Leaf Physiognomy Offers clues to the Past

By Eric Atkins

There are many techniques that can be used to offer insight to the past–a family of proxies that range from gas found in ice cores to fossilized feces. I have always been interested in fossils. The allure of something so ancient was introduced to me as a child. At the age of eight, I found a veiny imprint of a leaf in a chunk of sandstone. Fossils are a great tool for looking into the past. For nearly a century by paleoclimatologists and paleoecologists have been using leaf physiognomy as a proxy to deduce past climate environments. By looking at leaf mass per area, teeth area, number of teeth, and degree of blade dissection we can extrapolate information about past climates.

Fossilized Platanus leaf, Paleocene, Alberta, Canada. Via Wikimedia Commons.

Fossilized Platanus leaf, Paleocene, Alberta, Canada. Via Wikimedia Commons.

In recent years this type of proxy has evolved along with technology. Continue reading

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The past’s mark on the present as seen through LIDAR

By Erika Lyon

Light Detection and Ranging, also known as LiDAR, is a form of remote sensing used by various professions to examine landscape features in three-dimensions.  Imaging is generally performed by aircraft (though not always) that use lasers, scanners, and GPS to measure reflected light from Earth’s surface.  This light describes changes in distance between the aircraft and surface features (National Ocean Service 2013).  For terrestrial systems, a near-infrared laser is used to collect data (this is known as topographic LiDAR), while aquatic systems make use of green light, which can break through water surfaces (bathymetric LiDAR) (National Ocean Service 2013).  Data on height, latitude, and longitude of geographic features are generated and used to create models of the landscape (National Ocean Service 2013).  LiDAR’s applications have been used in the fields of archeology, geology, and paleontology to study natural and human history, but it is not fully utilized in paleoecological studies.  LiDAR is a powerful remote sensing tool that can provide invaluable information about Earth’s surface and can be especially useful for looking at evidence of past events and land use.

Past events can leave behind footprints on the Earth’s surface, and these footprints may not be easily distinguished from an aerial or satellite imagery alone.  For example, during the summer months of 2012, I inventoried abandoned mine lands in the Midwest, which are notorious for their dangerous highwalls and sinkholes that are often hidden from view by overgrown trees and shrubs.  LiDAR was a very valuable tool in the field because it made many of these hazardous features evident (Fig. 1).  Needless to say, I didn’t go to a mine site without a LiDAR hillshade map.

Fig. 1: Example of an aerial photo (left) and LiDAR hillshade image (right) of an abandoned surface mine.  Maps, like the ones above, are often utilized by state agencies to assess site conditions of abandoned mines.  For more maps of Iowa’s abandoned mines (including 1930s, 1950s, 2008 aerials, and LiDAR hillshade) click here. (Images created by GeoTREE and the Iowa Department of Natural Resources).

Fig. 1: Example of an aerial photo (left) and LiDAR hillshade image (right) of an abandoned surface mine.  Maps, like the ones above, are often utilized by state agencies to assess site conditions of abandoned mines.  For more maps of Iowa’s abandoned mines (including 1930s, 1950s, 2008 aerials, and LiDAR hillshade) click here. (Images created by GeoTREE and the Iowa Department of Natural Resources).

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Using the past to manage the future

By: Rob Brown

Disturbances such as climate change, biological invasions, pollution, and many others, have led to organizations to emerge with the purpose of restoring and conserving our natural resources. Both paleo- and modern ecological data can help inform resource managers as they implement restoration and conservation strategies.

Figure 1. Nutrient runoff has led to increased algal blooms in lakes and ponds and organizations to implement restoration projects. By Ildar Sagdejev, via Wikimedia Commons

Figure 1. Nutrient runoff has led to increased algal blooms in lakes and ponds and organizations to implement restoration projects. By Ildar Sagdejev, via Wikimedia Commons

 

Restoring ecosystems

Traditionally, the aim of restoration is to restore ecosystems to a natural baseline, or a pre-human disturbance state. However, Jackson and Hobbs (2009) made three observations that complicate finding natural baselines. Continue reading

The pitfalls of transfer functions (and how to avoid them!)

