| Summary: | The long‐chain diol index (LDI) is a new organic sea surface temperature (SST) proxy based on the distribution of long‐chain diols. It has been applied in several environments but not yet in subpolar regions. Here we tested the LDI on surface sediments and a sediment core from the Sea of Okhotsk, which is the southernmost seasonal sea ice‐covered region in the Northern Hemisphere, and compared it with other organic temperature proxies, that is, U k' 37 and TEX L 86 . In the surface sediments, the LDI is correlated with autumn SST, similar to the U k' 37 but different from the TEX L 86 that correlates best with summer sea subsurface temperature. Remarkably, the obtained local LDI calibration was significantly different from the global core‐top calibration. We used the local LDI calibration to reconstruct past SST changes in the central Sea of Okhotsk. The LDI‐SST record shows low glacial (Marine Isotope Stage, MIS 2, 4, and 6) and high interglacial (MIS 1 and MIS 5) temperatures and follows the same pattern as the U k' 37 ‐SST and a previously published TEX L 86 temperature record. Similar to the modern situation, the reconstructed temperatures during the interglacials likely reflect different seasons, that is, summer for the TEX L 86 and autumn for U k' 37 and LDI. During glacials, the reconstructed temperatures of all three proxies are similar to each other, likely reflecting summer temperatures as this was the only season free of sea ice. Our results suggest that the LDI is a suitable proxy to reconstruct subpolar seawater temperatures.
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