Archaeal GMGTs in Marine Sediments as Potential Indicators of Terrestrial Input

Abstract Archaeal glycerol monoalkyl glycerol tetraethers (GMGTs) remain far less constrained than the widely used glycerol dialkyl glycerol tetraethers (GDGTs). We analyzed GMGTs in five sediment cores from the northern South China Sea spanning nearshore to deep‐basin settings. GMGT‐0 was detected only in the two nearshore cores and a reference Tibetan peat, whereas offshore South China Sea and East China Sea cores yielded no detectable GMGTs. Several nearly co‐eluting compounds in marine sediments showed GDGT‐like MS 2 spectra, indicating that GMGT assignments require more than retention‐time agreement. In nearshore cores, GMGT abundance covaries with δ 13 C TOC and TOC/TN, and these relationships strengthen after normalization to crenarchaeol (GMGTs/CREN). Together, these observations support a predominantly terrestrial source for the detected GMGTs and suggest that, with careful chromatographic and spectral verification, GMGTs/CREN may provide a complementary tracer of terrestrial organic matter input to marine sediments.