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"En esta contribución se describen las distintas técnicas y mediciones magnéticas utilizadas en Magnetismo Ambiental y Paleomagnetismo. Tales mediciones ofrecen útiles indicadores para realizar estudios relacionados con cambios climáticos y ambientales, así como herramientas de datación. Si bien es ampliamente conocida la utilidad de la susceptibilidad magnética, en primer lugar se discute el potencial y necesidad del uso de parámetros adicionales obtenidos a partir de mediciones de magnetizaciones remanentes (natural, anhistérica e isotérmica), histéresis magnética y estudios termomagnéticos. A continuación se presentan resultados magnéticos obtenidos en sedimentos lacustres del Archipiélago James Ross (NE de la Península Antártica) como un caso de estudio. Se complementa con estudios sedimentológicos, hidroquímicos, geoquímicos y de estadística multivariada, pero se pone énfasis en los parámetros magnéticos y su relación con los distintos procesos que ocurren en los sistemas lacustres antárticos. Se analiza además el uso de las paleointensidades relativas como herramienta de datación en lagunas antárticas."

Most traditional paleoclimate proxies are either biased towards summer or assumed to record annual averages. We lack proxies for winter and transitional seasons. As a result, our vision of past climate is incomplete, which limits our understanding of climate mechanisms. A new paleothermometer has recently emerged and shows great potential to reconstruct past spring temperatures in freshwater lakes, the lacustrine alkenone biomarker. Alkenones are temperature-sensitive lipids produced specifically by Isochrysidales algae and have been widely used to reconstruct past sea surface temperatures. Alkenones are also found in lakes and have been linked to lake water temperatures in high latitude freshwater lakes. Monitoring studies in these lakes showed that alkenone production occurred during a short period after the ice melt. Depending on the timing of the ice-out, lacustrine alkenones record spring or summer temperatures. Lacustrine alkenones are increasingly reported in mid-latitude freshwater lakes but the seasonality of their production remained to be constrained. In our study, we monitored for the first time the alkenone production in a mid-latitude lake, Lake St Moritz in Switzerland. We sampled lake water and sediment trap contents during a year to follow the alkenone production in the lake. We also monitored the evolution through time of temperature and physico-chemical parameters of the lake water. We recorded the peak of alkenone production in spring 2022 and calculated the index of every sample containing alkenones to build an in-situ calibration. This calibration should allow us, in the future, to reconstruct spring temperatures in the past from Lake St Moritz sediments. Our goal is also to identify the drivers of the timing of alkenone production to better understand and interpret past variations of alkenone content in sediments. This study lays the foundations for the use of lacustrine alkenones as a spring paleothermometer in mid-latitude freshwater lakes., IAL-IPA 2022 Abstract Book - Lagos Memorias del Territorio

The records of the Little Ice Age (LIA) in lacustrine sediments from southern south America (SSA) are still rare. Indeed, most of the evidence of this period in SSA comes from tree rings records. Our main goal was identifying the signal of the LIA at Laguna Polo (49° 15’ 59.4” S, 72° 53’ 38.4” W), in Santa Cruz, southern part of Patagonia. For this multiproxy reconstruction, we analyzed a 54-cm long sediment core and conducted paleoecological analysis on testate amoebae and chironomids in combination with grain-size distribution and geochemical composition (TOC, TIC, TN, biogenic silica (BiSi), δ15N, δ13C and C/N). The age model, based on radiocarbon dates and tephrochronology, indicated a basal age of ca. AD 1300. Based on the biological proxies, we divided our record into 4 zones. In zone 3 an important ecological change in both bioproxies was detected for the period AD 1420 to 1780. On the one hand, testate amoebae show an increase in abundance but a decrease in diversity. Difflugids were highly abundant and were dominated by Difflugia glans. Chironomid assemblages, on the other hand, reveal a decrease in abundance of head capsules but an increase in diversity with the appearance of Cricotopus and Dicrotendipes. The taxa of both taxonomic groups found during this period have been reported as indicators of cold environments. Grain-size analyses indicate a concurrent proportional increase in silts and clays, whereas geochemical analyses record a decrease in TN, TOC, TIC, BiSi, δ13C and the C/N ratio, but an increase of δ15N which may be indicative of a cooler and wetter period, as has been previously described during the LIA period in Patagonia., IAL-IPA 2022 Abstract Book - Lagos Memorias del Territorio

