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On the Level

July 30, 2009
Paleontological field party on a beach ridge east of Churchill, Manitoba (photo David Rudkin, Royal Ontario Museum)

Paleontological field party on a beach ridge (an ancient beach) east of Churchill, Manitoba (photo © David Rudkin, Royal Ontario Museum)

I am often struck by the shock with which many in the media seem to greet the news that global sea level may be rising. No, I am not a global warming denier. We are using up the Earth’s precious carbon resources in a hasty, thoughtless manner, and this is bound to have negative outcomes. Climate change is just one of these, and sea level rise is obviously a likely outcome of climatic warming.

What I find somewhat surprising is the static view of the world that seems to be so deeply ingrained in so many people. The media in general remind me of a bunch of oldtimers sitting on the porch of the general store, talking about “young people these days” and “whatever will they think of next.” Note to the media: constant change is one of the basic truths that underlie the geological record. If the sea isn’t rising, it is falling. And if the world isn’t getting warmer, then it is getting colder.

One of the most interesting aspects of sea level change is that it is a local phenomenon, as well as a global one. On a local scale, the sea can be rising in one place while it becomes lower elsewhere. This is because sea level is relative: it is linked to both the rise and fall of the ocean’s surface, and the rise or fall of the shore on which we happen to be standing (the world’s landmasses are in both horizontal and vertical motion, though at rates that we cannot usually perceive directly).

Ed Dobrzanski stands beside ancient beach ridges at Button Bay, Hudson Bay. Beach ridges extend inland from Button Bay, providing abundant and often graphic evidence that the land has steadily rising (and local relative sea level falling) as a result of post-glacial rebound.

Ed Dobrzanski stands beside ancient beach ridges at Button Bay, Hudson Bay. Beach ridges extend inland from Button Bay, providing abundant and often graphic evidence that the land has been steadily rising (and local relative sea level falling) as a result of post-glacial rebound.

I thought of this last week, as my family was visiting old haunts near the mouth of the Bay of Fundy, New Brunswick (for those of you who have read my other posts: yes, I did look for jellyfish the whole time, but unfortunately I didn’t find any). What I did see was a fabulous geological story that I had not previously been aware of.

One day we took the ferry from Grand Manan Island to Whitehead Island, then wandered to the beach near the Whitehead lighthouse. As we walked along the beach near the water line, I began to notice wood sticking out of the gravel. At first, I thought that this was random driftwood. But then I began to notice that most of the pieces of wood were oriented near-vertical. Each of them rose out of the gravel into the air in exactly the way that floated-in pieces of driftwood do not. When I saw tree stumps sticking out of the beach in places, I developed an inkling of the true story: the wood represents the remnants of an old forest that is gradually disappearing beneath the sea, suggesting that the relative sea level is rising on this shore of Whitehead Island.

Tree stump buried in the beach on Whitehead Island

Tree stump buried in the beach on Whitehead Island

Later, I saw information describing a much better-preserved “drowned forest” and peat layer along the shore in front of Castalia Marsh, on Grand Manan itself. The wood, which has been carbon dated to more than three thousand years old, consists of stumps, roots, and other wood from conifers such as hemlock or spruce. These are embedded within the thick peat, which is itself composed of an immense quantity of compressed plant fibre. My friend Dick Grant, a retired geologist, kindly offered to show us the deposit at Castalia. So my family met up with Dick and his daughter Hannah, with dogs in tow (or, more realistically, the dogs were towing us).

Dick Grant with Noni at the beach beside Castalia Marsh, Grand Manan Island

Dick Grant with Noni at the beach beside Castalia Marsh, Grand Manan Island

The peat layer is only exposed when the sea is several feet below the high tide mark. Tree stumps and roots are visible within the peat, and when one sees the entire assemblage it is remarkably easy to imagine the ancient community. The wood is wonderfully preserved and unmineralized. When you hold a piece of it, it is very difficult to appreciate that it comes from trees that grew long before the time of the Roman Empire. The dogs were not burdened by these thoughts, and the two labs occupied themselves with pulling wood out of the peat and tearing it to bits with their teeth. It clearly had a superb vintage bouquet.

The stump that Dick and Noni were examining

One of the stumps that Dick and Noni were examining

This deposit appears to be part of a fascinating, continuing geological story. The peat in front of the modern beach ridge may have been deposited in a low-lying wood, and perhaps also under saltmarsh conditions. If sea level is rising in this area, then the beach is moving landward over the peat, and the peat to seaward is continuously eroding away.

The peat horizon is being rapidly eroded by the sea (Keita for scale)

The peat horizon is being rapidly eroded by the sea (Keita for scale)

A large quantity of wood is embedded in the peat

A large quantity of wood is embedded in the peat

Behind the beach is a semi-enclosed embayment, and behind that is saltmarsh and low coniferous trees. The seaward edge of the saltmarsh also exhibits a thick, eroded peat deposit. Meanwhile, trees along the front of the low-lying wood are now dead, possibly killed by increasingly salty conditions. All of these features appear to be consistent with a gradual sea level rise; the wood-salt marsh-embayment-beach could be considered as a conveyor belt that is being gradually fed into the sea.

Dead trees at the back of the saltmarsh may have been killed by an ongoing sea level rise.

Dead trees at the back of the saltmarsh may have been killed by an ongoing sea level rise.

Anyway, it seems to make a nice story, at least to my eye. But much detailed scientific work would need to be done to determine if such an interpretation is, in fact, correct. As Dick and I discussed all of this, the sea was beginning to rise over the peat. The dogs were engaged with their own concerns, as important to the grand scheme of things as any of our scientific considerations:

labs1

I hadn’t really considered dogs as agents of erosion, but seeing how they worked on the wood in this deposit, I have had to modify this opinion (I will try to add a video clip after I get home).

© Graham Young, 2009

(For general information on Castalia Marsh and the geology of Grand Manan, I referred to J. Gregory McHone’s Grand Manan Geology: Excursions in Natural History, which was kindly provided by the author.)

2 Comments leave one →
  1. Seahome permalink
    July 31, 2009 11:32 am

    Very well done post. I seldom see such well integrated text & pictures. A very interesting subject. We are all aware of sea level rise but often forget that the land is vertically flexible too. Thanks.

  2. August 4, 2009 1:33 am

    Years ago, before i entered my tertiary education, someone made a remark that the world was then ran by people holding qualifications like B(Econs), BA, B(Business), LLB (law degree), BA … and so on, and those are the businessman, CEOs, politicians, financier, brokers, bankers… and even there were science or medical graduates, they switched field, to become businessman (multi-leveled direct selling company…health plan..) So, that person advised me to take up business studies, finance, marketing and so on, to equip me the strength to jostle to the top of the world.

    He also advised me against taking up science subjects, because scientists would always worked under the above said group of people and never had the chance to amass wealth and fame aplenty.

    Well, I forgave him, given the custom of the society which was directed by the need to earning more.

    Today, I wourld have to agree that what he said was actually true, but that is the whole problem isn’t it!!!

    The world is ran by a bunch of people who do not understand the working of the planet, the eco-system, the importance of bio-diversity, and they even overlook the needs and basic functions of our bodies.

    That’s why we have all the environmental problems and deceases. Thanks to free market economy…

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