrations demonstrate that the form and intensity of interaction migrants maintain between homeland and host communities shape social dynamics, innovations, and identities. This dissertation applies a contemporary theoretical framework and biogeochemical analyses to elucidate the scale, processes, and impacts of migration in the hinterland of the pre-Hispanic Tiwanaku polity (ca. AD 500-1100). Social diversity is examined by reconstructing the migration histories and dietary choices of individuals interred at the Tiwanaku-affiliated site of Omo M10 in the Moquegua Valley of southern Peru. Radiogenic strontium and stable oxygen isotope data from human dental and skeletal elements are used to characterize intra- and inter-individual paleomobility patterns at Omo M10. When contextualized with archaeological evidence, these data reveal multigenerational interaction through migration between communities in the highland Tiwanaku heartland and at Omo M10. The observed greater mobility of females and juveniles at Omo M10 indicates that women and families played an essential role in maintaining social relationships and persistent cultural continuity in Moquegua Tiwanaku life. Contact with the highlands waned over time as disruption in the urban highland centers likely weakened ties to peripheral lowland communities. Stable carbon and nitrogen data from human dental and skeletal elements are employed to estimate intra- and inter-individual paleodietary patterns. Results indicate diet at Omo M10 varied depending on an individual’s community affiliation, sex, age, and level of mobility; diet broadly changed over time with shifting levels of interaction with highland Tiwanaku communities. Intra-individual biogeochemical analyses of migration and diet at Omo M10 contribute a nuanced perspective on the diverse experiences of multigenerational colonists on the periphery of the Tiwanaku polity. / Dissertation/Thesis / Doctoral Dissertation Anthropology 2019

The ocean is both a repository and reactor for chemicals at the Earth’s surface. As chemicals enter the ocean they are taken up by organisms, transported by currents, reacted with particle surfaces, and eventually buried at the seafloor. This dynamic set of chemical processes and exchanges are encapsulated by the term biogeochemistry. Marine biogeochemistry can be broadly deconstructed into two parts: ocean interfaces and internal cycling. Ocean interfaces are where chemical constituents enter and leave the ocean, including the air-sea boundary, mid-ocean ridges, continental margins, and rivers. Internal cycling is how chemical constituents are reacted, transported, taken up by organisms, and redistributed within the ocean. For a complete understanding of marine biogeochemical cycles, the input, output, and internal cycling rates of major and trace elements must be quantified. However, this rate information is difficult to infer from the observational snapshots of chemical concentrations typically collected on oceanographic expeditions. The long-lived radioisotopes of thorium (Th) and protactinium (Pa) provide an opportunity to quantify these elusive biogeochemical rates. The radiogenic isotopes 230Th and 231Pa are produced at a uniform rate throughout the water column by uranium decay. A third isotope, 232Th, is primordial and brought to the ocean by the dissolution of lithogenic matter. While uranium is highly soluble, Th and Pa are highly insoluble, and are rapidly removed from solution by adsorption onto settling particle matter. Due to their insolubility and known input rates, 230Th and 231Pa have well-constrained 1-d mass budgets between radiogenic production and scavenging removal. This thesis explores new ways Th and Pa isotopes can be used to understand and quantify rates of biogeochemical processes in the South Pacific Ocean, and to assess how measurements of sedimentary Th and Pa isotopes can be used to study these processes in the geologic past. In chapter 1, I characterize the effects of submarine hydrothermal activity on the distributions of 230Th and 231Pa, finding strong removal due to adsorption by Fe and Mn oxide particles. In chapter two, I utilize the radioactive disequilibria of two additional radiogenic thorium isotopes with much shorter half-lives, 234Th and 228Th, to constrain the kinetics of Th scavenging by hydrothermal particles. Chapter three switches gears towards quantifying the internal cycling of particulate organic carbon in the subtropical South Pacific. Using a new method based on measurements of particulate 230Th, I generated high-resolution water column profiles of particulate organic carbon flux to constrain carbon regeneration lengthscales in both oligotrophic and oxygen minimum zone settings. In chapter 4, I demonstrate the importance of isopycnal mixing in transporting 230Th, 231Pa, and 232Th into the Pacific Southern Ocean, showing the first high-resolution dissolved Th and Pa data from the region. Chapter 5 provides estimates of dust input spanning the South Pacific using two methods based on paired 230Th-232Th, evaluates the flux of dust-borne iron, and discusses the impacts on measured and modeled nitrogen fixation rates in the South Pacific gyre. Finally, in chapter 6 I present enigmatic profiles of Th and Pa isotopes from the semi-enclosed Peru and Bauer Basins, with anomalous Th and Pa removal extending 1-2km above the seafloor. I hypothesize that these depletions are related to the extent of water mass contact the seafloor, allowing for scavenging removal of Th and Pa by resuspended sediments.