Archaeological data suggests that humans commenced inhabiting the remote islands in the South Pacific around 3000 yr BP. Human occupation brought tremendous modifications to these small islands: clearing forests through burning, introduction of new flora and fauna, horticulture practices and the like. These practices were either drastic or gradual in some areas in the region, and may have been related to patterns of climate change. To better understand the peopling of this area, a 4.75 m composite sediment core, encompassing the period of human settlement, was retrieved from Lake Lanotō, Sāmoa. A multi-proxy approach, including micro-XRF scanning of the cores, grain size distribution, organic carbon content and molecular biomarkers from human and plant remains engraved in the sediment, is used to reconstruct past environmental changes. Combining these biomarker and elemental proxies will help us advance our knowledge on the timing of human expansion in Sāmoa, and in the South Pacific region. The generated data will shed valuable light on Pacific prehistory and complement the knowledge gained from archaeological data., IAL-IPA 2022 Abstract Book - Lagos Memorias del Territorio

In this work we integrated two approaches that are rarely used together in addressing the responses of biota to multiple environmental stressors –sediment cores and satellite images. The study area is a large subtropical reservoir (750 km2 ) that recurrently suffers severe cyanobacteria blooms, yet the trajectory of blooms since the building of the reservoir (in 1979) until the onset of the ongoing water quality monitoring program (ongoing since the year 2000) was unknown. In 2015 we performed sediment core studies, which were published in 2020, and our findings suggested that phytoplankton blooms initiated in 2003, about 24 years after the reservoir was built. Moreover, in this reservoir, as part of the current monitoring program, specific algorithms for chlorophyll estimation using satellites have been developed and published. Such algorithms allow phytoplankton chlorophyll estimation since 1984, thanks to the continuity of the Landsat mission (about 16 years prior to the monitoring program). Hence, we used images from 1984-2015 to explore if we could complement the information obtained using sediment cores. For this, we processed Landsat 5, 7 and 8 Landsat images (482, 350 and 67, respectively) in different areas of the reservoir, and calculated anomalies in chlorophyll (whenever chlorophyll was > 85 μg L-1). We found that before 2003, in average anomalies were only recorded about one time per year, whereas after 2003 the frequency of anomalies markedly increased (average 8 anomalies per year). Overall, the patterns found using sediment cores were like those encountered using satellite estimation of chlorophyll. Thus, these tools could be complementary used for analyzing recent trends (last 30 years, since satellites are operative in space) of phytoplankton trajectories., IAL-IPA 2022 Abstract Book - Lagos Memorias del Territorio

The colonization of Remote Oceania ~3000 years ago is attributed to the Lapita people, a population originating from South East Asia. First human settlements on these islands are associated with major landscape modifications. However, past hydroclimatic variations, which played a role in the colonization of remote islands, challenge a clear anthropogenic attribution of ecosystem changes. The archipelago of Vanuatu, with its extensive archeological remains of the Lapita culture, is considered a crucial location in the colonization of Remote Oceania. Here we present a sediment record retrieved near the Teouma archeological site, the earliest confirmed Lapita cemetery found in the Pacific Islands. We dated 43 macrofossils from a 4 m long peat core spanning the last 5000 years. Fecal sterols associated with human presence become more abundant during the Lapita period as well as the later Erueti phase. Palmitone downcore concentrations were quantified as a signature for taro, a staple crop introduced by early settlers, and applied as a proxy for the establishment of agriculture. Elemental changes were measured with X-ray fluorescence core-scanning to track soil erosion and provenance. The hydrogen isotopic composition of plant waxes, namely long-chain fatty acids, was measured as a proxy for hydroclimatic changes. A transition towards wetter climatic conditions corresponds to the initial human settlement indicated by archeological remains and fecal sterols. Coupling human-related and climatic proxies on a record spanning the last 5000 years allows us to reconstruct the pre-anthropogenic state of the site, and add insights to the timing of human arrival and the consequent landscape modifications., IAL-IPA 2022 Abstract Book - Lagos Memorias del Territorio