Ecological Changes During the Glacial & Interglacials of the late Paleozoic ice age of Pennsylvanian Carboniferous Argentina

Compositional turnover and ecological changes related to the waxing and waning of glaciers during the late Paleozoic ice age in ice-proximal regions (Pennsylvanian, western Argentina)

Author:

Balseiro

Abstract:

The late Paleozoic ice age (LPIA) had a profound effect on the biota. Despite much research having been focused on paleotropical regions or global-scale analyses, regional ecological changes have seldom been studied in ice-proximal basins. Here, I study the compositional turnover and diversity structure across the main Carboniferous glacial event recorded in western Argentina and the subsequent nonglacial interval. Brachiopod and bivalve data from western Argentina suggest that the transition from glacial to nonglacial climates caused major compositional changes. Turnover, however, was not uniform across the bathymetric gradient, being higher in deep environments. Because extirpation was concentrated in brachiopods, but immigration was similar in both clades, the taxonomic structure of the region was significantly modified. Although regional hierarchical diversity structure and occupancy distributions remained stable, dissecting the analysis in brachiopods and bivalves underscores that both clades had different responses to climate change. Brachiopods, on the one hand, show stability in the diversity structure and a very slight decrease in occupancies of intermediate genera, while bivalves show an important rise in diversity, both at the environment and regional scale, and an increase in genera with intermediate occupancies. The bathymetric diversity gradient was also modified from hump shaped with maximum diversity in the deep subtidal to a linear gradient with maximum values toward the offshore. However, relative compositional differences within environments remained stable, with maximum values at intermediate depths both in glacial and nonglacial intervals. Moreover, local-scale coexistence between brachiopods and bivalves changed in the nonglacial interval, showing significant segregation, which indicates relevant modifications in community assembly dynamics. Results from western Argentina highlight the magnitude of regional-scale ecological changes during the LPIA in ice-proximal regions, suggesting that the waxing and waning of glaciers was able to cause regional taxonomic turnover and medium-scale ecological changes even during intervals of relative macroevolutionary quiescence.

Human Caused Global Warming has Postponed the Next Glacial Cycle by at Least 50,000 Years

Humanity has become a geological force that is able to suppress the beginning of the next ice age, a study now published in the renowned scientific journal Nature shows. Cracking the code of glacial inception, scientists of the Potsdam Institute for Climate Impact Research found the relation of insolation and CO2 concentration in the atmosphere to be the key criterion to explain the last eight glacial cycles in Earth history. At the same time their results illustrate that even moderate human interference with the planet's natural carbon balance might postpone the next glacial inception by 100.000 years.

"Even without man-made climate change we would expect the beginning of a new ice age no earlier than in 50.000 years from now - which makes the Holocene as the present geological epoch an unusually long period in between ice ages," explains lead author Andrey Ganopolski. "However, our study also shows that relatively moderate additional anthropogenic CO2-emissions from burning oil, coal and gas are already sufficient to postpone the next ice age for another 50.000 years. The bottom line is that we are basically skipping a whole glacial cycle, which is unprecedented. It is mind-boggling that humankind is able to interfere with a mechanism that shaped the world as we know it."

For the first time, research can explain the onset of the past eight ice ages by quantifying several key factors that preceded the formation of each glacial cycle. "Our results indicate a unique functional relationship between summer insolation and atmospheric CO2 for the beginning of a large-scale ice-sheet growth which does not only explain the past, but also enables us to anticipate future periods when glacial inception might occur again," Ganopolski says.

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Did Massive Northern Hemisphere Volcanic Eruptions Warm and Disrupt the Pleistocene Quaternary Antarctic Ice Sheet?

Massive volcanic eruptions could cause localised warming that might destabilise some of the world's biggest ice sheets, according to new research from Durham University.

Scientists investigated links between very large volcanic eruptions and polar temperatures during the last Ice Age.

Their findings suggest that some periods of Antarctic warming between 30,000 to 80,000 years ago were triggered by huge volcanic eruptions in the Northern Hemisphere that caused a shift in the world's weather patterns.

The Northern Hemisphere cooled as volcanic particles reflected the sun's heat, forcing warmer weather fronts south which led to warming in Antarctica, the researchers said.

Conversely, their research suggests that Southern Hemisphere eruptions could also have triggered abrupt warming in Greenland during the last Ice Age.

