Mammalian dwarfing during ancient greenhouse warming events.

Bighorn Basin, Wyoming (Image: University of New Hampshire, College of Engineering and Physical Sciences)

The Paleocene-Eocene Thermal Maximum, known as PETM (approximately 55.8 million years ago), was a short-lived (~ 200,000 years) global warming event due to a rapid rise in the concentration of greenhouse gases in the atmosphere. It was suggested that this warming was initiated by the melting of methane hydrates on the seafloor and permafrost at high latitudes. This event was accompanied by other large-scale changes in the climate system, for example, the patterns of atmospheric circulation, vapor transport, precipitation, intermediate and deep-sea circulation, a rise in global sea level and ocean acidification.

The second largest hyperthermal of the early Eocene, known as ETM2, occurred about 2 million years after the PETM (approximately 53.7 Ma). Another smaller-amplitude hyperthermal, identified as “H2,” appears in the marine record about 100,000 years after ETM2 (approximately 53.6 Ma).

Sifrhippus sp. restoration in the Naturhistoriska Riksmuseet, Stockholm, Sweden (From Wikimedia Commons)

Dwarfing of mammalian taxa across the Palaeocene-Eocene Thermal Maximum (PETM) was first described in the Bighorn Basin, Wyoming. The basin has a remarkably fossil-rich sedimentary record of late Palaeocene to early Eocene age. The interval of the Paleocene–Eocene Thermal Maximum is represented by a unique mammalian fauna composed by smaller, but morphologically similar species to those found later in the Eocene. Diminutive species include the early equid Sifrhippus sandrae, the phenacodontids Ectocion parvus and Copecion davisi. 

Fossils of early equids are common in lower Eocene deposits of the Bighorn Basin, making a comparison between the PETM and ETM2 hyperthermal events possible. Using tooth size as a proxy for body size, researchers found a statistically significant decrease in the body size of mammals’ during the PETM and ETM2. Teeth in adult mammals scale proportionally to body size. For instance, Sifrhippus demonstrated a decrease of at least 30% in body size during the first 130,000 years of the PETM, followed by a 76% rebound in body size during the recovery phase of the PETM. Arenahippus, an early horse the size of a small dog, decreased by about 14 percent in size during the ETM2. (D’Ambrosia et al., 2017)

Arenahippus jaw fragment (Image credit: University of New Hampshire)

Body size change during periods of climate change is commonly seen throughout historical and geological records. Studies of modern animal populations have also yielded similar body size results. Tropical trees, anurans and mammals have all demonstrated decreased size or growth rate during drought years. In the case of mammals, the observed decrease in the average body size could have been an evolutionary response to create a more efficient way to reduce body heat.

The combination of global warming and the release of large amounts of carbon to the ocean-atmosphere system during the PETM has encouraged analogies with the modern anthropogenic climate change, which has already led to significant shifts in the distribution, phenology and behaviour of organisms. Plus, the consequences of shrinkage are not yet fully understood. This underlines the urgency for immediate action on global carbon emission reductions.

 

 

References:

Abigail R. D’Ambrosia, William C. Clyde, Henry C. Fricke, Philip D. Gingerich, Hemmo A. Abels. Repetitive mammalian dwarfing during ancient greenhouse warming events. Science Advances, 2017; 3 (3): e1601430 DOI: 10.1126/sciadv.1601430

Rankin, B., Fox, J., Barron-Ortiz, C., Chew, A., Holroyd, P., Ludtke, J., Yang, X., Theodor, J. 2015. The extended Price equation quantifies species selection on mammalian body size across the Palaeocene/Eocene Thermal Maximum. Proceedings of the Royal Society B. doi: 10.1098/rspb.2015.1097

Burger, B.J., Northward range extension of a diminutive-sized mammal (Ectocion parvus) and the implication of body size change during the Paleoc…, Palaeogeogr. Palaeoclimatol. Palaeoecol. (2012), http://dx.doi.org/10.1016/j.palaeo.2012.09.008

 

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Sea-surface temperatures during the last interglaciation.

 

203_co2-graph-021116

The relentless rise of carbon dioxide (Credit: National Oceanic and Atmospheric Administration.)

A proverb of Confucius states “Study the past if you would divine the future.” Human activity ensures that our climate will become warmer in the next century and remain warm for many millennia to come which makes particularly pertinent the study of periods in which at least sectors of the Earth system may have been “warmer” than today. The last interglaciation (LIG, 129 to 116 thousand years ago) was one of the warmest periods in the last 800,000 years with an associated sea-level rise of 6 to 9 m above present levels . A new study by Jeremy S. Hoffman and colleagues, compiled 104 published LIG sea surface temperature (SST) records from 83 marine sediment core sites. Each core site was compared to data sets from 1870-1889 and 1995-2014, respectively. The analysis revealed that 129,000 years ago, the global ocean surface temperature was similar to the 1870-1889 average. But 125,000 years ago, the global SST increased by 0.5° ± 0.3°Celcius, reaching a temperature indistinguishable from the 1995-2014 average. The result is worrisome, because it shows that changes in temperatures which occurred over thousands of years, are now occurring in the space of a single century. The study also suggests that in the long term, sea level will rise at least six meters in response to the global warming.

