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- Reconstruction of surface water dynamics in the North Atlantic during the Mid-Pleistocene (similar to 540-400 ka), as inferred from coccolithophores and planktonic foraminiferaPublication . Martinez-Sanchez, Marta; Flores, Jose-Abel; Palumbo, Eliana; Alonso-Garcia, Montserrat; Sierro, Francisco-Javier; Amore, Filomena OrnellaChanges in paleoclimate and paleoproductivity patterns have been identified by analyzing the coccolithophore assemblages from the IODP Site U1314, located in the subpolar North Atlantic, together with other proxy data available during the time interval from the Marine Isotope Stages (MIS) 14 to MIS 11 (ca. 540 to 400 ka). The comparison of this data with that of MD03-2699, located off the Iberian Margin, allowed us to study their common response to environmental changes in terms of paleoproductivity and temperature variability. Statistical analyses of the composition of coccolithophore assemblages revealed that the calcareous plankton dynamics were mainly driven by eccentricity, which controlled the alternating migration of the Polar Front (PF) and the North Atlantic Current (NAC) at glacial-interglacial timescales. The high frequency variability of paleoproductivity, over imposed onto glacial/interglacial variability at both sites, were related to NAC intensifications on a precessional timescale. The northward (southward) migration of the PF caused a strengthening (weakening) of the NAC, which created an intensification (weakening) of the Irminger Current (IC) at Site U1314 and the Portugal Current (PC) at MD03-2699. Furthermore, low-latitude processes have been shown to influence climate in the high-latitude during the late Pleistocene. During MIS 14 and 12, enhanced glacial strength affected both coccolithophores and planktonic foraminifera, indicating a southward movement of the NAC. Using the same proxies, a northward movement of the NAC is recorded during MIS 13 and 11. Alternatively, the spectral analyses performed on calcareous plankton assemblages allowed the identification of a pattern of periodic response of the plankton at the orbital and, in some cases, millennial level, as well as abrupt Heinrich-type time-scale variability during Termination V (TV). This was the most extreme event and was related to a massive iceberg discharge from high to mid-latitudes.
- Pronounced northward shift of the westerlies during MIS 17 leading to the strong 100-kyr ice age cyclesPublication . Goni, Maria Fernanda Sanchez; Ferretti, Patrizia; Polanco-Martinez, Josue M.; Rodrigues, Teresa; Alonso-Garcia, Montserrat; Javier Rodriguez-Tovar, Francisco; Dorador, Javier; Desprat, StephanieThe MIS 17 interglacial, similar to 715-675 ka, marks the end of the Mid-Pleistocene Transition as intensified, long and asymmetrical 100-kyr ice age cycles became eminently established. Increasing arrival of moisture to the Northern Hemisphere high latitudes, resulting from the northwestward migration of the Subpolar Front and the intensification of the Norwegian Greenland Seas (NGS) convection, has been put forward to explain the emergence of this quasi-periodic 100-kyr cycle. However, testing this hypothesis is problematic with the available North Atlantic precipitation data. Here we present new pollen-based quantitative seasonal climate reconstructions from the southwestern Iberian margin that track changes in the position and intensity of the westerlies. Our data compared to changes in North Atlantic deep and surface water conditions show that MIS 17 interglacial was marked by three major changes in the direction and strength of the westerlies tightly linked to oceanographic changes. In particular, we report here for the first time a drastic two-steps northward shift of the westerlies centered at similar to 693 ka that ended up with the sustained precipitation over southern European. This atmospheric reorganization was associated with northwestward migration of the Subpolar Front, strengthening of the NGS deep water formation and cooling of the western North Atlantic region. This finding points to the substantial arrival of moisture to the Northern Hemisphere high latitudes at the time of the decrease in summer energy and insolation contributing to the establishment of strong 100-kyr cycles. (C) 2019 Elsevier B.V. All rights reserved.
- Correction to: A two million year record of low-latitude aridity linked to continental weathering from the MaldivesPublication . Kunkelova, Tereza; Jung, Simon J. A.; de Leau, Erica S.; Odling, Nick; Thomas, Alex L.; Betzler, Christian; Eberli, Gregor P.; Alvarez-Zarikian, Carlos A.; Alonso-Garcia, Montserrat; Bialik, Or M.; Blättler, Clara L.; Guo, Junhua A.; Haffen, Sébastien; Horozal, Senay; Mee, Anna L. H.; Inoue, Mayuri; Jovane, Luigi; Lanci, Luca; Laya, Juan C.; Lüdmann, Thomas; Bejugam, Nagender N.; Nakakuni, Masatoshi; Niino, Kaoru; Petruny, Loren M.; Pratiwi, Santi D.; Reijmer, John J. G.; Reolid, Jesús; Slagle, Angela L.; Sloss, Craig R.; Su, Xiang; Swart, Peter K.; Wright, James D.; Yao, Zhengquan; Young, Jeremy R.; Lindhorst, Sebastian; Stainbank, Stephanie; Rueggeberg, Andres; Spezzaferri, Silvia; Carrasqueira, Igor; Yu, Siyao; Kroon, DickIn the original version of this article (Kunkelova et al. 2018), published on 18 December 2018, there was 1 error in the author name of Dr. Yu.
