Thermohaline circulation, Upwelling and Blue Whales

Salt changes water density: seawater is denser than freshwater Water= H20 (2 H+ and 1 O-) Atoms of opposing charge attract e/o Fresh water has H2O molecules that have lots of space between them In one container (volume) there are only so many H2O molecules The weight of the water in that container is called the DENSITY If one adds salt (NaCl or 1 Na+ and 1 Cl-) to fresh water, it will DISSOLVE into individual atoms of Na+ and Cl- Atoms place themselves close to opposing charges Water molecules now share the space with Na+ and Cl- So there are more atoms in the same container (volume)  container is heavier! HIGHER 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.

Thermohaline circulation (thermo=temperature, haline=salt) Water in the ocean is in motion: the wind pushes it around. As currents moves towards cold area is gets colder (denser) The wind evaporates water but not the salt  seawater becomes also saltier  denser Surface water sinks Currents at 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.

Blue Whales Biggest animal on earth: 100-150 tons Marine mammals Eat tiny animals named krill: more than 4 tons/day 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

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=process of deep, nutrient-rich bottom waters flowing to the surface of the ocean When the nutrients reach shallow water, where there is light, tiny algae (water plants) called phytoplankton can grow. These plants are the basis of the ocean food chain. Upwelling areas are therefore very important for all animal life: 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).

How does it work? Wind + Coriolis force coriolis animation= current flow N-hemisphere: right of wind direction S-hemisphere: left of wind direction “gaps” are filled with water from below: 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