Data from the study by Jeremy Hoffman et al. representing sample sites, sea surface temperatures, and historic carbon dioxide level

Data from the study by Jeremy Hoffman et al. representing sample sites, sea surface temperatures, and historic carbon dioxide level

The planet’s average surface temperature has risen about 2.0 degrees Fahrenheit (1.1 degrees Celsius) since the late 19th century. After the World War II, the atmospheric CO2 concentration grew, from 311 ppm in 1950 to 369 ppm in 2000. Glaciers  from the Greenland and Antarctic Ice Sheets are fading away, dumping 260 billion metric tons of water into the ocean every year. The ocean acidification is occurring at a rate faster than at any time in the last 300 million years, and  the patterns of rainfall and drought are changing and undermining food security which have major implications for human health, welfare and social infrastructure. In his master book L’Evolution Créatrice (1907), French philosopher Henri Bergson, wrote:  “A century has elapsed since the invention of the steam engine, and we are only just beginning to feel the depths of the shock it gave us.”

References:

J.S. Hoffman et al. Regional and global sea-surface temperatures during the last interglaciation. Science. Vol. 355, January 20, 2017, p. 276. doi: 10.1126/science.aai8464.

Past Interglacials Working Group of PAGES (2016), Interglacials of the last 800,000 years, Rev. Geophys., 54, 162–219, doi: 10.1002/2015RG000482. 

Bakker, P., et al. (2014), Temperature trends during the present and Last Interglacial periods—A multi-model-data comparison, Quat. Sci. Rev., 99, 224–243, doi: 10.1016/j.quascirev.2014.06.031.

A brief history of the Climate science

Large rift near the Pine Island Glacier tongue, West Antarctica. Credits: NASA/Nathan Kurtz

Large rift near the Pine Island Glacier tongue, West Antarctica. Credits: NASA/Nathan Kurtz

At the dawn of the Industrial Revolution the world experiences industrial and demographic boom. As a consequence of these substantial events, scientists of the time begin to question whether climate changes over time or not. In the 1760s, the ability to generate an artificial warming of the Earth’s surface was demonstrated by Horace Benedict de Saussure. In 1824, French mathematician Joseph Fourier published a scientific paper titled “Remarques generales sur les Temperatures du globe terrestre et des espaces planetaires” in the journal Annales de Chimie et de Physique, Tome XXVII (pp.136-167), where he presented some ‘general remarks’ on the temperature of the Earth and interplanetary space describing the Earth’s natural “greenhouse effect” without naming it. Terrestrial temperatures was on Fourier’s mind as early as 1807, when he wrote on the unequal heating of the globe. Following Fourier’s work, physicist C.S.M. Pouillet wrote in 1836 a memoir on solar heat, the radiative effects of the atmosphere, and the temperature of space.

Illustration of John Tyndall's setup for measuring the radiant heat absorption of gases (From Wikimedia Commons)

Illustration of John Tyndall’s setup for measuring the radiant heat absorption of gases (From Wikimedia Commons)

In 1861, Irish physicist John Tyndall demonstrated that gases such as methane and carbon dioxide absorbed infrared radiation, and could trap heat within the atmosphere. His interest in radiant heat and its passage through the atmosphere was triggered by his long-standing interest in glaciers and their mass balance. Tyndall’s experimental work suggested the possibility that by altering concentrations of these gases in the atmosphere, human activities could alter the temperature regulation of the planet. In his essay ‘On the Absorption and Radiation of Heat by Gases and Vapours’, Tyndall credited Fourier for the notion that ‘the interception of terrestrial rays [by the atmosphere exercises] the most important influence on climate’. 

In 1896, Svante Arrhenius  was the first to quantify the contribution of carbon dioxide to the greenhouse effect. He used infrared observations of the moon to calculate how much of infrared radiation is captured by CO2 and water vapour in Earth’s atmosphere and formulated his greenhouse law: “Thus if the quantity of carbonic acid increases in geometric progression, the augmentation of the temperature will increase nearly in arithmetic progression.”

Svante August Arrhenius (1859-1927). From Wikimedia Commons

Svante August Arrhenius (1859-1927). From Wikimedia Commons

Almost simultaneously, American geologist Thomas Chamberlin proposed that carbon dioxide fluctuations could cause large variations on Earth’s Climate, including Ice Ages.

By 1930s British engineer Guy Callender proves that temperature of Earth has risen compared to previous century, given records of 147 weather stations across the world. Moreover, he shows that carbon dioxide concentrations has increased at the same time and claims that it is the most plausible reason behind the global warming.

After the World War II, the impact of human activity on the global environment dramatically increased. In 1958, Charles Dave Keeling carries out a long-running experiment in Hawaii and Antarctica and enables unequivocal evidences of increasing carbon dioxide concentration in the atmosphere after four-year-research.

pet vs antropocene

Comparison of the effects of anthropogenic emissions (total of 5000 Pg C over 500 years) and PETM carbon release (3000 Pg C over 6 kyr) on the surface ocean saturation state of calcite. From Zeebe, 2013

In 1972, the United Nations summits the first environment conference in Stockholm and the climate change is determined as the agenda item. Since the conference the importance of this issue increases and public start to deal with the notion of climate change.

The earth’s climate has already reached a tipping point. Glaciers  from the Greenland and Antarctic Ice Sheets are fading away, dumping 260 billion metric tons of water into the ocean every year. The ocean acidification is occurring at a rate faster than at any time in the last 300 million years, and  the patterns of rainfall and drought are changing and undermining food security which have major implications for human health, welfare and social infrastructure.

