Minutes of the Fourth SO GLOBEC Science Investigator Meeting

9-11 December 2002

Arlington, VA

TUESDAY, 10 DECEMBER 2002

The meeting began with an explanation on the Raytheon travel reimbursement forms from Alice Doyle. She said to return the completed forms to her.

Hofmann summarized the results of the meeting of the co-editors for the SO GLOBEC DSR II volume that was held Monday evening after the close of the SO GLOBEC meeting. She said that there was a suggestion to publish a CD as part of DSR II volume. This CD would include the bathymetry data, appendices for papers in the volume, color figures, etc. Hofmann reminded everyone to obtain a contribution number for manuscripts from the GLOBEC data management office when the manuscript is accepted for publication. She also said that there will be an overview article on SO GLOBEC, to be written by the co-editors, as part of the volume. Part of this overview will be a listing of breakthroughs and highlights from the SO GLOBEC program and she requested that the various groups submit these from their research programs. Hofmann said that the titles and abstracts of the manuscripts submitted for the special topics volume will be posted on the SO GLOBEC website along with the status of the manuscript. Authors are encouraged to check the website and to contact other authors for copies of relevant manuscripts.

Wiebe said that the contribution number should be on all manuscripts coming from the program. This helps with tracking program results. He also said that the CD is a stand-alone contribution. Hofmann said that there will be an editorial review of the material on the CD. Bill Fraser asked if the CD material should be cited in the paper and told yes. Wiebe said that color illustrations can go on the CD to avoid page charges for color figures. Fraser said that this approach would allow documentation of the attachment methods for penguins without having to include this in the manuscript.

Bernie Lettau, program manager from the NSF Office of Polar Programs, gave a discussion of synthesis and modeling activities for SO GLOBEC. He said that synthesis is an activity that is going to be supported and that this is a process that will be ongoing for a reasonable amount of time. He said that the issue is how to fund a synthesis activity. He said that for now, a SO GLOBEC synthesis activity will likely be part of the core program and that a formal announcement for synthesis studies will not be issued. He said that issuing a special program announcement is complex. Lettau said that the proposals due on 1 June 2003 will be supported with FY04 funds. The Office of Polar Programs will need to generate new funds in FY05 to support a synthesis activity. If this happens then it is possible to issue a program announcement for an integrated synthesis program. He said that a special announcement could come out for FY05 and the budget for this needs to be to the Office of Management and Budget in February 2003. Lettau said that synthesis involves getting everyone together and that there is no reason for not funding synthesis activities without a special program announcement. He said that the next funding deadline for the Office of Polar Programs is 1 June 2003.

Following Lettau, Don Perovich presented results from the sea ice studies done on the winter 2002 process cruise. He said that the interest is in snow as a habitat and as a barrier. Snow and ice varies spatially and evolves temporally, which requires a multi-pronged approach for studying it. The techniques used in 2002 included snow pits, sea ice cores, surveys, and ice camps.

In winter 2002, the sea ice freeboard was negative only 20% of the time, as compared to 2001. Also in 2002 there was more snow, almost twice as much sea ice and less flooding of the sea ice surface. Also, the optical properties of the sea ice in 2002 show a strong biological signature. Three sea ice buoys were deployed on the winter cruise to measure barometric pressure, ice pressure, position, air, ice, and ocean temperature, snow depth, and ice thickness. Two of the three buoys are still transmitting. The trajectories followed by the ice buoys show ellipses, which may be tidal or inertial motions. Perovich indicated that the first analysis of the snow and ice studies is available on CD and that the second version will be available in spring 2003. He said that the future plans are to do physical modeling of the sea ice habitat, using Hydrolight to do radiative transfer modeling and to calculate the inherent optical properties of the sea ice.