By Erin Hayes-Pontius

Paleoecology, or the study of organisms and their environments in past times, has a specific branch known as paleolimnology, which deals with records left by lakes. Beyond being pleasant places for swimming, fishing, and other recreation, lakes are particularly valuable for paleo records. Not only do lakes archive the goings-on within themselves, but they also archive goings-on within their drainage basins. In the case of Lake Champlain, it has a drainage basin nearly 17 times that of its surface area (21,326 km2 : 1,269 km2), making it extra sensitive to changes in climate (Fig. 1).

Due to lakes’ positions at low points on the landscape, they integrate everything that happens within their drainage basin and are therefore important “sentinels of change” (Williamson et al. 2009).

Figure 1. Lake Champlain’s drainage basin. From Wikimedia Commons

Figure 1. Lake Champlain’s drainage basin. From Wikimedia Commons

Over time, a variety of things fall into lakes, such as diatoms (single-celled algae), pollen, chironomid midges, or needles, to name a few, and these things get buried by sediment. In some lakes- some, certainly not most- sediment deposits occur quickly enough to leave annual layers; if this interests you, definitely check out Rob’s post from a little while back. Unfortunately, this does not happen most of the time, and we’re left with a much coarser resolution to deal with. Rather than knowing about the diatom species every year, we may only know ‘who’ was there every few years, every decade, or even every few decades. Despite these challenges, lakes are still- and will continue to be- widely used in paleoecology. Continue reading

Splinters in Dendrochronological Analyses

By Audrey Cross

A tree corer used to drill into a trunk, and two tree cores. Rings are counted from these cores and used to date events or reconstruct climate change.  Wikimedia Commons.

A tree corer used to drill into a trunk, and two tree cores. Rings are counted from these cores and used to date events or reconstruct climate change. Wikimedia Commons.

In dendrochronology, most analyses rely on a number of underlying assumptions. For wood that was used by humans, a tree might have been used immediately after it died, and it could be found at a site nearby where the tree had lived. However, humans could obtain wood in different ways; it could be found, as with driftwood; recycled, as with beams in houses; or transported, as with boats.

The study of driftwood proposes an interesting twist to dendrochronological analysis because the amount of time that wood can spend in transport can vary greatly. Continue reading

Fecal proxies

By Dulcinea Groff

Dung fungus spores of Sporormiella australis. From Funghi Paradise.

Dung fungus spores of Sporormiella australis. From Funghi Paradise.

Feces of prehistoric organisms remaining in the sediment records harbor information that can lead to a picturesque reconstruction of an ecosystem from long ago.  It is quite remarkable how many examples of fecal proxies exist and provide more information than just an indication of the presence or absence of an animal.  In the early 1800’s, an eccentric paleontologist named William Buckland was the first to describe coprolites or fossilized feces.  When feces become fossilized the organic components are replaced with minerals and any clue as to what the organism ate is replaced.  Therefore, coprolites may not be very useful in understanding the ecology of past environments and organisms.  Instead, other things associated with feces become proxies in paleoecological studies. Continue reading

Teeth, tusks, and mammoth clues

By Sam Reynolds

A friend of mine produces and sells scrimshaw, engraved artwork on ivory or bone. He makes most of his money at craft fairs. There he patiently explains again and again to mortified fair-goers that the tusks he works on are not from elephants, but from mammoths. “Mammoths that lived at least several thousand years ago”, he politely clarifies—”Not the modern mammoth of today.”

Mammoth ivory—which is sometimes mislabeled fossil-ivory—is by no means ubiquitous. However there is a continuing supply of it, especially from the permafrosts of Siberia, where tusks are often treated as a raw material commodity, not as paleoecological specimens. Mammoth molars and tusks are essentially unregulated largely because they are distinct from contemporary elephant ivory, which is illegal save for a few exceptions. Though still recognizable as ivory, the teeth have often undergone partial diagenesis, consisting of both original and some fossilized material. Sometimes they are preserved nearly perfectly, with little more than staining. In either case, they tend are original material—and provide plentiful and accurate chemical snap-shots of the lives of their proboscidean owners. From a site in Switzerland, Mammoth teeth dated 45,000 years old contained oxygen-18 isotopes that indicated the average air temperature there was 4ºC cooler than today (Heuser, 2010). Teeth can also be analyzed for dietary information through values of carbon-13 and nitrogen-15.