References:

Hulme, M. (2009), On the origin of ‘the greenhouse effect’: John Tyndall’s 1859 interrogation of nature. Weather, 64: 121–123. doi:10.1002/wea.386

Tyndall J. 1861. On the absorption and radiation of heat by gases and vapours. Philos. Mag. 22: 169–194 and 273–285

Arrhenius, Svante; On the Influence of Carbonic Acid in the Air Upon the Temperature of the Ground. Philosophical Magazine and Journal of Science. 41 (5): 237–276. 1896.

Will Steffen, Wendy Broadgate, Lisa Deutsch, Owen Gaffney, and Cornelia Ludwig. The trajectory of the Anthropocene: The Great Acceleration. The Anthropocene Review, January 16, 2015 DOI: 10.1177/2053019614564785

Smith, B.D., Zeder, M.A., The onset of the Anthropocene. Anthropocene (2013),http://dx.doi.org/10.1016/j.ancene.2013.05.001

 

The Pliocene Warm Period, an analogue of a future warmer Earth.

 

Tuktoyuktuk Beach on the Arctic Ocean (From Wikipedia)

Tuktoyuktuk Beach on the Arctic Ocean (From Wikipedia)

Microfossils from deep-sea are crucial elements for our understanding of past and present oceans. Their skeletons take up chemical signals from the sea water, in particular isotopes of oxygen and carbon. Over millions of years, these skeletons accumulate in the deep ocean to become a major component of biogenic deep-sea sediments. The incorporation of Mg/Ca into the calcite of marine organisms, like foraminifera, is widely used to reconstruct the thermal evolution of the oceans throughout the Cenozoic. Planktic foraminifer Globigerinoides ruber is perhaps one of the most widely used species for reconstructing past sea-surface conditions. Additionally, Mg/Ca–oxygen isotope measurements of benthic foraminifera may be related to global ice volume and by extension, sea level (Evans et al., 2016). The importance of microfossils as tool for paleoclimate reconstruction was recognized early in the history of oceanography. John Murray, naturalist of the CHALLENGER Expedition (1872-1876) found that differences in species composition of planktonic foraminifera from ocean sediments contains clues about the temperatures in which they lived.

Scanning Electron Micrographs of Globigerinoides ruber (adapted from Thirumalai et al., 2014)

Scanning Electron Micrographs of Globigerinoides ruber (adapted from Thirumalai et al., 2014)

The most recent investigations have focused on unravelling the Pliocene Warm Period, a period proposed as a possible model for future climate. The analysis of the evolution of the major ice sheets and the temperature of the oceans indicates that during the middle part of the Pliocene epoch (3.3 Ma–3 Ma), global warmth reached temperatures similar to those projected for the end of this century, about 2°–3°C warmer globally on average than today.

The mid-Pliocene is used as an analog to a future warmer climate because it’s geologically recent and therefore similar to today in many aspects like the land-sea configuration, ocean circulation, and faunal and flora distribution. Mid- Pliocene sediments containing fossil proxies of climate are abundant worldwide, and many mid- Pliocene species are extant, making faunal and floral paleotemperature proxies based on modern calibrations possible (Robinson et al., 2012).

Surface air temperature anomalies of (top) the late 21st century and (bottom) the mid-Pliocene (from Robinson et al., 2012)

Surface air temperature anomalies of (top) the late 21st century and (bottom) the mid-Pliocene (from Robinson et al., 2012)

Foraminiferal Mg/Ca data suggest that the Pliocene tropics were the same temperature or cooler than present. At high latitudes, mid- Pliocene sea surface temperatures (SSTs) were substantially warmer than modern SSTs. These warmer temperatures were reflected in the vegetation of Iceland, Greenland, and Antarctica. Coniferous forests replaced tundra in the high latitudes of the Northern Hemisphere. Additionally, the Arctic Ocean may have been seasonally free of sea-ice, and were large fluctuations in ice cover on Greenland and West Antarctica (Dolan et al., 2011; Lunt et al., 2012).  These results highlights the importance of the Pliocene Warm Period to better understand future warm climates and their impacts.

Reference:

David Evans, Chris Brierley, Maureen E. Raymo, Jonathan Erez, Wolfgang Müller; Planktic foraminifera shell chemistry response to seawater chemistry: Pliocene–Pleistocene seawater Mg/Ca, temperature and sea level change; Earth and Planetary Science Letters, Volume 438, 15 March 2016, Pages 139-148

Jochen Knies, Patricia Cabedo-Sanz, Simon T. Belt, Soma Baranwal, Susanne Fietz, Antoni Rosell-Mel. The emergence of modern sea ice cover in the Arctic Ocean. Nature Communications, 2014; 5: 5608 DOI: 10.1038/ncomms6608

Robinson, M.; Dowsett, H. J.; Chandler, M. A. (2008). “Pliocene role in assessing future climate impacts”; Eos 89 (49): 501–502.

Climate Change and the Evolution of Mammals.

Wyoming_Bighorn_Basin

Bighorn Basin, Wyoming (Image: University of New Hampshire, College of Engineering and Physical Sciences).