Scott Gallager gave a presentation that essentially announced the availability of data from the SIMRAD EK500 on the N.B. Palmer. He said that this instrument is a three-frequency (38, 120, 200 kHz) echosounder. When on station ship noise is minimal and these data can be useful. Historically, the problem with this instrument is that there has not been a good calibration of the acoustic backscatter signals. On the winter cruise (NBP02-02) it was possible to do a type of calibration by running the SIMRAD at the same time that BIOMAPER-II was acquiring data. Correlations between the two data sets provide calibration for the SIMRAD data. Gallager then showed a correlation of the SIMRAD acoustic data with CMiPS data. The SIMRAD data show helical spirals, which the CMiPS data indicate are the result of turbulence. The acoustic backscattering is the result of reflection from the turbulence structure of the water column.

Carin Ashjian gave an overview of zooplankton distributions in the SO GLOBEC study region relation to water masses and specific density surfaces. The distribution data are obtained from the Video Plankton Recorder mounted on BIOMAPER-II. The plankton images are then captured from the video and identified. The Video Plankton Recorder provides size distribution as well. Ashjian said that the copepod abundances were greater in fall 2002 in the south. Copepod abundance however was high in the northern part of the study region in May 2002, which was a change from the conditions in April 2002, when the section was first occupied, which showed low copepod abundance. The copepods may be migrating with a diel periodicity. Larval krill abundance in 2002 was much less than in 2001. She said that the larval krill that were present in 2001 appeared mainly in the pycnocline. Most of the larval krill were seen in the 2001 fall cruise. Ashjian said that algal mats much more abundant in the northern part of the study region in fall 2002. The algal mats are basically dying diatom cells and may be an effective mechanism to move organic material to seafloor.

Wiebe followed Ashjian with a presentation on plankton distribution as determined by acoustic backscatter measured with BIOMAPER-II. This instrument has five frequencies, but the presentation was focused on 120 and 200 kHz acoustic backscatter. These frequencies show backscattering from diatoms, radiolarians, algal mats as well as zooplankton. Wiebe noted that the 1 MHz frequency showed a large plankton bloom in the upper 100 m on the 2001 fall cruise. He said that this bloom was not seen on the 2001 fall cruise, but that Uli Bathmann did see a diatom bloom off the middle of Adelaide Island during the German SO GLOBE cruise which was prior to the U.S. SO GLOBEC 2001 fall cruise. Torres mentioned that this like a classic case of marine snow as described by Alice Alldredge and co-workers.

Maria Vernet next presented transparencies of phytoplankton distributions from the 2001 and 2002 fall cruises. She said that the chlorophyll concentrations in the two were similar. The winter 2002 distribution shows remnants of the fall bloom, but at lower concentration. The winter 2002 chlorophyll distribution shows more at the shelf break, but overall chlorophyll concentrations in the winter were ten times lower than in the fall.

Gareth Lawson gave an overview of the krill distributions as determined from the BIOMAPER-II acoustic backscatter records from the survey cruises. The approach is to use acoustic backscattering to determine krill abundance in conjunction with the ground-truth samples obtained with the MOCNESS. The results to date show that, during the April-May 2001 survey cruise (NBP01-03), there was an along-shelf gradient in krill abundance, with more acoustic scattering in the south. There was also scattering in a deep layer and in Marguerite Bay in fall and winter of 2001. During NBP02-02 there were high scattering levels as well with a huge decrease in scattering levels during winter. There was also a substantial decrease in vertical krill distribution, as determined by backscattering. The vertical scattering profiles also show Kelvin-Helmholtz instability that looks like Langmuir cells in the upper water column that are produced by wind that then concentrate plankton. The exact identification of these features is still to be determined. Lawson noted that regions of complex bathymetry are “hot spots” for krill, as determined by acoustic backscattering. The highest levels of scattering were in Marguerite Bay in winter 2001 and the highest levels of backscattering were in areas of modified Upper Circumpolar Deep Water in fall 2001. Lawson showed overlays of the backscatter data on the dynamic height fields obtained from the hydrographic measurements. These comparisons showed that the highest backscatter values are concentrated in the southern part of the gyre. Lawson indicated the importance of combining the MOCNESS data with the acoustic backscattering data and said that the assumption should not be made that all backscattering is krill. Lawson said that there are now attempts being made to use the backscatter with other data sets to obtain taxa information from the acoustic distributions.

