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Hertzberg, J. E., Lund, D. C., Schmittner, A., & Skrivanek, A. L. (2016). Evidence for a biological pump driver of atmospheric CO2 rise during Heinrich Stadial 1. Geophys. Res. Lett., 43(23), 12,242–12,251.
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Hu, A., Meehl, G. A., Han, W., Lu, J., & Strand, W. G. (2013). Energy balance in a warm world without the ocean conveyor belt and sea ice. Geophys. Res. Lett., 40(23), 6242–6246.
Abstract: Under a strong global warming scenario, the global mean temperature could rise up to 10°C, causing the global ocean conveyor belt to collapse and the summer sea ice to disappear. This will lead to profound changes in our climate system and to impact drastically the living conditions of the globe. Here we study how the global heat redistribution and regional heat balance will respond to these changes using the National Center for Atmospheric Research Community Climate System Model version 4. Results show that the collapsed ocean conveyor belt reduces the oceanic northward meridional heat transport (MHT) by nearly 60% with a minor increase in the atmospheric MHT. The polar amplified warming is primarily caused by the increased absorption of longwave radiation due to the increased greenhouse gases and cloudiness and by the increased absorption of shortwave radiation due to a lower albedo associated with the disappeared summer sea ice.
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Johnson, N. T., Martinez, C. J., Kiker, G. A., & Leitman, S. (2013). Pacific and Atlantic sea surface temperature influences on streamflow in the Apalachicola-Chattahoochee-Flint river basin. Journal of Hydrology, 489, 160–179.
Abstract: Large scale climate phenomena can provide valuable information for regional climate and streamflow in many parts of the world. Several climate phenomena may impact a given area and their value for providing information on streamflow is dependent on first establishing the local relationship. This study was conducted to establish the individual and coupled impacts of the El Nino-Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), and Atlantic Multidecadal Oscillation (AMO) on streamflow in the Apalachicola-Chattahoochee-Flint (ACF) river basin. Differences in annual and seasonal streamflow using two unimpaired streamflow datasets based on the phase(s) of ENSO, the PDO, and the AMO were evaluated using the nonparametric rank-sum test. Few statistical differences were found for the individual impacts of ENSO and the PDO on annual and seasonal streamflow; differences based on ENSO were largely confined to the southern portion of the basin. Significant differences in annual streamflow based on the AMO were largely confined to the northern half of the basin. Differences in seasonal streamflow based on the AMO were found for much of the year in the northern portion of the basin but were confined to the winter season in the southern portion. Significant differences in annual and seasonal streamflow were found between the La Nina/positive AMO phase and the El Nino/negative AMO phase, between the positive AMO/negative PDO phase and the negative AMO/negative PDO phase, and there appears to be a modulation of the impacts of La Nina by the phase of the AMO. A greater number of stations and a greater magnitude of significant differences were found for the coupled impacts than for the individual impacts of ENSO, the PDO, and the AMO; indicating the importance of the coupled impacts on regional streamflow when establishing the role of annual, decadal, and multidecadal climate variability.
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Lee, S. - K., Park, W., van Sebille, E., Baringer, M. O., Wang, C., Enfield, D. B., et al. (2011). What caused the significant increase in Atlantic Ocean heat content since the mid-20th century? Geophys. Res. Lett., 38(17).
Abstract: As the upper layer of the world ocean warms gradually during the 20th century, the inter-ocean heat transport from the Indian to Atlantic basin should be enhanced, and the Atlantic Ocean should therefore gain extra heat due to the increased upper ocean temperature of the inflow via the Agulhas leakage. Consistent with this hypothesis, instrumental records indicate that the Atlantic Ocean has warmed substantially more than any other ocean basin since the mid-20th century. A surface-forced global ocean-ice coupled model is used to test this hypothesis and to find that the observed warming trend of the Atlantic Ocean since the 1950s is largely due to an increase in the inter-ocean heat transport from the Indian Ocean. Further analysis reveals that the increased inter-ocean heat transport is not only caused by the increased upper ocean temperature of the inflow but also, and more strongly, by the increased Agulhas Current leakage, which is augmented by the strengthening of the wind stress curl over the South Atlantic and Indian subtropical gyre.
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Liu, Y., & Minnett, P. J. (2015). Evidence linking satellite-derived sea-surface temperature signals to changes in the Atlantic meridional overturning circulation. Remote Sensing of Environment, 169, 150–162.
