Minutes of the Fourth SO GLOBEC Science Investigator Meeting
9-11 December 2002
The Fourth U.S. Southern Ocean GLOBEC (SO GLOBEC) Science Investigator Meeting started with a welcome from Eileen Hofmann, which was followed by introductions of the meeting attendees. Hofmann next went over general meeting information and indicated that copies of some of the SO GLOBEC cruise reports, the SO GLOBEC article from Oceanography magazine, the special issue of Oceanography magazine of U.S. GLOBEC, the meeting agenda, meeting abstracts, and meeting participant list were available. She also indicated that a poster describing the second SO GLOBEC field season had been prepared and that a copy of the poster is available on request to interested persons.
Hofmann gave a report of activities undertaken by the SO GLOBEC Planning Office since the last Science Investigator Meeting. A primary future effort for the Planning Office is the first SO GLOBEC Deep-Sea Research II Special Topics volume. The editors for this volume are Peter Wiebe, Jose Torres, Dan Costa and Hofmann. Hofmann gave the schedule for manuscript submission for this volume and said that Julie Morgan will act as the administrative person for the volume. Morgan will take care of details of obtaining manuscript reviews and she will post updates of the status of the manuscripts on the SO GLOBEC web site.
reviewed the upcoming meetings that have sessions that are appropriate for SO
GLOBEC. She also indicated that there
will be a special session on SO GLOBEC proposed for the next Ocean Sciences
Meeting that will occur in late January 2004 in
gave an overview of upcoming SO GLOBEC cruises.
The British Antarctic Survey SO GLOBEC cruise is scheduled to occur in
January-February 2003. This is the
cruise that was originally scheduled for October-November 2002. Also there is a proposed second German SO
GLOBEC program in the
Next was a
discussion of a follow-on program to SO GLOBEC.
The GLOBEC program as a whole will end in 2007. There is now an effort from the International
Geosphere-Biosphere Program (IGBP) and the Scientific
Committee of Oceanic Research (SCOR) to develop an OCEANS initiative which will
focus on marine biogeochemistry and food webs and the feedbacks from these to
climate. A poster on a new Southern
Ocean initiative is being proposed as part of the OCEANS program. A poster describing this initiative will be
presented at the OCEANS Open Science Meeting which will be held in
comments from Hofmann, Bob Beardsley gave an overview of the 2002 current meter
mooring recovery and re-deployment cruise.
He said that in 2001 the six Woods Hole Oceanographic Institution (WHOI)
moorings were deployed in two lines. The
A line off
Beardsley said that the hydrophones on the acoustic moorings record continuously at 500 Hz. These acoustic records show many calls from blue whales, but these whales were not sighted by the International Whaling Commission (IWC) observers on the SO GLOBEC cruises. Beardsley also said that the IWC observers were on the mooring recovery/re-deployment cruise and that they did sighting surveys and biopsy sampling of the whales. The latter activity was very successful. The blubber samples from the whale biopsies are being analyzed for a range of proteins, lipids and hydrocarbons and the skin tissue if being used for genetic studies.
gave a brief overview of meteorological measurements from the two Automatic
Weather Stations (AWS) deployed in Marguerite Bay during the first SO GLOBEC
cruise (April-May 2001). These data show
that the mean wind stress at both AWS sites is towards the south. This differs from the wind data collected at
the Rothera, the British Antarctic Survey base on
Peter Wiebe next
gave an overview of the 2002 SO GLOBEC survey cruises. The first cruise (April-May 2002) took place
in basically open water; the second (August-September 2002) only had open water
Wiebe said that
on both survey cruises the inland passage (through
Wiebe said that meteorological data were acquired on the winter cruise in spite of occasional frozen instruments. He said that the largest decrease in daylight was at the end of fall cruise; and that light was more prevalent during the winter cruise because the days are getting longer. He noted that BIOMAPER-II provided temperature, salinity, and fluorescence measurements in addition to acoustic measurements on both cruises. There were some problems with towing BIOMAPER-II on the winter cruise because of the sea ice conditions. Also on the winter cruise it was possible to do remotely-operated vehicle (ROV) under-ice surveys during the time that the sea ice group was making its collections. This was an efficient use of ship time that worked well. Wiebe noted that the new bathymetry mapping system on the Palmer was not operational for the NBP02-04 cruise. However, in spite of loosing the bathymetry data on this cruise, the data from the previous three cruises are providing a much better realization of the bathymetry in the study area than was previously available.
