Beyond climate variations, local factors such as geology, sediment composition, and vegetation also played a role in the lake\u2019s transition to a peat bog\u2014a waterlogged ecosystem where the lack of oxygen slows the decomposition of organic matter. These findings suggest that tropical ecosystems can respond to climate change in diverse and complex ways. \u201cOur data shows that this transformation process is older than previously thought\u2014going back 500,000 years\u2014and more intricate than a simple response to global climate patterns,\u201d explains Marquardt. The research could offer insights into future changes in wetland environments and underscores the importance of their conservation.<\/p>\n
\u201cThe diatom record was essential for understanding how a lake changes over time. And that\u2019s highly relevant today\u2014many lakes are evaporating or undergoing similar transformations due to climate change and heavy water use for irrigation,\u201d says French paleoecologist Marie-Pierre Ledru, a researcher at the Research Institute for Development (IRD) in France and one of the coauthors of the study.<\/p>\n
To collect diatom samples, the research team used a manual hammering system mounted on a tripod to insert a core tube to a depth of 14.7 meters (m). The deepest layers represent the oldest material, while the uppermost layers are the most recent. From this sediment core, samples were taken at intervals of 3 to 4 centimeters between depths of 14.7 and 8 meters. Each segment yielded a small volume of soil\u2014just 0.5 cm\u00b3\u2014resulting in 160 subsamples for the analysis of fossilized microalgae.<\/p>\n
The samples underwent a chemical treatment to remove organic matter and carbonates, leaving behind the diatoms\u2019 frustules\u2014their silica shells, made up of two interlocking valves\u2014which could then be examined under a microscope. For each slide, researchers counted a minimum of 400 valves, identifying the species and classifying them as either planktonic (suspended in the water column) or benthic (attached to submerged surfaces like rocks, plants, or sediment).<\/p>\n
The presence of planktonic diatoms suggests an active, open lake environment with high water levels, typically associated with humid glacial periods. In contrast, the prevalence of benthic species points to shallower conditions or a transition to a peat bog, indicating drier phases or dense vegetation covering the water\u2019s surface.<\/p>\n
\u201cWe were able to identify the species collected and discovered that many of them in Col\u00f4nia have never been described before. It\u2019s an extremely diverse environment,\u201d says Marquardt.<\/p>\n
![\"\"](\"https:\/\/revistapesquisa.fapesp.br\/wp-content\/uploads\/2025\/11\/RPF-paleo-cratera-2025-05-800.jpg\")
Eduardo Cesar\u2009\/\u2009Pesquisa FAPESP<\/span>The crater, located in Parelheiros, is around 4 km in diameterEduardo Cesar\u2009\/\u2009Pesquisa FAPESP<\/span><\/p><\/div>\n The research was conducted during her postdoctoral work at what was then the Botanical Institute of S\u00e3o Paulo, which became part of the Environmental Research Institute (IPA) in 2021. Funded by FAPESP, the project aimed to track changes in diatom communities and use them as biological indicators for paleoenvironmental reconstruction in the Col\u00f4nia basin.<\/p>\n Although the study focused on the S\u00e3o Paulo site, the findings\u2014published in December\u2014were compared with sediment records from Lake Titicaca in the Andes. Despite differences in altitude and geography, both environments showed similar climatic responses to global oscillations: colder periods were marked by greater humidity and expanded water bodies, while warmer intervals brought reduced moisture and lower water levels.<\/p>\n However, differences in the types of diatoms found suggest that global climate alone does not explain all environmental changes. In Lake Titicaca, benthic species dominated during glacial periods, pointing to shallow conditions. In contrast, the Col\u00f4nia basin showed a predominance of planktonic species in the same periods\u2014indicating deeper, more dynamic waters. This led researchers to hypothesize that local factors such as topography, vegetation, and water depth may have played an equal or even greater role than global climate shifts in shaping ecological dynamics.