Emerita analoga, aka sand crabs or sand fleas, live buried in the swash zone, dug in tail-first and facing the water, with only its eyes and a pair of antennae poking above the surface. Each time a wave drains back over it, the crab uncoils a second set of feathery antennae and combs the backwash for plankton. They migrate up and down the beach with the tide to stay in that band, and on the right fine-sand beach they pack in by the thousands per square meter, so one bed can stipple a whole patch of sand with V’s.

Backwash thins and speeds up as it runs down the slope, and by the time it’s a sheet a few millimeters deep it’s moving fast enough that anything sticking up throws a standing wake, the same way a rock in a quick creek kicks up a fixed little peak. It holds in place because the water is draining downhill faster than the wake can climb back up against it, so the disturbance gets pinned right where the obstacle is. The flow scours a shallow horseshoe around the crab and trails that wake behind it, which is why the point of the V sits at the animal and the arms open seaward. Finding bait is pretty easy when they’re around.

But most of the V’s on the sand aren’t crabs. Walk ten feet up the face to where the sand is tiled edge to edge with the same diamond pattern and start checking the points and you’ll find nothing there. No crab, no shell, no pebble, no bump at the apex of any of them. These are rhomboid marks, and they don’t need an animal, or an obstacle of any kind. The water makes them on its own.

As the thin sheet of backwash drains down the slope, it organizes itself into a repeating lattice, the way fast shallow water patterns up into a regular grid instead of running smooth. The draining flow sets up standing waves, with the angle of the diamonds tied to how fast the sheet moves against the slope. The whole field freezes the direction of the last sheet to leave the beach.

In order to figure out what caused the shape, check the apex. A V with a little lump at its landward point, especially a few of them clustered together, is something solid sitting in the flow, usually a crab, sometimes a shell or the tube of a buried worm. A clean grid of V’s across open sand with nothing at any of the points is just the backwash itself.

Further reading:

Sand crabs

Backwash

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Turbines pull momentum out of the air, and downwind of the array sits a wake of slower wind that can run for tens of kilometers. Less wind over the water means less energy feeding the waves growing under it. The modeling puts the result at a few percent off the wave height near the farm, fading to almost nothing within twenty kilometers or so. It lands mostly on the local chop being generated right there, not on the long-period groundswell that was generated far away.

A bottom-mounted turbine sits on a single pile maybe ten meters across. Setting that against a swell whose crests run two or three hundred meters apart, the pile is a pencil standing in a doorway to the shelf. It scatters a sliver of energy, nudges the direction a touch, and the effect on wave height comes in under a few percent.

A few hundred piles in tidy rows looks like it should reflect waves back out to sea, the way evenly spaced bars on the seabed bounce a swell (Bragg reflection). The usual dismissal is that the spacing is wrong, that piles a kilometer apart would need a two-kilometer wave to resonate and surf is far shorter than that. The dismissal itself is wrong, however. The reflection also happens at higher multiples of the spacing, so a coarse grid does not fail to resonate, it just resonates with the swell at a higher order.

The piles block maybe a percent of each row, the rows are never perfectly spaced, and real swell shows up smeared across a band of periods and angles. Sharp reflection needs a dense, precise lattice and one clean wavelength, and a wind farm is none of those. A little energy comes back at a few specific frequencies, but most slips through.

So for the farms standing on the seabed today, the swell crosses the array and arrives about the way it left. If anything the water is slightly cleaner, since the wind the farm skims off would otherwise be stacking up chop.

Floating turbines are a bit of a different story. They do not stand on a pole, they ride on a platform of fat, half-submerged columns, and a column that wide compared to the wave does not diffract neatly. Idealized modeling has a single floating platform cutting the wave height behind it by more than half under the right conditions, with a shadow trailing about a kilometer downwave.

Whether a shadow a kilometer long still matters several kilometers down the line is genuinely unsettled, tangled up in how fast the wave field heals around the gap. The waves we ride should mostly survive the steel bolted to the seabed. The ones riding on top are worth watching.

This is an article based on a comment from Dr. Lonneke Goddijn-Murphy of SeaLetters on a previous article. If anyone has a question they want answered, I’d love to hear it.

Further reading:

Wind farms

Wind farms affecting surface waves

Floating wind farms

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At Scripps, my research focused on internal waves on the inner shelf, the region of the coastal ocean between roughly 10-100m depth and home to lots of physical and biological processes. I studied two specific types of internal waves: superinertial coastal trapped waves (CTWs) and shoaling non-linear internal waves (NLIWs).

The first chapter is a rewrite of my first peer-reviewed paper, where I describe how these CTWs drive stronger currents than the tides do. The paper answers a question going back nearly 60 years in this region: why is the sea surface elevation at the semidiurnal frequency not correlated with the currents on the inner shelf?

To follow up this paper, we ran a nonlinear model that showed these waves are coherent over long distances, as in 100s of kilometers. We also reanalyzed the data to show that the inner shelf currents can actually be predictable, finding that more than half of the current 90 days out is explainable by this CTW signal. This paper is currently in review and one that I feel very proud of.

And to close out the dissertation, the final paper pivoted to detection of the NLIWs on a fiber optic instrument. Using machine learning algorithms from self-driving cars, I built an algorithm that automatically detects these waves on the instrument in real time and used it to show how these shoaling waves lead to a significant portion of the mixing on the inner shelf. This one will be submitted soon as I finish up a postdoc at Scripps.

All together, these three chapters add a bit of understanding to the inner shelf dynamics of the Southern California Bight, with applications to other regions where similar signatures have been observed: Tasmania, Hawaii, etc. for the CTWs and the Oregon coast, offshore of Japan, etc. for the NLIWs.

