Seasonal changes in water temperature, clearly evident in the mean temperature profile, penetrate the water column to a maximum depth of about 30 meters. The evolution of the thermocline with time and depth shows the lag between the solar solstice, which occurs around June 21, and the maximum depth of the thermocline, which occurs in mid September. Surface water is at its lowest temperature in February, while at 70 meters depth the water does not reach its lowest temperature until April. The interannual variability of water temperature is highest from June to September. This is because maximum insolation is greatest during this period and so is strongly influenced by interannual variations in cloud cover. near the bottom of the water column, at a depth of 65 to 70 meters, there is a layer of water that exhibits very low interannual variability. Water at this depth is only weakly influenced by interannual variability in solar insulation.

Phytoplankton are phototrophs, which means that they consume light and turn it into chemical energy. When a plankton cells absorbs sunlight, not all of the light absorbed is utilized by photosynthesis. Some of the light is reemitted by a process called fluorescence. The quantity of phytoplankton in the water column may therefore be estimated by measuring fluorescence. This figure shows clearly the annual bloom of phytoplankton during the spring (March to April) and the fall (August to October). It also demonstrates these blooms are typically confined to the top 30 meters of the water column and that the spring bloom is different in structure than the fall bloom. Interannual variability in fluorescence is greatest where the mean is greatest. This indicates what statisticians call multiplicative variability, which occurs when the variability of the data is proportional to its mean. Multiplicative variability is very typical of biological systems.

This figure shows the evolution of salinity over time and depth. Notice that the salinity near the surface is highly variable compared to the salinity at depth. This is because the salinity near the surface is strongly influenced by precipitation. The periods when salinity is exceptionally low on the surface correspond to periods of heavy precipitation.

The primary source of the oxygen in seawater is the air-sea exchange with oxygen in the atmosphere. For this reason oxygen concentration decreases with depth, and the first meter or so of the water column is oxygen saturated. Changes in oxygen concentration occur with season due mainly to biological processes. In the climatological profiles shown here the effect of the spring bloom on oxygen concentration is evident. From March to June, peaking around mid April, highly oxygenated water extends all the way to almost 70 meters depth. Interannual variability in oxygen and oxygen saturation is greatest where the oxygen level are lowest, below 30 meters from September to February.

The primary source of the oxygen in seawater is the air-sea exchange with oxygen in the atmosphere. For this reason oxygen concentration decreases with depth, and the first meter or so of the water column is oxygen saturated. Changes in oxygen concentration occur with season due mainly to biological processes. In the climatological profiles shown here the effect of the spring bloom on oxygen concentration is evident. From March to June, peaking around mid April, highly oxygenated water extends all the way to almost 70 meters depth. Interannual variability in oxygen and oxygen saturation is greatest where the oxygen level are lowest, below 30 meters from September to February.

The mean density profile indicates (1) that density is greater with increased depth and (2) there is a seasonal cycle in the density near the surface, which is an indication of annual patterns in precipitation. Variability in density occurs mostly in the first meter or so of the water column. This variability penetrates to depths of up to 20 meters in the fall, which is caused by increased vertical mixing of the water column driven by a decrease in insolation and an increase in average wind speed.