Report of Activities on the RVIB N.B. Palmer Cruise 02-04

18 August 2002


On 18 August we continued the transit started around 1800 on 17 August between stations 65 and 41. The purpose of the transit was to assist the L.M. Gould move from their first time-series pack ice station to the second. The straight line distance between the two stations was 84 nm, but the route that had to be taken was circuitous.  We had learned from experience over the past several days that trying to traverse the central portion of the continental shelf off Alexander Island and outer Marguerite Bay was tough indeed. So the two vessels moved along the outer continental shelf in a series of broad leads, evident on the satellite imagery, that eventually allowed us to turn to the northeast towards the coast and in the direction of station 41, located southwest of Adelaide Island. We were able to travel in the leads to a position east of station 42 some 18 nm from station 41. At that point, the easterly course became impossible as we ran into very thick pack ice that required inordinate effort to get through.  It was hoped that a lead to the south that we then traveled along would provide access to more easily traversed pack ice in the direction of station 41, but this did not happen.  Around 2300, it became clear that we were not destined to reach station 41 and radio discussion began between the Gould and the Palmer about an alternate location. The pack ice conditions where we stopped, while suitable for a time-series study of the ice, were deemed not suitable for a week to ten-day stay. This was primarily because of the possibility that the ice pack conditions could become much worse making it difficult or impossible for the Palmer to assist the Gould move to another location when the time came. The night ended with the Palmer and the Gould backtracking to a location near station 42.


During 18 August, there was no over-the-side station work done from the Palmer. Seabird and Marine Mammal observations were made during the daylight periods and an XBT survey was conducted along the route. As described below, the XBTs provided insight into why we were able to travel so far toward the inshore destination in open water or thin ice afforded by the leads.


Weather conditions for the convoy toward station 41 were very nice with little wind (mostly < 10 kts) and relatively warm temperatures. Air temperatures varied between -6.7ºC at night and -3.6ºC during the mid-afternoon.  Visibility, however, varied dramatically.  There were high clouds during the morning and good visibility.  Off to the northeast in the direction we intended to go, the darkness of “water sky” areas contrasted sharply with the lightness of clouds over the pack ice.  In the distance, there were also areas where a layer of white fog-like clouds pressed low against the pack ice.  During a portion of the afternoon, an ice fog similar to the one we experienced a couple of days ago set in and it was probably related to the large expanses of open water we traveled through. At other times in the afternoon, the viewing was really excellent.  We passed by a series of gigantic icebergs with a couple that were several times the height of the vessels. With the Gould following close behind us, the stage was set for some good picture-taking opportunities of that ship passing the icebergs. Fortunately, we passed the bergs when the visibility was good.  During the day, the barometer began a steady decline from around 1000 mb at midnight of 17/18 August to 977 mb around midnight of 18/19 August, a sign that the fine weather was about to end.


CTD Group report (Baris Salihoglu, Eileen Hofmann, Bob Beardsley, Chris MacKay, Francisco (Chico) Viddi, Sue Beardsley)

In the evening of 17 August, we began a transit to escort the Gould to process site two, which is in the vicinity of survey station 41 off the southern end of Adelaide Island.  The proposed transit line covered a distance of about 84 nm and extended from the outer shelf edge directly across to station 41.  Soon after starting the transit, the CTD group began a XBT survey.  The nominal spacing between XBT drops was 10 nm; however, several areas with shallowing and deepening bathymetry were crossed along the proposed trackline.  So a primary goal of the XBT survey was to look at the effect of steep bathymetry on vertical temperature distributions.  Thus, the plan was to add XBTs in areas where the bathymetry changed rapidly to provide better spatial resolution.


Like many things, the plan for the XBT survey worked better in theory than in practice.  The considerable sea ice encountered soon after beginning the transit resulted in deviations from the proposed transit line to take advantage of leads and areas of thin sea ice, where available.  Also, the inability to obtain consistent and accurate bathymetry readings from the various depth sounders (due to interference from sea ice) made it nearly impossible to target specific bathymetric features.  As a result the XBT survey was done at 10-nm intervals and along a rather unusual survey line.


