Ocean circulation is driven by many forces, both large-scale (e.g., wind and density-driven mixing, variations in solar heating by latitude) and small-scall (e.g., internal waves and friction along the seafloor and other bathymetric features). As the ocean's water moves it carries with it varying levels of heat, salt, and nutrients, which create currents, long- and short-term climate variations, and help determine areas of high and low productivity. Scientists are interested in studying the dynamics of ocean mixing - how it happens, what are the driving forces behind it, and what local/regional influences exist - in order to better understand how the ocean works and its role in determining the planet's physical climate. The Dynamics of Abyssal Mixing and Interior Transports Experiment (DynAMITE) is an NSF-funded research project intended to improve our understanding of mixing and circulation in the deep ocean.
What is DynAMITE?
This field program investigates the processes by which the densest waters in the Atlantic Meridional Overturning Circulation (MOC) are transformed into warmer, lighter density classes (Lower North Atlantic Deep Water, or LNADW) and the resulting circulation through the interior western basin. The dense waters originate as stratified inflows from the South (Antarctic Bottom Water, or AABW) and from the North (Denmark Strait Overflow Water, or DSOW). Along their flow paths, turbulent mixing causes these dense waters to entrain overlying warmer waters changing the characteristics of the bottom flows, weakening their stratification, and making them more buoyant. This mixing of waters with different densitites is termed "diapycnal mixing" and the resulting upward transfer of mass has consequences for the abyssal circulation and for ocean budgets of heat, mass and tracers that are important to Earth's climate system. Most of this water mass transformation takes place between 20° – 40° N where turbulent mixing is enhanced over rugged topography along the Mid Atlantic Ridge and Bermuda Rise, and in the high kinetic energy regime associated with the deep Gulf Stream. DynAMITE is designed to measure the structure and strength of this diapycnal mixing (where? how much? why?) and the flows through the interior western North Atlantic basin that result.
The Field Experiment
The field experiment, conducted between 20°N and 50°N, between Bermuda and the Mid Atlantic Ridge, is composed of two components:
- An array of moored profilers, installed in September 2010 and recovered in June 2012, that measured the property and flow fields on the southeastern portion of Bermuda Rise - a primary pathway for the interior circulation. The 6 moorings directly measured water properties and velocities to quantify transports through the array. Combining these data with profiles from a mooring near 25°N, 52°W (maintained by the U.K. RAPID-WATCH program) will quantify the northward transport of bottom waters between Bermuda and the Mid Atlantic Ridge. Shipboard hydrography and sampling for tracers (CFCs, I129 and nutrients) are being used to ascertain the watermass origins of these flows.
- A shipboard survey aboard R/V Knorr (15May - 14June 2011) to obtain microstructure and velocity profiles (using the High Resolution Profiler), plus detailed bathymetry (SeaBeam) across a broad region, including several suspected hotspots of turbulent mixing. These data will be used to map the diapycnal mixing field and to construct improved parameterizations for use in ocean models.