Persistent deep water anoxia in the eastern South Atlantic during the last ice age

2021 ◽  
Vol 118 (49) ◽  
pp. e2107034118
Author(s):  
Natascha Riedinger ◽  
Florian Scholz ◽  
Michelle L. Abshire ◽  
Matthias Zabel
Keyword(s):  
Deep Water ◽  
Late Quaternary ◽  
Circulation Pattern ◽  
Oxygen Depletion ◽  
South Atlantic ◽  
Ice Age ◽  
Geochemical Data ◽  
Last Glacial ◽  
Last Ice Age ◽  
The Last Glacial

During the last glacial interval, marine sediments recorded reduced current ventilation within the ocean interior below water depths of approximately >1,500 m [B. A. Hoogakker et al., Nat. Geosci. 8, 40–43 (2015)]. The degree of the associated oxygen depletion in the different ocean basins, however, is still poorly constrained. Here, we present sedimentary records of redox-sensitive metals from the southwest African margin. These records show evidence of continuous bottom water anoxia in the eastern South Atlantic during the last glaciation that led to enhanced carbon burial over a prolonged period of time. Our geochemical data indicate that upwelling-related productivity and the associated oxygen minimum zone in the eastern South Atlantic shifted far seaward during the last glacial period and only slowly retreated during deglaciation times. While increased productivity during the last ice age may have contributed to oxygen depletion in bottom waters, especially on the upper slope, slow-down of the Late Quaternary deep water circulation pattern [Rutberg et al., Nature 405, 935–938 (2000)] appears to be the ultimate driver of anoxic conditions in deep waters.

scholarly journals Model evolution of the middle atmospheric palaeoenvironments

MAUSAM ◽  
2021 ◽  
Vol 52 (1) ◽  
pp. 297-306
Author(s):  
GUFRAN BEIG
Keyword(s):  
Vertical Distribution ◽  
Thermal Structure ◽  
Ice Core ◽  
Ice Age ◽  
Ozone Content ◽  
Glacial Period ◽  
Last Glacial Period ◽  
Last Glacial ◽  
Last Ice Age ◽  
The Last Glacial

Ice core air analysis has indicated a significant variation in the atmospheric contents of the greenhouse gases CO2, CH4 and N2O from the last ice age to the present period. This may have contributed in altering the vertical distribution of temperature and composition of the atmosphere about which not much information is available. The two dimensional interactive model of radiation, dynamics and chemistry has been used to reconstruct the annual vertical distribution of thermal structure and trace gas concentrations of the middle atmosphere for the periods extending from last ice age to the present. For this purpose, ice core air data of the above mentioned forcing parameters are used as input to the model for different time frames including Mounder Maximum, Roman maximum, pre-industrial period and the last glacial period. Model results show that the considerable reduction in the greenhouse gas content for the last ice age has resulted in colling of troposphere and a warming by about 10 to 15° K in the upper stratosphere as compared to present. The variation in temperature is closely related with the water vapour content. The percentage change in ozone concentration for the last glacial period is to a miximum of 50% near the poles in the upper stratosphere and about 10% in the tropics. A significant decrease in the hydroxyl content in the last ice age must have contributed in increasing the ozone content above 30 km. however, the total integrated ozone content appears to show marginal variations from last ice age to the present due to several counter-balancing effects.

Orbital cycle-related benthic-pelagic fluctuations in Foraminifera during the last glacial-interglacial interval in the western South Atlantic

2021 ◽  
Author(s):  
Jaime Yesid Suarez Ibarra ◽  
Cristiane Fraga Frozza ◽  
Sandro Monticelli Petró ◽  
Pamela de Lara Palhano ◽  
Maria Alejandra Gómez Pivel
Keyword(s):  
Deep Water ◽  
Bottom Water ◽  
South Atlantic ◽  
Water Masses ◽  
Meridional Overturning Circulation ◽  
Biological Pump ◽  
Sea Floor ◽  
Last Glacial ◽  
Surface Productivity ◽  
The Last Glacial

