CORALLINE ALGAE RESPONSE TO ENVIRONMENTAL CHANGE AT THE PALEOCENE-EOCENE THERMAL MAXIMUM, MEGHALAYA, INDIA

Coralline algae are important calcifying plants in modern oceans, producing carbonate sediment, providing food and shelter for many organisms, and cementing reef structures. Due to their high-Mg CaCO₃ skeletons, corallines are vulnerable to ocean acidification, although their current response is not well understood. Lab studies show negative effects of acidification on coralline physiology, although the nature and magnitude of effects varies between species and are difficult to extrapolate to a regional scale.

Hyperthermals occurred throughout Earth’s history and provide an opportunity to examine the impacts of acidification and warming over evolutionary timescales. The Paleocene-Eocene Thermal Maximum (PETM), the largest Cenozoic hyperthermal, is considered the best analogue for modern climate change, resulting in 5-8°C warming and widespread acidification over ~10 kyr. Paleoecological studies of PETM sediments reveal important biotic effects in many marine groups, but corallines have not been studied extensively.

In this study, I collected rock samples from the upper Paleocene- lower Eocene Lakadong Limestone in the Janita and Khasi Hills, Meghalaya, India, and used point counts to quantify coralline abundance (percentage of the thin section composed of corallines). I used carbon isotopes to locate the negative d¹³C excursion that marks the onset of the PETM.

Before the PETM, coralline abundance is generally <5%. Surprisingly, coralline abundance increases to >20% during the early PETM, suggesting initial warming and acidification were not detrimental to coralline health. Subsequently, a drastic decrease in coralline abundance during the PETM coincides with increased siliciclastic sediment. This may indicate corallines were unable to tolerate increased sedimentation due to decreased illumination or burial of the carbonate platform.