Rapid global climate change can lead to rapid evolutionary responses. The Paleocene-Eocene Thermal Maximum (PETM; 55.8 million years ago), was a short-lived (~ 200,000 years) global warming event attributed to a rapid rise in the concentration of greenhouse gases in the atmosphere. It was suggested that this warming was initiated by the melting of methane hydrates on the seafloor and permafrost at high latitudes. This event was accompanied by other large-scale changes in the climate system, for example, the patterns of atmospheric circulation, vapor transport, precipitation, intermediate and deep-sea circulation, a rise in global sea level and ocean acidification.

The PETM onset is also marked by the largest deep-sea mass extinction among calcareous benthic foraminifera (including calcareous agglutinated taxa) in the last 93 million years. Similarly, planktonic foraminifera communities at low and high latitudes show reductions in diversity, while larger foraminifera are the most common constituents of late Paleocene–early Eocene carbonate platforms.

Phenacodus

Phenacodus by Heinrich Harder (1858-1935) . From Wikimedia Commons.

During the PETM, around 5 billion tons of CO2 was released into the atmosphere per year, and temperatures increased by 5 – 8°C. The rise in temperature coincided with a dramatic decrease in the body size of marine and terrestrial organisms. Dwarfing of mammalian taxa across the Palaeocene-Eocene Thermal Maximum (PETM) was first described in the Bighorn Basin, Wyoming. The basin has a remarkably fossil-rich sedimentary record of late Palaeocene to early Eocene age.  The interval of the Paleocene–Eocene Thermal Maximum is represented by a unique mammalian fauna composed by smaller, but morphologically similar species to those found later in the Eocene. Diminutive species include the early equid Sifrhippus sandrae, the phenacodontids Ectocion parvus and Copecion davisi. Two main hypotheses have been proposed to explain the observation of smaller body sizes during the global warming event. The first hypothesis is that mammal population decreased the average body-size in response to the environmental conditions that existed during the PETM global warming event. The second hypothesis is that the observed decrease in the average body-size was the result of extrinsic forces, such as the range extension of small species into the Bighorn Basin, displacing larger species (Burger, 2012). 

Comparison of the effects of anthropogenic emissions (total of 5000 Pg C over 500 years) and PETM carbon release (3000 Pg C over 6 kyr) on the surface ocean saturation state of calcite. From Zeebe, 2013

Comparison of the effects of anthropogenic emissions (total of 5000 Pg C over 500 years) and PETM carbon release (3000 Pg C over 6 kyr) on the surface ocean saturation state of calcite. From Zeebe, 2013

New findings revealed that the remarkable decrease in mean body size across the warming event, occurred through anagenetic change and immigration. However, species selection also was strong across the PETM but, intriguingly, favoured larger-bodied species, implying some unknown mechanism(s) by which warming events affect macroevolution (Rankin et al., 2015). 

Climate change is the major threat to biodiversity. The combination of global warming and the release of large amounts of carbon to the ocean-atmosphere system during the PETM has encouraged analogies to be drawn with modern anthropogenic climate change. Reduction in nutrients, food availability and water will probably have negative implications and are interrelated with climate change and shrinking organisms.  We need to understand how and why organisms are shrinking, and what it means for biodiversity and humanity.

References:

Rankin, B., Fox, J., Barron-Ortiz, C., Chew, A., Holroyd, P., Ludtke, J., Yang, X., Theodor, J. 2015. The extended Price equation quantifies species selection on mammalian body size across the Palaeocene/Eocene Thermal Maximum. Proceedings of the Royal Society B. doi: 10.1098/rspb.2015.1097

Barnosky, A. D. 2004 Biodiversity response to climate change in the middle Pleistocene: the Porcupine Cave fauna from Colorado. Berkeley, CA: University of California Press.

Burger, B.J., Northward range extension of a diminutive-sized mammal (Ectocion parvus) and the implication of body size change during the Paleoc…, Palaeogeogr. Palaeoclimatol. Palaeoecol. (2012), http://dx.doi.org/10.1016/j.palaeo.2012.09.008

Jablonski, D. 2008, Species selection: theory and data. Annu. Rev. Ecol. Evol. Syst. 39, 501–524.

Sheriden, J. A; Bickford, D. 2011, Shrinking body size as an ecological response to climate change. Nat. Clim.

Wright JD, Schaller MF (2013) Evidence for a rapid release of carbon at the Paleocene-Eocene thermal maximum. Proc Natl Acad Sci USA 110(40):15908–15913.

The Megafauna extinction in South América.

 

Megatherium americanum Cuvier, 1796. Museo Argentino de La Plata.

Megatherium americanum Cuvier, 1796. Museo Argentino de La Plata.

During the Pleistocene and the early Holocene,  most of the terrestrial megafauna became extinct. It was a deep global-scale event. The extinction was notably more selective for large-bodied animals than any other extinction interval in the last 65 million years. Multiple explanatory hypotheses have been proposed for this event: climatic change, over hunting, habitat alteration, and the introduction of a new disease. Traditionally, the focus of research and debate has been on the Eurasian and North American extinctions. In North America, two mammalian orders (Perissodactyla, Proboscidea) were eliminated completely. At the species level, the extinction was total for mammals larger than 1000 kg and greater than 50% for size classes between 1000 and 32 kg. Early observations confirm that extinctions could be severe even in relatively climatically stable regions where the vegetation changed little. In South America the event was  more severe, with the loss of 50 megafaunal genera. Three orders of mammals disappeared (Notoungulata, Proboscidea, Litopterna), as did all megafaunal xenarthrans and at the species level, the extinction was total for mammals larger than 320 kg (Koch and Barnosky, 2006).