<p>Paleoceanographic studies reconstructing surface paleoproductivity and benthic conditions allow us to measure the effectiveness of the biological pump, an important mechanism in the global climate system. In order to assess surface productivity changes and their effect on the sea-floor environment, a multiproxy paleoceanographic analysis was conducted on the core SAT-048A (1542 m.b.s.l.), recovered from the continental slope of the southernmost Brazilian continental margin, western South Atlantic. We assessed sea surface productivity using different planktonic foraminiferal proxies: (1) the relative abundances of the species <em>Globigerina bulloides</em> and <em>Globigerinita glutinata</em> and (2) the δ<sup>13</sup>C signal of shells of the species <em>Globigerinoides ruber ruber</em>. To assess the organic matter (OM) flux to the seafloor, the foraminiferal planktonic:benthic ratio and the δ<sup>13</sup>C signal of shells of the benthic foraminifer <em>Uvigerina</em> spp. were used. To study dissolution effects occurring at the sea-floor, the Fragmentation Intensity (i.e., the proportion of fragments and broken foraminiferal shells), the number of planktonic foraminiferal tests per gram of dry sediment, and the CaCO<sub>3</sub> and Sand contents of the sediment were measured. Superimposed on the climate-induced changes related to the last glacial-interglacial transition, the reconstruction indicates paleoproductivity changes synchronized with the precessional cycle. From the reconstructed data, it was possible to identify the glacial and postglacial stages: surface productivity, flux to the seafloor, and dissolution rates of planktonic foraminiferal tests where high during the glacial and low during the postglacial. Furthermore, within the glacial, enhanced productivity was associated with higher insolation values, which can be explained by increased NE summer winds that strengthened the Brazil Current transport and, in turn, promoted meandering and upwelling of the nutrient rich South Atlantic Central Water. Changes in the Atlantic Meridional Overturning Circulation and the reorganization of bottom water masses may change the CO<sub>3</sub><sup>2-</sup> saturation levels and, consequently, influence carbonate preservation. However, the δ<sup>13</sup>C values from shells of <em>Uvigerina</em> spp. are different from present-day δ<sup>13</sup>C values from dissolved inorganic carbon for the Upper Circumpolar Deep Water and the North Atlantic Deep Water, which is likely linked to varying OM fluxes. Future studies (e.g., εNd in benthic Foraminifera) must quantify the effect of the reorganization of the bottom water masses on the dissolution of the planktonic foraminiferal tests, to better understand the effect of the biological pump removing carbon from the seawater and its subsequent sequestration in the seafloor sediments.</p>

A multidisciplinary approach to reveal the Sicily Climate and Environment over the last 20 000 years

2010 ◽  
Vol 2 (2) ◽  
Author(s):  
Alessandro Incarbona ◽  
Giuseppe Zarcone ◽  
Mauro Agate ◽  
Sergio Bonomo ◽  
Enrico Stefano ◽  
...  
Keyword(s):  
Vegetation Pattern ◽  
Significant Loss ◽  
Climatic Conditions ◽  
Ice Age ◽  
Geochemical Data ◽  
Climatic Fluctuations ◽  
The Holocene ◽  
Last Glacial ◽  
General Decline ◽  
The Last Glacial

AbstractWe present a thorough review of the knowledge on the climate and environment in Sicily over the last 20 000 years, taking into account results of several studies carried using terrestrial and marine records. We obtain a coherent framework of the most important changes succeeded in the island, even if some points need further investigation.All the reconstructions of surface temperatures of the seas and the air surrounding Sicily point out severe climatic conditions during the last glacial period. The steppe- and semisteppe-like vegetation pattern testifies, together with additional evidence from geochemical data of lacustrine evidence, markedly arid conditions. Fi-nally, significant episodes of sea level drop connected Sicily to the Italian Peninsula and favoured the dispersion of faunal elements from southern Italy.The transition between the last glacial and the Holocene was not characterized by a gradual warming but was punctuated by two abrupt suborbital climatic fluctuations: Bølling-Allerød (warm) and Younger Dryas (cold), as recognized in the sediments recovered close to the northern and southern coast of Sicily. A denser arboreal cover is possibly indicated by the occurrence of dormouse and Arvicola remains.Finally the sensitivity of Sicily to climate perturbations is demonstrated by the occurrence of repeated subtle climatic anomalies during the Holocene, including the Little Ice Age, also known from historical chronicles. Forests, woods and Mediterranean maquis developed in the early-middle Holocene. Thereafter was a general decline of arboreal vegetation, following a general aridification trend that seems to be a common feature in southern Europe and North Africa. Science Greek colonization (7th century before Christ), the landscape was intensively modelled for agriculture and breeding, leading to a significant loss of vegetation cover.

