Modeled Export of Ancient, Thick Sea Ice from the Arctic, and its Role in Abrupt Climate Change
Nontechnical This research will address fundamental questions regarding both paleo-climate and paleo-circulation of the ocean by identifying what may have triggered past abrupt climate change. In the late nineteenth century, Sir George Nares came across 15-18 m thick, immobile, ice extending 480 km off the northern Ellesmere coast. The characteristics of the ice were very different from the 2-3 m thick ice now circulating the Arctic Ocean. Similar accounts from other arctic explorers from this time provided insight into what must surely have been a far thicker and more persistent ice cover over the Arctic Ocean during full glacial conditions than we see today. Indeed, low biological productivity and extremely low, or absent, sediment deposition in the Arctic during glacial periods suggest that parts of the central and western Arctic Ocean were covered by very thick, perennial ice. This research will explore how such ice could have covered much of the Arctic Ocean during glacial periods, how thick it could have been, and whether its eventual mobilization and demise could have produced freshwater output to the North Atlantic large enough to weaken the deep water formation and trigger abrupt climate cooling. Using a suite of sophisticated, high-resolution, coupled numerical model experiments, this group will address these questions and highlight the connection between changes in the Arctic hydrological cycle and global climate. Each investigator has a serious commitment to education and public outreach, and the project will support and train a graduate student who will work with the investigators in all aspects of the research. Each investigator has been involved with local primary and secondary schools, either by making presentations, hiring students for the summer, mentoring science fair projects, or contributing to curriculum development. They will contribute to the on-going middle and high school science teacher training activities by developing a web-based, interactive, sea ice-learning tool to teach school children about the mechanisms behind sea ice formation and how ice will change as the arctic climate warms. In addition, well-developed relationships with local community organizations will help promote public understanding of abrupt climate change. The idea of thick sea ice in the Arctic has a remarkable ability to capture the public imagination in much the same way as it did in the Victorian period when explorers returned from the Arctic with tales of thick impenetrable ice, conveying the concept of the important role that the Arctic plays in global climate. Technical The intellectual merit of this project stems from its ability to establish a link between the physical arctic system (circulation, sea ice, icebergs) and global climate. Numerical models have recently shown that freshwater sourced from the Arctic is twice as effective at disrupting climate than freshwater released from more southerly sources, but to the present the subject of freshwater and abrupt climate change has been dominated by discussion of meltwater floods emanating from glacial lake outbursts. Determining whether the export of sea ice and associated superimposed ice from the Arctic to the North Atlantic could supply enough freshwater to the Nordic Seas to cause the Earth's climate to cool will provide new insight into the mechanisms that trigger abrupt climate change. By quantifying the sensitivity of Atlantic meridional overturning circulation to arctic freshwater forcing the researchers will also be able to better examine whether changes in the arctic hydrological cycle in the near future (from sea ice melt and freshwater export from the Beaufort Gyre) pose a threat to the stability of modern-day climate and human society. In addition, the numerical model developed for this project will resolve ocean circulation, sea ice, and iceberg transport at a resolution approx. 0.17 degrees (ca. 19 km), 5-10 times higher than that of existing paleo-climate models, and have the capability of simulating narrow coastal boundary currents, shelf-breaks, and frontal zones important for freshwater transport along the continental margins, and other features not captured by the current generation of paleo-climate models.