provided an overview of the 2002 April-May process cruise on the L.M.
Gould. As compared to the 2001 fall
process cruise, the 2002 cruise experience much less wind and a much larger
amount of sea ice. Five process sites
were originally planned and an additional site was added in
Dan Costa gave
an overview of the 2002 August-September process cruise. He said that this cruise was characterized by
lots of sea ice, which was very different from the 2002 fall cruise. He said that the penguin and seal predator
work done in
gave an update on the status of the bathymetry data set for the SO GLOBEC study
region. He said that the goal of this
effort is to construct the best possible digital bathymetry data base by
merging the available digital bathymetry data with the latest Smith and Sandwell ETOPO2 data base.
He said that the George VI Sound area is much better defined with new
data added to the ETOPO2 database. The
deep troughs and other bathymetric features are now evident. He said that the latest bathymetry data set
for the SO GLOBEC study area can be obtained from the web site, www.whoi.edu/science/PO/so_globec/
(bathymetry), and downloaded via ftp.whoi.edu. He gave the username and password needed to access
the ftp site. He also indicated that
either himself or Tom Bolmer should be contacted
if there were questions or problems in obtaining the bathymetry data. He said that a proposal has been submitted to
NSF Office of Polar Programs to obtain funding to continue with the development
of the bathymetry data base. This
proposal is still pending. Wiebe asked
if these data will be used to update the Smith and Sandwell
bathymetry data base. Beardsley said
that they will have access to new bathymetry data and that the data will be
submitted to the
Wiebe and Dicky Allison (GLOBEC Data Management Office) gave a presentation that explained the data and information management system that is being used for GLOBEC. Wiebe said that the basic philosophy is that the data should be served when useful (as quickly as possible), usually within six months. Data are generally more useful when used in the context of other data sets. He said that there is an effort by the data management office to have a consistent listing of the names of data types for all GLOBEC programs. It is the responsibility of the science investigator for ensuring data quality control He said that the data system has open accessibility with a web-based data retrieval system. The data are to be archived with this system. Wiebe said that individual science investigators can send data to data management office to be served or the science investigator can serve the data from the home institution using the data management software, which the GLOBEC data manager will install for the investigator.
Wiebe said that the event log is the essential piece of information because it is the explanation for how to find the data. He said that the data files available through the data management office can be compressed and downloaded. Matlab is a preferred software package for working with the data. Other data manipulation options include kriging and GeoZui3D. The latter software package has specific hardware requirements that require the user to have enhanced graphics options available on his/her computer. Wiebe said that the data management office will work on meta-data records for inclusion in larger databases. He reiterated the need to use the common courtesy of telling the “owners” of specific data sets when the data are being used in another study or publication.
Dicky Allison next said that the data management office exists to serve the data and the user community; it is a consumer-driven system. She said that the data management office preference is to serve the data from the individual science investigator's computer (a distributed system), particularly if data sets are large. However, the data management office will serve the data sets if this is the preference of the science investigator. She said that scientists should contact the data management office if their data are not served within one week of sending them to the office. She requested that everyone who submits data also provide the corresponding documentation for the data. Allison indicated that the data management office should receive the raw (if appropriate) and processed data sets. She went over which SO GLOBEC data sets are missing in the data management office data base. She said that linking to individual websites from the data management system is acceptable, but actually serving the data is preferable.
