scholarly journals Major environmental changes recorded by lacustrine sedimentary organic matter since the last glacial maximum near the equator (Lagoa do Caçó, NE Brazil)

2004 ◽  
Vol 205 (3-4) ◽  
pp. 183-197 ◽  
Author(s):  
Jérémy Jacob ◽  
Jean-Robert Disnar ◽  
Mohammed Boussafir ◽  
Abdelfettah Sifeddine ◽  
Bruno Turcq ◽  
...  
Keyword(s):  
Organic Matter ◽  
Last Glacial Maximum ◽  
Environmental Changes ◽  
Glacial Maximum ◽  
Sedimentary Organic Matter ◽  
Last Glacial ◽  
The Last Glacial Maximum ◽  
The Last Glacial

scholarly journals Were the Larsemann Hills ice-free through the Last Glacial Maximum?

2001 ◽  
Vol 13 (4) ◽  
pp. 440-454 ◽  
Author(s):  
D.A. Hodgson ◽  
P.E. Noon ◽  
W. Vyverman ◽  
C.L. Bryant ◽  
D.B. Gore ◽  
...  
Keyword(s):  
Last Glacial Maximum ◽  
Climate Changes ◽  
Environmental Changes ◽  
Glacial Maximum ◽  
Radiometric Dating ◽  
Supporting Evidence ◽  
Last Glacial ◽  
Larsemann Hills ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Lake sediments in the Larsemann Hills contain a great diversity of biological and physical markers from which past environments can be inferred. In order to determine the timing of environmental changes it is essential to have accurate dating of sediments. We used radiometric (210Pb and 137Cs), radiocarbon (AMS 14C) and uranium series (238U) methods to date cores from eleven lakes. These were sampled on coastal to inland transects across the two main peninsulas, Broknes and Stornes, together with a single sample from the Bolingen Islands. Radiometric dating of recent sediments yielded 210Pb levels below acceptable detection limits. However, a relatively well-defined peak in 137Cs gave a date marker which corresponds to the fallout maximum from the atmospheric testing of atomic weapons in 1964/65. Radiocarbon (AMS 14C) measurements showed stratigraphical consistency in the age-depth sequences and undisturbed laminae in some cores provides evidence that the sediments have remained undisturbed by glacial action. In addition, freshwater surface sediments were found to be in near-equilibrium with modern 14CO2 and not influenced by radiocarbon contamination processes. This dating program, together with geomorphological records of ice flow directions and glacial sediments, indicates that parts of Broknes were ice-free throughout the Last Glacial Maximum and that some lakes have existed continuously since at least 44 ka bp. Attempts to date sediments older than 44 ka bp using 128U dating were inconclusive. However, supporting evidence for Broknes being ice-free is provided by an Optically Stimulated Luminescence date from a glaciofluvial deposit. In contrast, Stornes only became ice-free in the mid to late Holocene. This contrasting glacial history results from the Dålk Glacier which diverts ice around Broknes. Lakes on Broknes and some offshore islands therefore contain the oldest known lacustrine sediment records from eastern Antarctica, with the area providing an ice-free oasis and refuge for plants and animals throughout the Last Glacial Maximum. These sediments are therefore well placed to unravel a unique limnological sequence of environmental and climate changes in East Antarctica from the late Pleistocene to the present. This information may help better constrain models of current climate changes and ensure the adequate protection of these lakes and their catchments from the impacts of recent human occupation.

scholarly journals CO<sub>2</sub> air-sea exchange due to calcium carbonate and organic matter storage: pre-industrial and Last Glacial Maximum estimates

2004 ◽  
Vol 1 (1) ◽  
pp. 429-495 ◽  
Author(s):  
A. Lerman ◽  
F. T. Mackenzie
Keyword(s):  
Organic Matter ◽  
Surface Water ◽  
Last Glacial Maximum ◽  
Glacial Maximum ◽  
Atmospheric Co2 ◽  
Last Glacial ◽  
Surface Ocean ◽  
Ocean Layer ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Abstract. Release of CO2 from surface ocean water owing to precipitation of CaCO3 and the imbalance between biological production of organic matter and its respiration, and their net removal from surface water to sedimentary storage was studied by means of a model that gives the quotient θ=(CO2 released to the atmosphere)/(CaCO3 precipitated). The surface ocean layer is approximated by a euphotic zone, 50 m thick, that includes the shallower coastal area and open ocean. θ depends on water temperature, CaCO3 and organic carbon mass formed, and atmospheric CO2 concentration. At temperatures between 5 and 25°C, and three atmospheric CO2 pressures – 195 ppmv corresponding to the Last Glacial Maximum, 280 ppmv for the end of pre-industrial time, and 375 ppmv for the present – θ varies from a fraction of 0.38 to 0.79, increasing with decreasing temperature, increasing atmospheric CO2 content, and increasing CaCO3 precipitated mass (up to 45% of the DIC concentration in surface water). For a surface ocean layer that receives input of inorganic and organic carbon from land, the calculated CO2 flux to the atmosphere at the Last Glacial Maximum is 20 to 22×1012 mol/yr and in pre-industrial time it is 45 to 49×1012 mol/yr. In addition to the environmental factors mentioned above, flux to the atmosphere and increase of atmospheric CO2 depend on the thickness of the surface ocean layer. The significance of these fluxes and comparisons with the estimates of other investigators are discussed. Within the imbalanced global carbon cycle, our estimates are in agreement with the conclusions of others that the global ocean prior to anthropogenic emissions of CO2 to the atmosphere was losing carbon, calcium, and total alkalinity owing to precipitation of CaCO3 and consequent emission of CO2. Other pathways of CO2 exchange between the atmosphere and land organic reservoir and rock weathering may reduce the imbalances in the carbon cycle on millenial time scales.

