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We present a new high-resolution cyclostratigraphic age model for the Messinian sediments of the Montemayor-1 core. This core was drilled in the Guadalquivir Basin in southern Spain, which formed part of the marine corridor linking the Mediterranean with the Atlantic in the Late Miocene. Tuning of high-resolution geochemical records reveals a strong precessional cyclicity, with maximum clastic supply from river run off coinciding with maximum summer insolation. We recognize a gradual change in the nature of the typical cyclic fluctuations in elemental compositions of the sediments through the core, which is associated with a gradual change in depositional environment as the basin infilled. After applying the new age model, the upper Messinian glacial stages and deglaciation are clearly identified in the oxygen isotope records of the Montemayor-1 core. Reinterpretation of existing planktonic and benthic oxygen isotope records for the core and comparison with equivalent successions in the Rifian Corridor in northern Morocco allow the re-evaluation of the influence of the different water masses in the region: North Atlantic Central Water and Mediterranean Outflow Water. We observe no direct influence of MOW immediately before or during the Messinian Salinity Crisis. [ABSTRACT FROM AUTHOR]

Abstract: Stable carbon and oxygen isotopes from benthic and planktic foraminifers, planktic foraminifer assemblages and ice rafted debris from the North Atlantic Site U1314 (Integrated Ocean Drilling Program Expedition 306) were examined to investigate orbital and millennial-scale climate variability in the North Atlantic and its impact on global circulation focusing on the development of glacial periods during the mid-Pleistocene (ca 800–400ka). Glacial initiations were characterized by a rapid cooling (6–10°C in less than 7kyr) in the mean annual sea surface temperature (SST), increasing benthic δ18O values and high benthic δ13C values. The continuous increase in benthic δ18O suggests a continuous ice sheet growth whereas the positive benthic δ13C values indicate that the flow of the Iceland Scotland Overflow water (ISOW) was vigorous. Strong deep water formation in the Norwegian Greenland Sea promoted a high transfer of freshwater from the ocean to the continents. However, low SSTs at Site U1314 suggest a subpolar gyre cooling and freshening that may have reduced deep water formation in the Labrador Sea during glacial initiations. Once the 3.5‰ threshold in the benthic δ18O record was exceeded, ice rafting started and ice sheet growth was punctuated by millennial-scale waning events which returned to the ocean part of the freshwater accumulated on the continents. Ice-rafting events were associated with a rapid reduction in the ISOW (benthic δ13C values dropped 0.5–1‰) and followed by millennial-scale warmings. The first two millennial-scale warm intervals of each glacial period reached interglacial temperatures and were particularly abrupt (6–10°C in ∼3kyr). Subsequent millennial-scale warm events were cooler probably because the AMOC was rather reduced as suggested by the low benthic δ13C values. These two abrupt warming events that occurred at early glacial periods were also observed in the Antarctic temperature and CO2 records, suggesting a close correlation between both Hemispheres. The comparison of the sea surface proxies with the benthic δ18O record (as the Southern sign) indicates the presence of a millennial-scale seesaw pattern similar to that seen during the Last Glacial period. [Copyright &y& Elsevier]

Land–sea climatic proxies have been obtained from the Last Glacial section of IMAGES core MD95-2043 (western Mediterranean Sea). Vegetation and alkenone derived SST curves indicate rapid (∼150 years) and synchronous terrestrial and marine climatic changes, paralleling the Dansgaard–Oeschger (D–O) climatic variability over Greenland. This frequency of climate change can be related to shifts between the two modes of operation of the North Atlantic Oscillation (NAO). Transfer functions applied to the pollen data indicate that there was an amplification of the climatic signal during Heinrich events (HEs) in comparison with other D–O stadials. The development and persistence of both Scandinavian and Atlantic Mobile Polar Highs over southwestern Europe may explain the extreme cooling (∼10 °C) and dryness (400 mm) during Heinrich events 5 and 4 in the Mediterranean region. Comparison of the results of core MD95-2043 with similar climatic data from IMAGES core MD95-2042, located off Portugal, indicates that thermal and precipitation gradients occurred between the Mediterranean and the Atlantic sides of Iberia within HEs. HEs 4 and 5 are associated with more humid conditions in the Atlantic (by 200 mm) than in the Mediterranean site, as is the case at the present time. This comparison also illustrates the different behaviour of these areas during the D–O stadials. In contrast with the Mediterranean site, the Atlantic site shows similar precipitation and temperature drops for all the D–O stadials, including those related to the HEs. Here we propose the operation of different Mobile Polar Highs (MPH) as the driving mechanism for this difference in behaviour between the Atlantic and Mediterranean sides of Iberia. HEs are related to a stronger influence of the Scandinavian MPH, forcing a severe aridification and cooling of the full Iberian Peninsula. The Atlantic MPH may have been dominant during the other stadials, which would preferentially affect Southwestern Iberia. [ABSTRACT FROM AUTHOR]

