Variability and controls of organic and carbonate carbon burial on the West Australian shelf during the Late Pleistocene

The mid and late Pleistocene are marked by large-amplitude fluctuations in global ice volume and pronounced climatic variability. Around ~1 Ma, Earth’s climate system underwent a fundamental reorganization, as glacial–interglacial variability shifted from predominantly 41-kyr cycles to higher-amplitude, quasi-100-kyr oscillations. This transition was accompanied by enhanced atmospheric CO₂ drawdown during glacial periods. However, how the global carbon cycle adjusted to this shift, and which reservoirs account for the lowered glacial atmospheric CO₂ concentrations, remains not fully quantitatively constrained. In this context, marine carbon burial, particularly on continental shelves, represents a potentially important yet underexplored long-term sink for atmospheric CO₂.

Here, we quantify variability in organic and carbonate carbon burial on the West Australian shelf and evaluate its potential contribution to Pleistocene atmospheric CO₂ drawdown. We measured δ¹³C and calculated relative burial fractions and mass accumulation rates for organic and carbonate carbon in sediments recovered from IODP Expedition 356 Site U1460 (27°22′S, 112°55′E), spanning the last ~210 kyr (MIS 7–MIS 1). The site was drilled at ~214 m water depth in the northern Perth Basin and is situated in a dynamic oceanographic setting influenced by the interaction between the warm, oligotrophic Leeuwin Current (LC) and the cooler, nutrient-rich West Australian Current (WAC).

Our results reveal two pronounced maxima in organic carbon burial relative to carbonate during glacial MIS 6 (~168 ka) and MIS 2 (~26 ka), as well as a more moderate increase at ~109 ka across the MIS 5a–d to MIS 5e transition. These patterns are consistent with previous suggestions of enhanced shelf organic carbon burial during glacial periods (Auer et al., 2021). Variations in organic-to-carbonate burial ratios are paced by eccentricity-modulated glacial–interglacial sea-level changes and Milankovic-driven shifts in seasonality, both of which influence the strength of the LC and its interaction with the WAC. High sea level and enhanced seasonality strengthen the LC, restricting nutrient supply to the West Australian shelf. Conversely, low sea level and reduced seasonality weaken the LC, allowing the nutrient-rich WAC to dominate, thereby enhancing primary productivity and organic carbon burial.

Finally, we use organic carbon mass accumulation rates to place first-order constraints on the potential for carbon storage on the West Australian shelf during Late Pleistocene glacials. Although organic carbon burial increased during glacial intervals, limited accommodation space on the shelf likely restricted total organic carbon accumulation, preventing it from exerting a major influence on global glacial–interglacial atmospheric CO₂ variability.