3.3.2 The surface salinity

Figure 10

There are two parts to this figure that show the change in salinity and E-P with latitude; part (a) is a line graph (above) and part (b) is a contour map (below).

Part (a): The line graph shows the change in both salinity and E-P with latitude.

The horizontal axis is labelled 'latitude' and is marked from 80° S to 80° N in intervals of 10°. There is an axis tick for 70° but no number on both the N and S sides. The scale of the axis is not linear and the size of each 10° interval increases the closer it is to the Equator. There is a single vertical gridline at the centre of the axis, at latitude of 0°, and this is labelled 'Equator'.

The vertical axis has two scales indicated. The vertical axis on the left is labelled 'salinity' and is marked from 33 to 36 in intervals of 1. There are no units indicated. The vertical axis on the right is labelled 'E−P/mm y⁻¹' and is marked from −1000 mm y⁻¹ to 1000 mm y⁻¹ in intervals of 500 mm y⁻¹. There is a single horizontal gridline at the centre of the axis, at E−P = 0 mm y⁻¹.

The salinity data are represented by a green line.

The E−P data are represented by a purple line.

Both lines follow a similar 'M' pattern with increasing and decreasing undulations.

The salinity line is low (33.8) at 70° S and steadily increases to a first peak of 35.6 near 25° S before falling again to 34.4 at approximately 3° N. There is another increase to 35.7 at 24° N and then a drop to 33.4 at 50° N.

The E−P line begins at approximately −100 mm y⁻¹ at 70° S and then has an initial drop to −600 mm y⁻¹ near 54° S before it rises steadily to its first peak of 500 mm y⁻¹ near 25° S. This is followed by a steady decrease to −750 mm y⁻¹ at 5° N and then an increase to a second peak of 500 mm y⁻¹ at 20° N. The line then decreases to −400 mm y⁻¹ at 50° N and rises to a minor peak of almost 0 mm y⁻¹ at 70° N.

Part (b) shows a world map, centred on the Pacific Ocean, showing contours of equal levels of salinity and with increasing levels of salinity indicated by increasingly darker shades of blue.

The edges of the map are marked to show longitude and latitude with labels along the top and left sides.

The longitude is marked along the top edge, in intervals of 20°, with numbered marks at intervals of 40°, from 40° E to 0°.

The latitude is marked, along the left edge, from 60° S to 60° N in intervals of 20°.

Contour lines of equal salinity are shown in the oceans with labelled, solid black lines. The salinity levels for the contour lines ranges from 32 to 37 in intervals of 1.

There are also some labels for specific point value for salinity.

The contour bands are indicated by different shades of blue. There is no key, but the shading is as follows:

salinity less than 34 = very pale blue

salinity from 34 to 36 = pale blue

salinity greater than 36 = dark blue.

The general patterns shown by the map are;

very pale blue bands at high latitudes.

a band of pale blue from approximately 50° S to 40° N with a finger of pale blue extending very far north in the Atlantic over Northern Europe and Scandinavia.

The dark blue areas are confined to five patches in the following general areas:

Arabian Sea between Saudi Arabia and India,

an area in the Indian Ocean off the east coast of Australia,

an area in the South Pacific Ocean between Australia and South America,

a large portion of the South Atlantic Ocean from the South American coast (20° S to 40° S) and extending almost to the west coast of Africa,

and the largest area is located in the North Atlantic Ocean from the Gulf of Mexico across to northwest Africa and Spain (10° N to 40° N), and also includes the Mediterranean Sea.