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Did the Carbon Cycle Drive the Pleistocene Quaternary Glacial-Interglacial Periods?

The Carbon Cycle as the Main Determinant of Glacial-Interglacial Periods

Authors:

Jiménez de la Cuesta et al

Abstract:

An intriguing problem in climate science is the existence of Earth's glacial cycle. We show that it is possible to generate these periodic changes in climate by means of the Earth's carbon cycle as the main source factor. The carbon exchange between the Ocean, the Continent and the Atmosphere is modeled by means of a Lotka-Volterra three species system and the resulting atmospheric carbon cycle is used as the unique radiative forcing mechanism. It is shown that the carbon dioxide and temperature paths that are thus obtained have the same qualitative structure as the 100 kyr glacial-interglacial cycles depicted by the Vostok ice core data, reproducing the asymmetries of rapid heating--slow cooling, and short interglacial--long glacial ages.

Sea Level Rose as Much as *5* Meters per Century During Pleistocene Interglacials

Land-ice decay at the end of the last five ice-ages caused global sea-levels to rise at rates of up to 5.5 metres per century, according to a new study.

An international team of researchers developed a 500,000-year record of sea-level variability, to provide the first account of how quickly sea-level changed during the last five ice-age cycles.

The results, published in the latest issue of Nature Communications, also found that more than 100 smaller events of sea-level rise took place in between the five major events.

Dr Katharine Grant, from the Australian National University (ANU), Canberra, who led the study, says: "The really fast rates of sea-level rise typically seem to have happened at the end of periods with exceptionally large ice sheets, when there was two or more times more ice on the Earth than today.

"Time periods with less than twice the modern global ice volume show almost no indications of sea-level rise faster than about 2 metres per century. Those with close to the modern amount of ice on Earth, show rates of up to 1 to 1.5 metres per century."

Co-author Professor Eelco Rohling, of both the University of Southampton and ANU, explains that the study also sheds light on the timescales of change. He says: "For the first time, we have data from a sufficiently large set of events to systematically study the timescale over which ice-sheet responses developed from initial change to maximum retreat."

"This happened within 400 years for 68 per cent of all 120 cases considered, and within 1100 years for 95 per cent. In other words, once triggered, ice-sheet reduction (and therefore sea-level rise) kept accelerating relentlessly over periods of many centuries."

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Small Changes in Pleistocene Quaternary Environment Meant Large Temperature Swings

During the last ice age a large part of North America was covered with a massive ice sheet up to 3km thick. The water stored in this ice sheet is part of the reason why the sea level was then about 120 meters lower than today. Young Chinese scientist Xu Zhang, lead author of the study who undertook his PhD at the Alfred Wegener Institute, explains. "The rapid climate changes known in the scientific world as Dansgaard-Oeschger events were limited to a period of time from 110,000 to 23,000 years before present. The abrupt climate changes did not take place at the extreme low sea levels, corresponding to the time of maximum glaciation 20,000 years ago, nor at high sea levels such as those prevailing today - they occurred during periods of intermediate ice volume and intermediate sea levels." The results presented by the AWI researchers can explain the history of climate changes during glacial periods, comparing simulated model data with that retrieved from ice cores and marine sediments.

How rapid temperature changes might have occurred during times when the Northern Hemisphere ice sheets were at intermediate sizes (see schematic depictions on http://bit.ly/1uQoI70).

During the cold stadial periods of the last ice age, massive ice sheets covered northern parts of North America and Europe. Strong westerly winds drove the Arctic sea ice southward, even as far as the French coast. Since the extended ice cover over the North Atlantic prevented the exchange of heat between the atmosphere and the ocean, the strong driving forces for the ocean currents that prevail today were lacking. Ocean circulation, which is a powerful "conveyor belt" in the world's oceans, was thus much weaker than at present, and consequently transported less heat to northern regions.

During the extended cold phases the ice sheets continued to thicken. When higher ice sheets prevailed over North America, typical in periods of intermediate sea levels, the prevailing westerly winds split into two branches. The major wind field ran to the north of the so-called Laurentide Ice Sheet and ensured that the sea ice boundary off the European coast shifted to the north. Ice-free seas permit heat exchange to take place between the atmosphere and the ocean. At the same time, the southern branch of the northwesterly winds drove warmer water into the ice-free areas of the northeast Atlantic and thus amplified the transportation of heat to the north. The modified conditions stimulated enhanced circulation in the ocean. Consequently, a thicker Laurentide Ice Sheet over North America resulted in increased ocean circulation and therefore greater transportation of heat to the north. The climate in the Northern Hemisphere became dramatically warmer within a few decades until, due to the retreat of the glaciers over North America and the renewed change in wind conditions, it began to cool off again.

