The Novel Hydroxylated Tetraether Index RI‐OH′ as a Sea Surface Temperature Proxy for the 160‐45 ka BP Period Off the Iberian Margin

Abstract

Abstract RI‐OH′ and RI‐OH (ring index of hydroxylated tetraethers) are two novel organic paleothermometers which could either complement or replace more established paleothermometric proxies, such as U K ′ 37 (C 37 ketone unsaturation ratio) and TEX 86 (TetraEther indeX of tetraethers consisting of 86 carbon atoms). Despite a few promising attempts, the paleothermometric potential of RI‐OH′ and RI‐OH is not fully constrained. Here we present new high‐resolution temperature records over the 160‐45 ka BP (before present = year 1950 CE) period using four organic proxies (RI‐OH′, RI‐OH, TEX 86 , and U K ′ 37 ) from three deep sea sediment cores located in a north‐south transect along the Iberian Margin. We analyzed all organic proxies from a single set of lipid extracts to optimize proxy‐proxy comparisons and phase relationship studies. RI‐OH′ responds to Dansgaard‐Oeschger and Heinrich events, better resembles U K ′ 37 than TEX 86 , and better records the influence of (sub)polar waters during Heinrich events than does RI‐OH. While RI‐OH′ gives realistic sea surface temperatures and latitudinal gradients coherent with those from independent paleothermometers, a more extensive RI‐OH′‐temperature calibration for the North Atlantic is clearly needed. However, the absence of a significant warm bias in RI‐OH′‐based temperatures compared to a shallow sea site suggests that endemic, deep‐dwelling archeal communities affect TEX 86 but not RI‐OH′ in the Iberian Margin. TEX 86 leads RI‐OH′ and U K ′ 37 during four Heinrich‐like events, potentially due to background fluxes from deep waters for nonhydroxylated tetraethers summed with primary productivity dependent fluxes from surface waters for all investigated lipid classes. Relationships with Greenland temperatures further support RI‐OH′‐based paleothermometry.