Thursday, May 29, 2014

A new pulse of tsunami debris?

A piece by King 5 news from 26 May 2014 investigating reports of another pulse of debris on SW Washington beaches

Recent media reports suggest that a new pulse of debris - some of it probably from the Tohoku tsunami, is littering beaches in Washington. There is the implication in these reports that this, finally, could be the leading edge of the massive wave that has been feared all along...but for the reasons below I am going to argue that this probably isn't the case.

Animation, based on numerical ocean modelling, of debris transport in the North Pacific following the March 2011 Tohoku Tsunami. Courtesy of the International Pacific Research Center

First off, if you watch the model results above (get the full suite of model animations here), you note that they suggest that as of right now, the highest concentration of debris appears to be far off the coast of California and Oregon, but that there are episodic "tongues" that are advected up towards the coast of Washington, B.C. and even Alaska. This is perhaps most obvious if you break out individual windage classes shown combined in the video above. Here, for example, are results from the "2% windage class" alone (see this white paper on how the modellers defined the various windage classes":

These model results are consistent with observations from our coast. Debris has seemed to arrive in pulses, and my overall impression based on the last three years is that late spring/early summer is a very likely time to see pulses of debris. Here is a media report, for example, from June 2012 investigating a general increase in the debris load, and June 2012 was when a large dock washed up on Oregon's Agate Beach. I reported on a June 2012 pulse in a talk given as part of the Olympic National Park's Perspective series based on the monitoring and clean-up work done by Russ Lewis on the SW WA is the slide:

Early summer of 2013 was quieter, but not without some apparent pulses. Here is the report from Russ from June 12 2013, "There was an uptick in long range debris overnight as there was a noticeable number of plastic bottles, small chunks of s-foam, some light bulbs, a few small fishing floats, larger plastics and also some local stuff in the mix such as rope, plastic bags". Why might late spring/early summer be associated with pulses of debris? It likely relates to the seasonal variation in near coastal winds, and its influence on currents along the west coast of the U.S.

Part of what motivated me to write this blog was my own brush with a suspected debris item, found May 14th banging around on the rocks in the high intertidal zone at San Juan County Park on the west side of San Juan Island. Its not clear to me what this was back before it was marine debris:

but when I flipped it over it was carrying the signature of a long ocean voyage - a heavy load of Lepas anatifera, also known as the Pelagic Gooseneck Barnacle:

and the evidence that it came from Asia? Clusters of large mussels that I have tentatively identified as being Mytilus galloprovincialis:

This species is native to the Mediterranean but is raised widely in Asia for food. This species occurred on the dock that washed up on Washington's coast a year and a half ago, and while it does occur as an invasive in Puget Sound, in combination with the Pelagic Gooseneck barnacles it suggests the possibility of Asian origin.

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