September 22, 2013
We are now 11 days into the Eastern Gulf’s fall cruise on the USFWS vessel
Tiglax. Thus far, we are working under the opposite weather conditions
encountered in the spring, in that weather for the Gulf of Alaska grid has
been great, while weather during the Seward Line component has been
challenging. BUT before I get ahead of myself let me set the stage.
The purpose of our cruise is basically to describe the state of the
physical, chemical and biological condition in the eastern Gulf of Alaska,
and then switch over to the Seward Line time-series in the north-central
Gulf. The sampling plan involves sampling 65 stations along a fixed grid
of 13 “lines” stretching across the south-eastern shelf at 10 nautical
mile spacing, and then 2 additional lines on our way back to the “Seward
Line domain”. Our general approach involves 3 main sampling tools: 1) the
CTD (Conductivity/salinity, temperature, Depth sensor) plus its various
accessory sensors, along with the “rosette” of 12 bottles attached to it
that are triggered at defined depths to provide samples for nutrients
(fertilizers), chlorophyll (plant pigments) and micro-plankton
(single-celled plants and animals), 2) Plankton nets – “butterfly” nets
attached to strong paired frames resembling a pair of spectacles or Bongo
drums used to catch the small animals in the water (we will be deploying 2
sets of Bongo nets of different sizes), 3) a special “metal-free” vane
with motorized water sampler and a towed water sampler used to collect
water for analysis of important micronutrient dissolved iron. Additional
measurement on temperature, salinity, plant pigments, and ocean
acidification are being made continuously on water pumped through the
ship. Finally, during daytime hours a dedicated observer records the
seabirds and marine mammals encountered.
Setup by our 12-member science team began midday Sept 11. The Tiglax was
early, but we soon discovered the crane requires to lift larger items onto
the ship was not working. After several hours of trying to fix the crane,
we scrambled late afternoon to locate a crane elsewhere in Seward to lift
our heaviest items: the iron van and the winch, each of which weight 3
tons. Setup was finally finished around t, and Captain Billy
Pepper had us to our first “test” station, RES2.5 and GAK1, at ~4
am on the 12th. Weather was perfect, and we began our 2-day trek across
the central Gulf of Alaska to meet up with the F/V Northwest Explorer.
The transit days provided a leisurely opportunity to setup and configure
equipment, as well as for the iron team to sample across the central Gulf
of Alaska.
We reached our first station at on the outer end of SEM linet on 13th.
Most of the people on this cruise had been on the
spring cruise, and we hit the ground running with high efficiency and few
equipment issues. The Northwest Explorer was initially ahead of us, but
within a few days we were caught up, and eventually passed them as we
worked the lines sequentially southward. Our only sampling problem
revolved around repeated failure of the iron sampling bottles to open and
close correctly – after several failed deployments, and no clear
solutions, we discontinued their use and concentrated on the towed iron
sampler instead. All was going well until we realized we were shipped
about half of the nutrient bottles needed to complete the cruise AND it
became clear from weather maps, that a large storm would be hitting us
very soon that could trap us in Southeast Alaska for several days.
After a few satellite-phone calls and e-mails over the weekend, plans were
in place to have more bottles air-shipped to Sitka. We ducked into early
on the morning of the 17th, then headed back out to resume sampling. The
lost time in Sitka and the looming storm required we drop two of the minor
lines (SED and SEB) to be out of the area ahead of the weather. By
mid-morning on the 18th our sampling was wrapped up and we were heading
north to Yakutak, while I sorted live zooplankton for caloric analysis by
other components of the project.
We managed to stay ahead of the weather, with relatively smooth sailing
northward. With a storm sitting over the Northern Gulf, and a brief
fair-weather window coming followed by an even larger storm, we had some
time to kill before moving eastward. All considered, a brief stop at the
town of Yakatak seemed possible for a few hours on the evening of the
19th. From there we headed to the final sampling line by Kayak Island
before ducking into Prince William Sound just ahead of the oncoming storm
with 45-50 knots winds at dawn on the 20th. I’ll take events up there
with the “Seward Line” component of the cruise next blog.
In terms of the science, our biggest surprise was how warm the surface
waters were still for September: over 140C at many stations. The
inner-most stations has a decidedly “coastal” assemblage of small
zooplankton species, while the outer stations, and particular those near
the shelf break, had larger copepods and krill were also often abundant.
I was also surprised to see what I consider “high” numbers of the large
arrow-shaped pteropod or sea-butterfly Clio pyramidata in many offshore
samples.
by Russ Hopcroft
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