“Descuartizando un gliptodonte. Escenas de la vida del hombre primitivo” (Quartering a glyptodont. Scenes from the life of primitive man). Painting by Luis de Servi. Museo de la Plata).

“Descuartizando un gliptodonte. Escenas de
la vida del hombre primitivo” (Quartering a
glyptodont. Scenes from the life of primitive man). Painting by Luis de Servi, Museo de la Plata.

Before the Great American Biotic Interchange, about 3 million years ago, the largest mammals in South America were mainly endemic notoungulates, litopterns and xenarthrans. But, during the interchange, many other megamammals and large mammals arrived to South America. The late Pleistocene in this region is first characterized by a rapid cooling. During the Pleistocene-Holocene transition pollen sequences suggest a change to sub-humid climatic conditions. In addition to rapid climate change, the extinctions are seen as the result of habitat loss, reduced carrying capacity for herbivores, resource fragmentation or disturbances in the co-evolutionary equilibrium between plants, herbivores, and carnivores. The death event of the gomphothere population in Águas de Araxá (Brazil)  about 55,000 years ago, is probably an example of individuals that were suffering with the climate changes during the Late Pleistocene.

Paleontological and archaeological data indicate that extinctions seem more common after the human arrival and during the rapid climate change between 11.200 and 13.500 years. This pattern suggests that a synergy of human impacts and rapid climate change—analogous to what is happening today — may enhance extinction probability (Prado et al., 2015).

 

References:

J.L. Prado et al. (2015). “Megafauna extinction in South America: A new chronology for the Argentine Pampas.” Palaeogeography, Palaeoclimatology, Palaeoecology 425: 41–49

Alroy, John. (2001). “A Multispecies Overkill Simulation of the End-Pleistocene Megafaunal Mass Extinction.” Science 292:1893-1896

Koch PL, Barnosky AD (2006) Late Quaternary extinctions: State of the debate. Annu Rev Ecol Evol Syst 37:215–250.

Prescott GW, Williams DR, Balmford A, Green RE, Manica A. (2012) Quantitative global analysis of the role of climate and people in explaining late Quaternary megafaunal extinctions. Proc. Natl Acad. Sci. USA 109,45274531

Barnosky AD, Lindsey EL.(2010) Timing of Quaternary megafaunal extinction in South America in relation to human arrival and climate change

 

Response of marine ecosystems to the PETM.

Biotic change among foraminifera during and after the PETM. (From Speijer et al., 2012)

Biotic change during and after the PETM. (From Speijer et al., 2012)

The Paleocene-Eocene Thermal Maximum (PETM; 55.8 million years ago), was a short-lived (~ 200,000 years) global warming event attributed to a rapid rise in the concentration of greenhouse gases in the atmosphere. It was suggested that this warming was initiated by the melting of methane hydrates on the seafloor and permafrost at high latitudes. During the PETM, around 5 billion tons of CO2 was released into the atmosphere per year, and temperatures increased by 5 – 9°C. This event was accompanied by other large-scale changes in the climate system, for example, the patterns of atmospheric circulation, vapor transport, precipitation, intermediate and deep-sea circulation and a rise in global sea level.

Dinoflagellate cysts: Adnatosphaeridium robustum and Apectodinium augustum (From Sluijs and Brinkhuis, 2009)

Dinoflagellate cysts: Adnatosphaeridium robustum and Apectodinium augustum (From Sluijs and Brinkhuis, 2009)

The rapid warming at the beginning of the Eocene has been inferred from the widespread distribution of dinoflagellate cysts. One taxon in particularly, Apectodinium, spans the entire carbon isotope excursion (CIE) of the PETM. The distribution of Apectodinium is linked to high temperatures and increased food availability.

The most disruptive impact during the PETM was likely the exceptional ocean acidification and the rise of the calcite dissolution depth, affecting marine organisms with calcareous shells (Zachos et al., 2005). When CO2 dissolves in seawater, it produce carbonic acid. The carbonic acid dissociates in the water releasing hydrogen ions and bicarbonate. The formation of bicarbonate then removes carbonate ions from the water, making them less available for use by organisms.

Nannofossil abundance changes during the PETM. (From Kump, 2009.)

Nannofossil abundance changes during the PETM. (From Kump, 2009.)

The PETM onset is also marked by the largest deep-sea mass extinction among calcareous benthic foraminifera (including calcareous agglutinated taxa) in the last 93 million years. Similarly, planktonic foraminifera communities at low and high latitudes show reductions in diversity, while larger foraminifera are the most common constituents of late Paleocene–early Eocene carbonate platforms.

The response of most marine invertebrates (mollusks, echinoderms, brachiopods) to paleoclimatic change during the PETM is poorly documented.

Coccolithus bownii and Toweius pertusus

Coccolithus bownii and Toweius pertusus (Adapted from Bown and Pearson, 2009)

The PETM is also associated with dramatic changes among the calcareous plankton,characterized by the appearance of transient nanoplankton taxa of heavily calcified forms of Rhomboaster spp., Discoaster araneus, and D. anartios as well as Coccolithus bownii, a more delicate form.

