Abstract
Past changes in the density and momentum structure of oceanic circulation are an important aspect of changes in the Atlantic Meridional Overturning Circulation and consequently climate. However, very little is known about past changes in the vertical density structure of the ocean, even very extensively studied systems such as the North Atlantic. Here we exploit the physical controls on the settling depth of the dense Mediterranean water plume derived from the Strait of Gibraltar to obtain the first robust, observations-based, probabilistic reconstruction of the vertical density gradient in the eastern North Atlantic during the last 30,000 years. We find that this gradient was weakened by more than 50%, relative to the present, during the last Glacial Maximum, and that changes in general are associated with reductions in AMOC intensity. However, we find only a small change during Heinrich Event 1 relative to the Last Glacial Maximum, despite strong evidence that overturning was substantially altered. This implies that millennial-scale changes may not be reflected in vertical density structure of the ocean, which may be limited to responses on an ocean-overturning timescale or longer. Regardless, our novel reconstruction of Atlantic density structure can be used as the basis for a dynamical measure for validation of model-based AMOC reconstructions. In addition, our general approach is transferrable to other marginal sea outflow plumes, to provide estimates of oceanic vertical density gradients in other locations.
Similar content being viewed by others
References
Alves M, Gaillard F, Sparrow M, Knoll M, Giraud S (2002) Circulation patterns and transport of the Azores front-current system. Deep-Sea Res II 49:3983–4002
Armi L, Farmer DM (1988) The flow of Mediterranean water through the Strait of Gibraltar. Prog Oceanogr 21:1–105
Bryden HL, Kinder T (1991) Steady two-layer exchange through the Strait of Gibraltar. Deep-Sea Res 38:S445–S463
Bryden HL, Brady EC, Pillsbury RD (1988) Flow through the strait of Gibraltar. In: Almazan JL, Bryden HL, Kinder T, Parilla G (eds) Seminario sobre la Oceanografia fisica del Estrecho de Gibraltar. SECEG, Madrid, pp 166–194
Garcia-Lafuente J, Delgado J, Sanchez Roman A, Soto J, Carracedo L, Diaz del Rio G (2009) Interannual variability of the Mediterranean outflow observed in Espartel sill, western Strait of Gibraltar. J Geophys Res 114. doi:10.1029/2009jc005496
Gomis D, Tsimplis MN, Martın-Mıguez B, Ratsimandresy AW, Garcıa-Lafuente J, Josey SA (2006) Mediterranean Sea level and barotropic flow through the Strait of Gibraltar for the period 1958–2001 and reconstructed since 1659. J Geophys Res-Oceans 111. doi:10.1029/2005JC003186
Gould WJ (1985) Physical oceanography of the Azores Front. In: Crease J, Gould WJ, Saunders PM (eds) Essays in oceanography: a tribute to John Swallow. progress in oceanography. Pergamon Press, Oxford, pp 167–190
Grootes PM, Sarnthein M, Kennett JP, Holbourn A, Nadeau MJ, Kuhn H (2008) Changes in MOC revealed by chronostratigraphic correlation of ocean sediment cores via C-14 plateau tuning. Geochim Cosmochim Acta 72:A331
Hall IR, Moran SB, Zahn R, Knutz PC, Shen CC, Edwards RL (2006) Accelerated drawdown of meridional overturning in the late-glacial Atlantic triggered by transient pre-H event freshwater perturbation. Geophys Res Lett 33. doi:10.1029/2006gl026239
Hayes A, Kucera M, Kallel N, Sbaffi L, Rohling EJ (2005) Glacial Mediterranean sea surface temperatures based on planktonic foraminiferal assemblages. Quat Sci Rev 24:999–1016
Julien PY (1998) Erosion and sedimentation. Cambridge University Press, Cambridge
Karim MF, Kennedy JF (1990) Menu of coupled velocity and sediment-discharge relations for rivers. J Hydraul Eng 116:978–996
Kuhlemann J, Rohling EJ, Krumrei I, Kubik P, Ivy-Ochs S, Kucera M (2008) Regional synthesis of Mediterranean atmospheric circulation during the Last Glacial Maximum. Science 321:1338–1340. doi:10.1126/science.1157638
Levine RC, Bigg GR (2008) Sensitivity of the glacial ocean to Heinrich events from different iceberg sources, as modeled by a coupled atmosphere-iceberg-ocean model. Paleoceanography 23:16. doi:10.1029/2008PA001613
Levitus S, Isayev G (1992) Polynomial approximation to the international equation of state for seawater. J Atmos Oceanic Technol 9:705–708
Lynch-Stieglitz J, Adkins JF, Curry WB, Dokken T, Hall IR, Herguera JC, Hirschi JJM, Ivanova EV, Kissel C, Marchal O, Marchitto TM, McCave IN, McManus JF, Mulitza S, Ninnemann U, Peeters F, Yu EF, Zahn R (2007) Atlantic meridional overturning circulation during the Last Glacial Maximum. Science 316:66–69
