Weekly Science Report 3: LMG01-06 Southern Ocean GLOBEC

Cruise days 10 August to 20 August inclusive
Science days 10 August to 20 August inclusive

I. LMG 01-06

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 Costa/Burns/Crocker - Foraging Ecology of Crabeater seals
BG-234-0 Fraser - Winter Foraging Ecology of Adélie Penguins
BG-235-0 Fritsen - Sea Ice Microbial Communities
BG-237-0 Harvey- Biochemical Determination of Age and Dietary History in the Krill Euphasia superba
OG-241-0 Smith/Martinson/Perovich Optical Environment of the Western Antarctic Peninsula Region
BG-244-0 Quetin/Ross- Winter Ecology of Larval Krill: Quantifying their interaction with the Pack Ice habitat

c. Cruise overview to date
August 10. The LMG was forced to relocate slightly from Process #2 by a large iceberg heading directly towards us.  We pulled up our stakes but left the complex CRREL buoy in place to be recovered during NBP 01-5.  Upon moving approximately 1.5 km from our previous work site we conducted a CTD cast and decided to find a suitable site for about 2 days more work.  While doing so we came across a group of Adélie penguins that were captured for diet sampling. We also came across a seal but it went into the water.  Teams collected ice samples.

August 11. After collecting diet samples from Adélie penguins last night the LMG continued to move in the immediate vicinity of Process #2 to find a suitable, iceberg-free location for more work.  In the process we became stuck for several hours in an area of ice pressure and active ridging.  Around midnight we broke free and hove to in an area of thinner ice.  At first light we identified a suitable floe for ice collections and diving operations and set up camp.  At approximately 15:00 we were forced to pull up stakes once again as winds caused the ship to move to starboard and crack the working floe.  However, we were able to complete one dive and an ice thickness transect before we had to move.

August 12. At daylight when the LMG attempted to move to a good location to conduct science we were unable to make any progress due to ice pressure and heavy ridging in our vicinity.  Meanwhile, some repairs were necessary on the main engines.  These two conditions led to the daily metric of UD.  Nevertheless, the ice coring team was able to collect some samples.

August 13. The LMG spent the morning maneuvering into position for a rendezvous with the NBP.  At approximately 14:25 local the two vessels met and the NBP led the way north through heavily rafted ice and extensive rubble fields for the LMG.  At 16:00 L the two ships exchanged equipment and then parted ways.  The NBP was to pick up where they left off on their survey grid, while the LMG planned on spending time in the open water near the southern end of Adelaide Island looking for predators and towing the MOCNESS net.

August 14. The past 24 hours have brought us the most extreme weather we've seen yet.  The barometer bottomed out at 936.5 mb, the air temperature dropped to -27.8 o C (wind chill of -55 to -60 o C), and we had zero visibility last night due to blowing snow in 40 knot winds.  The LMG thus hove to while awaiting the return of the NBP to escort us further north.  At first light this morning we continued our northward push through heavily ridged pack ice.  It's hard to believe that a week ago this area had only 4 inches of ice with 4 inches of snow on top!  No science is being planned or conducted during this transit to our study area.  Active discussions are taking place both on board and between the two ships as to what the best plan for the remainder of the cruise will be.

August 15. The NBP succeeded in escorting the LMG to our desired station location last night.  The two ships parted ways again at approximately 22:30, with the NBP returning to the south and the LMG remaining near Survey Station #19 to establish another Process site. At first light this morning we nosed around the weakly cemented floes looking for an ideal location when a seal was sighted.  The seal team handled the animal, then we conducted a CTD cast, and began work on the ice.  Cold temperatures and weak winds made it relatively easy to work outside.

August 16. The LMG continues to occupy GLOBEC Process Site #3 with good success.  Three scuba dives were completed today along with extensive ice coring and collection.  We were visited by a lone emperor penguin this afternoon, but the birders did not handle it.  The ship requires close care to keep it alongside the working floe as the pack ice is loose, but remains at 10/10 coverage.  Light winds and cold temperatures make for good working conditions.

August 17. The LMG continues to occupy Process Site #3.  As an experiment we erected a Scott tent over one of the two dive holes.  Overnight, there was enough freezing on the unprotected hole to walk across while on the covered hole the ice was so thin you could put your finger through it.  The tent also provided shelter against the wind for the tenders and helped to cut down on glare and visual shock for the divers coming out of a darker environment.  Air temperatures continue to be cold, but offshore winds should help relax the ice pack making it easier for the LMG to move about the area under its own power.

August 18. The LMG continues to occupy SO-GLOBEC Process Site #3.  Ice collections and dive operations are being conducted and we have seen no seals or penguins lately.  The news of the day is the rise in air temperature from around -20 o C to near -5 o C.  We are also experiencing a rather noticeable swell running though our area but the working ice floe is holding together.

