Hydroclimate variability during the last 2700 years based on stalagmite multi-proxy records in the central-western Mediterranean

This study presents the first high-resolution speleothem-based hydrological reconstruction for much of the last 2.7 kyr in the central-western Mediterranean. The paleohydrological information comes from a combination of five U-Th dated stalagmites from two Mallorca island caves. Interpretations are based on high-resolution records of d18O, d13C and trace element analyses combined with information from mineralogical X-ray diffraction, fabrics and morphological features, and cave monitoring data. None of the studied stalagmites cover the whole 2.7 kyr period but they provide sufficient overlap to replicate most of the discussed climatic intervals with the exception of the Medieval Climate Anomaly (MCA), which is represented by a hiatus. Taking into account the results of five years farmed calcite collected in glass plates and cave environmental parameters, we argue that main patterns in the stalagmite geochemical records are mostly controlled by changing rates of prior calcite precipitation (PCP) that respond to hydrological changes in the region. We apply a principal component analysis to the stalagmite geochemical data set and a composite d18O record to obtain a robust regional hydrological record. This record supports wet conditions for the early Roman Period (RP), the first half of the Early Middle Ages (EMA) and the Little Ice Age (LIA), and drier conditions for the late RP, the late EMA and the entire MCA. These results are discussed in the context of other climatic and oceanographic records from the region including paleo North Atlantic Oscillation (NAO) records. This ocean-atmosphere approach suggests complex non-stationary climate patterns for the last 2.7 kyr, including the occurrence of both wetwarm and wet-cold intervals and underlying the complex interaction of factors controlling climate evolution in the region. Overall, positive (negative) NAO phases appear coincident with drier (wetter) conditions for all the examined period at decadal time-scale

Paleoclimatic reconstruction of past interglacial periods and their transitions in the Iberian Peninsula and its surrounding seas = Reconstruccions paleoclimàtiques dels interglacials recents i les seves transicions a la Península Ibèrica i mars circumdants

