Tracing tetraether lipids from source to sink in the Rhône River system (NW Mediterranean)

Abstract

In this study, we investigated soils and river suspended particulate matter (SPM) collected in the Rhône and its tributary basins as well as marine surface sediments taken in the Rhône prodelta (Gulf of Lions, NW Mediterranean). Thereby, we traced the signal of branched glycerol dialkyl glycerol tetraethers (brGDGTs) from the source to sink via the Rhône River and its tributaries and identified sources of brGDGTs in rivers and marine sediments. Soil pH rather than the mean annual air temperature (MAAT) explains most of the observed variances of the brGDGT distribution in our soil dataset. The observed changes in the distribution of brGDGTs in the river SPM indicate that brGDGTs brought by the river to the sea are primarily derived from the lower Rhône and its tributary soils, even though in situ production in the river itself cannot be excluded. In marine surface sediments, it appears that the input of riverine brGDGTs is the primary source of brGDGTs in the Rhône prodelta, although the brGDGT composition may be further modified by the in situ production in the marine environment. More work is required to assess fully whether brGDGTs can be used to reconstruct the terrestrial paleoenvironmental changes using marine sediment cores taken in the Rhône prodelta close to the river mouth.

Reply on RC1 (David Naafs)

“…Based on the offset between brGDGT distributions in soils and SPM in the Lower Amazon River, collected during low flow conditions when soil input is limited, Zell et al (2013a,b) suggested that brGDGTs could also be produced in situ in the river. Similar offsets were also found in the Yangtze (Yang et al, 2013;Li et al, 2015), Rhône (Kim et al, 2015) and Tagus (Zell et al, 2014a) rivers. Later, in situ aquatic brGDGT production was linked to the occurrence of 6-methyl brGDGTs, based on their unexpectedly high relative abundance during low flow conditions in the Yenisei River (De Jonge et al, 2014b).…”

Assessing branched tetraether lipids as tracers of soil organic carbon transport through the Carminowe Creek catchment (southwest England)

“…For example, brGDGTs in soils along an altitudinal transect in the Ethiopian highlands revealed that brGDGTs mainly reflect the decrease in temperature with increasing elevation, regardless of drastic changes in land use along the transect (Jaeschke et al, 2018). However, other studies report that vegetation cover does exert a great influence on brGDGT signatures in soils from Minnesota and Ohio, USA ; around Lake Rotsee, Switzerland (Naeher et al, 2014); in the Tibetan Plateau (Liang et al, 2019); and paddy and upland soils from subtropical (China and Italy) and tropical (Indonesia, Philippines and Vietnam) areas (Mueller-Niggemann et al, 2016). The explanations for the similar distribution of brGDGTs under different land use types in the Carminowe Creek catchment could be the rotation and ploughing in land use in combination with the turnover time of brGDGTs.…”

From soil to sea: sources and transport of organic carbon traced by tetraether lipids in the monsoonal Godavari River, India

“…However, in downstream areas, stagnant waters, and periods with low flow, brGDGTs are also produced in rivers (e.g. Yang et al, 2013;Zell et al, 2013aZell et al, , b, 2014aDe Jonge et al, 2014b, 2015aKim et al, 2015;Freymond et al, 2017), which complicates their use as soil-specific tracers. For example, Zell et al (2013a, b) reported a mismatch between brGDGT distributions in soils and river suspended particulate matter (SPM) from the lower Amazon River in the dry season and attributed this difference to in situ aquatic brGDGT production.…”