Filter Results
84 results
  • Abstract: Planktonic foraminiferal faunas of the southeast Pacific indicate that sea surface temperatures (SST) have varied by as much as 8–10°C in the Peru Current, and by ∼5–7°C along the equator, over the past 150,000 years. Changes in SST at times such as the Last Glacial Maximum reflect incursion of high-latitude species Globorotalia inflata and Neogloboquadrina pachyderma into the eastern boundary current and as far north as the equator. A simple heat budget model of the equatorial Pacific shows that observed changes in Peru Current advection can account for about half of the total variability in equatorial SSTs. The remaining changes in equatorial SST, which are likely related to local changes in upwelling or pycnocline depth, precede changes in polar climates as recorded by d18O. This partitioning of processes in eastern equatorial Pacific SST reveals that net ice-age cooling here reflects first a rapid response of equatorial upwelling to insolation, followed by a later response to changes in the eastern boundary current associated with high-latitude climate (which closely resembles variations in atmospheric CO2 as recorded in the Vostok ice core). Although precise mechanisms responsible for the equatorial upwelling component of climate change remain uncertain, one likely candidate that may operate independently of the ice sheets is insolation-driven changes in El Niño/Southern Oscillation (ENSO) frequency. Early responses of equatorial SST detected both here and elsewhere highlight the sensitivity of tropical systems to small changes in seasonal insolation. The scale of tropical changes we have observed are substantially greater than model predictions, suggesting a need for further quantitative assessment of processes associated with long-term climate change. Category: geoscientificInformation Source: Supplement to: Feldberg, Melissa J; Mix, Alan C (2003): Planktonic foraminifera, sea surface temperatures, and mechanisms of oceanic change in the Peru and south equatorial currents, 0-150 ka BP. Paleoceanography, 18(1), 1016, https://doi.org/10.1029/2001PA000740 Supplemental Information: Not Availble Coverage: Not Available
    Data Types:
    • Other
    • Collection
  • Abstract: High-resolution palaeoclimate records based on oxygen isotope data have provided important insights into climate variability and rates of natural climate change on about a thousand-year timescale. Little is known, however, about the variation of climate and of palaeoceanographic conditions throughout the Quaternary on timescales of less than 1,000 years (at frequencies far greater than those of the Milankovitch orbital cycles). Here we show that such high time resolution is possible from molecular stratigraphic studies based on 'biomarker' organic molecules (alkenones). We have sampled alkenone stratigraphic records at 70- to 200-yr intervals across glacial terminations I, II and IV in sediment cores from OOP site 658, off northwest Africa. Sea surface temperatures (SSTs) derived from the alkenone (Uk 37) index vary rapidly beyond the range of analytical noise by up to 2.5 °C in 300 yr, showing hitherto unknown cycles with about 600-yr periodicities. Some of the changes parallel similar events in the oxygen isotope stratigraphy. SST oscillations may be linked, in part, to abrupt breakdowns in Atlantic deep-water ventilation resulting from meltwater events of Quaternary glacial terminations. Category: geoscientificInformation Source: Supplement to: Eglinton, Geoffrey; Bradshaw, S; Resell, A; Sarnthein, Michael; Pflaumann, Uwe; Tiedemann, Ralf (1992): Molecular record of secular sea surface temperature changes on 100-year timescales for glacial terminations I, II and IV. Nature, 356(6368), 423-426, https://doi.org/10.1038/356423a0 Supplemental Information: Depth is given as m.c.d. (meter composite depth). Coverage: EVENT LABEL: * LATITUDE: 20.749200 * LONGITUDE: -18.580800 * DATE/TIME START: 1986-03-04T00:00:00 * DATE/TIME END: 1986-03-08T00:00:00 * ELEVATION: -2274.0 m * Penetration: 537.1 m * Recovery: 541.5 m * LOCATION: Canarias Sea * CAMPAIGN: Leg108 * BASIS: Joides Resolution * DEVICE: Composite Core