The first presentation of the afternoon session was by Joey Comiso from NASA. Comiso presented Antarctic sea ice climatologies developed from the SSM/I data set (1978-2002) which show trends along the Antarctic Peninsula that indicate that this region is anomalously warm compared to rest of the continent. The trend over the entire Antarctic is an increase in sea ice extent of 0.8% per decade, while that for the Bellingshausen and Amundsen Seas region is a 7% per decade decrease in sea ice extent. There is an increase in sea ice cover in the Ross Sea over the same time. In winter months there is basically a circumpolar sea ice cover. Comiso noted that the northern tip of the Antarctic Peninsula was ice-free from January 2002 to March 2002. However, there was more sea ice in winter 2002 in the Antarctic Peninsula than seen in climatology. He also said that there is an embayment in sea ice coverage pattern at the northern tip of the Antarctic Peninsula that is seen in the 1978-2002 climatologies. The cause of this is unknown at present.
Comiso said that a new sensor was launched this year to monitor ice (AMSR-E) to work with AMSR sensor. This sensor is the successor to SSM/I and provides better resolution. It gives continual coverage (AM and PM sensor) and provides better definition of the 10% ice coverage that is used to define the ice edge. Comiso noted that the resolution of the MODIS data is as good as 250 m and that these data provide good validation for the actual spatial distribution of the sea ice cover.
Dick Limeburner made a presentation on the surface drifters that have been deployed as part of the U.S. SO GLOBEC field efforts. He indicated that the surface drifters have been modified to have an ice-strengthened buoy hull and cold weather batteries. A surface drifter was deployed every time a mooring was deployed, which is about 5 to 6 drifters per mooring cruise. The differences in the drifter paths between those deployed in 2001 and those deployed in 2002 is related to the sea ice cover. There was little sea ice in Marguerite Bay in March 2001, so the drifters were able to enter the Bay. However, in 2002 the extensive sea ice prevented the drifters from going deep into Marguerite Bay. One implication from the drifter trajectories is that sea ice does not appear to be flushed out of the SO GLOBEC study region. Limeburner also noted the occurrence of inertial oscillations and small scale eddies (about 6 km) in the drifter trajectories. Typical velocities associated with the eddy motions are 10 cm s-1 with amplitudes of up to 20 cm s-1.
Laurie Padman next gave an overview of the status of the ADCP data sets collected on the SO GLOBEC survey cruises. The ADCP data are available at http://www.esr.org/globec/globec.html or through the GLOBEC data management office at WHOI. Padman encouraged everyone to look at the ADCP data and to use it. He said first analyses of the ADCP show that the data include high frequency signals, mainly tides and near-inertial motions, as well as other frequencies of motion. Padman also mentioned the CTD-mounted Microstructure Profiling System (CMiPS) which was used on the 2002 survey cruises to investigate processes that might cause turbulence in the pycnocline. One objective of using this instrument was to determine the diffusivity in the pycnocline separating Upper Circumpolar Deep Water and the overlying Winter Water or Antarctic Surface Water layers. He noted that the use of CMiPS on the survey cruises was the first time that microstructure measurements have been made in this region. He said that these data suggest that double diffusive processes are more likely to be prominent in the continental shelf waters near Palmer Station as compared to Marguerite Bay. A tentative conclusion on microstructure at this point is that there is more mixing at the main pycnocline than previously thought.
