Report of Activities
on the RVIB N.B. Palmer Cruise 02-02
On April 19, the N.B.
Palmer was working on survey line 4 mostly in the mid-continental shelf
region just north of
Work was completed at stations 18, 19, 20, and 21. The CTD
was deployed at all of the stations with the microstructure sensor package and
the FRRF, with the exception of station 19, which was too deep to deploy the
FRRF. A 1-m ring net tow for surface
zooplankton was done at Station 19 and a MOCNESS tow was done at station 21. An
APOP cast was also done at this station with adolescent krill individuals,
which have been kept alive since they were caught at station 7. Underway
measurements included the sea bird and mammal surveys and BIOMAPER-II towyos between all of four stations. Two sonobuoys were
also deployed along the trackline.
CTD Group report (John Klinck, Tim Boyer, Chris Mackay,
Julian Ashford, Andres Sepulveda, Kristin Cobb)
The CTD group did four casts today almost completing the 380
line across the shelf. These stations continue to be typical of the shelf
without oceanic influence, even station 21 on the outer part of the shelf. The
middle/outer shelf stations have high surface chlorophyll compared to most measurements
made on this cruise. The Winter Water (WW) layer at all stations has nearly
eroded away, likely due to the deepening wind mixed layer that has penetrated
to WW layer. Small-scale variability, double diffusive layering, continues to
occur in the pycnocline of most stations.
Station 18 (cast 21, 379 m). There
was a 20 m thick surface layer with increasing temperature and salinity, while
the mixed layer extended to 55 m. Surface chlorophyll was 0.2
ug/l. The WW layer had nearly eroded. Weak layering was occuring
in the pycnocline. There was no temperature maximum
and bottom temperature was 1.3ºC.
Station 19 (cast 22, 615 m). The Surface layer was uniform to 60 m. Surface chlorophyll was 0.2 ug/l. Thick (10 m) layering was seen in upper pycnocline. There was a thin temperature maximum (1.5ºC) at 300 m.
Station 20 (cast 23, 484 m). The
surface layer was uniform to 50 m. Surface chlorophyll was 0.55 ug/l. Small scale
variability occurred in pycnocline. Temperature below
200 m was uniform at 1.3ºC.
Station 21 (cast 24, 467 m) The surface layer had uniform
temperature and salinity to 50 m. Surface chlorophyll was 0.4 ug/l. Thicker (10 m) layering was occurring in the upper pycnocline. The temperature maximum (1.3ºC) was at 300 m.
ADCP Data report (John Klinck, Tim Boyer, Chris Mackay,
Julian Ashford, Andres Sepulveda, Kristin Cobb)
The hydrography group is currently
analyzing the water velocity information collected with the shipboard Acoustic
Doppler Current Profiles (ADCP) on the N.B.
Palmer. The system was set up by a project
from Eric Firing (University of Hawaii) and Teri Chereskin
(Scripps Institution of Oceanography, UCSD) and automatically collects,
calibrates, and produces a series of graphs and data files with the magnitude
and direction of the currents along the ship track. Thanks to this system, any scientist on board
can have a graph of the change of the velocity field in the current cruise without
the difficulty of manipulating the raw data. More details on how this works can
be found at http://peale.
The work of hydrography group is
to make sense of the graphs that are automatically produced by the system by
further processing this information, plotting the data, and calculating other
parameters that help understand the dynamical processes in the
Nutrients Status Report (Rob Masserini)
Nutrients are being analyzed from water samples taken from the CTD casts by Yulia Serebrennikoiva and Rob Maserini. To date, the first four survey lines transect of the SO GLOBEC grid, which included 22 stations, have been completed, and nutrient analyses have been run on 492 seawater samples taken from rosette and the data processed. Essentially, every niskin bottle on every cast is sampled. The seawater samples are analyzed for dissolved inorganic nutrients which include nitrate, nitrite, ammonia, phosphate, and silicic acid. Thus, 2460 individual analyses have been completed, not including the approximately 4000 associated standards and other quality control analyses that are run to insure that our data are of the highest possible quality, accuracy, and precision. The analysis of seawater samples have been conducted according to the JGOFS/WOCE suggested protocols for nutrient analysis.