Abstract: This study explores an application of satellite-derived Sea Surface Temperature (SST) to climate studies by focusing on a connection with the Atlantic Meridional Overturning Circulation (AMOC). Here we focus on SSTs from the advanced very high resolution radiometer and report a 99% significant correlation between the changes of in situ measured AMOC transport and the variation of 1-month leading SST anomalies in the subpolar North Atlantic region (45 degrees N-70 degrees N) based on analyses of an 85-month period. The leading mode of the singular value decomposition analysis of SST and Sea Level Pressure (SLP) for 31 years (1981/12-2012/12) shows an apparent North Atlantic Oscillation (NAO) forcing on the SST fields. Specifically, the 551 and SLP one-month phase lag covariance is notable at temporal scales of 4 to 11 months. After removing the first order component of the NAO, the residual SST (RESST) provides better estimates of the AMOC on a shorter time scale than the SST. This is because that RESST is less likely to be affected by the local SLP on these time scales. The high correlation is primarily between the RESST and variations of the geostrophic Upper Mid-Ocean transport component of the AMOC. The 31-year RESST time series in the North Atlantic subpolar region is also significantly correlated with the Gulf Stream path SST anomalies with a one-month lead, implying a fast signal transport from the subpolar North Atlantic to the Gulf Stream. A similar fast adjustment signal is also found in 500-year control simulations of the GFDL model CM2.1. These results indicate a prospective capability of satellite-derived SSTs to predict AMOC variability.
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Lopez, H., Goni, G., & Dong, S. (2017). A reconstructed South Atlantic Meridional Overturning Circulation time series since 1870. Geophys. Res. Lett., 44(7), 3309–3318.
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Maleski, J. J., & Martinez, C. J. (2018). Coupled impacts of ENSO AMO and PDO on temperature and precipitation in the Alabama-Coosa-Tallapoosa and Apalachicola-Chattahoochee-Flint river basins. Int. J. Climatol, 38, e717–e728.
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Misra, V., Selman, C., Waite, A. J., Bastola, S., & Mishra, A. (2017). Terrestrial and ocean climate of the 20th century. In E. P. Chassignet, J. W. Jones, V. Misra, & J. Obeysekera (Eds.), Florida's climate: Changes, variations, & impacts (pp. 485–509). Gainesville, FL: Florida Climate Institute.
Abstract: The Florida peninsula, with its close proximity to the equator surrounded by robust surface and deep water ocean currents, has a unique climate. Generally, its climate is mild with variations on numerous time scales, punctuated by periodic extreme weather events. In this chapter, we review the mechanisms by which some well-known natural variations impact the regional climate and modulate the occurrence of extreme weather over Florida and its neighboring oceans. In addition, we explore the role of land cover and land use changes on the regional climate over the same area. It is made apparent from the review that remote variations of climate have an equally important impact on the regional climate of Florida as the local changes to land cover and land use.
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Morey, S., Koch, M., Liu, Y., & Lee, S. - K. (2017). Florida's oceans and marine habitats in a changing climate. In E. P. Chassignet, J. W. Jones, V. Misra, & J. Obeysekera (Eds.), Florida's climate: Changes, variations, & impacts (pp. 391–425). Gainesville, FL: Florida Climate Institute.
Abstract: Florida’s peninsula extending ~700 km north-to-south, extensive shoreline (2,100 km), and broad carbonate platform create a diversity of marine habitats (estuaries, lagoons, bays, beach, reef, shelf, pelagic) along the coast, shelf, and deep ocean that are influenced by continental, oceanographic, and atmospheric processes all predicted to shift with a rapidly changing climate. Future changes of the global ocean circulation could result in a 25% reduction in the Atlantic Meridional Overturning Circulation (AMOC), leading to a subsequent slowing of Florida’s regional/local current systems (Yucatan, Loop, Florida and Gulf Stream) and eddies. While downscaled climate models suggest that slowing of the Loop Current by 20-25% during the 21st century will moderate the increase in surface temperatures in the Gulf of Mexico to 1.4oC - 2.8oC, this warming is predicted to have wide-ranging consequences for Florida’s marine habitats (e.g., enhanced coral bleaching, lower O2 in surface waters, increased harmful algal blooms, reduced phytoplankton and fisheries production, and lower sea turtle reproduction). The reduction in the AMOC is also predicted to reduce hurricane frequency, albeit with increased intensity (2-11%) due to ocean warming. Climate projections affecting Florida’s oceans include rises in sea level, changes in coastal circulation impacting larval and nutrient transport, changes in marine biogeochemistry including ocean acidification, and loss of coastal wetlands that protect Florida’s coastline. Understanding the consequences of these projected climate impacts and gaining a more complete understanding of complex changes in atmospheric processes (e.g., ENSO, AMO, convection, wind shear), air-sea interaction, currents, and stratification under a changing climate is critical over the next few decades to prepare and protect the state of Florida.
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Shinoda, T., Han, W., Zamudio, L., Lien, R. - C., & Katsumata, M. (2017). Remote Ocean Response to the Madden-Julian Oscillation during the DYNAMO Field Campaign: Impact on Somali Current System and the Seychelles-Chagos Thermocline Ridge. Atmosphere, 8(9), 171.
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Smeed, D. A., Josey, S. A., Beaulieu, C., Johns, W. E., Moat, B. I., Frajka-Williams, E., et al. (2018). The North Atlantic Ocean Is in a State of Reduced Overturning. Geophys. Res. Lett., 45(3), 1527–1533.