This study combines cave speleothems and marine sediments to gain an insight into the climate variability of the Iberian Peninsula (IP) and its surrounding seas associated with previous warm interglacial periods. In particular, it centres in the interglacials comprised within the Marine Isotopic Stages (MIS) 13, 11, 9, 7, and 5, and their associated transitions. The speleothems are used as archives for changes in atmospheric moisture availability by means of stable isotopes and Mg/Ca analysis. The studied speleothems correspond mostly from the Balearic Islands (Minorca and Mallorca) but also from the Pyrenees. Marine conditions for the penultimate termination (T-II) and the MIS 5 have been reconstructed in the base to three sediment cores from three different marine locations around the IP: the Cantabrian Sea, the Alboran Sea, and the Balearic Sea. Surface conditions were explored by means of pair analyses of δ18O and Mg/Ca ratios measured in carbonate shells of the planktonic foraminifera Globigerina bulloides. These measurements let to the reconstruction of Sea Surface Temperatures (SST) and sea water δ18Osw values as a proxy of major changes in the regional precipitation/evaporation balance or as an indicator of the arrival of melting waters. In addition, changes in the intensity of western Mediterranean deep convection are explored through additional measurements of grain size distribution and XRF-geochemical ratios performed in the Balearic core (MD99- 2343). The studied speleothem collection provides a nearly continuous 450 kyr record, unique for the Mediterranean region. Interglacial periods are characterized by light δ13C and low Mg/Ca ratios pointing to enhanced precipitation and climate amelioration that allowed the expansion of the vegetation cover. On the contrary, heavier/higher δ13C and Mg/Ca ratios during glacial stages highlight their dry conditions with reduced vegetation activity. The δ18Ospeleo records reveal also the overall dominance of lighter values during interglacial periods in contrast to the glacial periods but with a strong 23-kyr (precessional) imprint in the signal. The extraordinary resemblance between the cave and marine δ18O records support a strong influence of Mediterranean source rains over the studied caves whose δ18O signal was dominated by the precession control on the evaporation/precipitation ratio on the Mediterranean basin. The MIS 11 appears in the studied speleothem as a long and stable interglacial with rather constant water availability over the Balearic Islands. The speleothem covering the MIS 9 and MIS 7 allows identifying sub-stage structures with wetter conditions associated with the warm periods. This record presents extraordinary resemblance to previously published pollen sequences from the Mediterranean region. The MIS 5 is studied in detail through the integrated study of marine and speleothem records. During the Last Interglacial (LIG), the sea surface temperature evolution was heterogeneous around the IP with gradients among the three studied seas larger than those from today. The LIG end was coincident with an accelerated aridification phase that marked the glacial inception at 116.5 kyr BP. This was the first of a series of stadials that punctuated the early glaciation and where the sea thermal gradient almost disappeared around the IP. These intense coolings during stadials led the development of drier but intense westerlies over southern European latitudes that favoured deep convection in the western Mediterranean Sea. In contrast to this regional homogeneity among the studied records during stadial periods, the interstadials periods were rather heterogeneous pointing to much complex ocean-atmosphere interconnections during these warm intervals. Glacial terminations (T-III, IV, and V) appear as periods of low rates in speleothem growth while T-II is only represented by growth interruptions. The marine δ18Osw for the T-II supports the occurrence of a major freshening event in correspondence to the Heinrich Event (HE) 11. Previous terminations are represented by an early light δ18Ospeleo anomaly, likely reflecting that this early deglacial major melting over the Atlantic Ocean was a rule for deglacial initiations.L’estudi combinat tant de sediments marins com d’espeleotemes ha permès determinar la variabilitat climàtica durant períodes interglacials recents (MIS 13, 11, 9, 7, i 5) a la Península Ibèrica i als seus mars circumdants. S’han utilitzat sediments marins de tres localitzacions diferents, del Mar Cantàbric, el Mar d’Alboran i el Mar Balear, en els quals s’han determinat les condicions superficials del mar, a partir del càlcul de les temperatures superficials (Mg/Ca-SST) i el δ18Osw mesurats en el foraminífer planctònic Globigerina bulloides. Addicionalment, s’han caracteritzat canvis en la intensitat de la corrent profunda a partir de la distribució granulomètrica i l’anàlisi elemental per fluorescència de raig X dels sediments del testimoni del Mar Balear. Per un altre banda l’anàlisi geoquímic tant d’isòtops estables com de la relació Mg/Ca mesurats en espeleotemes de les illes Balears i dels Pirineus han sigut utilitzats com indicadors de precipitacions. La nova col·lecció d’espeleotemes obtinguda en aquesta tesis doctoral ha proporcionat un registre continental pràcticament continu de 450 kyr únic a la zona de la Mediterrània. Els resultats d’aquesta tesis mostren que els períodes interglacials, caracteritzats per valors lleugers de δ13C i baixes relacions de Mg/Ca en espeleotemes, varen tindre cobertures vegetals més extenses que durant els períodes glacials i varen ser períodes humits degut al augment de les precipitacions. A més, els resultats indiquen peculiaritats entre els diferents períodes interglacials estudiats i permeten identificar sub-estructures climàtiques interestadials/interglacials. En concret el MIS 5, període estudiat amb detall, mostra alts gradients tèrmics de les aigües superficials marines entre les tres localitzacions estudiades al voltant de la Península Ibèrica, indicant una interconnexió oceà-atmosfera complexa durant aquests períodes més càlids. Contràriament, durant períodes estadials freds, els gradients tèrmics pràcticament varen desaparèixer, i juntament amb el desenvolupament de condicions atmosfèriques àrides varen afavorir la convecció profunda del mediterrani occidental

Reconstruccions paleoclimàtiques dels interglacials recents i les seves transicions a la Península Ibèrica i mars circumdants

