Ocean processes in the Southwest North Atlantic (SWNA) play an important role in long-term earth and ocean climate change. This region is also a resource-rich coastal zone with abundant fisheries and other material assets. Combined, the previously released NCEI Northwest Atlantic (NWA) regional climatology (RC) and newly developed SWNA RC provide complete coverage of the Gulf Stream system, which is the critical element of northward heat transport and the Atlantic Meridional Overturning Circulation. The SWNA RC is a collection of high-resolution quality-controlled temperature and salinity fields on standard depth levels from the sea surface to 4,900 m depth. This RC is based on temperature and salinity observations from the 2018 release of the World Ocean Database. The coverage includes the years 1955 to 2017 by annual, seasonal, and monthly fields for the entire period, as well as for each of the six decades. All fields computed on three horizontal grids: 1°x1°, 1/4°x1/4°, and 1/10°x1/10° degree. The SWNA RC is instrumental for assessing ocean climate changes in this region of the North Atlantic Ocean over the 1955-2017 time period and can be used in various climate studies, environmental research projects, and related applications.

Ocean heat analyses of the North Atlantic Ocean based on the new high-resolution Northwest Atlantic (NWA) Regional Climatology (RC) developed at the NOAA’s National Centers for Environmental Information (NCEI) revealed decadal variability of the Eighteen Degree Water (EDW) depth that may be instrumental for understanding the localized heat accumulation in the NWA. The EDW is an important element of the Northwest Atlantic heat balance and an indicator of the ocean-atmosphere interaction in this region. The EDW deepening, or “heaving”, on decadal timescales are most likely caused by increasing Ekman pumping due to changes in the wind stress curl pattern over the NWA. The NCEI’s NWARC has also revealed that the highest rates of heat gain occur in the Sargasso Sea, southeast of the Gulf Stream path in the region occupied by the EDW. The volume of EDW depends on many factors, of which the most important are: Ekman pumping, heat fluxes at the air-sea surface, and heat advection within the Gulf Stream and the subtropical recirculation gyre. However, heat accumulation in several “pockets” southeast of the Gulf Stream and its extension seem to be most closely connected to EDW heaving. The depths of EDW for two independent ~30-year periods and their differences were computed and analyzed in conjunction with the changes in the curl of wind stress. As the comparison between the EDW depths mapped on three different spatial grids with 1°x1°, 1/4°x1/4°, and 1/10°x1/10° resolutions illustrate, the grid resolution does matter for mapping EDW on decadal timescales. The 30-year climate shift of the EDW depths between 1985-2010 and 1955-1984 compares quite well with the climatic shift in Ekman vertical velocities derived from the changes in the wind stress curl over the same time period. Comparing the eddy-permitting EDW heaving inferred from the NCEI’s NWARC and the ~30-year shift of the curl of wind stress, and consequently Ekman pumping, confirms a strong resemblance of the eddy-permitting and eddy-resolving EDW heaving patterns with two tightly localized pockets of heat accumulation southeast of the Gulf Stream and its extension.

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.