Weekly Science Report 1: LMG01-04 Southern Ocean GLOBEC

(Jose Torres, Chief Scientist)

Cruise days 20 April to 5 May inclusive

Science days 29 April to 5 May inclusive

I. LMG 01-04

a. Mission statement:

Overall goal is to elucidate shelf circulation processes and their effect on sea ice formation and Antarctic krill distribution, and to examine the factors that govern krill survivorship and availability to higher trophic levels, including seals, penguins, and whales.

b. Projects represented on the process cruise

    BG-232-0 Dan Costa and Jennifer Burns - seal ecology
    BG-234-0 Bill Fraser - seabird ecology
    BG-235-0 Chris Fritsen - SIMCO and water column phytoplankton communities
    BG-236-0 Kendra Daly - Krill ecology and physiology
    BG-245-0 Jose Torres - krill and fish ecology, krill physiology
    BG-248-0 Meng Zhou - krill ecology, behavior, and modeling

c. Cruise overview to date

    20 APR 01 LMG departed PA
    24 APR 01 LMG arrived at KGI to pick up field party (O-196 :Dr. Brenda Hall) and began transit to Livingston Island.
    25 APR 01 LMG arrived at Livingston Island. Lost a day to weather.
    26 APR 01 dropped off Dr. Hall's team began transit to Palmer Station
    27 APR 01 Arrive Palmer Station
    28 APR 01 Depart Palmer Station for study site
    29 APR 01 Began sampling at process station 1.
    5 MAY 01 Concluded sampling at process station 1, transited to process station 5 and initiated sampling.

d. Synopsis

Process station 1 is located at the Western Antarctic Peninsula (WAP) shelf edge in line with the axis of the main cross-shelf canyon that runs from the shelf break into George V Sound. It is bounded by the following coordinates: 66.411° S 70.637° W, 66.0453° S 71.5988° W, 66.6551° S 71.2118° W, 66.2718° S 72.1079°W. The station was initiated with an 18 h ADCP survey that covered off-shelf and on-shelf locations. Discussions among the science party led us to divide process station 1 into an off-shelf (site A) and on-shelf (site B) component. We spent 3 d sampling off-shelf at depths of about 3000 m and 2 d on-shelf at depths of about 500 m. A typical sampling day was as follows:

    0000-1030 MOC 1 (ZHOU)
    1100-1200 CTD (MARSCHALL-STEWART) (Fritsen)
    1230-1430 LIVE NETS (DALY/TORRES)
    1430-1530 HTI (DALY)
    1530-2130 MOC 10 (TORRES)
    2130-2330 LIVE NETS

Winds were moderately high during most of our occupation of process station 1. Twenty five to thirty knot wind speeds were encountered daily and seas hovered at about 15 feet much of the time. Despite the rough weather a considerable amount of sampling and lab experiments were successfully accomplished. It should be noted that process station 1 was an open water station so that our two predator groups, Costa/Burns (BG 232-0) and Fraser (BG 234-0) were unable to take any samples. Their data acquisition will begin with our early occupation of process station 5 that is taking place right now.

E. Individual group reports

1. BG 232-0 ( Burns)
We arrived in Punta Arenas on April 18th, and loaded into the L. M. Gould without too much difficulty. All the essential gear was in place, and the group arrived in Chile largely intact. Mark Hindell lost his luggage in Santiago, but it was found, and was sent south on the N.B. Palmer. The stop in at Palmer Station (4/27) was extremely helpful, as we were able to obtain the last few supplies we needed, and use the science lab facilities to preweigh chemicals (the boat's movement prevents the use of balances at sea). We left Palmer eager to get started, but knowing we would have to wait through Process Site One (PS1) before our part of the cruise could begin. On the way from Palmer to PS1, we did some whale observations for the IWC, and organized all our field gear, so that when we arrived in an area with seals, we would be ready to go. We also started testing the satellite relay data loggers that we plan to deploy on the seals, and found a few programming glitches. Most of the troubles have been worked through, but we have a few tests remaining to complete. Bill Frasier's arrival on the boat has allowed us to talk about likely sites to see penguins and seals, and we are working together to plan the predator captures. We will help Bill with penguin handling when possible, and he and Chris will help us with seal handling when possible. At PS1, we were able to start our collection of potential prey items from the tucker trawls and MOC-10 nets that were deployed by Jose's group. We have some krill and Electrona antarcticum in the freezer at this time. By the end of the cruise we are hoping to have at least 10 specimens from each of the fish species and krill size classes that crabeater seals may be foraging upon. We will use these specimens for the stable isotope ratio and fatty acid analyses of diet. We also worked with Jose, Skip, the Captain, and Bill to identify where we wanted to go after PS1 was completed. We have decided to move inside Marguerite Bay to Process Site 5 (PS5) inorder to have the highest chance of finding predators while there is still some light available to work with. As PS1 comes to a close, we are looking forward to getting started.

