Semester of Graduation

Summer 2023


Master of Science (MS)


Geology and Geophysics

Document Type



Warm Circumpolar Deep Water (CDW) upwelling in the Southern Ocean currently circulates underneath Antarctic ice shelves in many areas. The associated melting reduces the ice-shelf buttressing effect, which can subsequently accelerate flow and cause retreat of grounded and floating ice. Upwelled CDW may have also been a primary driver of post-Last Glacial Maximum (LGM) deglaciation, but there are few proxy data from which upwelling history and paleo-ocean temperatures can be reconstructed. Here we build on previous deep, cold-water coral studies (e.g., Stewart et al., 2020) to detect CDW intrusion on the western Ross Sea continental shelf using lithium-to-magnesium ratios (Li/Mg) as a proxy for temperature and paired (radiocarbon and U-Th) ages as a fingerprint of water masses. We present a high-resolution temperature record spanning the life of three coral specimens from Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) and newly generated ΔR values from paired ages. We show that Li/Mg derived temperatures from a modern Scleractinia south of the Drygalski Ice Tongue agree well with current Ross Sea seawater temperatures with our reconstructed temperatures averaged annually ranging from -2.9ºC to 2.8ºC and an average of 0.1°C. The data reflect oscillations between this range on a decadal time scale reflecting a dynamic mixing of waters deep on the continental shelf. We show these same decadal temperature oscillations ranging from -2.4°C to 3.3°C and an average 1.2°C from a sample located near Cape Adare that is U-Th dated to ~1400 yrs BP. Paired ages yield distinct reservoir ages and corresponding ΔR values (defined as the local deviation from the global reservoir correction) (ΔR=749±17 and 673±18) at different times (U-Th dates of 309±5 BP and 1406±8 BP, respectively) in two samples near Cape Adare. In a specimen located near Cape Adare we show that the highest ΔR values (749 ±17) and warmest temperatures (average temperature = 2.3°C) correspond with a vii CDW upwelling event reported by King et al., (2018). These data suggest time-varying mixing of water masses in western Ross Sea that include a potential intrusion of CDW.



Committee Chair

Philip Bart



Available for download on Thursday, May 21, 2026