Fig. 3: Sample PRR50489 SEM-EDS image and comparison to climate records.
a Slab and SEM-EDS image of sample PRR50489. b Slab and SEM-EDS image of second piece of sample PRR50489. This piece of sample includes material above angular unconformity. Scale bars are 1 cm. c Ca concentration of subglacial precipitate sample PRR50489. High values represent calcite precipitation; low values represent opal precipitation. U-series dates include 2σ uncertainties bars. d δD measured in EPICA Dome C Ice Core (EDC)109,110. EDC record is detrended and converted to a z-score by zero-mean normalization to eliminate orbital trends. Gray dashed line delineates threshold value for magnitude of ice thickness change necessary to elicit subglacial hydrologic response. e Reduced complexity model of ice sheet thermodynamics (RCMIST) output of basal heat budget over the formation period of sample PRR50489 in units of mm/year of equivalent basal freezing rate. Negative values indicate freezing. Positive values correspond to basal melting and are truncated at 0 mm/yr. Forcing for RCMIST is provided by ice thickness changes at the foothills of the Transantarctic Mountains, which are parameterized as a linear function of the ice core isotopic record. The magnitude and scale of these thickness changes is shown on the y-axis in c. f Binary measure of fit between mineral cyclicity in c and climate threshold on EDC data in d. A fit is defined as points where both EDC values fall above the climate threshold and calcite is precipitated, or EDC values fall below the threshold and opal is precipitates. Otherwise, the point is considered misfit. g Southern Hemisphere summer insolation (75°S) over the period of PRR50489 formation. Record in d is synchronized to AICC2012 chronology.
