ROSS SEA OCEAN-TEMPERATURE RECONSTRUCTION AND MARINE RADIOCARBON RESERVOIR EFFECT CALIBRATION FROM MODERN AND PRE-MODERN SCLERACTINIA

Abstract

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.