Thursday, September 29, 2011

Consumed by Wood

We have lots of wood around here, and some of it naturally makes it into the marine environment, delivered by flooding rivers and eroding banks. And then sometimes we help it along. Many harbors in the Puget Sound region are finding that they are "polluted" with wood waste. Decades of log rafting and storage in the quiet corners of the Salish Sea coated the bottom with logs, bark, twigs and wood fragments that can be meters thick.

Yesterday I had the opportunity to dive a site slated for a shoreline restoration by the Lower Elwha Klallam Tribe. Its an old log loading ramp - a place where trucks could drive over the water and dump their logs. Here is the site as it looked in 1990:

and here it is in 2009, after most of the over-water structure had been removed by the WA DNR:

Two things struck us as we descended to 60 feet under the surface that historically supported vasts rafts of logs. First, there wasn't a lot living in this environment. In particular, I was struck by the lack of shellfish. There were a few small Dungeness crab, a few monster Red Rock crab, and a Short-Spined sea stars (Pisaster brevispinus). Once we moved out of the major impact area I also spotted a large California cucumber (Parastichopus). In deeper water on some of the logs there were larger Metridium anenomes. But in the substrate itself - nothing that I could detect. No clams, no tube-worms, no amphipods.

Next, that there was an impressive amount of wood waste on the bottom. I could stick my entire arm into the bottom, up to my shoulder, and feel only bark and twigs. Even after being out of commission for 20+ years, there wasn't much sediment deposited on top of this waste. I suspect that the lack of shellfish and other life in the substrate is because there was no substrate - just wood.

We found many old log tags, some marked with the company name, "ITT Rayonier"

A giant Metridium. This one was almost almost a meter high.

One of those big Red Rocks, somehow getting big with nothing to eat? Look at the substrate - the pieces that look like big cornflakes? Those are big chunks of bark covering the bottom.

Big raft chain

Monday, September 26, 2011

Facebook as an oceanographic tool

Today my facebook page was full of accounts, from friends living on Puget Sound proper, of high winds. Here in Port Angeles though it was quite calm, in stark contrast to the apparent wind tunnel effect that turned Admiralty Inlet, just 30 miles away as the crow flies, into a froth of foam and waves. I wasn't there, but I saw the video.

So this told me that this particular wind storm was probably from the south, and while Port Angeles was protected by the mass of the Olympics behind us, Puget Sound was hammered. So, on to the oceanography. The real indicator that this was a region-wide south wind event comes from the tidal gauge in Port Angeles:

Note the little green line at the bottom of the plot - this is the "tidal residual", or the difference between the predicted water level and the actual water level. This is also called "storm surge" - piles of water that move in response to changing atmospheric pressure. Today's residual was almost 50 cm, or over a foot, of extra water - quite a bit when you consider that our normal tidal range is around 8-9 feet.

Now on to the cool part. Where is this extra water coming from? Those strong south winds in Puget Sound were even stronger on the outer coast:

This plot from plots wind observations from Destruction Island offshore of the Washington coast. We see high winds - exceeding 50 knots in some cases - blowing w/o pause from the south.

That strong wind pushes water in front of it but the rotation of the earth causes an apparent diversion (the Coriolis "force") of that water mass to the right - into and up the Strait of Juan de Fuca. So, despite the fact that we didn't feel any of today's strong winds, we certainly experienced them as an extra high-tide.

Tuesday, September 20, 2011

Tides at D-Day

The deeper I dig the more I find the history of my field (loosely defined as some mix of coastal oceanography, coastal geology and benthic ecology) fascinating. It turns out that a major turning point in our understanding of both waves and tides was motivated by World War II, and specifically the need to safely land a huge number of soldiers and equipment on the beach at Normandy.

Physics Today just published a really nice historical summary of tidal predictions, and their link to D-Day. It is a suggested read for the coast nerd. Find it here.