It has been a process of ups and downs, wave jokes a necessary evil in the field. This is one of the ups and it is nice to share some of the work that I have done with you; I hope you enjoyed this one.

Further Reading:

When my dissertation is published, I will send it to anyone interested.

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The gray was never really about cold water by itself. It requires cold water at the surface and a band of warmer air parked on top of it like a lid. The bigger the temperature jump between the two, the stronger the lid, and the better it traps the damp air underneath that cools and condenses into our morning cloud. The cold water matters mostly because it widens the gap, which is why our coast, fed by chilly northern water, gets so much more of this than the warm-watered East Coast ever does.

Warming the surface closes the temperature gap some. A smaller jump is a weaker lid, and a weaker lid holds less gray. So yes, warmer water should mean less marine layer. But the honest version of this argument is that the water is not dimming the clouds directly. It is loosening the lid that lets them pool near the coast. Warming waters look like the cloud base creeping higher, until some days it never really commits at all. The sun normally has to chew through a thick gray ceiling but meets a thinner one, and clears it earlier in the day.

You can watch this dial move across a single summer without any heatwave involved. June is the grayest month along the Southern California coast, then the gloom starts surrendering through July. A good chunk of that is the local water warming as the season runs on, and warming faster here than it does up north. Up in Northern California, where the water stays cold longer, the grayest stretch doesn’t show up until July, a full month behind us. The effect happens every year on its own without a heatwave, so a heatwave just turns the same knob harder.

So should the warmest ocean on record hand us a clear June this spring? The 20.6°C headline is mostly a northern, open-water number, with the core of the heat sitting up toward the Gulf of Alaska across something like eight million square kilometers of sea. May Gray answers to a much smaller patch, a thin band of water right off our coast. The California Current still drags cold water down from the north, and upwelling keeps pulling more up from the deep, so the coastal strip can hold its own temperature while the rest of the basin cooks.

It is plausible we get a shorter June Gloom this year, if that warm anomaly works its way down the coast and settles into the water off the Bight. But it leans on a lot of moving parts. Where the warm water actually pools, how hard the coastal winds blow, whether upwelling keeps the nearshore cold, and whether the El Niño now building on top of the heatwave nudges things one way or the other. Whether our particular stretch of coast gets to tan this spring is a toss-up.

Further Reading:

Marine layer

Warmer waters

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A 17-second North Pacific groundswell can hold waves at the coast for a week, the dominant period stepping down a second or two each day. A 9-second windswell can show up and be flat within a day or two. The difference between the two has to do with the generation offshore rather than anything at the break itself.

Wind dragging on the ocean surface starts by making short, choppy waves at the top of the spectrum. That wind blowing over a big enough patch of ocean works the surface into longer, bigger waves. A 20-second peak only emerges after days of sustained generation. Shorter storms only output shorter periods.

Back to the big storm: while the long end of the spectrum fills in slowly, the wind is still making 14-second, 12-second, 10-second, and shorter waves at the same time. We talk about “an 18-second swell” because that’s the dominant period at the buoy, but the whole mess is leaving the storm together.

Walter Munk’s 1963 work tracking Southern Ocean swells to Alaska showed how dramatically period controls travel speed in deep water. A 20-second wave moves at about 35 mph, but a 10-second wave moves at just half that. The further the waves travel, the more they spread out in time. Because of this, a storm 4,000 miles offshore sends its 18-second leading edge to the buoy more than a day before the 12-second component arrives.

But when the buoy reads 8 to 10-second primary with no long-period leading edge, we can expect a shorter run of swell. The storm didn’t blow long enough or over enough fetch to develop the longer period swell, so there is a smaller window of time to surf it. Short-period waves also dissipate much faster as they travel. The longer end of the wave spectrum crosses a basin without much energy loss, but the short stuff burns itself out within a few hundred miles. Most short-period swells at the coast are generated locally in the past day or two, not days to weeks before like the long period.

The one exception is a productive storm that sits close to the coast. North Pacific lows in winter sometimes track right past California, throwing 15 to 17-second swell from a few hundred miles offshore. The storm still had to last long enough to make those periods, so the spectrum is still there. But without much ocean distance to do the dispersion sorting, the longer and shorter components arrive bunched together. The event fires for a day or two and disappears. There are plenty of waves, just no slow tapering tail. Gotta get ‘em while they’re hot.

Further Reading:

Dispersion

Spectrum

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Behind your face are four pairs of air-filled cavities called the paranasal sinuses: maxillary under each cheekbone, frontal above the eyebrows, ethmoid between the eyes, and sphenoid tucked deep behind the nose. Each is lined with mucus and tiny hairs called cilia that constantly sweep debris toward the throat. They connect to the nasal cavity through small openings called ostia, typically 1 to 4 mm wide, about the width of a wooden pencil tip.

The maxillary sinus is the biggest of the four, roughly walnut-sized, and its drainage ostium sits not at the bottom of the cavity but near the top of the medial wall. The official medical phrasing is “poorly positioned for free drainage.” The frontal sinus is the other troublemaker, with what the literature calls the most complex and variable drainage of any paranasal sinus, routing everything through a twisting frontonasal duct before it can reach the nose. Basically, the drains are on the ceiling for both of these.

Physics is a pesky part of this problem as well. Water in a tube only a few millimeters across forms a concave meniscus, the molecules at the surface clinging to the walls and to each other strongly enough to support the column’s weight. The effect is called capillary action, and it’s the same mechanism that lets paper towels wick up spilled coffee against gravity. In your sinus ostia, it creates an air lock, preventing gravity from clearing the last close out.

