Report of Activities on the RVIB N.B.
Palmer Cruise 02-04
8 August 2002
Our first day on the transit to
the southern sector of the Southern Ocean GLOBEC grid off Alexander and Charcot Islands
was fraught with difficulty. Since we entered Crystal
Sound on 5 August, there apparently
had been a buildup of very dense brash ice just outside the entrance to the
sound. Although we began the journey before midnight
on 7 August, by mid-morning on the 8th we had made about 6 nm and our progress
was a snails pace. A part of the problem
was that the wind was out of the northeast at about 20 kts
and this had caused the ice to pack in close to the shore. While the Palmer
could make it through this pack ice with relative ease, the L.M. Gould could not. Even with the Gould very close behind, the Palmer's
wake region closed up with the dense brash ice to such an extent that the Gould could not push forward through it
and within a short time came to a stop. The Palmer
then either had to back down to reopen the path in front of the Gould and start out again or to circle
and come up alongside the Gould, cut
right in front, and then move forward with the Gould again trying to follow behind. For most of the day the convoy
went nowhere fast. About 1700, as we
moved west beyond the vicinity of three very large icebergs, the character of
the ice changed and the wake region no longer closed up so abruptly. The Gould finally could follow the Palmer and we were able to move consistently
along the transit route to the southwest.
Several hours later while
steaming off the northern end of Adelaide
Island, the ice pack thinned
significantly and there were pools of open water amongst the floes. An XBT
survey with drops at 10 nm intervals was started in this area to see if the
water column characteristics were indicative of offshore water coming into the
area and contributing to an increased upward heat flux that reduced the rate of
sea ice formation. Indeed, as described below, the deep water was much warmer
indicative of the ACC water coming onto the shelf. The slow pace of the transit made it a good
day to go computer virus hunting. The ship's PC computers were hit by the klezH@mm virus making life miserable for many of the
investigators and crew using PCs and causing significant problems with the data
acquisition systems. The ship's network
was shut down in the morning and all of the laptop computers were brought to a
main lab for virus checking and cleaning. All other PCs throughout the ship were also
checked and cleaned. Virus checking had
started a couple of days ago when it first turned up, but a few computers were
found to still have the virus. By late afternoon, all machines had been scanned/cleaned
and the network brought back up with no sign of the virus.
During the day, the skies were
overcast and, like a couple of days ago, there was almost no contrast between
sea ice and sky. Huge icebergs, which
dotted the area, blended into the background so that they were barely
visible. The winds were persistently out
of the northeast (050) around 20 kts. The air
temperature varied from -2.5ºC in the morning to -3.4ºC in the evening. The
barometer continued its slow decline moving from 1006.2 mb
to 1001.4 mb by evening.
CTD Group report (Eileen
Hofmann, Baris Salihoglu,
Bob Beardsley, Chris MacKay, Francisco (Chico)
Viddi, Sue Beardsley)
During early evening of 8 August,
we began an XBT survey along the course taken for the transit to the first
process site. The XBT survey was to
begin after exiting Crystal Sound
and turning south along the north coast of Adelaide
Island. However,
the survey was started earlier because a region of thin ice with large areas of
open water was encountered soon after leaving an area of extensive sea ice that
covered the shelf just to the north of Adelaide
Island. The thought was that warm water may be
present at depth that then mixes upward, keeping surface waters above freezing
and resulting in less sea ice cover.
The vertical temperature profiles
from the first two XBTs show warm (1.44ºC) water at
depths below 200 m to 250 m. Surface
water temperatures were -1.77ºC to -1.78ºC, which is above freezing. Thus, it appears that the presence of the
warmer modified Circumpolar Deep Water at depth may be related to the reduced
ice cover at the surface. Understanding the dynamics of this interaction is a
primary goal of many of the components of the SO GLOBEC program.
We are continuing to drop either
T-7 (maximum depth of 760 m) or T-4 (maximum depth of 460 m) XBT probes,
depending on the bottom depth, at about 10 nm intervals along the southward
transit. The results from the XBT
section will be described in a later report after the section is finished.
Nutrients (Yulia
Serebrennikova and Steve Bell)
Nutrient analysis of the water
samples taken from the CTD casts during the Crystal
Sound survey was completed. The
samples were taken from all seven CTD casts; a total of 113 seawater samples
were analyzed for nitrate, nitrite, silicic acid,
phosphate, and ammonium. The analyses of seawater samples have been conducted
according to the JGOFS/WOCE suggested protocols.
The nutrients have a nearly
classical winter distribution for both transects across Matha Strait
and Crystal Sound.
