Climate variability reconstructions for the last millennium from several Iberian lake and marine records shed light on the spatial and temporal hydroclimate and associated climate mechanisms during the Medieval Climate Anomaly

Belmonte, A.

Cacho Lascorz, Isabel

Canals Artigas, Miquel

Conzález, P.

Corella, Juan Pablo

Frigola Ferrer, Jaime I.

Martín, C.

Morellón, Mario

Moreno, Ana

Pérez, A.

Valero Garcés, Blas Lorenzo

Vegas Vilarrúbia, Teresa Elena

Martín-Puertas, Celia

Diposit Digital de la Universitat de Barcelona

16 PAGES news • Vol 19 • No 1 • March 2011Science Highlights: Medieval Climate Was there a common hydrological pattern in the Iberian Peninsula region during the Medieval Climate Anomaly?AnA Moreno1, M. Morellón2, C. MArtín-PuertAs3, J. FrigolA4, M. CAnAls4, i. CACho4, J.P. CorellA1, A. Pérez1, Á. BelMonte5, t. VegAs-VilArrúBiA6, P. gonzÁlez-sAMPériz1 And B.l. VAlero-gArCés11Pyrenean Institute of Ecology (CSIC), Zaragoza, Spain; amoreno@ipe.csic.es2Department of Surface Waters – Eawag, Dübendorf, Switzerland; 3German Research Center for Geoscience (GFZ), Potsdam, Germany; 4CRG Marine Geosciences, University of Barcelona, Spain; 5Department of Earth Sciences, University of Zaragoza, Spain; 6Departament of Ecology, University of Barcelona, SpainClimate variability reconstructions for the last millennium from several Iberian lake and marine records shed light on the spatial and temporal hydroclimate and associated climate mechanisms during the Medieval Climate Anomaly.In order to understand the causes and spa-tial extent of the Medieval Climate Anomaly (MCA;  ca.  900-1350  AD)  and  the  Little  Ice Age (LIA; ca. 1350-1850 AD), a better charac-terization of temperature and precipitation changes in a larger number of sites around the  globe  is  required.  Understanding  the dynamics of MCA in the climatically-vulner-able  Mediterranean  region  is  particularly interesting  since  it  encompasses  a  com-parison between the hydrological response to  a  generally  accepted warm period  (the MCA)  and  to  the present  global warming. To tackle the question of how the MCA and the present  global warming  compare,  the most pertinent approach is to study highly resolved records that are mostly driven by moisture  changes.  Sediments  from  small lakes that experience considerable fluctua-tions  in  terms  of  lake  level  and  chemistry and  biological  proxies  record  such  infor-mation  on  effective  moisture  variability. Coastal and marine sediments also provide evidence  of  changes  in  sea  surface  tem-perature (SST), river sediment delivery, and wind patterns related to climate.The Iberian MCA signal: Marine and terrestrial recordsTheir  relative  small  size,  direct  connection to  surface  aquifers,  and  rapid  response  to precipitation  make  Iberian  karstic  lakes particularly  sensitive  to moisture  changes. Detailed  sedimentological  and  geochemi-cal analyses, complemented with the study of biological proxies (chironomids, diatoms and pollen), have been performed on long sedimentary records retrieved in 2004 from several Spanish lakes.  In Figure 1 we show the location of the lakes where the MCA sig-nal is recorded, together with some marine cores discussed below.Most of the studied lakes (e.g., Estanya, Taravilla, Zoñar, Arreo and Montcortés)  re-cord  relatively  shallower  lake  levels  and more arid conditions during the MCA. This is indicated by higher chemical concentra-tions  in  the water,  and  the predominance of sclerophyllous Mediterranean vegetation, heliophytes  and  more  evergreen  trees  in the  catchment.  In  Figure  2,  the most  rep-resentative  Iberian  records  are  compared with  global  reconstructions,  such  as  the number of sunspots (Vaquero et al., 2002). The  fact  that  each  lake  is  unique  and  re-sponds differently to climate variability ac-cording to its geological, hydrological, and limnological characteristics makes it neces-sary to use case-specific proxies and apply local  individualized  interpretations.  