@inproceedings{PAR00003007,
  title = {{P}aleohydrology of tropical {S}outh {A}merica since the {L}ast {G}lacial {M}aximum : insights from the δ{D} of algal and terrestrial molecular markers in lake sediments},
  author = {{J}acob, {J}. and {H}uang, {Y}. and {S}padano {A}lbuquerque, {A}.{L}. and {S}ifeddine, {A}bdelfettah and {D}isnar, {J}.{R}.},
  editor = {},
  language = {{ENG}},
  abstract = {{T}here is renewing evidence that the {T}ropics might strongly influence climate dynamics on millennial time-scales. {P}art of this "tropical forcing" is related to changes in the water cycle that impacts atmospheric and oceanic processes on a broad scale. {P}ast variations of the continental hydrology are poorly documented due to the few available records and the lack of quantitative data on climate parameters. {T}he deuterium/hydrogen ratio (δ{D}) of algal derived biomarkers captures the isotopic composition of meteoric waters ({H}uang et al., 2002; {S}achse et al., 2004). {I}n turn, terrestria lly-derived biomarkers captures the isotopic composition of meteoric waters through their δ{D} but with a strong influence of the evapotranspiration. {A} combination of these two factors should thus allow the quantification of the variations in relative humidity (i.e. precipitation-evaporation; {P}-{E}). {W}e applied such an approach to estimate hydrological changes in {N}orthern {B}razil during the last 20,000 yr. {T}he δ{D} of algal (n-{C}18) and land plant (n-{C}30) fatty acids ({FA}) have been measured on 30 samples selected on a 6 m long lacustrine sediment core. {I}n a first approximation, we considered a mean hydrogen isotope fractionation of -157 ~ between the n-{C}18 {FA} and water and between the n-{C}30 {FA} and water of -128 ~ (e.g. {S}achse et al., 2004). {B}ecause the amount of precipitation is the major control on the isotopic composition of meteoric waters in tropical systems, we used the {D}wat-alg (δ{D} of the water used by algae for lipid synthesis, estimated from the δ{D} of the n-{C}18 {FA}) as a proxy of precipitation amount. {T}he δ{D}wat-hp (δ{D} of the water used for land plant lipids synthesis) is measured from the {D} of the n-{C}30 {FA} and used to estimate relative moisture ({P}-{E}). {T}he difference in isotope fractionation between land plants and phytoplankton (δ{D}wat-hp - δ{D}wat-alg) is used to quantify evapotranspiration (evaporation from soils and transpiration from plants). {T}hese results allowed to distinguish five contrasted periods in our 20,000 yr record (see below). {T}he 20-19 kyr period is characterized by high precipitation associated with high evapotranspiration, i.e. a semi-arid climate. {B}y comparison, from 19 to 17 kyrs, both precipitation and evapotranspiration are both reduced. {T}he resulting climate is nevertheless dryer than during the previous stage. {D}uring the {L}ateglacial interval, i.e. from 17 up to 13.5 kyrs, evapotranspiration is reduced but the precipitation which remains at the same level than before entails a more humid climate. {T}he {Y}ounger {D}ryas interval ({YD}) shows higher precipitation levels but stronger evapotranspiration, thus a dryer climate than during the {L}ateglacial but nevertheless more humid than at the end of the {L}ast {G}lacial {M}aximum ({LGM}). {F}inally, the {H}olocene shows a decreasing trend in the amount precipitation and with few variations of the evapotranspiration that finally delineate a drying trend. {T}hese results are coherent with independent data produced by palynology and biomarker analysis ({L}edru et al., 2001; {J}acob et al., 2004) and give clue information on the variations in water cycling in the {T}ropics since the {LGM}.},
  keywords = {{BRESIL}},
  numero = {},
  pages = {2  multigr.},
  booktitle = {{I}nternational meeting of organic geochemistry},
  year = {2005},
  URL = {https://www.documentation.ird.fr/hor/{PAR}00003007},
}