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  • 1
    Publication Date: 2000-01-11
    Description: Sedimentary time series of color reflectance and major element chemistry from the anoxic Cariaco Basin off the coast of northern Venezuela record large and abrupt shifts in the hydrologic cycle of the tropical Atlantic during the past 90,000 years. Marine productivity maxima and increased precipitation and riverine discharge from northern South America are closely linked to interstadial (warm) climate events of marine isotope stage 3, as recorded in Greenland ice cores. Increased precipitation at this latitude during interstadials suggests the potential for greater moisture export from the Atlantic to Pacific, which could have affected the salinity balance of the Atlantic and increased thermohaline heat transport to high northern latitudes. This supports the notion that tropical feedbacks played an important role in modulating global climate during the last glacial period.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Peterson, L C -- Haug, G H -- Hughen, K A -- Rohl, U -- New York, N.Y. -- Science. 2000 Dec 8;290(5498):1947-51.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, FL 33149, USA. lpeterson@rsmas.miami.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/11110658" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 2
    Publication Date: 2001-08-18
    Description: Titanium and iron concentration data from the anoxic Cariaco Basin, off the Venezuelan coast, can be used to infer variations in the hydrological cycle over northern South America during the past 14,000 years with subdecadal resolution. Following a dry Younger Dryas, a period of increased precipitation and riverine discharge occurred during the Holocene "thermal maximum." Since approximately 5400 years ago, a trend toward drier conditions is evident from the data, with high-amplitude fluctuations and precipitation minima during the time interval 3800 to 2800 years ago and during the "Little Ice Age." These regional changes in precipitation are best explained by shifts in the mean latitude of the Atlantic Intertropical Convergence Zone (ITCZ), potentially driven by Pacific-based climate variability. The Cariaco Basin record exhibits strong correlations with climate records from distant regions, including the high-latitude Northern Hemisphere, providing evidence for global teleconnections among regional climates.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Haug, G H -- Hughen, K A -- Sigman, D M -- Peterson, L C -- Rohl, U -- New York, N.Y. -- Science. 2001 Aug 17;293(5533):1304-8.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Earth Sciences, Eidgenossische Technische Hochschule-Zentrum, CH-8092 Zurich, Switzerland.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/11509727" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 3
    Publication Date: 2005-05-14
    Description: Since the first evidence of low algal productivity during ice ages in the Antarctic Zone of the Southern Ocean was discovered, there has been debate as to whether it was associated with increased polar ocean stratification or with sea-ice cover, shortening the productive season. The sediment concentration of biogenic barium at Ocean Drilling Program site 882 indicates low algal productivity during ice ages in the Subarctic North Pacific as well. Site 882 is located southeast of the summer sea-ice extent even during glacial maxima, ruling out sea-ice-driven light limitation and supporting stratification as the explanation, with implications for the glacial cycles of atmospheric carbon dioxide concentration.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Jaccard, S L -- Haug, G H -- Sigman, D M -- Pedersen, T F -- Thierstein, H R -- Rohl, U -- New York, N.Y. -- Science. 2005 May 13;308(5724):1003-6.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Earth Sciences, Sonneggstrasse 5, ETHZ, 8092 Zurich, Switzerland. jaccard@erdw.ethz.ch〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/15890879" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 4
    Publication Date: 2005-06-11