At roughly 3.5% salinity, seawater is nearly four times saltier than the fluid in your tissues, hypertonic enough to pull water out of mucosal cells and stress the lining on contact. Cold makes this even worse, triggering vasodilation and a rush of mucus in the sinuses. The lining swells, narrowing the ostia further, sometimes closing them completely. The already small exit gets clamped down, and the water sits awaiting an awkward moment to emerge.

Eventually something tips the balance, often the first or second inversion of the day. Maybe you bend over to towel off your feet and the head angle finally beats the meniscus. Maybe the swelling subsides after an hour or two. Or maybe a sneeze creates enough pressure to break the seal on an unsuspecting guest. Around 35% of swimmers report nasal congestion after a session, and the timing of release is mostly unpredictable. The phenomenon is recognized enough that ENTs have a name for the chronic version, “swimmer’s sinusitis.”

Our sinuses evolved for breathing air, warming and humidifying it on the way to the lungs, with the mucus-and-cilia system handling the occasional bit of dust. Repeated head-first dunks in cold salt water came along later, and the design hasn’t caught up.

Further Reading:

Sinuses

Meniscus

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California Department of Fish and Wildlife confirmed in late March that starvation, not avian flu, is the primary cause. Brown pelicans and common murres are dying alongside the cormorants, almost all of them young birds in their first year. 2025 was an unusually strong breeding year for these species, which means a larger-than-usual cohort of juveniles is now competing for whatever food is available.

On September 9, 2025, the northeast Pacific reached the highest average temperature ever recorded in the basin: 20.6°C, nearly half a degree above any previous record. The marine heatwave responsible, designated NEP25A by NOAA, first emerged in the Gulf of Alaska that May and expanded through the summer to roughly 8 million square kilometers (about half a Russia), larger by area than any prior northeast Pacific heatwave on record. It shrank through October and November, then swelled again along the coast in December. As of early 2026 it persists, with an El Niño developing on top of it.

Warm surface water pushes anchovy and sardine schools deeper into cooler layers, away from some seabirds’ reach. A brown pelican can only dive about six feet, so a small change is significant. Common murres can dive much further, hundreds of feet, but each dive is intensive and burns lots of calories. A juvenile that hasn’t dialed in its hunting yet runs its energy budget into the red trying.

Warm surface water also resists mixing with the colder water below it. That matters because the deep water carries the nutrients (nitrate, phosphate, silicate) that phytoplankton need to grow. Less mixing means less fertilizer reaching the sunlight, and phytoplankton, the base of the food web, runs short. The community shifts from large, fat-rich diatoms toward smaller dinoflagellates. Their predators, zooplankton, follow: warm-water copepods are smaller and carry less fat than the subarctic species they replace, so a fish eating the same number of copepods gets fewer calories. Krill hit an 18-year low in southern California during the 2013-2016 Blob. Pyrosomes, gelatinous tube-shaped colonies that are essentially low-calorie filler, proliferate and absorb energy that would otherwise have moved up the chain.

Each link in the chain loses calories. A fish eating smaller, leaner copepods gets less energy from a meal, and a cormorant eating that fish gets less still. The bird has to catch more fish to compensate, but the fish are deeper than they used to be.

The 2013-2016 Blob, the previous benchmark for this kind of event, killed roughly a million common murres and 400,000 Cassin’s auklets along the same coastline. NEP25A is bigger by area and now in its second year. The juveniles washing up this spring are the cohort that would have started breeding around 2029.

Further Reading:

Marine heatwave tracker

Effect of heatwave on phytoplankton

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Most channel boards have four or six grooves running roughly parallel toward the tail, starting somewhere around the front fins and exiting at the back. The pitch is just short of a miracle cure: they generate lift by compressing water flow, push water toward the tail for “drive,” add bite on rail, and cut through tail rocker to flatten the back of the board. Like most cure-alls, these qualities don’t all hold up equally well.

The first issue is that parallel walls don’t compress flow along the length of the board. The compression-creates-lift story gets borrowed from single concaves, where a curved, narrowing surface really does squeeze water toward the tail, drop the pressure, and push the board up. That mechanism needs the curve to work. Channels run flat-walled and parallel, which is the geometry that doesn’t compress flow in the direction it matters. The Bernoulli explanation that fits a concave bottom gets applied to channels too, even though the shape isn’t doing the same thing.

The rocker effect is the part that holds up. Cutting half-inch grooves through a curved tail leaves a series of flatter planing surfaces in the back of the board, while the rail rocker stays kicked up where it needs to be for turns. Less curve under the planing surface means earlier planing and less drag at speed. It might be the most defensible thing channels actually do. Some shapers describe channels as a way to run extreme tail rocker without the board bogging under the back foot, which is the same effect in “feel” language.

When we search the peer-reviewed literature for surfboard hydrodynamics, we mostly find fins. Multiple CFD studies on three-fin and four-fin configurations, grooved fin designs, fin position, even pressure sensors embedded in fins on a river wave. But bottom contours barely show up. The closest thing to a direct test on channels is Riccardo Rossi’s CFD work for Firewire, where the channel-bottomed Sci-Fi showed lower drag and friction than the rounded-tail Omni, with the tail channels credited as a key factor. The boards also differed in tail shape and rocker, so the channels weren’t cleanly isolated. The same testing found that half an inch of tail rocker shifted dynamic lift by about 50%, which makes the rocker-straightening case stronger than the flow-compression one.

