Constraints on the applicability of the organic temperature proxies U&amp;lt;sup&amp;gt;K'&amp;lt;/sup&amp;gt;&amp;lt;sub&amp;gt;37&amp;lt;/sub&amp;gt;, TEX&amp;lt;sub&amp;gt;86&amp;lt;/sub&amp;gt; and LDI in the subpolar region around Iceland

M Rodrigo-Gámiz,S W Rampen,S Schouten,J S Sinninghe Damsté,M Baas,H De Haas

doi:10.5194/bg-12-6573-2015

Abstract

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 (UK'37; TEX86; and the long-chain diol index, LDI) regarding their potential applicability for SST reconstruction in the subpolar region around Iceland. UK'37, TEX86 and TEXL86 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 UK'37) and positive (up to 5 °C for TEX86) offset with satellite-derived SSTs and temperature estimates derived from the underlying surface sediment. UK'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.

Highlights

Several organic proxies, based on different lipids, have been developed for estimating sea surface temperatures (SSTs) (Brassell et al, 1986; Schouten et al, 2002; Rampen et al, 2012)
UK37-derived SSTs in suspended particulate matter (SPM) and sedimenting particles are generally lower than annual mean SST
UK37derived SSTs in the surface sediments around Iceland correlate well with summer mean SST, which seems in agreement with the observation of elevated alkenone fluxes during late spring and early summer

Summary

Introduction

Several organic proxies, based on different lipids, have been developed for estimating sea surface temperatures (SSTs) (Brassell et al, 1986; Schouten et al, 2002; Rampen et al, 2012). The UK37 index may be affected by variations in nutrient concentrations, light limitation, and diagenesis (e.g., Hoefs et al, 1998; Gong and Hollander, 1999; Prahl et al, 2003; Rontani et al, 2013). Another organic temperature proxy commonly used in the last decade is the TEX86 (Schouten et al, 2002, 2013), based on a ratio of glycerol dialkyl glycerol tetraethers (GDGTs) with a varying number of cyclopentane moieties in the membrane lipids of marine Thaumarchaeota (Sinninghe Damsté et al, 2002). The TEX86-SST calibrations by Kim et al (2010) distinguish between low-temperature (< 15 ◦C, TEXL86) and Published by Copernicus Publications on behalf of the European Geosciences Union

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Discussion

Conclusion