High Latitude Circulation Global wind field - westerlies to easterlies Drive subpolar & polar wind-driven gyres Gyre patterns are broken up by land masses Very different in northern/southern hemispheres Intense heat losses & seasonal sea ice Drive convection & deep water formation Descending branch of the conveyor belt

Global Wind Field

Subpolar or Subarctic Gyres Westerlies to easterlies give subpolar gyres Easterlies Low Dynamic Height Upwelling Divergence of Ekman Transports Westerlies

Subpolar or Subarctic Gyres

Subpolar or Subarctic Gyres High productivity in subpolar gyre Less apparent in southern hemisphere

Global Wind Field

Polar Gyres Easterly winds around polar high give gyres Easterlies NP Easterlies High Dynamic Height Downwelling Convergence of Ekman Transports

Arctic Ocean Distribution of land is important Beaufort current is a polar gyre Irminger & Labrador currents are subpolar gyres

Seasonal Sea Ice Formation Microwave emission imagery from 78/79

Arctic Sea Ice is Thinning

Arctic Sea Ice is Thinning Ice cover for Sept 2005 Red = typical Sept Blue = typical Mar Serreze et al. [2007] Science Sea-ice extent (bright white area) for September 2005. Median ice extents based on the period 1979 to 2000 for September (red line) and March (blue line) illustrate the typical seasonal range.

Arctic Sea Ice is Thinning Sept 2005 ig. 2. Time series of arctic sea-ice extent for alternate months and least-squares linear fit based on satellite-derived passive microwave data from November 1979 through November 2006. Listed trends include (in parentheses) the 95% confidence interval of the slope. Ice extent is also declining for the six months that are not shown, ranging from –2.8 ± 0.8% per decade in February to –7.2 ± 2.3% per decade in August.

Arctic Sea Ice is Thinning Sept 2005 Fig. 3. Spatial pattern of the percent of IPCC AR4 model simulations (SRES A1B scenario) with at least 15% ice concentration for March (left) and September (right), averaged over the decade 2075 to 2084. For example, a value of 60% at a given location means that 60% of simulations predicted sea ice. Results are based on 11 models with realistic 20th-century September sea-ice extent.

Thinning of Arctic Sea Ice Submarine obs Compared 1958 to 1976 with 1994 to 1997 Draft of ice sheet

Thinning of Arctic Sea Ice Unclear if this is a climate cycle or global warming signal

Arctic Circulation Arctic ocean remains mostly ice covered Anti-cyclonic polar gyres are found (Beaufort current) Much of the Eurasian Basin clears of sea ice each year Changing in time - global warming??

Southern Ocean Circulation Distribution of land is again important Salinity is important Strong Antarctic Circumpolar Current CCW polar current Localized fronts & gyres

Across Drake Passage Temperature Salinity

Seasonal Sea Ice Formation Microwave emission imagery from 78/79

Antarctic Deep Waters - AAIW WOCE hydrography One time survey 1985 to 1997 Look at P18

P18 - Potential Temperature

P18 - Salinity

P18 – CFC-11 Concentrations

High Latitude Circulation Global wind field - westerlies to easterlies Drive subpolar & polar wind-driven gyres Gyre patterns are broken up by land masses Very different in northern/southern hemispheres Intense heat losses & seasonal sea ice Drive convection & deep water formation Descending branches of the conveyor belt