2.  BG-235 (Stewart and Marschall for Fritsen)
Vertical profiles of in vivo fluorescence, irradiance (PAR), salinity, and temperature were obtained daily from CTD casts conducted at or around local noon. Casts on 04-29 and 05-04 were done in on-shelf waters (~bottom depth of 550m); all other casts were done off-shelf (~bottom depth of 2800m). Water column samples were taken concurrent with CTD/Rosette deployment from depths of 0, 5, 10, 15, 20, 30, 50, and 100m. Sub-samples were preserved for later determination of dissolved organic carbon (DOC), dissolved organic carbon (DIC), particulate organic carbon (POC), and bacterial and viral abundance, filtered for on-ship determination of chlorophyll a concentration, and assayed for estimates of bacterial production and photosynthesis-irradiance relationships (PE curves, at 5 and 30m only). Not all parameters were sampled/measured on each cast. The depth of the thermocline was ~60-70 at off-shelf stations and ~70-75 m for on-shelf stations. Fluorescence at all stations remained consistent down to the thermocline with peaks at or near the surface; chlorophyll concentrations averaged ~0.22 mg l-1 throughout the euphotic zone at off-shelf stations and ~0.30 mg l-1 at the same depths at the on-shelf station sampled on 04-29. Bacterial production was estimated at only two stations. Production was consistent down to 100m with a peak at 5 m at the on-shelf station, and decreased linearly (R2 = 0.77) from the surface to 100 m at the off-shelf station. Primary production over a range of light levels was elevated at 5m relative to 30m. Process site 1 was ice-free; ice in its earliest stages of formation (grease, pancake, nilas ice) was not observed.

3. BG 236-0 (Daly)
The HTI acoustic system was deployed after we first arrived on Station 1 to complete the noise tests and collect data. However, the rough seas caused a significant noise problem as well as causing some damage to the towed body. During the 5 days on station, the seas only calmed down enough to deploy the HTI on two occasions during a 10 m2 MOCNESS tow. All told, about 4 hours of acoustic data were collected at the off-shelf site and about one hour at the on-shelf site.

At the off-shelf site, a thin layer was detected on both the 38 kHz and the 120 kHz systems at about 60 m, which coincided with the pycnocline. Both frequencies also detected a significant layer about 250 m deep. Net tows collected myctophid fishes and Euphausia triacantha from this depth region. On shelf, the sea state conditions were marginal (27 kt winds and very choppy sea state) and the data often were obscured by noise. Nevertheless, both frequencies again detected a thin layer at ca. 60 m and a deeper layer about 180 m. Net collections indicated that the deeper layer was composed of myctophids. The deteriorating weather prevented the HTI from being deployed with the 1m2 MOCNESS. Later in the early morning, the HTI tail fin was damaged by green water swamping the back deck during the transit to Process Station #5. Repairs are currently underway.

At Process Station #1, live tows collected large abundances of Euphausia superba larvae (i.e., calyptopis and furcilia) in the upper 50-60 m at both the off-shelf and on-shelf sites. Experiments to measure growth and molting rates, egestion rates, and ingestion rates were successfully completed. Several hundred larvae were frozen for dry weights and chemical composition.