- Magnetic properties of early Pliocene sediments from IODP Site U1467 (Maldives platform) reveal changes in the monsoon systemPublication . Lanci, Luca; Zanella, Elena; Jovane, Luigi; Galeotti, Simone; Alonso-Garcia, Montserrat; Alvarez-Zarikian, Carlos A.; Bejugam, Nagender Nath; Betzler, Christian; Bialik, Or M.; Blattler, Clara L.; Eberlik, Gregor P.; Guo, Junhua Adam; Haffen, Sebastien; Horozal, Senay; Inoue, Mayuri; Kroon, Dick; Laya, Juan Carlos; Mee, Anna Ling Hui; Luedmann, Thomas; Nakakunir, Masatoshi; Niino, Kaoru; Petruny, Loren M.; Pratiwi, Santi D.; Reijmer, John J. G.; Reolid, Jesus; Slagle, Angela L.; Sloss, Craig R.; Su, Xiang; Swart, Peter K.; Wright, James D.; Yao, Zhengquan; Young, Jeremy R.We report a study of the magnetic stratigraphy and the anisotropy of isothermal remanent magnetization of Pliocene sediments from International Ocean Discovery Program (IODP) Site U1467 drilled in the Maldives platform (Indian Ocean) during Exp. 359. Magnetic stratigraphy gives a precise record of geomagnetic reversals of the early Pliocene from approximately 5.3 Ma to 3.1 Ma providing a detailed age model in an interval where the biostratigraphic record is scarce. We use the anisotropy of isothermal remanent magnetization (AIRM) to investigate the statistical orientation of fine magnetic particles and provide data on the strength and direction of bottom currents during the early Pliocene. The strength of bottom currents recorded by the AIRM, shows a prominent increase at the top of Chron C3n.1n (about 4.2 Ma), and the current direction (NE - SW) is consistent with that of modern instrumental measurements. Since bottom currents in the Maldives are driven by the monsoon, we speculate that the 4.2 Ma increase of bottom currents could mark the onset of the present-day setting, probably related to the coeval uplift phase of the Himalayan plateau.
- Sea-surface temperature, productivity and hydrological changes in the Northern Indian Ocean (Maldives) during the interval similar to 575-175 ka (MIS 14 to 7)Publication . Alonso-Garcia, Montserrat; Rodrigues, Teresa; Abrantes, Fatima; Padilha, M.; Alvarez-Zarikian, C. A.; Kunkelova, T.; Wright, J. D.; Betzler, C.The South Asian Monsoon (SAM) drives seasonal changes in the atmospheric and ocean circulation of the tropical Indian Ocean, affecting precipitation on land and oceanic primary productivity. This work examined sediments from the International Ocean Discover Program (IODP) Site U1467 (IODP Expedition 359) located in the Maldives Inner Sea (Northern Indian Ocean) at a water depth of 487 m. The Maldives Inner Sea is a perfect location to study past changes in tropical climate and ocean circulation related to monsoon dynamics in the Equatorial Indian Ocean. This study focuses on the similar to 575-175 ka interval, from Marine Isotope Stage (MIS) 14 to 7, an important period for human evolution and dispersal to Eurasia. We reconstructed sea-surface temperature (SST), based on alkenone unsaturation index (U-37(K')), hydrological changes, based on terrestrial input of n-alkanes, and past surface ocean productivity, based on total C-37 alkenones concentration. The U-37(K')-SST record shows a difference of about 1.5 degrees C between glacial and interglacial periods, clearly showing all stages and substages from MIS 14 to 7, and revealing a connection between ice sheets extension and SST at the equatorial region. The n-alkanes concentration and average chain length index indicate vegetation changes at the Indian Peninsula with drier conditions generally associated with glacial periods. Precipitation increases abruptly at the end of terminations, lasting for a variable time interval in each interglacial period, except for MIS 13. However, other mechanisms superimposed to the glacial-interglacial forcing, such as the Indian Ocean Dipole (IOD) mode, have been invoked to explain shorter-scale variability in precipitation over India. The total alkenone concentration record indicates that primary productivity at Site U1467 is strongly associated with orbital changes, probably related to the summer inter-tropical insolation gradient (SITIG, 23N-23S on June 21st). High primary productivity occurred during intervals of low SITIG, which resulted in strong inter-monsoon (April-May and October-November) Indian Ocean Equatorial Westerlies (IEW) and reduced precipitation in the equatorial region. This mechanism may also be related to the IOD, which affects the strength of the IEW.
