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

16 April 2002

During the 16th of April, the broad-scale survey activities were focused work at stations 8 to 11 on survey line 2 that extends 81 nm from inshore off the northern end of Adelaide Island to just beyond the continental shelf break. Early in the day, the winds were up some from those experienced yesterday and were running in the low to mid-20 kt range out of the northeast (053). The barometer dropped to 971.9 mlb, but the air temperature held steady (-0.3ºC) and was about the same as the water temperature (-0.518ºC). Off and on during the day, it snowed moderately and with the wind, the flakes were being driven horizontally across the deck. The snow again caused problems for the bird and mammal surveyors. In the afternoon, the winds dropped down to around 15 kts, and in the evening there was little wind and seas became calm.

At each of the stations, a CTD cast was made with both the microstructure profiler and the FRRF, except that the FRRF was removed for the cast at station 11 due to its depth limitations. In addition, two satellite tracked drogues were deployed at stations 8 and 9 to provide Lagrangian measurements of the surface currents in this northern area of the grid. Two sonobuoys were also deployed along the trackline. At station 11, quantitative zooplankton collections were made with the MOCNESS and a live animal collection was made with the 1-m Reeve net. BIOMAPER-II was towyod between stations and was only taken out of the water at Station 11 to make it possible to deploy the MOCNESS. To the extent possible, seabirds and mammal observations were made while transiting between stations.

As described below, the event of note was the discovery of an intrusion of offshore water at station 9. This prompted a brief deviation from the survey trackline to measure to the horizontal extent of the intrusion perpendicular to the trackline. After completing the station work, BIOMAPER-II was towyoed along a transect perpendicular to the survey line, which was 5 km long on either side of the station location. Additional physical observations were made at each end of this short transect and some were also added to the survey line as we transited between stations 9 and 10.

We are now well enough into the cruise so that the kinks in the various science programs have been worked out and the individuals on each of the research teams are working more efficiently and effectively. Thus far we are on schedule and our work is progressing nicely.

CTD Group report (John Klinck, Tim Boyer, Chris Mackay, Julian Ashford, Andres Sepulveda, Kristin Cobb)

The CTD group did 2 CTD and 7 XBT casts today. The description of one station done yesterday is included here.

The CTD cast at station 9 detected an intrusion of oceanic water with temperatures above 1.7ºC and a maximum of 1.8ºC. An ad hoc sampling was implemented with an XBT station 5 km northeast of the station followed by a BIOMAPER-II transit through the station to a XBT 5 km southwest of the station. Additional XBTs were dropped 5, 10, 20 and 30 km from station 9 on the transit to station 10.

Preliminary analysis of the XBT casts indicate that the intrusion was at and northeast of station 9 and was only weakly evident to the southwest. The temperature maximum along the track between stations decreased to 1.5 and increased to 1.9, but there was no consistent pattern, from this preliminary look at the observations. There was no trace of the intrusion at the next station (10).

Station 8 (Cast 10, 316 m) had a uniform mixed layer to 40 m, a winter water layer (-0.8ºC) centered on 80 m, and increasing temperature and salinity to the bottom. Deep temperatures were 1.3ºC, but there was no temperature maximum. Strong temperature reversals occur from the base of the mixed layer to 200 m.

Station 9 (Cast 11, 500 m) had uniform conditions to 30 m, a second uniform layer to 70 m and a weak Winter Water (WW) layer to 100 m. A thick layer of water above 1.7ºC extended from 180 m to 270 m with a temperature maximum of 1.8ºC. Below was uniform temperature (1.3ºC), except for a 30 m thick bottom layer (1.0ºC). Strong temperature reversals occurred between 100 and 300 m depth.

Station 10 (Cast 12, 471 m) had a mixed layer to 80 m with increasing temperature and salinity. A 20 m thick WW layer (-0.8ºC) sat over the pycnocline. The temperature increases, with ragged reversals, to 1.5ºC at 275 m.

Chlorophyll remained high (0.2-0.3 mg/l) in the surface layer at all stations. Deeper chlorophyll reduced across the pycnocline to small values below.

Microstructure Profiler (CMiPS) report (Chris Mackay)

The microstructure instrument has now been deployed on CTD for casts 3 to 11. As the instrument and its installation on the CTD are new, procedures for its operation are evolving. The instrument has to be turned on by inserting a plug in the battery housing just before the CTD is lifted to be swing out over the side and turned off as soon as possible upon its recovery. Keeping the period that it is on as short as possible saves battery power and data storage space in the instrument. Great care must be exercised to ensure that nothing makes contact with the very delicate probes at the bottom of the instrument. This is now becoming routine. Data collected so far appears good and the probe is operating as expected. It is now important to clearly identify what it is that the instrument is measuring . This requires observation and evaluation of any factors which may be affecting the water the sensors pass through to establish that it has not been disturbed by any part of the CTD package. One such possible influence being looked at is the weight hanging beneath the CTD to detect the bottom. The wake shed by this weight may be measured by the microstructure sensors resulting in contaminated data.

