South America's second-largest wetland accumulated 5 meters of peat over 10,000 years. Pollen analysis reconstructs how climate shifts transformed the landscape from forest to marsh.
Evelyn Proimos, CC BY 2.0, via Wikimedia Commons
A layered history of climate
The Iberá Wetlands, a vast complex of marshes and lagoons covering over 13,000 square kilometers, hold a detailed climate archive within their soil. For the last 10,000 years—the entire Holocene epoch—decomposing vegetation has slowly built up thick layers of peat. In some areas, these deposits reach depths of five meters. This dark, saturated soil is it is a layered environmental history book waiting to be read by scientists.
The process relies on the unique chemistry of wetlands. Waterlogged conditions create an anaerobic, or low-oxygen, environment. This slows decomposition to a crawl, preserving organic materials that would otherwise decay. Over millennia, this material compacts into peat. Scientists can drill into these deposits to extract sediment cores, cylinders of earth where each layer represents a different period in time. By using radiocarbon dating on the organic matter within these layers, a precise timeline can be established, turning the peat core into a vertical calendar.
Reading the pollen record
The way to decipher this archive lies in palynology, the study of pollen grains. Plants release immense quantities of pollen, and each grain has a unique shape and size specific to its parent species. These grains, protected by a durable outer shell, fall into the wetland and become trapped in the accumulating peat. By analyzing the pollen found in each dated layer of a sediment core, researchers can reconstruct what the dominant plant life was at any given time.
Pollen studies from the western margin of Iberá reveal a dynamic history of environmental change. Analyses of cores spanning from approximately 6,000 to 3,000 years before present show alternating periods of wet and dry conditions. During drier times, wind-blown sand formed dunes in the region. The appearance of tree pollen in the record around 3,500 years ago marks the beginning of the modern hygrophilous, or water-loving, forest.
A shift in pollen from forest species to grasses and sedges indicates a transition from woodland to open marsh, likely driven by changes in rainfall and temperature. Finding pollen from species like Amaranthus or trees such as Schinopsis and Celtis allows scientists to create a detailed picture of the floral composition and how it responded to climate shifts over thousands of years. This granular data, preserved micro-fossil by micro-fossil, shows the long-term ecological rhythms of South America's second-largest wetland.
💡Fun Facts
The name Iberá comes from the Guaraní words "Y berá," which translates to "bright waters."
The Iberá Wetlands are a designated Ramsar Site, recognizing them as a wetland of international importance.
Peatlands are immense carbon sinks, storing more carbon globally than all the world's forests combined.
Some of the floating islands of vegetation, known as *embalsados*, can become thick enough to support small forested areas.
The Iberá National Park has multiple access portals, each with its own infrastructure and hours. Colonia Carlos Pellegrini is a primary access town and is generally accessible year-round. Check the official park website for specific portal information.
Admission
Varies by park entrance. Some areas may be free while others have an entrance fee for access to specific reserves or activities.
Accessibility
Terrain is generally flat but consists of unpaved roads, grasslands, and wetlands. Many wildlife viewing opportunities are from boats or raised walkways. Accessibility for individuals with mobility challenges may be limited in many areas.