Nitrate, phosphate, and silicic acid exhibit high
concentrations from near-bottom depths up to 200-m and slightly lower
concentrations approaching the surface. There is a slight increase of silicic acid and decrease of nitrate and phosphate near the
bottom below 700 m. The approximate deepwater concentrations (in micromolar units) are 34, 2.4, and 105 and the upper mixed
layer concentrations are 31.5, 2.25, and 90 for nitrate, phosphate, and silicic acid respectively. The concentrations of these nutrients
in the upper mixed layer are about 5% higher toward the inside of Crystal
Sound. Elsewhere, there is no
substantial horizontal gradient of these nutrients. Nitrite has essentially zero concentration throughout
the water column for all 7 CTD stations. Ammonium levels are low also. The
highest ammonium concentration, 0.1 micromolar, was
found at station 1 in the northern part of
Matha
Strait.
ADCP/OPC/MOCNESS Studies (Ryan
Dorland)
Single ping data collected by the
ADCP are read continuously from the ship network and processed by software
developed by Meng Zhou (University of
Massachusetts Boston) and Eric
Firing (University of Hawaii). The single ping amplitude data from the ADCP
serve as a proxy for acoustic backscattering from particles in the water
column. A near real-time display of the
amplitude data, along with continuous display of Simrad
EK500 data, allow for quick identification of potentially high backscattering
layers and patches. A patch with a high
Volume Target Strength (VTS) of -60 db was observed on 6 August (Julian Day
218) at 1900, during the second Tucker trawl of the evening. The patch extended
0.5 nautical miles along the ship track at -66º 34.0′S; -67º 08.0′W
heading NW, and was present near the surface to a depth of 75 m. The Tucker trawl was towed through
approximately 2/3 of this patch, and contained a high abundance of adult krill
and other zooplankton.
The first 1-m MOCNESS tow of the
cruise was conducted at 1345 on 7 August at -66º 31.67′S; -67º 19.17′W
under calm conditions. The target depth
of 500 m was not reached due to a sharp rise in bathymetry near the starting
point of the tow, measured by the Simrad EK500 and
ADCP. The MOCNESS was taken to a depth of 300 m and was fished towards the surface
at a variable speed of up to 3 knots.
Mounted on the MOCNESS is an Optical Plankton Counter (OPC, Focal
Technologies) and flowmeter. The OPC measures the
abundance and estimated spherical diameter (esd) of particles
between 250 m and 2 cm passing a beam of light in a flow-through tunnel. The OPC provides rapid continuous sampling of
marine organisms and allows for estimation of biomass. The count frequency and esd
distribution is displayed in the dry lab while the instrument is deployed. High counts per second (>30) were observed
during the first tow below 250 m, corresponding to a VTS of -85 db from ADCP
measurements. Count frequency was less
than 10 cps in the upper 75 m. The size
distribution data from the first tow have yet to be processed.
On-station ADCP current
measurements tended to be weak and variable in Crystal Sound, reaching maximum
velocities of 10 cm/s. It was observed that
noise from ice coverage eliminated ensemble velocity profiles when ship
velocities were greater than 4 knots.
The recent rendezvous with the Gould
provided an opportunity to acquire the raw and ensemble ADCP data for the first
portion of their cruise, allowing for comparison between the two ADCP
systems.
Special thanks go out to Fred
Stuart for his assistance with eliminating cross-talk problems between the
MOCNESS and OPC systems, and to Andy Nunn on the Gould for retrieving the ADCP files on short notice.
Sea Birds (Chris Ribic and Erik Chapman)
The ship spent the day in a
restricted area trying to free the L.M. Gould
from the ice. We didn't cover much
ground and remained on the southern side of Matha Strait,
just north of Adelaide Island,
during daylight. During that time, two
Blue-eyed Cormorants, a Kelp Gull, and a Snow Petrel, and no penguins were
observed. We hope to get in some survey
time during the next few days as we head toward station #77, in the southern
portion of the study grid.
Current Position and
Conditions
The second day of our steam
towards the southern sector of the SO GLOBEC grid with the L.M Gould following in our wake has gone very well. Our current
position at 2305 on 9 August is -67º 29.996′S; -71º 29.001′W. The ice
pack is 10/10 with few leads. The air
temperature is -11.5ºC and the sea temperature is -1.835ºC, causing sea smoke
to appear in the ship's wake. Winds are
out of the east (085) at about 6 kts. The barometer
is at 984.6 mb and the skies are cloudy.
Cheers, Peter