- Refinement of Miocene sea level and monsoon events from the sedimentary archive of the Maldives (Indian Ocean)Publication . Betzler, C.; Eberli, G. P.; Luedmann, T.; Reolid, J.; Kroon, D.; Reijmer, J. J. G.; Swart, P. K.; Wright, J.; Young, J. R.; Alvarez-Zarikian, C.; Alonso-Garcia, Montserrat; Bialik, O. M.; Blattler, C. L.; Guo, J. A.; Haffen, S.; Horozal, Senay; Inoue, Mayuri; Jovane, L.; Lanci, L.; Laya, J. C.; Mee, A. L. Hui; Nakakuni, M.; Nath, B. N.; Niino, K.; Petruny, L. M.; Pratiwi, S. D.; Slagle, A. L.; Sloss, C. R.; Su, X.; Yao, Z.International Ocean Discovery Program (IODP) Expedition 359 cored sediments from eight borehole locations in the carbonate platform of the Maldives in the Indian Ocean. The expedition set out to unravel the timing of Neogene climate changes, in particular the evolution of the South Asian monsoon and fluctuations of the sea level. The timing of these changes are assessed by dating resultant sedimentary alterations that mark stratigraphic turning points in the Neogene Maldives platform system. The first four turning points during the early and middle Miocene are related to sea-level changes. These are reliably recorded in the stratigraphy of the carbonate sequences in which sequence boundaries provide the ages of the sea-level lowstand. Phases of aggradational platform growth give precise age brackets of long-term sea-level high stands during the early Miocene and the early to middle Miocene Climate Optimum that is dated here between 17 to 15.1 Ma. The subsequent middle Miocene cooling coincident with the eastern Antarctic ice sheet expansion resulted in a long-term lowering of sea level that is reflected by a progradational platform growth. The change in platform architecture from aggradation to progradation marks this turning point at 15.1 Ma.& para;& para;An abrupt change in sedimentation pattern is recognized across the entire archipelago at a sequence boundary dated as 12.9-13 Ma. At this turning point, the platform sedimentation switched to a current-controlled mode when the monsoon-wind-driven circulation started in the Indian Ocean. The similar age of the onset of drift deposition from monsoon-wind-driven circulation across the entire archipelago indicates an abrupt onset of monsoon winds in the Indian Ocean. Ten unconformities dissect the drift sequences, attesting changes in current strength or direction that are likely caused by the combined product of changes in the monsoon-wind intensity and sea level fluctuations in the last 13 Ma. A major shift in the drift packages is dated with 3.8 Ma that coincides with the end of stepwise platform drowning and a reduction of the oxygen minimum zone in the Inner Sea.& para;& para;The strata of the Maldives platform provides a detailed record of the extrinsic controlling factors on carbonate platform growth through time. This potential of carbonate platforms for dating the Neogene climate and current changes has been exploited in other platforms drilled by the Ocean Drilling Program. For example, Great Bahama Bank, the Queensland Plateau, and the platforms on the Marion Plateau show similar histories with sediment architectures driven by sea level in their early history (early to middle Miocene) replaced by current-driven drowning or partial drowning during their later history (Late Miocene). In all three platform systems, the influence of currents on sedimentations is reported between 11 and 13 Ma.
