Dr. Contreras-Quintana, Sergio

African climate is generally considered to have evolved towards progressively drier conditions over the past few million years, with increased variability as glacial–interglacial change intensified worldwide1,2,3. Palaeoclimate records derived mainly from northern Africa exhibit a 100,000-year (eccentricity) cycle overprinted on a pronounced 20,000-year (precession) beat, driven by orbital forcing of summer insolation, global ice volume and long-lived atmospheric greenhouse gases4. Here we present a 1.3-million-year-long climate history from the Lake Malawi basin (10°–14° S in eastern Africa), which displays strong 100,000-year (eccentricity) cycles of temperature and rainfall following the Mid-Pleistocene Transition around 900,000 years ago. Interglacial periods were relatively warm and moist, while ice ages were cool and dry. The Malawi record shows limited evidence for precessional variability, which we attribute to the opposing effects of austral summer insolation and the temporal/spatial pattern of sea surface temperature in the Indian Ocean. The temperature history of the Malawi basin, at least for the past 500,000 years, strongly resembles past changes in atmospheric carbon dioxide and terrigenous dust flux in the tropical Pacific Ocean, but not in global ice volume. Climate in this sector of eastern Africa (unlike northern Africa) evolved from a predominantly arid environment with high-frequency variability to generally wetter conditions with more prolonged wet and dry intervals.

Paleolimnological studies in western South America, where meteorological stations are scarce, are critical to obtain more realistic and reliable regional reconstructions of past climate and environmental changes, including vegetation and water budget variability. However, climate and environmental geochemical indicators must be tested before they can be applied with confidence. Here we present a survey of lacustrine surface sediment (core top, 0 to ~1 cm) biogeochemical proxies (total organic carbon [TOC], total nitrogen [TN], carbon/nitrogen ratio [C/N ratio] and bulk organic δ13C and total δ15N) from a suite of 72 lakes spanning the transition from a Mediterranean climate with a patchwork of cultivated vegetation, pastureland, and conifers in central Chile to a rainy temperate climate dominated by broadleaf deciduous and evergreen forest further south. Sedimentary data are compared to the latitudinal and orographic climatic trends of the region based on the climatology (precipitation and temperature) produced with Climate Forecast System Reanalysis (CFSR) data and the modern Southern Hemisphere Westerly Winds (SWW) location. The geochemical data show inflection points at ~42°S latitude and ~1500 m elevation that are likely related to the northern limit of influence of the SWW and elevation of the snow line, respectively. Overall the organic proxies were able to mimic climatic trends (Mean Annual Precipitation [MAP] and temperature [MAT]), indicating that they are a useful tool to be included in paleoclimatological reconstruction of the region.

PBDEs (10 congeners) were analyzed using GC–MS in superficial sediments and organisms of the Concepción Bay after the 2010 Tsunami. From all congeners analyzed PBDE-47, -99, -100 and -209 were the most frequently detected. Concentrations (ng g1 d.w.) in sediments for RPBDE-47, -99, -100 were low (0.02–0.09). However, PBDE-209 showed significantly higher values 20 ng g1 d.w. This result were 10 times lower than those reported in a previous study of the 2010 Tsunami. The high result might be influenced by the massive urban debris dragged by the 2010 Tsunami. In organisms, concentrations of PBDE-47, -99, -100 (0.4 ng g1 d.w.) were higher than those found in sediments (0.04 ng g1 d.w.). Differences in PBDE pattern were also observed between different levels of the trophic food chain (primary and secondary consumers). This is the first attempt to assess the current status of Concepción Bay after the 2010 Tsunami.

Climate variability during Pleistocene glacial/interglacial transitions is well documented in marine and ice-sheet isotopic records, but terrestrial records showing the continental response to these transitions are scarce, especially for earlier in the Pleistocene. Cyclic intervals of warm interglacial and cold glacial conditions preserved in terrestrial records such as lake sediments provide opportunities to probe the biosphere's response to climate change. In this study, we track climate and plant type changes, specifically the presence of C3 and C4 plants, using the abundance and δ13C signatures of leaf waxes in paleolacustrine sediments from Valles Caldera in New Mexico. Through these changes, weassess there sponse of vegetation to climate variability in southwestern North America through two mid-Pleistocene glacial/interglacial transitions (Marine Isotope Stage [MIS] 14/13 and 12/11). Leaf wax data show that the C3 forest taxa were dominant through the entire record whereas C4 plants, better adapted to warm conditions and competitive under water stress, are favored during warming and extended arid periods during interglacials. The δ13C signature in leaf wax n-alkanes suggests that C4 plants persisted in the water shed throughout the interglacials and that some summer rainfall (which is required to support C4 grasses) was maintained even during prolonged dry periods. The abundance and carbon isotope composition of leaf waxes together with new MBT/CBT (methylation index of branched tetraethers/cyclization index of branched tetraethers) temperature data confirm warmer and more arid conditions during MIS 13 than during MIS 11, in spite of relatively low greenhouse gas concentrations during MIS 13. This suggests that variations in incoming solar radiation have played a major role in regulating the surface temperature, regional hydrological systems and vegetation in southwestern North America, likely through changes in the North American Monsoon coupled with variations in the location of the mid-latitude westerlies.

Surface water samples from the environmental continuum spanning rivers (Petrohue, Cochamo, Puelo), fjord (Reloncaví), and the inner sea of Chiloé in Chilean Patagonia were analyzed to estimate concentration and distribution of dissolved Organochlorine pesticides (OCPs). High concentrations of HCHs, DDTs and endosulfan found in surface waters from rivers suggest that rivers are the major source of dissolved OCPs to coastal marine ecosystems. We interpret variations in the distribution and concentration as an apparent oscillation between rain and snow-scavenging processes that might determine the type of OCPs that can be preferentially deposited on mountains, glaciers, rivers, estuaries, and finally transferred to the marine realm. Predominance of α-HCH, γ-HCH, p,p′-DDE and α-endosulfan compounds suggest that the main deposition mechanism of OCPs to the Chilean Patagonia is rain scavenging. Snow and rain can be additional sources of OCPs that must be considered for future studies in fjord systems in Chilean Patagonia.