[eng] This study combines cave speleothems and marine sediments to gain an insight into the climate variability of the Iberian Peninsula (IP) and its surrounding seas associated with previous warm interglacial periods. In particular, it centres in the interglacials comprised within the Marine Isotopic Stages (MIS) 13, 11, 9, 7, and 5, and their associated transitions. The speleothems are used as archives for changes in atmospheric moisture availability by means of stable isotopes and Mg/Ca analysis. The studied speleothems correspond mostly from the Balearic Islands (Minorca and Mallorca) but also from the Pyrenees. Marine conditions for the penultimate termination (T-II) and the MIS 5 have been reconstructed in the base to three sediment cores from three different marine locations around the IP: the Cantabrian Sea, the Alboran Sea, and the Balearic Sea. Surface conditions were explored by means of pair analyses of δ18O and Mg/Ca ratios measured in carbonate shells of the planktonic foraminifera Globigerina bulloides. These measurements let to the reconstruction of Sea Surface Temperatures (SST) and sea water δ18Osw values as a proxy of major changes in the regional precipitation/evaporation balance or as an indicator of the arrival of melting waters. In addition, changes in the intensity of western Mediterranean deep convection are explored through additional measurements of grain size distribution and XRF-geochemical ratios performed in the Balearic core (MD99- 2343). The studied speleothem collection provides a nearly continuous 450 kyr record, unique for the Mediterranean region. Interglacial periods are characterized by light δ13C and low Mg/Ca ratios pointing to enhanced precipitation and climate amelioration that allowed the expansion of the vegetation cover. On the contrary, heavier/higher δ13C and Mg/Ca ratios during glacial stages highlight their dry conditions with reduced vegetation activity. The δ18Ospeleo records reveal also the overall dominance of lighter values during interglacial periods in contrast to the glacial periods but with a strong 23-kyr (precessional) imprint in the signal. The extraordinary resemblance between the cave and marine δ18O records support a strong influence of Mediterranean source rains over the studied caves whose δ18O signal was dominated by the precession control on the evaporation/precipitation ratio on the Mediterranean basin. The MIS 11 appears in the studied speleothem as a long and stable interglacial with rather constant water availability over the Balearic Islands. The speleothem covering the MIS 9 and MIS 7 allows identifying sub-stage structures with wetter conditions associated with the warm periods. This record presents extraordinary resemblance to previously published pollen sequences from the Mediterranean region. The MIS 5 is studied in detail through the integrated study of marine and speleothem records. During the Last Interglacial (LIG), the sea surface temperature evolution was heterogeneous around the IP with gradients among the three studied seas larger than those from today. The LIG end was coincident with an accelerated aridification phase that marked the glacial inception at 116.5 kyr BP. This was the first of a series of stadials that punctuated the early glaciation and where the sea thermal gradient almost disappeared around the IP. These intense coolings during stadials led the development of drier but intense westerlies over southern European latitudes that favoured deep convection in the western Mediterranean Sea. In contrast to this regional homogeneity among the studied records during stadial periods, the interstadials periods were rather heterogeneous pointing to much complex ocean-atmosphere interconnections during these warm intervals. Glacial terminations (T-III, IV, and V) appear as periods of low rates in speleothem growth while T-II is only represented by growth interruptions. The marine δ18Osw for the T-II supports the occurrence of a major freshening event in correspondence to the Heinrich Event (HE) 11. Previous terminations are represented by an early light δ18Ospeleo anomaly, likely reflecting that this early deglacial major melting over the Atlantic Ocean was a rule for deglacial initiations.[cat] L’estudi combinat tant de sediments marins com d’espeleotemes ha permès determinar la variabilitat climàtica durant períodes interglacials recents (MIS 13, 11, 9, 7, i 5) a la Península Ibèrica i als seus mars circumdants. S’han utilitzat sediments marins de tres localitzacions diferents, del Mar Cantàbric, el Mar d’Alboran i el Mar Balear, en els quals s’han determinat les condicions superficials del mar, a partir del càlcul de les temperatures superficials (Mg/Ca-SST) i el δ18Osw mesurats en el foraminífer planctònic Globigerina bulloides. Addicionalment, s’han caracteritzat canvis en la intensitat de la corrent profunda a partir de la distribució granulomètrica i l’anàlisi elemental per fluorescència de raig X dels sediments del testimoni del Mar Balear. Per un altre banda l’anàlisi geoquímic tant d’isòtops estables com de la relació Mg/Ca mesurats en espeleotemes de les illes Balears i dels Pirineus han sigut utilitzats com indicadors de precipitacions. La nova col·lecció d’espeleotemes obtinguda en aquesta tesis doctoral ha proporcionat un registre continental pràcticament continu de 450 kyr únic a la zona de la Mediterrània. Els resultats d’aquesta tesis mostren que els períodes interglacials, caracteritzats per valors lleugers de δ13C i baixes relacions de Mg/Ca en espeleotemes, varen tindre cobertures vegetals més extenses que durant els períodes glacials i varen ser períodes humits degut al augment de les precipitacions. A més, els resultats indiquen peculiaritats entre els diferents períodes interglacials estudiats i permeten identificar sub-estructures climàtiques interestadials/interglacials. En concret el MIS 5, període estudiat amb detall, mostra alts gradients tèrmics de les aigües superficials marines entre les tres localitzacions estudiades al voltant de la Península Ibèrica, indicant una interconnexió oceà-atmosfera complexa durant aquests períodes més càlids. Contràriament, durant períodes estadials freds, els gradients tèrmics pràcticament varen desaparèixer, i juntament amb el desenvolupament de condicions atmosfèriques àrides varen afavorir la convecció profunda del mediterrani occidental