Despite the lack of literature, people still chase down channel-bottomed boards for heavy hollow waves in Western Australia and Indonesia, and the design hasn’t gone away despite half a century of competing alternatives. That kind of long anecdotal record carries real signal, just not the kind a controlled experiment would.

A study of two identical boards differing only in whether they have channels, tested side by side, has never been run. This would help close the gap between how confidently channels get explained and how little has actually been measured.

Further Reading:

CFD Comparison

Bernoulli Equation

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Inside a Sofar Spotter, a common surface wave buoy for shorter deployments, the GPS records where the hull sits in three dimensions 2.5 times per second. Older designs like the Datawell buoys use accelerometers and tilt sensors to get the same information a different way. Either way, the whole measurement comes from one point in the water, three axes of motion, and about half an hour of recording.

Water particles in a passing wave don’t just go up and down. They trace circles in deep water, moving forward on the crest and back in the trough, and the buoy rides those orbits. The diameter of each orbit at the surface is roughly equal to the wave height, so big waves make the buoy swing through big circles and small waves through small ones. Vertical motion tells us how tall the wave is, while horizontal motion at the same instant tells us which way it’s going. In deep water, the vertical and horizontal motions are locked a quarter-cycle apart, which is what makes the math work cleanly. The direction the wave is traveling shows up in whether that horizontal motion is mostly east-west, mostly north-south, or some mix of the two.

Thirty minutes of motion data gets fed through something called a Fast Fourier Transform, which splits a signal over time into its constituent frequencies. A 15-second swell shows up as a peak near 0.067 Hz (1 divided by 15). A 6-second wind chop shows up higher (1 divided by 6). The frequency spectrum is what a wave buoy actually produces, and everything else makes use of it. Significant wave height is a statistic computed from the area under the curve. Peak period is the frequency where the curve is tallest. A messy sea with several things happening at once turns into a clean plot of energy against frequency, where separate swells become separate peaks instead of overlapping confusion.

At each frequency, direction is encoded in how vertical motion correlates with horizontal motion. A wave from the west pulls the buoy up and east-west together. A wave from the south pulls up and north-south. Sorting those correlations by frequency gives us a bearing for each component of the seastate. More simply: if there are two swells, one from the south and one from the west, we can pick that out of the data. A second pair of correlations tells us how tightly the waves at a given frequency stack around that direction, which is where directional spread comes from. A clean groundswell shows up as a narrow peak with a sharp direction. Local wind chop smears across the compass as the buoy is tossed around.

While the measurement of offshore swells is relatively stable and straightforward, what arrives at the break takes a few more steps that introduce a lot of error in prediction. But we all know that about the forecasts.

Further Reading:

Sofar Ocean

Fourier Transform

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The biggest fossil fuel user is foam. A shaped 6’2” shortboard holds roughly a kilogram of foam. Both ingredients that make polyurethane foam, the polyol and the isocyanate, come from crude oil or natural gas. About a quarter to a third of the original blank never even makes it into the board, and even though it gets planed and sanded off during shaping, it still had to be produced to make the board.

The resin is the other heavyweight. A standard comp-glass shortboard soaks up about 1.2 kg of polyester resin across the lamination coats and the sanding coat. Also petroleum-based, styrene and polyester are both refined from oil. The fiberglass cloth, the stuff most people assume is the environmental villain due to its pervasive itchiness in insulation form, is made from melted sand and minerals. The stringer running down the middle is wood. Those two are about the only parts of your board that didn’t come out of an oil well.

Then there’s everything you bolt or stick onto the board. Fin boxes are plastic. A thruster set, made from about 200 grams of fiberglass-reinforced nylon, is roughly 70% petroleum by weight. The leash cord is urethane and the cuff is neoprene and nylon. Surf wax is paraffin, which is a direct byproduct of crude oil refining. If you run a traction pad, it’s likely EVA foam. The accessories don’t weigh much individually, but they add a few hundred grams of petroleum on top of the board.

Add it all up and a shortboard contains roughly 2.7 kg of petroleum-derived material. To produce those 2.7 kg of finished plastics and resins, you need an estimated 1.3 to 1.6 gallons of crude oil as feedstock. But raw materials are only part of the story. According to a lifecycle study by Sustainable Surf using data from Channel Islands and Firewire, a standard poly shortboard produces around 48 kg of CO2 from blank to surf shop. Manufacturing energy, running the shaping bay, heating resin, ventilation, is actually the single biggest contributor to that footprint.

For context, a petroleum-based neoprene wetsuit sits in roughly the same ballpark, somewhere between 55 and 77 kg of CO2 per suit depending on the study. Similar footprint to a board on a per-unit basis, but wetsuits wear out much faster unless you’re snapping your board yearly. Boards can last to double digit years if you take care of them. Over a five-year window, a surfer who replaces a wetsuit every 18 months racks up far more petroleum consumption than someone riding the same board the whole time.

The 48 kg of CO2 per board sounds like a number worth caring about until you compare it to getting yourself to the surf. A one-way flight from LAX to Honolulu puts roughly 280 kg of CO2 into the atmosphere per passenger. One surf trip to Hawaii wipes out the carbon math of about six surfboards.

The only scientifically valid reason for Locals Only.