Marine Mammal report (Debra Glasgow)

April 16 was another day of fog and very poor visibility of less than 1 nautical mile for most of the day with rare exceptions. The only sightings of the day were of several fur seals. One group of 3-5 fur seals seemed to be accompanying the ship for more than an hour, occasionally being very active and porpoising near the bow of the ship. At other times, they were following at the stern.

Sea Birds (Erik Chapman and Matthew Becker)

On April 16th, surveying for sea birds lasted for 2 hours and 53 minutes between stations 9 and 10 in foggy and snowy conditions. Visibility varied between 1.5 km and less than 300 m and we were forced to go off effort for extended periods during the transit. The most common species observed was the Southern Fulmar, with Cape Petrel, Blue Petrel, and Antarctic Petrel also well represented. Species were observed that we had previously seen more off the continental shelf on the previous line, though we were still some distance from the shelf break. It will be interesting to see whether there is an association of these species with the intrusion of Antarctic Circumpolar Deep water apparent in CTD and XBT data collected near station 9. Night surveying was not done due to snowfall this evening. While the MOCNESS was being towed at station 11 late in the evening, two Cape Petrels landed on the bow of the ship. We looked for regurgitated stomach contents (there were none), then captured the bird and took morphometric measurements of the bird before releasing it. We noted that there were many birds around the ship, flying in the ship's lights, including a Black Browed Albatross and several Cape Petrels. A summary of the observations follows:

Species (common name)	Species (scientific name)	Number observed
Cape Petrel (“Pintado Petrel”)	Daption capense	17
Southern Fulmar	Fulmarus glacialoides	28
Antarctic Petrel	Thalassoica antarctica	7
Blue Petrel	Halobaena caerulea	15
Unidentified Prion		0
Grey-headed Albatross	Diomedea chrysostoma	2
Wilsons Storm-petrel	Oceanites oceanicus	3
unidentified large Skua		0
Southern Giant Petrel	Macronectes giganteus	0
Antarctic Fur Seal	Arctocephalus gazella	4

Water Sampling for Clone libraries (Mark Dennett)

At Station 9, surface water from the CTD and other selected depths was filtered for the development of eukaryotic clone libraries. Samples were frozen and will be returned to Woods Hole for amplification and further processing. These will be some of the initial samples to be used for methods testing in preparation for a return trip to the Antarctic in 2003. Along with samples collected on a previous cruise to the Ross Sea, we plan to construct group and genus specific oligo probes for use in trying to better understand community structure in this cold environment. Water for this purpose will be collected at several more stations along the transect grid.

Zooplankton (MOCNESS/BIOMAPER-II) report (Carin Ashjian, Peter Wiebe)

The third MOCNESS tow of the cruise was conducted at standard station #11 around midnight April 16. We were in deep water heading off shelf (started at about 800 m of water and ended in >2000 m of water). It was a very successful tow. The net flew very well. We sampled down to 1000 m. Again, the net response failed to function.

Despite filtering large volumes of water, the catch in the deep nets (400-1000 m) was quite sparse and composed primarily of copepods with a few euphausiids, chaetognaths, worms, shrimp, and fish. Of note was the large ctenophore with a dark purple interior that was caught in the 800-1000 m depth range. Above 400 m, the catch still contained few crustaceans, despite the presence of a strong scattering layer between 150-400 m observed during the tow on both the ADCP and the Simrad EK500. Large krill were present in very low abundances from 100-400 m. A few furcilia were observed from 100-200 m. Chaetognaths were seen from 200-400 m. From 50-100 m, the plankton was composed primarily of copepods. The upper 50 m was dominated by phytoplankton, classified by Wendy Koslowski as Chaetoceros and Thalassiosira. It was abundant in the 25-50 m depth range and massively numerous in the 0-25 m depth range, requiring 5 jars to hold the sample. Very few, if any, crustaceans could be discerned through the thick green glop.

This abundance of phytoplankton corresponded to observations of clumps of phytoplankton chains observed on the VPR on the BIOMAPER. Examination of the cells from the MOCNESS revealed that they did not contain much viable chlorophyll, but rather were more brown in color, supporting observations that the algal mats were composed of dying or dead cells that were fluxing downwards through the water column to the benthos.

The along track measurements being made with BIOMAPER-II continued between all of the stations occupied during 16 April. In addition, as a result of the discovery by the CTD group of deep water with 1.8ºC temperatures, which implies an intrusion was coming onto the shelf from offshore, a plan was implemented to map the distribution of the water and to get some additional biological information about the structure of the intrusion. We had the bridge mark spots on their chart 5 km to the northeast (perpendicular to our trackline) and 5 km to the southeast. BIOMAPER-II then did a shallow towyo while steaming to the northeast point. After reversing course at the northeast point, a deep towyo to 250 m was done, which got into the deep warm water about where station 9 was located. There was little evidence in the backscattering for krill schools, but there were a number of fish-like targets about 160 m below the surface that seemed to be more abundant than elsewhere along the survey line. Once to the southwestern point, we again reversed course and went back to Station 9 before heading out along the survey trackline.

For the most part, the backscattering along survey line 2 was moderate to low. The diffuse band of scatterers above the bottom persisted as we steamed offshore and at one point where the bottom was over 500 m deep, it was nearly 180 meters thick.

Cheers, Peter