The combination of global warming and the release of large amounts of carbon to the ocean-atmosphere system during the PETM has encouraged analogies to be drawn with modern anthropogenic climate change. The current rate of the anthropogenic carbon input  is probably greater than during the PETM, causing a more severe decline in ocean pH and saturation state. Also the biotic consequences of the PETM were fairly minor, while the current rate of species extinction is already 100–1000 times higher than would be considered natural. This underlines the urgency for immediate action on global carbon emission reductions.

Comparison of the effects of anthropogenic emissions (total of 5000 Pg C over 500 years) and PETM carbon release (3000 Pg C over 6 kyr) on the surface ocean saturation state of calcite. From Zeebe, 2013

Comparison of the effects of anthropogenic emissions (total of 5000 Pg C over 500 years) and PETM carbon release (3000 Pg C over 6 kyr) on the surface ocean saturation state of calcite. From Zeebe, 2013

 

References:

Maria Rose Petrizzo, The onset of the Paleocene–Eocene Thermal Maximum (PETM) at Sites 1209 and 1210 (Shatsky Rise, Pacific Ocean) as recorded by planktonic foraminifera, Marine Micropaleontology, Volume 63, Issues 3–4, 13 June 2007, Pages 187-200

Zeebe RE and Zachos JC. 2013 Long-term legacy ofmassive carbon input to the Earth system: Anthropocene versus Eocene. Phil Trans R Soc A 371: 20120006. http://dx.doi.org/10.1098/rsta.2012.0006.

Wright JD, Schaller MF (2013) Evidence for a rapid release of carbon at the Paleocene-Eocene thermal maximum. Proc Natl Acad Sci USA 110(40):15908–15913.

Kump, L.R., T.J. Bralower, and A. Ridgwell. 2009. Ocean acidification in deep time. Oceanography 22(4):94–107, http://dx.doi.org/10.5670/oceanog.2009.100

Raffi, I. and de Bernardi, B.: Response of calcareous nannofossils to the Paleocene-Eocene Thermal Maximum: observations on composition, preservation and calcification in sediments from ODP Site 1263 (Walvis Ridge – SW Atlantic), Mar. Micropaleontol., 69, 119–138, 2008.

Robert P. SPEIJER, Christian SCHEIBNER, Peter STASSEN & Abdel-Mohsen M. MORSI; Response of marine ecosystems to deep-time global warming: a synthesis of biotic patterns across the Paleocene-Eocene thermal maximum (PETM), Austrian Journal of Earth Sciences. Vienna. 2012. Volume 105/1.

The Great Acceleration.

 

Iron and Coal, 1855–60, by William Bell Scott illustrates the central place of coal and iron working in the industrial revolution (From Wikimedia Commons)

Iron and Coal, 1855–60, by William Bell Scott illustrates the central place of coal and iron working in the industrial revolution (From Wikimedia Commons)

During a meeting of the International Geosphere-Biosphere Programme (IGBP) celebrated in Mexico, in 2000, the Vice-Chair of IGBP, Paul Crutzen, proposed the use of the term Anthropocene to designate the last three centuries of human domination of earth’s ecosystems, and to mark the end of the current Holocene geological epoch. He suggested that the start date of the Anthropocene must be placed near the end of the 18th century, about the time that the industrial revolution began, and noted that such a start date would coincide with the invention of the steam engine by James Watt in 1784.

Although there is no agreement on when the Anthropocene started, researchers accept that the Anthropocene is a time span marked by human interaction with Earth’s biophysical system. It has been defined, primarily, by significant and measurable increases in anthropogenic greenhouse gas emissions from ice cores, and other geologic features including synthetic organic compounds and radionuclides. Eugene Stoermer, in an interview in 2012, proposed that the geological mark for the Anthropocene was the isotopic signature of the first atomic bomb tests. Hence,  Anthropocene deposits would be those that may include the globally distributed primary artificial radionuclide signal (Zalasiewicz et al, 2015).

 

anthropocene

Alternative temporal boundaries for the Holocene–Anthropocene boundary (calibrated in thousand of years before present) From Smith 2013

 

Human activity is a major driver of the dynamics of Earth system. After the World War II, the impact of human activity on the global environment dramatically increased. This period associated with very rapid growth in human population, resource consumption, energy use and pollution, has been called the Great Acceleration.

During the Great Acceleration, the atmospheric CO2 concentration grew, from 311 ppm in 1950 to 369 ppm in 2000 (W. Steffen et al., 2011). About one third of the carbon dioxide released by anthropogenic activity is absorbed by the oceans. When CO2 dissolves in seawater, it produce carbonic acid. The carbonic acid dissociates in the water releasing hydrogen ions and bicarbonate. Then, the formation of bicarbonate removes carbonate ions from the water, making them less available for use by organisms. Ocean acidification affects the biogeochemical dynamics of calcium carbonate, organic carbon, nitrogen, and phosphorus in the ocean, and will directly impact in a wide range of marine organisms that build shells from calcium carbonate, like planktonic coccolithophores, molluscs,  echinoderms, corals, and coralline algae.

Clastic plastiglomerate containing molten plastic and basalt and coral fragments (Image adapted from P. Corcoran et al., 2014)

Clastic plastiglomerate containing molten plastic and basalt and coral fragments (Image adapted from P. Corcoran et al., 2013)

One important marker for the future geological record is a new type of rock formed by anthropogenically derived materials. This type of rock has been named plastiglomerate, and has been originally described on Kamilo Beach, Hawaii. This anthropogenically influenced material has great potential to form a marker horizon of human pollution, signaling the occurrence of the Anthropocene epoch (Corcoran et al., 2013).