Nitrate and phosphate exhibit the classic distribution of these
nutrients, being of higher concentration at depth increasing slightly just
below the mixed layer and then decreasing substantially within the euphotic zone. The
approximate concentrations (all concentrations are given in micromolar
units) for nitrate and phosphate in these regions are as follows: deepwater
32.8 and 2.32, just below the mixed layer 35.3 and 2.47, euphotic
zone 22.5 and 1.6, respectively. Nitrite
and ammonia concentrations are essentially zero below the mixed layer (zero
here defined as less than the detection limit of the chemistries
employed). Within the mixed layer the
average nitrite and ammonia concentrations are approximately 0.23 and 1.6,
respectively. Within the mixed layer,
ammonia exhibits an enrichment in the near shore
stations at a depth of approximately 50 meters to 1.8 micromolar. The ammonia concentrations in the mixed layer
seen thus far are comparable with those of the Fall SO GLOBEC I cruise last
year for the same region, which are higher than the Winter SO GLOBEC II cruise
values. The nitrite concentrations
exhibit a subsurface maxima near the bottom of the
mixed layer increasing to roughly 0.33 micromolar. Also, approximately twenty nautical miles
from the furthest offshore station, a region of even higher nitrite concentrations
have been sampled between approximately 70 and 100 meters, with nitrite
reaching a concentration of roughly 0.4 micromolar.
Silicic acid, like ammonia, exhibits an increase in concentration
near shore within the mixed layer. In
general, it also exhibits a classic nutrient structure with
an average concentrations below the mixed layer of roughly 110 micromolar decreasing to 50 micromolar
within the euphotic zone. One feature of note in the silicic acid data is the presence of a
bolus of depleted silicic acid at a depth of
approximately 260 meters associated with 1.8º water seen at station 9 on
transect 2. This water mass had a
silicic acid concentration of approximately 90 micromolar, 10 micromolar less
than the water surrounding it.
Marine Mammal report (Debra Glasgow)
April 19 was the best day of observations so far on this voyage with 31 fur seals counted (the majority were resting at the surface) and 7 whale sightings with a total of 21 whales. These were 2 minke, 3 unidentified baleen whales, 2 humpback-like whales and 14 humpbacks, including one juvenile humpback. Surveying began at 0841 as we started our transit at -67 12.30ºS; -70 14.29ºW to Station 20 and ended as we reached Station 21 in fading light at 1730. Though overcast, good visibility and a sea state of Beaufort 3 persisted throughout the day creating good conditions for cetacean observations. Most of the whales seemed to be surface feeding or were socializing and three groups approached the ship closer than 200 meters. Identification photographs were taken of two groups of humpbacks.
Sea Birds (Erik Chapman and Matthew Becker)
The sea bird survey in the mid-shelf region between stations
19 and 21 lasted almost 7 hours on 19 April and once again, we saw a dramatic
shift in species assemblage and densities today. There were few birds overall for the transit
distance and for the first time, Snow Petrel was the most common species
observed. This species is typically
associated with sea ice, though we did not travel through ice today. The Snow Petrels were either following the
ship or flying relatively high in groups of 5 or more, probably in transit to
some other place. We did not see much
feeding by any birds today. Once again both
A surface tow was taken at station 19 and the catch was
again dominated by a lot of green diatom sludge, with amphipods and copepods
also in the mix. The BIOMAPER-II crew
directed us toward some regurgitated stomach contents from an unknown bird that
appeared overnight on the helicopter deck.
