Literature Review: The Cenozoic Era

by Carl Strang

This week we look at some recent studies of the time between the Mesozoic Era and the present day. In recent years there has been much interest in the dynamics of climate change across the ages of the Earth.

A huge amount of carbon today is sequestered in the permafrost soils of the North.

A huge amount of carbon today is sequestered in the permafrost soils of the North.

Robert M. DeConto, et al. Past extreme warming events linked to massive carbon release from thawing permafrost. Nature, 2012; 484 (7392): 87 DOI: 10.1038/nature10929 They combined modeling with the Earth’s orbital dynamics to show the likelihood that in the Paleocene, when the Earth’s orbit became more eccentric and tilt became greater, this resulted in thawing and decomposition of permafrost, releasing huge amounts of carbon dioxide and resulting in a positive feedback loop that produced the Paleocene-Eocene Thermal Maximum.

Pitcher plants, Big Thicket. The following study traces their origin.

Pitcher plants, Big Thicket. The following study traces their origin.

Ellison AM, et al. (2012) Phylogeny and Biogeography of the Carnivorous Plant Family Sarraceniaceae. PLoS ONE 7(6): e39291. doi:10.1371/journal.pone.0039291 They studied nuclear, mitochondrial and plasmid genes to sort out relationships and evolutionary history of the pitcher plants. They conclude that the family appeared in South America 44-53mya (million years ago, Eocene), and by the end of the Eocene was widespread in North and South America.

G. Grellet-Tinner, et al. (2012) The First Occurrence in the Fossil Record of an Aquatic Avian Twig-Nest with Phoenicopteriformes Eggs: Evolutionary Implications. PLoS ONE 7(10): e46972. doi:10.1371/journal.pone.0046972 They found fossils of a basal flamingo in association with eggshells and a floating nest that are like those of modern grebes, in an early Miocene shallow-lake wetland with high evaporation, in Spain. Though they agree that there was an earlier split between the grebes and the flamingos, they mention that fossil flamingos are known from the Oligocene, grebes from the Miocene. Apparently the bones are insufficient to provide much of an understanding of this early flamingo’s appearance.

Zhang Z, Feduccia A, James HF (2012) A Late Miocene Accipitrid (Aves: Accipitriformes) from Nebraska and Its Implications for the Divergence of Old World Vultures. PLoS ONE 7(11): e48842. doi:10.1371/journal.pone.0048842 They describe a fossil bird from Nebraska that links New World hawks and eagles to the Gypaetinae, one of the subfamilies of Old World vultures. This places the timing of that group’s origin in the Miocene, and supports its evolutionary separation from the other Old World vulture subfamily, the Aegypiinae.

Elderfield, H., et al. 2012. Evolution of ocean temperature and ice volume through the mid-Pleistocene climate transition. Science 337:704-709. (Comment by Peter U. Clark on pp. 656-658 in the same issue). They sorted through various isotopic proxies in marine sediments from New Zealand, and found an association between the mysterious change in ice age periodicity around 900,000 years ago (from cycles of 41,000 years to the more recent cycles of 100,000 years, a change not connected to the Earth orbit fluctuations now known to be the underlying cause of ice age cycling generally) and an increase in the volume of ice around Antarctica. They suggest that “an anomalously low Southern Hemisphere summer insolation” failed to melt the Antarctic ice during one interglacial period, and that the ice added during the following ice age was enough to produce the observed period change. The sea level drop during ice ages changed from 70 meters to 120 meters as a result. Their data also argue against a gradual cooling, from changes in atmospheric carbon dioxide, as the primary driver of the periodicity change.

Jeremy D. Shakun, et al. Global warming preceded by increasing carbon dioxide concentrations during the last deglaciation. Nature, 2012; 484 (7392): 49 DOI: 10.1038/nature10915 From an article in ScienceDaily: “Here is what the researchers think happened.

