Does the Gulf Stream Regulate Hydrography in Walsingham Cave, Bermuda? Implications for Developing High-resolution Records of Holocene Gulf Stream Variability

Peter van Hengstum, Geology & Geophysics
Jeff Donnelly, Geology & Geophysics



There still remains a poor understanding of how Atlantic Meridional Overturning Circulation (AMOC) responded to, or forced, intervals of abrupt climate change in the Holocene.  In the North Atlantic, proxy evidence suggests reduced transport of the Florida Current or North Atlantic Deep Water Formation during intervals of Holocene cooling (e.g., Little Ice Age, 5.0 ka), implying that AMOC variability played a key role regulating Holocene climate.  High-resolution (sub-centennial) oceanographic records are still needed, however, to determine the precise timing of AMOC changes with respect to other modes of climate forcing (e.g., solar, North Atlantic Oscillation).  Submarine caves present as an innovative solution to the problem because cave hydrography appears intimately linked to surface ocean currents, cave sediments can be sub-decadally resolved, and they contain carbonate organisms suitable for traditional geochemical analysis (e.g., Mg/Ca, δ18O).  Applying these sediment archives to paleoceangraphic problems is currently hampered, however, by a poor-understanding of their long-term internal hydrography—a prerequisite for (i) verifying that submarine caves faithfully observe regional oceanographic conditions, and (ii) calibrating geochemical proxies in submarine caves.  Here we propose continuous annual sampling of temperature and salinity in Walsingham Cave (WC), Bermuda.  Preliminary measurements suggests that the hydrography in WC is intimately linked to the Gulf Stream, with sedimentation rates suitable for sub-decadal climate analysis through the late Holocene.  Using advanced cave-SCUBA diving techniques, four hydrographic stations will be installed into WC in December 2011.  These stations will sample temperature, salinity, and depth continuously throughout 2012 (every 5 mins.).  This data will provide a cave-wide perspective of hydrographic variability, which can then be compared to regional heat sources from the Gulf Stream and insolation, and oceanographic variability in coastal lagoons and the western Sargasso Sea.  This research will (i) be the first complete hydrographic analysis in a submarine cave using a temporally-continuous and spatially-distributed observation network, (ii) provide essential preliminary data and infrastructure to leverage into an NSF funded program completing a cave-wide calibration program of carbonate geochemistry in submarine caves (foraminifer and ostracode Mg/Ca, δ18O, δ13C), and (iii) provide evidentiary support for sediment coring targets to generate a high-resolution reconstruction of surface current variability through the mid- to late-Holocene.