An official website of the United States government
Abstract This study of the first continuous multiyear observations of the East Reykjanes Ridge Current (ERRC) reveals a highly variable, mostly barotropic southwestward flow with a mean transport of 10–13 Sv. The ERRC effectively acts as a western boundary current in the Iceland Basin on the eastern flank of the Reykjanes Ridge. As part of the Overturning in the Subpolar North Atlantic Program (OSNAP), continuous measurements of the ERRC have been maintained for the first time using acoustic Doppler current profilers, current meters, and dynamic height moorings at six mooring sites near 58°N since 2014. Together with satellite altimetry and Argo profile and drift data, the mean transport, synoptic variability, water mass properties, and upstream and downstream pathways of the ERRC are examined. Results show that the ERRC forms in the northeastern Iceland Basin at the convergence of surface waters from the North Atlantic Current and deeper Icelandic Slope Water formed along the Iceland‐Faroe Ridge. The ERRC becomes denser as it cools and freshens along the northern and western topography of the Basin before retroflecting over the Reykjanes Ridge near 59°N into the Irminger Current. Analysis of the flow‐weighted density changes along the ERRC's path reveals that it is responsible for about one third of the net potential density change of waters circulating around the rim of the subpolar gyre.
more »
« less
Directly Measured Currents and Estimated Transport Pathways of Atlantic Water between 59.5oN and the Iceland-Faroes-Scotland Ridge
Using vessel-mounted acoustic Doppler current profiler data from four different routes between Scotland, Iceland and Greenland, we map out the mean flow of water in the top 400 m of the northeastern North Atlantic. The poleward transport east of the Reykjanes Ridge (RR) decreases from 8.5 to 10 Sv (1 Sverdrup 106 m3 s1) at 59.58N to 618N to 6 Sv crossing the IcelandFaroesScotland Ridge. The two longest 1200 km transport integrals have 1.40.94 Sv uncertainty, respectively. The overall decrease in transport can in large measure be accounted for by a 1.5 Sv flow across the RR into the Irminger Sea north of 59.58N and by a 0.5 Sv overflow of dense water along the IcelandFaroes Ridge. A remaining 0.5 Sv flux divergence is at the edge of detectability, but if real could be accounted for through wintertime convection to 400 m and densification of upper ocean water. The topography of the Iceland Basin and the banks west of Scotland play a fundamental role in controlling flow pathways towards and past Iceland, the Faroes and Scotland. Most water flows north unimpeded through the Iceland Basin, some in the centre of the basin along the Maury Channel, and some along Hatton Bank, turning east along the northern slopes of George Bligh Bank, Lousy Bank and Bill Bailey’s Bank, whereupon the flow splits with 3 Sv turning northwest towards the IcelandFaroes Ridge and the remainder continuing east towards and north of the Wyville-Thomson Ridge (WTR) to the Scotland slope thereby increasing the Slope Current transport from 1.5 Sv south of the WTR to 3.5 Sv in the FaroesShetland Channel
more »
« less
- Award ID(s):
- 1658364
- PAR ID:
- 10101460
- Date Published:
- Journal Name:
- Tellus. Series A, Dynamic meteorology and oceanography
- Volume:
- 67
- ISSN:
- 1600-0870
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
The densest overflow water from the Nordic Seas passes through the Faroe Bank Channel and contributes to the headwaters to the lower limb of the Atlantic Meridional Overturning Circulation. The upstream pathways of this dense overflow water are not well known. Using data from a high-resolution hydrographic/velocity survey in 2011, as well as long-term moored velocity and shipboard hydrographic measurements north of the Faroe Islands, we present evidence of a current following the continental slope from Iceland toward the Faroe Bank Channel. This narrow current, which we call the Iceland-Faroe Slope Jet (IFSJ), is bottom-intensified and associated with dense water banked up on the slope. North of the Faroe Islands the IFSJ is situated beneath the Faroe Current, and its variability is tightly linked to the flow of Atlantic Water above. The bulk of the IFSJ’s volume transport is confined to a small area in ϴ-S space centered near a potential density anomaly of 28.06 kg m-3. This is slightly denser than the transport mode of the North Icelandic Jet, which follows shallower isobaths along the slope north of Iceland in the opposite direction and feeds the Denmark Strait overflow. However, the similarity of the hydrographic properties suggests that the two currents have a common source. The average transport of water denser than σϴ = 27.8 kg m-3 in the IFSJ is on the order of 1 Sv, which may account for roughly 50% of the overflow through the Faroe Bank Channel.more » « less
-
Abstract The Iceland Scotland Overflow Water (ISOW) plume supplies approximately a third of the production of North Atlantic Deep Water and is a key component of the meridional overturning circulation (MOC). The Overturning in the Subpolar North Atlantic Program (OSNAP) mooring array in the Iceland Basin has provided high‐resolution observations of ISOW from 2014 to 2020. The ISOW plume forms a deep western boundary current along the eastern flank of Reykjanes Ridge, and its total transport varies by greater than a factor of two on intra‐seasonal timescales. EOF analysis of moored current meter records reveal two dominant modes of velocity variance. The first mode explains roughly 20% of the variance and shows a bottom intensified structure concentrated in the rift valley that runs parallel to the ridge axis. The transport anomaly reconstructed from the first mode explains nearly 80% of the total ISOW plume transport variance. The second mode accounts for 15% of velocity variance, but only 5% of the transport variance. The geostrophically estimated transport (2.9 Sv) recovers only 70% of the total ISOW transport along the ridge flank estimated from the direct current meter observations (4.2 Sv), implying a significant ageostrophic component of ISOW mean transport and variability. Ageostrophic flow is strongly linked to the leading mode of velocity variability within the rift valley. The ISOW transport variability along the upper and middle part of the ridge is further shown to correlate with changes in the strength of deep MOC limb across the basin‐wide OSNAP array.more » « less
-
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.more » « less
-
The North Icelandic Jet (NIJ) is an important source of dense water to the overflow plume passing through Denmark Strait. The properties, structure, and transport of the NIJ are investigated for the first time along its entire pathway following the continental slope north of Iceland, using 13 hydrographic/velocity surveys of high spatial resolution conducted between 2004 and 2018. The comprehensive dataset reveals that the current originates northeast of Iceland and increases in volume transport by roughly 0.4 Sv (1 Sv ≡ 10 6 m 3 s −1 ) per 100 km until 300 km upstream of Denmark Strait, at which point the highest transport is reached. The bulk of the NIJ transport is confined to a small area in Θ– S space centered near −0.29° ± 0.16°C in Conservative Temperature and 35.075 ± 0.006 g kg −1 in Absolute Salinity. While the hydrographic properties of this transport mode are not significantly modified along the NIJ’s pathway, the transport estimates vary considerably between and within the surveys. Neither a clear seasonal signal nor a consistent link to atmospheric forcing was found, but barotropic and/or baroclinic instability is likely active in the current. The NIJ displays a double-core structure in roughly 50% of the occupations, with the two cores centered at the 600- and 800-m isobaths, respectively. The transport of overflow water 300 km upstream of Denmark Strait exceeds 1.8 ± 0.3 Sv, which is substantially larger than estimates from a year-long mooring array and hydrographic/velocity surveys closer to the strait, where the NIJ merges with the separated East Greenland Current. This implies a more substantial contribution of the NIJ to the Denmark Strait overflow plume than previously envisaged.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- The DOI is not currently available.