August 19. Visibility is very poor due to falling and blowing snow.  Nevertheless, we are continuing to collect ice and brine samples and to measure an ice thickness transect.  Conditions are judged to be too poor to allow for safe scuba diving.  Work was completed at Process Station #3 today. The plan is to move to the east and/or north tomorrow during daylight.  This will allow us to search for seals and penguins as well as hopefully find open water to tow the 1-m MOCNESS.

August 20. The plan for the day was to steam towards Adelaide Is in an attempt to find open water to carry out some final MOCNESS tows and to look for penguins for diet sampling and a final seal to tag. Prior to departure we completed a CTD cast and then steamed to the North looking for leads that would allow us to move to the East. It was slow going. We had to back and ram multiple times and our speed was only 2 Knots. When we left our process station we were 17 miles from our planned waypoint, when we shut down in the evening we had 11 miles left to the waypoint. During the night we had considerable winds from the NE such that by morning when we started again we were now 22 miles away from our waypoint! However, the ice team was able to get samples from this station.

d. Individual group reports.
BG-232 Costa, Burns and Crocker. Field team D. Costa, N. Gales, S. Trumble & B. McDonald. Our research focuses on how crabeater seals forage within the seasonal winter pack ice. Since our last report we failed to see any hauled out animals at Process Station #2. Our last seal was tagged on August 9. We sailed past one easily accessible crabeater seal while the NBP was escorting us to the new process station. It was hard to pass this one by, however, it seemed inappropriate to hold up both ships while we worked up a seal. Finally, at first light on the morning of August 15th while looking for an ideal location to set up the ice station, we sighted a crabeater seal. We immediately went into action and tagged our 7th seal. It was a 234 kg 202 cm male crabeater seal, which was in excellent condition. He was one of the cleanest seal's we have seen so far, with a really clean and luxuriant coat (for a crabeater seal). We have gotten quite good at the capture and tagging of the animals. The whole procedure lasted about an hour. We were also quite fortunate as we broke one of the legs of our tripod weighing our last seal. However, the magician's (MTs S. Alessandrini and J. Spillane) managed to replace the broken leg. The fixed tripod worked fine, better than the original! We now have only one tag left to deploy. Although, we sighted many animals in the water at this station none of them hauled out. Several animals were observed in the dive hole and one started to haul out, but at the last minute chose not to.

We continue to receive updates on the progress of the 15-tagged crabeater seals. There has been a significant movement to the north of all of the animals. Whereas a few animals had been working in the southern regions of Marguerite Bay (off Alexander Is) now only one animal remains inside Marguerite Bay and only two of 4 animals tagged at process station #2 (just offshore the mouth of Marguerite Bay) remain in that area. The remaining 4 seals (including the most recently tagged seal) have moved well to the north of Adelaide Is in the vicinity of Crystal Sound and the Biscoe Islands, while one of the seals tagged at Process Station 2 moved into the LeBoeuf channel, the area between Adelaide Island and the Peninsula.

BG-234 Fraser.  Field team W. Fraser & S.Muth. Attempts to obtain Adélie penguin diet samples, one of the key objectives we are still trying to complete, have met with only limited success.  On the evening of August 10th, we were able to capture and lavage five penguins.  Although the diet samples obtained were quite digested, we nevertheless were able to determine that males were feeding predominantly on krill and females on fish.  This pattern was also noted in the May GLOBEC cruise, hence these preliminary winter diet data suggest the pattern continues into the winter.  On August 15th, we captured another group of birds and selected a male and female to deploy the SDR-T16 tags, which in addition to providing data on foraging location, will also provide information on dive depth and other foraging parameters.  These tags are at this writing operating perfectly, and preliminary data indicate that the male's dive depth is, on average, about 60 meters deeper than the female's.  Whether this explains the differences in diets seen between the sexes is still uncertain, but the male's dive depths do show coherence with krill distributions during daylight hours.  As we reported last week, the 10 PTTs deployed earlier are all operational and providing excellent data. An analysis of these data through 19 August indicates that Adélie penguins are still foraging along the edges of a polynya south of Adelaide Island.

BG-235 Fritsen. Field team C. Fritsen, S. Marschall & J. Memmott. When we initially occupied the long term Ice Station Robert (Aug. 5) we were working on ice that was ca. 35 cm thick which had a snow cover of 15 to 20 cm.  The majority of this snow thickness was flooded with seawater (i.e. the snow load had depressed the surface of the ice below sea level and the seawater infiltrated through the ice and resided on the ice surface).  Air temps at the start were ca. -1oC.  Air temps did change and dropped to approximately -15oC which lead to the freezing of the flooded seawater in the snow and the total ice thickness quickly increased to 50+ cm.  In addition, it started snowing again and we ended up with an additional 10-20 cm of snow on top of this new formed ice.  This net increase in ice thickness (over 5 days) and additional snow cover presented the LMG with a challenge in regards to its maneuverability capabilities.    Hence, when departing Ice Station Robert the LMG operated with the aid of the NBP.

