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Abstract Tropical lakes harbour high levels of biodiversity, but the temporal and spatial variability of biological communities are still inadequately characterised, making it difficult to predict the impact of accelerated rates of environmental change in these regions. Our goal was to identify the spatiotemporal dynamics of the planktic diatom community in the Cajas Massif in the tropical Andes.We analysed seasonal diatom and environmental data over a period of 1 year from 10 lakes located in geologically distinct basins and modelled community–environment relationships using multivariate ordination and variation partitioning techniques. Generalised additive models with a full‐subset information theoretic approach also were used to determine which environmental variables explain single‐species abundance.Although the lakes are monomictic and thus have variable thermal structure across the year, seasonal variability of water chemistry conditions was negligible, and seasonal differences in diatom community composition were small. Across space, diatom community composition was correlated primarily with ionic content (divalent cations and alkalinity), related to bedrock composition, and secondly with lake thermal structure and productivity. The ionic gradient overrode the effect of the thermal structure–productivity gradient at the diatom community level, whereas individual diatom species responded more sensitively to variables related to in‐lake and catchment productivity, including chlorophyll‐aand iron, and the proportion of wetlands in the catchment.Our results indicate that the spatiotemporal variability of Cajas lakes and their diatom communities is the result of multiple intertwined environmental factors. The emergence of the ionic and thermal structure–productivity gradients in a rather small tropical lake district suggests segregation of ecological niches for diatoms that also may be important in other high‐elevation lake regions. Future studies that track tropical Andean lakes under natural and anthropogenically mediated change, both in contemporary times and in palaeoenvironmental reconstructions, would benefit from the modelling approach (community and species levels) developed here. 

Northern northeastern Brazil (NEB) is a climate change hotspot due to its high biological and social vulnerability to ongoing and future hydroclimate changes. Precipitation in this region is influenced by the Intertropical Convergence Zone (ITCZ), which is largely controlled by the strength of the Atlantic Meridional Overturning Circulation (AMOC). Accordingly, the projected weakening of the AMOC due to anthropogenic global warming may substantially change NEB hydroclimate. Heinrich Stadials (HS), past millennial-scale events during which the AMOC was significantly weaker, provide important insights into the AMOC-ITCZ dynamics. This is especially true for those HS that occurred under similar to modern boundary conditions. HS10 (ca. 110 thousand years ago) was the first HS of Marine Isotope Stage 5, providing an ideal target for investigating AMOC-ITCZ dynamics under relatively warm climate conditions. Here we investigate the response of the surface and deep western equatorial Atlantic (WEA) circulation, as well as NEB precipitation to HS10. Therefore, we use foraminiferal carbon and oxygen stable isotopes and bulk sediment major elemental data from a marine sediment core retrieved from the WEA. Our results record a weakening of the AMOC during HS10 and show a concurrent increased WEA upper stratification and precipitation over NEB. We suggest that the mechanism controlling the WEA upper ocean stratification during HS depends on the background climate. Furthermore, we infer that the southward shift of the ITCZ during HS10 was more limited if compared to the shifts that occurred under colder climate background. Our findings provide useful insights into how a weakening of the AMOC under a relatively warm climate can impact the ITCZ and tropical South American precipitation. 

The Amazonia biome hosts upland closed and open vegetation ecosystems, in which the current biogeographical patterns relate to the evolution of the physical landscape. Therefore, understanding the origin and timing of the substrates supporting different ecosystems is indispensable for better comprehension of Amazonian biogeography. Here we used quartz optically stimulated luminescence (OSL) and thermally transferred optically stimulated luminescence (TT-OSL) for dating sandy substrates of closed and open vegetation environments in Central and Eastern Amazonia, from both outcrop and drill core samples (Autazes core: PBAT-15-43). These sandy substrates present ages ranging from 1 ka up to almost 2 Ma, that were primarily interpreted as depositional ages of fluvial terraces. Moreover, ages are discussed in terms of potential geomorphic processes leading to the formation of substrates, such as soil mixing and apparent age of quartz from the parent bedrock. The coupling between OSL and TT-OSL techniques allow us to date sedimentary deposits covering the whole Quaternary, which implies a new time window for the Amazonia history.