Reconstruction of tropical rainfall variability in the Caribbean during the last glacial period (115,000 - 12,000 ka)
Final Report Abstract
We established a cave monitoring program in Cueva Larga, Puerto Rico, which started in November 2012 and is still running. This results in a data set of more than 5 years in total. It includes measurements of several parameters at the surface and inside the cave (e.g., temperature, relative humidity, pCO 2, drip rate). In addition, rain and drip water samples are collected at monthly intervals for analysis of geochemical data, such as pH, trace element content and δ18O and δD values. The cave monitoring data represent the basis to interpret the speleothem proxy data and were evaluated and interpreted in close collaboration with the colleagues from Puerto Rico. The 2 m-long stalagmite Larga-1 from Cueva Larga, Puerto Rico, was precisely dated by 74^230Th/U-ages showing that it grew between 46 and 15 ka. Stable carbon and oxygen isotopes as well as the concentration of various trace elements were analysed at high resolution. The δ18O values are interpreted to reflect past changes in rainfall amount, temperature variability as well as effects of isotope fractionation under conditions of disequilibrium. δ13C values and P/Ca ratios are interpreted to be influenced by changes in vegetation density and soil productivity. The data suggest that climate on Puerto Rico during the last Glacial was generally cooler and drier than today. Warm Dansgaard/Oeschger (D/O) interstadials are characterized by relatively warm and humid conditions. The δ18O values of D/O’s 7 and 11 are even comparable to modern values. In contrast, the proxy data suggest a temperature decrease of ca. -3 to -5 °C and increased aridity during cold Heinrich stadials (HS), which were partly accompanied by a decline in vegetation and soil productivity. Based on our record, HS 1 was by far the coolest and driest of all recorded HS. The observed relationship with warm (DO’s) and cold (HS) temperatures in the North Atlantic is ascribed to the southerly movement of the ITCZ and a variable strength of the Atlantic Meridional Overturning Circulation. Stalagmite Cuba Medio was dated by 40^230Th/U-ages in total and grew during two major growth phases. The uppermost part covers the early Holocene, whereas the remaining section grew between ca. 80 and ca. 13 ka. δ18O and δ13C values as well as various trace elements were determined at high resolution. Al/Ca ratios were used for the identification of detrital layers associated with hiatuses. Large U/Ca and P/Ca ratios are accompanied by relatively high δ13C values suggesting a relationship with past changes in vegetation density. Mg/Ca, Sr/Ca and Ba/Ca ratios are mainly controlled by calcite-water interaction, such as prior calcite precipitation, incongruent calcite dissolution and calcite recrystallization, with larger values reflecting drier conditions. The δ18O values are interpreted as a proxy for past changes in precipitation amount and are mainly controlled by the amount effect. On glacial-interglacial time-scales, they also reflect changes in ice volume and sea surface temperature. Finally, the δ13C values reflect both changes in vegetation density and hydrological conditions with lower values corresponding to more humid conditions and increased vegetation density. The proxy data confirm our previous observations that rainfall variability on Cuba is related to changes in insolation and tropical North Atlantic and Caribbean SSTs as well as to the strength of the AMOC and high-latitude temperature variability. The Last Glacial Maximum was relatively cool, but not particularly dry. Nevertheless, the large P/Ca and U/Ca ratios as well as δ13C values suggest a strong decline in vegetation and soil dynamics. North Atlantic cold events, in particular the HS, were associated with relatively cold and dry conditions on Cuba or even growth stops suggesting very dry conditions. In contrast, the DO’s, in particular during MIS 5, were characterised by relatively warm and wet conditions. During MIS 3 and MIS 4, the response to high latitude warming recorded in the speleothem CM was less pronounced.
Publications
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(2018) Hurricane Impact on Seepage Water in Larga Cave, Puerto Rico. J. Geophys. Res. Biogeosci. (Journal of Geophysical Research: Biogeosciences) 123 (3) 879–888
Vieten, Rolf; Warken, Sophie; Winter, Amos; Schröder‐Ritzrau, Andrea; Scholz, Denis; Spötl, Christoph
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(2018) Reconstruction of late Holocene autumn/winter precipitation variability in SW Romania from a high-resolution speleothem trace element record. Earth and Planetary Science Letters 499 122–133
Warken, Sophie F.; Fohlmeister, Jens; Schröder-Ritzrau, Andrea; Constantin, Silviu; Spötl, Christoph; Gerdes, Axel; Esper, Jan; Frank, Norbert; Arps, Jennifer; Terente, Mihai; Riechelmann, Dana F.C.; Mangini, Augusto; Scholz, Denis
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(2016) Seasonal temperature variations controlling cave ventilation processes in Cueva Larga, Puerto Rico. International Journal of Speleology 45, 259-273
Vieten, R., Winter, A., Warken, S.F., Schröder-Ritzrau, A., Miller, T.E. and Scholz, D.
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(2018) Monitoring of Cueva Larga, Puerto Rico – a First Step to Decode Speleothem Climate Records, in: White, W.B., Herman, J., Herman, E., Rutigliano, M. (Eds.), Karst Ground Water Contamination and Public Health. Springer, Cham, pp. 319-331
Vieten, R., Warken, S., Winter, A., Scholz, D., Miller, T., Spötl, C. and Schröder- Ritzrau, A.