Late Quaternary paleoenvironmental changes in East Africa: a review of multiproxy evidence from palynology, lake sediments, and associated records

2006 ◽  
Vol 30 (5) ◽  
pp. 633-658 ◽  
Author(s):  
Lawrence M. Kiage ◽  
Kam-biu Liu
Keyword(s):  
East Africa ◽  
Last Glacial Maximum ◽  
Late Quaternary ◽  
Climatic Conditions ◽  
Glacial Maximum ◽  
Ice Age ◽  
Last Glacial ◽  
Paleoenvironmental Changes ◽  
The Last Glacial Maximum ◽  
The Last Glacial

This paper presents an overview of paleoenvironmental changes in East Africa during the late Quaternary based on evidence from pollen, diatoms, microscopic charcoal, and lake level records and associated proxies. The paleoenvironmental records derived from different proxies complement each other to provide a more accurate and complete assessment of the paleoenvironmental changes in East Africa. The records show that the period prior to c. 42,000 14C yr BP was characterized by warm climatic conditions similar to the present. This was followed by a change to cold dry conditions from 42,000 to 30,000 14C yr BP, and cold and moist conditions from 30,000 to 21,000 14C yr BP. Temperatures during the latter period leading to the Last Glacial Maximum (LGM) were probably 2 to 4.1°C lower than the present. Between c. 21,000 and 12,500 14C yr BP East Africa's environment was generally cool, punctuated by two significant episodes of prolonged desiccation. Warm and moist conditions punctuated by rapid climatic changes prevailed in the region during the deglacial and middle Holocene period. Ice core records document two significant and abrupt drought events in the region, one at 8300 14C yr BP and the other at 5200 14C yr BP. The onset of a longer and more extensive desiccation period commencing 4000 14C yr BP was registered in nearly all sites. The climate of East Africa was generally drier than present during the Medieval Warm Period (MWP) while fairly wet conditions prevailed during the Little Ice Age (LIA) interrupted by three episodes of aridity, more severe than those of more recent times. Whereas this review advances our understanding of climate and vegetational changes in East Africa beyond the Last Glacial Maximum, it also highlights limitations of the paradigms that explain the forcing mechanisms behind the changes. However, unequivocal interpretation of the multiproxy data from East Africa with respect to paleoenvironmental changes becomes extremely complex and challenging especially when the anthropogenic input is considered.

scholarly journals <i>δ</i><sup>13</sup>C decreases in the upper western South Atlantic during Heinrich Stadials 3 and 2

2017 ◽  
Vol 13 (4) ◽  
pp. 345-358 ◽  
Author(s):  
Marília C. Campos ◽  
Cristiano M. Chiessi ◽  
Ines Voigt ◽  
Alberto R. Piola ◽  
Henning Kuhnert ◽  
...  
Keyword(s):  
Climate Change ◽  
South Atlantic ◽  
Meridional Overturning Circulation ◽  
Glacial Period ◽  
Last Deglaciation ◽  
Last Glacial Period ◽  
Last Glacial ◽  
Change Events ◽  
The Last Glacial ◽  
Millennial Scale

Abstract. Abrupt millennial-scale climate change events of the last deglaciation (i.e. Heinrich Stadial 1 and the Younger Dryas) were accompanied by marked increases in atmospheric CO2 (CO2atm) and decreases in its stable carbon isotopic ratios (δ13C), i.e. δ13CO2atm, presumably due to outgassing from the ocean. However, information on the preceding Heinrich Stadials during the last glacial period is scarce. Here we present δ13C records from two species of planktonic foraminifera from the western South Atlantic that reveal major decreases (up to 1 ‰) during Heinrich Stadials 3 and 2. These δ13C decreases are most likely related to millennial-scale periods of weakening of the Atlantic meridional overturning circulation and the consequent increase (decrease) in CO2atm (δ13CO2atm). We hypothesise two mechanisms that could account for the decreases observed in our records, namely strengthening of Southern Ocean deep-water ventilation and weakening of the biological pump. Additionally, we suggest that air–sea gas exchange could have contributed to the observed δ13C decreases. Together with other lines of evidence, our data are consistent with the hypothesis that the CO2 added to the atmosphere during abrupt millennial-scale climate change events of the last glacial period also originated in the ocean and reached the atmosphere by outgassing. The temporal evolution of δ13C during Heinrich Stadials 3 and 2 in our records is characterized by two relative minima separated by a relative maximum. This w structure is also found in North Atlantic and South American records, further suggesting that such a structure is a pervasive feature of Heinrich Stadial 2 and, possibly, also Heinrich Stadial 3.

