Aaron Goldner

Antarctic glaciation caused ocean circulation changes at the Eocene–Oligocene transition

Two main hypotheses compete to explain global cooling and the abrupt growth of the Antarctic ice sheet across the Eocene–Oligocene transition about 34 million years ago: thermal isolation of Antarctica due to southern ocean gateway opening, and declining atmospheric CO2 (refs 5, 6). Increases in ocean thermal stratification and circulation in proxies across the Eocene–Oligocene transition have been interpreted as a unique signature of gateway opening, but at present both mechanisms remain possible. Here, using a coupled ocean–atmosphere model, we show that the rise of Antarctic glaciation, rather than altered palaeogeography, is best able to explain the observed oceanographic changes. We find that growth of the Antarctic ice sheet caused enhanced northward transport of Antarctic intermediate water and invigorated the formation of Antarctic bottom water, fundamentally reorganizing ocean circulation. Conversely, gateway openings had much less impact on ocean thermal stratification and circulation. Our results support available evidence that CO2 drawdown—not gateway opening—caused Antarctic ice sheet growth, and further show that these feedbacks in turn altered ocean circulation. The precise timing and rate of glaciation, and thus its impacts on ocean circulation, reflect the balance between potentially positive feedbacks (increases in sea ice extent and enhanced primary productivity) and negative feedbacks (stronger southward heat transport and localized high-latitude warming). The Antarctic ice sheet had a complex, dynamic role in ocean circulation and heat fluxes during its initiation, and these processes are likely to operate in the future.

Bringing high performance climate modeling into the classroom

Climate science educators face great challenges on combining theory with hands-on practices in teaching climate modeling. Typical model runs require large computation and storage resources that may not be available on a campus. Additionally, the training and support required to bring novices up to speed would consume significant class time. The same challenges also exist across many other science and engineering disciplines. The TeraGrid science gateway program is leading the way of a new paradigm in addressing such challenges. As part of the TeraGrid science gateway initiative, The Purdue CCSM portal aims at assisting both research and education users to run Community Climate System Model (CCSM) simulations using the TeraGrid high performance computing resources. It provides a one-stop shop for creating, configuring, running CCSM simulations as well as managing jobs and processing output data. The CCSM portal was used in a Purdue graduate class for students to get hands-on experience with running world class climate simulations and use the results to study climate change impact on political policies. The CCSM portal is based on a service-oriented architecture with multiple interfaces to facilitate training. This paper describes the design of the CCSM portal with the goal of supporting classroom users, the challenges of utilizing the portal in a classroom setting, and the solutions implemented. We present two student projects from the fall 2009 class that successfully used the CCSM portal.

Science Policy: Using Your Voice to Inform and Inspire

In recent decades, scientific research that addresses complex and critical global issues, such as climate change, has become increasingly politicized, leaving many scientists feeling as though they cannot directly engage decision makers and simultaneously preserve the integrity of their work. Now at a time when policy makers and the public struggle to understand the technical nature of these issues, scientists who want to communicate their findings clearly and effectively can turn to science policy to better understand how to engage in this process.