CAREER: Signals from the deep: the influence of the Mid-Atlantic Ridge on the ocean and climate

University Of Wisconsin-Madison, Madison WI

Investigators

Abstract

North Atlantic Ocean circulation influences climate globally through its transport of heat, freshwater, and carbon; however. Climate model simulations do not reproduce the observations with good fidelity in the North Atlantic. Reducing model biases requires fundamental research that informs model development, especially on processes relevant to resolution and parameterizations, such as flow over topography. Recent work suggests that local topography and coastlines may have greater control on the North Atlantic Ocean’s circulation than previously appreciated. This study will explore how a key basin-scale topographic feature, the Mid-Atlantic Ridge (MAR), impacts the ocean and climate in two different climate model families. The MAR will be removed in an otherwise realistic configuration, allowing attribution of its impact on the ocean and climate. This project supports societally beneficial broader impacts including informing climate model development, scientific workforce training, improving STEM education, and increasing public scientific literacy. The research will inform ocean and climate model development, which is particularly needed given large model biases in the North Atlantic Ocean state that lead to model SST errors and degradation of downstream climate. Scientific training for graduate and undergraduate students will occur in this project. Cross-campus education and public outreach will be supported through a transdisciplinary ocean, climate, and music project with faculty and students in the Mead Witter School of Music. Scientific training of both science and music students will occur through traditional graduate scientific training, through novel undergraduate research opportunities with sonification, and through collaboration with student composers on ocean and climate inspired music. Public performances with scientific discussion will be planned for multiple venues, including classrooms. These events will bring scientific concepts to new audiences, increasing public scientific literacy. Preliminary results with these two models show large but differing impacts to the gyres and overturning. These results will be investigated in greater depth to determine how the MAR affects the North Atlantic Ocean and climate, including with potential vorticity budgets, and to investigate whether the MAR’s presence is necessary for Atlantic multidecadal variability (AMV). Experiments would also be performed to compare the influence of North American coastlines relative to the MAR. Finally, the absence of a Pacific mid-ocean ridge is an untested feature that distinguishes Atlantic and Pacific geometry. The effect of a Mid-Pacific Ridge will be investigated to assess if its addition makes the two oceans more similar. Finally, simpler versions of the Modular Ocean Model will be used to deduce the fundamental physics in the complex models. While the study of bathymetric features on the ocean can be traced back to classic papers in the 1960s and 1970s, several key threads in this area have been dropped. Mid-ocean ridges have not been investigated as a possible feature that could explain why overturning exists only in the Atlantic and not the Pacific, despite the MAR’s many key interactions with North Atlantic currents. Similarly, studies that point to aspects of continental configuration as the explanation for this key climate asymmetry often use idealized geometries and simplified physics. The approach here – starting from the realistic end of the model hierarchy and gradually removing single pieces – differs from past idealized work and will lead to differing conclusions or strong confirmation of past results, both valuable contributions to the field. The analogous atmospheric work (removal of the Rockies or Himalaya alone) are classic results often presented in atmospheric dynamics classes. The MAR removal experiments here has the potential to fill a similar hole in oceanography texts. Finally, testing the hypothesis that the MAR is essential for AMV, will inform the continuing debate on whether North Atlantic variability can be ocean-driven or externally forced. If AMV weakens with the MAR’s removal, it would point to the ocean as a fundamental driver of AMV. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.