scholarly journals Calcium carbonate dissolution triggered by high productivity during the last glacial-interglacial interval at the deep western South Atlantic

2021 ◽  
Author(s):  
Jaime Y. Suárez-Ibarra ◽  
Cristiane Fraga Frozza ◽  
Sandro Monticelli Petró ◽  
Pamela Lara Palhano ◽  
Maria Alejandra Gomez Pivel
Keyword(s):  
Calcium Carbonate ◽  
South Atlantic ◽  
Carbonate Dissolution ◽  
High Productivity ◽  
Last Glacial ◽  
Calcium Carbonate Dissolution ◽  
The Last Glacial

scholarly journals Constant wind regimes during the Last Glacial Maximum and early Holocene: evidence from Little Llangothlin Lagoon, New England Tablelands, eastern Australia

2016 ◽  
Vol 12 (7) ◽  
pp. 1435-1444 ◽  
Author(s):  
James Shulmeister ◽  
Justine Kemp ◽  
Kathryn E. Fitzsimmons ◽  
Allen Gontz
Keyword(s):  
Last Glacial Maximum ◽  
High Elevation ◽  
Glacial Maximum ◽  
Early Holocene ◽  
Luminescence Dating ◽  
Ice Age ◽  
Last Glacial ◽  
Eastern Australia ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Abstract. Here we present the results of a multi-proxy investigation – integrating geomorphology, ground-penetrating radar, and luminescence dating – of a high-elevation lunette and beach berm in northern New South Wales, eastern Australia. The lunette occurs on the eastern shore of Little Llangothlin Lagoon and provides evidence for a lake high stand combined with persistent westerly winds at the Last Glacial Maximum (LGM – centring on 21.5 ka) and during the early Holocene (ca. 9 and 6 ka). The reconstructed atmospheric circulation is similar to the present-day conditions, and we infer no significant changes in circulation at those times, as compared to the present day. Our results suggest that the Southern Hemisphere westerlies were minimally displaced in this sector of Australasia during the latter part of the last ice age. Our observations also support evidence for a more positive water balance at the LGM and early Holocene in this part of the Australian sub-tropics.

scholarly journals A high-resolution model of the 100 ka ice-age cycle

1997 ◽  
Vol 25 ◽  
pp. 58-65 ◽  
Author(s):  
L. Tarasov ◽  
W. R. Peltier
Keyword(s):  
Large Scale ◽  
Climate Model ◽  
Relaxation Times ◽  
Ice Age ◽  
Adjustment Process ◽  
Glacial Cycle ◽  
Ice Dynamics ◽  
Last Glacial ◽  
The North ◽  
The Last Glacial

Significant improvements to the representation of climate forcing and mass-balance response in a coupled two-dimensional global energy balance climate model (EBM) and vertically integrated ice-sheet model (ISM) have led to the prediction of an ice-volume chronology for the most recent ice-age cycle of the Northern Hemisphere that is close to that inferred from the geological record. Most significant is that full glacial termination is delivered by the model without the need for new physical ingredients. In addition, a relatively close match is achieved between the Last Glacial Maximum (LGM) model ice topography and that of the recently-described ICE-4G reconstruction. These results suggest that large-scale climate system reorganization is not required to explain the main variations of the North American (NA) ice sheets over the last glacial cycle. Lack of sea-ice and marine-ice dynamics in the model leaves the situation over the Eurasian (EA) sector much more uncertain.The incorporation of a gravitationally self-consistent description of the glacial isostatic adjustment process demonstrates that the NA and EA bedrock responses can be adequately represented by simpler damped-relaxation models with characteristic time-scales of 3–5ka and 5 ka, respectively. These relaxation times agree with those independently inferred on the basis of postglacial relative sea-level histories.