Langdon Quetin showed video of dive observations made during the process cruise ice camps during the 2001 and 2002 winters. The video showed larval krill in association with the under-ice surface. The video also showed the divers. Quetin said that drift nets were deployed through the sea ice to catch larval krill during the ice camps and that the catches were higher at night. The larval krill seem to be concentrated at surface. There seems to be a decrease in krill length northward and the intermolt periods measured on the winter cruises were similar to those from historical data.

Gallager's second presentation concerned results from the Remotely Operated Vehicle (ROV) under-ice surveys that were done during the survey cruises. The ROV surveys provide a measure of the large-scale distribution of larval krill and provide a means for relating krill furcilia distribution to under-ice topography. He showed video from the ROV surveys to illustrate these points. The video from the under-ice surveys will be digitized to obtain motion vectors for individual krill larvae which will be used to quantify swimming behavior over time. The distribution of larval krill from the ROV surveys suggests that the counter-clockwise gyre overlying the continental shelf in the study area could explain the regions of high concentrations of larval krill. Gallagher also noted that large under-ice krill aggregations were associated with rough ice and deep protrusions.

Following the presentation from Gallagher, the meeting was adjourned for lunch.

Ashjian's second presentation focused on results from the MOCNESS data collected during the 2001 survey cruises. She presented a comparative comparative analysis for four midshelf regions, one offshelf region, and in Marguerite Bay for the fall and winter. The zooplankton biomass was greater in the fall than in the winter, except in the offshore region. Zooplankton abundance was greater in the fall than in the winter in all six regions. The zooplankton biomass was greater in Marguerite Bay in fall and the abundance of copepods overall was usually greater in the fall. Krill were most abundant in Marguerite Bay and in during the fall.

In the vertical distributions of biomass, diel migration by the zooplankton was not obvious. The zooplankton biomass differed above and below the pycnocline and the overall vertical zooplankton biomass and abundance were lower in winter than in fall. Four taxa, (small copepods, large copepods, krill, larval krill, appear to partition the water column vertically.

Rodger Harvey gave results from nutritional condition and krill diet studies that were done during the fall 2002 process cruise. These studies consisted of morphological measurements (eye diameter, total length), demographic structure, feeding strategy, and nutritional status of krill. An overall goal is to do a comparison of Pacific and Antarctic krill populations. The results from SO GLOBEC indicate that krill adults under the sea ice in winter in the study region do not show significant shrinkage. The regressions of krill eye diameter versus krill total length do not show differences between the fall and winter cruises, which implies no shrinking of krill under the ice. Lipofuscin (age pigments) studies are now underway to look at krill age, winter nutrition, and diet. However, final analysis of the lipofuscin data will not be done until krill growth experiments, which are needed to provide a calibration for the lipofuscin-age relationship, are finished. The krill are being grown in collaboration with Steve Nicol from the Australian Antarctic Division. Harvey said that there is a correlation between polyunsaturated fatty acids and ice algae that provide potential food for krill furcilia in that individual fatty acids can be linked to specific algal pigments and individual sterols can be used as markers of ingestion. The ice algae were sampled via ice coring. He said that examination of the krill stomach contents showed that copepods were providing much of the krill diet. Harvey also said that Antarctic krill appears to be less dependent on lipid stores than does E. crystallorophias (Crystal krill).

Gallager next made his third presentation of the day in which he described microzooplankton distributions and krill furcilia feeding experiments. He said that the objective of these studies was to understand the role of microplankton, which are 50-200 μm, as prey for krill furcilia. Microzooplankton samples were obtained from water collected in Niskin bottles on the CTD casts. Samples taken and preserved with Lugols and some were DAPI-stained. These were used to determine the fall and winter particle concentrations. Preliminary analyses of these data show that the fall particle concentration is greater than that in the winter. Also, krill furcilia, captured in net tows, were exposed to particulates to do shipboard feeding experiments. The experiments were designed to obtain a functional response curve for furcilia feeding on small particles. The results show that as the furcilia begins to feed, feeding accelerates as particulate concentration increases. The rates derived from these experiments apply to krill furcilia that are feeding under sea ice. The experiments show that krill furcilia are not selective feeders. The feeding rate data combined with the distributional data suggest that there are regions of the study area where there is top-down control on particle concentration via feeding by the furcilia (i.e., an inverse relationship between krill and microzooplankton/particles).