- Cyclic anoxia and organic rich carbonate sediments within a drowned carbonate platform linked to Antarctic ice volume changes: Late Oligocene-early Miocene MaldivesPublication . Swart, Peter K.; Blattler, Clara L.; Nakakuni, Masatoshi; Mackenzie, Greta J.; Betzler, Christian; Eberli, Gregor P.; Reolid, Jesus; Alonso-Garcia, Montserrat; Slagle, Angela L.; Wright, James D.; Kroon, Dick; Reijmer, John J. G.; Mee, Anna L. Hui; Young, Jeremy R.; Alvarez-Zarikian, Carlos A.; Bialik, Orr M.; Guo, Junhua Adam; Haffen, Sebastian; Horozal, Senay; Inoue, Mayuri; Jovane, Luigi; Lanci, Luca; Laya, Juan Carlos; Luedmann, Thomas; Nath, B. Nagender; Niino, Kaoru; Petruny, Loren M.; Pratiwi, Santi Dwi; Su, Xiang; Sloss, Craig R.; Yao, ZhengquanThis paper reports on the newly discovered occurrence of thick sequences (similar to 100 m) of Late Oligocene and Early Miocene (similar to 24.9 to similar to 20 Ma) interbedded organic-rich sediments (sapropels) and pelagic (organic poor) carbonates at Sites 01466 and U1468 drilled in the Maldives archipelago during the International Ocean Discovery Program (IODP) Expedition 359. This occurrence is unusual in that this sequence is located > 1000 m above the surrounding ocean floor within an inter-atoll basin and not linked to any known global oceanic events. Total organic content reaches as high as 35% in the darker layers, while the interbedded carbonates have concentrations of less than 0.1%. Trace elements characteristic of anoxic waters, such as Mo, V, Cr, U, and Pb, correlate positively with concentrations of organic carbon. Nitrogen isotopic data show no evidence that the intervals of high total organic carbon are related to enhanced productivity driven by upwelling. Instead, high organic carbon is associated with intervals of anoxia. We propose that sea-level fluctuations linked to changes in Antarctic ice volume restricted exchange with the open ocean causing bottom waters of the inter-atoll basin to become anoxic periodically. The architecture of the platform at the end of the Oligocene, combined with the global sea-level highstand, set the stage for orbitally-driven sea-level changes producing cyclic deposition of sapropels. The proposed mechanism may serve as an analogue for other occurrences of organic carbon rich sediments within carbonate platform settings. (C) 2019 Elsevier B.V. All rights reserved.
- A 1-Ma record of sea surface temperature and extreme cooling events in the North Atlantic: A perspective from the Iberian MarginPublication . Rodrigues, Teresa; Alonso-Garcia, Montserrat; Hodell, D. A.; Rufino, MM; Naughton, F.; Grimalt, J. O.; H L Voelker, Antje; Abrantes, FatimaThe Iberian Margin is a sensitive area to track high and low latitude processes, and is a key location to understand major past climatic and oceanographic changes. Here we present new biomarker data from IODP Site U1385 ("Shackleton site") (1017-336 ka) that, when combined with existing data from Cores MD01-2443/4 (last 335 ka), allows us to assess the evolution of sea surface temperature (SST) and meltwater influx over the last 1 Ma at the Iberian Margin. Interglacial periods throughout the last 1 Ma show SST close to 20 degrees C, even during the so-called "luke-warm" interglacials that are marked by relatively low atmospheric CO2 concentrations. During glacial periods, extremely cold stadial events are recognized at the Iberian Margin, and are very likely related to meltwater discharges from the European and British-Irish ice sheets into the NE Atlantic, which were transported southwards by the Portugal Current. We subdivided the record into four intervals on the basis of the timing and the magnitude of these extremely cold stadials: 1) from 1017 to similar to 900 ka, only minor sporadic freshwater input occurred during deglaciations; 2) from 900 to 675 ka extreme cold events occur as terminal stadial events at the beginning of the deglaciations, which results in abrupt deglacial SST shifts; 3) from 675 to 450 ka only a few, very short-lived events are recorded and seldom is there freshwater input at the Iberian Margin; 4) during the last 450 ka the extreme cold events occurred under full glacial conditions, with particularly severe events during MIS 6 and 8. We propose these mid -glacial events are associated with a strong discharges of European ice sheet (EIS). The fact that these extreme cold events do not coincide with deglaciations questions the role of European ice sheet discharges in triggering deglaciations. (C) 2017 Elsevier Ltd. All rights reserved.
