Biomarker Proxy Calibration Along the AMT Transect: Alkenone Uk37' and δD

This study analyzes 60 suspended particulate organic matter (SPOM) samples from an Atlantic Meridional Transect (AMT20), spanning approximately 105° latitude (Southampton to Punta Arenas), for key biomarker proxy signatures: alkenone unsaturation (Uk37') and hydrogen isotopic (δD) composition. The wide range in surface ocean characteristics along the transect offers a unique opportunity to refine our understanding of these proxies. Initial alkenone δD values correlate - to a first order - with water column δD signatures, which in turn parallel salinity values along the AMT20 transect. Other factors that have been shown to influence δD will be discussed as well. The Uk37' data presented are in good agreement with previously published SPOM data, though we offer an alternative regression model to relate Uk37' to sea surface temperatures (SST); the Richards curve (Richards, 1959). This non-linear regression model uniquely accounts for both the fact that the Uk37' index is a proportion, and so must lie between 0 and 1, as well as for an apparent reduction in slope at temperature extremes. The inverse of this relationship allows estimation of SST from a measured Uk37' value with quantitative estimates of uncertainty. Further, we have identified a pronounced seasonal sampling bias in the SPOM dataset analyzed in this and prior studies (e.g. Conte et al. 2006), which may be contributing to a reported offset between surface particulate and core-top Uk37'- SST calibrations for this proxy.