The bird was gone, but we found 8 or 9, fresh 35 to 45 mm Euphausia superba on the deck. Because Southern Fulmars are rarely found on
the ship, this bird was probably a
Species (common name) |
Species (scientific name) |
Number observed |
|
Daption capense |
30 |
Southern Fulmar |
Fulmarus glacialoides |
25 |
Antarctic Petrel |
Thalassoica |
0 |
Blue Petrel |
Halobaena caerulea
|
0 |
Unidentified Prion |
|
0 |
Grey-headed Albatross |
Diomedea chrysostoma |
4 |
|
Oceanites oceanicus
|
3 |
Unidentified Skua |
|
0 |
Snow Petrel |
Pagodroma nivea |
41 |
Southern Giant Petrel |
Macronectes giganteus |
5 |
Antarctic Tern |
Sterna vittata |
0 |
Antarctic Fur Seal |
Arctocephalus gazella |
26 |
Material Properties of Zooplankton Report (Dezang Chu, Peter Wiebe)
In the evening after the MOCNESS tow at station 21, the
second APOP cast of the cruise was conducted in the same way as reported
earlier (at 20 m depth intervals down to 200 m). Since attempts to capture more
live krill over the past two days with the Reeve net have not been successful,
the juvenile krill caught on the 15 April were used. These krill had been kept
alive in the aquarium. This cast was intended to compare the material
properties of the juveniles to those acquired for the adults a couple of days
ago. The exoskeleton of these smaller juvenile krill feels softer than larger
adult krill and they are more fragile than adult krill. More than 40 juvenile
krill were put into the APOP acoustic chamber. The average size of these krill
was 26.9 mm, with a standard deviation of 6.1 mm. After the cast, all animals,
but one, were alive and a few of them seemed sluggish, with visible color
change on part of their body (from almost transparent to pale). After putting
them into a bigger container, the color changed back to transparent. The
preliminary results showed that the sound speed contrast of these juvenile
krill was smaller than that of the adult krill. There was slightly an increase
in sound speed contrast as a function of depth (less than 1%). There was a small difference between the down
cast and up cast. The mean sound speed contrasts were 1.0145 and 1.0212 for
down and up casts, respectively, and the overall mean value was 1.0179, slightly
lower than that of the adult krill (1.0238).
About a half hour after the sound speed measurements, the density of the same krill were measured. Their density
contrast was 1.007 +- 0.005, which is much lower than the adult krill.
Combining the results from sound speed and density
measurements, it appears that the juvenile krill are less efficient scatterers than adult krill. This result, however, is preliminary
and more measurements are needed.
Zooplankton (MOCNESS/BIOMAPER-II) report (Carin Ashjian, Peter Wiebe)
MOCNESS #6 was conducted in the middle portion of the
continental shelf along transect line #4 at Station 21. This station is situated off of
The towyoing with BIOMAPER-II went
smoothly during 19 April, as we steamed between station 18, 19, 20 and 21. At station 21, the towed body was brought
onto the deck to make way for a MOCNESS tow at this station. During the late
night transit between stations 18 and 19, a number of interesting backscattering
targets were observed just below the surface turbulence zone created by the
ship in the 15 to 30 m depth zone. They
were very intense and had fairly small vertical and horizontal dimensions.
These features were observed infrequently on earlier survey lines, but now they
seem to be occurring more persistently.
In the daylight period of steaming between stations 19 and 20, the backscattering
on all of the frequencies was relatively light and there were no major patches
of scatterers evident, except for a few right at the surface.
At many locations along the transect line especially in mid- and outer
shelf areas, the 1.0 MHz transducers had high backscattering levels in the 0-60
m depth interval presumably from the very high diatom concentrations that can
be observed on the Video Plankton Recorder.
A diatom bloom of significant proportions has been occurring in the
northern portion of the SO GLOBEC survey grid.
Upon leaving station 21 around 2300, backscattering levels in the surface layer were
moderately strong on the 120 to 1000 MHz ducers, but
very little backscattering was evident on the 43 kHz echogram. The midwater zone for the 43 kHz had a now familiar faint
scattering layer 240 to 300 m below the surface. This coincided with where the
deep scattering layer started on the 120 kHz echogram. The latter intensified
with increasing depth to the bottom, which was greater than 500 meters.
Cheers, Peter