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High-Resolution Sea Surface Reconstructions Off Cape Hatteras Over the Last 10 Ka C High-resolution sea surface reconstructions off Cape Hatteras over the last 10 ka C. Cléroux, Maxime Debret, Elsa Cortijo, J.C. Duplessy, F. Dewilde, J. Reijmer, Nicolas Massei To cite this version: C. Cléroux, Maxime Debret, Elsa Cortijo, J.C. Duplessy, F. Dewilde, et al.. High-resolution sea surface reconstructions off Cape Hatteras over the last 10 ka. Paleoceanography, American Geophysical Union, 2012, 27 (1), pp.PA1205. 10.1029/2011PA002184. hal-00737002 HAL Id: hal-00737002 https://hal.archives-ouvertes.fr/hal-00737002 Submitted on 17 Sep 2020 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. PALEOCEANOGRAPHY, VOL. 27, PA1205, doi:10.1029/2011PA002184, 2012 High-resolution sea surface reconstructions off Cape Hatteras over the last 10 ka Caroline Cléroux,1,2 Maxime Debret,3 Elsa Cortijo,1 Jean-Claude Duplessy,1 Fabien Dewilde,1 John Reijmer,4 and Nicolas Massei3 Received 8 June 2011; revised 6 December 2011; accepted 6 December 2011; published 9 February 2012. [1] This study presents high-resolution foraminiferal-based sea surface temperature, sea surface salinity and upper water column stratification reconstructions off Cape Hatteras, a region sensitive to atmospheric and thermohaline circulation changes associated with the Gulf Stream. We focus on the last 10,000 years (10 ka) to study the surface hydrology changes under our current climate conditions and discuss the centennial to millennial time scale variability. We observed opposite evolutions between the conditions off Cape Hatteras and those south of Iceland, known today for the North Atlantic Oscillation pattern. We interpret the temperature and salinity changes in both regions as co-variation of activities of the subtropical and subpolar gyres. Around 8.3 ka and 5.2–3.5 ka, positive salinity anomalies are reconstructed off Cape Hatteras. We demonstrate, for the 5.2–3.5 ka period, that the salinity increase was caused by the cessation of the low salinity surface flow coming from the north. A northward displacement of the Gulf Stream, blocking the southbound low-salinity flow, concomitant to a reduced Meridional Overturning Circulation is the most likely scenario. Finally, wavelet transform analysis revealed a 1000-year period pacing the d18O signal over the early Holocene. This 1000-year frequency band is significantly coherent with the 1000-year frequency band of Total Solar Irradiance (TSI) between 9.5 ka and 7 ka and both signals are in phase over the rest of the studied period. Citation: Cléroux, C., M. Debret, E. Cortijo, J.-C. Duplessy, F. Dewilde, J. Reijmer, and N. Massei (2012), High-resolution sea surface reconstructions off Cape Hatteras over the last 10 ka, Paleoceanography, 27, PA1205, doi:10.1029/2011PA002184. 1. Introduction These fluctuations probably persisted throughout the Holo- cene, together with centennial to millennial variability. [2] The last decade of paleoclimate research has shown [3] External climate forcing across the Holocene changed that the Holocene is not the stable, climatic event-free period with both solar insolation and, on shorter timescales, solar as previously thought: both external and internal (oceanic) irradiance (sun activity). At 30°N, changes in the configu- forcings have caused major climatic changes. Abrupt events ration of the earth’s orbit from 10 to 0 ka resulted in a such as the 8.2 ka event [Alley et al., 1997] or the end of the summer insolation decrease but a very weak mean annual African Humid Period [deMenocal et al., 2000], periodic 2 insolation increase (+0.025 Watt/m [Laskar, 1990; Laskar variability like the 1500 years Bond’s cycle [Bond et al., et al., 2004]). On top of these orbital settings, solar irradi- 1997] or the large shifts in Asian monsoon intensity [Wang ance varies on much shorter time scales. Its impact on Earth et al., 2005] demonstrate the dynamic range of Holocene shows a high frequency variability of about 1 Watt/m2 over climate and make this epoch a particularly interesting target the last 9.3 ka [Steinhilber et al., 2009]. Recent events, like of study. On a shorter time scale, observations over about the the Maunder Minimum (17th century), illustrated climate last 50 years show interannual and decadal climate change. sensitivity to solar variation [Waple et al., 2002]. On the millennial time scale, periodicities of about 2250-year, 1000-year, 550-year, 400-year or 220-year [Debret et al., 1 2007; Dima and Lohmann, 2009; Knudsen et al., 2009; Laboratoire des Sciences du Climat et de l’Environnement, CEA- CNRS-UVSQ/IPSL, Gif-sur-Yvette, France. Rimbu et al., 2004; Steinhilber et al., 2010] have been 2Now at Lamont-Doherty Earth Observatory, Columbia University, attributed to solar variability. Model simulation [Swingedouw Palisades, New York, USA. et al., 2011] and past reconstructions [Knudsen