A total of 15 XBTs, either T-7 (depth of 760 m) or T-4 (depth of 460 m), were dropped along the transit line.  Of these, 10 returned data for the entire, or nearly entire, operational depth of the XBT probe. The remaining casts covered only the upper portion of the water column because the wire broke on sea ice before the probe hit the bottom or reached its maximum depth.  However, the partial casts do provide temperature observations for the upper water column.


A benefit of our unusual route to a possible process site two was that we went over a part of the continental shelf that would have otherwise been missed.  The XBT-derived temperature profile from this site (-67º 33.604′S; -73º 17.926′W) showed a maximum of 1.75ºC at 350 m.  Surface waters at this site were about -1.7ºC, which is above the freezing point.  Also, the well mixed surface layer was reduced to the upper 50 m, rather than the 80 m to 100 m observed at nearby locations.  An interesting coincidental observation is that sea ice was reduced around the region where the warm water at depth and the warmer surface waters were observed.  Also, there were large regions of open water and areas of newly forming sea ice.  The transfer of heat from depth to the upper waters and the subsequent effect on sea ice and biological properties is a topic of considerable interest to many components of SO GLOBEC and is an area of active study.


The maximum water temperature near this same site observed during NBP02-02 (April-May 2002) was about 1.4ºC.  The temperature increase observed during this cruise suggests that Upper Circumpolar Deep Water has moved into the central portion of the survey region.  We are now analyzing the entire XBT survey and hope to supplement these observations with those from CTD casts in the next few days.  The results will be presented in subsequent reports.


Report on CTD performance during NBP02-04 (Bob Beardsley, Eileen Hofmann, Baris Salihoglu, Chris MacKay, Francisco (Chico) Viddi, Sue Beardsley)

The NBP SeaBird 911-plus CTD is equipped with a primary and secondary set of temperature (T) and conductivity (C) sensors, a new SBE dissolved oxygen (DO) sensor, plus sensors for pressure P, PAR, beam transmission, and fluorescence.  The primary and secondary T/C sensor sets are attached to their own pumps, and the DO sensor is placed in line between the primary T/C set and its pump.  The effects of the inclusion of the DO sensor and the extra tubing between the T/C set and pump were not known prior to the cruise, since the DO sensor is of a new design used for the first time in SO GLOBEC on NBP0202 cruise. At the minimum, the extra tubing increases the lag time between DO and pressure readings.  Preliminary estimates of this lag time were during CTD casts 25-30, assuming that the DO hysteresis between DO and pressure during those parts of the down and up casts made at 40 m/min was due entirely to pressure.  These tests suggest that the DO value corresponds to the pressure value taken about 15 sec earlier.


The CTD-mountable Microstructure Profiling System (CMiPS) has been mounted on the CTD rosette frame during most CTD casts during this cruise.  CMiPS is a self-contained instrument that records temperature, conductivity, and pressure measured with two fast-response thermistors, a microconductivity probe, and precision pressure sensor all sampled at 512 Hz.  The data, recorded internally to disk, are downloaded to a PC after the CTD is back on deck after a cast.  The data are then processed to obtain two high-resolution temperature (HRT), one conductivity (HRC), and a pressure (HRP) time series.  To help synchronize the CMiPS and CTD time series, the CMiPS raw temperature voltage is digitized inside the CTD fish and included in its scan data stream received and recorded by the CTD deck unit. 


