1,721,021 research outputs found
Southern Ocean surface sediment diatom abundances
No full textDiatom percentage abundances in the surface sediments for five Southern Ocean marine sediment cores (TC290, TC288, TC287, U1361A and BC508). Abundances are presented for 45 species and groups and reflect a time-averaged environmental signature for the last 500 yrs at each core site. For each sample a minimum of 300 diatoms were counted with a light microscope (BH-2 Olympus, x1000 magnification). </span
TPC288 Diatom Abundance for MIS 5e
No full textThe downcore combined relative percentage abundance of two diatom species, Fragilariopsis curta and Fragilariopsis cylindrus (F. c+cy), for the period covering MIS 5e in the marine sediment core TPC288. The F. c+cy abundance is related to the seasonal sea ice extent (SSIE) using the thresholds in Gersonde & Zielinski (2000), with values >3% (>1%) indicating a location south of the average (maximum) SSIE. The age model for this core was produced by Pugh et al. (2009).
Gersonde R. & Zielinski U. 2000. The reconstruction of late Quaternary Antarctic sea-ice distribution - the use of diatoms as a proxy for sea-ice. Palaeogeography, Palaeoclimatology, Palaeoecology, 162: 263-286.
Pugh R.S., McCave I.N., Hillenbrand C-D. & Kuhn G. 2009. Circum-Antarctic age modelling of Quaternary marine cores under the Antarctic Circumpolar Current: Ice-core dust-magnetic correlation. Earth and Planetary Science Letters, 284(1-2): 113-123.</span
Age-model tiepoints for cores DSDP 594, MD88-770, MD02-2488, MD84-551, ODP site 1094, SO136-003, PS1768-8, PS2102-2 and MD97-2120
No full textTiepoints used to place the cores DSDP 594, MD88-770, MD02-2488, MD84-551, ODP site 1094, SO136-003, PS1768-8, PS2102-2 and MD97-2120 onto the LR04 benthic stack chronology. The δ18O data for each core is correlated to the LR04 benthic stack (Lisiecki &amp; Raymo 2005) using the Analyseries software (Paillard et al. 1996). LR04 ages are presented against depth in the core with the exceptions of cores DSDP 594, MD88-770 and SO136-003 where the LR04 age is presented against the "age" published in Barrows et al. (2007). The MIS stage boundaries use the LR04 ages from Lisiecki &amp; Raymo (2005) and the MIS 5 sub-stage boundaries use the ages from Govin et al. (2009). Benthic δ18O data is used for the correlation of cores DSDP 594 (Nelson et al. 1993), MD88-770 (Labeyrie et al. 1996) and MD02-2488 (Govin et al. 2009) to the LR04 benthic stack. Planktic δ18O data is used for the correlation of cores MD84-551 (Pichon et al. 1992), ODP site 1094 (Kanfoush et al. 2002), SO136-003 (Barrows et al. 2007), PS1768-8 (Mulitza et al. 1999), PS2102-2 (Niebler 1995) and MD97-2120 (Pahnke et al. 2003) to the LR04 benthic stack.
Barrows T.T., et al. 2007. Long-term sea surface temperature and climate change in the Australian-New Zealand region. Paleoceanography, 22(2): PA2215.
Govin A., et al. 2009. Evidence for northward expansion of Antarctic Bottom Water mass in the Southern Ocean during the last glacial inception. Paleoceanography, 24(1): PA1202.
Kanfoush S.L., et al. 2002. Comparison of ice-rafted debris and physical properties in ODP Site 1094 (South Atlantic) with the Vostok ice core over the last four climatic cycles. Palaeogeography, Palaeoclimatology, Palaeoecology, 182: 329-349.
Labeyrie L., et al. 1996. Hydrographic changes of the Southern Ocean (southeast Indian Sector) Over the last 230 kyr. Paleoceanography, 11(1): 57-76.
Lisiecki L.E. &amp; Raymo M.E. 2005. A Pliocene-Pleistocene stack of 57 globally distributed benthic δ18O records. Paleoceanography, 20(1): PA1003.
Mulitza S., et al. 1999. Foraminifera isotopes of sediment core PS1768-8. PANGAEA.
Nelson C.S., et al. 1993. Oceanographic and climatic changes over the past 160,000 years at Deep Sea Drilling Project Site 594 off Southeastern New Zealand, Southwest Pacific Ocean. Paleoceanography, 8(4): 435-458.