    Data Types:
    • Tabular Data
    • Dataset
  • Abstract: A marine sediment core (JM09-KA11-GC) from the Kveithola Trough at the western Barents Sea margin has been investigated in order to reconstruct sub-surface temperatures and sea ice distribution at a sub-centennial resolution throughout the Holocene. The relationship between past variability of Atlantic water inflow and sea ice distribution has been established by measurement of planktic foraminifera, stable isotopes and biomarkers from sea ice diatoms and phytoplankton. Throughout the early Holocene (11 900–7300 cal yr BP), the foraminiferal fauna is dominated by the polar species Neogloboquadrina pachyderma (sinistral) and the biomarkers show an influence of seasonal sea ice. Between 10 900 and 10 700 cal yr BP, a clear cooling is shown both by fauna and stable isotope data corresponding to the so-called Preboreal Oscillation. After 7300 cal yr BP, the sub-polar Turborotalita quinqueloba becomes the most frequent species, reflecting a stable Atlantic water inflow. Sub-surface temperatures reach 6 °C and biomarker data indicate mainly ice-free conditions. During the last 1100 cal yr BP, biomarker abundances and distributions show the reappearance of low-frequency seasonal sea ice and the planktic fauna show a reduced salinity in the sub-surface water. No apparent temperature decrease is observed during this interval, but the rapidly fluctuating fauna and biomarker distributions indicate more unstable conditions. Category: geoscientificInformation Source: Supplement to: Berben, Sarah M P; Husum, Katrine; Cabedo-Sanz, Patricia; Belt, Simon T (2014): Holocene sub-centennial evolution of Atlantic water inflow and sea ice distribution in the western Barents Sea. Climate of the Past, 10(1), 181-198, https://doi.org/10.5194/cp-10-181-2014 Supplemental Information: Not Availble Coverage: EVENT LABEL: * LATITUDE: 74.874820 * LONGITUDE: 16.484820 * ELEVATION: -345.0 m * Recovery: 3.83 m * LOCATION: Norwegian Sea * CAMPAIGN: JM09702 * BASIS: Jan Mayen * METHOD|DEVICE: Gravity corer
    Data Types:
    • Other
  • Abstract: We reconstructed subsurface (~45-200 m water depth) temperature variability in the eastern Antarctic continental margin during the late Holocene, using an archaeal lipid-based temperature proxy (TEX86L). Our results reveal that subsurface temperature changes were probably positively coupled to the variability of warmer, nutrient-rich Modified Circumpolar Deep Water (MCDW, deep water of the Antarctic circumpolar current) intrusion onto the continental shelf. The TEX86L record, in combination with previously published climatic records, indicates that this coupling was probably related to the thermohaline circulation, seasonal variability in sea ice extent, sea temperature, and wind associated with high frequency climate dynamics at low-latitudes such as internal El Niño Southern Oscillation (ENSO). This in turn suggests a linkage between centennial ENSO-like variability at low-latitudes and intrusion variability of MCDW into the eastern Antarctic continental shelf, which might have further impact on ice sheet evolution. Category: geoscientificInformation Source: Supplement to: Kim, Jung-Hyun; Crosta, Xavier; Willmott, Verónica; Renssen, Hans; Bonnin, Jerome; Helmke, Peer; Schouten, Stefan; Sinninghe Damsté, Jaap S (2012): Holocene subsurface temperature variability in the eastern Antarctic continental margin. Geophysical Research Letters, 39, L06705, https://doi.org/10.1029/2012GL051157 Supplemental Information: Data were obtained within the framework of the ERC PACEMAKER project (Grant number: 226600) and ANR CLIMICE (ANR-08-CEXC-012-01), provided for the data compilation of the Past4Future Project. Coverage: EVENT LABEL: (MD032601) * LATITUDE: -66.051200 * LONGITUDE: 138.557200 * DATE/TIME: 2003-02-08T08:51:00 * ELEVATION: -746.0 m * Recovery: 40.3 m * LOCATION: Southern Ocean * CAMPAIGN: MD130 * BASIS: Marion Dufresne (1995) * METHOD/DEVICE: Calypso Corer
    Data Types:
    • Tabular Data
    • Dataset
