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It is likely that our smaller measured gradient between G. Oxygen isotopes and G. For example, likely coincides with the Mi4 event that marks a major pulse of ice- the Hodell and Vayavananda study shows increased G. Flower and Kennett, , ; Westerhold et al. A number of these latter events correlate 1. One This results in an expanded feed the ITF today Fig. A third possible follow this trend Quinn, , personal organic-rich terrigenous and shallow marine sediments associated communication; Table 3.

Taken together, late Miocene surface waters with Antarctic glaciation and sea level fall Berger and Vincent, ; of the WEP were likely somewhat saltier and slightly cooler than present Bickert et al.

Carbon isotopes Northern Component Water Lear et al. Kennett, This nannofossil genus Reticulofenestra at Site Takayama, Fig. Continuous planktic foraminiferal stable isotope and population assemblage data for ODP Site Panel F mixed layer assemblage 2 abundances yellow; Globoturborotalita spp.

Panel G mixed layer assemblage 1 abundances Globigerinoides spp. Panel H Other species i. Also noteworthy in the Site record are the assemblages. At 6 Ma, G. Assemblage results values once again. Stratigraphic changes in planktic foraminiferal assemblages closely track changes in the stable isotopes. These natural groupings are also 4.

Foraminiferal test fragments supported by multivariate statistical techniques, including R-mode species associations Principal Components Analysis and Q-mode Foraminiferal test fragments a proxy for dissolution at Site sample groupings Cluster Analysis, but are not discussed here were at a minimum from After 12 Ma, test because of space limitations. A 10 Ma. Thermocline species abundances increase in the interval from et al.

Test fragmentation increases abundances of Neogloboquadrina spp. Hole Core-section, interval Replicate Ca conc. Discussion mol Eq 6 B 34H-1, 59 R1 Pre-closure trans-Equatorial circulation Interval 1: During early middle Miocene B 26H-4, R1 The dominance of mixed layer taxa and paucity of B 26H-6, 35 R1 However, the highly B 21H-1, R2 A sharp drop in planktic foraminiferal simple diversity praemenardii, and Globigerinoides sacculifer.

For example, many of the pre The elevated abundances of radiolarians and Neo- large isotopic gradient between G.

At other times the thermocline deepened as Abundances of thermocline species and mixed layer assemblage 2 suggested by the reduced gradient values. Such isotopic variability display high amplitude variability from 9. This is an indicates that a stable warm pool did not exist prior to Noteworthy is the related to equator crossing during the pre The very and Neogloboquadrina spp. For occurrence of G. Our isotope paleoecologic example, Globorotalia spp.

All four of these Nathan, Furthermore, the sharp decline 8. These intervals correspond with in G. Relative abundances of major taxa through Site based on counts of at least specimens. See text for explanation of the four groups. Simple diversity of planktic foraminiferal species through the study interval of Site panel A and calculated evolutionary rates per million year rates; panels B and C based on Chaisson and Leckie and updated to an age model based on orbitally-tuned datums of Chaisson and Pearson ; refer to Table 1.

Key Planktic Foram Evolutionary Events highlight the evolutionary turnover of thermocline-dwelling planktic foraminifers in the middle to late Miocene transition at Site P. Data from Chaisson and Leckie updated to orbitally-tuned datum levels of Chaisson and Pearson Two-step formation of a proto-warm pool Interval 2: We interpret these layer assemblages as seen by the sharp decline in Globigerinoides spp.

The and the rise of Globigerinita glutinata Fig. In both cases, warming of the thermocline increase in the relative abundances of thermocline species Fig. Relative abundances of upper thermocline-dwelling Globorotalia spp. In addition, the two-step Hodell and Vayavananda , p. Here, we hypothesize that sea level G.

Interval 2, they are comparable to those seen in a modern box core sample from near the equator on Ontong Java Plateau Table 2, Fig. Hodell and Vayavananda , p. By analogy with modern equatorial current Fig. Many sea- menardii during times of a proto-warm pool Fig. Because Site level curves depict a rise in sea-level after 9 Ma Haq et al. We can only speculate may explain why G. In addition, the biserial planktic than the upper thermocline, and sea surface temperatures warmed as foraminifer genus Streptochilus, known to be associated with productivity well Fig.