Further Reading:

Lifecycle Study

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Seawater comes in at about 1,025 kg/m³. Surf wax, mostly paraffin with some beeswax and petroleum jelly mixed in, lands around 900 to 930 kg/m³. And the foam core of your board, whether PU or EPS, ranges from about 25 to 40 kg/m³. That makes wax roughly 90% as dense as water, while foam is about 3% as dense. The gap between foam and water is the reason your board floats: every liter of foam displaces seawater that outweighs it by roughly 995 grams, generating nearly a kilogram of buoyancy per liter. Wax displaces water too, but a liter of it only generates about 105 grams of net buoyancy. Same volume but only a tenth of the float.

A standard bar of Sex Wax weighs about 75 grams, with most brands falling between 75 and 85 grams per bar. Waxing up a fresh board, say a 40-liter midlength, takes roughly one bar. Archimedes told us the board will sink until the weight of displaced seawater equals the total weight it’s supporting - board, rider, and wax included. The extra 80 grams works out to about 0.08 liters of additional submersion, or 0.2% of your board’s volume.

How about if you surf a few times a week, reapply every couple sessions, and haven’t scraped in months? Maybe you’ve stacked three to five bars’ worth, somewhere between 240 and 400 grams of accumulated wax. The board sits an extra 0.25 to 0.4 liters deeper in the water. On a 40-liter board carrying an 80 kg surfer, that’s only about 1% of the board’s total displacement. Even the worst case, the board that is now gray with 500 to 800 grams of crusty wax buildup, loses maybe 0.5 to 0.8 liters of effective displacement, only around 1 to 2% of a 40-liter board.

Your lungs hold about 6 liters of air, and a single deep breath shifts a few liters of buoyancy, far more than months of wax accumulation. Your wetsuit absorbs a few hundred grams of water during a session too, riding on your body the whole time, and nobody loses sleep over that.

A single cup of seawater that seeps through a ding in the board weighs about 240 grams and contributes exactly zero buoyancy, because water doesn’t float in water. A neglected ding is costing you more float than a year of lazy wax habits ever could.

Layer it up, use a comb, whatever works to keep you on the board.

Further Reading:

Archimedes’ Principle

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Every wave that washes up the beach leaves behind a thin film of seawater in the spaces between sand grains. Seawater carries about 35 grams of dissolved salt per liter, mostly sodium chloride. When the sun heats the surface and that water evaporates, the salt has nowhere to go. It stays behind, clinging to the grain surfaces and concentrating in the water that remains.

Water deeper in the sand gets pulled upward through the narrow gaps between grains by capillary action, the same force that draws water up a paper towel. The smaller the spaces, the stronger the pull. Beach sand has pore spaces on the order of tenths of a millimeter, small enough to maintain a steady upward supply of moisture from the water table below. As fast as the surface evaporates, capillary forces are resupplying it with more salt water from underneath. It’s a conveyor belt for dissolved salt, continuously delivering NaCl to the evaporation front at the surface.

A 2016 study published in Scientific Reports by Geng, Boufadel, and Jackson measured pore-water salinity on an estuarine beach and found that evaporation drove near-surface concentrations to roughly double that of normal seawater. The effect was strongest in the upper intertidal zone during low tide on hot days, when the sand surface was exposed to air and the capillary fringe was actively pumping moisture upward. The deeper sand stayed closer to ambient ocean salinity while extra salt was concentrating right at the top.

Once the pore water at the surface reaches supersaturation, sodium chloride begins to crystallize. The crystals precipitate at the contact points between them, forming tiny mineral bridges that lock neighboring grains together. The same process destroys ancient stone buildings and monuments over centuries, salt crystals wedging into pore spaces and generating enough pressure to crack rock from the inside. On a beach, the result is less dramatic but mechanically identical: a thin brittle pancake of sand held together by crystalline NaCl cement, just waiting to be tossed and shattered.

The crust has almost no flexibility. Salt crystals are rigid and the connections between grains are thin. One footprint is enough to collapse the structure back into loose sand. Underneath, where evaporation hasn’t concentrated the salt, the grains never bonded in the first place.

The crust forms best on hot, calm days with low humidity, above the high tide line where the sand hasn’t been recently swashed. Fog or a high tide dissolves the crystals and resets the process and morning dew can weaken it. You’ll rarely feel the crunch on a beach that’s been washed by waves in the last few hours, but give the upper beach a full day of sun and it’ll be there.

Further Reading:

The paper

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The reason is that you’re not standing on the same beach, not really at least. Most sandy beach profiles are concave. Down near the low tide line, the slope might be two or three degrees. Up near the berm, where the high tide waterline sits, it can steepen to ten or fifteen. When the tide rises, waves stop interacting with the flat part and start hitting the steep part.

How a wave breaks depends on the relationship between the slope it encounters and its own steepness. There’s a ratio for this called the Iribarren number. A low Iribarren number, meaning a gentle slope relative to the wave steepness, produces spilling breakers. These are the mushy waves that crumble gradually and spend their energy across a wide surf zone. A high Iribarren number, steep slope relative to the wave, produces surging or collapsing breakers. These waves don’t fully break. They charge up the face and reflect back, sometimes retaining more than half their energy.

At low tide on a gentle slope, a wave might break fifty meters out and spend itself gradually on the way in. At high tide on the steep upper beachface, that same wave surges up a few meters of sand and comes right back. The energy that would have been chewed up by friction and turbulence across a wide, flat surf zone instead bounces off the steep face like sound off a wall. When that reflected water meets the next incoming wave, the two collide and stack. If you happen to be in the right place, you get launched.

That collision point also builds what’s called a beach step, a submerged ledge of coarse sand and shell at the base of the beachface where the backwash vortex dumps the heaviest material it’s carrying. It’s the little shelf you trip over wading out at high tide that doesn’t seem to be there at low tide.

