# WATER COLUMN AND SEA ICE PRODUCTION STUDIES WORKING GROUP REPORT

## First U.S. Southern Ocean GLOBEC Science Investigator Meeting
Arlington, VA
25-26 May 2000

## Chris Fritsen, Working Group Chair

## Participants: Maria Vernet, Angela Gibson, Don Perovich, Karl Newyear

The working group discussed issues concerning the objectives of the participants and how these objectives are likely to be realized utilizing both the survey and process cruises during the proposed April-May and July-August periods. These discussions primarily centered on the common goals and how the operations and use of resources could be structured to meet the common needs of those involved in this working group and how these would interface with the other study participants. Below is the report on the specific topics discussed during the working group meetings.

General Objectives of Water Column and Sea Ice Production Studies
Determine the distribution, composition, activity, biomass and dynamics of phytoplankton and sea ice microbial communities in context of their seasonally changing physical/chemical environments and how these relate to the utilization of these energy sources by krill.

### Water column studies

Survey Cruises: Collection of discrete samples from water column will be accomplished using the Rosette (instrumented with CTD, Fluorometer, PAR sensor). Bottle sizes and sampling depths will be determined based on results of iterations with Hydrography and nutrient studies. Bottle samples will provide water for determinations of chlorophyll a, CHN, macronutrients, bacteria as well as water for productivity assays. Simulated in situ (on-deck) incubations will be conducted in the April-May cruise in order to compare to those experiments conducted in the laboratory during both the April-May cruise as well as the July-August survey cruise.

The frequency of conducting hydrocasts for productivity assays will be dictated by time-constraints and will most likely be limited to 2-stations per day. If more stations are occupied in a day then some stations will consist of sampling for biomass alone. There was a consensus that this would still yield sufficient coverage of the study area for determination of water column primary rates.

-The suggestion was made that assays be consistent with LTER-primary productivity protocols to ensure data will have compatibility with existing data sets.

- Plans for deploying a FF radiometer on an intermittent basis are planned and should enhance the ability to extrapolate from bottle experiments of primary production and enhance modeling efforts for seasonal changes in primary production regimes.

Process Cruises: At least one water column profile/hydrocast for determination of water column biomass, nutrients and productivities will be completed at each of the process study sites. Primary production assays will be consistent with those being conducted on the survey cruise. The additional possibility of doing in situ incubations of bottles deployed beneath ice floes posses a unique opportunity to couple productivity measurements with continual radiation monitoring by sensors above, within and below the ice (when ice is present) These measurements will be conducted in coordination with the planned optics activities (i.e., Martinson, Perovich and Smith) primarily on the July-August cruise.

### Sea ice studies

Survey Cruise: It is anticipated that the April-May survey cruise will not be operating in sea ice. Therefore, an extensive sea ice sampling and observation program will not be implemented on this cruise. However, in the regions were sea ice is present the ice studies will greatly benefit from the implementation of the ice observation protocol that will be used throughout the U.S. SO-GLOBEC program. Hence, efforts should be made to have personnel on board this survey cruise that are capable of making these observations. These observations during the survey cruise will also aid in the selection of the process study sites being conducted during the same time-period.

The survey cruise in the July-August should occur primarily in sea ice. Hence, there will be coordinated sea ice observation and sampling program during these survey operations. The observational program will be implemented to determine the types and coverage of different types of ice (according to the ASPECT observational protocol) as well as thickness categories as determined during steaming (also known as the bouncing-ball observations). These observations should be implemented in conjunction with the NASA remote-sensing participant and to the extent possible with the observations of marine mammals and birds.

To complement the broad-scale observation program ice cores and brine samples will be taken for determination of biomass and productivity. Samples for biomass determinations will consist of collecting cores/samples from the different ice habitats near each hydrographic station. Accessing the ice during deployment of the Rosette may be possible depending on ice conditions. If not possible, additional time will be needed for accessing ice floes during the second survey cruise. The frequency of access will depend on the ice types present. The goal is to collect sufficient number of ice cores from the different ice types to yield summary statistics on the composition of microbes in the ice types present throughout the study region

Extensive experiments for determining rates of primary and secondary production in sea ice will not be conducted on this cruise. Rather, a select set of assays will be conducted to compliment the more extensive experimentation that will be completed during the process cruises.

Process Cruise: Vertical distributions of biomass will be determined from ice cores collected in conjunction with the thickness transects and ice coring planned by the ice/optics and sea ice microbial community programs. Cores will be processed to determine the vertical profiles of crystal structure (in conjunction with optics group), salinity and microbial biomass. Samples obtained from ice cores will be processed for determinations of chlorophyll a, CHN, bacteria numbers, microalgal/protist composition and cell biovolume. Horizontal variability in each of these parameters will be assessed by sampling multiple (~5) sites within any given ice type. The distribution of microbial biomass and activities at ice/water interfaces in deformed areas will be determined in conjunction with the Krill census and SCUBA operations.

Productivity assays (bacterial secondary production, as well as primary production) will be conducted on sections of ice-core meltwater, on brine collected from within ice floes as well as on samples collected from ice/water interfaces via SCUBA. Protocols are to be consistent with those implemented for the Water Column productivity assays. The process cruise studies will allow a comparison between results obtained under simulated conditions in laboratory incubators and those conducted in situ.

### Logistics Issues

A number of logistics and operational issues pertinent to the implementation of the water column and sea ice productivity studies were identified and discussed during the working group meeting. These logistics issues include: the following list of items. We fully anticipate more logistics issues will become apparent as planning progresses.

- Radioisotope vans are needed on both ships during both cruises.
- On-deck incubators needed for each ship during the April-May cruises.
- Walk-in freezer space (-15 to -20°C) is needed on both process cruises and on the second (July-August) survey cruise for processing ice cores.
- Walk-in cold rooms (+4°C) or additional incubator space is needed on the LMG during the process cruise. Walk-in cold rooms on the NBP have been sufficient in past cruises.
- Updated ice coring equipment needed for both LM Gould and NB Palmer (SIPRE core barrels and fiberglass variety core barrels are in need of updating).
- Microscope space needed on both process cruises as well as on the second survey cruise.