Reconstruction of atmospheric CO2 from ice-core data and the deep-sea record of ontong Java plateau: the Milankovitch chron     

Wolfgang H. Berger  Memorie K. Yasuda  Torsten Bickert  Gerold Wefer 《International Journal of Earth Sciences》1996,85(3):466-495

We provide a reconstruction of atmospheric CO₂ from deep-sea sediments, for the past 625000 years (Milankovitch chron). Our database consists of a Milankovitch template of sea-level variation in combination with a unique data set for the deep-sea record for Ontong Java plateau in the western equatorial Pacific. We redate the Vostok ice-core data of Barnola et al. (1987). To make the reconstructions we employ multiple regression between deep-sea data, on one hand, and ice-core CO₂ data in Antarctica, on the other. The patterns of correlation suggest that the main factors controlling atmospheric CO₂ can be described as a combination of sea-level state and sea-level change. For best results squared values of state and change are used. The square-of-sea-level rule agrees with the concept that shelf processes are important modulators of atmospheric CO₂ (e.g., budgets of shelf organic carbon and shelf carbonate, nitrate reduction). The square-of-change rule implies that, on short timescales, any major disturbance of the system results in a temporary rise in atmospheric CO₂.  相似文献   

The Silurian of Gotland (Sweden): facies interpretation based on stable isotopes in brachiopod shells     

Chr Samtleben  A. Munnecke  T. Bickert  J. Pätzold 《International Journal of Earth Sciences》1996,85(2):278-292

The Silurian of Gotland, Sweden, consists of 440 m of carbonate deposits. Repeatedly, uniform sequences of micritic limestones and marls are interrupted by complex-structured reefs and by adjacent platform sediments. Generally, the alteration of facies is interpreted as the result of sea-level fluctuations caused by a gradual regression with superimposed minor transgressive pulses. The purpose of this study is a facies interpretation based on both field observations and stable isotope measurements of brachiopod shells. Approximately 700 samples from stratigraphically arranged localities in different facies areas have been investigated. The carbon and oxygen isotopes show principally parallel curves and a close relationship to the stratigraphic sequence. Lower values occur in periods dominated by deposition of marly sequences. Higher values are observed in periods dominated by reefs and extended carbonate platforms. The oxygen isotope ratios are interpreted to reflect paleosalinity changes due to varying freshwater input, rather than to paleotemperature. Carbon isotope ratios are believed to have been connected to global changes in the burial of organic carbon in black shales during periods of euxinic deep water conditions. Consequently, the facies succession on Gotland results from global paleoclimatic conditions. Changes in terrigenous input due to different rates of weathering and freshwater runoff, rather than sea-level fluctuations, control the carbonate formation of the Silurian on Gotland.  相似文献   

Depth habitats and seasonal distributions of recent planktic foraminifers in the Canary Islands region (29°N) based on oxygen isotopes     

Iris Wilke  Helge Meggers  Torsten Bickert 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(1):89-106

Seasonal depth stratified plankton tows, sediment traps and core tops taken from the same stations along a transect at 29°N off NW Africa are used to describe the seasonal succession, the depth habitats and the oxygen isotope ratios (δ¹⁸O_shell) of five planktic foraminiferal species. Both the δ¹⁸O_shell and shell concentration profiles show variations in seasonal depth habitats of individual species. None of the species maintain a specific habitat depth exclusively within the surface mixed layer (SML), within the thermocline, or beneath the thermocline. Globigerinoides ruber (white) and (pink) occur with moderate abundance throughout the year along the transect, with highest abundances in the winter and summer/fall season, respectively. The average δ¹⁸O_shell of G. ruber (w) from surface sediments is similar to the δ¹⁸O_shell values measured from the sediment-trap samples during winter. However, the δ¹⁸O_shell of G. ruber (w) underestimates sea surface temperature (SST) by 2 °C in winter and by 4 °C during summer/fall indicating an extension of the calcification/depth habitat into colder thermocline waters. Globigerinoides ruber (p) continues to calcify below the SML as well, particularly in summer/fall when the chlorophyll maximum is found within the thermocline. Its vertical distribution results in δ¹⁸O_shell values that underestimate SST by 2 °C. Shell fluxes of Globigerina bulloides are highest in summer/fall, where it lives and calcifies in association with the deep chlorophyll maximum found within the thermocline. Pulleniatina obliquiloculata and Globorotalia truncatulinoides, dwelling and calcifying a part of their lives in the winter SML, record winter thermocline (～180 m) and deep surface water (～350 m) temperatures, respectively. Our observations define the seasonal and vertical distribution of multiple species of foraminifera and the acquisition of their δ¹⁸O_shell.  相似文献   