    Description: The Paleocene-Eocene thermal maximum (PETM) has been attributed to the rapid release of approximately 2000 x 10(9) metric tons of carbon in the form of methane. In theory, oxidation and ocean absorption of this carbon should have lowered deep-sea pH, thereby triggering a rapid (〈10,000-year) shoaling of the calcite compensation depth (CCD), followed by gradual recovery. Here we present geochemical data from five new South Atlantic deep-sea sections that constrain the timing and extent of massive sea-floor carbonate dissolution coincident with the PETM. The sections, from between 2.7 and 4.8 kilometers water depth, are marked by a prominent clay layer, the character of which indicates that the CCD shoaled rapidly (〈10,000 years) by more than 2 kilometers and recovered gradually (〉100,000 years). These findings indicate that a large mass of carbon (〉〉2000 x 10(9) metric tons of carbon) dissolved in the ocean at the Paleocene-Eocene boundary and that permanent sequestration of this carbon occurred through silicate weathering feedback.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Zachos, James C -- Rohl, Ursula -- Schellenberg, Stephen A -- Sluijs, Appy -- Hodell, David A -- Kelly, Daniel C -- Thomas, Ellen -- Nicolo, Micah -- Raffi, Isabella -- Lourens, Lucas J -- McCarren, Heather -- Kroon, Dick -- New York, N.Y. -- Science. 2005 Jun 10;308(5728):1611-5.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Earth Sciences Department, Earth and Marine Sciences Building, University of California, Santa Cruz, Santa Cruz, CA 95064, USA. jzachos@emerald.uscs.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/15947184" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 5
    Publication Date: 2013-03-30
    Description: Growing evidence suggests that the low atmospheric CO2 concentration of the ice ages resulted from enhanced storage of CO2 in the ocean interior, largely as a result of changes in the Southern Ocean. Early in the most recent deglaciation, a reduction in North Atlantic overturning circulation seems to have driven CO2 release from the Southern Ocean, but the mechanism connecting the North Atlantic and the Southern Ocean remains unclear. Biogenic opal export in the low-latitude ocean relies on silicate from the underlying thermocline, the concentration of which is affected by the circulation of the ocean interior. Here we report a record of biogenic opal export from a coastal upwelling system off the coast of northwest Africa that shows pronounced opal maxima during each glacial termination over the past 550,000 years. These opal peaks are consistent with a strong deglacial reduction in the formation of silicate-poor glacial North Atlantic intermediate water (GNAIW). The loss of GNAIW allowed mixing with underlying silicate-rich deep water to increase the silicate supply to the surface ocean. An increase in westerly-wind-driven upwelling in the Southern Ocean in response to the North Atlantic change has been proposed to drive the deglacial rise in atmospheric CO2 (refs 3, 4). However, such a circulation change would have accelerated the formation of Antarctic intermediate water and sub-Antarctic mode water, which today have as little silicate as North Atlantic Deep Water and would have thus maintained low silicate concentrations in the Atlantic thermocline. The deglacial opal maxima reported here suggest an alternative mechanism for the deglacial CO2 release. Just as the reduction in GNAIW led to upward silicate transport, it should also have allowed the downward mixing of warm, low-density surface water to reach into the deep ocean. The resulting decrease in the density of the deep Atlantic relative to the Southern Ocean surface promoted Antarctic overturning, which released CO2 to the atmosphere.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Meckler, A N -- Sigman, D M -- Gibson, K A -- Francois, R -- Martinez-Garcia, A -- Jaccard, S L -- Rohl, U -- Peterson, L C -- Tiedemann, R -- Haug, G H -- England -- Nature. 2013 Mar 28;495(7442):495-8. doi: 10.1038/nature12006.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Geological Institute, ETH Zurich, 8092 Zurich, Switzerland. nele.meckler@erdw.ethz.ch〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/23538831" target="_blank"〉PubMed〈/a〉
    Keywords: Africa ; Atlantic Ocean ; Atmosphere/chemistry ; Carbon Dioxide/analysis/metabolism ; *Ice Cover ; Oceans and Seas ; Seawater/*chemistry ; Silicates/*analysis/*metabolism ; Temperature ; Tropical Climate
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 6
    Publication Date: 2011-03-18
