About the cruise

In Southern Drake Passage the extension of the Antarctic Peninsula into the Antarctic Circumpolar Current (ACC) leads to the injection of Weddell Sea waters, with unique physical and biogeochemical properties, into the global circulation. Exchange between the Weddell Sea and the ACC depends intricately on a collection of interacting frontal currents that occupy the continental shelf and slope along the southern boundary of Drake Passage. Satellite and in situ observations suggest that mesoscale eddies and variability emanating from the Weddell Sea, or “Weddies,” are prevalent, yet the physical processes that lead to their formation and evolution (e.g. baroclinic and barotropic instabilities, thermohaline intrusions, tides, interactions with bathymetry) remain uncertain. The objective of this proposal is to observe and quantify the dominant spatial and temporal scales of variability in this region as well as the physical mechanisms that give rise to it. We propose to continuously monitor the fronts in southern Drake Passage for a period of 15 weeks by deploying and piloting a pair of ocean gliders that will collect approximately 1000 profiles of temperature, salinity, dissolved oxygen, fluorescence and optical backscatter. Multiple reoccupations of two transects across the continental slope will allow tracking of the southern ACC fronts with unprecedented resolution and will permit direct calculation of cross-shelf eddy fluxes of heat and salinity. Analysis of the glider data in concert with ongoing and historical observations will provide key insight into the physical processes that control upwelling and ventilation along the southern boundary of the ACC in Drake Passage.

Oceanographers are realizing that robot technology now offers exciting possibilities to observe our environment in ways we have only dreamt of. We will use a fleet of three robots roaming the ocean near Antarctica to answer science questions that are critical to our ability to predict and manage the ocean and its living resources in an era of unprecedented change.

The robots we will use are called ocean gliders. Much like the familiar airborne gliders, they do not have a propeller. Batteries drive a pump to move fluid between one area within the glider and another outside its hull, thus changing whether the glider is denser than seawater, so it sinks, or less dense than seawater, so it rises to the sea surface. It glides up and down, communicating via mobile phone with the scientists controlling it each time it comes to the surface. Using gliders as part of our future ocean and climate observing systems is essential as some ocean observations can be done much more efficiently by remotely controlled gliders. Gliders can also observe the ocean when we’d really rather not be there with ships, such as in winter or in strong winds and heavy seas. This project plans to show that these possibilities are within our grasp.

In addition to the ocean gliders, the field program will be augmented with a surface Waveglider, which will permit an analysis of how small-scale submesoscale dynamics influence mixed layer variability across the southern boundary of the ACC. A major driver of submesoscale variability is the interaction between atmospheric winds and oceanic surface velocities, especially at ocean fronts. At present direct measurements of wind velocities at the relevant temporal and spatial scales—typically 1 to 10 kilometers and one day—are extremely rare. The use of a surface Waveglider that includes a weather station will enable these direct measurements. An understanding of mixed layer dynamics in the southern region of Drake Passage is critical as this is a key site of isopycnal outcropping and thus carbon exchange with the atmosphere. Global estimates of carbon fluxes are typically based on infrequent ship-based transects and the range of variability in these fluxes are poorly constrained. This component of the project will be critical to improving models of mixed-layer variability that influence ventilation and air-sea exchange processes.