Niebler H.-S. 1995. Reconstruction of paleo-environmental parameters using stable isotopes and faunal assemblages of planktonic foraminifera in the South Atlantic Ocean. Reports on Polar Research, 167: 1-198.
Paillard D., Labeyrie L. &amp; Yiou P. 1996. Macintosh program performs time-series analysis. Eos, 77: 379.
Pahnke K., et al. 2003. 340,000-Year Centennial-Scale Marine Record of Southern Hemisphere Climatic Oscillation. Science, 301: 948-952.
Pichon J.J., et al. 1992. Surface Water Temperature Changes in the High Latitudes of the Southern Hemisphere over the Last Glacial-Interglacial Cycle. Paleoceanography, 7(3): 289-318.</span
Reconstructing Antarctic winter sea-ice extent during Marine Isotope Stage 5e
No full textEnvironmental conditions during Marine Isotope Stage (MIS) 5e (130-116 ka) represent an
important ‘process analogue’ for understanding the climatic responses to present and future
anthropogenic warming. Our understanding of the response of Antarctic sea ice to global warming
is particularly limited due to the short length of the observational record. Therefore, reconstructing
Antarctic winter sea-ice extent (WSIE) and Southern Ocean sea-surface temperatures (SSTs) during
MIS 5e provides insights into the temporal and spatial patterns of sea ice and SST change under a
warmer than present climate.
This thesis presents new MIS 5e proxy records from a set of marine sediment cores located south
of the Antarctic Polar Front, between 55 and 70 o
S, alongside an analysis of published Southern
Ocean records. The MIS 5e diatom species assemblages in these new cores are used to reconstruct
and investigate changes in WSIE and SSTs between the three Southern Ocean sectors. The new
proxy reconstructions of MIS 5e WSIE and SSTs are also compared to state-of-the-art climate model
outputs.
There was high variability in both WSIE and SSTs in the Atlantic and Indian sectors during MIS
5e, compared to the largely stable conditions found in the Pacific sector. All three Southern Ocean
sectors reached their minimum WSIE during MIS 5e concurrently, within chronological
uncertainties, both with each other and with the peak atmospheric temperature in the EPICA Dome
C ice core record. The high variability in the Atlantic sector records is attributed to high glacial
meltwater flux into the Weddell Sea whereas the high variability in the Indian sector likely resulted
from large latitudinal migrations of the Antarctic Circumpolar Current occurring on a millennial�scale. The different variability and sensitivity of Antarctic WSIE and SSTs between the three
Southern Ocean sectors may have significant implications for the Southern Hemisphere climate
system under future warming.
The latest climate models are currently unable to recreate the MIS 5e WSIE and SSTs seen in
these new proxy records, with colder SSTs and a greater WSIE in the models than the proxy records.
Inclusion of Northern Hemisphere Heinrich 11 meltwater forcing into model runs reduces the
discrepancy with proxy values, but longer duration (~3-4 ka) model runs, with Heinrich 11
meltwater forcing included, are required to fully test whether state-of-the-art climate models can
match Southern Ocean MIS 5e WSIE and SSTs reconstructed from proxy records
Reconstructing Antarctic winter sea-ice extent during Marine Isotope Stage (MIS) 5e
No full textMIS 5e (130-116 ka) is an important ‘process analogue’ for understanding the high latitude climatic feedbacks and forcings active under future anthropogenic warming. Antarctic sea-ice extent is a critical component of the Earth’s climate system through its impact on global albedo and Southern Hemisphere atmospheric and ocean circulation. Published marine sediment core records are located too far north to accurately constrain the timing and extent of the winter sea-ice (WSI) minimum during MIS 5e (Chadwick et al., 2020) and researchers/models have therefore assumed that this minimum occurs synchronously with peak warming in Antarctic ice core records (Holloway et al., 2017). This study presents new reconstructions of Southern Ocean (SO) WSI extent for MIS 5e based on the diatom assemblage records in marine sediment cores. These records have robust age models, which allow for the different timings and patterns of WSI retreat throughout the SO to be examined. In particular, the difference between the relatively stable WSI extent in the Pacific sector of the SO and the more dynamic WSI extent in the Atlantic sector of the SO. Using sediment cores located south of 55 o S creates a novel synthesis for assessing the evidence for the considerable MIS 5e WSI reduction predicted by model simulations (Holloway et al., 2017)
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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