Our water planet and our water hemisphere

Role of the ocean in climate Main roles: Storage and transport of heat Storage and transport of CO2 Production of Cloud Condensation Nuclei Other potentially important roles: Methane hydrate release Production of N2O Ocean/ice sheet interactions

Temperature N-S Section Atlantic N-S Section Pacific

Salinity N-S Section Atlantic N-S Section Pacific

Observed meridional heat transports Trenberth and Caron (2001) J. Clim.

Upper ocean circulation

A snapshot of surface temperature distribution in the western North Atlantic

A representation of ocean thermohaline circulation

Detailed meridional overturning circulation

Deep current observations at 30 S off Chile

Meridional flow at 30 S in the Chile Basin Deep poleward boundary current,  10 Sv Deep equatorward Flow,  3 Sv east of the East Pacific Rise AAIW flow in the western Chile Basin Shaffer et al. (2005), Deep Sea Research

Atlantic overturning circulation

THC influence on climate (1): Zonal temperature deviations

THC influence on climate (2): Surface temperature changes after a THC shutdown

Global distribution of recent temperature trends Temperatura Global distribution of recent temperature trends                                                                                                                          IPCC-2001

What drives the thermohaline circulation?

Opening and evolution of Drake Passage over the past 40 million years

High latitude Southern Hemisphere currents

Meridional flows and water mass transformations around Antarctica

THC sensitivity to mixing and Southern Ocean winds in a GCM

Model THC changes for future global warming (quadrupling of CO2 in 140 years) Gregory et al. (2005), GRL

THC hysteresis in coupled climate models Rahmstorf et. al. (2005), GRL, 32, L23605

Ice core and ocean sediment records of 18O Millennial-scale cycles are also evident in high-resolution, ocean sediment data Intermediate depth, 18O decreases can preliminarily be interpreted as warming during cold conditions in Greenland Heinrich events always start during cold conditions in Greenland and result in significant surface layer freshening. Greenland Antarctic Surface 1020 m heinrich events 3148 m

Our low order climate model Ocean: High vertical resolution Frictional model for N-S flow Stability-dependent vertical diffusion ”Horizontal gyre” mixing Southern Ocean shelf water formation and Ekman transport Drake Passage effect Atmosphere: Seasonal and orbital forcing Energy and moisture transports Oxygen isotopic composition of moisture Ice/snow: Variable sea ice/snow cover Prescribed ice cap extents

Model Holocene and LGM overturning circulations Holocene (0 kyr BP) LGM (22 kyr BP)

Model millennial-scale climate oscillations Key features: Abrupt onset of overturning and convection after gradual intensification. Abrupt shutdown after gradual weakening. Alternating NADW and AABW dominance in the deep ocean with AABW confined below 2000 m.

Subsurface 18Oc changes reflect mainly temperature changes Ocean temperature changes over the oscillations Strong warming occurs at intermediate depths during the cold phase of the oscillation This warming is due to lack of cooling from North Atlantic deep convection to oppose diffusive warming at low latitudes Subsurface 18Oc changes reflect mainly temperature changes

Last glacial period simulation Time dependent forcing: Insolation Ice cap extent Atmospheric CO2 Wind stress 6 kyr Heinrich event cycle Key features: Oscillations for intermediate glacial conditions. Surface/intermediate depth calcite 18O vary out of phase with Greenland temp. Deep ocean calcite 18O and Antarctic temp vary in phase with symmetric shape. 40o-90oN 40o-90oS Surface 1000 m 3000 m

Yearly mean solar insolation difference between 40S-40N and 40N-90N