According to observations taken over the last century, the anthropogenic rate of atmospheric CO2 level increase is at an 800,000-year maximum. Current and impending climate warming from greenhouse gas emissions poses an existential threat to human civilization. Climate scientists increasingly recognize the Southern Ocean, the vast ocean surrounding Antarctica, as a critical player in influencing our planet’s climate on both long and short timescales. Importantly, the Southern Ocean accounts for half of the annual global ocean uptake of CO2 and more than half of the uptake of heat released to the atmosphere. In other words, the Southern Ocean represents the largest oceanic territory responding to global warming.
Despite the key role of the Southern Ocean in the dynamics of our planet’s climate, much about its role in global thermohaline circulation is still a mystery. The appearance in the mid-1970’s of the Weddell Sea Polynya, a large hole in an otherwise continuous sheet of sea ice covering the Weddell Sea in the winter, exposed a previously unknown mechanism for Southern Ocean influence on the rest of the planet. However, modeling the heat and moisture exchange taking place through these holes has proved difficult. Many models are too coarse (that is, the grid for the models has too much space between any two points) to effectively produce realistic polynyas. Even newer models that exhibit convection in the Weddell sea display large differences in behavior.
My research project this summer focused on the mechanisms behind and the consequences of convection in the CM2c model developed by the National Oceanic and Atmospheric Administration’s Geophysical Fluid Dynamics Laboratory. In this model, the Southern Ocean oscillates, vacillating between periods of strong convection from the ocean to the surface and periods of heat buildup and storage deep underwater. Differential equations governing temperature and salinity in the Weddell Sea form a coupled oscillator, with data implying a period of about 70 years. This matched heat storage, sea ice coverage, and other climatological data in the region, which to a large degree move in phase with temperature. As you travel northward from Antarctica to the top of the strong belt of winds and moving water known as the Antarctic Circumpolar Current, the oscillatory behavior becomes increasingly out of phase with Weddell Sea temperature, ending up at about a 20-year time lag. This implies that signals travelling through the ocean take about 20 years to pass through the ACC. Future research will investigate the effects of this convective behavior on different water masses and extend the conclusions of my work to other climate models.
Over the course of my work this summer, I learned about the important role the Southern Ocean plays in global climate. I got to investigate in detail the unique dynamics of the Weddell Sea Polynya, and I gained valuable experience in scripting, data analysis and visualization, and interpreting scientific literature. I also learned about the future of our planet, and I am excited to continue working in the exciting and important field of climate dynamics.