Polissar, P , Abbott, M , Shemesh, A , Wolfe, A , Bradley, R

POLISSAR, P., ABBOTT, M., SHEMESH, A., WOLFE, A. and BRADLEY, R.: Holocene hydrologic balance of tropical South America from oxygen isotopes of lake sediment opal, Venezuelan Andes, Earth and Planetary Science Letters, 242(3-4), 375–389, doi:10.1016/j.epsl.2005.12.024, 2006.

Holocene hydrologic balance of tropical South America from oxygen isotopes of lake sediment opal, Venezuelan Andes

HP 6890 GC, Finnigan MAT Delta+ XL mass spectrometer

Check that inferred material is correct (soil water vs lake water). ; change mathematical relation = "it depends..." to nonlinear?

Given the lack of correlation between dDlw and pollen- inferred mean July temperatures (Fig. 6), the downcore dDlw changes likely represent either a change in the ratio of soil water and precipitation utilized by the vegetation and/ or a change in source and pathway of regional precipita- tion. The dDlw data may indicate a heavy reliance of terrestrial plants on cool-season derived soil moisture from 11,000?8000 cal yr BP when conditions were dry. Growing- season precipitation may have been too low to provide sufficient water to the plants. An alternative and not mutually exclusive interpretation is that growing-season precipitation was not enriched in deuterium from 11,000?8000 cal yr BP because the presence of high pressure over the Laurentide ice sheet prevented the northward advection of humid, sub-tropical airmasses that are important for summer precipitation today. Both interpre- tations are consistent with Shuman and Donnelly?s (2006) interpretation that low lake levels prior to ca 8200 cal yr BP resulted from low summer precipitation rates and a high ratio of winter to summer precipitation.

circulation changes caused by ice sheet topography. Precipitation seasonality.

depends on the source area and transport path to the study site

depends on which season provides source moisture for plants

match with pollen based January temperature, C16 n-acids are produced by aquatic plants, and ponds in this region are recharged mainly by winter precipitation (Shuman and Donnelly, 2006, Quat Res, 65:44-56)