Search for: All records

Abstract This study presents the first continuous observations of Iceland Scotland Overflow Water (ISOW) passing through the Bight Fracture Zone (BFZ), the northernmost deep bathymetric channel across the Reykjanes Ridge between the Iceland and Irminger Basins in the subpolar North Atlantic. Data from two 2‐year moorings, measuring temperature, salinity, and current velocity from 2015 to 2017, along with a set of deep ISOW‐embedded RAFOS floats, are used to investigate ISOW transport and water property variability through the BFZ, as well as advective pathways between the Iceland and Irminger Basins. The mooring‐derived record‐mean ISOW transport through the BFZ was −0.59 ± 0.27 × 1e6 m³/s (westward) and varied seasonally with weaker transport in winter and stronger transport in summer. Flow direction of ISOW through the BFZ was consistently westward except in winter, when week‐long flow reversals were frequently observed. The previously reported subpolar North Atlantic freshening event of the 2010s is evident in the BFZ mooring records beginning about January 2017. About one‐quarter of floats deployed in ISOW at 1800‐m depth upstream in the Iceland Basin show a direct advective pathway into the BFZ that appears to be primarily determined by bathymetry. Another quarter of the floats crossed over the ridge to the Irminger Sea through other gaps prior to reaching the Charlie‐Gibbs Fracture Zone. 

Abstract Understanding the variability of the Atlantic Meridional Overturning Circulation is essential for better predictions of our changing climate. Here we present an updated time series (August 2014 to June 2020) from the Overturning in the Subpolar North Atlantic Program. The 6-year time series allows us to observe the seasonality of the subpolar overturning and meridional heat and freshwater transports. The overturning peaks in late spring and reaches a minimum in early winter, with a peak-to-trough range of 9.0 Sv. The overturning seasonal timing can be explained by winter transformation and the export of dense water, modulated by a seasonally varying Ekman transport. Furthermore, over 55% of the total meridional freshwater transport variability can be explained by its seasonality, largely owing to overturning dynamics. Our results provide the first observational analysis of seasonality in the subpolar North Atlantic overturning and highlight its important contribution to the total overturning variability observed to date. 

Two 2-year moorings were placed in the Bight Fracture Zone (BFZ), one in the north channel and one in the south channel, between July 2015 to July 2017. Each mooring was instrumented at four depths with a pair of instruments comprised of an SBE MicroCAT and a Nobska MAVS-4 Acoustic Current Meter. The four pairs of instruments were placed at 1500, 1750, 2000 meters depth and 22 meters above the bottom of the channel (2440 meters depth in the north channel and 2115 meters depth in the south channel). The initial processing for both the MicroCAT and MAVS-4 consisted of removing data collected while out of water, replacing data outliers with NaNs, and correcting drifts in the data. In addition, the MAVS-4 data were transformed from instrument coordinates to earth coordinates and magnetic declination was correction was applied.