TY - JOUR
T1 - Glycerol dialkyl glycerol tetraethers in surface sediments from three Pacific trenches
T2 - Distribution, source and environmental implications
AU - Xu, Yunping
AU - Jia, Zehua
AU - Xiao, Wenjie
AU - Fang, Jiasong
AU - Wang, Yasong
AU - Luo, Min
AU - Wenzhöfer, Frank
AU - Rowden, Ashley A.
AU - Glud, Ronnie N.
PY - 2020/9
Y1 - 2020/9
N2 - Glycerol dialkyl glycerol tetraethers (GDGTs) have been widely used to elucidate sources of sediment total organic carbon (TOC), past temperature and presence of methanogenesis in diverse environments. However, their applicability to hadal trenches with their unique deposition dynamics remains unknown. Here, we analyzed GDGTs and their stable isotope values and content of TOC in surface sediments from the Kermadec Trench region (KT; 6080–10010 m), New Britain Trench region (NBT; 1553–8931 m), and Atacama Trench region (AT; 2560–8085 m). These regions are at very different distances from terrestrial sources and have varying net primary productivity (NPP) in the waters above them. The GDGT concentration was highly variable (54.5–2416 μg g−1 TOC) within and between trench regions and was not directly related to local NPP or apparent terrestrial inputs. This finding is presumably due to complex deposition dynamics within the trench interior. Isoprenoidal GDGTs (isoGDGTs; 75.4–99.1%) were dominant over branched GDGTs (brGDGTs, 0.91–24.6%) in all samples, leading to low levels of Branched versus Isoprenoidal Tetraether (BIT) index (0.01–0.27). Thus, sediment TOC is mainly derived from marine sources. However, compared to adjacent non-hadal sites, trench axis sites have a higher BIT index, lower acyclic hexa-/pentamethylated brGDGT and lower δ13C, supporting relative enrichment of terrestrial organic carbon at the trench axis. The application of TetraEther indeX of tetraethers consisting of 86 carbon atoms (TEX86) resulted in sea surface temperature (SST) estimates of 18.9–23.7 °C in the KT, 28.6–30.2 °C in the NBT, and 17.9–20.4 °C in the AT. The close agreement between TEX86-SST with observed in situ SST suggests that isoGDGTs are not selectively degraded during the transport towards the hadal realm, and that TEX86 from hadal settings robustly records an integrated regional SST signal.
AB - Glycerol dialkyl glycerol tetraethers (GDGTs) have been widely used to elucidate sources of sediment total organic carbon (TOC), past temperature and presence of methanogenesis in diverse environments. However, their applicability to hadal trenches with their unique deposition dynamics remains unknown. Here, we analyzed GDGTs and their stable isotope values and content of TOC in surface sediments from the Kermadec Trench region (KT; 6080–10010 m), New Britain Trench region (NBT; 1553–8931 m), and Atacama Trench region (AT; 2560–8085 m). These regions are at very different distances from terrestrial sources and have varying net primary productivity (NPP) in the waters above them. The GDGT concentration was highly variable (54.5–2416 μg g−1 TOC) within and between trench regions and was not directly related to local NPP or apparent terrestrial inputs. This finding is presumably due to complex deposition dynamics within the trench interior. Isoprenoidal GDGTs (isoGDGTs; 75.4–99.1%) were dominant over branched GDGTs (brGDGTs, 0.91–24.6%) in all samples, leading to low levels of Branched versus Isoprenoidal Tetraether (BIT) index (0.01–0.27). Thus, sediment TOC is mainly derived from marine sources. However, compared to adjacent non-hadal sites, trench axis sites have a higher BIT index, lower acyclic hexa-/pentamethylated brGDGT and lower δ13C, supporting relative enrichment of terrestrial organic carbon at the trench axis. The application of TetraEther indeX of tetraethers consisting of 86 carbon atoms (TEX86) resulted in sea surface temperature (SST) estimates of 18.9–23.7 °C in the KT, 28.6–30.2 °C in the NBT, and 17.9–20.4 °C in the AT. The close agreement between TEX86-SST with observed in situ SST suggests that isoGDGTs are not selectively degraded during the transport towards the hadal realm, and that TEX86 from hadal settings robustly records an integrated regional SST signal.
KW - Atacama Trench
KW - Biomarker
KW - GDGTs
KW - Hadal trenches
KW - Kermadec Trench
KW - New Britain Trench
U2 - 10.1016/j.orggeochem.2020.104079
DO - 10.1016/j.orggeochem.2020.104079
M3 - Journal article
AN - SCOPUS:85088375877
SN - 0146-6380
VL - 147
JO - Organic Geochemistry
JF - Organic Geochemistry
M1 - 104079
ER -