Doctor of Philosophy (PhD)
Geology and Geophysics
The Antarctic Ice Sheets (AIS) began to retreat from their Last Glacial Maximum (LGM) position sometime after 19,000 years ago. However, the corrosive waters circulating around Antarctica has prevented the recovery of radiocarbon-dateable material, hindering the development of deglacial chronologies. During Expedition NBP1502B to the eastern Ross Sea, an unprecedented quantity of fossil foraminifera and bivalves were recovered. Radiocarbon-dated specimens have been used to constrain the timing of West-AIS retreat from Whales Deep basin and Ross Bank. Whales Deep samples show that the WAIS retreated from its LGM position on the continental shelf edge by 14,700 ± 400 calibrated radiocarbon years ago (cal yr BP). Additional ages, seafloor geomorphology and core sedimentology show that the WAIS paused several times before rapidly retreating south of the modern Ross Ice Shelf 11,500 ± 300 cal yr BP. These retreat events are concomitant with Meltwater Pulse -1a and -1b suggesting these two rapid sea-level rise events played a primary role. This finding potentially resolves a point of contention amongst Antarctic scientists.
An additional factor influencing ice sheet retreat includes subglacial meltwater hydrology. Subglacial meltwater generation and drainage may have significantly influenced retreat of Antarctic ice streams in the past and at present. Oxygen isotope ratios (δ18O) from porewater recovered from Whales Deep Basin sediment cores are characteristic of modern Ross Sea waters indicating that fresh meltwater was not preserved in subglacial or glaciomarine sediment. This suggests that subglacial meltwater hydrology did not significantly affect the early stages of WAIS retreat in the Whales Deep Basin.
Ross Bank – a seamount rising to 174 meters below sea level – is covered with a thin layer of pelagic sediment. A box core recovered an abundance of calcareous fossils. Radiocarbon ages indicate that the Ross Ice Shelf was grounded on Ross Bank until ~600 cal yr BP when it retreated to its present position. This is significant because it suggests that three topographic features acted to buttress the Ross Ice Shelf up until the last few centuries. Since unpinning, there are only two features, Roosevelt Island and Ross Island, that stabilize the modern Ross Ice Shelf calving front.
DeCesare, Matthew, "When, How, and Why Did the West Antarctic Ice Sheet Retreat in the Ross Sea Since the Last Glacial Maximum Using Foraminiferal And Porewater Geochemistry" (2017). LSU Doctoral Dissertations. 4143.