Abstract: A high-resolution record of radiolarian assemblages from Site U1314 was studied to reconstruct hydrographic and climatic changes in the North Atlantic Ocean during the Mid-Pleistocene Transition period (1069–779ka). Besides the faunal record, absolute accumulation of radiolarians and total biogenic opal are used to determine changes in surface water productivity. Results show that the North Atlantic Arctic Front shifted back and forth repeatedly at a glacial/interglacial timescale, bringing the site under the influence of both cold Arctic (glacial), and much warmer Atlantic (interglacial) waters. During glacial intervals and “ice-rafted debris” (IRD) events, the deep-dwelling taxon Cycladophora davisiana was the greatest contributor of the radiolarian assemblage, suggesting cold surface conditions, melt-water discharge and changes in deep and intermediate circulation. Interglacial intervals were characterized by abundant shallow-dwelling taxa like Pseudodyctiophimus gracilipes and Lithomelissa setosa, increased opal accumulation, and higher radiolarian diversities, indicating a northward flow of warm Atlantic surface waters to the Site U1314 area. A marked change in the structure of the radiolarian assemblage occurred after MIS 22 (~860ka), with large taxa differences between warm and cold periods, probably in response to changing ocean conditions due to the higher amplitude of glacial/interglacial changes as the dominant periodicity of high-latitude climate oscillations shifted from 41-kyr to 100-kyr. Thus, we conclude that the radiolarian assemblage from the North Atlantic have changed drastically along with variations in ocean circulation in response to orbital and millennial-scale climatic variations that occurred in the Early and Mid-Pleistocene. [Copyright &y& Elsevier]

Abstract: Global climate changes attract the attention of researchers working with paleoceanographic proxies for reconstructing past ocean circulation changes and the physico-chemical parameters that control environmental conditions. Moreover, recent studies highlight the importance of climate change on deep sea benthic biodiversity. Deep sea benthic fauna are not isolated from atmospheric processes and climate changes controlling surface ocean biota, for benthic assemblages respond to changing climatic conditions as well. Substrate and physico-chemical characteristics of bottom waters have particularly strong influence on ostracod species distribution in all marine settings, making them excellent environmental indicators. This paper focuses on changes in ostracod assemblages at MD99-2348 site, located on the continental slope of the Gulf of Lions to determine the relationship between climatic-driven oceanographic changes and ostracod diversity and abundance. High abundances of Henryhowella asperrima and Echinocythereis echinata during Heinrich events (HE1 and HE2) may result from increased oxygenation of the bottom water and a more pulsed supply of nutrients (organic matter). Formation of surface cold water that increases the oxygen content in deep layers in the water column is linked to the intensification of northerly wind (Tramontane and Mistral) in northwestern Mediterranean during the acme of HEs, when high latitudes bodies of cold air (Mobile Polar Highs) reach the Mediterranean area. Moreover, the concomitant high abundance of Krithe pernoides, which proved to be very sensitive to variable oxygen levels, probably records even shorter (millennial to centennial scale) climate oscillations. Changes in environmental conditions are illustrated by the shift of C. testudo–Loxoconcha spp. vs. Pseudocythere sp.–Macrocypris sp. that indicates detrital input, primary productivity and the possible impact of sea level oscillation on benthic assemblages since the LGM. [Copyright &y& Elsevier]

Abstract: The IMAGES core MD99-2343, recovered from a sediment drift north of the island of Minorca, in the north-western Mediterranean Sea, holds a high-resolution sequence that is perfectly suited to study the oscillations of the overturning system of the Western Mediterranean Deep Water (WMDW). Detailed analysis of grain-size and bulk geochemical composition reveals the sensitivity of this region to climate changes at both orbital and centennial–millennial temporal scales during the last 50kyr. The dominant orbital pattern in the K/Al record indicates that sediment supply to the basin was controlled by the insolation evolution at 40°N, which forced changes in the fluvial regime, with more efficient sediment transport during insolation maxima. This orbital control also modulated the long-term pattern of the WMDW intensity as illustrated by the silt/clay ratio. However, deep convection was particularly sensitive to climatic changes at shorter time-scales, i.e. to centennial–millennial glacial and Holocene oscillations that are well documented by all the paleocurrent intensity proxies (Si/Al, Ti/Al and silt/clay ratios). Benthic isotopic records (δ13C and δ18O) show a Dansgaard–Oeschger (D–O) pattern of variability of WMDW properties, which can be associated with changing intensities of the deep currents system. The most prominent reduction on the WMDW overturning was caused by the post-glacial sea level rise. Three main scenarios of WMDW overturning are revealed: a strong mode during D–O Stadials, a weak mode during D–O Interstadials and an intermediate mode during cooling transitions. In addition, D–O Stadials associated with Heinrich events (HEs) have a very distinct signature as the strong mode of circulation, typical for the other D–O Stadials, was never reached during HE due to the surface freshening induced by the inflowing polar waters. Consequently, the WMDW overturning system oscillated around the intermediate mode of circulation during HE. Though surface conditions were more stable during the Holocene, the WMDW overturning cell still reacted synchronously to short-lived events, as shown by increments in the planktonic δ18O record, triggering quick reinforcements of the deep water circulation. Overall, these results highlight the sensitivity of the WMDW to rapid climate change which in the recent past were likely induced by oceanographic and atmospheric reorganizations in the North Atlantic region. [Copyright &y& Elsevier]