Diatom-inferred ecological responses of an oceanic lake system to volcanism and anthropogenic perturbations since 1290 CE

The impacts of natural- and human-induced processes on lake ecosystems in remote oceanic islands remain to be fully elucidated. These lakes are excellent candidates to analyze the importance of anthropogenic vs. natural forces driving lacustrine long-term ecological evolution from previous pristine pre-colonized conditions. Disentangling the effects of both is particularly relevant in highly active volcanic areas, where catastrophic eruptions can act as an atypical natural driver altering the lake's long-term ecological trajectories. In this paper we study past ecological changes occurring in Lake Azul (São Miguel island), a crater lake from the remote Azorean archipelago, to address which were the main causes of its long-term trophic history. We analyzed diatom assemblages, sedimentology, and bulk organic matter of sediments deposited since ca. 1290 CE, when a huge local eruption occurred. This episode drove the evolution of Lake Azul through six distinct phases, commencing with a restart of ecological succession after tephra deposition disrupted biogeochemical cycling. The alteration was so profound that the lake underwent a state of oligotrophic conditions for approx. 650 yr. Nutrients were sourced by fish-induced internal recycling and the overflow of the near Lake Verde during this period, rather than by allochthonous nutrient inputs modulated by climate variability and/or vegetation cover changes in the watershed after the official Portuguese colonization. It was only after recent artificial fertilization when the system overcame the volcanic-induced long-term resilience. This over-fertilization and a reduction in water turnover exacerbated the recent symptoms of eutrophication after 1990 CE. Contrary to other studies, Lake Azul constitutes an uncommon case of long-term resilience to trophic change induced by a cataclysmic volcanic eruption. It brings new insights into the fate of lake ecosystems which might be affected by similar events in the future

Impact of the historical introduction of exotic fishes on the chironomid community of Lake Azul (Azores Islands)

Little is known about the effect of top predator introduction in historically fishless communities, especially on remote islands. This issue is important because it might strongly affect climate reconstructions derived from biota assemblages such as chironomids. Head capsule larval remains of chironomids have been studied in a 660 years lacustrine sedimentary sequence from Lake Azul (Sao Miguel Island, Azores archipelago) to assess the extent and timescale of the effect of the predator introduction occurring in this historically fishless lake. Analysis of similarity showed that the chironomid assemblage was statistically different before and after predator introduction (R = 0.78; p < 0.001). Abundance of chironomids was about 40% greater in the fishless lake period compared to the period in the presence of predator. Results show major change in chironomid assemblage coinciding with the first time of goldfish introduction (around 1790 CE), followed by carp (1890 CE) and pike (1979 CE) introductions. The composition of feeding group guilds changed following a pattern characterized by a decrease in abundance of detritivorous and predaceous taxa and an increase in abundance of grazing chironomid taxa. This study suggests that predator introduction was the most important factor affecting the chironomid assemblages in this natural, Azorean fishless lake, but predators did not affect all chironomid species. Other external forcings like major climate oscillations, anthropogenic activities in the catchment basin, and volcanic eruptions seem to play an additional role. The latest stage of the warm and arid Medieval Climate Anomaly (1000-1300 CE) favoured the occurrence of some warm-adapted chironomid taxa, which were absent through the Little Ice Age (ca. 1450-1850 CE) cool period

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

Climate change facilitated the early colonization of the Azores Archipelago during medieval times

