Final Activity Report Summary - FLOODS (Fate of land-derived organic compounds in the coastal ocean)
The branched and isoprenoid tetraether (BIT) index was introduced as a new means for the estimation of the relative amounts of fluvial derived terrestrial organic matter (OM) in marine sediments.
This index was based on a group of branched glycerol dialkyl glycerol tetraethers (GDGTs) derived from presumably anaerobic bacteria which were omnipresent in soils and a structurally related isoprenoid GDGT crenarchaeol, which was predominantly produced by marine planktonic crenarchaeota. Since the branched GDGTs were often found in coastal areas near major rivers, it was hypothesised that branched GDGTs preserved in marine sediments were derived from soil erosions and transported to the ocean via rivers. Studies that were carried out in the Têt River and the Gulf of Lions showed that this transport mechanism was indeed responsible for transferring branched GDGTs from land to the adjacent coastal zones and that the BIT index was even more specific than anticipated as a proxy of soil OM input from land to the ocean via rivers.
In particular, the study carried out in the Têt River showed that variations in the branched GDGTs concentration were closely related to water and sediment discharge depicting the flood events. The applications of this index to marine surface sediments in the Gulf of Lions showed that values of the BIT index and the sum of branched GDGT concentration were much higher along the coast than those from other shelf and the continental slope. Soil OM estimates based on the BIT index were therefore up to 50 % higher along the coast, while those from the outer shelf and the continental slope were below 10%.
Consequently, the results from the Têt River and the Gulf of Lions supported that the BIT index could be used as a tool to estimate the relative proportion of fluvial derived soil OM in marine sediments. Furthermore, the BIT index had a potential to serve as a tool for reconstructing integrated signals of precipitation and river runoff changes over a large but broadly definable regional or continental scale for various geological time scales. This would open a new horizon for validating climate models currently used for our future climate prediction, as well as for designing long-term strategies for water and risk management through the incorporation of paleodata into various modelling procedures for risk assessments.
This index was based on a group of branched glycerol dialkyl glycerol tetraethers (GDGTs) derived from presumably anaerobic bacteria which were omnipresent in soils and a structurally related isoprenoid GDGT crenarchaeol, which was predominantly produced by marine planktonic crenarchaeota. Since the branched GDGTs were often found in coastal areas near major rivers, it was hypothesised that branched GDGTs preserved in marine sediments were derived from soil erosions and transported to the ocean via rivers. Studies that were carried out in the Têt River and the Gulf of Lions showed that this transport mechanism was indeed responsible for transferring branched GDGTs from land to the adjacent coastal zones and that the BIT index was even more specific than anticipated as a proxy of soil OM input from land to the ocean via rivers.
In particular, the study carried out in the Têt River showed that variations in the branched GDGTs concentration were closely related to water and sediment discharge depicting the flood events. The applications of this index to marine surface sediments in the Gulf of Lions showed that values of the BIT index and the sum of branched GDGT concentration were much higher along the coast than those from other shelf and the continental slope. Soil OM estimates based on the BIT index were therefore up to 50 % higher along the coast, while those from the outer shelf and the continental slope were below 10%.
Consequently, the results from the Têt River and the Gulf of Lions supported that the BIT index could be used as a tool to estimate the relative proportion of fluvial derived soil OM in marine sediments. Furthermore, the BIT index had a potential to serve as a tool for reconstructing integrated signals of precipitation and river runoff changes over a large but broadly definable regional or continental scale for various geological time scales. This would open a new horizon for validating climate models currently used for our future climate prediction, as well as for designing long-term strategies for water and risk management through the incorporation of paleodata into various modelling procedures for risk assessments.