A Nutrient Effect on the TEX₈₆ Paleotemperature Proxy

The (Formula presented.) paleotemperature proxy is widely used to reconstruct ocean surface temperatures over the past 100 million years. However, archaeal culture experiments show that nutrient stress elevates (Formula presented.) values by increasing glycerol dialkyl glycerol tetraether (GDGT) cyclization. Here, we demonstrate that this “nutrient effect” is also recorded in sedimentary GDGTs. Using an expanded core-top database, we find a significant negative correlation between (Formula presented.) and nitrate concentrations ((Formula presented.) = −0.31; P (Formula presented.) 0.001) once the thermal effect is removed. There are stronger correlations ((Formula presented.) −0.73 to −0.91; P (Formula presented.) 0.001) in regions with steep nitrate gradients. Comparisons between (Formula presented.) and (Formula presented.) -based reconstructions from the Arabian Sea and Tasman Sea suggest that nutrient stress influenced GDGT distributions during glacial-interglacial cycles. Our findings underscore the need to account for nutrient effects when applying (Formula presented.) paleothermometry.