Boundary current a basin (such as the Gulf Stream, a current on the western side of the Atlantic Ocean) are stronger than those on the eastern boundary (such as the California Current, on the eastern side of the Pacific Ocean). Western intensification was first explained by the American oceanographer Henry Stommel. In 1948, Henry Stommel published a paper in "Transactions, American Geophysical Union" titled "The Westward Intensification of Wind-Driven Ocean Currents", in which he used a simple, homogeneous, rectangular ocean model to examine the streamlines and surface height contours for an ocean at a non-rotating frame, an ocean characterized by a constant
North Atlantic Gyre warms. This is due to a weakening of the westerly winds, resulting in reduced wind stress and heat exchange, providing a greater period of time for the gyre water temperatures to rise. Collections of aerosols, marine particles, and ocean water in the North Atlantic Gyre from 1990-1992 have led to measurements in lead isotope ratios. These measurements exceed those associated with atmospheric pollution carried from Europe by the trade winds, implying that the majority of lead contamination in the gyre in the early 1990s was primarily caused by American emissions. The surface layers of the Sargasso Sea were used to