Oceanography: Global Productivity

Key points

-Equatorial divergence drives upwelling and productivity. -Coastal upwelling regions are also regions of high productivity -Subtropical convergence limits upwelling and productivity. -High latitude upper ocean is more easily mixed than low latitude surface ocean. -High latitudes are light limited (unlike low latitudes) and experience strong spring/summer blooms.

Coastal downwelling

Coastal downwelling in the Northern hemisphere is when wind from the south drives onshore surface flow and downwelling.

Coastal upwelling

Coastal upwelling occurs in the northern hemisphere. Here, the wind from the north drives th ekman transport of the surface water offshore. The deep water upwells to replace this surface water.

Cold-core rings

Cold-core rings are the primary mechanism for getting nutrient-rich water south of the gulf stream. Cold-core rings are the primary mechanism for getting nutrient-rich water south of the Gulf Stream. They are LOW pressure systems.

Costal upwelling fogs

Costal upwelling brings cold deep water to the surface. The winds are flowing across the cold water and they experience cooling. Water vapor in these winds condense into fog.

Downwelling

Downwelling is the vertical downward movement of water often due to Ekman convergence. Convergence of water at the surface prevents the upwelling of cold, nutrient-rich water, causing thicker thermocline.

Vertical mixing

Greater stratification makes vertical mixing more difficult. Mixing of high nutrient water into the surface ocean occurs more easily in the high latitudes.

Productivity

HIGH latitude regions are generally more productive than LOW latitude regions.

Seasonal variations in productivity

Happens. Gulf bloom, etc. High latitudes are light-limited and experience strongs spring and summer blooms.

Low altitude productivity

High productivity in the low latitudes is limited to upwelling regions. This would be along the equator or in costal areas with upwelling favorable winds.

River inputs

In some areas, large rivers deliver enough nutrients to drive substantial productivity in the oceans.

Subtropical gyres

The subtropical gyres have low productivity due to downwelling.

High latitude productivity

The temperature profile in the high latitudes is nearly iso-thermal. There is less solar input at the surface and the warm ocean loses heat to the cold atmosphere.

Equatorial regions

There is high productivity in the equatorial regions due to upwelling.

Warm and cold-core rings

These are about 100-300 km in diameter and surrounded by swift currents, they persist for weeks to months.

Upwelling

Upwelling is vertical upward movement of water, often due to Ekman divergence. The divergence of water at the surface causes deeper water to upwell to the surface. Upwelling brings cold, nutrient rich water into the photic zone, causing thinner thermocline.

Vertical motion in high and low pressure systems

Vertical motion is upward in low pressure systems. Vertical motion is downward in high pressure systems.

Warm-core rings

Warm-core rings are nutrient-depleted water from subtropical gyres. They are important for transporting heat across the gulf stream. They sometimes contain Sargassum communities. They consist of nutrient-depleted water from subtropical gyres. They are important for transporting heat across the gulf stream. HIGH pressure systems.