Climate change, shifts in oceanic pH, loss of biodiversity and widespread pollution have all been identified as potential planetary tipping point. Since the industrial revolution, the wave of animal and plant extinctions that began with the late Quaternary has accelerated. Calculations suggest that the current rates of extinction are 100–1000 times above normal, or background levels. We are in the midst of  the so called “Sixth Mass Extinction”.

Dealing with the transition into the Anthropocene requires careful consideration of its social, economic and biotic effects. In his master book L’Evolution Créatrice (1907), French philosopher Henri Bergson, wrote:  “A century has elapsed since the invention of the steam engine, and we are only just beginning to feel the depths of the shock it gave us.”

 

References:

Will Steffen, Wendy Broadgate, Lisa Deutsch, Owen Gaffney, and Cornelia Ludwig. The trajectory of the Anthropocene: The Great Acceleration. The Anthropocene Review, January 16, 2015 DOI: 10.1177/2053019614564785

Jan Zalasiewicz et al. When did the Anthropocene begin? A mid-twentieth century boundary level is stratigraphically optimal. Quaternary International, published online January 12, 2015; doi: 10.1016/j.quaint.2014.11.045

Smith, B.D., Zeder, M.A., The onset of the Anthropocene. Anthropocene (2013),http://dx.doi.org/10.1016/j.ancene.2013.05.001

Ellis, E.C., 2011. Anthropogenic transformation of the terrestrial biosphere. Philosophical Transactions of the Royal Society A 369, 1010–1035.

 

African paleoclimate and early hominin evolution.

Olduvai Gorge. From Wikimedia Commons

Olduvai Gorge. From Wikimedia Commons

Over the last ten million years the landscape of East Africa has been altered dramatically. It has changed from a relatively flat, homogenous region covered with tropical mixed forest, to a heterogeneous region, with mountains over 4 km high and vegetation ranging from desert to cloud forest. Long-term climate change seems to be modulated primarily  by tectonic changes. The progressive formation of the East African Rift Valley led to increased aridity and the development of numerous lake basins.

Five major transitions have influenced African climate during the early stage of human evolution: 1)  the emergence of  and expansion of C4 biomes (~8 Ma); 2) The Messinian Salinity Crisis (~ 5.3 Ma); 3)  the Intensification of Northern Hemisphere Glaciation during the Pliocene epoch between 3.6 and 2.7 million years ago;  4) the development of the Walker Circulation; 5) the Early-Middle Pleistocene Transition.

Map of East Africa with modern lake and paleolake basins (from Maslin et al., 2014)

Map of East Africa with modern lake and paleolake basins (from Maslin et al., 2014)

It has been hypothesized that both the uplift of the Tibetan Plateau about 8 Ma ago and the reduction of the Paratethys Sea intensified the seasonal Indian monsoon climate,  and that the more seasonal climate favored grasses over trees.

The isolation of the Mediterranean Sea from the Atlantic Ocean was caused by the tectonic closure of the Strait of Gibraltar. During the Messinian Salinity Crisis, the Mediterranean Sea went into a cycle of partly or nearly complete desiccation and removed nearly 6% of all dissolved salts in the oceans.

The Intensification of  Northern Hemisphere Glaciation (iNHG), the third regional climate event,  was characterised by periodic advances and retreats of ice sheets on a hemispherical scale and was the culmination of long-term high latitude cooling, which began with the Late Miocene.

Diatomites of the genera Stephanodiscus and Aulacoseira. (From Kingston et al., 2007)

Diatomites of the genera Stephanodiscus and Aulacoseira. (From Kingston et al., 2007)

The Early-Middle Pleistocene Transition, represents a major global climatic reorganization that profoundly affected ocean and atmospheric circulation, ice sheets and the distribution and evolution of biota.

The diatomite deposits from Pliocene lakes in the Baringo Basin suggest that the lakes appear rapidly, remain part of the landscape for thousands of years, then disappear in a highly variable and erratic way. Two dominant genera of diatoms present in East African lakes and Pliocene-Recent deposits helps to understand the dynamic of these humidity/aridity cycles: Aulacoseira predominates under cool windy conditions, while Stephanodiscus predominates under warmer, less windy conditions. The segregation of Aulacoseira and Stephanodiscus into subtle layers on a scale of < 100 mm and the presence of micro-laminae on a scale of one hundred to a few hundred microns suggest cyclic variation in a time frame of one to a few years (Kingston et al., 2007).

Early human evolutionary theories and climate change. From Maslin et al. 2014

Early human evolutionary theories and climate change. From Maslin et al. 2014

The major events in hominin evolution have occurred in East Africa. Several theories have been developed to explain the interaction between African paleoclimate and early hominid evolution. The savannah hypothesis suggested that hominins were forced to descend from the trees and adapted to life on the savannah facilitated by walking erect on two feet. This idea was already outlined by Lamarck in his Philosophie zoologique (1809], where he describes in details how an early ancestor of primeval human abandons an arboreal life to adapt itself to open plains.

