Manolo Castellote with NOAA and Michael Stocker prepair one of four hydrophone moorings in the lower Cook Inlet to monitor a 420 sq. mi. seismic survey being performed by Polarcus, under contract to oil company Hilcorp
Despite the ongoing moratorium on offshore oil leasing in the US, there are a few locations where offshore leasing remains in play: the western 2/3 of the Gulf of Mexico, the American and Canadian Arctic, and the Alaskan Cook Inlet, which is where I’ve been of late. A recent lease in the Lower Cook Inlet is currently being surveyed by geophysical survey company Polarcus at the behest of Hilcorp, who have picked up a 420 sq. mi. area off the Kachemak Bay and the town of Homer.
While we knew it was coming, the survey sort-of snuck up on us a few weeks back. Given that Homer is a lot more accessible to us than the Arctic, I called Manolo Castellote, a pal and colleague who works with the University of Washington under a NOAA grant monitoring beluga whales in the upper Cook Inlet, to see if he would be interested in setting up a couple of hydrophone moorings to monitor the survey acoustics.
To get all readers up to speed: Marine seismic surveys involve towing an array of airguns behind a survey vessel that pops off – or blasts (depending on size) explosive impulses every 5 to 15 seconds. The impulses penetrate the sea floor and the return echo is read by hydrophone streamers and processed to construct a map of what lies beneath the ocean bottom, including oil gas, and other geological features.
The biological problem with the surveys is that the noise doesn’t just go down into the seabed, it also propagates horizontally, saturating huge areas of the ocean to continuous explosions that will occur (in this case) every seven seconds, around the clock until the end of October.
Oddly, Manolo had not been informed about the survey, which may have an impact on the belugas he’s been studying over the last decade. I definitely called the right guy, because within a couple of days we had four hydrophone moorings available, and were in conversations with geophysicists at the Bureau of Ocean Energy Management (BOEM) about analyzing the data in this geophysically complex arena.
If you have not been to Alaska, I can most accurately (and briefly) describe it as ‘another planet’ – a place of extremes. In the case of the Cook Inlet, the tidal swing in the survey area is over 20 feet! In an area 30 miles wide and 100 miles long, 20 feet of water is a lot of water. And given that the flood tide is saline, and the ebb tide allows lots of fresh glacial and river water to flow into the inlet, the density changes over the tidal swings are a sound-propagation modeler’s wet dream.
So from my original humble assumption of two moorings – one under the survey area, and one remotely located, last week we deployed four moorings across the inlet, from which we may be able to map out the propagation characteristics over the duration of the survey.
Why is this important? As inferred earlier, the Cook Inlet is not just a geophysical environment, it is also a biological one. For Manolo, he can see if and how the surveys affect the belugas he’s been studying for a decade. On our two deployment days we came across scads of humpback whales, and groups of fin whales were seen from above. These animals were in the area because their food – zooplankton was available. The surveys commenced on our second deployment day. Should these great whales vanish over the subsequent days, we might assume that the surveys had something to do with their departure. We’ll keep the moorings in place until few weeks after the end of the survey, which should shed light on the whales before, during, and after the survey.
This deployment is somewhat unique, inasmuch as while there have been concurrent programmatic studies of seismic survey propagation and marine mammal behavior, most of these studies have been sponsored by the survey operators, and thus not readily available for public scrutiny. By the end of November, we should have a lot of broadband recordings of the surveys, and the biological habitat in which they are taking place.