Comparing the Efficiency of Automatic and Manual Extraction Methods for Measuring TEX86 in Antarctic and Gulf of Mexico Continental Shelf Sediments.

Glycerol dialkyl glycerol tetraethers (GDGT) are archaeal membrane lipids often preserved in marine sediments, and their sedimentary distribution is used to calculate the Tetra Ether index of 86 carbon atoms (TEX86), a sea surface temperature proxy. GDGTs are extracted from bulk marine sediments. Previous research demonstrates that manual extraction via sonication produces higher GDGT yields than automatically accelerated solvent extraction (ASE). However, extraction methods have not been tested for sediments from polar regions, where GDGT abundance can be low.

We compared the efficiency and precision of manual and automatic extraction techniques for GDGTs used to calculate the TEX86 index from continental shelf sediments recovered from Antarctica (cold) and the Gulf of Mexico (warm). We test the efficiency and precision of different bulk extraction methods by analyzing the GDGTs via UHPLC-MS from six sediment samples extracted by sonication (Antarctica (4); Gulf of Mexico (2)) and eight samples extracted using ASE (Antarctica (6), Gulf of Mexico (2)). The maximum difference in mean TEX86 value in Antarctic samples extracted by sonication is 0.010 (n=4; 1°C) and by ASE is 0.039 (n=6; 3.1°C) TEX86 units. A similar result was obtained for Gulf of Mexico samples, where the maximum difference in mean TEX86 values extracted by manual sonication is 0.006 (n=2; <1°C) and by ASE is 0.010 TEX86 units (n=2; <1°C). Our results suggests that manual sonication produces more precise TEX86-derived temperatures than the ASE method in both polar and temperate sediments. However, Gulf of Mexico (warm) TEX86 values are less sensitive to extraction style compared to polar samples. Thus, we recommend that researchers using the TEX86 paleotemperature proxy in polar sediments, where GDGT abundance is low (e.g., glaciomarine muds and diamicts), extract GDGTs via manual sonication.