scholarly journals Millennial-Scale Environmental Variability in Late Quaternary Deep-Sea Sediments from the Demerara Rise, NE Coast of South America

Oceans ◽  
2021 ◽  
Vol 2 (1) ◽  
pp. 246-265
Author(s):  
Steve Lund ◽  
Ellen Platzman
Keyword(s):  
Magnetic Material ◽  
Grain Size ◽  
South America ◽  
Deep Sea ◽  
Magnetic Measurements ◽  
Phase Relationship ◽  
Cariaco Basin ◽  
Magnetic Intensity ◽  
Average Position ◽  
Millennial Scale

We carried out a rock magnetic study of two deep-sea gravity cores from the Demerara Rise, NE South America. Our previous studies provided radiocarbon and paleomagnetic chronologies for these cores. This study presents detailed rock magnetic measurements on these cores in order to characterize the rock magnetic mineralogy and grain size as indicators of the overall clastic fraction. We measured the magnetic susceptibility, anhysteretic remanence, and isothermal remanence and demagnetized the remanences at several alternating field demagnetization levels. The magnetic intensities estimate the magnetic material concentration (and indirectly the overall clastic fraction) in the cores. Ratios of rock magnetic parameters indicate the relative grain size of the magnetic material (and indirectly the overall clastic grain size). Rock magnetic intensity parameters and rock magnetic ratios both vary systematically and synchronously over the last 30,000 years in both cores. There is a multi-millennial-scale cyclicity, with intervals of high magnetic intensity (high magnetic and clastic content) with low magnetic ratios (coarser magnetic and clastic grain size), alternating in sequence with intervals of low magnetic intensity with high magnetic ratios (finer grain size). There is also a higher-frequency millennial-scale variability in intensity superposed on the multi-millennial-scale variability. There are nine (A–I) multi-millennial-scale intervals in the cores. Intervals A, C, E, G, and I have high magnetic and clastic content with coarser overall magnetic and clastic grain size and are likely intervals of enhanced rainfall and runoff from the NE South American margin to the coastal ocean. In contrast, intervals B, D, F, and H have lower clastic flux with finer overall grain size, probably indicating lower continental rainfall and runoff. During the Holocene, high rainfall and runoff intervals can be related to cooler times and low rainfall and runoff to warmer times. The opposite pattern existed during the Pleistocene, with higher rainfall and runoff during interstadial conditions and lower rainfall and runoff during stadial conditions. We noted a similar pattern of Pleistocene multi-millennial-scale variability in a transect of deep-sea sediment cores along the NE Brazilian margin, from the Cariaco Basin (~10 N) to the NE Brazilian margin (~1° N–4° S). However the NW part of this transect (Cariaco Basin, Demerara Rise, Amazon Fan) has an out-of-phase relationship with the SE part of the transect (NE Brazilian margin) between warm–cold and wet–dry conditions. One possible cause of the high–low rainfall and runoff patterns might be oscillation of the Intertropical Convergence Zone (ITCZ), with higher rainfall and runoff associated with a more southerly average position of the ITCZ and lower rainfall and runoff associated with a more northerly average position of the ITCZ.

scholarly journals Millennial-Scale Response of a Western Mediterranean River to Late Quaternary Climate Changes: A View from the Deep Sea

2014 ◽  
Vol 122 (6) ◽  
pp. 687-703 ◽  
Author(s):  
Lucile Bonneau ◽  
Stéphan J. Jorry ◽  
Samuel Toucanne ◽  
Ricardo Silva Jacinto ◽  
Laurent Emmanuel
Keyword(s):  
Deep Sea ◽  
Climate Changes ◽  
Late Quaternary ◽  
Western Mediterranean ◽  
Mediterranean River ◽  
Quaternary Climate ◽  
Scale Response ◽  
Quaternary Climate Changes ◽  
Millennial Scale

scholarly journals Quality assessment of chronologies in Latin American pollen records: a contribution to centennial to millennial scale studies of environmental change

2015 ◽  
Vol 11 (2) ◽  
pp. 1219-1262 ◽  
Author(s):  
S. G. A. Flantua ◽  
H. Hooghiemstra ◽  
M. Blaauw
Keyword(s):  
South America ◽  
Quality Assessment ◽  
Latin American ◽  
Time Windows ◽  
Uncertainty Assessment ◽  
Last Deglaciation ◽  
Age Model ◽  
Millennial Time Scale ◽  
Pollen Records ◽  
Millennial Scale

Abstract. The newly updated inventory of the Latin American Pollen Database (LAPD) offers an important overview of data available for multi-proxy and multi-site purposes. However, heterogeneous paleoecological databases are not suitable to be integrated without an uncertainty assessment of existing chronologies. Therefore, we collected all chronological control points and age model metadata from the LAPD literature to create a complementary chronological database of 5116 dates from 1097 pollen records. We start with an overview on chronological dating and reporting in Central and South America. Specific problems and recommendations for chronology reporting are discussed. Subsequently, we implement a temporal quality assessment of pollen records from northwest South-America to support research on climate forcers and responses at a centennial-millennial time-scale. New chronologies are generated for 233 pollen records based on updated calibration curves. Different time windows are discussed on sample resolution and temporal uncertainty. Approximately one in four pollen diagrams depicts < 500 years resolution data at the Younger Dryas/Holocene transition. Overall, our analyses suggest that the temporal resolution of multi-site syntheses of late Pleistocene fossil pollen records in the northwest South-America is ca. 240 years, a resolution which allows analysis of ecological responses to centennial-millennial-scale climate change during the last deglaciation.

scholarly journals Breeding Malting Barley under Stress Conditions in South America