New Mediterranean speleothem records for glacial Terminations IV and III

Speleothem archives spanning the glacial terminations IV and III (TIV and TIII) are particularly scarce in the western Mediterranean region. This study presents unprecedented geochemical records measured on a speleothem from Minorca Island that grew continuously through the period from Marine Isotope Stage 11 to 7. Its U/Th chronological model provides an accurate and excellent chronology for both terminations which are recognized as intervals with slow growth rates. Hence revealing the difficulty of the speleothem to grow during these periods of rapid melting, suggesting major distortions in the hydrological conditions associated to glacial terminations. The Mg/Ca and d13C records indicate that deglaciations were characterized by rapid transitions towards more humid conditions. However, the d18O results shows a deglacial freshening that led in time the hydrological signal, with a remarkably larger time-led at the TIV. These earlier depletions of the d18O are interpreted to mark the onset of the glacial melting, a freshening signal that propagated through the surface ocean and transferred from the rain source into the stalagmite. The co-existence of comparable deglacial d18O depleted episodes within the marine records, brings the possibility to review the marine chronologies, independently of the orbital tuning. An exercise that indicates a significant bias in the timing of the melting onset associated to TIV

MAGY project: MAllorca hydroloGY over the last few centuries. Instrumental validation of speleothem archives

Geochemical analyses of speleothems and cave monitoring offer a complete framework for cave systems concerning hydrological changes and climate variability at very different timescales. In this regard, one critical target becomes the period when paleoclimatic records overlap with the directly measured instrumental records of climate. In order to improve the interpretation of speleothems as paleoclimatic records and therefore elucidate past climate changes in the western Mediterranean region, the MAGY project intent is the comparison of a new collection of speleothem records from Mallorca Island, which spans the last centuries, with precipitation and temperature data acquired in the weathering station from the Mallorca airport. This information is particularly critical on this island which is likely to face high hydrological stress under the current conditions of climate change. The implementation of this study requires high-resolution trace element profiles obtained by LA-ICP-MS to detect even seasonality variability in the speleothems and parallel well-resolved age models. The combination of U/Th dating, the 14C technique, and the confocal laser scanning microscopy technique, which allows annual layer counting, will provide solid chronologies. Preliminary results show that the Mg/Ca signal corresponds with the precipitation patterns recorded by regional instrumental records

Rapid northern hemisphere ice sheet melting during the penultimate deglaciation

The research was funded by HIDROPAST (CGL2010-16376) OPERA (CTM2013-48639-C2-1-R) and CHIMERA (CTM2016-75411-R) all to HMS, IC, and AM, and ETH core funding to HS. JT and MI were funded by doctoral FPI fellowships of CTM2013-48639-C2-1-R, and OK by doctoral Fellowship ETH-13 18-1. CP and HC acknowledge NSFC Grant 41888101, AM acknowledges CGL2016-77479-R, and R.L.E acknowledges NSF 1702816 and the 111 program of China grant D19002. IC and JT acknowledge Generalitat de Catalunya Grups de Recerca Consolidats grant 2017 SGR 315 to GRC Geociències Marines, and IC acknowledges the ICREA-Academia programme from the Generalitat de Catalunya and PID2019-105523RB-I00. EG is funded by a Royal Society University Research Fellowship (R1/180317).The rate and consequences of future high latitude ice sheet retreat remain a major concern given ongoing anthropogenic warming. Here, new precisely dated stalagmite data from NW Iberia provide the first direct, high-resolution records of periods of rapid melting of Northern Hemisphere ice sheets during the penultimate deglaciation. These records reveal the penultimate deglaciation initiated with rapid century-scale meltwater pulses which subsequently trigger abrupt coolings of air temperature in NW Iberia consistent with freshwater-induced AMOC slowdowns. The first of these AMOC slowdowns, 600-year duration, was shorter than Heinrich 1 of the last deglaciation. Although similar insolation forcing initiated the last two deglaciations, the more rapid and sustained rate of freshening in the eastern North Atlantic penultimate deglaciation likely reflects a larger volume of ice stored in the marine-based Eurasian Ice sheet during the penultimate glacial in contrast to the land-based ice sheet on North America as during the last glacial.Publisher PDFPeer reviewe

Last deglacial reorganization of the western Mediterranean thermohaline circulation: evidences from sedimentological and Nd isotopes proxies

Last glacial/interglacial transition involved significant changes in western Mediterranean (Med) thermohaline circulation that culminated with the formation of an organic rich layer (ORL) in the Alboran Sea from 14.5 to 9 ka BP. This event pre-dated the eastern Med stagnation associated with the Last Sapropel (S1: 10.8-7.1 kyr BP). Here we aim to gain in the understanding that those two events had in the oceanography of the westernmost Med and ultimately its impact on the Med outflow waters (MOW). Our approach combines sedimentological indicators (grain-size and XRF-core scanner data) with Nd isotopes measured in foraminifera diagenetic coatings as a proxy of water mass source. The studied material includes a set of cores covering a depth range from the Alboran Sea (from 300 to 1800 m) combined with a core from the Balearic Basin and another from the Gulf of Cadiz..