The purpose of CMiPS is to collect microstructure TC data to help identify and quantify turbulent mixing within the water column sampled by the CTD.  To calibrate the CMiPS temperature and pressure scaling (i.e., the conversion from A/D counts to scientific units), the CMiPS HRT/HRP data were compared with the 1m-averaged CTD T/P data from several casts, resulting in approximate linear scaling rules for the HRT and HRP data.  These comparisons suggested that the CTD primary T sensor did not response as quickly to sharp changes in HRT as the secondary T sensor.  To investigate this further, the raw (un-averaged) 24 Hz CTD data were examined, and salinity spiking first minimized when lags of 2 and -1 scans were used in processing the primary and secondary T/C data.  After these lag corrections were made, the primary sigma-t profile became everywhere stable while the secondary sigma-t profile remained stable.  While difficult to quantify, these comparisons of the 24 Hz lagged CTD data with the 512 Hz CMiPS data suggested that the primary T/C set has a longer response time than the secondary T/C set.  For this reason, the lagged secondary T/C data should be used forfurther scientific analysis.


Water samples are drawn from 10-liter Niskin bottles closed at various depths during each cast for use in checking the CTD conductivity cell performance during the cruise.  The conductivity of the bottle samples is measured at 24ºC using a Guildline AutoSal (model 8400B) salinometer located in a new temperature-controlled Salinity Lab on the NBP.  These conductivity values are then converted to bottle salinities (Sb) using MatLab Sea-Water Toolbox codes.   These bottle salinities are compared with the CTD primary and secondary salinities (S0 and S1) computed using the primary and secondary T/C/P data recorded when the bottles were fired and the same MatLab codes.  To monitor the CTD conductivity cell, the bottle salinity Sb and CTD temperature T are used to compute the equivalent bottle conductivity Cb at the in-situ primary and secondary temperatures T0 and T1.  


Plots of differences between primary and secondary temperature (T1-T0), conductivity (C0-C1), salinity (S0-S1), bottle and primary salinity (Sb-S0), and bottle and secondary salinity (Sb-S1) were made on August 18 using data collected during the first 28 CTD casts. The CTD difference data show very small, but consistent offsets between the primary and secondary measurements (Table 1) that appear constant in time.  The CTD-bottle salinity differences show offsets that appear to change in time after sample 47.  The first 47 samples had been run as the batch on the AutoSal, while the remaining samples had been run in two separate batches by different operators.  It appears that the AutoSal was not properly standardized during the first batch. Using the later samples starting with 48, the CTD-bottle salinity and corresponding conductivity offsets were small and appear constant in time (see table below).  These offsets should be used to correct the raw 24 Hz CTD conductivity data before computing depth averages and further analysis.  


In summary, over the first 28 CTD casts made during NBP02-04, the CTD has worked quite well, exhibiting very small DC offsets in primary and secondary temperature and conductivity values with water samples taken in well-mixed waters. At this stage, final processing of the CTD data should follow the following steps:


1.      Set conductivity lags for raw 24 Hz CTD data (2 scans for C0, -1 scan for C1)


2.      Add CTD-bottle mean conductivity offsets to C0 and C1


3.      Compute salinity and other derived variables (i.e., σt) for each scan using MatLab code


4.      Lag DO 15 sec with respect to pressure to account for the delay time introduced by the tubing between T/C and DO cells (see DO sensor section)


5.      Construct depth-bin averaged data if desired.


6.      Use secondary sensor T/C/S data for final scientific analysis.


It seems clear for the limited analysis to date that the DO sensor being inline between the primary T/C sensors and their pump does not adversely affect their accuracy in regions of very weak T and S vertical stratification.  However, the apparently slower response of the primary system to rapid changes seen in the secondary and CMiPS data suggests that the flow rate in the primary system may be reduced by the added flow friction caused by the additional tubing and the DO cell. 


Mean and 95% confidence limits of the mean difference between CTD primary (0) and secondary (1) temperatures, conductivities, and salinities with the bottle sample salinities and conductivities at the CTD temperatures. The number of samples in each group is given in the right column.




95% Confidence Limit

Sample Number



+/- 0.0003             




+/- 0.0003




+/- 0.0003             




+/- 0.0005             




+/- 0.0005             




+/- 0.0004             




+/- 0.0003             




Sea Birds (Chris Ribic and Erik Chapman)

On August 18, seabird and Crabeater seal surveying was conducted for 8 hours as the ship traveled with the L.M. Gould from station 65 to 41.  The first few hours of surveying were conducted in very thick ice-cover and the ship was forced to back and ram its way forward.  We soon found an opportune lead that extended in the direction we were heading, so during most of the day we found ourselves in open water and 7 to 8-tenths ice-coverage.   This was a relatively large lead and we saw more open water today than any other day in the study area.