The coincidence with the Mi5 and Mi6 benthic oxygen isotope interval from 8. The increased abundances of excursions is compelling. We suspect that warm pool development and Streptochilus and radiolarians suggest higher productivity. The question is productivity in the surface waters of the WEP. A similar collapse of large Reticulo- most deep-sea records e. However, the Westerhold et al. Further, John et al. This documented pulses of increased kaolinite accumulation on the Marion interval also coincides with a sharp increase in phosphorous MARs in the Plateau northeast Australian margin during the middle Miocene and Indian Ocean Hermoyian and Owen, This latter lowstand also correlates with a major 6.

Absence of a proto-warm pool Interval 4: 8. Panel A Sea level based on Westerhold et al. Mi4—Mi6 Miocene isotope events based on Wright et al. Percent radiolarians relative to total foraminifers picked from Site This interval is characterized by an Neogloboquadrina decreased in relative abundance and Globorotalia increase in the relative abundance of Neogloboquadrina, a tropical genus increased.

Collectively, these observations suggest that productivity indicative of seasonal productivity Fig. We suggest that these biotic and physical changes in the upper water column indicate 6. Brief return of a proto-warm pool Interval 5: 6. Also noteworthy is the large drop in species assemblages. These changes in There is a question of whether the observed changes in WEP equatorial circulation and productivity may also lead to a better hydrography were triggered by falling sea level near the end of the understanding of the variable character, timing, and magnitude of the Miocene similar to that of Interval 2 Hodell et al.

Aharon et al. The thermocline 6. This scenario conditions. Con- versely, when the proto-warm pool was weak or non-existent, especially 7. We refer to these long-term changes in upper water column gradient i. Tick marks represent water depth in km.

These proxy arc and collision with the northwestern corner of South America Duque- records suggest development of a proto-warm pool twice during the late Caro, ; Coates et al.

Lowering of sea-level during Mi5 may Miocene as summarized below. The tectonic constriction of both seaways and a succession of calcareous nannofossil Kameo and Sato, and planktic foraminifer sea level falls Mi4, Mi5, and Mi6 events may have reached a critical assemblages Chaisson and D'Hondt.

North Atlantic. This Fig. Chavez et al. Kemp et al. Foundation OCE grant Conclusions Research Grant Program. The authors also thank Bill gradients correspond with a deep thermocline, while expanded Chaisson and the Ocean Drilling Program for samples. Supplementary data thermocline, which are tracked by changes in the relative abundances of Globorotalia spp. Changing Supplementary data associated with this article can be found, in carbon isotopic gradients between the mixed layer and upper thermo- the online version, at doi Oxygen and carbon isotope stratigraphy of the middle Miocene, Holes B and B.

In: Berger, W. Ocean Acton, G. In: Radhakrishna, T. Opal sedimentation shifts in Piper, J. Geological Society of India, Memoir, 44, pp. Aharon, P. Sea-level events in the Covey, C.

The role of ocean heat transport in climatic change. Geology 21, — Science Reviews 24, — Backman, J. Calibration of Miocene nannofossil events to orbitally-tuned Curry, W. Seasonal changes in the isotopic composition cyclostratigraphies from Ceara Rise.

In: Shackleton, N. Earth and Bralower, T. Dekens, P. The mid-Cretaceous was ism Figure Other studies have proposed impor- tant linkages between increased submarine volcanism hydrothermal activity , primary productivity, and black 5. Hydrothermal vents asso- productivity in nutrient-poor, oligotrophic waters [Cho ciated with spreading centers are major sources of dissolved and Azam, ; Laybourn-Parry, ; Falkowski et al. Iron during the broad OAE1b event.

By contrast, the subsequent availability greatly enhances nitrogen fixation by cyanobac- OAEs were likely initiated by changing forcing factors. For teria [Codispoti, ; Falkowski, ], and it stimulates example, beginning in the Albian, an increasingly stratified increased production in the eukaryotic phytoplankton [Mar- water column limited the availability of nutrients to the tin and Fitzwater, ; Martin et al.

The heterotrophic bacteria of structure, reducing export production, and providing a the microbial loop compete with prokaryotic and eukaryotic positive feedback for the global warming that persisted autotrophs for this limiting micronutrient [Kirchman, ].

