Arctic - SubArctic Ocean Fluxes Rationale Scope & Methods

ASOF RATIONALE The Earth is warming. è Including 2002, all ten of the warmest years since records began in 1861, have occurred since 1990 (Jones & Moberg, 2003) è The 4 warmest years of all are 1998, 2002, 2001 and 1997 (descending order) è With El Niño event currently in progress, the UK Hadley Centre predicts 50% probability that 2003 will be as warm or warmer than 1998 è The rate of increase of average global temperature (  0.6  C over the past Century (IPCC, 2001)) has increased  0.2°C per decade over the past two decades.

ASOF RATIONALE Proxy records suggest that NAO in the 1990s may also have been at a 600 year extreme positive state The Ice Extent at end of August 2002 was at a record minimum (Pers. Comm. J. Morison, APL-UW)

ASOF RATIONALE When we plot air temperature as function of latitude and time. It is clear that the recent episode of warming is different in one important aspect: in the last two decades the distribution of warming has become global. Courtesy of Tom Delworth, GFDL

Change in Global Mean Air Temperature 0-10 years after MOC shutdown. (Courtesy Michael Vellinga, Hadley Centre) ASOF RATIONALE The role of the ocean in this change is likely to involve the redistribution of heat by the so called “Meridional Overturning Circulation” or MOC. Most coupled climate models anticipate a slow down of MOC under GHG forcing as result of freshening and warming of subpolar seas. The Met Office HADCM3 coupled model predicts a rapid cooling of N. Hemisphere when the MOC is shut down by spreading freshwater across subpolar seas.

ASOF SCOPE The aim of ASOF is to measure and model the variability of fluxes between the Arctic Ocean and the Atlantic Ocean with a view to implementing a longer-term system of critical measurements needed to understand the high-latitude ocean’s steering role in decadal climate variability. Schematic of the northern loop of the thermohaline circulation: warm, salty sub-tropical waters pass north, give up their heat and return as cold dense overflow crossing the Greenland-Scotland Ridge through the Denmark Strait and Faroes-Shetland Channel. Courtesy of M. McCartney, WHOI

ASOF SCOPE Density surface depth (top) and salinity (right) at OWS M, Norwegian Sea, (Courtesy of S. Osterhus, UiB) Depth of  = 28.0 Our observations show that this thermohaline loop is currently experiencing an enormous perturbation. The freshwater accession to the Nordic Seas has increased steadily over the past 4 decades leading to a long term freshening to depth > 1 km.

ASOF SCOPE The entire system of overflow and entrainment that ventilates the deep Atlantic Ocean has undergone a remarkably rapid and steady freshening over the past four decades. ASOF is expected to monitor the Atlantic thermohaline system and help understanding the cause of the observed perturbations. Courtesy of R. Dickson, CEFAS

ASOF DOMAIN & TASKS ASOF WG Chairs / Deputies: 1. Loeng (IMR, NO) / Haugan (UiB, NO 2. Fahrbach (AWI, GER) / E. Hansen (NPI, NO) 3. Osterhus (UiB, NO) / Meincke (IfM-H, GER) 4. B.Hansen (FL, Faroes) / Meincke (IfM-H, GER) 5. Haine (JHU, USA) / Pickart (WHOI, USA) 6. Rhines (UW, USA) / Prinsenberg (BIO, CA) 7. Karcher (AWI, GER) / Wood (UKMO, UK)

ASOF ORGANIZATION In moving from Science Plan towards Implementation, the scales of ASOF management have purposely been decreased. The ISSG remains, but tasks are planned by groups with the practical expertise to do so. The Numerical Modelling Group [Task 7] retains its overall view.

ASOF EAST ASOF components funded by EU Framework 5 (3 years starting December 2002) ASOF-EC West: To measure the variability of the dense water and freshwater fluxes between the Arctic Ocean and the North Atlantic off SE Greenland and understand their response to climatic forcing, especially NAO. Institutions: IFM Hamburg, CEFAS Lowestoft, SAMS Oban, MRI Reykjavik, FIMR Helsinki. ASOF-EC North: To measure and model the transports across the boundaries between the Arctic Ocean and the Nordic Seas understand the control processes, and establish a well-calibrated flux-array. Institutions: A-W-I B’rhaven, IFM Hamburg, FIMR Helsinki, IOPAS Sopot, LODYC Paris, NPI Tromso. ASOF-EC East: To measure and model the fluxes and characteristics of exchanges between the North Atlantic and the Nordic Seas from direct and continuous measurements, and to assess the effect of anthropogenic climate change on the MOC. Institutions: UiB Bergen, WRI, MRI, Reykjavik, DMI Copenhagen, IFM Hamburg, MISU Stockholm, KUNBI Copenhagen

ASOF EAST NOClim, PROClim and the Polar Climate Research Initiative of the Reaseach Council of Norway contribute to ASOF. The Weathership straddles the path of the unconstrained offshore branch of the Atlantic Current where it passes through the Norwegian Sea. This station will be used to study its rate, variability and dynamics. Courtesy of S. Osterhus. UiB.

ASOF WEST The Sub-Polar Gyre Experiment (proposal): regional model/data assimilation system to synthesize data. Courtesy of T. Haine, JHU ASOF and ASOF-relevant field work (left). Sea Surface Height from 1/6° MIT GCM (top)

ASOF WEST Courtesy of S. Prinsenberg, BIO

ASOF WEST Courtesy of K. Falkner, OSU

ASOF WEST Courtesy of C. Lee and J. Cuny, UW

ASOF Information:  WEB PAGE  ASOF CHAIR: B. Dickson, CEFAS, UK  DEPUTY CHAIR ASOF-EAST: J. Meincke, IfM-H, GER  DEPUTY CHAIR ASOF-WEST: P. Rhines, UW, USA  ASOF PROJECT SCIENTIST: R. Boscolo, CSIC, ES