Late Quaternary meltwater pulses during Termination I on the southwestern South Atlantic margin

Abstract

The Argentine continental shelf reveals the significant influence of Late Quaternary climatic changes on its evolution. A sedimentary core, retrieved at 40ºS- 57º W from the outer shelf, documents the environmental evolution of the coast during the Late Glacial-early Holocene, influenced by significant post-Last Glacial Maximum (LGM) sea-level changes. Between the LGM and 15 cal. ka BP, an isolated coastal lagoon was established. It was characterized by reducing and low-energy conditions. Microfossils with continental and marine affinities suggest a brackish environment influenced by continental runoff, originating from increased precipitation in southeastern South America during Heinrich Stadial 1. Subsequently, between ~15-14 cal. ka BP, the environment rapidly evolved into a coastal lagoon with marine connection. This change coincides with Meltwater Pulse 1A, which caused a rapid sea-level rise, integrating the lagoon with the open marine environment. The continuous rise in sea level allowed the formerly isolated lagoon to be connected to the open sea around ~14 cal. ka BP, forming a mesohaline, tide-dominated paleobay. This vegetated tidal flat was characterized by greater stability and a high diversity of ostracods and foraminifera. Then, around 13.7 cal. ka BP, a storm-dominated shoreface is interpreted, indicating high-energy and fully marine conditions. A coarse bioclastic interval reflects repeated storm events on the shelf, mainly during the Younger Dryas and Meltwater Pulse 1B, which marks the last rapid pulse of mid- and outer shelf inundation. The Holocene sediments represent typical outer shelf conditions, characterized by relict sands formed by the reworking of pleistocene continental and marginal marine sediments. These results align with similar studies in the western South Atlantic. Research on the continental shelf of Brazil and Patagonia also reveals the influence of post-LGM eustatic events, highlighting the response of marginal marine environments to post-LGM sea-level rise and meltwater pulses. This study contributes to a broader understanding of the paleoenvironmental evolution of the South American continental margin, underscoring the importance of global sea-level changes in coastal and shelf dynamics. Our findings are crucial for reconstructing post-LGM sea-level changes and predicting future coastal responses to climate change.