The reconstruction of lake level in Lake Estanya in the Pre-Pyrenees, mostly based on sedi-mentary facies and elemental and isotopic geochemistry  (Morellón  et  al.,  in  press), clearly shows a lake level increase from the end of the MCA to the LIA (Fig. 2). Similarly, the presence of gypsum-rich laminated fa-cies in Arreo Lake (northern Ebro Basin, Fig. 1) suggests generally lower lake levels dur-ing  the  MCA  (Corella  et  al.,  unpublished), while  a  thermophilous  plant  association recorded in the Montcortés Lake sedimen-tary  sequence  (Rull  et  al.,  in  press)  points towards warmer climate in the central Pre-Pyrenees. A comparable paleohydrological signal  is recorded in Lake Taravilla,  located in  the  Iberian  Range.  In  this  lake,  coarser grain-size  layers  with  higher  siliciclastic content  reflect  paleoflood  events  during periods  of  increased  run-off  triggered  by intense rainfall (Moreno et al., 2008). These layers are more frequent during the LIA and almost absent during the MCA (Fig. 2). Rb/Al ratios and Si concentration, used as prox-ies  for  run-off  in Lakes Zoñar and Basa de la Mora, further indicate that a drier climate extended across the Iberian Peninsula dur-ing  the  MCA,  compared  to  the  following centuries (Martín-Puertas et al., 2010; Pérez et al., unpublished data). Despite  local dif-ferences  and  some  dating  uncertainties, the MCA stands out as a  relatively dry pe-riod, which was characterized by decreased lake water balance in the eastern and, likely, the southern part of the Iberian Peninsula.The  western  Iberian  Peninsula  lacks high-resolution lake records of the MCA, but marine  sediment  cores  provide  some  pa-leohydrological  information.  Several  stud-ies  conducted  offshore  of  Lisbon  indicate that the MCA was a dry interval as inferred from reduced run-off (Abrantes et al., 2005; Lebreiro et al., 2006). On the Mediterranean side,  the percentage of  coarse particles  in Figure 1: Satellite image of the Iberian Peninsula region with the location of lake records (stars) and marine sites (dots) discussed in the text. Image from: Jacques Descloitres, MODIS Rapid Response Team, NASA/GSFC.17 PAGES news • Vol 19 • No 1 • March 2011Science Highlights: Medieval Climatea sediment core from north of Minorca, lo-cated in a contourite drift, highlights an epi-sode of weaker deep-water formation after 1300 AD, corresponding to the LIA (Fig. 2). At that location, particle grain-size is direct-ly related to the intensity of deep-water cur-rents that are formed in the nearby Gulf of Lions (Frigola et al., 2007). This result points to weaker westerlies during the MCA, which is consistent with a positive North Atlantic Oscillation (NAO) index at this latitude.Climatic versus anthropogenic forcingsThe areas surrounding some of the studied Iberian  lakes  were  well  populated  during medieval times. This raises the need to dis-criminate  climatically  forced  signals  from anthropogenic effects on  the  lake dynam-ics (Rull et al., in press). For instance, in both Montcortés and Arreo lakes, sedimentation rates  increased  during  the  MCA  (Fig.  2). However,  discerning  whether  the  higher sediment delivery was the result of climatic factors  (increase  in  high-intensity  storm events,  relatively  lower  lake  levels  due  to higher  temperatures, more  intense evapo-ration and decreased precipitation or more development  of  littoral  environments)  or produced by changes in land use practices (deforestation,  farming  and  intensification of  cultivation)  is  not  an  easy  task.  Most likely, human impact and climate variability had  a  joint  effect  on  Iberian  lakes  during historical  times.  Fortunately,  an  integrated multiproxy  approach  provides  some  clues to detangle both  factors.  In Taravilla  Lake, peak contents of Cerealia and other ‘‘anthro-pogenic’’  taxa  associated  with  crops  and ruderal plants occur at  the base of  the se-quence when terrigenous paleoflood layers are scarce (Fig. 2). Thus significant removal of vegetation by human attributed fires or deforestation  practices  cannot  be  consid-ered the main forcing for the increase in ter-rigenous layers (Moreno et al., 2008). In the same  period,  pollen  reconstructions  from Estanya (Morellón et al., in press), and Mont-cortés  (Rull  et  al.,  in  press)  reflect warmer and drier  conditions  in  a  landscape domi-nated by junipers, Mediterranean elements (evergreen Quercus, Olea,  Phillyrea,  Buxus, Thymelaea and Rosmarinus), a relatively low presence of mesophylic woody taxa, helio-phytes, some cultivated plants and a poorly developed