(warm introspective music) - Hello, I'm Joe Kelley.

I'm a marine geologist at the University of Maine.

I study the geology of the sea floor and coastlines.

And we're here to look at how those kinds of come together in Acadia National Park, this is Thompson Island, understanding how water changes where it is on the Earth over ti I mean, the shoreline is often called timeless, but it's really just constantly We'll see some evidence later when we look around here for the fact that the ocean was hundreds of feet over our head just 10,000 years ago, and hundreds of feet below us within that same interval.

Here today, we're gonna be consi what's happening right now.

Sea level is rising.

And this particular place is nothing unusual.

You can see what we'll be lookin almost any place along the coast There's evidence that the ocean' We can look around and see thing that would not look this way if the ocean were at the same elevation all of the time.

Here, you can see the way it's eroding along the edge here.

There's tree stumps where mature trees have come into contact with the ocean and died and been cut off by the park service or fallen into the water.

These are mature trees.

They couldn't be born in this en They were born when the shoreline was out there.

But the shoreline has come to me because the ocean has risen.

And the accoutrements of our society are around us too.

These are the remnants of fire p They're all over this area.

The park service put them in.

And the ocean has come and remov To protect them, you can see these granite blocks that were emplaced, nobody remembers now, maybe 50 y to kind of hold the shoreline in They've been ineffective.

The ocean has come around it.

And then you can even sort of ge for how much the shoreline has changed here by considering that these rocks were probably put right at the e of what was the upland at that t (warm introspective music) We're at another common coastal along the Maine coast.

This is Thompson Island, but beh you can see this grassy area her It's a special kind of grass.

This is a salt marsh.

And this particular grass here is called salt hay because in the olden days, the colonists used to graze their cows on it.

But what's important to us here is that this grass lives within a vertical range of about, oh, five or six inches It can't go above it because it will be outcompeted by the upland plants.

It can't go below it because the ocean will drown it.

That's how it's narrowly confine between mean high water, the average height of high tide, and the highest high water that will happen on a full moon or a new moon when the tides are unusually hig So it's trapped.

It can't move.

What's astounding is that if we This is a park, we can't core he but if we could drill down here, we would come up with meters and of peat from this plant always living in the same envelope of the tidal range between mean high water and mean highest high water.

But we can go down meters below this, 10 feet, and it'll be the same plant.

So it tracks the fact that the ocean level has risen because this plant can only live in that narrow restricted range.

We have means to radiocarbon date this plant from the bottom.

I can know when that was mean hi and subsequently track it coming up through cores.

And we've done that all along the Maine coast and been able to measure how sea level has risen along the coast over the last few thousand years.

So there's been a huge addition of water to the ocean, and it's gotten warmer, which means it's expanded and takes up room, but so much so that the shorelin is just literally being driven l by this rise in the ocean.

(warm introspective music) Over here is the Bar Harbor tide Tide gauges are devices that are installed by the federal government to measure and predict the tides And they exist in all US cities.

This one was built in 1947, Portland was in 1912, and others go into the 1800s.

And they're very good at that.

They help us predict tides.

But by the 1940s, when this was people began looking at the reco and they observed that the tides just didn't go up and down.

They went up more than they went And as a consequence, they came to the conclusion that contemporary sea level is r Here, it has risen at 2.3 millimeters per year.

Seems small, but it's every year In my lifetime, the water level here has risen 6.3 inches.

That's a fair amount.

That's the base level.

In a storm, of course, it's much And that's happening all over th The water is just slowly but surely coming up, and we're finding areas, particularly manmade land like this is a parking lot here, the Portland waterfront, will be underwater more and more as the ocean simply comes up.

These structures were built at a different time to a different level of the ocea and now they're succumbing to th that the ocean is rising.

(boat engine rumbling) (warm introspective music) Behind me is a sea cave, it's called Anemone Cave, and it's built into this cliff h of granite and some other rocks.

But what's important to us about is that it's where caves along the ocean have to be.

It's pretty much at the high wat the average level of high tide.

You can't form a cave above high tide in this kind of rock because the waves don't get there often enough, and you can't form it below it because there's no way to excava So a cave like this marks the average level of high tide until it collapses, but then a new cave will form.

We'll see that there are other caves on this island and in other places that are well above the present level of the ocean, suggesting to us that the ocean, at one point in the past was much higher than today.

If we were standing here 15,000 there would be glaciers receding in the distance, but they would be what are called tidewater.