4. BG 245-0 (Torres)
Five successful MOC 10 tows, 3 to 1000 m and 2 to 500 m, and 8 live net tows were executed during the occupation of process site 1. Depth strata sampled in the 1000 m MOC 10 tows were as follows: 0-1000 m, 1000-500 m, 500-200 m, 200-100 m, 100-50 m, and 50-0 m. MOC 10 tows in the upper 500 m sampled depths of 0-500 m, 500-300 m, 300-200 m, 200-100 m, 100-50 m, and 50-0 m. Our 1000 m MOC 10 tows revealed a typical oceanic fauna, with a rough breakdown as follows.

1000-500 m: Cyanomacurus piriei (rattail or grenadier fish), Pasiphaea scotiae, Gymnoscopelus braueri (myctophid), Gnathophausia, Bathylagus antarcticus, Euphausia triacantha, Thysanoessa macrura, Gigantocypris mulleri, Gennadas.

500-200 m: Periphylla, Electrona antarctica (myctophid), Gymnoscopelus braueri, Bathylagus antarcticus (deep-sea smelt)

200-100 m: Gymnoscopelus, Electrona, Euphausia triacantha. This depth stratum had highest fish numbers. E. triacantha numbered about 50.

100-50 m: Salpa thompsoni, Euphausia triacantha, Thysanoessa macrura

50 - 0 m: Periphylla, beaucoups salps, Themisto gaudichaudii

Our samples on the shelf revealed a very similar faunal composition with depth. One of the dominant fish species in the 500-1000 m depth stratum, Bathylagus antarcticus, had largely dropped out at the shelf break. It should be noted that Euphausia triacantha was very abundant in our nets both on and off the shelf. The author considers it to be a good indicator species for the presence of circumpolar deep water.

We have had good luck with our live animal captures. E. superba furcilia are very abundant and our physiological measurements are going well. We have about 100 respiration runs already complete.

5. BG 248-0 (Zhou)
The first ADCP survey started at Study Site 1 from 66 24.341°S, 70 45.512°W at 17:25 LT on 4/29/01, and finished at 18:30 LT on 4/30/01. The study site is chosen at the shelf break where a relatively deep channel leads to the deep canyon into Marguerite Bay. The survey consisted of 4 cross-shelf transects, and covered an area of 56 km at the cross-shelf break direction and 28 km along-shelf break direction. The shelf break is centered at the middle of the cross shelf transects.

The measurements up to 310 m (the maximum depth of good ADCP measurements) show a northeastward current of approximately 20-25 cm/s representing the Antarctic Circumpolar Current (ACC) in the water deeper than the 3000 m isobath. A clockwise mesoscale eddy of 11-18 km was discovered in our study area off the shelf break. This eddy penetrated from the surface to the maximum depth of ADCP measurements, and it remained during our study period from 4/29/01 to 5/04/01. On the shelf, the current was northeastward at the surface;it rotated to a cross shelf direction at 230 m. The measurements demonstrated a cross-shelf intrusion of Upper Circumpolar Deep Water (UCDW) onto the west Antarctic Peninsula continental shelf, and into the deep canyon which links to Marguerite Bay.

The CTD measurements showed the surface water was at -0.617°C and 33.748 ppt on the shelf. The mixed layer was up to 70 m. In the off-shelf area the surface water was at -0.894°C and 33.746 ppt. The mixed layer depth was approximately 50 m shallower than that of on shelf. Below the mixed layer, it was the Antarctic Winter Water that was coolest (-1.31°C on the shelf and -1.71°C off the shelf). The maximum temperature is 1.52°C at 259 m on the shelf and 1.82°C at 210 m off the shelf.

The processed ADCP echo intensity measurements along the transects showed the highest-backscattering layer between 150-250 m and having a horizontal scale from 5 to 15 km. A second layer at a depth of 50-100 was also present but weaker. There was no difference between on-shelf and off-shelf areas. The data did not show any diel difference in the vertical structure.

The surface zooplankton aggregations measured by the ADCP were consistent with the measurements of our Optical Plankton Counter (OPC). The OPC shows a maximum of zooplankton abundance at the krill larvae size, which is confirmed by samples from MOCNESS tows. However, what is responsible for the highest backscattering between 150-250 m cannot be confirmed by either OPC or MOCNESS. In this depth range, the OPC counts and sizes show no difference from the surrounding, and MOCNESS samples show a few large krill which would not contribute to such high backscattering. This question needs to be further investigated.