Paleoecology and Late Quaternary Environments of the Colorado Rockies

2001 ◽  
Author(s):  
Scott A. Elias
Keyword(s):  
North America ◽  
Late Quaternary ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Rocky Mountain ◽  
Mountain Region ◽  
Ice Age ◽  
Rocky Mountain Region ◽  
Last Ice Age ◽  
Teton Range

Present-day environments cannot be completely understood without knowledge of their history since the last ice age. Paleoecological studies show that the modern ecosystems did not spring full-blown onto the Rocky Mountain region within the last few centuries. Rather, they are the product of a massive reshuffling of species that was brought about by the last ice age and indeed continues to this day. Chronologically, this chapter covers the late Quaternary Period: the last 25,000 years. During this interval, ice sheets advanced southward, covering Canada and much of the northern tier of states in the United States. Glaciers crept down from mountaintops to fill high valleys in the Rockies and Sierras. The late Quaternary interval is important because it bridges the gap between the ice-age world and modern environments and biota. It was a time of great change, in both physical environments and biological communities. The Wisconsin Glaciation is called the Pinedale Glaciation in the Rocky Mountain region (after terminal moraines near the town of Pinedale, Wyoming; see chapter 4). The Pinedale Glaciation began after the last (Sangamon) Interglaciation, perhaps 110,000 radiocarbon years before present (yr BP), and included at least two major ice advances and retreats. These glacial events took different forms in different regions. The Laurentide Ice Sheet covered much of northeastern and north-central North America, and the Cordilleran Ice Sheet covered much of northwestern North America. The two ice sheets covered more than 16 million km2 and contained one third of all the ice in the world’s glaciers during this period. The history of glaciation is not as well resolved for the Colorado Front Range region as it is for regions farther north. For instance, although a chronology of three separate ice advances has been established for the Teton Range during Pinedale times, in northern Colorado we know only that there were earlier and later Pinedale ice advances. We do not know when the earlier advance (or multiple advances) took place. However, based on geologic evidence (Madole and Shroba 1979), the early Pinedale glaciation was more extensive than the late Pinedale was.

Northern-sourced water dominated the Atlantic Ocean during the Last Glacial Maximum

Geology ◽  
2020 ◽  
Vol 48 (8) ◽  
pp. 826-829 ◽  
Author(s):  
F. Pöppelmeier ◽  
P. Blaser ◽  
M. Gutjahr ◽  
S.L. Jaccard ◽  
M. Frank ◽  
...  
Keyword(s):  
Last Glacial Maximum ◽  
Water Mass ◽  
Stable Carbon Isotope ◽  
Glacial Maximum ◽  
Meridional Overturning Circulation ◽  
Ice Age ◽  
Δ13c Values ◽  
Last Glacial ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Abstract Increased carbon sequestration in the ocean subsurface is commonly assumed to have been one of the main causes responsible for lower glacial atmospheric CO2 concentrations. Remineralized carbon must have been stored away from the atmosphere for thousands of years, yet the water mass structure accommodating such increased carbon storage continues to be debated. Here, we present new sediment-derived bottom-water neodymium isotope records that allow fingerprinting of water masses and provide a more complete picture of the Atlantic Meridional Overturning Circulation geometry during the Last Glacial Maximum. These results suggest that the vertical and meridional structure of the Atlantic water mass distribution only experienced minor changes since the last ice age. In particular, we find no compelling evidence supporting glacial southern-sourced water substantially expanding to shallower depths and farther into the Northern Hemisphere than today, which had been previously inferred from stable carbon isotope (δ13C) reconstructions. We argue that depleted δ13C values observed in the deep Northwest Atlantic do not necessarily indicate the presence of southern-sourced water. Instead, these values may represent a northern-sourced water mass with lower than modern preformed δ13C values that were further modified downstream by increased sequestration of remineralized carbon, facilitated by a more sluggish glacial deep circulation, corroborating previous evidence.

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