  • Abstract: A multiproxy record has been acquired from a piston core (SO139-74KL) taken offshore southern Sumatra, an area which is situated in the southwestern sector of the tropical Indo-Pacific Warm Pool. The high-resolution data sets (X-ray fluorescence, total organic carbon, and C37 alkenones) were used to track changes in paleoproductivity, freshwater budget, and sea surface temperature (SST) of the tropical climate system at orbital time scales over the past 300 ka. Our paleoclimatic data show that enhanced marine paleoproductivity was directly related to strengthening of coastal upwelling during periods of increased boreal summer insolation and associated SE monsoon strength with a precessional cyclicity. Changes in freshwater supply were primarily forced by precession-controlled changes in boreal NW winter monsoon rainfall enclosing an additional sea level component. SST variations of 2°-5°C occurred at eccentricity and precessional cyclicity. We suggest that the sea surface temperature variability off southern Sumatra is predominantly related to three major causes: (1) variations in upwelling intensity; (2) an elevated freshwater input into the southern Makassar Strait leading to reduced supply of warmer surface waters from the western Pacific and increased subsurface water transport via the Indonesian Throughflow into the Indian Ocean; and (3) long-term changes in the intensity or frequency of low-latitude climate phenomena, such as El Niño-Southern Oscillation. Category: geoscientificInformation Source: Supplement to: Lückge, Andreas; Mohtadi, Mahyar; Rühlemann, Carsten; Scheeder, Georg; Vink, Annemiek; Reinhardt, Lutz; Wiedicke, Michael (2009): Monsoon versus ocean circulation controls on paleoenvironmental conditions off southern Sumatra during the past 300,000 years. Paleoceanography, 24(1), PA1208, https://doi.org/10.1029/2008PA001627 Supplemental Information: Not Availble Coverage: EVENT LABEL: * LATITUDE: -6.543000 * LONGITUDE: 103.833000 * ELEVATION: -1690.0 m * Recovery: 19.3 m * LOCATION: Indonesia * CAMPAIGN: SO139 * BASIS: Sonne * METHOD/DEVICE: Piston corer (BGR type)
    Data Types:
    • Collection
  • Abstract: Most of the helium-3 in oceanic sediments conies from interplanetary dust particles (IDPs), and can therefore be used to infer the accretion rate of dust to the Earth through time (Ozima et al., 1984, doi:10.1038/311448a0; Takayanagi and Ozima, 1987, doi:10.1029/JB092iB12p12531; Farley, 1995, doi:10.1038/376153a0). 3He records from slowly accumulating pelagic clays indicate that the accretion rate varies considerably over millions of years, probably owing to cometary and asteroidal break-up events3. Muller and MacDonald have proposed (Muller and MacDonald, 1995, doi:10.1038/377107b0) that periodic changes in this accretion rate due to a previously unrecognized 100-kyr periodicity in the Earth's orbital inclination might account for the prominence of this frequency in climate records of the past million years (Imbrie et al., 1993, doi:10.1029/93PA02751). Here we report variations in the 3He flux to the sea floor that support this idea. We find that the flux recorded in rapidly accumulating Quaternary sediments from the Mid-Atlantic Ridge oscillates with a period of about 100 kyr. We cannot yet say, however, whether the 100-kyr climate cycle is a consequence of, a cause of, or an effect independent of these periodic changes in the rate of delivery of interplanetary dust to the sea floor. Category: geoscientificInformation Source: Supplement to: Farley, Kenneth A; Patterson, D B (1995): A 100-kyr periodicity in the flux of extraterrestrial 3He to the sea floor. Nature, 378(6557), 521-644, https://doi.org/10.1038/378600a0 Supplemental Information: Core disruption between cores 94-607-2 and 94-607-3 precludes accurate determination of sedimentation rates in this interval; the mean value of the other 10 cycles has been adopted for this cycle. Coverage: EVENT LABEL: * LATITUDE: 41.001200 * LONGITUDE: -32.957300 * DATE/TIME: 1983-07-06T00:00:00 * ELEVATION: -3427.0 m * Penetration: 284.4 m * Recovery: 248.6 m * LOCATION: North Atlantic/FLANK * CAMPAIGN: Leg94 * BASIS: Glomar Challenger * DEVICE: Drilling/drill rig
    Data Types:
    • Tabular Data
    • Dataset
