Assessing the impact of bioturbation on sedimentary isotopic records through numerical models

The disturbance of seafloor sediments by the activities of bottom-dwelling organisms, known as bioturbation, significantly alters the marine paleorecord by redistributing particles in the upper sediment layers. Consequently, ‘proxy’ signals recorded in these sediment particles, such as the size, abundance, or isotopic composition of plankton shells, are distorted by particle mixing. Accordingly, bioturbation can alter the apparent timing, duration, and magnitude of recorded events by smoothing climatic and oceanographic signals. In an extreme scenario, biological mixing can significantly obscure our view of the past by homogenizing the bioturbated layer, destroying sediment layering, and distorting the relative timing and intensity of past climatological events. Here we explore how bioturbation distorts proxy records of environmental events from a modeling perspective. First, we provide an overview and comparison of different numerical models created for simulating the movement and structural alteration of sediment by bioturbation. Next, we use an updated particle resolving model – iTURBO2 – to illustrate how various modes and intensities of bioturbation distort the signature of past climatological events, considering a range of conceptual shapes of vertical proxy profiles. Finally, we demonstrate how sampled proxy records can differ due to the combined effects of particle mixing and differential abundance changes that often concur with environmental transitions. We make the iTURBO2 MATLAB code openly available to facilitate further exploration of proxy biases due to bioturbation to aid the interpretation of the climatological record preserved in marine sediments.