Response of Antarctic ocean circulation to increased meltwater

• Main Author: Moorman, Ruth
• Format: Other/Unknown Material
• Language: English
• Subjects: Antarctic Circulation; Ocean Circulation; Computer Simulation; Ice-Shelf Melt; Sea-level; Climate Modelling; Antarctica; Southern Ocean; Overturning; Antarctic Bottom Water; Climate Change; Antarctic; The Antarctic; Antarctic Peninsula; Weddell Sea; Weddell; Antarctic Ocean; Antarc*; Ice Shelf; Sea ice
• Online Access: http://hdl.handle.net/1885/187134; https://doi.org/10.25911/5de4da691ed03; https://openresearch-repository.anu.edu.au/bitstream/1885/187134/4/u5808670_Honours_thesis_ANU.pdf.jpg

The implications of ocean freshening from accelerating Antarctic land-ice loss are poorly understood, due to the scarcity of observations near the Antarctic coast, and the high spatial and temporal resolution required to resolve Antarctic continental shelf processes in ocean models. Here, a high-resolution global ocean--sea-ice model is used to investigate the response of Antarctic continental shelf circulation to increasing meltwater. Two freshwater perturbation experiments are conducted, using projected Antarctic ice-loss rates under RCP 4.5 and RCP 8.5 emissions scenarios at 2100.We find that surface freshening near the Antarctic coast increases stratification and reduces the formation of cold, dense waters on the Antarctic continental shelf that, in the current climate, drive abyssal ocean circulation and ventilation. In our simulations, the connection between the abyssal ocean and the cold Antarctic shelf collapses within 10 years following the application of projected 2100 meltwater forcing, as downwelling surface waters on the continental shelf are freshened by glacial runoff, leaving them too buoyant to sink to the abyssal ocean. Around Antarctica, coastal freshening increases lateral density gradients between the cool, fresh shelf and the warm, saline open ocean, strengthening frontal structures that separate the adjacent water-masses, and accelerating geostrophic currents that flow westward along the coast and along the continental shelf break. This process acts to homogenise shelf waters and increasingly isolate the cool continental shelf from the warmer open ocean, leading to a net cooling on the continental shelf. Acceleration of the circumpolar coastal current results in remote temperature feedbacks unique to these experiments; most notable being a strong cooling signal on the West Antarctic shelf, an historically warm region associated with high rates of ice shelf melt, generated by the advection of cold Weddell Sea shelf waters around the Antarctic Peninsula by the strengthening coastal current. ...