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Oh that's deep

08 Jul 2020 | News Roundup

Sea level rise would be a complicated topic even if it were not politicized. People often talk as though the seabed were like a bathtub, rigid and immobile, into which water either pours or does not. But it’s not; it rises and falls in complex local patterns, it erodes and accumulates, it shifts about. And it seems to be drifting downward if you get our drift. Which is continental, because a new study says thanks to land masses moving away from one another the seas are about 250 metres deeper than they were in the heyday of the dinosaurs and the seabeds are older than they’ve ever been. The effect on ocean currents, heat absorption and climate is… unclear.

It’s strange to realize that, deep as the seas are, they’re not very deep, in the sense that you wouldn’t think a 2.3 mile car ride very far. You may have heard that if the Earth were the size of a billiard ball it would be smoother, a very cool factoid lacking just one key quality: accuracy. Actually the Earth’s surface is rough, like sandpaper. But there is an important truth hidden in that urban legend: The mighty mountains and ocean depths that stir our souls are as grains of sand to the Earth. If our planet were the size of a billiard ball, (namely 5.715 cm give or take .127 mm) Mt. Everest would be 0.04 millimetres high, which would certainly simplify one item on the old bucket list. And the awesome Marianas Trench would be barely bigger, at 0.045 mm. (Don’t ask how big you’d be unless you fancy a session in the Total Perspective Vortex.)

So yes, even the Marianas Trench is nothing to the planet, despite the intricate way life depends not just on oceans but ocean tides. As to the importance of ocean depth to the biosphere, well, it’s hard to tell, isn’t it? Back when Allosaurus roamed the Earth, there were very high levels of CO2 and it was warmer (which are not causally related) and despite Al Gore’s blather about a “nature hike through the Book of Revelation” life was doing pretty well… except the stuff that blundered into the path of Allosaurus. But how much of the warmth, and biological abundance, is related to the oceans being relatively shallower around the slowly separating Laurasia and Gondwana? Did it contribute to the Jurassic being more lush than the Triassic? And if so how? It’s very complicated.

It’s even hard to know what exactly we’re trying to measure when it comes to current “sea-level rise” given that some places, including study author Krister Karlsen’s native Norway, have risen hundreds of metres since the ice last retreated and are still rising a few millimetres a year in a rebound from the glaciers’ crushing mass. But we have bigger fish to fry here, possibly caught at greater depths.

Are deeper oceans bad for life? Are the currents different? How does this depth, and capacity to store more water, affect other processes including climate? Notwithstanding the science being settled, no one knows. But over the last 2.5 million years the planet has seen some very harsh conditions for life, with prolonged glaciations and desertification proving that cold is bad and warmth is good. Does it also prove deep oceans are bad for life?

If so, there’s hope on the horizon. Regrettably it’s the geological horizon. According to this study, continental drift has moved the various bits of land that resulted when Pangaea broke up as far apart as they can get, and the farther apart they are the older and deeper the seabed gets. Now they should start moving back together again to form a new supercontinent for which the boring name Pangaea Proxima has been proposed. Before Pangaea there was Rodinia c. a billion years ago and “Earlier yet, the supercontinent Nuna might have existed more than 1.5 billion years ago.”

Those names sure beat calling them Pangaea I, II and III or Pangaea Praevia or some dumb thing. But focus on the “might have” there. Don’t we know? Well, it turns out we don’t. In fact, the article says, “whether this cycle is related to a sea level supercycle remains uncertain. ‘It's hard to say anything about the regularity of such a possible cycle,’ says Karlsen.”

With all this uncertainty, it’s important to hang on to the key point: Sea levels are rising because of bad people doing bad things and it will be bad for the good things. For instance we noted last week that after years of warnings that the oceans cannot absorb the man-made CO2 that therefore hangs around in the air cooking the planet and it’s a catastrophe, we were suddenly told the oceans were absorbing too much man-made CO2 and it’s a catastrophe. But this week we’re again told they can’t absorb enough of it, at least in the western Arctic Ocean and, you’ll never guess, it’s a catastrophe.

That’s always the punchline, which at least saves you the trouble of listening carefully to the joke. Thus “Thresholds of mangrove survival under rapid sea level rise” warns us that mangroves cannot cope with the supposed recent doubling in sea-level rise although “The response of mangroves to high rates of relative sea level rise (RSLR) is poorly understood.”

In fact NASA is boasting that this November it will launch the best “state-of-the-art” satellite ever to “collect the most accurate data yet on sea level—a key indicator of how Earth's warming climate is affecting the oceans, weather and coastlines.” Not whether, you notice. They already made the finding. Now they just need to corral suitable data.

They’re quite up-front about it. NASA boasts that “These measurements are important because the oceans and atmosphere are tightly connected. ‘We're changing our climate, and the clearest signal of that is the rising oceans,’ said Josh Willis, the mission's project scientist at JPL. ‘More than 90% of the heat trapped by greenhouse gases is going into the ocean.’ That heat causes seawater to expand, accounting for about one-third of the global average of modern-day sea level rise. Meltwater from glaciers and ice sheets account for the rest. ‘For climate science, what we need to know is not just sea level today, but sea level compared to 20 years ago. We need long records to do climate science,’ said Willis.”

Um if you don’t even know how sea level today compares to 20 years ago, let alone 2000 or 2 million or 200 million, how do you already know that the clearest signal that “we” are changing our climate is rising oceans, and that about a third is expanding seawater and two-thirds is meltwater? Verdict first, huh?

One comment on “Oh that's deep”

  1. The continents "float" on a ball of magma. When ice builds up at the poles during an ice age, it pushes the northern parts of the continents down, and raises the southern parts of the continents up. It is much like when you get onto a floating surf board at one end: your weight pushes the end you are climbing onto into the water, and the other end goes up into the air. (Except that the continental movements are less dramatic.) At the same time as Norway is springing back up after the weight of the last ice age melted, the south of Spain and France and Italy are going down into the Mediteranean Sea. That's why some of the caves along the south coast that were occupied by Neanderthal and early modern humans 40,000 years ago are now under water. I'm guessing the same phenomenon explains why that recently discovered ochre mine in an underwater cave in Mexico Yucatan Peninsula was above water 8,000 years ago when it was being mined.

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