The macro in the micro: a case study from Edisto Inlet (Ross Sea, Antarctica)

Paleoenvironmental reconstructions are used to understand the evolution of past environmental conditions in a particular area. Traditional approaches include geochemical, sedimentological, and micropaleontological proxies to retrieve different environmental characteristics. Micropaleontological analyses have traditionally focused on foraminifera, diatoms, and other microorganisms, correlating changes in species with the physiochemical characteristics of the environment. Nevertheless, microfossils belonging to macrofaunal communities have been poorly studied, especially for the Holocene. Here, we examine a marine sediment core (TR17-08) that spans the last 3.6 kyrs BP, located in the northwestern part of the Ross Sea. Our findings demonstrate that the use of macrofaunal microfossils, in the present case echinoderms, can yield detailed and complex information about recent past conditions. Two distinct groups were identified: ophiuroids (Ophionotus victoriae) and irregular echinoid. Estimating the populations size can be complicated due to the great number of ossicles released upon the decay of the dead organism. To address this, we utilized Generative Additive Models to model the presence/absence distribution over time. By comparing the model output with other proxies derived from the same record and ones derived from nearby cores, we were able to successfully use echinoderms as a new “macrofaunal proxy”. O. victoriae presence can be associated with interannually stable sea-ice cycles with yearly organic deposition, while simultaneously indicating periods of a mature benthic community. Irregular echinoids forms have been associated with the presence of organic matter on the seafloor. By comparing different proxies, we were able to distinguish specific climatic phases in accordance with previous studies, while revealing additional insight into the environmental evolution of the area, unattainable with traditional proxies. In conclusion, this study provides compelling evidence that the inclusion of macrofaunal-related proxies in paleoenvironmental reconstructions is crucial for capturing complex interactions between the environment and the ecosystem.