More recent, the pulsed climate variability hypothesis  highlights the role of short periods of extreme climate variability specific to East Africa in driving hominin evolution and subsequent dispersal events (Maslin and Trauth, 2009). These periods of ‘pulsed climate variability’ are characterized by the appearance and disappearance of large, deep lakes in the East African Rift Valley. Paleoclimatic information derived from benthic foraminifera, regional aeolian dust flux data and the East African lake record indicates that hominin speciation events and changes in brain size seem to be statistically linked to the occurrence of ephemeral deep-water lakes (Shultz and Maslin, 2013).

References:

Maslin M.A., C. Brierley, A. Milner, S. Shultz, M. Trauth, K. Wilson “East African climate pulses and early human evolution” Quaternary Science Reviews (2014).

Maslin M.A., ‘Cascading uncertainty in Climate Change models and its implications for policy’ Geographical Journal 179, 264-271 (2013)

Ashley, G., Bunn, H., Delaney, J., Barboni, D., Domínguez-Rodrigo, M., Mabulla, A., Gurtov, A., Baluyot, R., Beverly, E., Baquedano, E., 2014. Paleoclimatic and paleoenvironmental framework of FLK North archaeological site, Olduvai Gorge, Tanzania. Quat. Int. 322e323, 54-65.

Shultz S, Maslin M (2013) Early Human Speciation, Brain Expansion and Dispersal Influenced by African Climate Pulses. PLoS ONE 8(10): e76750. DOI: 10.1371/journal.pone.0076750

John D. Kingston et al., Astronomically forced climate change in the Kenyan Rift Valley 2.7- 2.55 Ma: implications for the evolution of early hominin ecosystems, J Hum Evol (2007), doi:10.1016/j.jhevol.2006.12.007

Palynological reconstruction of the Antarctic Cretaceous-Paleocene climate.

Artist’s impression of the eastern flank of the Antarctic Peninsula during theMaastrichtian (Artist: James McKay, University of Leeds.)

Artist’s impression of the eastern flank of the Antarctic Peninsula during the Maastrichtian (From Bowman et al, 2014, Artist: James McKay, University of Leeds.)

Past fluctuations in global temperatures are crucial to understand Earth’s climatic evolution. During the Late Cretaceous the global climate change has been associated with episodes of outgassing from major volcanic events, orbital cyclicity and tectonism before ending with the cataclysm caused by a large bolide impact at Chicxulub, on the Yucatán Peninsula, Mexico.
The Antarctic Peninsula is an area of specific interest to modern and past climatic studies, as it seems particularly sensitive to change (Kemp et al., 2014). Most of the studies are focused on Seymour Island which has one of the most expanded Cretaceous–Paleogene successions known. The K-Pg boundary occurs in the uppermost part of the López de Bertodano Formation, where it is marked by a minor iridium anomaly.

The terrestrial palynomorph record at the López de Bertodano Formation was divided into six phases. The first one contains an assemblage dominated by Nothofagidites spp. and Podocarpidites spp., with aquatic fern spores (Azolla spp., Grapnelispora sp.) and rare freshwater algal spores, suggesting a cool and relatively humid period.

 

Two examples of grains pollen from the Lopez de Bertodano Formation: Podocarpidites sp. (left) and Nothofagidites asperus (right)

Two examples of grains pollen from the Lopez de Bertodano Formation: Podocarpidites sp. (left) and Nothofagidites asperus (right). From Bowman et al, 2014.

In the phase two the increased abundance of Phyllocladidites mawsonii implies a gradual increase in humidity. During phase three, bryophytes began to increase. The phase four is characterised by relatively high abundances of Podocarpidites spp. and relatively low levels of Nothofagidites spp.
The phase 5 is characterised by a rapidly changing sequence of abundance peaks of different taxa, which may indicate a successional turnover in forest composition. The phase six suggests a return to a cool climatic conditions with high abundances of Araucariacites australis and Nothofagidites at the top of the section. It seems that Araucariaceae were capable of surviving long periods of adverse climatic conditions during the Early Pleistocene, but most modern araucarians have subtropical to mesothermal climatic preferences.

The nature of vegetational change in the south polar region suggests that terrestrial ecosystems were already responding to relatively rapid climate change prior to the K–Pg catastrophe. The composition of the terrestrial palynoflora indicates that the Maastrichtian climate fluctuated from cool, humid conditions, through a rapid warming about 2 million years prior to the K–Pg event – which is consistent with the evidence from the marine palynomorph record –  followed by cooling conditions in the earliest Danian.

 

Two examples of spores from the  Lopez de Bertodano Formation: Grapnelispora sp. (left) and Azolla sp.(right).

Two examples of spores from the Lopez de Bertodano Formation: Grapnelispora sp. (left) and Azolla sp.(right). From Bowman et al, 2014.

 

Reference:

Vanessa C. Bowman, Jane E. Francis, Rosemary A. Askinb, James B. Riding, Graeme T. Swindles, Latest Cretaceous–earliest Paleogene vegetation and climate change at the high southern latitudes: palynological evidence fromSeymour Island, Antarctic Peninsula, Palaeogeography, Palaeoclimatology, Palaeoecology, 408. 26-47. 10.1016/j.palaeo.2014.04.018
David B. Kemp, Stuart A. Robinson, J. Alistair Crame, Jane E. Francis, Jon Ineson, Rowan J. Whittle, Vanessa Bowman, and Charlotte O’Brien, A cool temperate climate on the Antarctic Peninsula through the latest Cretaceous to early Paleogene, Geology (2014) doi: 10.1130/G35512.1