28 BIO 2008 IN REVIEW EXCITATION-EMISSION MATRIX SPECTROSCOPY Excitation-emission matrix spectroscopy (EEMS) is an extension of 2D UVFS, where emission fluorescence is measured in response to UV light shone on a sample over a range of wavelengths rather than just one. New laboratory equipment obtained by COOGER has allowed EEMS to be applied to suspensions of oil in seawater to obtain unique, three-dimensional (3D) fingerprints of the oil. More importantly, these 3D spectra have allowed the effect of chemical dispersants on oil fluorescence to be defined in greater detail. In effect, the 3D spectrum obtained by EEMS is the unique fingerprint of an oil, and also provides a definitive picture of the effect of chemical dispersant on the fingerprint. In Figure 2, the contour plots of 3D spectra highlight just how strongly emission fluorescence is enhanced at 445 compared to 340 nm. This has evolved into the idea that the effect of chemical dispersant on 3D spectra can be expressed simply as a ratio between fluorescence at 340 nm divided by fluorescence at 445 nm. This, in turn, leads to an important conclusion: emission ratios can be used as direct indices of whether oil is dispersed effectively or poorly. FUTURE DEVELOPMENTS FOR FIRST RESPONDERS More important than the utilization of an emission ratio to determine the extent of oil dispersion is the fact that the ratio can be applied without having to measure oil concentration. This means that a field instrument can be developed to determine the ratio continuously, in real time, and in situ without external calibration. This is a distinct advantage for Coast Guard crew acting as first responders during a spill emergency. An emission-ratio instrument that is capable of tracking oil dispersion in situ provides the up-front information required for the rapid implementation of a remediation strategy. This instrument will be developed as a collaborative project between scientists at COOGER and colleagues in private industry. The Labrador Sea is one of the primary areas in the world’s oceans where an important global ocean circulation pattern called the “ocean conveyor belt” or “meridional overturning circulation” is replenished by the episodic sinking of cold, dense water to interme- diate or greater depths. Strong atmospheric cooling during severe winters makes this sinking particularly massive, mixing surface waters with underlying layers and producing a water mass known as Labrador Sea Water (LSW). After sinking to depths of 800-2,400 m (the penetration depth and horizontal extent of this process depend on the severity of the winter and ocean conditions) LSW spreads equatorward and eastward, becoming the major intermediate-depth water mass in the northern North Atlantic. The portion that flows equatorward in the North Atlantic’s Deep Western Boundary Current is an important component of the ocean conveyor belt which transfers biogeochemical substances, heat, and fresh water between equatorial and polar regions, thereby regulating the Earth’s climate and making our planet habitable. The North Atlantic has a pronounced east-west temperature gradient (Figure 1) associated with its warm subtropical and cool subpolar gyres, atmospheric cooling, and Arctic outflows. Relatively warm upper-ocean waters are carried northeastward by the Gulf Stream system, while cooler waters are transported equa- torward along the western boundary by the Labrador Current, the intermediate-depth flow of LSW, and the Deep Western Boundary Current at greater depth (Figure 2). Changes in the overall three- dimensional circulation pattern, associated with the upper-ocean gyres and the production rates of the deep and intermediate waters such as the LSW, have been an important factor in past glacial climate variability and are expected to be an important factor to the rate and impact of global and regional climate change under green- house warming. DFO’s Ocean Sciences and Ecosystem Research divisions have been conducting annual oceanographic surveys of the Labrador Sea for the past two decades as part of DFO’s ocean climate moni- toring program. (See BIO 2007 In Review.) Physical, chemical, and biological measurements are made each spring along a line (referred to as AR7W) extending from Labrador to Greenland (Figure 1). Since 2002, these observations have been comple- Replenishment of Labrador Sea Water to the Ocean Conveyor Belt in 2008 Igor Yashayaev and John Loder BIO SCIENCE IN PARTNERSHIP Figure 2. Graphics are contour plots of three-dimensional (3D) spectra of Mesa crude oil dispersed in seawater (A) and dispersed with the chemical dispersant, Corexit 9500, in seawater (B). Note the strong enhancement of emission fluores- cence intensity (EmFI) centred on an emission wavelength of 445 nm over a broad range of excitation wavelengths (Em ) applied to the samples.