Modern and Pleistocene boron isotope composition of the benthic foraminifer Cibicidoides wuellerstorfi     

Brbel Hnisch  Torsten Bickert  N. Gary Hemming 《Earth and Planetary Science Letters》2008,272(1-2):309-318

Here we present the first species-specific study of boron isotopes in the epibenthic foraminifer species Cibicidoides wuellerstorfi. Coretop samples from a water depth profile from 1000 to 4500 m on the northern flank of the Walvis Ridge are 4.4‰ lower than the values expected, based on calculations of the δ¹¹B_borate of ambient seawater. Similar values for this foraminifer species are presented from ODP site 668B at the Sierra Leone Rise, in the equatorial Atlantic. The consistency between data of the same species suggests the offsets are primary, rather than diagenetic. Glacial C. wuellerstorfi from ODP 668B and Walvis Ridge have boron isotope compositions only slightly different to interglacial samples, that is no larger than + 0.10 pH units, or + 23 µmol kg^− 1 in [CO₃²⁻] above the reconstructed glacial lysocline, and − 0.07 pH units, or − 14 µmol kg^− 1 in [CO₃²⁻] below. We use these results to suggest that glacial deep water pH in the Atlantic was similar to interglacial pH. The new data resolve the inconsistency between the previously reported high bottom water pH and the lack of significant carbonate preservation of the glacial deep ocean.  相似文献   

Peculiarities of the Tectonomagmatic Processes in the Interaction Area between the Icelandic Plume and the Bight Transform Fault (North Atlantic)     

Skolotnev  S. G.  Peyve  A. A.  Sanfilippo  A.  Ivanenko  A. N.  Ligi  M.  Veklich  I. A.  Petracchini  L.  Basch  V.  Kuleshov  D. A.  Ferrando  C.  Dobrolyubov  V. N.  Sani  C.  Shkittin  N. A.  Bickert  M.  Dokashenko  S. A.  Muccini  F.  Yakovenko  E. S.  Palmiotto  C.  Cuffaro  M. 《Doklady Earth Sciences》2022,504(1):233-239

Doklady Earth Sciences - Geological and geophysical data collected during the 53rd cruise of the R/V Akademik Sergey Vavilov are presented. It is shown that the lateral distribution of the...  相似文献   

Geological-Geophysical Investigations in the North Atlantic during Cruise 53 of the R/V Akademik Sergey Vavilov     

Skolotnev  S. G.  Peyve  A. A.  Sanfilippo  A.  Ivanenko  A. N.  Ligi  M.  Veklich  I. A.  Petracchini  L.  Ponomarenko  E. P.  Basch  V.  Kuleshov  D. A.  Ferrando  C.  Dobrolyubov  V. N.  Sani  C.  Shkittin  N. A.  Bickert  M.  Dokashenko  S. A.  Muccini  F.  Yakovenko  E. S.  Palmiotto  C.  Pugacheva  T. L.  Cuffaro  M. 《Oceanology》2022,62(4):575-577

Oceanology - We provide information on geological and geophysical investigations of the structure of the area between the Bight and Charlie Gibbs transform faults in the North Atlantic during...  相似文献   

New Data on the Geological Structure of the Eastern Flank of the Charlie Gibbs Fracture Zone (North Atlantic)     

Skolotnev  S. G.  Peyve  A. A.  Ivanenko  A. N.  Dobrolyubova  K. O.  Sanfilippo  A.  Ligi  M.  Sokolov  S. Yu.  Veklich  I. A.  Petracchini  L.  Basch  V.  Ferrando  C.  Sani  C.  Bickert  M.  Muccini  F.  Palmiotto  C.  Cuffaro  M.  Kuleshov  D. A.  Dobrolyubov  V. N.  Shkittin  N. A.  Dokashenko  S. A.  Yakovenko  E. S. 《Doklady Earth Sciences》2022,504(2):333-337

Doklady Earth Sciences - The geological structure of a large volcanic edifice in the eastern flank of the large Charlie Gibbs Fracture Zone in the region of the Eastern Thule submarine rise (North...  相似文献   

Micro-properties of coal aggregates: Implications on hyperbaric filtration performance for coal dewatering     

