Decadal Variability Of The Gulf Stream North Wall Position And Its
Connection To Ocean Heat Content
Abstract
To trace the Gulf Stream (GS) path across five decades from 1965 to
2017, we mapped the annually averaged positions of the Gulf Stream North
Wall (GSNW) defined by the 15°C isotherm at 200 m depth computed using
in situ seawater temperature records from the World Ocean Database 2018
(WOD18). Inter-annual GSNW variability is noticeably different west and
east of ~50°W. There are two distinct variability zones
west and east of that longitude—a zone with a rather narrow envelope
(~3° of latitude-wide) west and a zone with a twice as
wide envelope (~ 6° of latitude-wide) east of that
longitude. The more disperse annual pathways are near the Mid-Latitude
Transition Zone. Moreover, within the ~50-year timeline,
the quasi-decadal period of 2005–2017 is marked by far larger spread in
the annual GSNW positions than the previous decades, especially between
50°W and 40°W. The principal conclusion of our analysis, is that the GS
between Cape Hatteras and the Grand Banks (west of 50°W) is not only
stiff but maintains its position with astounding resiliency. The GSNW
average position along that stretch of longitudes migrates slowly
northward as a whole, but it is unlikely that such a slow and spatially
insignificant migration could cause substantial changes in the Atlantic
Meridional Overturning Circulation (AMOC). In contrast, near the Grand
Banks (east of 50°W), the GSNW northward shift is quite
noticeable—over 2.6° in latitude over ~50 years—and
thus could have some impacts on the AMOC long-term dynamics. There are
significant correlations between the GSNW and Ocean Heat Content (OHC)
variability east of 50°W that may be critical for the GS path resilience
and its future changes over decadal and longer time scales. Furthermore,
the significant correlations between OHC and GSNW in the extension zone
rose from r=0.5 for annual to r=0.8 for pentadal to r=0.9 decadal time
scales. We assert that the OHC may become the best indicator of the GS
path’s variability on decadal and longer time scales.