<\/p>\n \u201cOur current climate models are based on about 40 years of data. A record like the one presented in this study\u2014with such deep historical insight, even revealing variations within a single sub-basin\u2014is extremely valuable,\u201d says Brazilian biologist Luciane Fontana, now at Lanzhou University in China.<\/p>\n A specialist in paleoenvironmental reconstruction, Fontana uses diatoms and other biological markers in her own research, although she was not involved in Marquardt\u2019s study. She emphasizes the importance of this type of data: \u201cThe predictive models we use today can and should incorporate this kind of information to become more robust, as diatoms are excellent bioindicators\u2014they respond quickly to environmental changes.\u201d<\/p>\n Another study, published in March in the journal Review of Palaeobotany and Palynology<\/em>, highlights the rich diversity of fossil pollen and spores preserved in the sediments of the Col\u00f4nia basin, also dating from the Middle Pleistocene (between 530,000 and 370,000 years ago). Authored by Paraguayan paleoecologist Olga Aquino-Alfonso and Marie-Pierre Ledru, the article identifies 146 types of palynomorphs (microscopic organic particles) that document the ancient vegetation of the Atlantic Forest prior to the onset of the planet\u2019s 100,000-year glacial cycle.<\/p>\n Combining microscopy techniques and ecological analysis, the study reveals a humid and diverse forest, with species that are now rare, such as araucarias and podocarps, and the absence of others like Acaena and Ephedra, suggesting major environmental shifts over time. \u201cWe found a mix of Cerrado species alongside plants now considered cold-adapted, from the Pampa region,\u201d says Ledru.<\/p>\n She explains that during the ice ages, sea levels were about 100 meters lower, pushing the coastline farther away and reducing the humidity needed to sustain the Atlantic Forest. \u201cThe coast was farther out. As humidity decreased, drier species began to take hold and expand\u2014until the moisture returned and the sea level rose again,\u201d she explains. These records, she adds, underscore the need for careful monitoring of today\u2019s biomes, as their boundaries may shift more rapidly than expected under current climate change scenarios.<\/p>\n Projects<\/strong>
\n1.<\/strong> Changes in diatom assemblages in response to climate and environmental changes during glacial and interglacial cycles in an Atlantic Forest region located in an urban area (n\u00b0 18\/23399-0<\/a>); Grant Mechanism<\/strong> Postdoctoral Fellowship; Supervisor<\/strong> Carlos Eduardo de Mattos Bicudo (Instituto de Bot\u00e2nica); Beneficiary<\/strong> Gisele Carolina Marquardt; Investment<\/strong> R$177,857.36.
\n2.<\/strong> Challenges for biodiversity conservation in the face of climate change, pollution, and land use and occupation (PDIp) (n\u00b0 17\/50341-0<\/a>); Grant Mechanism<\/strong> Research Grant \u2013 State Research Institutes Modernization Program; Principal Investigator<\/strong> Luiz Mauro Barbosa (Instituto de Pesquisas Ambientais); Investment<\/strong> R$9,612,432.65.
\n3.<\/strong> Dimensions US-Biota S\u00e3o Paulo: Integrating disciplines for predicting Atlantic Forest biodiversity in Brazil (n\u00b0 13\/50297-0<\/a>); Grant Mechanism<\/strong> Biota Program; National Science Foundation (NSF) Agreement; Principal Investigator<\/strong> Cristina Yumi Miyaki (USP); Investment<\/strong> R$4,517,876.44.
\n4.<\/strong> Paleolimnological reconstruction of the Guarapiranga dam and diagnosis of the current water and sediment quality in springs in the S\u00e3o Paulo Metropolitan Area with regard to water supply management (n\u00b0 09\/53898-9<\/a>); Grant Mechanism<\/strong> Thematic Project; Principal Investigator<\/strong>: Carlos Eduardo de Mattos Bicudo (Instituto de Bot\u00e2nica); Investment<\/strong> R$1,725,042.01.<\/p>\n