When suspect that elevated rates of hydrothermal activity indi- iron is limited, more of the dissolved organic carbon rectly contributed to these events. Ocean Circulation, Rising Sea Level, [48] In the modern ocean, it is the larger phytoplankton and Chalk Deposition cells, principally the diatoms, that show the greatest pro- [52] Reduced export production after the early Albian was ductivity response to increased iron availability [Martin et closely related to rising sea level, global warming, and al.

Planktic and However, diatoms did not reach their pinnacle of impor- benthic foraminiferal isotopic data from the western North tance in marine food webs until the Cenozoic [Harwood Atlantic Blake Nose show that sea surface temperatures and Nikolaev, ]. Because temperature has teau volcanism, and higher rates of seafloor spreading such an important effect on metabolic rates [e. Coupled atmosphere- and Kolber, ]. Mechanisms that enhance iron avail- ocean general circulation models with two different bio- ability, such as increased aeolian dust deposition during the geochemical schemes predict that rising levels of CO2 and Last Glacial Maximum [Martin, ] or, as we and others global warming will cause increased ocean stratification suspect, iron fertilization by submarine volcanism during leading to reduced nutrient supply to the euphotic zone and the mid-Cretaceous, can result in increased rates of primary increased light efficiency longer growing season , with productivity.

However, in a warm Cretaceous world, ele- both effects causing a reduction in export production [Bopp vated rates of denitrification in low-oxygen environments et al.

Crane, ; Crane et al. According to Tappan [50] We suggest that the availability of iron at times of [], the evolution of land plants during the Phanerozoic heightened submarine volcanism and oceanic crustal pro- limited the delivery of land-derived nutrients to the marine duction stimulated and sustained the production of nitrogen- plankton.

The partitioning of nutrients between the land and fixing cyanobacteria and improved the efficiency of the the marine environment may have been further exacerbated microbial loop, both of which facilitated greater export during times of higher eustatic sea level owing to the production during the OAEs.

Elevated trace metal abun- sequestering of organic matter and nutrients in coastal dances in OAE1a and OAE2 strata suggest a linkage wetlands and estuaries.

In addition, the growth of warm, between these OAEs and submarine volcanism [Orth et oxygen-poor epicontinental seas may have increased the al. Of these two events it is possible that only ity of fixed nitrogen for oceanic phytoplankton [Codispoti, OAE1a was directly triggered by submarine volcanism and ; Falkowski, ].

Nutrient limitation would have iron fertilization as suggested by Larson and Erba []. The autotrophic seas, which persisted through Late Cretaceous time. These two euphotic zone became stratified and nutrient-starved. This event suggests that an OAE2. We propose that increased marine productivity intermediate water connection between the North and South during latest Aptian-early Albian OAE1b was also linked Atlantic Ocean basins may have existed by early Albian to increased ridge crest volcanism and hydrothermal activity time.

A number of different mechanisms intermediate or deep water northward along the margin of created the conditions necessary to accumulate the multiple northwest Africa. The prominent unconformity in the but geographically restricted black shale events of OAE1b. Later deep during late Aptian-early Albian time Ticinella bejaouaen- water oxygenation events occurred at or near the end of the sis-Hedbergella planispira biozones indicate that this inter- Cenomanian stage [Tucholke and Vogt, ; Summer- val was associated with significant disruptions in the global hayes, ].

The propensity for black could elevated marine productivity be sustained for — shale deposition in the basins of the Atlantic and European years? We conclude that the mid-Cretaceous OAEs Tethys became progressively minimized during Albian- were linked to submarine volcanic activity. We hypothesize Cenomanian time. The conse- the OAEs by way of iron fertilization of the water column. Perhaps only OAE1a was directly epicontinental seas, and the open ocean, 3 changes in triggered by submarine volcanism, but we suggest that oceanic circulation and water mass sources as epicontinental active hydrothermal activity, in particular, indirectly helped seas linked Tethys with the higher latitudes and as the to sustain marine productivity on a global scale during the deepwater gateway between the North and South Atlantic OAEs.

