The anoxic coast of Oregon
A few weeks ago, my family and I took a vacation on the Oregon coast and found the weather to be refreshingly cool with the high temperatures in the low 60s and nights which often reached into the low 50s. Everyone understood that, in this region of the coast, the water, even in midsummer, is too cold for normal swimming, such that the brave few who entered the water always did so in wet suits. So the most frequent form of beach activity reverted to that of waiting for low tide, at which time visitors ventured out along the rocky ocean beaches to see the holdings of the many tide pools that were carved out of stone and stocked with invertebrates. In that region, strong tidal forces plunge the Pacific ocean against the rocky coast which submits by giving way to neatly carved stone and sand tide pools that nestle along the beach and usually harbor a rich array of invertebrates. Near the tide pools one could see photographers shooting scenes of starfish feeding on clams while unidentified, trapped invertebrates scurried about for a place of safety or escape, usually just a high tide away. A tide pool is a microscopic world of violence, but everything seems to move in slow motion, beyond our tolerance to wait, watch or investigate more closely. Things in tide pools move as if marking with a geologic time scale. One would need the patience of an A.O. Wilson or Rachel Carson to gain an understanding of nature’s dynamics in the tide pool environment. Yet, one can’t help but feel some sense of security in knowing that life is abundant in the tide pool, that perhaps it’s a safe outpost of nature, seemingly untouched by man’s intrusion into the ocean ecosystems. But is that true? Maybe not!
Fig 1. A description of this figure is found at the bottom of this posting
Recently I was reading about the Oregon coast and discovered that, since 2002, the region has experienced sudden periods during the summer months in which the shallow ocean water dramatically loses oxygen levels below those required to sustain normal marine life. The first occurrence of this event took place between Newport and Florence along the Oregon coast, and included Yachats, the small town where we stayed. Though I did not personally see any evidence of fish or invertebrate kills, these surges of hypoxic coastal ocean water take place further out in the shallow ocean water beyond the shores and are evident at depths up to about 50 meters or so: because of the intense wave action, tidal pools probably get effective oxygenation through wave aeration; its an excellent mechanism for mixing water and air and the Pacific ocean seems very adept at creating intense wave activity. I have always appreciated how much better the Pacific ocean is at generating large, strong waves when compared to its Atlantic cousin.
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