C. Selomulya  J.Y.H. Liao  G. Bickert  R. Amal   《International Journal of Mineral Processing》2006,80(2-4):189-197

The recovery of ultrafine coal can be enhanced significantly by flocculating the particles prior to dewatering. It is thus crucial to be able to quantify the effects of aggregated particles on the separation efficiency, of which they are still not fully understood. This study focused on the relationship between the micro-properties (size, structure, and strength) of flocculated coal particles and the characteristics of filter cakes obtained through hyperbaric filtration. Tools such as small angle light scattering and confocal scanning laser microscopy were used to determine the aggregate structure. The comparative bond strength of aggregates generated under different flocculation conditions was measured through a non-dimensional approach. The effects of these properties on specific cake resistance, saturation, and moisture content, as indicative of the filtration performance, were observed. It was found that flocs generated using a moderate amount of flocculant dosage (60–100 g of polymer/tonne of coal) for this ultrafine coal (97% < 35 μm) optimised the properties of dewatered filter cakes. Although cakes composed of larger and stronger aggregates with more flocculant were found to have higher porosity, the effects on specific cake resistance and cake saturation were detrimental, possibly due to the increasing proportion of intra-aggregate pores that were harder to dewater. The trend was less noticeable at low filtration pressures where most of the dewatering occurred within the larger capillaries of the inter-aggregate zones. In addition, the presence of polymer molecules was responsible in absorbing residual moisture that could not be removed through mechanical means. Through a series of tests using pre-formed filter cakes, the amount of moisture retained by the flocculant was quantified to be approximately 10.2 mg of water for every addition of 1 g of polymer/tonne of coal, calculated per 100 g of filter cake produced from hyperbaric filtration in this case.  相似文献   

Link between the North and South Atlantic during the Heinrich events of the last glacial period   总被引：2，自引：0，他引：2  

L. Vidal  R.R. Schneider  O. Marchal  T. Bickert  T.F. Stocker  G. Wefer 《Climate Dynamics》1999,15(12):909-919

High resolution benthic oxygen isotope records combined with radiocarbon datings, from cores retrieved in the North, Equatorial, and South Atlantic are used to establish a reliable cronostratigraphy for the last 60 ky. This common temporal framework enables us to study the timing of the sub-Milankovitch climate variability in the entire surface Atlantic during this period, as reflected in planktonic oxygen isotope records. Variations in sea surface temperatures in the Equatorial and South Atlantic reveal two warm periods during the mid-stage 3 which are correlated to the warming observed in the North Atlantic after Heinrich events (HL) 5 and 4. However, the records show that the warming started about 1500 y earlier in the South Atlantic. A zonally averaged ocean circulation model simulates a similar north-south thermal antiphasing between the latitudes of our coring sites, when pertubated by a freshwater flux anomaly. We infer that the observed phase relationship between the northern and the southern Atlantic is related to periods of reduced NADW production in the North Atlantic, such as during HL5 and HL4. Received: 24 November 1998 / Accepted: 16 May 1999  相似文献   

Late Miocene stable isotope stratigraphy of SE Atlantic ODP Site 1085: Relation to Messinian events     

L. Vidal  T. Bickert  G. Wefer  U. R  hl 《Marine Geology》2002,180(1-4):71-85

High-resolution benthic oxygen isotope and XRF (Fe and Ca) records from Site 1085 drilled in the Mid-Cape basin (ODP Leg 175) are used to investigate global climate changes during the Late Miocene in relation to Messinian geological events. The cyclic fluctuations of the time series at Site 1085 enable us to establish a reliable chronology for the time interval 7.3–4.7 Ma. Spectral analysis of the δ¹⁸O record indicates that the 41-kyr period of orbital obliquity dominates the Late Miocene record. A global climate record was extracted from the oxygen isotopic composition of benthic foraminifera. Both long- and short-term variabilities in the climate record are discussed in terms of sea-level and deep-water temperature changes. The time interval 7.3–6.25 Ma characterized by low-amplitude δ¹⁸O variations is followed by a period marked by maximum in the δ¹⁸O values (6.25–5.57 Ma). At about 5.56 Ma, a rapid decrease in δ¹⁸O values is documented that may reflect a warming of deep-water temperature associated with a global warming period. Comparison between the timing of the oceanic isotope events and the chronology of the Mediterranean Salinity Crisis suggest that global eustatic processes were not essential in the Mediterranean Salinity Crisis history. From our data, we infer that the global warmth documented in the Early/mid-Pliocene probably started during the Late Miocene (at 5.55 Ma). At the same time, the onset of evaporite deposition in the central basin of the Mediterranean Sea took place. Sharp changes in the sedimentation rates, mainly driven by terrigenous input at this site, are observed during the Messinian Stage.  相似文献