It has been estimated that 80% of the organic carbon preserved in marine sediments occurs in 'terrigenous-deltaic' regions near river mouths. The Louisiana coast, which contains the most prolific deltaic regions in the U.S. (Atchafalaya and Mississippi rivers), provides an excellent field laboratory to compare the effects of differential sedimentation rates and redox conditions on organic carbon burial using pigments as biomarkers Application of HPLC/MS has led to identification of high concentrations of bacteriopigments in sediments collected in area with recorded hypoxia on the Louisiana shelf. This confirmed the development of anaerobic photosynthetic community (purple and green sulfur bacteria) over a large deltaic area. Downcore distributions of bacteriopigments in sediments indicated the highest concentrations occurred between 1960 and the present, coinciding with increased nutrient loading from the Mississippi River Four novel decay products, esters of carotenols and chlorins (carotenol chlorins esters, CCEs), were also identified in sediments from the LA shelf. Our laboratory copepod grazing experiment confirmed that similar to sterol chlorin esters (SCEs), CCEs can be produced through zooplankton grazing on diatom, providing excellent class-specific biomarkers of zooplankton grazing on phytoplankton. Pigment inventories indicated that pheophytin-a , pyropheophytin-a, chlorophyllone-a, CCEs and SCEs were major decay products in LA shelf sediments. Absence of the two grazing biomarkers, CCEs and SCEs, in river sediments suggested that grazing activity was minimal in river waters. However, chlorophyllone- a was present in river sediments and its abundance in river sediments was comparable with that in shelf sediments. This suggested that chlorophyllone- a was not closely associated with grazing like CCEs and SCEs. Downcore distribution of pigments, bulk organic carbon and nitrogen, and radioactive isotopes (210Pb, 137Cs, 7Be) suggested that a 9--10 cm surface mixed layer was common for samples collected in areas with low sedimentation. It was observed that pigment decay rate constants in the mixed layer were greater than the accumulation layer by 1--3 orders of magnitude. Decay rates of pigments in the upper mixed layer were variable and primarily dependent upon differences in the inherent lability of pigment compounds and bulk carbon, while in the accumulation layer all pigments decayed at similar rates / acase@tulane.edu

Lignin and pigment biomarkers were analyzed in sediments of the Louisiana Continental margin along two major depositional pathways (along shore and offshore to the Mississippi Canyon) from SW Pass in July 2003. Results from surface sediments indicate resuspension and reworking of shelf sediments in shallow waters and mobile mud deposits were more effective at oxidizing terrestrial material west of SW Pass than to the southwest. Barataria Bay material may be a contributing source of sedimentary organic matter in shallow shelf areas bordering the Bay and is thus potentially important in carbon cycling. Hurricane Ivan mobilized sedimentary organic carbon (SOC) offshore and homogenized terrestrial sediment parameters and gradients Results from box-core profiles showed preferential loss of more labile pigment SOC during burial and diagenesis. Low burial efficiencies along the western transect for bulk and labile biomarkers indicate mobile muds were efficient in the remineralization of labile organic matter. Lignin appeared to be a useful paleo indicator in dynamic RioMar environments likely reflecting source input rather than diagenesis after initial deposition. Pigment concentrations and ratios may not be useful in a quantitative sense for paleo-reconstructions within dynamic RioMar regions. Oxic degradation of labile material in the Surface Active Zone was highly efficient, effecting the quantity and quality of material buried below Lignin profiles in age-dated cores (210Pb geochronology) indicate artificial reservoir retention as a major control on organic carbon quantity and quality post-1950 reaching the margin, whereas, pre-1950 sediments may reflect soil erosion due to land-clearing and farming practices. Terrestrially derived organic carbon signatures were mixed angiosperms over the last 150 yrs. Stochastic events such as hurricanes and large river floods have a measurable, albeit ephemeral, effect on the shelf SOC record. Land-use changes in the MR basin have likely affected carbon cycling and SOC burial on the LCM over a large spatial extent as observed by similar trends in cores from across and along margin. Finally, sediment focusing seems to be a very important aspect that can complicate down-core interpretation when trying to make comparisons over wide spatial scale / acase@tulane.edu

Organic and inorganic geochemical proxies from two cores in the northeastern (NE) and western Arabian Sea were employed to study orbital and suborbital climate variability of the Indian Ocean monsoons. In the NE Arabian Sea 230Th-nonnalized 232Th fluxes and authigenic uranium concentrations were interpreted as indicators for eolian input and paleo-productivity, respectively. The highest eolian fluxes occur at times consistent with the North Atlantic (NA) millennial-scale cold intervals recorded in the GISP2 ice core. Paleoproductivity was highest during warn interstadials when the SW monsoon was intensified. Maximum average eolian fluxes coincide with the timing of marine isotopic stage 2 and 4, while minimum fluxes occur during MIS 1, 3 and 5 231Pa/230Th activity ratios and diatom biomarker fluxes were measured in sediments from NE Arabian Sea to examine the influence global thermohaline circulation (THC) over the last 50 ka. 231Pa/230Th were significantly higher than the production ratio of 0.093, which indicates exceptionally high rates of particle scavenging. Lower average 231Pa/230Th ratios occurred during the last glacial with lowest 231Pa/230Th ratios coinciding with the timing of Heinrich Events 1 - 5. In the Holocene, high 231pa/230Th ratios may indicate enhanced 231 Pa export from the southern to the northern Indian Ocean via intensified THC Organic biomarker fluxes and alkenone-derived sea surface temperatures (SST) were measured in sediments from the western Arabian Sea. The average glacial-Holocene temperature difference was ∼3°C with an interval of exceptionally low SSTs between 19 to 18.1 ka BP (15.3°C at 18.5 ka). The lowest SSTs coincided with highest cumulative biomarker fluxes. We propose that intensification of the winter NE monsoon winds during the glacial period resulted in cold SSTs, deep convective mixing, and enhanced primary productivity. Following the last termination, and within the Holocene, SSTs vary by ∼2°C with high CBFs occurring at times of relatively warmer SSTs. Transitioning from the glacial to the Holocene, diatom fluxes relative to the total flux of organisms increased, while those of coccolithophorids decreased. A shift in the planktonic ecosystem structure in the Arabian Sea may have important implications for the global biogeochemical cycle of carbon / acase@tulane.edu