Transgression also facilitated the production of continued to open, 4 changes in the hydrologic cycle and marine organic matter and its burial and preservation as continental weathering, and 5 increasing water column condensed intervals of black shale deposition. Taken together, the cumulative effects of column structure were the causes of plankton turnover at climate, ocean fertility, ocean circulation, water column or near the OAEs.

For example, the heavily calci- fied nannofossils the nannoconids were seriously affected 6. This event was likely organisms. The spread of pelagic carbonate deposition thermocline due an abrupt deep-sea warming event.

The with rising sea level in the Albian also signals a changing turnover event associated with OAE1d in the latest Albian planktic trophic regime dictated by increased thermal and was likewise triggered by a collapse of upper water column fertility gradients. Fundamental changes in circulation, stratification due to surface water cooling or an intermediate water column structure, nutrient partitioning, and plankton water warming event. This research used samples provided by the Ocean much of the Late Cretaceous.

The ODP is sponsored by the U. Silva, Paul Wilson, and Richard Yuretich. A special thanks to Fatima Abrantes and Michael Arthur for the This interval also marks the beginning of the end of wide- opportunity to present an early version of this paper at the Sixth Interna- tional Paleoceanographic Conference held in Lisbon in This paper is spread black shale deposition and the initiation of chalk dedicated to the memory of William V.

Sliter, an international leader in deposition. According to the hypothesis of Stanley and Cretaceous micropaleontology and our mentor, colleague, and friend. References Arthur, M. Natland, Carbonaceous Arthur, M. Schlanger, and H. Jen- inina with special reference to the Aptian sediments in the North and South Atlantic: The kyns, The Cenomanian-Turonian oceanic an- assemblages of Speeton North Yorkshire, Eng- role of salinity in stable stratification of Early oxic event II, paleoceanographic controls on land , J.

Cretaceous basins, in Deep Drilling Results in organic matter production and preservation, Barron, E. Brooks and A. Fleet, pp. Talwani et al. Barron, E. Arthur, M. Dean, and L. Premoli Silva, Develop- Geochemical and climatic effects of increased ject , Palaeogeogr. Cita, pp. Brumsack, H. Jenkyns, ity studies, Paleoceanography, 5, — , demic, San Diego, Calif. Schlanger, Stratigraphy, geochemis- Sageman, Marine black try, and paleoceanography of organic carbon- Barron, E. Earth sources, Events, and Rhythms, edited by R.

Ginsburg and B. Beaudoin, pp. Schlanger, Cretaceous Kluwer Acad. Archean to Present, Geophys. Sundquist and W. Dean, D. Bottjer, and Azam, F. Long, Sea snow micro- Barron, E. Fawcett, W. Peterson, P. Scholle, Rhythmic bedding in Meso- cosms, Nature, , — , Pollard, and S. Fenchel, J. Field, J. Gray, R. Thingstad, The ecological graphy, 10, — , Hay, and S. Thompson, The edited by A. Berger, pp. Riedel, Ecol. Baker, E. German, and H. Elderfield, Earth history, Palaeogeogr.

Dean, and S. Schlanger, Hydrothermal plumes over spreading center Palaeoecol. Variations in the global carbon cycle during axes: Global distributions and geophysical in- Barron, E. Peterson, S. Thompson, the Cretaceous related to climate, volcanism, ferences, in Seafloor Hydrothermal Systems: and D. Humphries et al. AGU, Washington, D. Behrenfeld, M. Kolber, Widespread S. Broecker, pp. Desai, A review and revi- iron limitation of phytoplankton in the South D.

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Cycles, 15, 81 — 99, Banner, and J. Planktonic Foraminifera, pp. Cool, T. Caron, and M. Delamette, ing the paleoceanography of the Cretaceous Bralower, T. Hall, and M. Bergen, Cenomanian- ted by J. Williams, Dinoflagellate Cotillon, P. Capone, D. Zehr, H. Paerl, B. Berg- tral Atlantic , and in the Vocontian Basin Paleontol. Dean and man, and E. Carpenter, Trichodesmium, a France , Initial Rep. Deep Sea Drill. Arthur, pp. Science, , — , Crane, P. Friis, and K. Pedersen, The Bralower, T. Siesser, Cretaceous Caron, M.

