Understanding Alaskan Gulf Water Mixing: Factors and Processes

The waters of the Gulf of Alaska can appear to not mix due to several factors primarily related to temperature, salinity, and ocean currents. These natural phenomena contribute to striking visual contrasts in water color and clarity, beneath which the waters are in constant motion.

Thermal Stratification

The Gulf of Alaska experiences thermal stratification, where warmer, less dense water sits atop colder, denser water. This difference in temperature creates layers that resist mixing. The result is a visually distinct layering of water, which can give the impression of non-mixing despite the underlying dynamic of the waters.

Salinity Differences

Variations in salinity often caused by freshwater input from rivers and glaciers create distinct water masses. Less salty, fresher water is less dense and tends to stay on the surface, while saltier, denser water remains below. This salinity-driven stratification further contributes to the appearance of non-mixing in the waters of the Gulf of Alaska.

Ocean Currents

The complex system of ocean currents in the Gulf can lead to areas where water masses converge but do not mix significantly. The Alaska Current, for example, carries warmer water northward, while colder, nutrient-rich waters from deeper layers can upwell in certain areas, creating distinct water layers. This convergence can result in visually apparent non-mixing of waters.

Wind and Weather Patterns

Wind patterns can also influence the mixing of surface waters. While strong winds can cause turbulence and mixing, in calmer conditions, stratification can persist. These same calm conditions often contribute to the unique visual appearance of the Gulf of Alaska, making its waters seem less mixed.

Geographic Features

The geography of the Gulf, including its bathymetry, influences how water flows and mixes. Certain areas may have features that trap water or create barriers to mixing. These geographic features, in combination with the aforementioned factors, contribute to the visual stratification of the waters.

Despite the apparent non-mixing, the waters of the Gulf of Alaska do mix eventually. The Great Oceanic Conveyor Belt is a global system where warm surface waters gradually cool and sink, eventually overturning and mixing every drop in every sea. However, in the short-term, the factors mentioned here limit the extent of mixing in the Gulf of Alaska.

When waters from the Gulf of Alaska, which consists of saline Pacific Ocean waters, meet the fresh waters of incoming rivers, the mixing does not occur immediately. River water, less dense due to its low salinity, stays on the surface while the salty Gulf water remains below. Over time, the two waters gradually intersperse until their densities are the same, at which point they mix completely. The river water's different color — a result of glacial silt, giving it a light blue appearance — fades as it is absorbed into the saline Pacific, gradually blending with the ocean water.