aquatic component.A global context for the Iberian aridity during the MCAThe  Iberian  records  clearly  documenting warmer  conditions  during  the  MCA  are consistent with global paleoclimate recon-structions (e.g., Mann et al., 2009). Climate variability  during  the  last  millennium  has been  related  to  solar  irradiance  fluctua-tions  and  tropical  volcanic  eruptions  (e.g., Shindell  et  al.,  2001; Wanner  et  al.,  2008). Recently,  a  persistent  positive  mode  of the  NAO  during  the  MCA  has  been  sug-gested (Trouet et al., 2009). This would lead to  warmer  and  more  arid  climate  in  the western Mediterranean region. The Iberian Peninsula serves as a laboratory to explore the long-term pattern of the NAO index be-cause of  its  location at  the  southern edge of  the  storm  tracks  associated  with  mid-latitude westerlies. Thus, a dry climate dur-ing  the MCA  is  coherent with  a dominant positive phase of the NAO, characterized by lower  river  discharge  offshore  Lisbon  (Le-breiro et  al.,  2006; Alt-Epping et  al.,  2009), lower  lake  levels  in northeast  (Morellón et al.,  in press) and southwest  Iberia  (Martín-Puertas et al.,  2010),  fewer flood events  in the  Tagus  River  Basin  (Benito  et  al.,  2004; Moreno et al., 2008), and less intense west-erly winds offshore Minorca Island (Frigola et al., unpublished data). Recent model sim-ulations  for  temperature and precipitation in the Iberian Peninsula during the last mil-lennium support the role of the NAO in cre-ating a dry anomaly during medieval times (Gómez-Navarro et al., 2010). More analyses in progress and improved chronologies will facilitate  a  more  detailed  comparison  of records to clarify the internal structure and spatial coherence of the main phases of en-vironmental change during the MCA in the Iberian Peninsula.MaximunMinimunSpörerDaltonMaunderWolfLate MedievalMedievalDarkAgesByzantineLate Roman1350 1360 137002004006008001000120014001600180020000 2 4 6 8 -0.4       -0.2           01.2 1.6 2 2.412 14 16 18Solar Irradiance (W/m2) SST (ºC)Offshore Taguscold warm0       0.2    0.4PaleofloodsTaravilla LakeLessrainfallIntenserainfallSun spots NH T anomaliesRb/AlZoñar LakeGLOBAL IBERIAN PENINSULA Age (years AD)wetdryLake levelEstanya LakewetdryLittleIce AgeMCARomanperiodDarkAgesNW windsCoarse particlesoff Minorca40 50 60 70 800 800 1600Si (cps)B. de la Morawetdry-3 -2 -1 0 1 2Detrital events/yearMontcortés LakeAnthropogenic activity0 2 4 6 8Figure 2: Compilation of global and Iberian climate reconstructions over the last 2000 years. Global records include sun spot numbers (Vaquero et al., 2002), solar irradiance (Bard et al., 2000) and temperature anomalies for the Northern Hemisphere (Jones and Mann, 2004). Iberian Peninsula records are aligned from west to east (see Fig. 1 for location) and include SST from marine cores offshore Tagus River (Rodrigues et al., 2009), lake level of Estanya Lake (Morellón et al., in press), number of floods observed in Taravilla Lake (Moreno et al., 2008), Rb/Al ratio from Zoñar Lake record (Martín-Puertas et al., 2010), number of detrital events per year recorded in Montcortés Lake (Corella et al., in press) and coarse detrital grain fraction from off Minorca (Frigola, unpublished data).18 PAGES news • Vol 19 • No 1 • March 2011Science Highlights: Medieval Climate ReferencesCorella, J.P., Valero-Garcés, B.L., Moreno, A., Morellón, M., Rull, V., Giralt, S., Rico, M.T. and Pérez-Sanz, A., in press: Sedimentary evolu-tion and palaeohydrology of karstic, meromictic Montcortés Lake (Spanish Pre-Pyrenees) during the last 6,000 years, Journal of Paleolimnology, doi: 10.1007/s10933-010-9492-7.Lebreiro, S., et al., 2006: Climate change and coastal hydrographic re-sponse along the Atlantic Iberian margin (Tagus Prodelta and Muros Ría) during the last two millennia, The Holocene, 16: 1003-1015.Martín-Puertas, C., Jiménez-Espejo, F., Martínez-Ruiz, F., Nieto-Moreno, V., Rodrigo, M., Mata, M.P. and Valero-Garcés, B.L., 2010: Late Holocene climate variability in the southwestern Mediterranean region: an integrated marine and terrestrial geochemical ap-proach, Climate of the Past, 6: 807-816.Moreno, A., Valero-Garcés, B.L., González-Sampériz, P. and Rico, M., 2008: Flood response to rainfall variability during the last 2000 years inferred from the Taravilla Lake record (Central Iberian Range, Spain), Journal of Paleolimnology, 40: 943-961.Morellón, M., et al., in press: Climate and human signatures during the Medieval Warm Period and the Little Ice Age in the Spanish Pre-Pyrenees: the Lake Estanya record, Journal of Paleolimnology, doi: 10.1007/s10933-009-9346-3.For full references please consult:http://www.pages-igbp.org/products/newsletters/ref2011_1.htmlMedieval drought in North America: The role of the  Atlantic Multidecadal OscillationroBert J. oglesBy1,2, s. Feng2, Q. hu2 And C. rowe11Department of Earth and Atmospheric Sciences, University of Nebraska at Lincoln, USA; roglesby2@unlnotes.unl.edu2School of Natural Resources, University of Nebraska at Lincoln, USAThe sea surface temperature anomalies associated with the Atlantic Multidecadal Oscillation may have been a major factor contributing to widespread drought in North America during Medieval times.The role of the Atlantic Multidecadal OscillationMedieval  times  (900-1330  AD;  hereafter referred  to  as MT)  in  central  and western North  America  were,  according  to  proxy data  reconstructions,  generally  warm, and  especially  dry  (Fig.  1),  with  numer-ous  decadal  or  longer  “megadroughts” that  were  the  worst  of  the  past  2000 years  (Woodhouse  and  Overpeck,  2000). Considerable  attention  has  been  paid  to the  role  of  sea  surface  temperature  (SST) anomalies  in  forcing  these prolonged pe-riods of drought,  especially  that of  the La Niña-like  condition  in  the eastern  tropical Pacific (e.g., Graham et al., 2007; Seager et al., 2007). Compelling recent evidence sug-gests  that North Atlantic SST,  through the Atlantic  Multidecadal  Oscillation  (AMO), may also have a strong effect on persistent summertime  drought  in  North  America (Fig. 1b). At present,  the AMO expresses a 60-80  year  cycle between  relatively warm (warm  phase)  and  cool  (cold  phase)  SST (Kerr, 2000; Enfield et al., 2001).We  investigated  the  role  of  the  AMO in  MT  drought  in  North  America  using modern  (present-day) observations, proxy paleo-data, and simulations from multiple climate models (Feng et al., 2010). Consid-ering  present-day  relationships,  for which instrumental observations can be used, the results  show  that  persistent  summertime droughts in the U.S. Great Plains and south-west North America  are  closely  related  to multidecadal  variations  of  North  Atlantic SST  (AMO).  During  the  AMO warm  (cold) phases, most of North America is dry (wet).Next,  the  influence  of  North  Atlantic SST  on  modern  North  American  drought was  examined  using  simulations  made by five global climate models  (Feng et al., 2010). When forced by warm North Atlan-tic SST anomalies, all models captured sig-nificant drying over North America despite some  regional  differences.  Specifically, all  the  models  simulate  dry  summers  in the  Great  Plains  and  southwestern  North America. The  response  of  precipitation  to a cold North Atlantic is much weaker, with greater  disagreement  among  the models. Overall,  the  ensemble  of  the  five  models reproduced the statistical relationships be-tween dry/wet fluctuations in North Amer-  A    Temperature anomalies during MWPB   PDSI (900 - 1200 minus 1901 - 2000 AD)120°W 90°W 60°W 30°W 0 30°E80°N60°N40°N20°NEQ20°S55°N50°N45°N40°N35°N30°N25°N130°W 120°W 110°W 100°W 90°W 80°W 70°WFigure 1: A) Spatial distribution of the proxy data of temperature changes during MT. Blue squares, gray dots and red squares indicate cooling, no changes and warming during Medieval Times, respectively. The contour lines are the observed temperature anomalies associated with AMO warm phases for the period 1901-2006 AD. The contour interval is 0.1°C. Details of the proxy data can be found in Feng et al. (2009). B) Difference in tree ring reconstructed Palmer Drought Severity Index (PDSI) for 900-1200 minus 1901-2000 AD. Shadings indicate the differences are significant at 95% confidence level by two-tailed student-test. The figure is adapted from Feng et al. (2010).

Was there a common hydrological pattern in the Iberian Peninsula region during the medieval Climate anomaly?

Was there a common hydrological pattern in the Iberian Peninsula region during the medieval Climate anomaly?

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