1DMS/USM, 2SERF, 3NRL/SSC, 4COAPS/FSU Transport of NSOW into and within the Irminger Sea: Insights from model Xiaobiao Xu1, William Schmitz Jr.2, Harley E. Hurlburt3, Patrick Hogan3, and Eric P. Chassignet4 1DMS/USM, 2SERF, 3NRL/SSC, 4COAPS/FSU 2ndAMOC annual meeting, June 7-9, 2010, Miami, FL

The area of interest Greenland Iceland *** Long-term transport measurements *** 1. TTO: 5.1 (Dickson and Brown, 1994) 2. ANG: 7.3[4] (Dickson et al., 2008) 3. SECF: 9.0[4.5] (Bacon and Saunders, 2010) 4. SEI: 3.2 (Saunders, 1996) 5. CGFZ: 2.4 (Saunders, 1994)

Flow over the Reykjanes Ridge? Figure 6 of Hansen and Osterhus (2000) Figure 1 of Shor et al. (1980) “Saunders (1994) very detailed flux measurement for the passage through the CGFZ seems to be too small to accommodate all the ISOW and this problem is augmented if his value includes a significant fraction of LDW … There is reason to believe that both the overflow flux measurements from SEI and those in the CGFZ do not cover the total flow… On the other hand, there is no reason to assume that all the overflow from the Iceland–Scotland Gap is transported into the Western Basin …”

Bathymetry of Reykjanes Ridge Bight Fracture zone Bathymetry based on V12.1 of Smith and Sandwell, (1997) with 1min resolution. Red triangles are 3 moorings discussed in Shor et al (1980), in which a westward transport of 2.4 Sv is estimated.

Model configurations HYbrid Coordinate Ocean Model (HYCOM, http://www.hycom.org) Atlantic experiment (20°S-80°N) 0.08° horizontal resolution (eddy-resolving) 32 layers (in 2) in vertical Thermobaric effect included Initialization with zero velocity and T/S from climatology GDEM Climatologically (ERA40) forced 10-year integration, time average of last 5 years is used as the model-based ‘mean’ state

Flow over the ReykRge

Modeled flow over the ReykRge Salinity (OSD from WOD2005) data-based salinity along the center of the Reykjanes Ridge and through the CGFZ Velocity (cm/s) Model-based salinity, normal velocity, and volume transport, over the Reykjanes Ridge (north of CGFZ)

Deep circulation in the Iceland Basin SEI mooring array of Saunders (1996) Transport per unit width (m) below  of 27.85 kg/m3 Red lines are the crest of Björn, Björnsson, and Gardar Drifts, from Saunders (2001)

Southeast of Iceland Fig. 2b Saunders (1996) Model Salinity ISOW LSW MNAW While the (three-layer) structure agrees approximately, the simulated salinity of MNAW (max of ~35.3) is higher than observed (max. of ~35.2); The velocity magnitude and distribution are similar to observation; Transport 3.4Sv (≥27.80) based on model and 3.2Sv by Saunders (1996) Velocity

Charlie-Gibbs Fracture zone I Transport per unit width (m) for water of   27.85 kg/m3. Red dots are eight mooring locations of Saunders (1994)

Charlie-Gibbs Fracture zone II Salinity Observation Model Velocity 2.4Sv for >27.80 2.8Sv based on model

Circulation in the Irminger Sea  ≥27.85 27.80 ≤ <27.85

Where do ISOW join DWBC/DSOW Accumulated transport along a NW-SE section in the IrSea The model-based transports suggest that the crossing, or the confluence of ISOW into DWBC, takes fairly uniformly for layer with 27.85 kg/m3, but in contrast more crossing takes place north of ANG for 27.80<27.85

Across the Irminger Sea SECF array ANG array Salinity Salinity 9.8 [5.7 for ≥27.85] Sv in model 9.0 [4.5] Sv in observation 8.0 [4.8 for ≥27.85] Sv in model 7.3 [4.0] Sv in observation

Velocity profiles of overflow (a) ANG array: data from Dickson et al. (2008, their Figure 19.6) The model reproduces to some extent the bottom-intensification of the overflow plume in deeper slope, but not in the (shallow) continental slope. (b) SECF array: data from Bacon and Saunders (2010, their table 2)

Summary Model results help to clarify some unresolved connections on NSOW transports. Results suggest that about 2 Sv of ISOW could flow into Iriminger Sea over the Reykjanes Ridge north of the CGFZ. This helps to resolve the well-known transport balance issue of observed ISOW through CGFZ and along western boundary of Irminger Sea. The model-based circulations in the Iceland Basin, through the CGFZ, and in the Irminger Sea are compared to available data. The modeled circulations are semi-consistent (with data) in reproducing transports of overflow waters (defined as ≥27.80 and 27.85 kg/m3) with roughly correct S (and T) characteristics. The simulated ISOW through the CGFZ is slightly more saline (denser) than observed, this might influence its spreading pathway west of CGFZ into the Irminger Sea. Although the transport along the western boundary of Irminger Sea compares well to observed (within ~1Sv). The vertical profile of the bottom-intensification over the shallow continental slope is not well represented.