Subsea Cable Fixed

Good news this week for many residents of northern and western Alaska: the Arctic undersea fiber optic cable that was damaged back in June has been repaired, allowing internet and phone service to get back to normal.  This is a story I've been following, because the cable was apparently severed by ice scouring on the sea bed about 35 miles north of Oliktok Point, just up the coast from Prudhoe Bay.  Read more here:

https://alaskapublic.org/2023/09/19/northern-alaska-cable-break-repaired-after-14-weeks-of-internet-outages/

https://alaskapublic.org/2023/06/12/cut-cable-causes-weeks-long-north-slope-northwest-alaska-internet-and-cellphone-outages/

The aspect I find interesting here is that the break occurred in water "about 90 feet deep", and it seems remarkable to me that Arctic sea ice could ever reach the ocean floor at that depth.  Frankly I was skeptical to begin with, thinking that either the depth was misquoted, or that the cable was damaged for some other reason.  But Quintillion's webpage confirms "ROV inspection shows 20 meters of accessible cable on the seabed floor. The target is 50-60 meters of accessible cable in order to reach the surface with workable slack for splicing operations. The water depth in the area is ~25 Meters."

The second article linked above cites Quintillion's president with the following explanation:

“It’s in an area where the land-fast ice and the sea ice kind of meet,” he said. “And so ice scour – which is essentially moving ice hitting the land ice and then (sinking) kind of like a tectonic plate – I suppose that it scarred the seabed floor, and then went down below the depth where we were buried.

(end quote)

It seems that a large wind stress event would be needed to drive sea ice down to such a great depth, so it's worth looking at the weather data.  As it happens, there is some evidence of high winds on June 11, the date the damage occurred.  The following chart shows hourly 10m wind speed from the ERA5 reanalysis at 71°N, 150°W, which is very close to the stated location of the event:

According to the ERA5 data, the wind speed peaked on the afternoon and early evening of June 10, from a direction just slightly north of easterly.  The peak sustained wind speed is not particularly high - less than 30mph - but the ERA5 wind speeds can't necessarily be taken at face value.  The Deadhorse ASOS reported sustained winds of 30-35mph, with higher gusts, at the same time, so the winds may have been somewhat higher over the ice (and there was still 100% ice cover at that time).

To put the peak ERA5 wind in context, I pulled out ERA5's maximum hourly wind speed for the month of June in past years at the same location.  Since 2000, nearly half of all years have seen a June wind speed higher than this year's event, so it really doesn't stand out as an unusual event.

Here's the surface analysis chart for the same time, 4pm AKDT on June 10, courtesy of Environment Canada; click to enlarge.  There's a modest pressure gradient across the near-coastal waters north of Alaska, consistent with brisk easterly winds, but again nothing especially unusual.

It seems that further analysis of the event would require information about ice thickness and motion in the area, and perhaps satellite imagery would reveal the ice subduction process described by Quintillion.

Any sea ice experts care to weigh in?