    Description: 'Hyperthermals' are intervals of rapid, pronounced global warming known from six episodes within the Palaeocene and Eocene epochs ( approximately 65-34 million years (Myr) ago). The most extreme hyperthermal was the approximately 170 thousand year (kyr) interval of 5-7 degrees C global warming during the Palaeocene-Eocene Thermal Maximum (PETM, 56 Myr ago). The PETM is widely attributed to massive release of greenhouse gases from buried sedimentary carbon reservoirs, and other, comparatively modest, hyperthermals have also been linked to the release of sedimentary carbon. Here we show, using new 2.4-Myr-long Eocene deep ocean records, that the comparatively modest hyperthermals are much more numerous than previously documented, paced by the eccentricity of Earth's orbit and have shorter durations ( approximately 40 kyr) and more rapid recovery phases than the PETM. These findings point to the operation of fundamentally different forcing and feedback mechanisms than for the PETM, involving redistribution of carbon among Earth's readily exchangeable surface reservoirs rather than carbon exhumation from, and subsequent burial back into, the sedimentary reservoir. Specifically, we interpret our records to indicate repeated, large-scale releases of dissolved organic carbon (at least 1,600 gigatonnes) from the ocean by ventilation (strengthened oxidation) of the ocean interior. The rapid recovery of the carbon cycle following each Eocene hyperthermal strongly suggests that carbon was re-sequestered by the ocean, rather than the much slower process of silicate rock weathering proposed for the PETM. Our findings suggest that these pronounced climate warming events were driven not by repeated releases of carbon from buried sedimentary sources, but, rather, by patterns of surficial carbon redistribution familiar from younger intervals of Earth history.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Sexton, Philip F -- Norris, Richard D -- Wilson, Paul A -- Palike, Heiko -- Westerhold, Thomas -- Rohl, Ursula -- Bolton, Clara T -- Gibbs, Samantha -- England -- Nature. 2011 Mar 17;471(7338):349-52. doi: 10.1038/nature09826.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California 92093, USA. P.F.Sexton@open.ac.uk〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21412336" target="_blank"〉PubMed〈/a〉
    Keywords: Atlantic Ocean ; Atmosphere/*chemistry ; *Carbon Cycle ; Foraminifera/metabolism ; Geologic Sediments/chemistry ; Global Warming/*history ; History, Ancient ; Oceans and Seas ; Seawater/*chemistry ; Temperature
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 7
    Publication Date: 2012-08-04
    Description: The warmest global climates of the past 65 million years occurred during the early Eocene epoch (about 55 to 48 million years ago), when the Equator-to-pole temperature gradients were much smaller than today and atmospheric carbon dioxide levels were in excess of one thousand parts per million by volume. Recently the early Eocene has received considerable interest because it may provide insight into the response of Earth's climate and biosphere to the high atmospheric carbon dioxide levels that are expected in the near future as a consequence of unabated anthropogenic carbon emissions. Climatic conditions of the early Eocene 'greenhouse world', however, are poorly constrained in critical regions, particularly Antarctica. Here we present a well-dated record of early Eocene climate on Antarctica from an ocean sediment core recovered off the Wilkes Land coast of East Antarctica. The information from biotic climate proxies (pollen and spores) and independent organic geochemical climate proxies (indices based on branched tetraether lipids) yields quantitative, seasonal temperature reconstructions for the early Eocene greenhouse world on Antarctica. We show that the climate in lowland settings along the Wilkes Land coast (at a palaeolatitude of about 70 degrees south) supported the growth of highly diverse, near-tropical forests characterized by mesothermal to megathermal floral elements including palms and Bombacoideae. Notably, winters were extremely mild (warmer than 10 degrees C) and essentially frost-free despite polar darkness, which provides a critical new constraint for the validation of climate models and for understanding the response of high-latitude terrestrial ecosystems to increased carbon dioxide forcing.