driftwood and currents - Formosahut forum

With regard to your observation about the driftwood coming and going on the beaches, i checked out something about the currents running up the coast of Taiwan.

Basically, there is one main one, known as the Black Tide in Taiwan (hei chao, or the Kuroshio current. It's one of the world's major ocean systems (called gyres) and travels in a circular path - we being on the western boundary of it. The direction is always flowing to the north past Taiwan.

However, there are these things called 'eddies' which are supposedly like the 'storms of the ocean'.
They seem to be quite large - several hundred km's across, and apparently can hold their form for several months and have a significant impact on the biology of the area they are affecting.

As for the driftwood - they could possibly explain why there was a period where more seemed to be washing up.
Of course the change in the monsoon direction would seem to be a pretty plausible explanation too.

Additionally, from the literature, there seems to be some interaction with ppe sea current which i don't quite understand, but it supposedly injects into the black tide during the south west monsoon. This interaction is also a contribuiting factor to the formation of eddies.

Thanks for the information. I've always found the maps of currents I've come across incredibly complex and it's something I know little about.

What you describe could very well explain the sudden disappearance of this particular driftwood. At the same time, if currents are the cause, I would assume the wood is washing up on some other shore, or perhaps it will just get bounced around for a few months until it makes its way back here.

The question remains whether the daily appearance of this wood was the norm interrupted by an anomaly or vice versa. I haven't lived here long enough to know, but it's something I plan on finding out.

One thing that I did notice at the same time the wood disappeared was that there were some extraordinary tides. And something was going on with the currents because entire beaches would be altered in a big way from one day to the next. Sandbars would be replaced by 6-8" rocks, and whole areas of beach that were normally sand would be completely covered in rock only to return to sand the next day. This was happening daily as of last weekend. I'll be spending more time at the beach over the next three days so it will be interesting to see what's going on.

The fishermen would know what's up.

A bit more reading on the eddies.

"They form and dissipate along fronts and move across the ocean. At the ocean surface eddies may manifest as swirling areas of high or low temperature or salinity, or elevated or depressed water levels."

"The sea level will rise if the density of the water decreases and fall if it increases. Changes in density occur in response to changes in ocean temperature and salinity. As water gets cooler or more salty it becomes denser and contracts. As it gets warmer or less salty it becomes less dense and expands"
http://www.pacificstormsclimatology.org/index.php?page=glossary

It seems that eddies may cause an upwelling of cold water which thus affects the water temperature which in turn would cause a contraction in the water thus resulting in lower tides - or vice verca for anti-cyclone eddies.

I do seem to remember that the time that you reported this extreme low tide was not during a full moon - which is the time of spring tides - so the eddy is a more likely explanation.

So my guess is that the driftwood disappeared due to an underwater cyclone - but normal transmission should be resumed at some point. Actually, the driftwood is actually on a continual giant loop around the Pacific ocean - occasionally disrupted by these eddies.

OK, this is getting interesting. Yesterday we were at a couple of Jinzun/Donghe beaches and there was an extraordinary amount of seaweed on the beach. We'd never seen that much before. And there was quite a bit of jumu in the seaweed. Very interesting.

Funny you say that about the seaweed - i remember we discussed before how the sea doesn't seem to have a sea smell here, and we worked it out that the smell is basically rotting seaweed, and we don't have much seaweed in Taiwan.

Then the other day i was driving along 11 and a couple of times i thought i did actually get a good strong whiff of the sea. I was surprised, and even doubted it, but your post about the seaweed explains it. Was it seaweed or kelp?

Whatever, i wonder why it suddenly appeared - there weren't particularly big seas recently - and what's the connection with jumu? Does that kind of wood actually float? Some woods don't. I know jumu is hard and heavy. Maybe it is being 'upwelled' from the bottom along with the seaweed in one of these underwater typhoons.

Check out this ocean imaging video on the global currents - looks like a moving van gogh painting.

http://www.youtube.com/watch?feature=player_detailpage&v=0B1xYBRQ3qE

Cool video. How in the heck did they make it?

You're right, the ocean has been very calm, and I had the same question with regards to why so much seaweed should appear under such calm conditions. The jumu was often entangled in the seaweed, suggesting that it had not been floating, but perhaps it simply got caught in the seaweed on its trip in. Still, there was a disproportional amount of jumu in the seaweed compared to other driftwood, again suggesting that it was not floating.

I often find jumu at the mid-tide line. It rarely washes up to the reaches of a high tide.

I also noticed a lot of, or at least more than usual, sponge over the last few days. Sponge in this area is actually fairly rare, but there was quite a bit on the beach on Monday.

This makes me wonder if perhaps a lot of lanbao has perhaps appeared recently.

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