Essential Question: What role do Thermohaline Circulation, Coriolis Effect and Upwelling play in Oceans?

Ocean Currents EXPLAIN: The teacher now relates both the effect of heat and salt on density. He explains how water masses, which are pushed northward by the winds, cool down (increased density) and loose water vapor (which also increases the density) when approaching the North Pole, and therefore sink to the bottom. Bottom currents then carry the water around the globe (the Thermohaline circulation), and it resurfaces in certain areas. These areas where deep water resurfaces are very important in terms of primary productivity. Wind-driven currents and tides are due to the gravity of moon and sun 2

Understanding Density The container represents volume The molecules represent mass The combination of the mass and volume is called DENSITY (heft). Density = Mass/Volume EXPLAIN: Salt increases water density. The teacher uses the simple schematics of two containers of equal volume, with an equal number of H and O atoms. One container has to share the space with additional atoms of Na and Cl, which causes hydrogen bonds to break and all the available atoms to be more closely packed together. As each atom has a weight, the total weight in the second container is higher, in other words it has a higher density.

Seawater is Denser than Freshwater Fresh water has H2O molecules that have lots of space between them, much like the cup of marbles In a container (volume) there are only so many H2O molecules (mass) The combination of the mass and volume of the water in a container is called the DENSITY (heft) Is there volume (space) for something to be added that will only change the mass? How will this impact density? EXPLAIN: Salt increases water density. The teacher uses the simple schematics of two containers of equal volume, with an equal number of H and O atoms. One container has to share the space with additional atoms of Na and Cl, which causes hydrogen bonds to break and all the available atoms to be more closely packed together. As each atom has a weight, the total weight in the second container is higher, in other words it has a higher density. 4

Water Density Seawater is Denser than Freshwater Fill two beakers each with 200 ml water Place ONE beaker on the scale and get the mass Add ONE spoonful of salt – stir How did this change the water level (volume)? How did this change the water’s mass? Why did the water level not change, but the mass level did? EXPLAIN: Salt increases water density. The teacher uses the simple schematics of two containers of equal volume, with an equal number of H and O atoms. One container has to share the space with additional atoms of Na and Cl, which causes hydrogen bonds to break and all the available atoms to be more closely packed together. As each atom has a weight, the total weight in the second container is higher, in other words it has a higher density. 5

How Does Freshwater and Saltwater Impact Oceans? Put a blue dye strip in the salty water and the red dye strip in the other – remove strips and dispose of them. EXPLAIN: Salt increases water density. The teacher uses the simple schematics of two containers of equal volume, with an equal number of H and O atoms. One container has to share the space with additional atoms of Na and Cl, which causes hydrogen bonds to break and all the available atoms to be more closely packed together. As each atom has a weight, the total weight in the second container is higher, in other words it has a higher density. 6

Water Density Seawater is Denser than Freshwater EXPLAIN: Salt increases water density. The teacher uses the simple schematics of two containers of equal volume, with an equal number of H and O atoms. One container has to share the space with additional atoms of Na and Cl, which causes hydrogen bonds to break and all the available atoms to be more closely packed together. As each atom has a weight, the total weight in the second container is higher, in other words it has a higher density. Pour the water into the two chambers as shown here 7

Water Density Seawater is Denser than Freshwater EXPLAIN: Salt increases water density. The teacher uses the simple schematics of two containers of equal volume, with an equal number of H and O atoms. One container has to share the space with additional atoms of Na and Cl, which causes hydrogen bonds to break and all the available atoms to be more closely packed together. As each atom has a weight, the total weight in the second container is higher, in other words it has a higher density. Carefully – without jiggling the box, pull the plastic divider out. Observe what happens – Why?? 8

Thermohaline circulation (thermo=temperature, haline=salt) Thermohaline circulation is the part of the ocean circulation which is driven by density differences. Sea water density depends on temperature and salinity. Differences arise from heating and cooling at the sea surface and the introduction of freshwater into the salty sea water. Heat sources at the ocean bottom play a minor role.  EXPLAIN: The teacher now relates both the effect of heat and salt on density. He explains how water masses, which are pushed northward by the winds, cool down (increased density) and loose water vapor (which also increases the density) when approaching the North Pole, and therefore sink to the bottom. Bottom currents then carry the water around the globe (the Thermohaline circulation), and it resurfaces in certain areas. These areas where deep water resurfaces are very important in terms of primary productivity. 9

Thermohaline circulation (thermo=temperature, haline=salt) As currents move water near cold areas, it gets colder (denser) The wind evaporates water but not the salt  seawater becomes saltier  denser Currents at the bottom of ocean that moves “packs” of water with different densities (combination of salt and temperature) around the globe  THERMOHALINE CIRCULATION EXPLAIN: The teacher now relates both the effect of heat and salt on density. He explains how water masses, which are pushed northward by the winds, cool down (increased density) and loose water vapor (which also increases the density) when approaching the North Pole, and therefore sink to the bottom. Bottom currents then carry the water around the globe (the Thermohaline circulation), and it resurfaces in certain areas. These areas where deep water resurfaces are very important in terms of primary productivity.

Coriolis Effect Water is flowing across the moving Earth – thus currents within the ocean are impacted by this movement. The water “follows the curve” caused by Earth’s spin. https://www.classzone.com/books/earth_science/terc/content/visualizations/es1904/es1904page01.cfm?chapter_no=visualization

How does upwelling work? Wind + Coriolis force create a current flow N-hemisphere: right of wind direction S-hemisphere: left of wind direction “Gaps” are filled with water from below, thus: UPWELLING!! EXPLAIN: Explain that ocean currents are the result of both winds blowing along the surface and the Coriolis force, that deviates things towards the right in the N-hemisphere and towards the left in the S-hemisphere (the teacher decides how detailed an explanation he wants to give. A rotating globe can help explain Coriolis). So Northern winds (blowing from N-S!) blowing along the California coast cause currents to move perpendicularly from the coastline (due W). As in nature everything strives towards balance, the “gap” in the ocean caused by the water that moves away needs to be filled. As there is land on one side, water can only come from the bottom. This upwelling is comparable to a giant “suction pump”. The teacher shows the students what happens in the S-hemisphere. It is also important to recall that the upwelling water, besides being very rich in nutrients is also dense, cold and salty. The students will now recreate this whole phenomenon on their own during the lab practice

Upwellings http://www.classzone.com/books/earth_science/terc/content/visualizations/es2405/es2405page01.cfm How could you use your straw, the saran wrap and some water to simulate this action?

Upwellings Nutrients accumulate in deep waters as they move out of the photic zone (where nutrients get used up in photosynthesis) and  the remains of organisms sink and decompose   Upwelling is the process by which deep, nutrient-rich bottom waters flow to the surface of the ocean When the nutrients reach shallow water, where there is light, tiny algae (water plants) called phytoplankton use this as their primary nutrient source. These plants are the basis of the ocean food chain. Upwelling areas are therefore very important for all animal life: from shrimp to blue whales EXPLAIN:   Recall the role of sunlight in photosynthesis and the importance of phytoplankton in sustaining life in the ocean (ask students if phytoplankton production is linked to us humans).

Aquatic Life Bigger sea-animals eat tiny animals and ocean floor debris They depend on areas where they can find lots of food, like upwellings EXPLAIN:   Blue whales have a gargantuan appetite (the students will appreciate hearing some amazing facts about these gentle giants of the oceans. The factsheet is a good source of information.) Where on Earth can blue whales find enough food? In areas where dense, nutrient-rich waters from the bottom well up to the surface of the ocean. Source: http://www.youtube.com/watch?v=fOMzFFh3rEA