Jose Torres presented results of physiological measurements made for zooplankton during the 2002 SO GLOBEC process and survey cruises. He began by showing historical data for Antarctic krill metabolism versus mass. These data show a reduction in winter rate reduction in animals from the Weddell Sea and near Palmer Station. This reduction is an energetic advantage because it represents approximately a 50% saving in daily energy usage. This gives a reduction in growth rate over winter months during time when food concentrations are low. Furcilia of Antarctic krill show a 10% to 20% drop in metabolic rates over winter. The metabolic data for T. macrura also suggest a metabolic rate decrease in winter. The data for E. crystallorophias do not indicate a change, but there are not yet enough data for this species to be sure of this result. Another euphausiid species, E. triacantha which is found in Circumpolar Deep Water, also does not show a change winter metabolic rate. However, this result is based on few data and may change as more data become available. Torres then discussed diapause, which is a state of arrested development with markedly reduced metabolism. He said that several Antarctic species, such as branciopoda, maxillopoda, C. acutus (copepod), and R. gigas (copepod), show this. He said that the metabolic rate reduction seen for E. superba is not true dormancy, but more likely the result of starvation.

Kendra Daly next made a presentation that focused on differences in krill between the 2001 and 2002 field studies. She said that krill recruitment depends on: 1) high reproduction, 2) larval survival in summer, 3) physical entrainment onto the shelf, 4) retention on the shelf, 5) condition prior to overwintering, and the 6) role of sea ice in relation to feeding and physiology of larval krill. She then discussed the sea ice conditions in the study area for 2001 and 2002 and indicated that the overall sea ice extent in the two years was similar but that the timing of the sea ice formation differed between years, with 2002 being earlier. She showed SeaWiFS images that indicated that phytoplankton blooms occurred in the study area in 2001. In 2002 there did not appear to be much food for krill underneath the sea ice. Sea ice biota was present, but this did not seem to be a major food source for overwintering krill. She noted the dominance of older krill stages at the shelf break in fall 2001, which were primarily near the surface. No krill larvae were seen on the shelf during NBP02-02. There was a decline in krill molting rate in 2002, with fall rate being 19 days and that in winter was 40 days. She said that there was high krill reproduction in 2001 and 2002 and that larval recruitment did appear to occur between 2001 and 2002 with the larvae present in 2001 surviving over the winter.

Meng Zhou presented results from ADCP and MOCNESS observations that are being used to investigate aggregation and migration behavior of euphausiids. Also the Optical Plankton Counter and MOCNESS data are being used to consider growth and mortality of mesozooplankton in the austral winter. The Optical Plankton Counter data show a 76% decrease in biomass, at a rate of 0.016 day^-1, between the austral fall and winter. There is also an 11% biomass change from night to day. He said that extensive krill aggregations were observed in Crystal Sound and that the ADCP data were used to target aggregations/swarms for net tows. The data indicate that krill are more active at night and passive during the day. The krill are actively swimming at their cruising speed at night and passively moving during the day. The krill swarms migrate down in water column during the day perhaps to avoid predators. Zhou said that an average aggregation scale is about 5 km.

Glenn Flierl next gave results of modeling studies that are designed to investigate why organisms aggregate and to examine the evolution of aggregation behavior. He pointed out that physical and biological processes can cause patchiness. The advantages of patches/aggregations are enhanced reproduction, escape/confuse predators, predator saturation, and to exploit a food location. The disadvantages are competition for resources and vulnerability to large/intelligent predators (e.g., whales). He then presented simulation results from models that incorporated: 1) reproduction and competition for resources, 2) intelligent predators (food supply is strongly increased by prey patchiness), and physical processes of stirring and mixing. These results show that aggregation behavior can evolve as the dominant animal trait for certain combinations of physical and biological conditions. One result is that weak stirring will not prevent aggregations, nor evolution of that behavior.

Following the presentation by Flierl, the meeting was adjourned for the day.