How much the temperatures declined depends on the region, but winters in Europe were cold enough to freeze canals and rivers that today are ice-free all year. There are many hypotheses as to the cause, but one is a disruption to the thermohaline current due to a large influx of freshwater entering the North Atlantic Ocean. Why is this a problem?Įurope's "Little Ice Age" was from about 1350 to about 1850, although the start and end dates are still being debated. So the thermohaline circulation belt slows or stops and Earth's climate is not moderated. So sea ice can't form, which means the brine doesn't form which means the thermohaline /deep ocean currents can’t form. This increases amount of fresh water in oceans and decreases density of sea water. The Earth heats up and ice at polar caps melt. It also distributes between ocean basins:īut what happens when the oceans heat up? Let's explore this. Thus, thermohaline currents help moderate Earth’s temperature by bringing cold water to the equators and warm water to the poles. The amount sinking in the polar regions = the amount rising in the equatorial areas. Some does “escapes into the North Atlantic and becomes a part of the North Atlantic Deep Water. The Arctic Bottom Water is mostly a closed system due to the continental shelf between Russia and Alaska blocking the path to the Pacific Ocean. The Arctic Ocean still has a fair amount of ice covering it, which makes exploring the region difficult. Filchner overflow is an important component for the production of Antarctic Bottom Water (AABW). This brine sinks towards the continental shelf and mixes with the Circumpolar Current.įrom the University of Bergen: Schematic of deep water formation in the Atlantic Ocean. Sea ice only holds 15% of salt, the rest forms a frigid brine beneath. The Antarctic Bottom Water forms in the Weddell Sea during winter. They typically move 1-2 m/day, but locally can move 60 cm/s. This current is also called thermohaline circulation: Therme = heat + halos = salt.īottom currents also called contour currents because they generally moves around features rather than over them. click here for a shockwave animation of brine exclusion in sea ice!.Factors creating a dense mass of water include: This brine sinks to the continental shelf and flows down the continental slope and rise with the downwelling current formed in the Antarctic Convergence.ĭeep-ocean currents form as a response to density differences in the water. This makes the seawater super saturated with salt - a brine. When ice forms, only a small fraction of the salts in seawater are incorporated into the ice. Note in the image above where the sea ice is located. And those "rings" of water moving about Antarctica? They are a part of that moving water within the water masses. This keeps the water moving and not stagnate. Deep water (between Intermediate water and 4000 m)Įach layer moves in a different direction from the one above it.Intermediate water (to ~1500 m) - aka the aphotic zone from this point downward.Central water (to bottom of main thermocline).Surface water (0-200 m) - aka the photic zone.Each has different properties and they don’t mix well. There are five water masses, and each corresponds with the layers discussed in the Seawater Lesson. Its expected age is 112 years.Water Masses and the Thermohaline Current It is shown that while model NADW has two distinct outcrops (in the Arctic and North Atlantic), its formation primarily takes place in the subpolar Labrador and Irminger seas. A bed of more persistent NASMW is detected below the mixed layer with an expected age of 8.7 years. Model NASMW is shown to have an expected age of 4.5 years and is predominantly eradicated by internal processes. Two test cases are detailed, examining the creation and fate of North Atlantic Subtropical Mode Water (NASMW) and North Atlantic Deep Water (NADW) in a 2∘ configuration of NEMO run with repeated annual forcing for up to 400 years. To represent surface (re-)ventilation, we optionally decrease the tracer concentration in the surface layer and track this concentration removal to produce a ventilation record. By terminating dynamic feedbacks in NEMOTAM, tagged water can be tracked forward and backward in time as a passive dye, producing a probability distribution of pathways and origins, respectively. In particular, NEMOTAM, the tangent-linear and adjoint counterpart to the NEMO ocean general circulation model, is modified to allow passive-tracer transport. In this study, we present a newly developed, probabilistic tool for offline water mass tracking. Water mass ventilation provides an important link between the atmosphere and the global ocean circulation.
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