“Small changes in Earth’s orbit around the sun affected the amount of sunlight striking the northern hemisphere, melting ice sheets that covered Canada and Europe. That fresh water flowed off of the continent into the Atlantic Ocean, where it formed a lid over the sinking end of the Atlantic Meridional Overturning Circulation — a part of a global network of currents that brings warm water up from the tropics and today keeps Europe temperate despite its high latitudes.

“The ocean circulation warms the northern hemisphere at the expense of the south, the researchers say, but when the fresh water draining off the continent at the end of the last Ice Age entered the North Atlantic, it essentially put the brakes on the current and disrupted the delivery of heat to the northern latitudes.

“ʻWhen the heat transport stops, it cools the north and heat builds up in the Southern Hemisphere,ʼ Shakun said. ʻThe Antarctic would have warmed rapidly, much faster than the time it takes to get CO2 out of the deep sea, where it was likely stored.

“ʻThe warming of the Southern Ocean may have shifted the winds as well as melted sea ice, and eventually drawn the CO2 out of the deep water, and released it into the atmosphere,ʼ Shakun said. ʻThat, in turn, would have amplified warming on a global scale.ʼ”

The study was a global review of the timing of temperature and atmospheric carbon dioxide changes at the end of the last period of continental glaciation.

Ghost of a Landscape

by Carl Strang

The places we live and work all were wilderness at one time. National parks, state parks, and nature preserves protect and restore areas intended to represent the landscape as it was before large scale agriculture began the sequence of alterations that have brought us to the present day. A number of studies have produced maps showing, in some detail, what the counties of northeast Illinois looked like 200 years ago. In the late 1980’s I decided to do the same for my home area, Union Township in Marshall County, Indiana. Here is a watercolor rendering of my results.

Union Twp painting 2a

I was reminded of that project by Scott’s excellent recent post on Houghton Lake in his blog, Through Handlens and Binoculars. Houghton Lake is the small lake closest to the map’s upper left corner. Recently it was acquired by The Nature Conservancy, and is getting the attention needed to preserve the rare plants and vegetation communities that have persisted there.

My mapping study began with a visit to the County Surveyor’s office in Plymouth, the county seat, to copy the original survey notes. Two different surveyors explored the local wilderness in 1834 and 1836, marking out the land on behalf of the federal government for purchase by American farmers. The 1836 survey covered the Indian reservations east of Lake Maxinkuckee, the township’s largest lake. That land became available to eastern farmers after the forced removal of the Potawatomis via the Trail of Death in 1838.

The surveyors’ main job was to mark the section corners and quarter-section corners (a section is a square mile). They also described the land, so that potential buyers back east could make informed choices. For example, after passing through what is now the center of the town of Culver, on Maxinkuckee’s west shore, surveyor David Hillis wrote, “Land rolling. 3d rate. Hickory etc.” Usually the description was dispassionate, but sometimes a surveyor revealed the sweat and discomfort of the experience. After crossing an extensive marsh at the south end of Maxinkuckee, Jeremiah Smith allowed, “In Sec. 34, at 1.20 (an) inlet 80L. wide coming from S.E. A nasty place.”

One of the surveyor’s helpers blazed and inscribed two “witness trees” at each section corner. The surveyor wrote down the species of tree along with its distance and direction from the corner. The tree species suggests to us what kind of vegetation community occupied that corner, and the tree’s distance from the corner hints at how close together the trees grew in that spot.

The surveyors also were careful to map the edges of lakes and rivers. In Union Township only Lake Maxinkuckee and Lost Lake, off its west edge, still have their 1834 outlines. Houghton Lake, and Moore Lake beside it, today are remnants of the larger water bodies they were in the early 1800’s. Two other lakes in the west-central part of the township no longer exist. They were shallow and easily drained for agricultural purposes before 1900.

Plant communities described by the surveyors as “wet prairies” or “marshes” were extensive mixtures of cattail marshes, sedge meadows and wet to moist prairies. Some of these featured insect-eating plants, the pitcher plants and sundews. See Scott’s post for photographs of some of the botanical beauty preserved around Houghton Lake. I’ll continue this account tomorrow.

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