Hofmann made a presentation on the hydrography data sets collected during the 2002 fall and winter survey cruises (available as a PowerPoint presentation). She noted that the coverage during the two cruises differed because of the extensive winter sea ice coverage. Hydrographic distributions from the April-May cruise (NBP02-02) showed a distinction between inner shelf and continental shelf waters, which was not present in the winter. Also, during the winter cruise (NBP02-04) the Antarctic Surface Water was gone and replaced by a thick (80-100 m) Winter Water layer. Hofmann noted that the hydrographic distributions during the 2002 austral fall were similar to those seen in the 2001 austral winter. She said that during the 2002 cruises, the southern boundary of the Antarctic Circumpolar Current was along the shelf break. The hydrography shows a clockwise gyre in northern part of study region during both 2002 survey cruises. There also appeared to be some mesoscale flow features during NBP02-04. Hofmann said that the next step in the analysis of the hydrographic data sets is to calculate volume exchanges across the shelf break to get an estimate of the across-shelf exchange of Circumpolar Deep Water, which provides an input of water to the shelf at depth. She said that the heating and cooling differences over the study area may show regions of polynya formation. The hydrographic data do show the importance of topographic mixing on producing breaches in the Winter Water layer that allow Circumpolar Deep Water to mix with the surface waters. These tend to be regions where surface waters are above freezing and where sea ice is absent or then.
Doug Martinson made a presentation on the hydrographic data sets collected during about ten years as part of the Palmer Long-term Ecological Research (LTER) program. Most of these data are from January, the austral summer. These data show that the surface water is fresher and cooler (coastal water), likely due to glacial run-off or convergence of melting sea ice, that ACC-derived water has a small range in temperature-salinity space, and that there is a shift in the pycnocline between summer and winter. He noted that the LTER hydrographic data set is now getting long enough to investigate interannual variability in water mass properties.
Jason Hyatt discussed the role of vertical mixing in the transport of heat, salt, and nutrients from the Upper Circumpolar Deep Water to the upper water column. This mixing may occur via double diffusive convection and shear instabilities. He said that the ADCP data can be used to estimate shear effects and that the CTD data can be used to calculate buoyancy frequency to determine water column stability. Preliminary calculations indicate higher estimates from shear mixing (more energy) than previously thought. The issue is to now determine where the shear energy is coming from. One possibility is near-inertial gravity waves.
Kent Fanning gave an overview of the nutrient data collected on the SO GLOBEC survey cruises. *(view presentation in slide show mode to see animation)* He said that the replication of replication stations provided remarkable data that allowed nutrient variability to be studied and processes estimated. The biointermediate nutrients, nitrate, phosphate, silica, nitrite, do not go to zero on any of the cruises. Ammonium, however, quickly goes to zero on all cruises, in most cases by 200-300 m. The silica distributions suggest that diatoms may be of more importance in offshore waters than inshore. He noted that the maxima in ammonium lies along path of coastal current and that this current may be moving ammonium from inside Marguerite Bay to the continental shelf. There was a substantial autumn-winter increase in nitrate, phosphate, and silica in the mixed layer and substantial autumn-winter decrease in ammonium. He said that silica is an excellent tracer of upwelling and horizontal injection of offshore waters onto the west Antarctic shelf.
Padman made a second presentation on a tidal model that has been applied to the SO GLOBEC region. He noted that tides contribute to benthic stirring and pycnocline mixing and that tidal currents are “noise” in the ship-derived ADCP measurements. The tidal model that is being used is a two-dimensional model (Circum-Antarctic Tidal Simulation, CATS) that extends from 58ºS. It is a dynamical model. Padman said that the tidal solutions are sensitive to the bathymetry which needs to be adjusted to include the most recent bathymetry for the study region. The tidal solutions show evidence of strong tides near shelf break. A three-dimensional tidal model, based on the Princeton Ocean Model, shows weak tidal currents, except at the shelf break.
John Klinck described and presented results from a numerical ocean circulation model that has been developed for the SO GLOBEC study region. The simulated circulation fields show observed meandering of the Antarctic Circumpolar Current, onshelf flow of Circumpolar Deep Water, and southward flow along the inner shelf. Comparisons of observed circulation distributions with the simulated distributions indicates that the circulation model is reproducing the basic flow of the west Antarctic Peninsula shelf. Klinck showed that the onshelf transport of Circumpolar Deep Water is correlated with curvature of shelf break and that the on/offshore flux of this water is due to a combination of bathymetric curvature and the prevailing shelf circulation. Klinck ended with a description of future plans for improvement of the circulation model.