Constraints on the applicability of the organic temperature proxies U37K', TEX86 and LDI in the subpolar region around Iceland.

Subpolar regions are key areas to study 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^37K', TEX₈₆ and LDI) on their potential applicability for SST reconstruction in the subpolar region around Iceland. U^37K', TEX₈₆ and TEX₈₆^L temperature estimates from suspended particulate matter result in a substantial discrepancy with instrumental data, while long chain alkyl diols were below detection limit in most of the stations. In the northern Iceland basin sedimenting particles revealed a seasonality in lipid fluxes similar to that in the bulk flux and the net primary production, i.e. highest flux of alkenones and GDGTs were measured during late spring-summer, and late summer for long chain alkyl diols. The flux-weighted average temperature estimates had a significant negative (ca. 2.3 °C for U^37K') and positive (up to 5 °C for TEX₈₆) offset with satellite-derived SSTs and the temperature derived from the underlying surface sediment. In contrast, sedimentary U^37K' estimates temperatures around Iceland correlate well with summer mean temperatures, while TEX₈₆ derived temperatures correspond well with either annual or winter mean 0-200m 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 diatom is the major source of long chain alkyl diols in this area rather than eustigmatophyte algae, and therefore the LDI cannot be applied in this region. [ABSTRACT FROM AUTHOR]