3
1 Introduction
practical salinity units (psu, we use dimensionless salinity hereafter), respectively;
typical differences are 2–5 °C and 0.3–1.0 psu. The vertical extents of fronts vary
from a few meters to more than a kilometer, with some major fronts reaching the
open ocean bottom at depths exceeding 4 km (Belkin et al. 2009). Circulation at
the fronts is usually associated with a density difference between the two meeting
waters, which can drive relatively intense (geostrophic) flows in the along-front
direction. Fronts are also sustained by convergence at the surface or bottom boundary, approximating an interface, even in the presence of diffusive effects (Largier
1993). Unlike other oceanographic phenomena, marine fronts are physically tangible. Fronts are characterized by surface manifestations such as lines of rips and
foam, rough water zones, accumulations of floating objects, marked changes in
water color, and high biological activity (Fig. 1.2). They are not abstract demarcation boundaries between equally abstract water masses, or mere tightening of isolines, but real, complex and varied dynamic phenomena (Uda 1938; Fedorov 1986).
Fronts have been noted by fishermen, early voyagers and marine scientists centuries ago (Box 1). Though the name “front” was not in use, they were recorded
in the literature for over two centuries taking note of their most evident characteristics: the profusion of life and the contrasting features (color; roughness) of the
Fig. 1.2 Some fronts are characterized by surface manifestations such as marked changes in
water color and/or roughness. Fronts at a Mobile Bay, USA (L. Chiaverano), b Patos Lagoon
mouth, Brazil (O. Möller), c Río de la Plata (Argentina-Uruguay) (M. Framiñan), d meeting of
the Baltic and North seas (Denmark) (E. Spencer http://top10rate.com/top-10-spectacular-oceanphenomena/facts)
1 Introduction
practical salinity units (psu, we use dimensionless salinity hereafter), respectively;
typical differences are 2–5 °C and 0.3–1.0 psu. The vertical extents of fronts vary
from a few meters to more than a kilometer, with some major fronts reaching the
open ocean bottom at depths exceeding 4 km (Belkin et al. 2009). Circulation at
the fronts is usually associated with a density difference between the two meeting
waters, which can drive relatively intense (geostrophic) flows in the along-front
direction. Fronts are also sustained by convergence at the surface or bottom boundary, approximating an interface, even in the presence of diffusive effects (Largier
1993). Unlike other oceanographic phenomena, marine fronts are physically tangible. Fronts are characterized by surface manifestations such as lines of rips and
foam, rough water zones, accumulations of floating objects, marked changes in
water color, and high biological activity (Fig. 1.2). They are not abstract demarcation boundaries between equally abstract water masses, or mere tightening of isolines, but real, complex and varied dynamic phenomena (Uda 1938; Fedorov 1986).
Fronts have been noted by fishermen, early voyagers and marine scientists centuries ago (Box 1). Though the name “front” was not in use, they were recorded
in the literature for over two centuries taking note of their most evident characteristics: the profusion of life and the contrasting features (color; roughness) of the
Fig. 1.2 Some fronts are characterized by surface manifestations such as marked changes in
water color and/or roughness. Fronts at a Mobile Bay, USA (L. Chiaverano), b Patos Lagoon
mouth, Brazil (O. Möller), c Río de la Plata (Argentina-Uruguay) (M. Framiñan), d meeting of
the Baltic and North seas (Denmark) (E. Spencer http://top10rate.com/top-10-spectacular-oceanphenomena/facts)