et al., 2009; 3 Laboratoire de Morphodynamique Continentale et Côtière, Lohmann et al., 2004; Morley et al., 2011] support an ocean- Département de Géologie, Université de Rouen, UMR CNRS/INSU 6143, Mont-Saint-Aignan, France. atmosphere mechanism amplifying the impact of small total 4Department of Sedimentology and Marine Geology, FALW, irradiance change on the climate. VU University Amsterdam, Amsterdam, Netherlands. [4] The atmospheric circulation in the North Atlantic is described by the descending branch of the Hadley cell at Copyright 2012 by the American Geophysical Union. midlatitudes and the ascending branch of the Polar cell at high 0883-8305/12/2011PA002184 PA1205 1of14 PA1205 CLÉROUX ET AL.: OFF CAPE HATTERAS VARIABILITY, 10 KA PA1205 reduced (NAOÀ, weakened wind circulation) [Frankignoul et al., 2001]. The STG and the subpolar gyre (SPG) are both affected by the basin-scale atmospheric circulation. Using long records of hydrographic observations from the Labrador Sea Basin and Bermuda, Curry and McCartney [2001] demonstrated that the pressure difference between the subtropical and subpolar gyre centers is an oceanic analogue for the NAO atmospheric pressure. Circulations within the gyres are alternatively weakened and strength- ened between the NAO+ and NAOÀ periods. Looking at observations and model results for the northeastern Atlantic region, Hatun et al. [2005] concluded that SPG circulation controls both the salinity and the strength of the North Atlantic current in this region, both of which are important for deep-water formation. Indeed, both Böning et al. [2006] and Gao and Yu [2008] used model experiments to show a tight link between the SPG circulation and the strength of the meridional overturning circulation (MOC). It is worth noting that many studies that look at the relationship Figure 1. (a) Spatial correlation map of mean winter sta- between the Gulf Stream and atmospheric circulation have tion temperature and sea surface temperature (SST) corre- related the Gulf Stream position (north/south displacement) lated against the NAO index. SST reflects a tripole pattern with the NAO [de Coëtlogon et al., 2006]. This link reflects with a cold anomaly in the subpolar region, a warm anomaly the changes in the shape of the STG that occur under dif- in the midlatitudes region centered off Cape Hatteras, and a ferent wind regimes [Lohmann et al., 2009]. Interdecadal cold subtropical anomaly between the equator and 30°N. and millennial climate variability may result from complex From Visbeck et al. [2001]. (b) Close-up of Cape Hatteras interactions between gyre circulation, atmospheric forcing, region, satellite image in false color. The warm Gulf Stream Gulf Stream anomaly transport and thermohaline circulation is seen as the dark red filament along Florida, the green color [Dong and Sutton, 2005]. represents the cold Labrador Current (or Slope Water). [6] In this paper, we present temperature and salinity Location of cores RAPiD-12-1K, MD99-2203 and MD99- reconstructions off Cape Hatteras (North Carolina, USA) that 2201 are plotted. cover the last 10 ka and discuss variability at the centennial- millennial time scale. We combined trace element and oxygen isotopic composition analyses on two planktonic latitudes (50°N), creating the Azores subtropical high and foraminifera species to estimate past SST, past surface the Icelandic subpolar low respectively. This system oscillates seawater oxygen isotopic values (a proxy for salinity) and in strength, and it has been well known since the first 18th upper thermocline conditions. We performed wavelet anal- century explorations that Europe and Greenland winter con- ysis on high-resolution surface reconstructions to find the ditions evolve like a seesaw [Stephenson et al.,2003].The periodicity embedded in our signals. In the discussion, we modern conceptualization of this climate pattern is the North first compare our results with northeastern Atlantic climate Atlantic Oscillation (NAO) [Hurrell et al., 2003] (Figure 1). reconstructions and evaluate NAO-like patterns. Second, we Reconstruction as far back as the 16th century defines the compare the paleo-hydrology off Cape Hatteras with a past NAO as a mode of multidecadal variability [Gray et al., 2004], reconstruction from a Great Bahamas Bank core, which but NAO-like variability may also occur on centennial- represents the ‘pure’ Gulf Stream signal, and discuss the millennial timescales [Rimbu et al., 2003]. For NAO-like possible link with large-scale currents or MOC changes. variability to occur on longer timescales, an interplay between Finally, we discuss the periodicities highlighted by the the thermohaline circulation (THC) [Latif et al., 2006], sea wavelet analysis and suggest a solar origin. surface temperature (SST), and the wind-driven ocean circu- lation must take place [Marshall et al., 2001].
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