How does one establish possible relationships between rates of sea level rise and climate fluctuations? The predictions of future rates of sea level rise are invaluable to coastal inhabitants, and it is exactly these rates Professor Ellen Thomas is hoping to determine in her research.

One of the ways one could determine these rates is to look at the sea level rise rates of the past. Salt marshes are ideal for this research for the following reasons: Basically, in a salt marsh a lot of grasses are growing, and when those grasses die, their roots remain. The roots do not rot, because there is so much organic material there isn’t enough oxygen present to rot it all. In the roots of these grasses sand is present, trapped amid the tendrils. If the sediment (deposited by the roots and sand) piled up at the same rate the sea level rose, they would stay exactly at equilibrium. The environment would stay the same, though it would move inland, because the sea is rising.

However, in reality, the rate of sediment accumulation and the rate of sea rise are not the same. The rates are close but they vary. This creates a unique problem if a scientist wants to roughly see how fast the sea is coming up. Professor Thomas wanted to determine the age of the earth at specific depths below the present day marsh surface, and the marsh surface of two thousand years ago is located beneath the marsh surface of the present.

The problem dealing with Long Island Sound is the difference of heights of the eastern and western end of the Sound. The intertidal zone is approximately 2.2 vertical meters on the western end, but only 0.8 vertical meters on the eastern end. There is a change in tidal range. Thus, if you say the rise has been somewhere within 2.2 meters that is not precise enough. Professor Thomas wanted to know exactly what place inbetween high and low tide the foraminifera could have lived. To calculate this she looked at the foraminifera fossils.

Foraminifera are microscopic organisms at the base of the food chain. Scientists look at the foraminifera because they live in zones parallel to mean sea level. Because foraminifera are sea dwelling organisms they cannot survive in dry environments. Now, in the intertidal zone at high water, part of the zone is dry, thus the name intertidal. This portion is only covered by sea at high tide. And so, the higher you get, the less often a specific spot is covered by water, because not all high tides are equal. There are spring tides and neap tides for instance. And so, there are spots that are covered even in the lousiest neap tides, but there are other spots that are only covered by the highest high tide. There are even areas that are just covered if you have a big storm coming in during high tide. And so, higher and higher elevations are less and less of the time under water. Fewer and fewer foraminifera survive because they are sea creatures and only a very few species can survive exposure to the air. Using slices of peat core and utilizing the aforementioned benthic foraminifera fossils Professor Thomas reconstructs the type of environment that existed thousands of years ago.

The peat samples are thus extremely important. Before Professor Thomas works on a marsh she "must figure out what it looks like on the ground." Using a hard corer she and her associates walk in a grid and then at right angles until the cores are spaced about twenty meters apart. When Professor Thomas sees something strange in-between two cores the spot is scrutinized.

Professor Thomas uses a dating system based on a naturally occuring radioactive isotope called Carbon 14 or C14 for short. As Professor Thomas explained: "Carbon fourteen does not ‘decompose’, it ‘decays’ is the official word." It is naturally occurring, but it is not stable. It is made in the upper atmosphere by intense radiation from the sun which hits nitrogen, 80 % of the atmosphere. Professor Thomas explained: "Nitrogen has fourteen protons and when zapped with high energy radiation from the sun, some of the nitrogen fourteen gets changed into carbon fourteen by loss of an electron. Those free carbons are oxidized and they get into carbon dioxide. That means that carbon dioxide, containing carbon fourteen, is taken up by plants in photosynthesis." In the atmosphere 14 C is made continuously by this high radiation from the sun. Once caught in a plant, it is out of contact with the atmosphere. If the existing carbon fourteen decays, the plant contains less and less carbon fourteen. The amount of carbon fourteen that you find in an object, such as food, tells you how long ago that object was formed from the atmosphere. "About half of the carbon decays in five thousand five hundred or something years." And so, if one finds pieces of wood or pieces of plant or root, they can be analyzed. "You know how much any given object or organism should have if it formed nowadays, so from the difference between those we can derive how old it actually is."