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Sixth Mass Extinction Wars: Climate Change and Botanical Diversity Loss Caused Megafauna Die off?

It was climate that killed many of the large mammals after the latest Ice Age. But what more specifically was it with the climate that led to this mass extinction? The answer to this is hidden in a large number of sediment samples from around the Arctic and in the gut content from permafrozen woolly rhinos, mammoth and other extinct ice age mammals.

It is a bit of a shift in paradigme Willerslev and co-workers publish in this week's edition of the journal Nature. The common image of a light-brown grass-steppe dominating the northern hemisphere during the Ice Age does not hold any longer. The landscape was far more diverse and stable than today, and big animals like woolly rhino and mammoth fed on grasses and particularly on protein-rich forbs. But at the Last Glacial Maximum 25,000 – 15,000 years ago, at a time when the climate was at its coldest and driest, a major loss of plant diversity took place. The animals barely survived.

After the Ice Age ended about 10,000 years ago it became warmer again. After the large reduction of plant diversity during the Last Glacial Maximum another kind of vegetation now appeared. One of the key food sources of the large mammals– the protein-rich forbs – did not fully recover to their former abundance. This likely proved fatal for species like woolly rhino, mammoth, and horse in Asia and North America. Even though it became warmer again after the end of the Ice Age the old landscapes did not return.

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Disc and Star Shaped Microbial Fossils From an Interglacial Maikhanuul/Ma Nantuo Glaciation of Ediacaran NeoProterozoic Mongolia

Fossil microbial colonies in Neoproterozoic interglacial rocks of Western Mongolia

Authors:

Serezhnikova et al

Abstract:

Glaciogenic deposits are widely distributed in the Neoproterozoic successions around the world, but only few of them are associated with occurrences of authentic macroscopic fossils. Problematical circular remains recovered from intertillite beds of the Neoproterozoic Maikhanuul Formation, Zavkhan basin, Western Mongolia may be a new record of biogenic structures in ancient glacial rocks. The Maikhanuul tillites were deposited between 732–777 Ma (the underlying volcanic rocks of the Neoproterozoic Dzabkhan Formation) and 632 ± 14 Ma (the overlying limestones of the Ediacaran — Nemakit–Daldynian Tsagaanolom Formation). The assemblage of microfossils from the Tsagaanolom Formation is comparable to the assemblage known from the 635–551 Ma Doushantuo Formation of South China. The Maikhanuul glacial event may therefore be correlated with the 635 Ma Nantuo glaciation. Morphological, taphonomic, biometric and geochemical observations have allowed us to interpret the problematical circular remains from the Maikhanuul tillites as microbial communities preserved in situ on the floor of an ancient glacial basin. Many discoidal fossils from Precambrian strata have been compared with extant microbial colonies that have a similar external morphology. However, ultrastructure of the hypothetical Precambrian microbial communities has not hitherto been reported. Scanning electron microscopy of the circular remains from the Maikhanuul tillites revealed filamentous and star-shaped microfossils closely resembling modern bacteria. Some filaments and especially the star-shaped grains are considerably enriched in iron (up to 50%) that may be attributed to bacterial activity. Furthermore, the star-shaped microremains can be compared with modern star-shaped bacteria known from freshwater and terrestrial environments. Although the presence of microbial colonies couldn’t be used for global correlation, it does provide information on prokaryotic diversity and ecology as well as on palaeoenvironmental conditions

Ice Age Limits on Productivity

Global constraints on net primary production and inorganic carbon supply during glacial and interglacial cycles

Authors:

Pelegri et al

Abstract:

Relaxation-type models have good skill at reproducing glacial-interglacial transitions in climatic variables. Here we propose a simple two-box and two-state relaxation-type model for the upper ocean (surface and permanent thermocline layers) where dissolved inorganic carbon/nutrients are supplied by the deep-ocean and through remineralization within the upper ocean. The model is tuned using genetic algorithms to simulate the atmospheric CO2 time series for the last four glacial-interglacial cycles. The fit to the data is very good, with correlations above 0.8, as the upper ocean responds to shifts in (1) the intensity of the Meridional Overturning Circulation (MOC), from off to on during the glacial-interglacial transition, and (2) the size and sign of net primary production, with respiration greatly exceeding primary production during interglacial periods and production larger than respiration during the glacial phase. The glacial-interglacial transitions are interpreted as shifts between two distinct metabolic states of the Earth system, with high/low supply of dissolved inorganic carbon and nutrients to the productive upper ocean during interglacial/glacial periods.