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Teegavarapu, R. S. V., & Nayak, A. (2017). Evaluation of long-term trends in extreme precipitation: Implications of in-filled historical data use for analysis. Journal of Hydrology, 550, 616–634.
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Teegavarapu, R. S. V., Goly, A., & Obeysekera, J. (2013). Influences of Atlantic multidecadal oscillation phases on spatial and temporal variability of regional precipitation extremes. Journal of Hydrology, 495, 74–93.
Abstract: A major teleconnection, Atlantic multidecadal oscillation (AMO) under two phases (cool and warm) influencing precipitation extremes in Florida, USA, is the main focus of this study. Long-term extreme precipitation data from several rain gages from temporal windows that coincide with the AMO phases are evaluated for changes in spatial and temporal variability across the region. Assessments of precipitation extremes for nine durations in different meteorologically homogenous rainfall areas as well as in the entire region are carried out. Methods of assessment included parametric unpaired t-tests and nonparametric Mann�Whitney U tests, kernel density estimates using Gaussian kernel for distribution-free comparative analysis and bootstrap sampling-based confidence intervals. Depth-duration-frequency (DDF) curves are also developed using generalized extreme value (GEV) distributions characterizing the extremes. Analysis of data indicated increase in precipitation extremes in warm phases of AMO for durations greater than 24 h. The influence of warm or cool phases of AMO on precipitation extremes is not spatially uniform in the region. Temporal shifts in occurrences of extremes from the later part of the year in warm phase to earlier in the year for the cool phase are evident. These shifts will have implications on flooding events in different regions of Florida. Magnitudes of extremes for a 25 year return period based on DDF curves were higher for all nine durations when data from cool or warm phase alone were compared to those obtained from data from two phases. Precipitation extremes for durations longer than a day are associated with increased landfalls of hurricanes occurring in the region in the AMO warm phases.
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Xu, X., Chassignet, E. P., Johns, W. E., Schmitz Jr, W. J., & Metzger, E. J. (2014). Intraseasonal to interannual variability of the Atlantic meridional overturning circulation from eddy-resolving simulations and observations. J. Geophys. Res. Oceans, 119(8), 5140–5159.
Abstract: Results from two 1/12° eddy-resolving simulations, together with data-based transport estimates at 26.5°N and 41°N, are used to investigate the temporal variability of the Atlantic meridional overturning circulation (AMOC) during 2004–2012. There is a good agreement between the model and the observation for all components of the AMOC at 26.5°N, whereas the agreement at 41°N is primarily due to the Ekman transport. We found that (1) both observations and model results exhibit higher AMOC variability on seasonal and shorter time scales than on interannual and longer time scales; (2) on intraseasonal and interannual time scales, the AMOC variability is often coherent over a wide latitudinal range, but lacks an overall consistent coherent pattern over the entire North Atlantic; and (3) on seasonal time scales, the AMOC variability exhibits two distinct coherent regimes north and south of 20°N, due to different wind stress variability in the tropics and subtropics. The high AMOC variability south of 20°N in the tropical Atlantic comes primarily from the Ekman transport of the near-surface water, and is modulated to some extent by the transport of the Antarctic Intermediate water below the thermocline. These results highlight the importance of the surface wind in driving the AMOC variability.
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Xu, X., Chassignet, E. P., & Wang, F. (2019). On the variability of the Atlantic meridional overturning circulation transports in coupled CMIP5 simulations. Clim Dyn, 52(11), 6511–6531.
Abstract: The Atlantic meridional overturning circulation (AMOC) plays a fundamental role in the climate system, and long-term climate simulations are used to understand the AMOC variability and to assess its impact. This study examines the basic characteristics of the AMOC variability in 44 CMIP5 (Phase 5 of the Coupled Model Inter-comparison Project) simulations, using the 18 atmospherically-forced CORE-II (Phase 2 of the Coordinated Ocean-ice Reference Experiment) simulations as a reference. The analysis shows that on interannual and decadal timescales, the AMOC variability in the CMIP5 exhibits a similar magnitude and meridional coherence as in the CORE-II simulations, indicating that the modeled atmospheric variability responsible for AMOC variability in the CMIP5 is in reasonable agreement with the CORE-II forcing. On multidecadal timescales, however, the AMOC variability is weaker by a factor of more than 2 and meridionally less coherent in the CMIP5 than in the CORE-II simulations. The CMIP5 simulations also exhibit a weaker long-term atmospheric variability in the North Atlantic Oscillation (NAO). However, one cannot fully attribute the weaker AMOC variability to the weaker variability in NAO because, unlike the CORE-II simulations, the CMIP5 simulations do not exhibit a robust NAO-AMOC linkage. While the variability of the wintertime heat flux and mixed layer depth in the western subpolar North Atlantic is strongly linked to the AMOC variability, the NAO variability is not.
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