The influences of the AMO and NAO on the sedimentary infill in an Azores Archipelago lake since ca. 1350 CE

The location of the Azores Archipelago in the North Atlantic makes this group of islands an excellent setting to study the long-term behavior of large oceanic and atmospheric climate dynamic patterns, such as the Atlantic Multidecadal Oscillation (AMO) and the North Atlantic Oscillation (NAO). Here, we present the impacts of these patterns on Lake Empadadas (Azores Archipelago) from the Medieval Climate Anomaly (MCA) - Little Ice Age (LIA) transition to the present based on sedimentological, geochemical and biological characterizations of the sedimentary record. Multivariate analyses of a number of proxies including X-ray fluorescence (XRF), X-ray diffraction (XRD), total organic and inorganic carbon (TOC and TIC) and diatom life forms abundance reveal that the sedimentary infill evolution has been controlled by (i) fluctuations in the lake level and (ii) variations in organic matter accumulation. Both processes are governed by climate variability and modulated by anthropogenic activities associated with changes on the lake catchment. Changes in these two sedimentary processes have been used to infer five stages: (i) the MCA-LIA transition (ca. 1350-1450 AD) was characterized by a predominantly positive AMO phase, which led to intermediate lake levels and high organic matter concentration; (ii) the first half of the LIA (ca. 1450 - 1600 AD) was characterized by predominant lowstand conditions and intermediate organic matter deposition mainly related to negative AMO phases; (iii) the second half of the LIA (ca. 1600 - 1850 AD) was characterized by negative AMO and NAO phases, implying intermediate lake levels and high organic matter deposition; (iv) the Industrial era (ca. 1850 - 1980 AD) was characterized by the lowest lake level and organic matter accumulation associated with negative AMO phases; and (v) the period spanning between 1980 AD and the present reveals the highest lake levels and low organic matter deposition, being associated with very positive AMO conditions. At decadal-to-centennial scales, the influence of the AMO on Azorean climate plays a larger role than previously thought. In fact, the AMO appears to exert a stronger influence compared to the NAO, which is the main mode of climate variability at shorter time scales

Comparison of dissolved and particulate arsenic distributions in shallow aquifers of Chakdaha, India, and Araihazar, Bangladesh

International audienceBackground The origin of the spatial variability of dissolved As concentrations in shallow aquifers of the Bengal Basin remains poorly understood. To address this, we compare here transects of simultaneously-collected groundwater and aquifer solids perpendicular to the banks of the Hooghly River in Chakdaha, India, and the Old Brahmaputra River in Araihazar, Bangladesh. Results Variations in surface geomorphology mapped by electromagnetic conductivity indicate that permeable sandy soils are associated with underlying aquifers that are moderately reducing to a depth of 10–30 m, as indicated by acid-leachable Fe(II)/Fe ratios 5 mg L-1. More reducing aquifers are typically capped with finer-grained soils. The patterns suggest that vertical recharge through permeable soils is associated with a flux of oxidants on the banks of the Hooghly River and, further inland, in both Chakdaha and Araihazar. Moderately reducing conditions maintained by local recharge are generally associated with low As concentrations in Araihazar, but not systematically so in Chakdaha. Unlike Araihazar, there is also little correspondence in Chakdaha between dissolved As concentrations in groundwater and the P-extractable As content of aquifer particles, averaging 191 ± 122 ug As/L, 1.1 ± 1.5 mg As kg-1 (n = 43) and 108 ± 31 ug As/L, 3.1 ± 6.5 mg As kg-1 (n = 60), respectively. We tentatively attribute these differences to a combination of younger floodplain sediments, and therefore possibly more than one mechanism of As release, as well as less reducing conditions in Chakdaha compared to Araihazar. Conclusion Systematic dating of groundwater and sediment, combined with detailed mapping of the composition of aquifer solids and groundwater, will be needed to identify the various mechanisms underlying the complex distribution of As in aquifers of the Bengal Basin

Territorial Justice: The Fight for Black Educational Rights in the Oklahoma Courtroom

This dissertation explores previously unstudied and undiscovered court challenges brought by Black settlers during Oklahoma’s territorial period (1889-1907) in the United States. These Black pioneers challenged new legislation that segregated previously integrated territorial schools. Black citizens in Oklahoma Territory had equal rights to land under the Homestead Act and the territory’s Organic Act. They had historic access to integrated education in other states, in Indian Territory, and on military posts. Yet in the legal era that increasingly determined that segregation was equality after the Plessy v. Ferguson decision in 1896, Black settlers began to see the narrowing of their rights. These families sought the protective wing of the nascent courts whose judges were federal appointees. Territorial courts heard more challenges to segregating schools than in any state. This was a time of unique confluence of law, public education, and defining Black citizenship. Would schools be the gateway to full civic and economic participation? Or would schools be a gatekeeper, denying access to some in order to maintain dominance for others? Territorial courts tackled these questions. Historians frequently have argued that the country’s failure to provide Blacks with civil rights resulted from its failure to redistribute land and/or from a premature end to federal oversight in the South after 1876. But in Oklahoma Territory, neither of these variables was in play: Black settlers had land, federal oversight, and the ability to vote. Nevertheless, they watched their civil rights diminish as the popular will established segregated education. The loss of access to education was key in re- inscription of second-class citizenship for Black Americans

Paleoenvironmental evolution of a late Holocen lake in the Azores archipelago

[Abstract] A major source of interannual variability in the atmospheric circulation is the North Atlantic Oscillation (NAO), which is associated with changes in the surface westerlies across the North Atlantic onto Europe. Irregularities in the NAO are responsible for storm track paths across the Atlantic Ocean towards Europe and, therefore, for the amount and timing of precipitation on this continent. Despite its importance, few historical and long-term reconstructions have been carried out and few multiproxy reconstructions of NAO evolution have been conducted in the Azores islands located at one end of the dipole. Since the NAO has a strong and direct influence on lacustrine ecosystems in many ways, the study of lake sediments can provide precise information on the long-term evolution of this climate mode. Characterization of sedimentary facies, organic matter geochemistry and remains of diatoms have been used in this study to determine three different climatic phases in a sediment core from Lake Empadadas Norte (São Miguel Island, Azores). The period 1340-1460 AD is defined by a decreasing trend in productivity and moderately shallow waters, as terrestrial inputs dominated, suggesting a humid climate with abundant precipitations indicating a NAOphase. Between 1460 and 1930 AD, and despite gaps in our data, the site was characterized by a more arid climate, related to a NAO+ phase, with lower lake level and productivity, with carbon appearing to be from mixed sources, although a series of catastrophic events are apparent in the form of massive instantaneous alluvial depositions. Finally, the period 1930-1950 AD, corresponds to a humid phase where lake level and productivity is high suggesting a return to low NAO values, although not as high as during 1340-1460 AD, and organic matter has a high percentage of terrestrial content as a result of increased run-off. This indicates NAO variability might be the main factor controlling water level fluctuations. We conclude that in order to accomplish a better understanding of climate change associated to the NAO, further and more ample studies are needed.Traballo fin de grao (UDC.CIE). Bioloxía. Curso 2012/201