Climatic changes during the last deglaciation recorded in sediment cores from the northeastern Brazilian Continental Margin

1999 ◽  
Vol 19 (3) ◽  
pp. 209-218 ◽  
Author(s):  
H. W. Arz ◽  
J. Pätzold ◽  
G. Wefer
Author(s):  
J. C. Duplessy ◽  
L. Labeyrie ◽  
J. Moyes ◽  
J. L. Turon ◽  
J. Duprat ◽  
...  

2020 ◽  
Author(s):  
Andrea Burke ◽  
Rosanna Greenop ◽  
James Rae ◽  
Rhian Rees-Owen ◽  
Paula Reimer ◽  
...  

<p>Paleoclimate records from the North Atlantic show some of the most iconic signals of abrupt climate change during the ice ages. Here we use radiocarbon as a tracer of ocean circulation and air-sea gas exchange to investigate potential mechanisms for the abrupt climate changes seen in the North Atlantic over the last deglaciation. We have created a stack of North Atlantic surface radiocarbon reservoir ages over the past 20,000 years, using new synchronized age models from thirteen sediment cores refined with thorium normalization between tie-points. This stack shows consistent and large reservoir age increases of more than 1000 years from the LGM into HS1, dropping abruptly back to approximately modern reservoir ages before the onset of the Bolling-Allerod. We use the intermediate complexity earth system model cGENIE to investigate the potential drivers of these reservoir age changes. We find that sea ice, circulation and CO<sub>2</sub> all play important roles in setting the reservoir age. We use these coherently dated records to revisit the sequence and timing of climatic events during HS1 and the last deglaciation, and show that Laurentide Heinrich Events are a response to stadial conditions, rather than their root cause.</p>


2013 ◽  
Vol 9 (2) ◽  
pp. 767-787 ◽  
Author(s):  
S. Desprat ◽  
N. Combourieu-Nebout ◽  
L. Essallami ◽  
M. A. Sicre ◽  
I. Dormoy ◽  
...  

Abstract. Despite a large number of studies, the long-term and millennial to centennial-scale climatic variability in the Mediterranean region during the last deglaciation and the Holocene is still debated, including in the southern Central Mediterranean. In this paper, we present a new marine pollen sequence (core MD04-2797CQ) from the Siculo-Tunisian Strait documenting the regional vegetation and climatic changes in the southern Central Mediterranean during the last deglaciation and the Holocene. The MD04-2797CQ marine pollen sequence shows that semi-desert plants dominated the vegetal cover in the southern Central Mediterranean between 18.2 and 12.3 ka cal BP, indicating prevailing dry conditions during the deglaciation, even during the Greenland Interstadial (GI)-1. Across the transition Greenland Stadial (GS)-1 – Holocene, Asteraceae-Poaceae steppe became dominant till 10.1 ka cal BP. This record underlines with no chronological ambiguity that even though temperatures increased, deficiency in moisture availability persisted into the early Holocene. Temperate trees and shrubs with heath underbrush or maquis expanded between 10.1 and 6.6 ka, corresponding to Sapropel 1 (S1) interval, while Mediterranean plants only developed from 6.6 ka onwards. These changes in vegetal cover show that the regional climate in southern Central Mediterranean was wetter during S1 and became drier during the mid- to late Holocene. Wetter conditions during S1 were likely due to increased winter precipitation while summers remained dry. We suggest, in agreement with published modeling experiments, that the early Holocene increased melting of the Laurentide Ice Sheet in conjunction with weak winter insolation played a major role in the development of winter precipitation maxima in the Mediterranean region in controlling the strength and position of the North Atlantic storm track. Finally, our data provide evidence for centennial-scale vegetation and climatic changes in the southern Central Mediterranean. During the wet early Holocene, alkenone-derived cooling episodes are synchronous with herbaceous composition changes that indicate muted changes in precipitation. In contrast, enhanced aridity episodes, as detected by strong reduction in trees and shrubs, are recorded during the mid- to late Holocene. We show that the impact of the Holocene cooling events on the Mediterranean hydroclimate depend on baseline climate states, i.e. insolation and ice sheet extent, shaping the response of the mid-latitude atmospheric circulation.


2012 ◽  
Vol 8 (6) ◽  
pp. 5687-5741 ◽  
Author(s):  
S. Desprat ◽  
N. Combourieu-Nebout ◽  
L. Essallami ◽  
M. A. Sicre ◽  
I. Dormoy ◽  
...  