However, before leaving the vicinity of Ice Station Robert, we characterized yet another ice floe in the region.  This floe was extremely interesting as it also had large areas of slush/flooded snow measuring 10-20 cm in thickness.  This slush, however was cold (below -2 oC ) (as opposed to seawater temperatures of -1.8oC ) .  We confirmed the cold temperatures with measures of the salinity that were in excess of 50 psu.  Hence, the slush on the surface of this also was in the process of freezing.  The observation by the krill divers of "brine tube chandeliers" provides consistent anecdotal evident that this process was leading to the net rejection of brine into the water column.   Ice thickness transects, slush collections, core collections, snowpits and an ice optics station were accomplished by the synergistic activities of BG-235, OG-241 (Elder, Stammerjohn and Claffey) and BG-244 (Gibson and Dovel).

While in transit to survey station #19 BG-235 personnel processed samples, conducted photosynthesis and bacterial production experiments and ate cookies with Kerry Claffey before banishing him to the NBP where he has had to endure the woes of ping editing and cookieless breakfasts.

When we reached the vicinity of survey station we established what would become known as Ice Station Billy (named after Dr. Fraser because it was his Birthday).  This ice station was located on relatively undeformed first year ice having a thickness of 35-40 cm.  Operations 15 August to the morning of 20 August were focused on establishing the baseline information for learning about the floe's mass balance, thermodynamics, biotic composition and biotic activity.  To accomplish these general goals the combined activities from BG-235, OG-244 (Elder & Stammerjohn) and BG-244 (Gibson and Dovel) as well as the stellar expertise of the "Back Deck Gang" (Alesandrini & Spillane) lead to the tremendously successful and safe implementation of the following:

  • Repeated ice thickness transects.
  • Experiments on photophysiology and heterotrophic activity
  • Nested spatial sampling of cores for biological composition, chemical composition, and physical structure.
  • Deployment of a simple buoy (which we hope will help Stammerjohn et al. find this piece of ice once again).
  • Deployment of a snow stake array (which has already provided a snowfall/accumulation information and will provide information on snowfall accumulation, ice growth and flood-freeze cycles if the revisit by the LTER is successful.
  • Snow characterizations through snow pits
  • Collections of ice water-interface samples for determinations of biotic composition
  • Ice and snow optics stations
  • Deployment of a long-term thermistor string
  • Collections of brine samples for characterization of the bacterial community's 16S rRNA diversity.

  • While at this station the repeated measures from snow and ice thickness stakes as well as ice thickness transects showed the net growth of 3 to 6 cm the ice sheet.  This net growth occurred at the base of the ice at the ice-water interface and provides a direct contrast to the processes that lead to net ice growth through the flooding and freezing process that was documented at Ice Station Robert.  We note, however, that as we were leaving Ice Station Billy (on Aug 20th) the floe had and was accumulating considerable snow cover during a sustained snowstorm.  This new snow accumulation coupled with increases in air temperatures would leave this floe highly susceptible to flooding, the formation of slush and the potential for net ice thickening through the flood-freeze cycle.  We hope Ice Station Billy will be reoccupied by the LTER ice cruise in order for the entire story of this floe to be determined.

    BG-237 Harvey. Field team consists of R. Harvey and S. Ju. Heavy ice conditions and planned ice station work did not allow additional MOCNESS tows and no additional samples were collected since weekly report 2. As a result, priority has been given to samples in hand and 500 + krill have been dissected and age markers extracted and analyzed. Protein measures for samples are now being completed. With the shortfall in samples of adult krill, additional effort has been made to expand opportunistic sampling of ice cores, brines and samples collected by divers for detailed pigment analysis. In cooperation with BG-235, 6 ice cores at process site 3 were collected and are undergoing detailed pigment analysis. BG-244 kindly provided samples of material "slurped" from under the ice during dives for comparison with ice cores and larval animals. Pigment analysis completed to date already shows strong differences ice cores verses surface waters collected by CTD, with a greater concentration and diversity of pigments in ice. This includes the contribution of dinoflagellates (reflected by the presence of peridinin) to ice communities, which do not occur in the water column. Water samples from CTD casts (0-200 M) are being included for pigment analysis to provide information on phytoplankton distributions and comparative information with ice algal communities. These water column samples invariably show much lower concentrations of chlorophyll and other pigments than ice cores, with variable concentrations in the mixed layer and strong decreases at depth. We are also comparing processing methods to determine the influence of salinity shifts during thawing on the pigment distributions seen by HPLC.

