A New Multivariate Calibration of Sea Surface Temperature Based on Long‐Chain Alkyl Diols in an Upwelling‐Affected Marginal Sea

Abstract The long‐chain diol index (LDI) is widely used for reconstructing sea surface temperature (SST), but its application in upwelling‐influenced marginal seas is often hindered by interference from terrigenous inputs, Proboscia ‐derived diols, and the delayed response of LDI to upwelling‐induced cooling. Here, we assess the feasibility of using sedimentary long‐chain diols (LCDs) for SST reconstruction in the upwelling‐ affected East China Sea (ECS). Riverine input indicated by FC 32 1,15‐diol was minimal beyond the Changjiang Estuary, and Proboscia contributions inferred from FC 28 1,12‐diol were also negligible, suggesting limited interference from these sources. Two upwelling zones—offshore of the Changjiang Estuary and southeast of Hangzhou Bay—were identified using the upwelling proxy DI‐2. Additionally, the nutrient proxy nutrient diol index (NDI) correlated strongly with phosphate concentrations in these regions, supporting its potential to trace subsurface Kuroshio water intrusion. LDI aligned best with autumn SST, which is attributed to its inherent 27°C upper temperature limit, and regional calibration still overestimated SST in upwelling zones. To overcome this, we developed a multivariate calibration incorporating both LDI and DI‐2, resulting in significantly reduced SST reconstruction errors in upwelling regions, with mean offsets of 0.17 ± 0.15°C (summer), 0.08 ± 0.35°C (autumn), and 0.04 ± 0.48°C (annual). Validation against published ECS LCDs data sets further confirmed the improved accuracy of SST estimates. Our results demonstrate that integrating upwelling intensity into temperature calibration effectively corrects seasonal biases and expands the applicability of LCDs‐based proxies in dynamic marginal marine settings.