Humans have made such dramatic and permanent changes to Earth's landscapes that much of it is now substantially and irreversibly altered from its preanthropogenic state. Remote islands, until recently isolated from humans, offer insights into how these landscapes evolved in response to human-induced perturbations. However, little is known about when and how remote systems were colonized because archaeological data and historical records are scarce and incomplete. Here, we use a multiproxy approach to reconstruct the initial colonization and subsequent environmental impacts on the Azores Archipelago. Our reconstructions provide unambiguous evidence for widespread human disturbance of this archipelago starting between 700 -60/+50 and 850 -60/+60 Common Era (CE), ca. 700 y earlier than historical records suggest the onset of Portuguese settlement of the islands. Settlement proceeded in three phases, during which human pressure on the terrestrial and aquatic ecosystems grew steadily (i.e., through livestock introductions, logging, and fire), resulting in irreversible changes. Our climate models suggest that the initial colonization at the end of the early Middle Ages (500 to 900 CE) occurred in conjunction with anomalous northeasterly winds and warmer Northern Hemisphere temperatures. These climate conditions likelyinhibited exploration from southern Europe and facilitated human settlers from the northeast Atlantic. These results are consistent with recent archaeological and genetic data suggesting that the Norse were most likely the earliest settlers on the islands

Late Holocene Climate Variability in the North Atlantic based on biomarker reconstruction: The lake Azul (São Miguel, Azores archipielago) case

[eng] The principal objective of this PhD thesis is to obtain a high resolution reconstruction of the climate (temperature and precipitation) in the north Atlantic for the late Holocene. This new reconstruction is from a sedimentary lacustrine record located in Azores (Lake Azul) that has been compared and discussing with principal other climate reconstructions published on the North Atlantic region. Climate in the North Atlantic is modulated by the conjunction of atmospheric patterns and ocean dynamics. The main atmospheric pattern is the North Atlantic Oscillation (NAO) but, other climatic modes such as the Eastern Atlantic (EA) and the Atlantic Meridional Oscillation (AMO) are also present. The use of biomarkers has appeared as a cutting edge technique to reconstruct climate and their validity has been proved by previous works. The Azul lacustrine sedimentary sequence occupied the last 660 years, and on it has been applied a multiproxy study including: facies analysis, X-Ray Diffraction (XRD), X-Ray Fluorescense (XRF), Total Organic Carbon (TOC), Total Nitrogen (TN), bulk isotopes of Carbon (δ13C) and Nitrogen (δ15N) and biomarkers (GDGTs and δD leaf waxes). Facies were grouped in two main facies types according to the velocity of sedimentation and the organic matter origin: (1) “Continuous facies” accumulated by a more or less continuously sedimentation processes and dominated by lake organic matter, and (2) “rapid facies” deposited from flood events and transporting mainly terrestrial organic matter. An accurate age-depth model based on 14C and 210Pb dates and XRF data was built to figure out those sudden changes (the Dynamic Age Model, DAM). The DAM calculates the age of the samples redistributing the time along the profile according to the amount of crystalline terrestrial particulated material. DAM can acquire short and long-term sedimentation rate (SR) changes and previous models only acquire long- term fluctuations. The biomarkers (GDGTs and δD leaf waxes) were extracted and studied on the continuous lacustrine facies to reconstruct temperature and precipitation. The relative percentage of GDGTs was transferred into temperature by the use of Pearson et al., (2011) calibration. The climatic factor affecting δD fractionation was assessed by the weekly collection of rain water showing a clear depletion with the amount of precipitation. Results from realized reconstruction suggested a climatic model that converge oceanic currents with the principal atmospheric patterns, defining the NAO as the main factor triggering the others. The temperature in Azores depends on the position of the Gulf Stream (GS). A positive (negative) NAO phase enhances (reduces) the Gulf Stream (GS) velocity that increases (reduce) the amount of Eddies around Bermuda driving towards north (east) the GS and heating up high (medium) latitudes. Therefore, a negative phase of NAO favors the GS heat to reach Azores. Since the temperature in Azores is modulated by the oceanic circulation, the AMO also plays an important role. The AMO is reflected in Ponta Delgada by the amplitude between maximum and minimum mean annual temperatures, which means an increase on seasonality. The AMO positive phase is reflected as an increase on temperatures in Lake Azul reconstruction. Otherwise, the AMO negative phase is masked by other climatic patterns. The precipitation in Azores is mainly triggered by the NAO phase, increasing (decreasing) precipitation during NAO negative (positive). The comparison with other reconstructions in the North Atlantic area suggested that an increase of precipitation in São Miguel produces an increase at other Azorean islands, the Iberian Peninsula and Morocco. This pattern has been observed for the last 700 years except for the period comprised between 1680 and 1920 AD where a possible southeastern shift of the NAO south dipole seemed to be produced. We suggest that this movement is produced by the occurrence, simultaneously, of an in phase and positive NAO and EA conjunction