Abstract. Despite a large number of studies, the long-term and millennial to centennial-scale climatic variability in the Mediterranean region during the last deglaciation and the Holocene is still debated, in particular in the Southern Central Mediterranean. In this paper, we present a new marine pollen sequence (MD04-2797CQ) from the Siculo-Tunisian Strait documenting the regional vegetation and climatic changes in the Southern Central Mediterranean during the last deglaciation and the Holocene. The MD04-2797CQ marine pollen sequence shows that semi-desert plants dominated the vegetal cover in the Southern Central Mediterranean between 18 and 12.3 kyr BP indicating prevailing dry conditions during the deglaciation, even during the Greenland Interstadial (GI)-1. Such arid conditions likely restricted the expansion of the trees and shrubs despite the GI-1 climatic amelioration. Across the transition Greenland Stadial (GS)-1 – Holocene, Asteraceae-Poaceae steppe became dominant till 10.1 kyr. This record underlines with no chronological ambiguity that even though temperatures increased, deficiency in moisture availability persisted into the Early Holocene.Temperate trees and shrubs with heaths as oak forest understorey or heath maquis expanded between 10.1 and 6.6 kyr, while Mediterranean plants only developed from 6.6 kyr onwards. These changes in vegetal cover show that the regional climate in Southern Central Mediterranean was wetter during Sapropel 1 (S1) and became drier during the Mid- to Late Holocene. Wetter conditions during S1 were likely due to increased winter precipitation while summers remained dry. We suggest, in agreement with published modelling experiments, that the increased melting of the Laurentide Ice Sheet between 10 to 6.8 kyr in conjunction with weak winter insolation played a major role in the development of winter precipitation maxima in the Mediterranean region in controlling the strength and position of the North Atlantic storm track. Finally, our data provide evidences of centennial-scale vegetation and climatic changes in the Southern Central Mediterranean. During the wet Early Holocene, alkenones-derived cooling episodes are synchronous to herbaceous composition changes that indicate muted changes in precipitation. In contrast, enhanced aridity episodes, as detected by strong reduction in trees and shrubs, are recorded during the Mid- to Late Holocene. We show that the impact of the Holocene cooling events depend on the baseline climate states insolation and ice sheet volume, shaping the response of the mid-latitude atmospheric circulation.


2020 ◽  
Vol 17 (12) ◽  
pp. 3165-3182
Author(s):  
Zeynep Erdem ◽  
Joachim Schönfeld ◽  
Anthony E. Rathburn ◽  
Maria-Elena Pérez ◽  
Jorge Cardich ◽  
...  

Abstract. Deciphering the dynamics of dissolved oxygen in the mid-depth ocean during the last deglaciation is essential to understand the influence of climate change on modern oxygen minimum zones (OMZs). Many paleo-proxy records from the eastern Pacific Ocean indicate an extension of oxygen-depleted conditions during the deglaciation, but the degree of deoxygenation has not been quantified to date. The Peruvian OMZ, one of the largest OMZs in the world, is a key area to monitor such changes in near-bottom-water oxygenation in relation to changing climatic conditions. Here, we analysed the potential to use the composition of foraminiferal assemblages from the Peruvian OMZ as a quantitative redox proxy. A multiple regression analysis was applied to a joint dataset of living (rose-bengal-stained, fossilizable calcareous species) benthic foraminiferal distributions from the Peruvian continental margin. Bottom-water oxygen concentrations ([O2]BW) during sampling were used as the dependant variable. The correlation was significant (R2=0.82; p<0.05), indicating that the foraminiferal assemblages are rather governed by oxygen availability than by the deposition of particulate organic matter (R2=0.53; p=0.31). We applied the regression formula to three sediment cores from the northern part of the Peruvian OMZ between 3 and 8∘ S and 997 and 1250 m water depth, thereby recording oxygenation changes at the lower boundary of the Peruvian OMZ. Each core displayed a similar trend of decreasing oxygen levels since the Last Glacial Maximum (LGM). The overall [O2]BW change from the LGM and the Holocene was constrained to 30 µmol kg−1 at the lower boundary of the OMZ.


2004 ◽  
Vol 39 ◽  
pp. 445-451 ◽  
Author(s):  
Cristinamaria Salvi ◽  
Gianguido Salvi ◽  
Barbara Stenni ◽  
Antonio Brambati

AbstractA detailed study of organic carbon content obtained from two sediment cores collected in the Joides basin, western Ross Sea, Antarctica, was carried out. The variations observed during the last deglaciation and the Holocene were compared to the high-resolution climatic records (EPICA DC and Taylor Dome) preserved in the ice. The importance of the carbon content as a proxy for palaeoclimatic and palaeoenvironmental changes was investigated. A dramatic decrease in the Ross Sea palaeoproductivity was observed during the Antarctic Cold Reversal (12.5–14 kyr BP). Another decrease in total organic carbon in the second half of the Holocene (after 5–6 kyr BP) confirms the climate worsening observed in previous studies.


Radiocarbon ◽  
2007 ◽  
Vol 49 (2) ◽  
pp. 963-968 ◽  
Author(s):  
Ken'ichi Ohkushi ◽  
Masao Uchida ◽  
Kaori Aoki ◽  
Minoru Yoneda ◽  
Ken Ikehara ◽  
...  

We measured radiocarbon ages of planktic foraminifera in 4 sediment cores from the northwestern Pacific region off northern Japan in order to estimate marine reservoir ages during the B⊘lling-Aller⊘d period. The ages of deglacial tephra markers from 2 Japanese source volcanoes identified in these sediment cores had been previously estimated from 14C ages of terrestrial charcoal and buried forests. By comparing the foraminiferal and tephra ages, we estimated the surface water reservoir age during the B⊘lling-Aller⊘d period to be ∼1000 yr or more in the region off northern Japan. The deglacial reservoir ages were more than 200 yr higher than the Holocene values of ∼800 yr. The older deglacial ages may have been caused by active upwelling of deep water during the last deglaciation and the consequent mixing of “older” deep water with “younger” surface waters.


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