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Nature, , — , a. Pa- Bralower, T. CoBabe, B. Clement, W. Sliter, C. Osburn, and J. Our mission is to transform the most popular works of legendary authors to modern reading room. We publish pdf books on many subjects for readers of all ages including Fiction, Non-Fiction, Academic and Children's writings. Evolutionary Biology , Geology , and Ecology. Subtropical to temperate late Neogene to Quaternary planktic foraminiferal biostratigraphy across the Kuroshio Current Extension, Shatsky Rise, northwest Pacific Ocean more.

Multidisciplinary and PLoS one. While the Eagle Ford north of the San Marcos Arch and its stratigraphic equivalents to the east of the Sabine Arch are shallow-water sediments dominated by terrigenous clastics, the more distal localities in south Texas are dominated by hemi-pelagic carbonates draped over an Early Cretaceous carbonate platform, called the Comanche Platform, and adjacent submarine plateaus and basins. This region was strongly affected by major oceanographic changes during the Cenomanian-Turonian, particularly a significant transgression that drove localized upwelling and organic matter burial in the Lower Eagle Ford prior to the global Oceanic Anoxic Event 2 OAE2.

These pre-OAE2 organic-rich shales are the basis of Eagle Ford shale gas play, which has spurred commercial and academic research into many aspects of the geology of the E The editor of Paleoceanography welcomes original scientific contributions dealing with the marine sedimen- tary record from the present ocean basins and margins and from exposures of ancient marine sediments on the continents.

A wide range of approaches may be employed, including sedimentology; i Seismic stratigraphy and Marine Sediment. Late Neogene and Quaternary diversity and taxonomy of subtropical to temperate planktic foraminifera across the Kuroshio Current Extension, northwest Pacific Ocean more. Mark Leckie and Adriane Lam. Patterns of diversity in the modern planktic foraminifera indicate a latitudinal diversity gradient LDG , which peaks in the mid-latitude regions.

Plankton distributional patterns are often most strongly associated with temperature and Plankton distributional patterns are often most strongly associated with temperature and are expected to change in response to expanded tropical water masses. Defining the underlying causes of climatic and oceanographic processes, however, requires detailed, local-scale diversity curves and evolutionary metrics, as well as solid taxonomic concepts of planktic foraminifera, to test the oceanographic processes driving evolution of marine plankton.

Currently, diversity estimates for the planktic foraminifera are mainly based on global datasets skewed towards tropical to subtropical sites and conducted at coarse resolutions that hamper investigations of evolutionary processes, especially for short-lived climate perturbations.

Here, we present kyr resolution diversity curves and kyr resolution local first appearance and extirpation rates of planktic foraminifera for four Ocean Drilling Program sites that extend from the temperate northern edge of the modern-day position of the Kuroshio Current Extension KCE to the tropics.

We provide an updated taxonomic review of late Neogene planktic foraminiferal species from within the influence of the KCE. These data allow for investigations of the western Pacific LDG and patterns of evolution through the late Neogene in response to tectonic and climate events.

Our results indicate that a mid-latitude diversity peak has been prominent in the western Pacific since at least Development of the modern North Pacific gyre system due to closure of the Central American Seaway and constriction of the Indonesian Throughflow increased the LDG between the tropics and the northernmost site, likely in response to KCE intensification.

With intensification of Northern Hemisphere glaciation came a decrease in diversity at the northernmost site, hypothesized to be caused by subtropical gyre constriction and southward displacement of subpolar surface waters. The beginning of the mid-Pleistocene transition marks an increase in diversity gradients, especially between the northernmost and tropical sites. A detailed taxonomic evaluation of planktic foraminiferal species has led to synonymization of what we consider regional morphological variants, as well as revised taxonomic concepts of key subtropical to temperate late Neogene planktic foraminifera.

Scanning electron micrographs capture the morphological variability within a species concept for the first time in great detail for this part of the world ocean. These data and updated taxonomic concepts provide a framework for future studies to link evolutionary patterns with high-resolution geochemical and sedimentological data to further interpret localized drivers of diversification in the planktic foraminifera.

Publication Date: Publication Name: Micropaleontology. Mark Leckie and Khalifa Elderbak. Testing different techniques for microfossil extraction from limestone and marlstone more.