Constraints on the applicability of the organic temperature proxies U^K'₃₇, TEX₈₆ and LDI in the subpolar region around Iceland

Abstract. Subpolar regions are key areas for studying natural climate variability due to their high sensitivity to rapid environmental changes, particularly through sea surface temperature (SST) variations. Here, we have tested three independent organic temperature proxies (U^K'₃₇; TEX₈₆; and the long-chain diol index, LDI) regarding their potential applicability for SST reconstruction in the subpolar region around Iceland. U^K'₃₇, TEX₈₆ and TEX^L₈₆ temperature estimates from suspended particulate matter showed a substantial discrepancy with instrumental data, while long-chain alkyl diols were below the detection limit at most of the stations. In the northern Iceland Basin, sedimenting particles revealed a seasonality in lipid fluxes, i.e., high fluxes of alkenones and glycerol dialkyl glycerol tetraethers (GDGTs) were measured during late spring and during summer and high fluxes of long-chain alkyl diols during late summer. The flux-weighted average temperature estimates had a significant negative (ca. 2.3 °C for U^K'₃₇) and positive (up to 5 °C for TEX₈₆) offset with satellite-derived SSTs and temperature estimates derived from the underlying surface sediment. U^K'₃₇ temperature estimates from surface sediments around Iceland correlate well with summer mean sea surface temperatures, while TEX₈₆-derived temperatures correspond with both annual and winter mean 0–200 m temperatures, suggesting a subsurface temperature signal. Anomalous LDI-SST values in surface sediments and low mass flux of 1,13- and 1,15-diols compared to 1,14-diols suggest that Proboscia diatoms are the major sources of long-chain alkyl diols in this area rather than eustigmatophyte algae, and therefore the LDI cannot be applied in this region.