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Pross, Jorg -- Contreras, Lineth -- Bijl, Peter K -- Greenwood, David R -- Bohaty, Steven M -- Schouten, Stefan -- Bendle, James A -- Rohl, Ursula -- Tauxe, Lisa -- Raine, J Ian -- Huck, Claire E -- van de Flierdt, Tina -- Jamieson, Stewart S R -- Stickley, Catherine E -- van de Schootbrugge, Bas -- Escutia, Carlota -- Brinkhuis, Henk -- Integrated Ocean Drilling Program Expedition 318 Scientists -- England -- Nature. 2012 Aug 2;488(7409):73-7. doi: 10.1038/nature11300.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Paleoenvironmental Dynamics Group, Institute of Geosciences, Goethe University Frankfurt, Altenhoferallee 1, 60438 Frankfurt, Germany. joerg.pross@em.uni-frankfurt.de〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/22859204" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Antarctic Regions ; Atmosphere/chemistry ; Carbon Dioxide/analysis ; Cell Respiration ; Ecosystem ; Geologic Sediments/chemistry ; Greenhouse Effect/*history ; History, Ancient ; Human Activities ; Lipids/analysis ; Models, Theoretical ; Photosynthesis ; Pollen ; Reproducibility of Results ; Seasons ; Spores/isolation & purification ; *Temperature ; Trees/growth & development ; *Tropical Climate
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 8
    Publication Date: 2013-04-20
    Description: The circum-Antarctic Southern Ocean is an important region for global marine food webs and carbon cycling because of sea-ice formation and its unique plankton ecosystem. However, the mechanisms underlying the installation of this distinct ecosystem and the geological timing of its development remain unknown. Here, we show, on the basis of fossil marine dinoflagellate cyst records, that a major restructuring of the Southern Ocean plankton ecosystem occurred abruptly and concomitant with the first major Antarctic glaciation in the earliest Oligocene (~33.6 million years ago). This turnover marks a regime shift in zooplankton-phytoplankton interactions and community structure, which indicates the appearance of eutrophic and seasonally productive environments on the Antarctic margin. We conclude that earliest Oligocene cooling, ice-sheet expansion, and subsequent sea-ice formation were important drivers of biotic evolution in the Southern Ocean.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Houben, Alexander J P -- Bijl, Peter K -- Pross, Jorg -- Bohaty, Steven M -- Passchier, Sandra -- Stickley, Catherine E -- Rohl, Ursula -- Sugisaki, Saiko -- Tauxe, Lisa -- van de Flierdt, Tina -- Olney, Matthew -- Sangiorgi, Francesca -- Sluijs, Appy -- Escutia, Carlota -- Brinkhuis, Henk -- Expedition 318 Scientists -- Dotti, Carlota Escutia -- Klaus, Adam -- Fehr, Annick -- Williams, Trevor -- Bendle, James A P -- Carr, Stephanie A -- Dunbar, Robert B -- Flores, Jose-Abel -- Gonzalez, Jhon J -- Hayden, Travis G -- Iwai, Masao -- Jimenez-Espejo, Francisco J -- Katsuki, Kota -- Kong, Gee Soo -- McKay, Robert M -- Nakai, Mutsumi -- Pekar, Stephen F -- Riesselman, Christina -- Sakai, Toyosaburo -- Salzmann, Ulrich -- Shrivastava, Prakash K -- Tuo, Shouting -- Welsh, Kevin -- Yamane, Masako -- New York, N.Y. -- Science. 2013 Apr 19;340(6130):341-4. doi: 10.1126/science.1223646.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Earth Sciences, Laboratory of Palaeobotany and Palynology, Faculty of Geosciences, Utrecht University, Budapestlaan 4, 3584 CD Utrecht, Netherlands. Alexander.Houben@TNO.nl〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/23599491" target="_blank"〉PubMed〈/a〉
    Keywords: *Adaptation, Physiological ; Animals ; Antarctic Regions ; Cold Temperature ; Dinoflagellida/*physiology ; *Ecosystem ; Fossils ; *Ice Cover ; *Oceans and Seas ; Phytoplankton/*physiology ; Zooplankton/*physiology
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 9
    Publication Date: 2007-10-08
    Description: Records of organic matter accumulation, organic carbon isotopic composition and iron content covering the last 1.7 Ma are presented for the Congo Fan Ocean Drilling Program (ODP) Site 1075, and are compared with their counterparts from ODP Site 663 in the equatorial upwelling region. They are discussed with regard to variations in African precipitation and Congo River discharge and in the context of changes in trade-wind-driven marine productivity for the tropical Atlantic at periodicities typical of Milankovitch forcing. On the Congo Fan, elevated total organic carbon mass accumulation rates (TOC MAR) and Fe intensities occur predominantly during interglacial periods when the African monsoon was most intense. Band-pass filtering applied to TOC MAR shows distinct precessional variations, indicating