    BG-244 Quetin and Ross. Field Team: L. Quetin, C.Boch, S.Dovel, A. Gibson, T.Newberger, L.Quetin, S.Oakes, M.Thimgan, J.Watson. Since August 8 we have completed 9 dives and occupied 2 process stations for 4 days each.  Our efficiency at working a process station continues to increase.  At both stations we were able to establish permanent transect lines.  At the second process station we were able to work in much closer to the ice sampling than at the first station and were able to establish transect lines directly below the ice team's transects for ice depth.  We will follow this sampling design in the future.  Some preliminary results from our surveys indicate that larval Euphausia superba were much more abundant at the inshore station (near Globec sta. 42) than at the offshore station (near Globec sta. 19).  Adult Euphausia superba, as noted on previous cruises, continue to be absent from the underice community.  Other observations of larval behavior were similar to past observations.

    We continue to collect krill for measurements of feeding activity and growth.  We have nearly completed 9 experiments on growth rates; have completed 4 experiments to determine a clearance rate and 2 to establish initial levels of feeding activity for larval krill.  Though we have yet to thoroughly analyze the experiments on growth rates, it appears that the inter-molt period is greater at the offshore than inshore station.  In addition, we continue to collect krill larvae for length and stage frequency analysis, chemical composition and CHN analysis.

    Feeding experiments on krill larvae with natural assemblages of micro plankton have been difficult due to low abundances of micro plankton in the ice.  However, we recently completed one successful experiment using brine obtained at the offshore station.  In addition, 3 feeding experiments were completed using a monoculture to determine feeding rates at different phytoplankton concentrations.

    OG-241 Martinson, Perovich, Smith. Field team B. Elder, S. Stammerjohn & K. Claffey. Ice observations while under way, plus cross calibration between ice observations taken aboard the Palmer while we were following them. Complete Ice station conducted at Ice Station Billy (Station 19). We performed ice optics (albedo, transmission of both with the snow pack and then we removed the snow and measured again with bare ice.) of cold snow covered with a thickness of 30cm.

    A 76 m transect line was put in place where ice thickness, free board, snow depth and wicked layer (lower part of the snow pack that is wet as it has wicked up brine from the surface). The transect lines were located such that the divers under ice transects were directly beneath our thickness transect so that we might get a better idea of what the underside of the ice looks like. In this part of Marguerite Bay there is very little ice that is undeformed. Even where the ice may look nice and flat on the surface, there may be blocks trapped underneath. These blocks are not solidly frozen to the underside in many cases, evident from when you are drilling; you can push the blocks up and down with the drill string. Here at this ice station we had much colder temperatures than at Robert. We were on station for a long enough period of time with the freezing front reaching the bottom of the ice sheet that we had the chance to measure ice growth over the length of the station. The level ice portions of the line over the 4 days on station had an average ice growth of 3-4cm. On the last 2 days of the station an average of 15cm of snow was deposited in drifts (some >30cm deep) over the site, which depressed the ice sheet 1-2 cm thus bringing the free board level down to near sea level. With just a little more snow, the surface will be depressed below sea level and the flood-freeze cycle will begin once more. Snow pits were done at various locations to characterize the snow pack. Temperature, salinity and density profiles were measured as well as visually measuring grain size, type and hardness.

    Nested array of 10 ice coring locations were sampled for temperature, salinity, d18O profiles along with structure. Cores were co-located with the other ice groups such that we have inter-comparisons of data. We are now processing thin and thick sections in the freezer van to better characterize the ice for ice type, bubble and brine features.

    The remaining 2 buoys were deployed. One "simple" buoy at ice station Billy, which transmits air temperature, barometric pressure and GPS position. Along with the buoy we deployed a bamboo stake array, which we hope will be found by the next LTER cruise and the ice/snow measurements can be conducted on these same locations to get a 4-6 week time series. With this Fritsen deployed a "hobo" thermistor string. The last "complex" ice buoy was deployed by Kerry Claffey whom we traded to the Palmer for a band saw. This buoy was deployed at station 74. In addition to the data which we receive from the simple buoy, this buoy measures, water temperature, a flourometer, an acoustic sensor to measure bottom ice growth/melt, a surface acoustic sensor to measure snow deposition, air temperature and a string of 28 thermistors that measure temperatures at 5cm spacing from the air, through the snow and ice and into the water immediately below the ice. From this buoy we can watch the mass balance of the ice sheet change with weather and season.

    Submitted by:

    Daniel Costa                          Karl Newyear
    Chief Scientist                        Marine Projects Coordinator