The Gulf Stream (GS) is the northeastward-flowing surface limb of the Atlantic Ocean's meridional overturning circulation (AMOC) "conveyer belt" that flows towards Europe and the Nordic Seas. Changes in the GS position after its separation from the coast at Cape Hatteras, i.e., from 75 degrees W to 50 degrees W, may be key to understanding the AMOC, sea level variability and ecosystem behavior along the east coast of North America. In this study we compare secular change and inter-annual variability (IAV) of the Gulf Stream North Wall (GSNW) position with equator-ward Labrador Current (LC) transport along the southwestern Grand Banks near 52 degrees W using 21 years (1993-2013) of satellite altimeter data. Results at 55 degrees, 60 degrees, and 65 degrees W show a significant southward (negative) secular trend for the GSNW, decreasing to a small but insignificant southward trend at 70 degrees W. IAV of de-trended GSNW position residuals also decreases to the west. The long-term secular trend of annual mean upper layer (200 m) LC transport near 52 degrees W is positive. Furthermore, IAV of LC transport residuals near 52 degrees W along the southwestern Grand Banks are significantly correlated with GSNW position residuals at 55 degrees W at a lag of +1-year, with positive (negative) LC transport residuals corresponding to southward (northward) GSNW positions one year later. The Taylor-Stephens index (TSI) computed from the first principal component of the GSNW position from 79 degrees to 65 degrees W shows a similar relationship with a more distal LC index computed along altimeter ground track 250 located north of the Grand Banks across Hamilton Bank in the western Labrador Sea. Increased (decreased) sea height differences along ground track 250 are significantly correlated with a more southward (northward) TSI two years later (lag of +2-years). Spectral analysis of IAV reveals corresponding spectral peaks at 5-7 years and 2-3 years for the North Atlantic Oscillation (NAO), GSNW (70 degrees - 55 degrees W) and LC transport near 52 degrees W for the 1993-2013 period suggesting a connection between these phenomena. An upper-layer (200 m) slope water volume calculation using the LC IAV rms residual of +1.04 Sv near 52 degrees W results in an estimated GSNW IAV residual of 79 km, or 63% of the observed 125.6 km (1.13 degrees) rms value at 55 degrees W. A similar upper-layer slope water volume calculation using the positive long-term, upper-layer LC transport trend accounts for 68% of the mean observed secular southward shift of the GSNW between 55 degrees and 70 degrees W over the 1993-2013 period. Our work provides additional observational evidence of important interactions between the upper layers of the sub-polar and sub-tropical gyres within the North Atlantic over both secular and inter-annual time scales as suggested by previous studies.
- Secular change and inter-annual variability of the Gulf Stream position, 1993-2013, 70 degrees-55 degrees W
- James J. Bisagni - University of Massachusetts DartmouthAvijit Gangopadhyay - University of Massachusetts DartmouthAlejandra Sanchez-Franks - National Oceanography Centre
- Deep-sea research. Part I, Oceanographic research papers, Vol.125, pp.1-10
- Elsevier
- 10
- English
- NA11NOS0120038 / NOAA [for the implementation of the Mid Atlantic Regional Association Coastal Ocean Observing System (MARACOOS)] 1536851 / Directorate For Geosciences; National Science Foundation (NSF); NSF - Directorate for Geosciences (GEO) 1536586 / Division Of Ocean Sciences; National Science Foundation (NSF); NSF - Directorate for Geosciences (GEO) OCE-0815679; OCE-0535379; OCE-0825418 / NSF; National Science Foundation (NSF) noc010012 / Natural Environment Research Council; UK Research & Innovation (UKRI); Natural Environment Research Council (NERC)
- Journal article
- 9914419412701301