2011 ◽  
Vol 40 (No. 4) ◽  
pp. 140-147 ◽  
Author(s):  
E. Germán S
Keyword(s):  
Grain Size ◽  
South America ◽  
Grain Yield ◽  
Leaf Rust ◽  
Production Efficiency ◽  
Malting Quality ◽  
Malt Extract ◽  
Malting Barley ◽  
Net Blotch ◽  
Early Maturity

The annual average area sown with barley (Hordeum vulgare) in South America during 1999&ndash;2003 was 795 000 ha. In Argentina, Brazil, Chile and Uruguay, two-rowed spring cultivars are used mostly for malt production. Research has been developed in private malting companies and official institutions supported by the industry. In Argentina, tolerance to drought and heat stress during grain filling are important in drier areas. Yield and malt extract had been improved in cultivars released from 1940 to 1998. In Brazil, progress in grain yield, grain size, malting quality, early maturity, and resistance to net blotch, powdery mildew, and leaf rust has been achieved by EMBRAPA and malting companies. Higher tolerance to soil acidity and resistance to spot blotch are required. Since 1976, malting barley breeding in INIA-Chile has improved grain yield, grain size, beer production efficiency, and resistance to scald, net blotch, stripe rust, and leaf rust. Uruguay produces high quality malt exported mainly to Brazil. Malting companies have released locally bred and introduced cultivars since the early 1970&rsquo;s. Initiated in 1988, INIA-Uruguay breeding program has improved yield, malting quality, and lodging and disease resistance. Fusarium head blight is a new challenge for research in Brazil and Uruguay. Information regarding malting barley production, the most important stresses in different areas of production, and breeding progress under South American conditions is provided. &nbsp;

Permeability of Marine Sediments and Tropical Volcanic Soils

2012 ◽  
Author(s):  
Horst G. Brandes
Keyword(s):  
Grain Size ◽  
Marine Sediments ◽  
Deep Sea ◽  
Carbonate Content ◽  
Clayey Soils ◽  
Index Properties ◽  
Volcanic Soils ◽  
Fine Grained ◽  
Deep Sea Sediments ◽  
Tropical Volcanic Soils

Permeability values for a range of fine-grained deep-sea sediments are presented and evaluated in terms of index properties such as plasticity, grain size and carbonate content. It is found that whereas clay-rich sediments have similar permeabilities to those of equivalent land-based fine-grained soils, the presence of volcanic, carbonate and other non-clay fractions tends to increase permeability somewhat. Volcanic silty-clayey soils from Hawaii have comparable permeability values, although they can be slightly more permeable.

South America-Africa missing links revealed by the taxonomy of deep-sea molluscs: Examples from prochaetodermatid aplacophorans

2018 ◽  
Vol 132 ◽  
pp. 16-28 ◽  
Author(s):  
Paulo Vinicius Ferraz Corrêa ◽  
Marcel Sabino Miranda ◽  
Flávio Dias Passos
Keyword(s):  
South America ◽  
Deep Sea

Environmental and rock magnetic investigations into provenance and processes of west Iberian margin sediments

2020 ◽  
Author(s):  
Matthew Nichols ◽  
Chuang Xuan ◽  
David A. Hodell ◽  
Carl Richter ◽  
Gary D. Acton ◽  
...  
Keyword(s):  
Magnetic Material ◽  
Grain Size ◽  
Rock Magnetism ◽  
Sediment Cores ◽  
Hysteresis Loops ◽  
Ice Cores ◽  
Sediment Provenance ◽  
The West ◽  
Significant Difference ◽  
Iberian Margin

&lt;p&gt;Ocean sediment records from the West Iberian margin can be correlated to both Antarctic and Greenland ice cores as well as to European terrestrial pollen data. Previous studies have focussed on comparatively short sediment cores collected from relatively deep-water sites (i.e. &gt;~2500mbsl). Here we present magnetic mineralogy and grain size from Integrated Ocean Drilling Programme Sites U1385 (2585mbsl) and U1391 (1085mbsl) to further understand magnetic sediment provenance and palaeocurrent evolution on the west Iberian margin dating back to ~416 ka. The gradient of IRM acquisition curves, shape of hysteresis loops, and marked decrease in magnetic susceptibility at ~580&amp;#176;C indicate that magnetite is the dominant magnetic phase at Site U1391. At depth, increased contributions of a higher coercivity component are seen at intervals where the concentration of magnetic material is low. FORC diagrams indicate the presence of a narrow ridge elongated along the Bc axis consistent with a higher coercivity component observed in IRM acquisition data. Magnetic grain size proxy (k&lt;sub&gt;ARM&lt;/sub&gt;/k) records from Site U1391 also show a significant difference in pattern of variability at depth. After ~130 ka k&lt;sub&gt;ARM&lt;/sub&gt;/k closely follows relative sea level, however prior to ~130 ka there is higher frequency variability with apparent coarser magnetic grain size, suggesting the higher coercivity component could have resulted from diagenetic processes. This is particularly apparent during warm intervals where magnetic material concentration is low (MIS 7, 9 and 11). This behaviour differs from that observed at either Site U1385, or in the younger portion of the record at Site U1391. We infer that the intervals of diagenetically effected sediments at U1391 could have resulted from increased productivity, vertical migration of the Mediterranean outflow water and associated changes in bottom water ventilation. Further understanding of sediment composition, redox conditions, transport and provenance through the last few glacial cycles underpins much of the other palaeoclimatic investigation at these sites. Results from our analysis of rock magnetism will be used to guide the reconstruction of reliable relative palaeointensity records from the Iberian Margin sediments to assess past geomagnetic changes in the region.&lt;/p&gt;

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