The Impact of Hurricane Bertha on Seepage Water in Cueva Larga, Puerto Rico

Tuesday, 24 January 2017
Ballroom II (San Juan Marriott)
Rolf Vieten1, Sophie Friederike Warken2,3, Amos Winter1,4, Denis Scholz2, Christoph Spӧtl5, Andrea Schrӧder-Ritzrau3, Alice Samson6 and Jago Cooper7, (1)University of Puerto Rico Mayaguez, Marine Science, Mayaguez, PR, United States, (2)Johannes Gutenberg University of Mainz, Institute for Geosciences, Mainz, Germany, (3)University of Heidelberg, Institute of Environmental Physics, Heidelberg, Germany, (4)Indiana State University, Earth and Environmental Systems, Terre Haute, IN, United States, (5)University of Innsbruck, Institute of Geology, Innsbruck, Austria, (6)University of Leicester, Leicester, United Kingdom, (7)British Museum, London, United Kingdom
Abstract:
Because hurricanes have significantly more negative δ18O values than other tropical rain and result in extremely high rainfall amounts, these events can overprint the δ18O value of seepage water and leave a trace in the δ18O value of speleothems. This permits the extension of the hurricane history far beyond the instrumental record. For this study, we examined speleothems from Cueva Larga, Puerto Rico as a potential archives of past hurricane events.

We measured δ18O values of rainfall from hurricane Isaac at hourly resolution during its passage over Puerto Rico (23 August 2012). The values were -4.0 to -8.8‰ more negative than the usual rainfall (‑3.0±1.1‰) confirming the more negative δ18O values of hurricane events. In 2014, two tropical systems passed Puerto Rico: hurricane Bertha (3 August 2014) and a large tropical rain event (27 October 2014) producing 193 and 178 mm of local precipitation, respectively. We measured δ18O values in cumulative monthly rain water samples and monthly δ18O values and trace element ratios in instantaneous cave drip water samples. Over the monitoring period, the geochemical drip water composition (δ18O and trace element ratios) showed no changes. We assume that seepage water was well mixed and that the karst acted as a low-pass filter because the signal transmission time from the surface to the cave appears to be several months to a few years, prohibiting the signal transmission of individual extreme rain events. Thus, speleothems from Cueva Larga are well suited to investigate multi-annual climate changes but cannot be used to reconstruct individual hurricane events.

Caves with shallow overburden resulting in a short residence time of the drip water are necessary to study extreme rainfall events. One promising possibility that we currently pursue are speleothems from flank margin caves on Mona Island, a carbonate platform between Puerto Rico and the Dominican Republic. Speleothems from these caves grew during the Holocene and cave observations indicate fast water transfer from the surface to these caves opening the possibility to obtain a Holocene record of Caribbean hurricanes.

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