that the African climate was largely controlled by low-latitude insolation changes. Only for the last 0.6 Ma, an interval of enhanced glacial-interglacial climate changes, is the precessional TOC MAR signal superimposed by a strong 100 ka oscillation. In contrast, variations in terrestrial iron input to the Congo Fan indicate pronounced 100 ka variance already well before global glacial-interglacial cycles increased in amplitude between 0.9 and 0.6 Ma. Obliquity cycles in the Fe signal are strongly expressed for the last 0.9 Ma. The highest amplitudes in the precessional variance of fluvial Fe input occur when amplitudes in the 100 ka oscillation were at intermediate levels and reveal a 800 ka cycle in phase shift with respect to precessional forcing. Together with a pronounced 800 ka signal in the 100 ka amplitude variations during the last 1.7 Ma, the Congo Fan iron record therefore suggests that eccentricity modulation of the low-latitude insolation directly influenced the equatorial African monsoon system and probably the weathering conditions on land. It further suggests that low-latitude precessional forcing and monsoonal response in the tropics might have played an important role for 100 ka cycles in global climate well before huge continental ice sheets existed.
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  • 10
    Publication Date: 2015-09-26
    Description: :  Results of studies involving numerous cores and ODP holes along the Great Barrier Reef (GBR) margin and adjacent Queensland Trough and Queensland Plateau have challenged the use of a reciprocal sedimentation model to describe the sedimentary response of slope and basin settings to glacioeustatic sea-level fluctuations. Upper-slope sedimentation results from the relationships between sea-level fluctuations, antecedent topography, and regional climate that play an important role in the type and amount of sediment deposited on the upper slope during glacial, deglacial, and interglacial times. During the Last Glacial Maximum (LGM, 〉 20 ka ago) upper-slope sediments generally lacked siliciclastic material and are characterized by very low accumulation rates, whereas early deglacial-time (Termination I, TI) deposits are dominated by a siliciclastic and neritic carbonate pulse. Siliciclastic sedimentation was significantly reduced in the Holocene, while carbonate sedimentation remains elevated. A new borehole, IODP Expedition 325 Hole M0058A (Hole 58A), recovered 82% of a 40.4 m hole on the upper slope east of Noggin Passage on the central GBR margin near Cairns, Australia. Hole 58A provides a detailed sedimentary record during Termination II (TII), Marine Isotope Stage 6/5e (MIS-6/5e), deglacial transition, and through most of interglacial MIS-5. This hole, along with two others (ODP Leg 133 Holes 820A and 819A from the upper slope east of Grafton Passage), show carbonate–siliciclastic cyclicity as the result of glacioeustatic change with the GBR shelf. Sedimentation at Hole 58A is consistent with that of previous studies along the GBR margin (focusing on the LGM to present), and extends the upper-slope sedimentary record back to TII and interglacial MIS-5. A siliciclastic pulse similar to the one during TI occurred during the penultimate deglaciation, TII; however, the maximum neritic aragonite export to the upper slope occurred not during peak MIS-5e highstand when sea level was a few meters above modern position, but subsequently during a time (MIS-5d to 5a) when lowered sea level fluctuated between 30 and 50 m below present sea level. Siliciclastic sediments were reworked and exported to the upper slope when the lowstand fluvial plain was re-flooded, whereas neritic carbonate export to the slope reached a maximum when sea level fell and much of the mid to outer shelf re-entered the photic zone, subsequent to a drowning interval. Thus, this analysis refines the mixed-sedimentation models of upper-slope sedimentation along the central GBR margin during the penultimate deglacial transgression and subsequent interglacial early and late highstand. This study provides further evidence that mixed carbonate–siliciclastic margins do not always behave in a predictable manner and that mixed margins both modern and ancient would benefit from detailed study of sediment transport in the context of sea-level rise and fall.
    Print ISSN: 1527-1404
    Topics: Geosciences
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