5.5 How does seawater salinity vary at the surface and with depth?

surface salinity variation

surface salinity varies depending on the latitude

• high latitudes: abundant precipitation and runoff and melting of freshwater icebergs —> decreases salinity ; cool temps limit amount of evaporation

• low latitudes: pattern of Earth’s atmospheric circulation causes warm, dry air to descend, so evaporation rates are high and salinity increases, also little precipitation and runoff

• equator: temps are warm near equator so evaporation rates are high enough to increase salinity but increased precipitation and runoff partially offset high salinity

salinity variation with depth

• salinity change w/ increasing depth for low-latitude regions: increased salinity at surface bc of evaporation and no precipitation, but with increasing depth, salinity gets lower

• salinity change w/ increasing depth for high-latitude regions: decreased salinity at surface, salinity increases as you get deeper

why does salinity vary widely at the surface but hardly at all in the deep ocean"?

bc all processes that affect seawater salinity occur at surface and have no effect on deep water below

• processes = precipitation, runoff, evaporation, melting icebergs, melting sea ice, ice forming

halocline

rapid change in salinity between depths of 300m-1000m

• low-lat curve: decrease in salinity

• high-lat curve: increase in salinity

**rapid changing salinity layer = halocline, which separates layers of different salinity in the ocean

why is there low surface salinity in high latitudes but high surface salinity in low latitudes?

(1) high: lots of precipitation, runoff, icebergs melting = lower salinity

(2) low: lot of evaporation with little precipitation, no icebergs/sea ice

explain the dip in surface salinity values near the equator

bc at equator, it’s hot so high evaporation rates but there’s also a lot of rain therefore a lot of precipitation and runoff, partially mitigating the evaporation rates and leading to not as high of a salinity

describe the halocline including where it occurs in the ocean.

300-1000m deep, layer of ocean where salinity changes rapidly