McCave IN, Hall IR (2006) Size sorting in marine muds: processes, pitfalls, and prospects for paleoflow-speed proxies. Geochem Geophys Geosyst 7:Q10N05. doi:10.1029/2006GC001284
McManus JF, Francois R, Gherardi JM, Keigwin LD, Brown-Leger S (2004) Collapse and rapid resumption of Atlantic meridional circulation linked to deglacial climate changes. Nature 428:834–837
MEDATLAS/2002 database (2002) Mediterranean and Black Sea database of temperature salinity and bio-chemical parameters. Climatological Atlas: IFREMER Edition (2002) MEDAR Group
Mikolajewicz U (2010) Modelling Mediterranean ocean climate of the Last Glacial Maximum. Clim Past 7:161–180
Millot C (2009) Another description of the Mediterranean Sea outflow. Prog Oceanogr 82:101–124
New AL, Jia Y, Coulibaly M, Dengg J (2001) On the role of the Azores current in the ventilation of the North Atlantic Ocean. Prog Oceanogr 48:163–194
O’Neill-Baringer M, Price JF (1997) Mixing and spreading of the Mediterranean outflow. J Phys Oceanogr 27:1654–1677
O’Neill-Baringer M, Price JF (1999) A review of the physical oceanography of the Mediterranean outflow. Mar Geol 155:63–82
Pinto L, Fortunato AB, Freire P (2006) Sensitivity analysis of non-cohesive sediment transport formulae. Cont Shelf Res 26:1826–1839
Price JF, O’Neill-Baringer M (1994) Outflows and deep water production by marginal seas. Prog Oceanogr 33:161–200
Price JF, O’Neill-Baringer M, Lueck RG, Johnson GC, Ambar I, Parilla G, Cantos A, Kenelly MA, Sanford TB (1993) Mediterranean outflow mixing and dynamics. Science 259:1277–1282
Robinson LF, Adkins JF, Keigwin LD, Southon J, Fernandez DP, Wang SL, Scheirer DS (2005) Radiocarbon variability in the western North Atlantic during the last deglaciation. Science 310:1469–1473. doi:10.1126/science.1114832
Rogerson M, Rohling EJ, Weaver PPE, Murray JW (2005) Glacial to interglacial changes in the settling depth of the Mediterranean Outflow plume. Paleoceanography 20:PA3007. doi:3010.1029/2004PA001106
Rogerson M, Rohling EJ, Weaver PPE (2006) Promotion of meridional overturning by Mediterranean-derived salt during the last deglaciation. Paleoceanography 21. doi:10.1029/2006PA001306
Rogerson M, Colmenero-Hidalgo E, Levine RC, Rohling EJ, Voelker AHL, Bigg GR, Schönfeld J, Cacho I, Sierro FJ, Löwemark L, Reguera MI, deAbreu L, Garrick K (2010) Enhanced Mediterranean-Atlantic exchange during Atlantic freshening phases. Geochem Geophys Geosyst 11:Q08013. doi:08010.01029/02009GC002931
Rogerson M, Schönfeld J, Leng M (2011) Qualitative and quantitative approaches in palaeohydrography: a case study from core-top parameters in the Gulf of Cadiz. Mar Geol 280:150–167
Schönfeld J, Zahn R (2000) Late glacial to holocene history of the Mediterranean outflow. Evidence from benthic foraminiferal assemblages and stable isotopes at the Portuguese margin. Palaeogeogr Palaeoclimatol Palaeoecol 159:85–111
Siddall M, Rohling EJ, Almogi-Labin A, Hemleben C, Meischner D, Schmelzer I, Smeed DA (2003) Sea-level fluctuations during the last glacial cycle. Nature 423:853–858
Skinner LC, Elderfield H (2007) Rapid fluctuations in the deep North Atlantic heat budget during the last glacial period. Paleoceanography 22:PA1205. doi:1210.1029/2006PA001338
Stanford JD, Rohling EJ, Hunter SE, Roberts AP, Rasmussen SO, Bard E, McManus J, Fairbanks RG (2006) Timing of meltwater pulse 1a and climate responses to meltwater injections. Paleoceanography 21:PA4103. doi:4110.1029/2006PA001340
Voelker AHL, Lebreiro SM, Schoenfeld J, Cacho I, Erlenkeuser H, Abrantes F (2006) Mediterranean outflow strengthening during northern hemisphere coolings: a salt source for the glacial Atlantic? Earth Planet Sci Lett 245:39–55
Acknowledgments
We warmly acknowledge the assistance of three anonymous reviewers, whose comments improved the quality of this manuscript. EJR acknowledges support from a Royal Society-Wolfson Research Merit Award. This study contributes to Natural Environment Research Council projects NE/H004424/1, NE/I009906/1, NE/D001773/1, and NE/E01531X/1 and EPSRC Consortium project FRMRC2. MR thanks Stuart McLelland and James Cooper for advise over selection of sediment entrainment parametrisation.
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
Cite this article
Rogerson, M., Bigg, G.R., Rohling, E.J. et al. Vertical density gradient in the eastern North Atlantic during the last 30,000 years. Clim Dyn 39, 589–598 (2012). https://doi.org/10.1007/s00382-011-1148-4
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s00382-011-1148-4