scholarly journals The Last Glacial Maximum and deglaciation in central Patagonia, 44°S–49°S

2017 ◽  
Vol 43 (2) ◽  
pp. 719 ◽  
Author(s):  
M. Mendelova ◽  
A.S. Hein ◽  
R. McCulloch ◽  
B. Davies
Keyword(s):  
Southern Hemisphere ◽  
Last Glacial Maximum ◽  
Environmental Changes ◽  
Convincing Evidence ◽  
Glacial Maximum ◽  
Future Research ◽  
Last Glacial ◽  
The Antarctic ◽  
The Last Glacial Maximum ◽  
The Last Glacial

This paper reviews published geochronological data on glacier fluctuations and environmental changes in central Patagonia (44° S - 49° S) from the Last Glacial Maximum (LGM) through to the Holocene. Well-dated glacial chronologies from the southern mid-latitudes can inform on the synchronicity of glacial advances worldwide and provide insight on the drivers of southern hemisphere glaciations. In central Patagonia, two large outlet lobes of the former Patagonian Ice Sheet advanced in broad synchrony with the global LGM. In contrast to other parts of Patagonia, there is no convincing evidence for a more extensive local LGM advance during Marine Isotope Stage 3. Deglaciation initiated at ca. 19 ka, earlier than in other parts of Patagonia and regionally in the Southern Hemisphere, and rapid deglaciation saw ice margins retreat in places by at least 80-120 km within a few millennia. The Lateglacial glacier margins are poorly constrained, but an ice mass substantial enough to maintain a large regional proglacial lake must have persisted at this time. The timing of lake drainage and opening of the Río Baker drainage route to the Pacific Ocean is debated; the only directly dated shoreline suggests this occurred at the end of the Antarctic Cold Reversal at 12.7 ka. Palaeoecological evidence for cooling during the Antarctic Cold Reversal or Younger Dryas remains equivocal, which may reflect both the eurythermic nature of Patagonian vegetation and shifting Southern Westerly Winds. Eastern outlet glaciers appear to have advanced or stabilised at the Lateglacial/Holocene transition when palaeoenvironmental records indicate warmer and drier conditions, but the reason for this is unclear. Our review reveals both spatial and temporal gaps in available data that provide avenues for future research.

Reconstructions of the past distribution of Testudo graeca mitochondrial lineages in the Middle East and Transcaucasia support multiple refugia since the Last Glacial Maximum

2021 ◽  
pp. 10-17
Author(s):  
Oguz Turkozan
Keyword(s):  
Middle East ◽  
Last Glacial Maximum ◽  
Glacial Maximum ◽  
Testudo Graeca ◽  
Last Glacial ◽  
The Past ◽  
Precipitation Seasonality ◽  
Multiple Refugia ◽  
The Last Glacial Maximum ◽  
The Last Glacial

A cycle of glacial and interglacial periods in the Quaternary caused species’ ranges to expand and contract in response to climatic and environmental changes. During interglacial periods, many species expanded their distribution ranges from refugia into higher elevations and latitudes. In the present work, we projected the responses of the five lineages of Testudo graeca in the Middle East and Transcaucasia as the climate shifted from the Last Glacial Maximum (LGM, Mid – Holocene), to the present. Under the past LGM and Mid-Holocene bioclimatic conditions, models predicted relatively more suitable habitats for some of the lineages. The most significant bioclimatic variables in predicting the present and past potential distribution of clades are the precipitation of the warmest quarter for T. g. armeniaca (95.8 %), precipitation seasonality for T. g. buxtoni (85.0 %), minimum temperature of the coldest month for T. g. ibera (75.4 %), precipitation of the coldest quarter for T. g. terrestris (34.1 %), and the mean temperature of the driest quarter for T. g. zarudyni (88.8 %). Since the LGM, we hypothesise that the ranges of lineages have either expanded (T. g. ibera), contracted (T. g. zarudnyi) or remained stable (T. g. terrestris), and for other two taxa (T. g. armeniaca and T. g. buxtoni) the pattern remains unclear. Our analysis predicts multiple refugia for Testudo during the LGM and supports previous hypotheses about high lineage richness in Anatolia resulting from secondary contact.

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