Evaluating the Behavior of 230Th and 3He Constant-Flux Proxies Across a Carbonate Preservation Gradient in the Cocos Ridge

We present a comparison of extraterrestrial 3He (3HeET) and excess 230Th (230Thxs) as constant flux proxies (CFPs) across a depth transect on the Cocos Ridge, evaluating their behavior as a function of carbonate dissolution, lateral sediment redistribution, and analytical reproducibility. Coretop data confirm that 230Thxs remains well preserved across a wide range of carbonate burial efficiencies, with no systematic deficits in their inventory observed in low-preservation settings. Despite large downcore increases in CaCO₃ content, over two orders of magnitude in some intervals, 230Thxs-derived mass accumulation rates (MARs) show no evidence of thorium loss during carbonate dissolution. In contrast, 3HeET -derived MARs are highly sensitive to analytical reproducibility because the low area-time product of our samples and our limited replication producing large uncertainties that propagate into flux estimates. One shallow site highlights the contrasting sensitivities of the two proxies to sediment redistribution, with the case of their discordance switching from He deficits to apparent Th excesses through time, underscoring their different responses to lateral sediment transport. Our work helps establish a pathway for using CFPs in high-resolution, globally distributed CaCO3 burial reconstructions, enabling direct constraints on the timing, magnitude, and drivers of burial changes and advancing our understanding of how the ocean–atmosphere carbon system responds to climate change.