Southern Ocean Responses to a Warmer World

Southwest Pacific Ocean response to a warmer world – insights from Marine Isotope Stage 5e

Authors:

1. G. Cortese (a)
2. G. B. Dunbar (b)
3. L. Carter (b)
4. G. Scott (a)
5. H. Bostock (c)
6. M. Bowen (d)
7. M. Crundwell (a)
8. B. W. Hayward (e)
9. W. Howard (f)
10. J. I. Martínez (g)
11. A. Moy (h,i)
12. H. Neil (c)
13. A. Sabaa (e)
14. A. Sturm (j)

Affiliations:

a. GNS Science, Lower Hutt, New Zealand

b. Antarctic Research Centre, Victoria University of Wellington, Wellington, New Zealand

c. National Institute of Water and Atmospheric Research (NIWA), Wellington, New Zealand

d. School of Environment, University of Auckland, Auckland, New Zealand

e. Geomarine Research, Auckland, New Zealand

f. Research School of Earth Sciences, Australian National University, Canberra, Australia

g. Ciencias del Mar, Dept. of Geology, Universidad EAFIT, Medellin, Colombia

h. Department of Sustainability, Environment, Water, Population and Communities, Australian Antarctic Division, Kingston, Tasmania, Australia

i. Antarctic Climate and Ecosystems Cooperative Research Centre, University of Tasmania, Hobart, Australia

j. Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany

Abstract:

Paleoceanographic archives derived from seventeen marine sediment cores reconstruct the response of the SW Pacific Ocean to the peak interglacial, Marine Isotope Stage (MIS) 5e (ca. 125 ka). Paleo-Sea Surface Temperature (SST) estimates were obtained from the Random Forest model – an ensemble decision tree tool - applied to core-top planktonic foraminiferal faunas calibrated to modern SSTs. The reconstructed geographic pattern of the SST anomaly (maximum SST between 120-132 ka minus mean modern SST) seems to indicate how MIS 5e conditions were generally warmer in the southwest Pacific, especially in the western Tasman Sea where a strengthened East Australian Current (EAC) likely extended subtropical influence to ca. 45oS off Tasmania. In contrast, the eastern Tasman Sea may have had a modest cooling except around 45oS. The observed pattern resembles that developing under the present warming trend in the region. An increase in wind stress curl over the modern South Pacific is hypothesized to have spun-up the South Pacific Subtropical Gyre, with concurrent increase in subtropical flow in the western boundary currents that include the EAC. However, warmer temperatures along the subtropical front and Campbell Plateau to the south suggest the relative influence of the boundary inflows to eastern New Zealand may have differed in MIS 5e, and these currents may have followed different paths compared to today.

Were There Three Major Rivers in the Sahara During the Last Interglacial?

Three ancient river systems, now buried, may have created viable routes for human migration across the Sahara to the Mediterranean region about 100,000 years ago, according to research published September 11 in the open access journal PLOS ONE by Tom Coulthard from the University of Hull, UK, and colleagues from other institutions.

Simulating paleoclimates in the region, the researchers found quantitative evidence of three major river systems that likely existed in North Africa 130,000-100,000 years ago, but are now largely buried by dune systems in the desert. When flowing, these rivers likely provided fertile habitats for animals and vegetation, creating 'green corridors' across the region. At least one river system is estimated to have been 100 km wide and largely perennial. The Irharhar river, westernmost of the three identified, may represent a likely route of human migration across the region. In addition to rivers, the researchers' simulations predict massive lagoons and wetlands in northeast Libya, some of which span over 70,000-square kilometers. "It's exciting to think that 100 000 years ago there were three huge rivers forcing their way across a 1000km of the Sahara desert to the Mediterranean -- and that our ancestors could have walked alongside them" said Coulthard.

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