Unusually low TEX86 values in the transitional zone between Pearl River estuary and coastal South China Sea: Impact of changing archaeal community composition

Seasonal distribution of archaeal lipids in surface water and its constraint on their sources and the TEX86 temperature proxy in sediments of the South China Sea

“…Comparatively, the dominant (average 70% of total reads of the archaeal 16SrRNA gene sequences) archaeal group, Euryarchaeota , in surface water in the SCS varied between different seasons, with cluster α prevailing during summer and cluster β during winter [ Xia et al ., ]. Euryarchaeota have been proposed as a significant source of isoGDGTs in oceanic settings [ Turich et al ., ; Lincoln et al ., ] and have also been suggested as a major source of the isoGDGT pool in the Pearl River estuary and adjacent coastal waters and as a cause for the low TEX 86 values that have been observed in the coastal SCS [ Wang et al ., ]. Therefore, our assumption that changes in archaeal community compositions may be responsible for the seasonal difference in the ‐SST relationship is compatible with existing archaeal community observations.…”

“…This observation is most likely associated with input of soil archaeal lipids via rivers combined with strong alongshore currents due to northeasterly monsoon wind [ Su , ]. This is supported by higher values of [0]/[Cren] ratios in sediments and soils in the lower Pearl River and its catchment (0.1–26.5 range, 2.6 average, and n = 30; data from Wang et al ., ). Higher [0]/[Cren] ratio values have also been observed in other soil‐river‐estuary continuums, such as the Yangtze River estuary [ Zhu et al ., ], and are supposed to be associated with methanogenic archaea that are generally an important source of GDGT‐0, but cannot synthesize crenarchaeol [ Blaga et al ., ; Zhu et al ., ].…”

“…In shelf sediments of the northern SCS, previous studies have reported that TEX 86 derived temperature values to be consistently lower than annual mean SSTs [ Wei et al ., ; Ge et al ., ; Zhang et al ., ; Zhou et al ., ]. This was interpreted as a result of (1) winter season bias of archaeal production and associated isoGDGT burial [ Zhang et al ., ] or (2) Euryarchaeota predominance with a different thermal response [ Wang et al ., ]. As shown above, ‐SST relationships in the surface water of the SCS differ from the global calibration both during summertime and wintertime.…”

“…However, this interpretation has recently been challenged by Wang et al . [], who attributed the anomalously low TEX 86 values to the contribution of GDGTs from planktonic Euryarchaeota . Therefore, different perspectives on the meaning of the TEX 86 proxy have been proposed both in the deep‐basin and in shallow‐shelf areas in the SCS.…”

Sea surface temperature variation during the last deglaciation in the southern Okinawa Trough: Modulation of high latitude teleconnections and the Kuroshio Current

“…These GDGTs are mainly produced by Thaumarchaeota (Sinninghe Damsté et al, 2002) and possibly planktonic Euryarchaeota (Turich et al, 2007;Lincoln et al, 2014;Wang et al, 2015). Compared to U K' 37 , the index can be applied at temperatures >28°C (Kim et al, 2010) and is less affected by diagenesis Kim et al, 2009).…”