Distribución de la salinidad, sílice y clorofila a en las playas del sector sur del golfo de Valencia

Los objetivos que se plantean en este estudio son los siguientes: - Determinar las variaciones espaciales en la concentración de Sílice y establecer la relación que existente con la salinidad de las aguas y con la producción fitoplanctónica. - Estableceremos la relación de concentración de Sílice y salinidad con la información hidrológica disponible para tener recopilada toda la información que nos pueda facilitar en próximos trabajos si existe una influencia debida a aguas subterráneas en este sector de la Comunidad Valenciana que estamos estudiando.Rubio De Inglés, MJ. (2009). Distribución de la salinidad, sílice y clorofila a en las playas del sector sur del golfo de Valencia. Universitat Politècnica de València. http://hdl.handle.net/10251/99273Archivo delegad

Climate reconstruction for the last two millennia in Central Iberia: the role of East Atlantic (EA), North Atlantic Oscillation (NAO) and their interplay over the Iberian Peninsula

A multi-proxy characterization of the uppermost sedimentary infill of an Iberian alpine lake (Cimera, 2140 m a.s.l.) was performed to establish the climatic and environmental conditions for the Iberian Central Range (ICR) over the last two millennia. This multi-proxy characterization was used to reconstruct the intense runoff events, lake productivity and soil erosion in the lake catchment and interpret these factors in terms of temperature and precipitation variability. The Roman Period (RP; 200 BCE - 500 CE) beginning was characterized by an alternation between cold and warm periods as indicated by shortlived oscillations of intense runoff conditions and soil erosion, although warm conditions dominated the end of the period and the Early Middle Age (EMA; 500-900 CE) onset in the ICR. A noticeable decrease in intense runoff events and a progressive decrease in soil erosion during the late EMA indicated a shift to colder temperatures. In terms of precipitation, both the RP and EMA climate periods displayed a transition from dry to wet conditions that led to a decrease in lake productivity. The Medieval Climate Anomaly (MCA; 900-1300 CE) was characterized by warm and dry conditions with frequent intense runoff episodes and increases in lake productivity and soil erosion, whereas the Little Ice Age (LIA; 1300 -1850 CE) showed the opposite characteristics. The Industrial Era (1850-2012 CE) presented an increase in lake productivity that likely demonstrates the influence of global warming. The spatio-temporal integration of the Cimera record with other Iberian reconstructions has been used to identify the main climate drivers over this region. During the RP and EMA, N-S and E-W humidity gradients were dominant, whereas during the MCA and LIA, these gradients were not evident. These differences could be ascribed to interactions between the North Atlantic Oscillation (NAO) and East Atlantic (EA) phases. During the RP, the general warm conditions and the EeW humidity gradient indicate a dominant interplay between a negative NAO phase and a positive EA phase (NAO- EA+), whereas the opposite conditions during the EMA indicate a NAO+ EA- interaction. The dominant warm and arid conditions during the MCA and the cold and wet conditions during the LIA indicate the interplay of the NAO+ EA+ and NAO- EA- , respectively. Furthermore, the higher solar irradiance during the RP and MCA may support the predominance of the EA- phase, whereas the opposite scenario during the EMA and LIA may support the predominance of the EA phase, which would favour the occurrence of frequent and persistent blocking events in the Atlantic region during these periods

The Status of a Common Currency Euro in the World Economy

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