Mammoth tusking showing characteristic banded patterning. Taken from the blog of Charlotte Bailey, a fossil-trader and educator; http://www.rocks-fossils.com.

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The Glaciation Fascination

By Rayna Campbell

The Earth’s history shows a wild mix of climates. Ranging from the toxic CO2-filled atmosphere of the earliest years, to global tropical conditions, to periods of intense and violent volcanic disturbances. In the incredibly short period of time humans have inhabited the earth, the climate has not had much time to change. But if we look back into our history, the last glacial maximum, or “The Ice Age” only occurred about  21,500 years ago (Editors). On the scale of geological time, this is very recent. So recent, in fact, we are still able to look to our paleoecological records and “see” evidence of the changes the environment went through during the presence of these huge ice masses.

Fig. 1) Glacial striations. Image courtesy of GNS Science (2009)

On the rocky coasts of lovely Maine in the summer, trips to the seaside provide not only a relaxing retreat from the summer heat, but a wealth of information about glacial movement thousands of years ago. Continue reading

Attaching dates to lake sediment cores: precise dating using varves

By: Rob Brown

There are many proxies paleoecologists use to determine past environments and communities (insects, pollen, diatoms, packrat middens, tree rings, etc.), many of which have been discussed on this blog previously. These proxies can be used to answer questions ranging from seasonal to millennial time scales. With the exception of tree rings, which were previously discussed on this post by Erin our reconstructions are often limited by errors in dating methods. However in some lakes, sediments are deposited in visible annual layers called varves. Varved sediments offer a unique situation where the temporal resolution necessary to determine annual to decadal changes relevant to a human lifetime can be achieved.

Figure 1. Varve sediment from Newbury, Vermont, USA. Note the alternating light and dark bands and different thicknesses. From Tufts University North American Glacial Varve Project

Figure 1. Varve sediment from Newbury, Vermont, USA. Note the alternating light and dark bands and different thicknesses. From Tufts University North American Glacial Varve Project

What are varves and where are they found?

Simply put, a varve is an annual layer of sediment that forms in distinct layers (Figure 1). A single year’s deposit includes a light (summer) layer and a dark (winter) layer.

Varves don’t form in all lakes, in fact they are found in very few. The main factor controlling varve formation is climate variability; there must be large seasonal differences in both temperature and precipitation. This sets up the succession of biotic life and the physical and chemical structure of the lake necessary to form the contrasting layers. Additionally, there needs to be no disturbance of the sediment once it is deposited. Processes such as underwater currents, sediment slumping (think underwater mudslides), degassing (air bubbles within the sediment), or bioturbation (organisms physically mixing the sediment) all mix the sediment layers and the annual deposits are lost (O’Sullivan, 1983). Continue reading

What can paleoecology offer Latin American archaeology?

By Audrey Cross

Archaeologists… they need help. They excavate sites, hopefully taking really good notes, ask for help from specialists, read, synthesize information, imagine past cultures and landscapes, theorize, question, and hopefully publish their findings. I don’t want to be an archaeologist, but since both of my parents were, it’s a part of me. Maybe without being an archaeologist myself, I can help them, though, because their work is best done with help from different types of specialists.

In the summer of 2012, I did a field school that my mother was running in the Rio Bravo Conservation Area in northwest Belize. My late mother had done work and run field schools there for as long as I’ve been alive, and I was finally getting a sense of what her work meant. Amongst the many facets of this field school that sparked my interest, the study of the nearby bajos got my mind thinking in terms of paleoecology.

Fig. 1. Members of the 2012 Maax Na field crew at Bolsa Verde, excavating a Mayan plaza. Perhaps 30m from the edge of this picture, there is a steep slope downwards towards to the bajo. (Photo by Audrey Cross)

Fig. 1. Members of the 2012 Maax Na field crew at Bolsa Verde, excavating a Mayan plaza. Perhaps 30m from the edge of this picture, there is a steep slope downwards towards to the bajo. (Photo by Audrey Cross)

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