And so we use various isotopes to date various things. Carbon fourteen is not ideal for older material because it decays in five thousand five hundred years. All the isotopic methods follow the same principle: you have something radioactive occurring naturally trapped in the sediment and it starts to decay. With time there is less and less and less and so you just measure how much of the material is left. A little math and you can determine the age.

Interesting enough, earthquakes may account for certain discrepancies in the information Professor Thomas has gathered. She started reconstructing rates of sea level rise over the last two thousand years. She used a dating method using the benthic foraminifera, invented by a group of people in Nova Scotia, namely a man named Dave Scott. Later, Professor Thomas and her associates started asking questions, such as: is this method reliable at varying tidal ranges? Long Island Sound is a superb location for such experiments because from east to west, the tidal range changes. Professor Thomas had a lot of curves reconstructed from the data on the foraminifera and from dating the sediment. Plotting this all together she deduced results parallel to the rate of sea level rise.

And so, Professor Thomas was just looking at yet another marsh to construct one of those curves. She did so, and sure enough a really nicely matching curve was plotted, but to complicate things tidal marshes are heterogeneous environments. There is an astounding amount of variability. If you have just one core a scientist can’t trust it, therefore Professor Thomas always does two or three cores. In this specific instance she drilled a core inland and another core further out to Long Island Sound. There was a strange discrepancy in the cores however, i.e., the age of certain slabs of earth did not match up. One possible hypothesis to explain this disparity in dates, is an earthquake. An earthquake may have caused the land to go down, thus making it seem as though the water level had risen higher. There is no way to tell the difference between these two phenomena without peat samples, also known as cores. One sample indicated the sea had risen up faster than the rate of rise of the land, but that simply is not possible because the sea goes up at the same rate everywhere. A drop in the land could explain this geological anomaly.

If one subtracts the curves, the difference between elevations, one finds a section which sunk rapidly. This suggests a number of earthquakes over the last eight hundred years or so. Each earthquake amazingly "displaced the seaward side of the faultline by about a foot or so".

Another crucial aspect of Professor Thomas’s research involves anoxia in Long Island Sound. Anoxia is the absence of oxygen in cold waters beneath the surface. This situation is toxic for organisms that require oxygen and thus all multicellular organisms perish. Plants that photosynthesize in the ocean float (in order to absorb sunlight) and these microscopic plants need the same fertilizers as plants on land. These elements are nitrogen and phosphorus and they must come from the land by weathering or the oxidation of organic matter. Some bacteria fix nitrogen and then the nitrogen is used by plants.

Professor Thomas explained that prior to colonization, Connecticut was probably covered with forest. In a forested environment a lot of the phosphorus and nitrogen are being used and reused by the trees, so not much makes it into the Sound. With colonization this changes drastically due to the amount of clear cutting. In addition to the increased nitrogen and phosphorus, according to the EPA (Environmental Protection Agency) the largest source of enriched nitrogen and phosphorus is sewage treatment plants. Sewage treatment plants attempt to get bacteria and other dangerous material out, but it’s all organic matter (sewage), therefore, it is enriched in nitrogen and phosphorus. This enriched nitrogen and phosphorus makes it into the rivers. The algae thrive, causing, in the immortal words of Professor Thomas "enormous algae blooms". This is bad because the Sound has a depth of about forty meters maximum. The sun shines on top but the deeper water remains cold. The density of the surface waters is much lower than the density of the water beneath. This causes stratification. The algae photosynthesize on the surface. When they die, they fall to the bottom where they rot. The decomposition process requires oxygen and eventually the oxygen at the bottom of the Sound is consumed. New oxygen cannot reach the bottom due to the stratification. The first time anoxia killed organisms is documented in 1971.

Professor Thomas’s research is absolutely vital to coastal inhabitants, scientists, and those curious intellectuals who want to know about the past in the hopes that the future might be a brighter place. Perhaps one day, more reseach will be done involving the Sound and people will attempt to ameliorate the devastating effects pollution and New York sewage plants have caused.