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Transcript
Major Ocean Currents (continue…) Indian Ocean Polar Regions (Southern Ocean; Arctic Ocean) Indian Ocean Unique in its topography and forcing (compared with the Atlantic & Pacific) WINDS Persian Gulf Arabian Sea Bay of Bengal Indian Ocean Strong seasonal wind pattern: summer monsoon Precipitation Winter is the “dry” season H Summer Monsoon brings one of the largest rainfall amounts in the world: causing flooding in India & Bangladesh L Indian Ocean Currents: • little northern Indian Ocean • subjected to very strong winds that reverse seasonally so it has a western boundary current that also reverses seasonally and is strongest during the SW monsoon. NE MONSOON (Winter) SW MONSOON (Summer) Note: Southern Indian Ocean is more “normal” – no significant seasonal change, there is always a SEC, though it gets pushed south in some seasons by an ECC which in this ocean is S of the equator rather than N. The Agulhas Current (western boundary current) extends beyond the tip of Africa and shed large eddies into the Atlantic Ocean Simulation of eddies shed from the Agulhas Current from the Fine Resolution Antarctic Model (FRAM; Webb et al. UK) Indonesian Throughflow: • Important role in the connection between the Pacific & Indian Oceans (input of warm-fresh Pacific waters to Indian Ocean) • Driven by higher sea level in the Pacific and lower in the Indian Ocean • Very complex- many islands and passages • Important for climate change (global ocean conveyer belt) Ocean Currents in Polar regions • Arctic and Antarctic regions are very different: – Arctic: a shallow sea connected to sub-arctic seas through narrow passages (is it a real ocean or a semi-enclosed sea?) – Antarctic: a continent surrounded by deep continuous current that connects all oceans • Both are important sources for deep water mass formation (more on this later…) Antarctic Circumpolar Current (ACC) • zonally continuous around the globe • transports waters between oceans • strongly forced yearround by westerly winds • strong currents concentrated at Polar and Subantarctic fronts • large mean (barotropic) transport (~150Sv) and large variability (seasonal, eddy) •unique momentum balance between windstress and bottom drag of ridges Drake Passage (Tonzak et al (2003) Drake Passage flow: • barotropic • large variability • influenced by topography ICE AROUND ANTARCTICA February Weddell Sea Ross Sea September Eddies in the Antarctic Circumpolar Currents from numerical ocean models (Geophysical Fluid Dynamics Laboratory, Princeton) Arctic Ocean Circulation: • wind-driving is small (ice cover), tides are weak. Circulation seems driven mostly by an eddy/topography interaction (shallow sea divided into sub basins). • The surface flow is driven by inflows from the Pacific (Bering Strait, 85km x 45m) and Atlantic (Fram Strait, 450km x 3000m). ARCTIC OCEAN SURFACE CIRCULATION: Input/output straits Transport drift Atlantic Ocean Pacific Ocean ICE COVER IN THE ARCTIC AND ANTARCTICA The shrinking Arctic ice median ice edge Average Ice Coverage 1979-1981 2003-2005 Antarctica: Another potential consequence of climate change- icebergs breaking from the shelf Satellite monitoring of icebergs Impact of climate change on ecosystem: Examples: Polar Bears in the Arctic and Penguins in Antarctica Reminders: Wednesday Oct-30: no class Monday Nov-4: review Wednesday Nov-6: Exam#2 Last part of the course: - Thermohaline circulation - Waves and Tides - The coastal ocean