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1. On the Role of the Gulf Stream in the Changing Atlantic Nutrient Circulation During the 21st Century

   https://doi.org/10.1002/9781119428428.ch4  

   Whitt, Daniel B (April 2019, Geophysical monograph)

   Takeyoshi Nagai, Hiroaki Saito (Ed.)

   The Gulf Stream transports macronutrients poleward as a part of the Atlantic meridional overturning circulation (AMOC). Scaling shows that this advective transport is greater than diapycnal transport from deep convection in the North Atlantic and is therefore crucial for sustaining the nutrient supply to the subpolar North Atlantic on interannual timescales. Simulations of the RCP8.5 emissions scenario with the Community Earth System Model (CESM) reveal 25% declines in the Gulf Stream volume transport above the potential density surface σθ = 27.5 kg/m3 and 35% declines in the associated nitrate transport between 2006 and 2080. The declining Gulf Stream transport largely explains contemporaneous 40% declines in zonally‐integrated volume and nitrate transports in the subtropical part of the AMOC. In addition, scaling suggests that the declining Gulf Stream nitrate transport (2.4 kmol/s per year) is the dominant driver of the declining export of particulate organic nitrogen across σθ = 27.5 kg/m3 in the subpolar North Atlantic (0.57 kmol/s per year), because the declining nitrate entrainment from water with σθ > 27.5 kg/m3 is only 0.44 kmol/s per year. A review of various small‐scale ocean physical processes suggests that the projected decline in the Gulf Stream nutrient flux is qualitatively robust to uncertainties associated with ocean physics. 

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2. Reduction in Ocean Heat Transport at 26°N since 2008 Cools the Eastern Subpolar Gyre of the North Atlantic Ocean

   https://doi.org/10.1175/JCLI-D-19-0323.1  

   Bryden, Harry L.; Johns, William E.; King, Brian A.; McCarthy, Gerard; McDonagh, Elaine L.; Moat, Ben I.; Smeed, David A. (March 2020, Journal of Climate)

   Abstract Northward ocean heat transport at 26°N in the Atlantic Ocean has been measured since 2004. The ocean heat transport is large—approximately 1.25 PW, and on interannual time scales it exhibits surprisingly large temporal variability. There has been a long-term reduction in ocean heat transport of 0.17 PW from 1.32 PW before 2009 to 1.15 PW after 2009 (2009–16) on an annual average basis associated with a 2.5-Sv (1 Sv ≡ 106 m3 s−1) drop in the Atlantic meridional overturning circulation (AMOC). The reduction in the AMOC has cooled and freshened the upper ocean north of 26°N over an area following the offshore edge of the Gulf Stream/North Atlantic Current from the Bahamas to Iceland. Cooling peaks south of Iceland where surface temperatures are as much as 2°C cooler in 2016 than they were in 2008. Heat uptake by the atmosphere appears to have been affected particularly along the path of the North Atlantic Current. For the reduction in ocean heat transport, changes in ocean heat content account for about one-quarter of the long-term reduction in ocean heat transport while reduced heat uptake by the atmosphere appears to account for the remainder of the change in ocean heat transport. 

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3. Observed decline of the Atlantic meridional overturning circulation 2004–2012

   https://doi.org/10.5194/os-10-29-2014  

   Smeed, D. A.; McCarthy, G. D.; Cunningham, S. A.; Frajka-Williams, E.; Rayner, D.; Johns, W. E.; Meinen, C. S.; Baringer, M. O.; Moat, B. I.; Duchez, A.; et al (January 2014, Ocean Science)

   null (Ed.)

   Abstract. The Atlantic meridional overturning circulation (AMOC) has been observed continuously at 26° N since April 2004. The AMOC and its component parts are monitored by combining a transatlantic array of moored instruments with submarine-cable-based measurements of the Gulf Stream and satellite derived Ekman transport. The time series has recently been extended to October 2012 and the results show a downward trend since 2004. From April 2008 to March 2012, the AMOC was an average of 2.7 Sv (1 Sv = 106 m3 s−1) weaker than in the first four years of observation (95% confidence that the reduction is 0.3 Sv or more). Ekman transport reduced by about 0.2 Sv and the Gulf Stream by 0.5 Sv but most of the change (2.0 Sv) is due to the mid-ocean geostrophic flow. The change of the mid-ocean geostrophic flow represents a strengthening of the southward flow above the thermocline. The increased southward flow of warm waters is balanced by a decrease in the southward flow of lower North Atlantic deep water below 3000 m. The transport of lower North Atlantic deep water slowed by 7% per year (95% confidence that the rate of slowing is greater than 2.5% per year). 

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4. The Impact of AMOC SST Fingerprints on Tropical Storm Risk Along the U.S. East & Gulf Coasts and Latin America

   https://doi.org/10.22541/essoar.175883392.28753009/v1  

   Karnauskas, Kristopher B; Kramer, Sydney M; Donnelly, Jeffrey P (September 2025, ESS Open Archive)

   Tropical storms pose a significant risk to coastal populations, including those throughout the Caribbean and along the Atlantic and Gulf coasts of North America. The impact of climate change on tropical storms is multifaceted, and patterns of sea surface temperature (SST) change may play a role in shaping future tropical storm risk. While the SST fingerprints associated with changes in the Atlantic Meridional Overturning Circulation (AMOC) may be uncertain, the North Atlantic Warming Hole (NAWH) and enhanced SST warming near the Gulf Stream are robust features of both past and projected future climate change. Here we use the Community Earth System Model version 2 (CESM2) to highlight the remote contributions of both of these potential SST fingerprints of AMOC decline to changes in tropical cyclone (TC) genesis potential in the Atlantic basin, and thus to uncertainty in future coastal climate risk. Both the NAWH and enhanced warming near the Gulf Stream lead to significant changes in TC genesis potential, particularly in the western North Atlantic (between Bermuda and the Bahamas), the northeastern Gulf of Mexico and the Caribbean Sea, where changes are on the order of ±10% over the full Atlantic hurricane season, with considerably stronger responses focused in the two halves of the season. Diagnosis of the Genesis Potential Index (GPI) indicates that changes in mid-tropospheric humidity and vertical wind shear are the most important factors driving these responses. The simulated changes in GPI occur in regions of considerable historical TC genesis, highlighting the need to further understand the historical and projected future patterns of SST change in the North Atlantic Ocean, including their relationship to AMOC and its potential decline. 

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5. Diatom hotspots driven by western boundary current instability.

   Oliver, H. (April 2021, Geophysical research letters)

   null (Ed.)

   Climatic changes have decreased the stability of the Gulf Stream (GS), increasing the frequency at which its meanders interact with the Mid-Atlantic Bight (MAB) continental shelf and slope region. These intrusions are thought to suppress biological productivity by transporting low-nutrient water to the otherwise productive shelf edge region. Here we present evidence of widespread, anomalously intense subsurface diatom hotspots in the MAB slope sea that likely resulted from a GS intrusion in July 2019. The hotspots (at ∼50 m) were associated with water mass properties characteristic of GS water (∼100 m); it is probable that the hotspots resulted from the upwelling of GS water during its transport into the slope sea, likely by a GS meander directly intruding onto the continental slope east of where the hotspots were observed. Further work is required to unravel how increasingly frequent direct GS intrusions could influence MAB marine ecosystems. 

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