Crabeater Seals were common in the morning along one particular section of the lead, but through most of the day seals were not abundant.  Snow Petrels were more abundant here than any other area in the study grid that we have surveyed to this point.  This is probably a result of the relatively large amount of open water and ice-edge near the ship, a habitat in which Snow Petrels typically forage.  In areas of the lead that were covered in new gray ice, we observed Snow Petrels landing on the ice and doing what seemed to be picking through small holes in the ice in search of food.   In late afternoon, a single Adélie Penguin was observed hauled out on the ice alongside the lead.  This was the first Adélie Penguin seen in several days. 


A summary of the birds and marine mammals observed on 18 August (YD 230) during 6 hours of survey time as the ship traveled between stations 65 and 41 is the following:


Species (common name)

Species (scientific name)

Number observed

Snow Petrel            

Pagedroma nivea  


Antarctic Petrel       

Thalassoica antarctica         


Adélie Penguin          

Pygoscelis adeliae             


Crabeater Seal         

Lobodon carcinophagus           




Marine Mammal report (Chico Viddi)

One week has passed since the great Minke whale day of 11 August. Since then, 15 sightings have been made, counting 30 whales in total in this “Minke Week”. To date, 125.1 hours of observation have been achieved, 57.7 of which were “effective effort” hours.  Eight hours of observation were done on 17 August, but only 45 minutes were effective effort, since most of the day we were at station 65. In contrast, 7.9 hours of observation were done in 18 August with 6 of them effective hours.  August 18 was characterized by some fog patches and overcast to partly cloudy skies.  There were ice floes of first year ice, shuga, and grey young ice varying from 6 to 10/10ths coverage, with variable sized leads of open water. In general, the day presented good viewing and weather conditions for the cetacean survey. Three whale sightings were made during these two days. A Minke whale was observed on 17 August during a MOCNESS tow (incidental sighting). This whale was seen at 1624 (-68º 07.37′S; -74º 39.44′W), 5º to starboard and 0.68 nm from the ship. The first sighting on 18 August was made at 1042 (-67º 31.28′S; -72º 50.65′W) 8º to port and 0.90 nm from the ship. Two whales, probably Minke (they could not be identified), surfaced in a large lead of open water. The second sighting of a Minke whale, was done at 1613 (-67º 35.42′S; -72º 01.85′W) 34º to port and 0.78 nm from the ship.


Only ten crabeater seals were seen on 17 August (seals which were close to the station), whereas 61 seals were observed on 18 August, most of them (34 seals) seen from 0900 (-67º 37.68′S; -73º 09.44′W) to 1000 (-67º 35.60′S; -73º 16.90′W).  A very peculiar and delightful observation was made on 17 August while towing the 1-m MOCNESS. The ship was going back and forth on a transect through a narrow lead of open water, while a crabeater seal would come along swimming and breaching beside the vessel. What is peculiar about this behavior is that every time the vessel would make its way back and forth and would get close to this seal, instead of escaping (as any other “normal” seal would do) it would get very excited and jump into the water and swim (“play”) along Palmer's way.


Current Position and Conditions

The plan to escort the Gould to station 41 was scratched due to bad ice conditions and a second plan to have the Gould make their second process station in the vicinity of grid stations 28 or 27 was ruled out this evening (19 August) for the same reason.  We are currently steaming to grid station 43, further offshore where it is hoped that ice conditions will permit the Gould's next process station to be established there.  Our current position on 19 August - 2325 hrs is -67º 21.339′S; -71º 25.638′W). Air temperature is -21.9ºC and the barometric pressure is 987.4 mb.  Winds are out of 230º (southwest) at 20 to 30 kts. Skies are partly cloudy.


Cheers, Peter