Reef breaks get some backwash as well, but through a different mechanism. Roughly speaking, a reef is a fixed ledge. The slope doesn’t change with the tide, so the Iribarren number stays about the same. Backwash at a reef break has less to do with the reef and more to do with what’s behind it. If the wave breaks on the reef and the remaining energy runs into a cliff, a seawall, or a steep rocky shore, it reflects. At low tide though, this reflector may be out of the water and not reachable at all, so no backwash.

Further Reading:

Backwash

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Three systems usually tell your brain where you are in space. Your inner ear tracks rotation and acceleration using fluid-filled canals and tiny calcium crystals called otoliths. Your eyes relay what’s moving and what isn’t. And receptors in your muscles and joints register pressure and body position. When all three agree, you feel fine. Sitting on a boat (or board in the case of the wretched few) in a rolling swell, your inner ear says movement while your eyes on the horizon say everything’s still.

Of all the possible responses to confused spatial information, throwing up seems unnecessary. The going theory is that when sensory inputs stop making sense, the most likely explanation in the wild isn’t a boat: it’s a neurotoxin. Having eaten bad food, poisonous plants, or anything else that messes with motor control and perception, the body’s move is to purge whatever you ate. The response is so deeply ingrained that even fish can get seasick during aquarium transport.

People who spend time on boats like to say everyone has their frequency. Some particular combination of swell period, wave direction, boat size, and boat speed that’ll eventually get you. And that’s mostly right. Susceptibility varies by a factor of about 10,000 across the population, and roughly a third of people are highly prone under normal conditions. Women get it more than men, about 5:3. Kids peak around age 9 or 10 and gradually adapt. The only people who seem truly immune are those who’ve lost their vestibular system. In the late 1950s, NASA recruited eleven deaf men whose childhood meningitis had wiped out their inner ear function. They sat in rotating rooms for days without a hint of nausea while their hearing colleagues were gripping their chairs for hours.

Ever notice how the driver of the car almost never gets carsick? When you’re controlling the motion, your brain can predict what’s coming and the three signals line up. Passengers reading in the back seat don’t get the visual cue and tend to roll down the window. The same thing applies in surfing. Paddling, popping up, and riding are all activities where your brain is generating those movements and anticipating the feedback. But sitting still in a rolling lineup waiting for a set…

If you are one of the “unlucky” group with strong hearing and sensitive stomach, drugs like Dramamine can make a world of difference. Diphenhydramine, an antihistamine, blocks receptors in the vestibular system, turning the system down enough to not get sick. Unfortunately for the booze-cruisers among us, Dramamine and alcohol interact fiercely.

Both diphenhydramine and alcohol are central nervous system depressants, but they work through different pathways. Together, the sedation multiplies. Two ocean beers tend to hit like six. When taking it, it may actually be better to stay thirsty instead, my friends.

Further Reading:

Seasickness

Vestibular System

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Instruments go where ships go, and ships go where commerce sends them. The Northern Hemisphere has the bulk of commercial shipping routes, research institutions, and national ocean monitoring programs. NOAA’s buoy network alone stretches from the Bering Sea to Hawaii and from the Gulf of Mexico to the North Atlantic, with over 100 moored buoys operating at any given time. The Southern Hemisphere has no equivalent, and ship-based measurements of temperature, salinity, and carbon dioxide have always reflected the routes ships actually travel. The global south has been measured mostly in passing.

The South Atlantic, the South Pacific, and the Indian Ocean are all part of this story, not just the waters near Antarctica. The southern portions of every major basin have consistently thin coverage, with measurements collected opportunistically rather than systematically. The majority of ocean carbon observations come from routes that favor the Northern Hemisphere. The subtropics and tropics of the Southern Hemisphere are nearly as sparse as the subpolar regions.

The Southern Ocean represents the extreme case. For most of the 20th century, sustained in-situ observations there amounted to two sub-Antarctic moorings, one of which has since gone offline. Winter data were rarest of all, because research cruises don’t run in the Southern Ocean in winter. Nobody wants to be on a ship at 50°S in July. The consequence is that the entire pre-2000 Southern Ocean winter profile database contained less data than autonomous floats now collect there in a single year.

Being a connected ocean system and all, this undersampling biased what scientists thought they knew. Ocean heat content estimates for the Southern Hemisphere were running roughly 40% too low through much of the mid-20th century record, a finding that only became apparent once better observations existed to compare against. Models built on that incomplete historical record inherited the bias. Reanalysis products, which are ocean model simulations constrained by observations, are only as good as the data assimilated into them, and in the Southern Hemisphere, the data were thin in space and time and almost nonexistent in winter.

For wave forecasting, this creates a specific problem. The storm belts of the Southern Hemisphere, the roaring forties and furious fifties, are among the most energetic sea-states on the planet and generate swell that propagates across entire ocean basins. These are also the regions where numerical wave models have historically had the least in-situ validation data. A model’s error in representing a storm’s size, track, or intensity at 50°S doesn’t stay at 50°S. It propagates outward with the swell. Forecast uncertainty at the source becomes forecast uncertainty everywhere downstream.

The Argo program, which began deploying profiling floats in the early 2000s, was the first instrument system to observe the Southern Hemisphere systematically and year-round. Argo floats don’t follow shipping lanes. They drift with ocean currents, park at depth for 10 days, and transmit data back at the surface regardless of season or sea state. By 2007 the array had achieved nominal global coverage. Southern Hemisphere ocean science effectively has a before-Argo and after-Argo era.

