REMEMBER: REsponses of neotropical freshwater ecosysteMs to climatE and environMental disturBance in the Mayan Region of Mexico during the Common Era

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The proposed REMEMBER project will generate high-resolution (decadal, centennial) data on biodiversity change and the historical development and response of freshwater ecosystems during the Common Era in the mid-elevations of the Lacandon Forest, Chiapas and in the lowlands of Quintana Roo, southern Mexico. We will jointly analyze chironomids, ostracodes and lipid biomarkers in 10 short sediment cores from karst lakes across an altitude (~1000 masl) and trophic state (oligo-, meso- and eutrophic) gradient to infer the effects and causes of climate and environmental change in the Maya region of Mexico. The selected locations and time intervals serve as a natural experiment to (1) study temporal and spatial changes in the relative abundance of freshwater taxa and (2) estimate the magnitude and velocity of changes in aquatic communities during the Pre-Columbian period, after European conquest, and during recent times. One focus of the lipid biomarker analyses will be placed on cyanobacteria as these frequently form harmful cyanobacterial blooms (cyanoHABs), which through the production of hepatotoxins, may negatively impact lake ecosystems and dwellers. Whereas some earlier studies in other nearby neotropical regions investigated historical shifts in the balance between evaporation and precipitation (E/P), little is known about air and water temperature changes that occurred in the past, e.g., during the Little Ice Age (LIA). Therefore, we chose chironomids and lipid paleothermometers (HDI26) to infer air and surface water temperatures at different elevations as they represent sensitive and reliable temperature proxies. To complement these lines of research, we will also use oxygen and carbon isotope values in ostracode shells as proxies for changes in evaporation and precipitation, temperature and productivity, and we will determine changes in mean annual air temperature using the MBT’5Me. Previous pollen studies for the LIA report that the “slight” but important cooling of about 2-3°C profoundly modified terrestrial plant communities in the northern Neotropics. However, the effect on aquatic ecosystems has not been investigated in depth and will be focus of this study. The generated data will enable us to infer temperature and E/P changes in the continental northern Neotropics, which will be compared with results from other paleoclimate archives, including speleothems, marine sediments and corals to understand the heterogeneous climate signals and responses that have been reported in the region but that yet remain to be resolved. Thus, REMEMBER will (1) provide high-resolution temperature time series over the last 2000 years for a tropical region that has been poorly represented in global climate databases, and (2) serve as a contribution to the conservation and management of freshwater ecosystems of southern Mexico.