Recent observations from the Greenland Sea: Seasonal to interannual variability of temperature and salinity and implications on water mass formation Katrin Latarius, Detlef Quadfasel [email protected] University of Hamburg

ABSTRACT I. DATASET The float dataset in the Nordic Seas consists of 3800 profiles measured The Greenland Sea gyre is known for open ocean convection since the first deployments in 2001. triggered by extreme heat loss to the atmosphere in winter. Starting in the Greenland Sea, since Since the late 1980’s, convection activity decreased and 2005 also the Norwegian and Lofoten reached only intermediate depths. Basin are maintained and since 2006 Data from ARGO floats and a profiling mooring, from 2000 to also the Iceland Sea. 2007, provide a hydrographic time series longer and of significantly higher temporal resolution than any timeseries Here only the float data from the Greenland Sea are analysed, which discussed before of that region. It enables us to describe the are appr. 500 profiles in 6 years typical seasonal cycle and associated interannual variability of giving a mean of 10 profiles per temperature and salinity for the last decade. The development month (within the closed f/H-contour of heat and freshwater content of the gyre is analysed with – yellow). respect to the atmospheric forcing and lateral advection. Top: ARGO-float profiles in the Nordic Seas Data gaps are closed with a 10-day 2001-2007, inside yellow contour: Greenland Sea, blue Diamond: Yoyo- subsample of the AWI-Yoyo-mooring- mooring data 1 from the central Greenland Sea II. HYDROGRAPHY Bottom: number of cycles per month in the Greenland Sea (position: blue diamond). Timeseries of potential Funding was provided by the temperature, salinity and European Union (Mersea), Argo density for the Greenland Germany/Norway/UK and the DFG Sea April 2001 to May 2007 (SFB512-E2). (monthly mean profiles of float and profiling-mooring data) III. HEAT CONTENT BUDGET •Seasonal cycle of Q : Q –Q temperature (warming phase NCEP/NCAR fl NCEP/NCAR development of heat (difference from April to September, PW content of the GS from between cooling phase from October to AW surface flux data observed and March) (NCEP/NCAR) estimated heat •Seasonal cycle of freshwater Q : development of content) gives input: maximum in late float DW heat content in the the order of summer upper 1000m from lateral exchange •Warming trend for the whole monthly mean float between gyre period EGC GS-gyre profiles and boundary. •Increasing salinity at 500 to EGC – East Greenland Current GS – Greenland Sea 1500 dbar for the whole period 2001 2003 2005 2007 A compensating heat flux of Between 0 and 800dbar an overall ~ 7 W/m 2 warming trend of 0.05°C/year is 84 W/m 2 is needed to close observed. There is no similar trend in the budget. This is equivalent the heat fluxes between ocean and to 5*10 20 J/year for the total ~ 77 W/m 2 atmosphere, therefore heat must be gyre area. transported into the region by lateral exchange with the boundary current. How is the budget closed? Extreme freshwater inputs have (see VI) 2 been observed in autumn 2002 and 84 W/m 2003 . Convection depths vary between VI. EXCHANGE GYRE - BOUNDARY 1335dbar (winter 01/02) and 145dbar (winter 02/03). How is the heat budget closed? Deep convection is suppressed by Due to eddy fluxes. extreme freshwater inputs and the Observations as well as eddy-resolving 2002 2004 2006 overall warming trend. models show the typical structure. The intermediate Tmax has developed in the 40 km First estimates from mooring data from early 90s, descending the East Greenland Current support the from 1990 to 2001 from Pot. temperature and float tracks in needed magnitude of exchange. the region of the Polar Front 500 to ~1700m . From (separating the Greenland Sea and (a) (b) 2001 to 2007 the depth the East Greenland Current) P. Lherminier et al., 1999 4 1982 2000 2001 2007 of the Tmax stayed

constant and at the end Development of intermediate Tmax , as observed from CTD ((a) Karstensen et al. 2005 2) and float measurements (b) . NAOSIM 0.0825°resolution of the timeseries R. Gerdes, F. Hacker, pers. com. 3 the signal got lost in the overall warming trend . This is supported Salinity at the depth of intermediate T by observations with deep CTDs (AWI-BHV summer survey 2007 1). max

REFERENCES [1] G. Budeus, Alfred-Wegener-Institut, Bremerhaven, German Euro-Argo Users Workshop [2] Karstensen, J., P. Schlosser, D. W. R. Wallace, J. L. Bullister, J. Blindheim , Water mass transformation in the Greenland Sea during the 1990s. Southampton, June 2008 Journal of Geophysical Research, 2005. [3] R. Gerdes, F. Hacker, Alfred-Wegener-Institut, Bremerhaven, Germany [4] P.Lherminier, Gascard, J.-C., Quadfasel, D., 1999. The Greenland Sea in Winter 1993 and 1994: preconditioning for deep convection. Deep-Sea Research.1999