Year‐Round Measurements of the Irminger Current: Variability of a Two‐Core Current System Observed in 2014–2016

• Published in: Journal of geophysical research. Oceans Vol. 125; no. 10
• Main Authors: Jong, M. F., Steur, L., Fried, N., Bol, R., Kritsotalakis, S.
• Format: Journal Article
• Language: English
• Published: 01.10.2020
• Subjects: AMOC; convection; Irminger Current; North Atlantic; observations; transport array
• ISSN: 2169-9275; 2169-9291
• DOI: 10.1029/2020JC016193

The Irminger Current (IC), flowing northeastward along the western flank of the Reykjanes Ridge, is an important component in the overturning of the North Atlantic subpolar gyre. A 2‐year (2014–2016) time series from moored observations shows that the IC consists of two highly variable current cores. A subsampling experiment, using an ocean reanalysis, showed that this current's variability is adequately captured by the array. The two current cores contribute nearly equally to the mean volume transport. The total 2‐year mean transport was found to be 10.6 Sv with a standard deviation of daily (monthly) values of 9.2 Sv (4.4 Sv) and a standard error of 1.4 Sv. Mean heat and freshwater transport were 0.21 PW and −22.5 mSv, respectively (Sref = 34.92). The volume transport is strongest in spring, and the average over the first year (8.6 Sv) was lower than that of the second year (12.4 Sv), coinciding with an increase in the density gradient over the array in the second year. The variability of the total transport is dominated by variations in the western core, while the warmer, saltier eastern core contributes more to the heat and (negative) freshwater transport. During the two observed winters, which were marked by exceptional deep convection in the central Irminger Sea, mixed layer deepening down to 400 m depth and outcropping of the 27.7 kg m3 isopycnal were observed within the IC. Plain Language Summary The Irminger Current flows northeastward along the Reykjanes Ridge in the Irminger Sea. It transports warm saline water originating from the North Atlantic Current in the upper layers and deep waters coming from the overflows on the Iceland‐Scotland Ridge. This paper describes the first year‐round moored observations of velocity, temperature, and salinity of this current system. These new observations show that the Irminger Current consists of two cores that contribute equally to the mean transport. The core closer to the top of the ridge is more stable and transports warmer, more saline water, while the core closer to the center of the Irminger Basin is more variable in location and transport. During the observed winters, strong atmospheric cooling created deep mixed layers down to 400 m at the mooring locations. This observed cooling and densification of the upper ocean waters indicate that this current system is an important contributor to the overturning in the Northeastern Atlantic. Key Points First year‐round observations of the two‐core Irminger Current over the Reykjanes Ridge show a mean transport of 10.6 ± 1.4 Sv (st error) IC transports are highly variable with a std of 9.2 Sv (daily values) and 4.4 Sv (monthly values); the western core is the most variable Mixing to densities near 27.7 kg m−3 occurred over the array in both winters (deepest in the west), contributing to the overturning