#OCEAN LAB ACTIVITY 1

OCEAN LAB ACTIVITY

HOW DOES SALINITY AND TEMPERATURE CHANGE WITH WATER DEPTH OVER TIME?

• Fundamental   concept:   Describe   how  temperature   and  salinity   relate  to  density stratification, depth and stability of water masses in the ocean.

The density of seawater increases as the temperature decreases but salinity increases. The temperature decreases as the depth increases (getting colder). The salinity increases as the depth increases. The seawater with higher density is colder than the seawater with lower density. Density increases as depth increases. (stability)

 

The ocean is layered like a cake according to differences in temperature and salinity. Temperature and salinity are important oceanographic parameters that play a vital role in driving   ocean   circulation   and   the   movement   of   heat   energy   around   the   globe. Understanding  properties  that  control  the  formation  and  movement  of these  different layers can give us insight into the effect of ocean circulation on primary productivity .

The  layering  of the  ocean  (and the  differences  in  temperature  and  salinity)  occur  in response to processes that occur at the surface of the ocean as a result of seasonal change.  The  processes  include  the  gain  or  loss  of  heat,  increase  in  evaporation  or precipitation, freezing and thawing of sea  ice,  and the  increase  in wind strength  and storms that are associated with the change of seasons. We can “see” the ocean layers by measuring temperature and salinity with depth and can make inferences about the processes at the ocean surface by observing how temperature and salinity change over time at a location.

Stratification describes the layering of water properties relative to depth. Layers where properties  are  changing  rapidly with  depth  are  called  “clines” ,  so where  temperature changes  quickly is the thermocline, where  salinity  changes fast  is the  halocline,  and where density changes rapidly is the pycnocline. Oftentimes, there are regions where there is no change with depth, and these are called mixed layers.

In this activity, you will explore how the layering of the ocean at one location changes over the course of a year.

 

Interpretation Questions:

• Does the depth range of the thermocline, halocline, and surface mixed layer change throughout the year with the seasons? If so, how?

Yes. The thermocline will appear in spring and be evident during the summer, weakens in autumn, and finally almost disappears in winter. The thermocline in summer is the deepest, and winter is the shallowest. The halocline will change with temperature and depth. The surface mixed layer will also change with the sea surface temperature.

Application Question:

• Suggest an explanation for the differences in the depth of the thermocline and the surface mixed layer between the summer and winter.

The thermocline is an oceanic layer where water temperature decreases as the depth increases. During the summertime, the weather is warmer, so the sea surface absorbs many heats causing the sea surface’s temperature increases. (the seawater is also less dense) While in the winter, the climate is much colder than in summer, so the sea surface is very cold. Since the sea surface already has a cold surface, and the thermocline is the layer that water temperature decreases as the depth increases, the thermocline in winter is less deep than in summer.

 The mixed layer does not change with depth. The mixed layer is deeper in winter than in summer. Because in the winter, the sea surface is cold, the seawater temperature can be constantly cold from the surface to a deeper area. But, in the summertime there’s an obvious change in seawater temperature in a different layer.

• Describe how the seasonal thermocline changes during the year at a temperate location.

The seasonal thermocline changes during the year at a temperate region can be very conspicuous. Because the temperate location has 4 different seasons that have obvious features. The thermocline will appear in spring and be evident during the summer, weakens in autumn, and finally almost disappears in winter.

Reflection Questions:

•   Primaryproductionin the ocean is limited to the euphotic zone – the layer of         seawater that receives enough sunlight for photosynthesis to occur. The depth of the euphotic zone varies with season and location, from a few meters in coastal waters   to 100s of meters in the tropical open ocean. Phytoplankton, the group of organisms responsible for most of the photosynthesis in the ocean, are drifters and unable to     swim against ocean currents or between strong gradients in density. These                organisms are therefore mixed throughout seawater layers such as the surface         mixed layer.
• How would you expect the depth of the thermocline to influence the ability of the phytoplankton to stay in the euphotic zone?

The thermocline is an oceanic layer where water temperature decreases as the depth increases. Different seasons has different depth of thermocline, which means seawater has different temperature and density. The depth of the euphotic zone varies with season and location, and the euphotic zone can be influenced by the thermocline’s depth. Since the phytoplankton cannot swim because the strong currents and strong gradients in density.Then thermocline’s varied depth and density can be a problem for phytoplankton to stay in the euphotic zone.

• During which season (summer, fall, etc.) would you expect water column stratification to be the most beneficial for phytoplankton primary production? Explain why.

I believe that spring and summer will be the best seasons for phytoplankton production. First of all, phytoplankton needs photosynthesis to produce food, so sunshine it’s crucial for them. Therefore spring and summer would be the best season that has strong sunlight which can fulfill their production requirement. Secondly, in the summer with a warm temperature, the thermocline is deeper than in other seasons. The warm water has a low density and cold water has a high density. Thus, during the summertime, there’s a very pronounced stratification. Two kinds of water will not mix together and form a gradient in density. Therefore, I believe that spring and summer are the most beneficial seasons for phytoplankton primary production.

• Global ocean conveyor belt circulation is driven by slight differences in seawater density as the density of seawater determines its tendency to move vertically. At  what latitudes is water column instability great enough to result in the sinking of  surface waters to thousands of meters of depth?

    At higher latitudes. At higher latitudes, the water’s temperature will decrease,so the density will increase. Then the high density,cold surface water will sink to thousands of meters of depth.

 

• Asour planet warms, polar surface seawater is getting warmer and fresher. What impact could this have on the density structuring or stratification in the ocean? On the stability of the water column at polar latitudes and ocean conveyor belt circulation?

Because the global warming, the ice berg melts and adds many freshwater into the ocean. This can lead to a lower sea water salinity and increased stratification. As our planet warms, polar surface seawater is getting less salty, so the stability of the water column will be influenced.Besides, the marine life that lives in the polar region will also be influenced. Because Global ocean conveyor belt circulation is driven by slight differences in seawater density. As our planet warms ,the seawater salinity decreased and density decreased. Therefore, this can destroy the Global ocean conveyor belt circulation.