  • Abstract: Date-32 is a fast and easily used computer program developed to date Quaternary deep-sea cores by associating variations in the earth's orbit with recurring oscillations in core properties, such as carbonate content or isotope composition. Starting with known top and bottom dates, distortions in the periodicities of the core properties due to varying sedimentation rates are realigned by fast Fourier analysis so as to maximise the spectral energy density at the orbital frequencies. This allows age interpolation to all parts of the core to an accuracy of 10 kyrs, or about 1.5% of the record duration for a typical Brunhes sequence. The influence of astronomical forcing is examined and the method is applied to provide preliminary dates in a high-resolution Brunhes record from DSDP Site 594 off southeastern New Zealand. Category: geoscientificInformation Source: Supplement to: Black, Kerry P; Nelson, Campbell S; Hendy, Chris H (1988): A spectral analysis procedure for dating Quaternary deep-sea cores and its application to a high-resolution Brunhes record from the Southwest Pacific. Marine Geology, 83(1-4), 21-30, https://doi.org/10.1016/0025-3227(88)90049-7 Supplemental Information: Not Availble Coverage: EVENT LABEL: * LATITUDE: -45.523500 * LONGITUDE: 174.948000 * DATE/TIME: 1983-01-03T00:00:00 * ELEVATION: -1204.0 m * Penetration: 505.1 m * Recovery: 300.7 m * LOCATION: South Pacific/CONT RISE * CAMPAIGN: Leg90 * BASIS: Glomar Challenger * METHOD|DEVICE: Drilling/drill rig
    Data Types:
    • Collection
    • File Set
  • Abstract: Since the seminal work by Hays et al. (1976), a plethora of studies has demonstrated a correlation between orbital variations and climatic change. However, information on how changes in orbital boundary conditions affected the frequency and amplitude of millennial-scale climate variability is still fragmentary. The Marine Isotope Stage (MIS) 19, an interglacial centred at around 785 ka, provides an opportunity to pursue this question and test the hypothesis that the long-term processes set up the boundary conditions within which the short-term processes operate. Similarly to the current interglacial, MIS 19 is characterised by a minimum of the 400-kyr eccentricity cycle, subdued amplitude of precessional changes, and small amplitude variations in insolation. Here we examine the record of climatic conditions during MIS 19 using high-resolution stable isotope records from benthic and planktonic foraminifera from a sedimentary sequence in the North Atlantic (Integrated Ocean Drilling Program Expedition 306, Site U1313) in order to assess the stability and duration of this interglacial, and evaluate the climate system's response in the millennial band to known orbitally induced insolation changes. Benthic and planktonic foraminiferal d18O values indicate relatively stable conditions during the peak warmth of MIS 19, but sea-surface and deep-water reconstructions start diverging during the transition towards the glacial MIS 18, when large, cold excursions disrupt the surface waters whereas low amplitude millennial scale fluctuations persist in the deep waters as recorded by the oxygen isotope signal. The glacial inception occurred at ~779 ka, in agreement with an increased abundance of tetra-unsaturated alkenones, reflecting the influence of icebergs and associated meltwater pulses and high-latitude waters at the study site. After having combined the new results with previous data from the same site, and using a variety of time series analysis techniques, we evaluate the evolution of millennial climate variability in response to changing orbital boundary conditions during the Early-Middle Pleistocene. Suborbital variability in both surface- and deep-water records is mainly concentrated at a period of ~11 kyr and, additionally, at ~5.8 and ~3.9 kyr in the deep ocean; these periods are equal to harmonics of precession band oscillations. The fact that the response at the 11 kyr period increased over the same interval during which the amplitude of the response to the precessional cycle increased supports the notion that most of the variance in the 11 kyr band in the sedimentary record