Connecting altimetry with ocean gyres and overturning circulations in the context of global ocean warming

Peter Rhines (Univ of Washington, United States)

CoAuthors

Sirpa Hakkinen (NASA Goddard Space Flight Center, United States)

Event: 2016 Ocean Surface Topography Science Team Meeting

Session: Science II: From large-scale oceanography to coastal and shelf processes

Presentation type: Type Oral


Surface ocean-current and SSH variability, made visible with altimetry, reflects the dominant circulations beneath. Transports of mass, heat and fresh water and adjustment of water-column stratification are the most important oceanographic products for climate and ecosystems. The complementary combination of profiling ARGO floats and altimetry has yielded impressive reconstruction of time-variable AMOC (Atlantic meridional overturning circulation) and time-mean 1000m-depth lateral circulation, as well as subsurface material transports by mesoscale eddies and their origins in boundary currents. Core potential vorticity and water-mass potential temperature/salinity (θ/S) tracers are carried long distances in virtually a new mode of circulation. It demonstrates a ‘mean circulation’ defined by key water masses (~conditioned Lagrangian average) which may circulate and mix differently than traditional time-averages of velocity (~Eulerian averaging).

We review connections between subtropical and subpolar surface gyre circulations and meridional circulations beneath. Ultimately oceanic overturning, transformation of water-masses and global warming are best described on the θ/S plane. Shallow-deep interaction and θ/S dynamics are seen in these striking events of altimetry-era Atlantic circulation:
o spin-down of the subpolar gyre and massive θ/S increase of the subpolar Atlantic and Nordic Seas
o the 45N transition zone and water-mass transformation site for Gulf Stream/North Atlantic Current connection between subtropics and high latitude
o global ocean warming studies applying circulation and eddy observations, incorporating the ‘thermohaline (θ/S-) vector’ of atmosphere/ocean interaction, and exploiting the altimetric measure of oceanic heat-content variability.
o deep convective mixing and interleaving at the Atlantic polar front (and AMOC ‘choke-point’) near Iceland, revealed by pairing Seaglider sections with altimetric surface velocity and satellite SST
(see figure left: SST (14 May 2009) and Seaglider tracks crossing Iceland-Faroe Ridge at polar front, right: AVISO surface velocity vectors/streamlines and (black) Norrona upper 150m adcp subsurface mean velocity, with ridge topography; below: glider-observed salinity anomaly section, due to mixing across the sloping polar front. Beaird, Rhines & Eriksen, J.Geophys. Res 2016)

Future observations of the subsurface water column will gain considerably by coordinating with satellite altimetry orbits: populating the world ocean with controllable, deep gliders along these lines, in efforts complementing the randomly drifting ARGO floats already in place.

 
Connecting altimetry with ocean gyres and overturning circulations in the context of global ocean warming

Oral presentation show times:

RoomStart DateEnd Date
Richelieu Wed, Nov 02 2016,14:00 Wed, Nov 02 2016,14:15
Peter Rhines
Univ of Washington
United States
rhines@ocean.washington.edu