Caitlin's Research

Research

The scales of turbulent mixing can be very small (on the order of centimeters), yet this turbulence can have global-scale implications for ocean physics ranging from the movement of water in the abyss to the exchange of heat between the ocean and air. My research projects are all motivated by the desire to understand when, where, and how these small scale mixing processes have an impact on larger scale physics and climate. To do this I observe these oceanic processes in a variety of physical contexts and over a range of scales. I also collaborate with modelers to glean additional insights into implications of oceanic mixing than can be accomplished using only observations.

This work could not be possible without hundreds of scientists contributing to the global datasets I use and the help of many collaborators, only a small fraction of whom are listed below.

MOTIVE: Mixing belOw Tropical Instability waVEs

The equatorial Pacific is home to a complex current system and the El Ninõ Southern Oscillation (ENSO), which has profound implications for ecosystems and human communities that surround the Pacific basin. Mixing processes are thought to play a key role in modulating the ENSO cycle, however the full range of mechanisms responsible for mixing are currently unknown. Recent studies suggest that Tropical Instability Waves (TIWs) (Figures b, c), which rim the equatorial cold tongue during La Ninã and neutral ENSO states, may set near equatorial mixing rates by altering the generation, propagation and/or breaking of internal waves (Possibly in Figures a, d). To investigate this, the proposed work will address the question: What processes govern the observed modulation of internal waves, and possibly turbulent mixing, by TIWs in the equatorial Pacific? This ongoing project is funded by the NSF and is in collaboration with a core team at three institutions including a postdoc Arachaporn (Waen) Antaliya at the University of Washington, Amy Waterhouse, Gunar Voet, graduate student Caique Dias Luko, and postdoc Zachary Taebel at Scripps Institution of Oceanography as well as Jim Moum at Oregon State University.

ARCTERX: Island Arc Turbulent Eddy Regional Exchange

The ocean is rich with eddies and fronts on a vast range of length scales including submesoscales (0.1s-10s km) and mesoscales (10s-100s km), as shown in (a). Energy is continuously transfered between the current features at various length scales. However when, why, and how this across-scale energy exchange occurs is not well understood, despite being fundamental to oceanic dynamics. The Office of Naval Research sponsored Direct Research Initiative ARCTERX focuses on observing and modeling the energy exchanges across scales in the Western Tropical North Pacific Ocean. As one of many PIs contributing to the program, I am contributing EM-Apex profiling floats (b) to the observational efforts in collaboration with UW graduate student Maya Gong.

Global Geography of Submesoscale Fronts

Whalen, C. B. and Kyla Drushka, Global distribution and governing dynamics of submesoscale density fronts. J. Phys. Oceanogr., 2025. (paper)

Near Inertial Shear and Kinetic Energy in the North Atlantic experiment (NISKINe)

NISKINe is a multi-institution Office of Naval Research Departmental Research Initiative, enabling the collaboration between observationalists, modelers, and theorists. Our goal is to understand the near-inertial shear (which is thought to originally derive most of it's energy from the winds) in a complex submesoscale and mesoscale environment. As a Co-PI on the project, I am working with Ren-Chieh Lien, Eric Kunze, and James Girton to collect data using EM-Apex floats in the North Atlantic.

The figure on the left shows on direction of horizontal (a) shear and (b) velocity, in addition to (c) of one EM-Apex float deployed during the Spring 2019 process cruise south of Iceland. (d) The trajectory, and maginute of the mean velocity of the float over time.

Girton, J. B., C. B. Whalen, R. C. Lien, E. Kunze, Coherent float arrays for near-inertial wave studies. Oceanography, 2024. (paper)

Voet, G., A. F. Waterhouse, A. Savage,... C. B. Whalen... J. B. Girton, Near-inertial energy variability in a strong mesoscale eddy field in Iceland Basin. Oceanography. (paper).

Stokes, I. A., S. M. Kelly, A. J. Lucas, A. F. Waterhouse, C. B. Whalen..., L. Centurioni, A generalized slab model. J. Phys. Oceanogr., 2024. (paper)

Kunze, E., R-C Lien, C. B. Whalen..., and M. C. Buijsman, Seasonal Variability of Near-Inertial/Semidiurnal Fluctuations and Turbulence in the Sub-Arctic North Atlantic. J. Phys. Oceanogr., 2023. (paper)

Whalen, C.B., C. de Lavergne, J. M. Klymak, A. C. Naveira-Garabato, J. A. MacKinnon, and K. Sheen, Internal wave-driven mixing: governing processes and consequences for climate, Nature Reviews Earth and Environment, 2020. (paper and read-only version)

Mixing and Stratification Change in a Changing Climate

As the climate changes, the the ocean is warming non-uniformly, causing the vertical density structure (i.e. stratification) of the ocean to also change since the temperature of the water alters its density. The changing stratification can alter how internal waves are generated, how they propagate, and where they dissipate their energy, therefore potentially altering the location, magnitude, and timing of mixing caused by these waves. Working with me, Helen Zhang (now a graduate student at Scripps Institution of Oceanography) investigated the changing stratification in the Southwest Pacific Basin (see Figure) and found significant changes in the abyss (Figure a, b) which are associated with changes in heat flux. This work was funded by the NSF and was in collaboration with Nirnimesh Kumar and Sarah Purkey

Zhang, H. J., C. B. Whalen, N. Kumar, and S. G. Purkey, 2021. Decreased Stratification in the Abyssal Southwest Pacific Basin and Implications for the Energy Budget Geophys. Res. Lett., 2018. (paper)

Caitlin Whalen