**3. Astronomical tides in the Southeast Atlantic**

The astronomical tides of the Atlantic Ocean have been explored since ancient times. As early as 600 CE, medieval monks documented tidal changes throughout the coast of England, and they properly grasped the link between tides, the location of the sun, and the phases of the moon. The utilization of precise tidal gauges for continuous gathering data, as well as advanced computers for modeling and prediction, has greatly increased tide table accuracy and knowledge of the numerous constituent forces that shape and influence tidal behavior.

The tide in the S-shaped north-south Atlantic basin may indeed be conceived of as a unique phenomenon that acts like a massive standing wave traveling across the basin. A variety of complicated elements govern the pace, path, size, and behavior of the Atlantic tide, involving shoreline unusual features, seafloor topography, and dynamical patterns of wind and current. The most frequent and prominent tidal variety in the Atlantic Ocean Basin is the semidiurnal, which has two high and two low tides every tidal day (lasting about 24 hours and 50 minutes). Semidiurnal tides occur over the entire eastern edge of the Atlantic, as well as across the majority of North and South America. Mixed tides, or those with both diurnal (one high and one low tide per day) and semidiurnal oscillations, predominate in the Gulf of Mexico and the Caribbean Sea, as well as along the southeastern coast of Brazil and Tierra del Fuego, in some areas of the Mediterranean, and along the coast of Labrador; the only purely diurnal tides occur in portions of the Gulf of Mexico.

Tidal dynamics for the Southeast Atlantic continental margin have been thoroughly discussed in Pietrafesa et al. [5]. As such, the tide on the NC and SC coasts consists of two principal constituents, the near semi-diurnal, M2, with a principal period of 12 hours, and 25 minutes and the diurnal, S1, of 24 hours. According to that study, the M2 and S1 tides are both Poincare Waves. The net result is that a parcel of water subjected to only the tides would traverse clockwise around an ellipse with a major onshore-offshore axis of 2 km and a minor alongshore axis of 1 km. The net

*On the Possibility of Non-Local and Local Oil Spills Striking the Shores of North Carolina... DOI: http://dx.doi.org/10.5772/intechopen.106679*

#### **Figure 3.**

*Water particle motions due to the M2 astronomical tides along the 28 m and 40 m isobaths off Georgia, South Carolina, and North Carolina. The calculations of the clockwise rotating water parcels are computed directly from Eulerian current meter observations [5]. The numbers on the ellipses indicate the ratios of the onshore/ offshore ellipse axes to the alongshore axes. The ellipse axes are about 2 km onshore/offshore and 1 km alongshore.*

result would be that every 12 hours and 25 minutes, a parcel of water would end back up where it started. These observed water particle motions are visualized in **Figure 3**. Therefore, the astronomical tide is discounted as having been the agent responsible for moving the dinoflagellates across the shelf. We next consider Gulf Stream variability and features.