- Sea-level and monsoonal control on the Maldives carbonate platform (Indian Ocean) over the last 1.3 million yearsPublication . Alonso-Garcia, Montserrat; Reolid, Jesus; Jimenez-Espejo, Francisco J.; Bialik, Or M.; Alvarez Zarikian, Carlos A.; Laya, Juan Carlos; Carrasquiera, Igor; Jovane, Luigi; Reijmer, John J. G.; Eberli, Gregor P.; Betzler, ChristianThe Maldives Archipelago (Indian Ocean), composed of two rows of atolls that enclose an inner sea, offers an excellent study site to explore the forcings of carbonate production at platforms. Glacial-interglacial sea-level changes have been claimed to be the main factor controlling the carbonate platform factories; however, climatic factors may also have an impact. In this work we used geochemical compositional records, obtained by X-ray fluorescence (XRF) core-scanning from the International Ocean Discovery Program (IODP) Site U1467 in the Maldives Inner Sea, to analyze the orbitally driven fluctuations on the carbonate production and export from the neritic environment into the Maldives Inner Sea over the last 1.3 million years.High Sr aragonite-rich carbonates (HSAC) from neritic settings were deposited in the Maldives Inner Sea during sea-level highstand intervals, increasing the Sr / Ca values. In contrast, low Sr / Ca values are observed coincident with sea-level lowstand periods, suggesting that large areas of the atolls were exposed or unable to grow, and therefore, there was a demise in the carbonate production and sediment export to the Maldives Inner Sea. However, comparison of the Sr / Ca values and the sea-level reconstructions for different interglacial periods before and after the mid-Brunhes event (MBE, similar to 430 ka ) indicates that sea level is not the only factor controlling the production of HSAC during sea-level highstands. The study of monsoon and primary productivity proxies ( Fe -normalized, Fe / K , and Br -normalized records) from the same site suggests that the intensity of the summer monsoon and the Indian Ocean dipole probably modulated the carbonate production at the atolls. Moreover, Marine Isotope Stage 11 stands out as a period with high sea level and extraordinary carbonate production in the Maldives platform. This outstanding carbonate production in the Maldives atolls (and in other low-latitude carbonate platforms) probably contributed to the mid-Brunhes dissolution event through a strong shelf-to-basin fractionation of carbonate deposition.
- A two million year record of low-latitude aridity linked to continental weathering from the MaldivesPublication . Kunkelova, Tereza; Jung, Simon J. A.; de Leau, Erica S.; Odling, Nick; Thomas, Alex L.; Betzler, Christian; Eberli, Gregor P.; Alvarez-Zarikian, Carlos A.; Alonso-Garcia, Montserrat; Bialik, Or M.; Blättler, Clara L.; Guo, Junhua A.; Haffen, Sébastien; Horozal, Senay; Mee, Anna L. H.; Inoue, Mayuri; Jovane, Luigi; Lanci, Luca; Laya, Juan C.; Lüdmann, Thomas; Bejugam, Nagender N.; Nakakuni, Masatoshi; Niino, Kaoru; Petruny, Loren M.; Pratiwi, Santi D.; Reijmer, John J. G.; Reolid, Jesús; Slagle, Angela L.; Sloss, Craig R.; Su, Xiang; Swart, Peter K.; Wright, James D.; Yao, Zhengquan; Young, Jeremy R.; Lindhorst, Sebastian; Stainbank, Stephanie; Rueggeberg, Andres; Spezzaferri, Silvia; Carrasqueira, Igor; Hu, Siyao; Kroon, DickIndian-Asian monsoon has oscillated between warm/wet interglacial periods and cool/dry glacial periods with periodicities closely linked to variations in Earth’s orbital parameters. However, processes that control wet versus dry, i.e. aridity cyclical periods on the orbital time-scale in the low latitudes of the Indian-Asian continent remain poorly understood because records over millions of years are scarce. The sedimentary record from International Ocean Discovery Program (IODP) Expedition 359 provides a well-preserved, high-resolution, continuous archive of lithogenic input from the Maldives reflecting on low-latitude aridity cycles. Variability within the lithogenic component of sedimentary deposits of the Maldives results from changes in monsoon-controlled sedimentary sources. Here, we present X-ray fluorescence (XRF) core-scanning results from IODP Site U1467 for the past two million years, allowing full investigation of orbital periodicities. We specifically use the Fe/K as a terrestrial climate proxy reflecting on wet versus dry conditions in the source areas of the Indian-Asian landmass, or from further afield. The Fe/K record shows orbitally forced cycles reflecting on changes in the relative importance of aeolian (stronger winter monsoon) during glacial periods versus fluvial supply (stronger summer monsoon) during interglacial periods. For our chronology, we tuned the Fe/K cycles to precessional insolation changes, linking Fe/K maxima/minima to insolation minima/maxima with zero phase lag. Wavelet and spectral analyses of the Fe/K record show increased dominance of the 100 kyr cycles after the Mid Pleistocene Transition (MPT) at 1.25 Ma in tandem with the global ice volume benthic δ18O data (LR04 record). In contrast to the LR04 record, the Fe/K profile resolves 100-kyr-like cycles around the 130 kyr frequency band in the interval from 1.25 to 2 million years. These 100-kyr-like cycles likely form by bundling of two or three obliquity cycles, indicating that low-latitude Indian-Asian climate variability reflects on increased tilt sensitivity to regional eccentricity insolation changes (pacing tilt cycles) prior to the MPT. The implication of appearance of the 100 kyr cycles in the LR04 and the Fe/K records since the MPT suggests strengthening of a climate link between the low and high latitudes during this period of climate transition.