Antarctic Oceanography

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Antarctic Surface Currents • Antarctic Circumpolar Current • Antarctic Coastal Current Antarctic Surface Currents • Antarctic Circumpolar Current (ACC) (West Wind Drift) – Flows eastward, driven by westerly winds – Largest current on Earth, ~130 Sv (with max up to 290 Sv!), compared to 85 Sv for Gulf Stream, and ~7 Sv for Leeuwin Current – Northern limit of current defines the Southern Ocean (near subtropical convergence) – Fairly slow current (4-15 cm/s) – Extends very deep • Most currents extend only a few hundred meters • In Drake Passage, at 2500 m, current is 10-30% of surface current • Why Antarctic Circumpolar Current • Wind drives surface current eastward – Coriolis causes motion away from continent: sea surface slopes away from continent • Little stratification in Antarctic – Vertical salinity and temperature gradients are small Pressure force due to horizontal density differences is distributed throughout water column (whereas in tropics much of it happens in the pycnocline) – Weak stratification allows transfer of momentum to lower water much more easily than for strong stratification – Therefore current is transmitted to great depths • Deep Current unimpeded all the way around continent – therefore water from Atlantic and Pacific and Indian Ocean is mixed well – Antarctica is earth’s main mixing region Antarctic Surface Currents • Antarctic Coastal Current (not ACC!) (East Wind Drift) – Between ACC and continent - narrow – Opposite flow from ACC (polar easterlies) – Current speed ~0.1 m s-1, transport ~8 Sv – Current interrupted by Antarctic Peninsula and Ross Sea – forms gyres with ACC pushed Shackleton’s party away from coast 4
Major Antarctic Water Masses Antarctic Region Major Antarctic Water Masses • Three Main layers (South of APFZ): – Antarctic Surface Water (AASW) – Circumpolar Deep Water (aka Warm Deep Water, aka Antarctic Circumpolar Water) (CDW or WDW or ACW) – Antarctic Bottom Water (AABW) • Other Water Masses – Antarctic Intermediate Water (AAIW) (North of APFZ) – Ice Shelf Water (ISF) Red lines are isotherms Antarctic Water Masses AASW Antarctic Surface Water (AASW): -1.9 to +4ºC, S < 34.5 Ant. Circumpolar Water (ACW): 1.5-2.5ºC (top), 0-0.5ºC (bot.); S~34.7 Ant. Intermediate Water (AAIW): 2-4ºC, S=34.2 Ant. Bottom Water (AABW): -2.0ºC, S=34.75, very dense 1. Antarctic Surface Water (AASW) – Between continent and Antarctic Polar Front (APF) – Cold (-1.9° to 4°C), relatively low salinity (S < 34.5 ppt) in upper 50-200 m north of continental slope – Low salinity from fresh water input • Where does the fresh water come – Forms from deep water that has upwelled and modified by cooling and ice formation at the surface • North Atlantic Deep Water upwelling • Brings nutrients to surface – important for marine life – Influenced by ice melt and surface freezing 5
Page 1 and 2: Objectives Antarctic Oceanography
Page 3: Antarctic Polar Front Antarctic Sur
Page 7 and 8: Antarctic Water Masses Fronts and Z
Page 9: Subtropical Subantarctic Conv. Fron

Antarctic Oceanography

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