They'd float up and down with th And this area that we're standing on right here just above the present sea level would have been about 150 feet d (inquisitive music) Behind me down below there is Monument Cove.

Now, it's a beautiful cove.

It's Boulder Beach.

You could see the big, rounded boulders of granite and the cliffs.

Common enough scene on the Maine This is a rather spectacular exa but there are beaches like this, there are cliffs like this, and there's a feature like this I'll talk about in a moment.

But to point out the boulders, people think of a beach as always been sand.

A beach is a deposit formed by w Here, there's no sand available, and so the waves have made a bea out of big, round granite boulde The rock erodes a bit, those blocks come off, they're a and truly in a winter of storms, they're rounded into almost sphe Boulder Beach, always at high ti you're not gonna find one down below necessarily, but then against the sea cliff in the backdrop, you can see a standing column of and it is bedrock.

It's attached to the granite at the bottom.

It's not something that moved th And it's an erosional feature.

Once it was a cave.

There used to be an arch over it It was an arch, a sea arch once.

It was a cave.

But it's evolved down to now that's all gone, and we have the freestanding sea And again, these exist pretty much at mean high water.

If you find them higher than tha well, then the water had to be higher than that because these don't form overnig These take some time to form.

But here we see a beautiful exam Today is a really beautiful, calm summer day.

These are not the conditions under which this beach formed or is even maintained.

In the winter, it is very differ We couldn't come down here.

The waves could even be crashing up this high.

Spray certainly would be.

And that's when the waves can co and quarry these large granite b You might think, "Well, can a wave move those?"

A wave can move those easily.

There's rocks all around me here that have been thrown up from below by storm waves.

So winter is the time.

Not easy to get to in the winter, quite dangerous.

I wouldn't be here in a big wint But that's when those boulders a And now that they've been freed up and are loose, literally waves will pick them u and smash them against that cliff in the background, continuing to erode it in.

And that process will just conti Next, we're going to go to a spot about 220 feet above this, and we're gonna look for some similar features to what we've seen: caves, cliffs, boulder beaches, and sea stacks, but not at sea level anymore.

We're gonna go to where the ocean once was, 200 or so feet above this elevat (inquisitive music) This is a cave.

You can see well into it.

And there's a rounded boulder in the very back of it.

But we're not at sea level today This is a paleo sea cave, 'cause the only way you can form a cave like this is for waves to break against th And if it were glaciers, you'd expect angular broken up rock fragments.

But when you look in there, you can see a spherical rock.

Probably the last big storm, the ice was still melting away back on the mainland, and the sea level was high because the ice weighed so much, it pushed the Earth's crust down and waves were rolling in here.

We're about 220 feet above contemporary sea level, but it's the same kind of featur we would see down below, the sea cliff, the sea cave.

If you could be here, well, of course you'd be under w I mean, the water would be right But there would've been no trees, obviously.

It would have been the ocean.

But then as the glaciers melted the land lifted up higher and hi to its normal elevation where it and the ocean fell, there still would have been no t It was a very cold climate then, It would take I'm guessing 1000 or 2000 years for plants to be able to come in here, colonize this, and eventually some trees would start to grow.

But certainly the indigenous people who lived in this area knew of this, nice place to go on a hot day to camp, maybe.

It's granite above and below, so there's no archeology site he You can't dig down and find anyt But I'm sure this has been used by many people for a very long period of time.

(water rushing) (inquisitive music) I'm here on Day Mountain in Acadia National Park.

It's a forest today, but it wasn I'm staring off here to the nort the direction from which our winter storm waves come.

And at the end of the last Ice A the Earth's crust was lowered he and the ocean came in.

And this was the shoreline.

Behind me was a sea cliff.

And specifically behind me right is a paleo or an ancient sea sta much like the one we observed down on Monument Cove.

Now, this would have been active for probably no more than 500 years 15,000 years ago, but waves would have struck here Nobody probably lived here then.

In fact, certainly nobody did.

And again, as the water went bac this would have become a tundra But for a brief period of time, 220 feet above modern sea level, this was the shoreline.

And if you really wanna come here, this is Day Mountain.

We came off the carriage path and you can walk along the lengt We're not gonna go there, but there's a boulder beach about a half a mile along that's really spectacular.

Seen a lot of changes in water volume in the ocean.

As the ice melted, the ocean ros the ice pushed the land's crust down and the ocean came in.

I'll thank you for watching.

You can see this and other thing at the Climate Change Institute at the University of Maine.