But, Argo floats can’t sample under sea ice or in shallow coastal waters. The deep ocean below 2,000 meters is still largely unobserved in the south. Biogeochemical measurements of carbon, oxygen, and nutrients require specialized sensors that only a fraction of floats carry. And the observing infrastructure that fills in around Argo’s gaps, the mooring arrays and coastal buoy networks that densify coverage in the North Atlantic and North Pacific, has no Southern Hemisphere counterpart of comparable scale. The baseline is better than it was. It’s still not close to symmetric.

Further Reading:

Southern Hemisphere

ARGO Floats

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In the Northern Hemisphere, trade winds blow westward across the tropics and westerlies blow eastward across the mid-latitudes. When these two wind belts push on the ocean surface in opposite directions at different latitudes, the water ends up spinning in a large clockwise loop called a gyre. The North Atlantic and North Pacific both have one, and both spin in the same direction. The difference is what happens on each side.

The Coriolis effect, which deflects moving objects to the right in the Northern Hemisphere, causes water to pile up in the center of each gyre. That creates a slight pressure gradient, and the whole system reaches a balance called geostrophic flow: water circling around the central mound rather than draining out of it. You’d expect the return flow to redistribute itself evenly around the gyre. But the Coriolis effect isn’t constant. It weakens toward the equator and strengthens toward the poles, and that variation breaks the symmetry. The return flow can’t spread itself evenly east to west, so it piles up on the western side of the basin instead. The result is a fast, narrow, deep, warm western boundary current.

In the Atlantic, that’s the Gulf Stream. It moves roughly 30 sverdrups of water — the equivalent of over 12 thousand Niagara Falls — in a current sometimes under 100 kilometers wide. It carries warm tropical water northward along the East Coast before peeling northeast toward Europe, and it keeps the water warm well offshore. Standing on the beach in North Carolina and dipping your toes in, you’re feeling sometimes-disturbingly-warm water that started near the Caribbean.

The California Current is the eastern boundary current of the North Pacific gyre. Eastern boundary currents are slow, broad, shallow, and cold. Rather than a concentrated ribbon of warm tropical water, the California Current is a wide drift of subarctic water moving southward down the West Coast. Broad and slow means less heat, more time for mixing, and a lot of exposure to persistent northwesterly winds that push surface water offshore. When that surface water gets pushed out, cold water from depth wells up to replace it. This upwelling is why the California Current is one of the most biologically productive systems on the planet and also why 4/3s are awesome.

This asymmetry is a feature of every major ocean basin. The warm Kuroshio Current runs up the eastern coast of Japan the same way the Gulf Stream runs up ours. In the Southern Hemisphere the gyres spin counterclockwise, but the same Coriolis asymmetry applies — western boundary currents still pile up on the western side of the basin, meaning the eastern coasts of continents still get the warm side. Brazil gets the Brazil Current; Chile gets the cold Humboldt.

Further Reading:

Ocean Gyres

Boundary Currents

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Salt gets into the ocean through river runoff and seafloor vents, and then it just stays. Evaporation pulls water out of the ocean and into the atmosphere, but salt doesn’t evaporate. It’s left behind. Rain adds freshwater back to the surface, diluting what’s there. So salinity is a ledger of how much freshwater a basin has gained or lost relative to its salt content. More evaporation than rainfall means saltier water. More rainfall than evaporation means the opposite.

The Atlantic loses more water to the atmosphere than it gets back from rain. The Pacific is wetter — precipitation outpaces evaporation across most of the basin. That alone would explain the difference. But the more interesting part is where the Atlantic’s evaporated water actually goes. Trade winds blow westward across the tropics, and the Central American isthmus is narrow enough (about 80 kilometers at its narrowest) that significant amounts of water vapor cross it in the atmosphere. The Atlantic is effectively exporting its freshwater to the Pacific through the air. Researchers estimate this cross-isthmus moisture flux moves on the order of 0.1 to 0.2 sverdrups of freshwater equivalent annually (100k-200k cubic meters per second - an absurd number), enough to matter over ocean timescales. The Atlantic loses salt-free water and gets saltier. The Pacific receives it and gets fresher.

The Atlantic connects to the Mediterranean Sea through the Strait of Gibraltar, and the Mediterranean is hypersaline. Intense evaporation and limited inflow from rivers make it one of the saltiest major bodies of water on earth, averaging around 38 parts per thousand. The dense, salty Mediterranean water sinks and spills westward into the Atlantic at depth through the strait, a slow but persistent input of high-salinity water. The Pacific has no equivalent. Nothing comparable is pouring extra salt into it from an adjacent basin.

The Indian Ocean sits in between, averaging around 34.5-35 ppt, but masks a wild internal range. The Arabian Sea runs closer to 36-37 parts per thousand because evaporation is high and few rivers drain into it. The Bay of Bengal, on the other side of the subcontinent, drops to 32-33 ppt because the Ganges, Brahmaputra, and monsoon rainfall pour freshwater in faster than the ocean can salt it back up. The Red Sea and Persian Gulf, both hypersaline, spill dense water into the Indian Ocean at depth the same way the Mediterranean does for the Atlantic, but the Bay of Bengal offsets it. Each basin ends up where its geography, rainfall, and neighbors leave it.

Saltier water is denser, so you float marginally higher in the Atlantic than the Pacific, but you’d never notice it. Your wetsuit has more effect on your position in the water than a 1.5 ppt salinity difference does. Two connected oceans ended up with different salt content because of where they sit, what sits next to them, and which way the wind blows.

