Award: OCE-0926423

Normal 0 false false false EN-US X-NONE X-NONE The main objective of this project was to provide logistic and management support for the first U.S. GEOTRACES campaign in the North Atlantic. The campaign took place in two cruises (the first, in October-November 2010 was terminated due to ship propulsion problems, and the second completed the effort in November-December 2011). GEOTRACES is an international research effort aimed at determining and studying the global oceanic distributions of a number of key trace elements and isotopes. It has been known for decades that certain trace elements play an important role in regulating biological productivity in the oceans. Although we have a clear idea how this regulation takes place, there is a dearth of knowledge about (a) what the large scale distributions of these important substances are in the ocean, and (b) what precisely are the rates and mechanisms whereby these substances are delivered to the oceans. These are important gaps, as understanding and predicting how the marine biosphere will respond to global change (both anthropogenic and natural) rests such knowledge. A primary motivation of the GEOTRACES program is to document the distribution of these elements in the world ocean, and characterize the rates and nature of processes that maintain and or modify those distributions. In addition to these bio-necessary elements, GEOTRACES is involved in documenting the distributions and transformations of global pollutants, such as lead and mercury. Understanding the marine fates and rates of these potentially hazardous pollutants is an important step to formulating sensible international policy on their use in industry. In managing and organizing the U.S. North Atlantic study, we coordinated a large number of state-of-the-art trace element and isotope (TEI) sampling and measurement programs on board the ship. Sampling of these properties without contamination is a daunting challenge, and extreme care must be taken. A range of sampling methods were used (see Figure 1). The cruise, shown in Figure 2, was designed to travel through a broad range of oceanic regions, ranging from the highly biologically active upwelling region off the coast of Africa where prevailing winds serve to force deeper water to rise near the shore, through the central subtropical "ocean desert" to the coast of North America, which forms the western boundary of the North Atlantic Ocean basin. As a result of ocean dynamics, intense boundary currents (for example, the northward flowing Gulf Stream at the sea surface and southward flowing deeper currents below) hug the North American continental shelf and slope. The station locations are mapped in Figure 2 on the subsurface distribution of apparent oxygen utilization (AOU, essentially the intensity of oxygen deficit due to in situ oxygen consumption by organisms). The main purpose is to document the contrasting behaviors of these TEIs in difference oceanic environments. These observations are subsequently used along with computer models to infer the underlying processes and their rates. Figure 3 is a sectional "map" of the distribution of AOU along the cruise track. Note the strong maximum in AOU due to biological consumption emanating from the highly biologically active African margin. As part of this project, we combined measured hydrographic properties (temperature, salinity, dissolved oxygen, and nutrients) to quantify the distributions of various water types (see Figure 4 for an example). This allows us to interpret the distributions of the TEIs measured on the cruise in terms of mixing of water masses from a broad range of geographic origins. Last Modified: 12/12/2013 Submitted by: William J Jenkins