The wrong kind of bottom…

Sunday, August 7:

After surveying in the bottom moorings for AUV navigation, we got the Mola Mola AUV in the water late yesterday for a short (45-minute) test run at around 450 m (roughly 1,475 feet) depth; it worked beautifully! We obtained a stream of pictures from the bottom and we were able to retrieve it with the ship’s inflatable rescue boat with little trouble when it surfaced.

bottom photo from MOLA MOLA of sea anemones

Sea anemones, shrimp, red crabs and fish photographed in Hudson Canyon by the NIUST Mola Mola AUV. (Credit: NIUST)

The pictures were great, but no corals yet (wrong kind of bottom). It was flat and muddy and we saw numerous of deep sea red crabs, witch flounders, merluccid hake, monkfish, and a high density of large (probably up to 15 cm diameter) non-burrowing anemones (Bolocera and an unidentified species). They appear to be a major structuring species, but it’s a mystery what they’re attached to; there’s no obvious hard substrate…just flat mud.

We were very anxious to do a 6-hour “production run” with Mola Mola today, but the weather has blown up a bit and it’s not safe for the small boat operations necessary to retrieve the AUV. The high freeboard of Henry Bigelow is a disadvantage, as it prevents us from retrieving directly onto the ship. Thankfully the seas are supposed to lay down tomorrow and for a few days thereafter, so we’ll have something to show the Deep Corals Workhop participants at Sandy Hook.

Mary Scranton collects water samples from rosette water sampler.

Mary Scranton collects water samples from the rosette water sampler (Credit: Peter Rona, Rutgers University).

Overnight we took a number of CTDs in the canyon and collected samples for stable carbon istopes as well as for methane analysis and phosphate. Isotopic ratios in the elevated dissolved methane in deep water can point to the origin of the methane (gas pockets vs. ice hydrates vs. newly decayed). As we expected, we are seeing the coldest bottom temperatures (7 degrees C, or 44 degrees F) at shelf depths and in the upper canyon now in August: it is normally warmer (up to 12 C, 0r 54 degrees F) in January during LMRCSC cruises.

We struck the bottom…probably drifted into the canyon wall…this morning with the rosette sampler. Several 5 L bottles were broken, but tests indicated that the ship’s 911 CTD is undamaged. Fortunately, Mary Scranton (Stony Brook) brought some of her own 8 L bottles and they fit on the rosette, so we will be able to complete the planned sampling
scheme.

Last night we also did a series of Patch Test calibration runs with the
ME70 (Fisheries Mode). We were advised to do this by Leonardo Macelloni (U. Mississippi: onboard). Without the software in the now defunct Bathymetric Option we can not use this data to autocorrect incoming multibeam signals, but Leo says he can use it to correct data in post-processing. Since we cannot use Mola Mola today we are running ME70 lines through the tilefish habitat area to document the extent of the typically hummocky burrowed bottom terrain. ME70 works well in 120-150 m depth, but because of its relatively high frequency (~90 kHz), we could not use it to map the final southern third of the canyon that we have not yet been able to do with the NIUST Eagle Ray AUV  (not onboard this year). ME70 seems to be working well and I hope to get some interesting results from it despite the lack of the Bathy Option, though we’re just lucky we’ve got Leo with his expertise aboard this time, or we’d be “dead in the water” so to speak.

On another acoustic note, we’ve been watching the EK60 multi-frequencysingle beam sonar and have noted this morning that a “cloud” of organisms visible at 18, 38, 120, and 200 kHz (the 70 kHz has been displaced by an NIUST acoustic modem) hangs over the canyon walls at about 150-200 m (roughly 500 – 650 foot) depth no matter where we cross the walls. I wish we had nets (and time) to sample this and figure out what’s going on. No whales yet today.

The weather may be too much for small boating, but it’s not unpleasant
aboard Henry Bigelow. Until last night it was sunny, breezy, and warm but not really hot and nearly calm. Now we’ve got showers and a gentle roll. Everybody seems fairly comfortable.

Vince Guida
Chief Scientist
HB11-04 Habitat Mapping Cruise

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