Further Reading:

Salinity

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Quartz makes up most of mainland beaches because it’s extremely hard and chemically stubborn. Softer minerals like feldspar dissolve or crumble along the way. By the time sediment reaches the coast, quartz is often the last man standing, which is why sand from San Diego to Santa Cruz looks more or less the same despite coming from very different source rocks.

Rivers are the main arteries in this system. Weathered sediment washes downstream, bumper-carting against riverbeds and other particles the whole way, getting smaller and rounder with every mile. A grain of sand on your beach might have started as part of a granite cliff face a few hundred miles inland. California has over 1,500 dams, and most of them are trapping sediment that would otherwise end up on the coast. With waves that keep pulling sand offshore, and rivers not restocking it the way they used to, the beaches run a deficit. Cliff erosion chips in locally, waves eating into coastal bluffs and dropping material directly into the surf zone and oblivious sunbathers, but it doesn’t come close to replacing the river supply.

In tropical environments, however, a huge portion of beach sand comes from biology. Parrotfish scrape algae off coral with their beak-like teeth, chewing up chunks of coral skeleton in the process. What comes out the other end is white sand. A single parrotfish can produce several hundred pounds of it per year. Hawaii’s green sand beach at Papakolea is olivine, a mineral in the local basalt that weathers out faster than the surrounding rock and concentrates on the shoreline. Those white Caribbean beaches are largely crushed shells, urchin spines, coral fragments, and literally-rock-hard fish poop.

Once any of this sediment reaches the coast, waves decide what stays. High-energy beaches exposed to open ocean swell lose their fine grains offshore, currents carrying the small stuff away and leaving coarser, heavier material behind. Sheltered beaches don’t generate enough force to move the fines, so they keep them. Push this far enough and sand disappears entirely. The rockier stretches around San Diego are hard local geology meeting persistent swell with no major river nearby to resupply. Whatever fines existed got stripped out long ago, leaving cobble that clacks together in the backwash, clipping your ankles as you time your paddle.

Further Reading:

Sand

Parrotfish - not kidding about the pooping out sand part

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The same growths have turned up in Homo erectus skulls and in Pre-Hispanic remains from coastal Gran Canaria, where archaeologists used their presence to figure out which individuals were the community’s designated swimmers. Surfer’s ear predates surfing by a species-wide margin.

What Boule found in that Neanderthal skull in 1911 is the same thing an ENT would find in yours after a couple decades of dawn patrols: new bone growing on the walls of the ear canal. Your skeleton slowly and permanently walling off the eardrum from the cold.

The tissue lining the ear canal sits almost directly on bone. When cold water floods in, blood vessels in that lining dilate, and the repeated cycle of cooling and inflammation triggers bone-producing cells to start laying down new layers. Over time, the body is narrowing the canal to protect the eardrum, which would be thoughtful if it didn’t also trap water and wax in there. Water below 19°C is the primary culprit, but wind-driven evaporative cooling allows warmer waters to lead to the same results. A study of surfers in Queensland, where the water barely dips below 20°C, still found exostoses in 70% of participants.

Most surfers don’t notice for a decade or more, which is why most diagnoses land in your mid-30s to late 40s. Water sits in your ear a little longer after sessions, then infections start showing up, then hearing goes. One ear is often worse than the other, depending on prevailing wind or which side of your head meets the wave first. All the more reason to surf lefts and rights, day and night.

The prevalence among surfers is pretty grim. A systematic review of roughly 3,000 surfers worldwide averaged around 68%. A smaller study of elite WSL competitors found it in every single one of them, and not one had ever worn ear protection.

Once bone grows, it doesn’t recede. Surgery is the only way to remove it, and it can grow right back with continued exposure. Earplugs and hoods keep cold water out of the canal and are the simplest way to slow the whole process down. If you’re like me, you should probably actually use the never-seen-water pair sitting in the bottom left corner of your trunk. So easy a caveman can do it.

Further Reading:

Tinkaus paper

Surfer’s ear

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A relaxed hand with fingers slightly apart outperforms a tight, squeezed hand. Multiple studies from research groups across Europe and Australia land on the same finding: a small spread of 3-8mm produces 5-10% more propulsive force than fingers pressed together. Marinho and colleagues at the University of Porto used CT scans of an Olympic swimmer’s hand to build three computational fluid dynamics models: fingers closed, small spread (3.2mm), and large spread (6.4mm). Across every angle of attack they tested, from flat to nearly vertical, the small spread consistently produced the highest drag coefficients. Not the closed hand. Not the wide spread. The relaxed middle ground.

Each finger drags a thin layer of slow-moving water along with it as it moves, called a boundary layer. When fingers are spaced just right, these boundary layers overlap between the gaps without merging completely. Water trying to pass through encounters this zone of slower-moving fluid and gets deflected around instead. Your hand effectively acts like it has more surface area than it actually does. Spread your fingers too far apart (more than about 15mm) and water passes through freely, losing the benefit. Keep them pressed together and you never create the overlapped mitten in the first place.

Why obsess over a few millimeters of finger spacing? Because the hand does most of the work while paddling. Your forearm has more surface area, but it’s cylindrical, so water flows around it relatively easily. The hand is flat, and flat surfaces generate far more drag when pushed through fluid. This is why swimming research focuses so heavily on hand position, and why those small percentage gains from optimal finger spread actually matter.

The optimal spacing, that 3-8mm range or roughly 10-12 degrees between fingers, matches almost exactly what your hand does when relaxed. The natural position of an unstressed hand falls right in the performance sweet spot.

There’s no need to think about millimeters mid-paddle. Just stop squeezing.

Further Reading:

The Paper

Drag on a cylinder

Boundary layers

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