is nonlinearly transferred from precession band oscillations. Considering that these periodicities are important features in the equatorial and intertropical insolation, these observations are in line with the view that the low-latitude regions play an important role in the response of the climate system to the astronomical forcing. We conclude that the effect of the orbitally induced insolation is of fundamental importance in regulating the timing and amplitude of millennial scale climate variability. Category: geoscientificInformation Source: Supplement to: Ferretti, Patrizia; Crowhurst, Simon J; Naafs, Bernhard David A; Barbante, Carlo (2015): The Marine Isotope Stage 19 in the mid-latitude North Atlantic Ocean: astronomical signature and intra-interglacial variability. Quaternary Science Reviews, 108, 95-110, https://doi.org/10.1016/j.quascirev.2014.10.024 Supplemental Information: Not Availble Coverage: Not Available
    Data Types:
    • Collection
    • File Set
  • high-frequency... oscillations
    Data Types:
    • Collection
    • Tabular Data
    • Text
  • Abstract: One of the most enigmatic features of Cenozoic long-term climate evolution is the long-lasting positive carbon-isotope excursion or “Monterey Excursion”, which started during a period of global warmth after 16.9 Ma and ended at not, vert, similar 13.5 Ma, approximately 400 kyr after major expansion of the Antarctic ice-sheet. We present high-resolution (1-9 kyr) astronomically-tuned climate proxy records in two complete sedimentary successions from the northwestern and southeastern Pacific (ODP Sites 1146 and 1237), which shed new light on the middle Miocene carbon-isotope excursion and associated climatic transition over the interval 17.1-12.7 Ma. We recognize three distinct climate phases with different imprints of orbital variations into the climatic signals (1146 and 1237 d18O, d13C; 1237 XRF Fe, fraction > 63 µm): (1) climate optimum prior to 14.7 Ma characterized by minimum ice volume and prominent 100 and 400 kyr variability, (2) long-term cooling from 14.7 to 13.9 Ma, principally driven by obliquity and culminating with rapid cryosphere expansion and global cooling at the onset of the last and most pronounced d13C increase, (3) “Icehouse” mode after 13.9 Ma with distinct 100 kyr variability and improved ventilation of the deep Pacific. The “Monterey” carbon-isotope excursion (16.9-13.5 Ma) consists overall of nine 400 kyr cycles, which show high coherence with the long eccentricity period. Superposed on these low-frequency oscillations are high-frequency variations (100 kyr), which closely track the amplitude modulation of the short eccentricity period. In contrast to d13C, the d18O signal additionally shows significant power in the 41 kyr band, and the 1.2 Myr amplitude modulation of the obliquity cycle is clearly imprinted in the 1146 d18O signal. Our results suggest that eccentricity was a prime pacemaker of middle Miocene climate evolution through the modulation of long-term carbon budgets and that obliquity-paced changes in high-latitude seasonality favored the transition into the “Icehouse” climate. Category: geoscientificInformation Source: Supplement to: Holbourn, Ann; Kuhnt, Wolfgang; Schulz, Michael; Flores, José-Abel; Andersen, Nils (2007): Orbitally-paced climate evolution during the middle Miocene “Monterey” carbon-isotope excursion. Earth and Planetary Science Letters, 261(3-4), 534-550, https://doi.org/10.1016/j.epsl.2007.07.026 Supplemental Information: Not Availble Coverage: EVENT LABEL: * LATITUDE: 19.456700 * LONGITUDE: 116.272917 * DATE/TIME START: 1999-03-21T00:00:00 * DATE/TIME END: 1999-03-29T00:00:00 * ELEVATION: -2091.5 m * Penetration: 1455.6 m * Recovery: 1451.7 m * LOCATION: South China Sea * CAMPAIGN: Leg184 * BASIS: Joides Resolution * METHOD/DEVICE: Composite Core EVENT LABEL: * LATITUDE: -16.007017 * LONGITUDE: -76.378083 * DATE/TIME: 2002-04-26T00:00:00 * ELEVATION: -3212.3 m * Penetration: 896.2 m * Recovery: 771 m * LOCATION: South Pacific Ocean * CAMPAIGN: Leg202 * BASIS: Joides Resolution * METHOD/DEVICE: Composite Core
    Data Types:
    • Collection
    • Tabular Data
    • Text
6