Siliceous microfossils record in the SW Gulf of Mexico during the Last Glacial-Interglacial transition

Indicators of biosiliceous production offer unique insights into the silica cycle at dynamic marine-continental interfaces, where seasonal discharges interact with a nutrient-depleted tropical ocean. This study reconstructs variations in siliceous paleoproductivity in the southwestern Gulf of Mexico (SW GoM) over the last 33.0 cal ka BP, investigating the complex interplay between oceanic circulation and continental nutrient forcing. Using a multiproxy approach, we integrated siliceous microfossils (diatoms, radiolarians, silicoflagellates, and sponge spicules) with bulk geochemical indicators (C org , CaCO 3 , and Si opal %wt) and total planktonic foraminifera. Our results reveal that while the SW GoM remained predominantly resource-limited, biogenic production exhibited significant variability across established Quaternary periods, with CONISS analysis delineating three distinct paleoceanographic stages over the Pleistocene-Holocene transition: (1) Last Glacial (33.0–19.0 cal ka BP), characterised by minimal biogenic accumulation across all microfossil groups due to enhanced stratification and reduced fluvial input relative to the current interglacial. (2) Deglaciation or Termination I (19.0–11.7 cal ka BP) was marked by a rise in diatom and sponge spicule abundance alongside peak planktonic foraminifera, indicating a carbonate-dominated system during marine transgression. (3) The interglacial (the last 11.7 cal ka BP) recorded the maximum biosiliceous accumulation, reflected in maximum C org and Si opal values, driven by sea-level stability and increased river discharge relative to the glacial. Our findings demonstrate that the siliceous fraction, although a minor component of total biogenic production, tracks the coupling between the silicon and carbon cycles. This study underscores the sensitivity of siliceous microfossils to land-sea interactions, demonstrating their crucial role in understanding the long-term evolution of tropical ecosystems.