During the past 48 hrs we have been keeping our eyes and thoughts on the weather, and for some, relearning patience at sea as the weather gods/goddeses test us with only three days left to get all our work done on this first Leg.
During the evening of June 25th, the seas and winds continued to build preventing Jason from taking heavy equipment to the seafloor. Because of this, following our dive at the methane seep site, Southern Hydrate Ridge, we transited to the Slope Base site to conduct a 'naked' dive, meaning that Jason took three coupled instruments down to the seafloor on its front porch without any package latched to its underbelly.
Slope Base is the deepest water site we dive at during the expedition – 2900 m (~ 9500 feet) beneath the oceans’ surface. During Jason Dive 1049, the vehicle descended at ~25 m/second, so it took nearly two hours to reach the sedimented seafloor. Macro animal life is not as dense here, but there is still plenty of life – brittle stars and sea pigs (scotoplanes) are common. However, octopus and deep sea fish are more rare in these cold, dark waters.
This year, as we worked at the seafloor, we remarked that there was more marine snow (mostly biologically-generated material) gently falling from above then we had seen in past years. Slope Base is >80 km offshore, but it is close to the continental margin where the California Current runs making the shallower waters highly productive.
During the dive, we turned instruments that measure ocean salinity, temperature, dissolved oxygen concentrations, and ocean turbidity (a measure of particle concentration in the waters). Jason also plugged in a pressure sensor that had been equilibrating on the seafloor since last year, and recovered one installed in 2014. This sensor provides important information on the influence of lunar tides o ocean processes, but also records tsunamis.
We were hoping to see our very rare deep sea fish friends we fondly call “Weird Fish that have visited us every year since 2014. The formal name of these bony fish is Genioliparis ferox. They are extremely rare and have been documented in the cold waters off Antarctica. These fish were filmed for the first time in 2014 by the Canadian ROV ROPOS during our Cabled Array VISIONS’14 expedition. Little is known about these fish other than that they are ferocious predators. This is the first year since 2014 that we have not seen them. The dive lasted 11 hrs.
With increasing winds and poor seastate, the decision was made early yesterday morning to go on a “weather hold” to insure safety of personnel and equipment. To efficiently use the ship, two water casts using a CTD and rosette with 24 niskin bottles were conducted to collect deep water and water for follow-on chemical analyses, the results of which are used to compare with real-time measurements coming off the cabled instruments. The students took full opportunity of these casts to learn how they are conducted, to help sample, and to learn how to measure oxygen concentrations shipboard on the collected waters.
Following the CTD casts, the Revelle transited to the Oregon Offshore site, and then to the novel seep site called Pythias Oasis to conduct multibeam bathymetric sonar surveys of the seafloor and water column. The survey ended at Southern Hydrate Ridge the early hours of this morning.
At ~11 am, under beautiful blue sunny skies, the seastate had improved and Jason went back into the water for Dive 1051! Happy we are to be back diving. The dive will focus on installing instruments to measure fluid flow into and out of the seafloor, and to measure fluid chemistry.