The research plan will be implemented by a combination of Time-Series Surveys and Process Studies carried out in three regions of the Southern Ocean: the Antarctic Peninsula region, the eastern Weddell Sea, and the Indian Ocean sector. Field studies should be preceded by modelling. This section describes the criteria for field studies and suggests how key measurements be made.

Two specific field programmes are recommended:

  1. Winter study

    The winter study would focus on overwintering strategies of target species and would last for a minimum of 6 months.

  2. Summer study

    The summer study would focus on processes of foraging, reproduction and recruitment in relation to physical dynamics, and would last at minimum 6 months.

4.1 Study areas

Three principal areas of operation are recommended (Figure 1). These are the:

  1. Antarctic Peninsula region
  2. eastern Weddell Sea, and
  3. Indian Ocean sector.

The choice of these areas presents important opportunities for Southern Ocean GLOBEC. First, it is possible to make geographical comparisons with respect to key processes such as overwintering strategies of zooplankton, or foraging behavior of top predators. Second, it is possible to compare ecosystems with different top predators (e.g. a penguin-dominated system in the Peninsula region vs. a crabeater-dominated system in the eastern Weddell Sea). Third, it will be possible to compare the influences of sea-ice, which may vary greatly among regions.

The Antarctic Peninsula region is broadly defined to range from the Bellingshausen Sea in the west, to the Scotia Sea and South Georgia in the east, and to the Peninsula itself in the south. This region provides a rich historical background and an abundance of shore-based predator populations. It is an area where krill, as well as many other target species, are abundant. A number of countries routinely operate research vessels in this area, including Argentina, Brazil, Chile, China, Japan, Korea, Spain, UK and USA. Airfields are maintained at Rothera (UK) on Adelaide Island and Eduardo Frei Base (Chile) on King George Island. Shore stations operated by many nations provide the possibility for complementary process studies.

The eastern Weddell Sea region is centered on the Lazarev Sea, which encompasses the eastern arm of the Weddell Gyre. Target species of importance include krill and crabeater seals; Adelie penguin colonies are notably absent. Research vessels are regularly operated in this region by Germany, Russia, South Africa, and the Nordic countries (Finland, Norway and Sweden).

The Indian Ocean sector, broadly defined, ranges at its southernmost extremity from Enderby Land (35 degrees E) to the Shackleton Ice Shelf (100 degrees E). A number of studies have been carried out in coastal areas of this region, notably in Lutzow-Holm Bay (37 degrees E) and Prydz Bay (70 degrees E). Important target species in this region include krill, crabeater seals and Adelie penguins. Countries that routinely operate research vessels in the vicinity are Australia, China, France and Japan. Continental stations at Syowa (Japan), Davis (Australia) and Tunshan (China) are complemented by a year-round sub-Antarctic base on Kerguelen Island (France).

The selection of specific research sites in each of the three Southern Ocean GLOBEC study areas will be determined at the next stage of the implementation process. A regional planning meeting for each research area will be convened to choose a specific site and to coordinate activities in accordance with scientific and logistic criteria described in the following section.

4.2 Time-Series Surveys

Time-series surveys are designed to adequately resolve temporal and spatial scales relevant to the key questions posed. The guiding principle is that surveys be nested in both space and time.

4.2.1 Criteria for Time-Series Surveys

a) Time scales that resolve population dynamics and seasonal variability

The relevant time scale of processes implied by the key questions is of order 1 to 10 weeks. For example, the factors affecting reproduction of zooplankton, which includes maturation, feeding history, and lipid accumulation, occur on this time scale. Similarly, the role of sea-ice dynamics in affecting the foraging and reproductive success of many top predators is expected to become apparent on a time scale of 1 to 10 weeks.

Continuous observations are required for a minimum period of 6 months to adequately resolve the population dynamics of either zooplankton or top predators. This period of time is necessary to observe mechanisms that lead up to reproduction, that affect the survival of young, and that determine recruitment - which for most species occurs on an annual time scale.

b) Eddy-resolving spatial scales

Mesoscale circulation dynamics contribute significantly to the retention and re-distribution of animal populations in the pelagic ecosystem. Time-series surveys must therefore be capable of resolving the Rossby radius at high latitudes, which may be of order 10 km. To determine the total size of the survey region involves two sets of tradeoffs. An area that is too large will lack synopticity. On the other hand, an area that is too small would have to be sampled more frequently than is logistically feasible.

c) Comparability among survey sites

Survey design in the Antarctic Peninsula, Indian Ocean, and eastern Weddell Sea areas should be sufficiently similar to permit unambiguous comparison of results between time-series surveys. The shape of the survey might be altered to accommodate local oceanographic dynamics, but the overall size of the survey area and the timing of cruises should provide for comparable resolution in space and time.

d) Adjacency to shore-based predator populations

GLOBEC field studies that include shore-based predator populations (e.g. penguins) should cover a region that encompasses the ocean adjacent to the shore-based colony. The potential foraging range of the species under study must be considered when determining the dimensions of the study region.

e) Augmented effort along survey lines

Many nations ply standard supply routes to and from Antarctica (Fig. 1). An effort should be made to locate time-series survey sites along or near such routes so that supplemental underway measurements can be made (e.g. seal counts, bioacoustics, meteorology). Measurements along survey lines will augment temporal coverage and provide latitudinal comparisons.

f) Standard measurements

Measurements of key variables should be standardised both within and among time-series survey sites. For example, zooplankton should be sampled with the same type of nets and at the same depth horizons; predator populations should be censused using standard techniques. An outline of key measurements and techniques is given in Section 4.2.2.

4.2.2 Measurements and methods for Time-Series Surveys

The following suite of measurements may be regarded as essential elements of a SO GLOBEC time-series survey; they are common to addressing many of the questions posed. For example, the stage-frequency distribution, depth distribution and abundance of zooplankton must be measured in time-series surveys in order to understand overwintering strategies (Zooplankton Question 5), factors affecting larval survival (Zooplankton Question 3), and the allocation of prey items among top predators (Predator Question 4). This section summarises recommended measurements, and suggests methods that might be used to make such measurements.

a) Stage-frequency distribution of zooplankton

Methods: nets, multi-nets, ROV, video plankton recorder, continuous plankton recorder.

b) Zooplankton abundance and depth distribution

Methods: nets, multi-nets, ROV, video plankton recorder, continuous plankton recorder, acoustics, optical plankton recorder

c) Physical dynamics and water mass properties

Methods: CTD, ADCP, Lagrangian drifters, moored instruments (e.g. current meters), satellite data (e.g. AVHRR), underway surface measurements

d) Distribution and production of particulate food

Methods: POC, PON, fluorometry, HPLC pigments, particulate ATP, species composition, particle counters, flow cytometry. Primary production measurements, microbial dynamics.

e) Sea-ice distribution and dynamics

Methods: Satellite, visual observations, meteorology (wind forcing), CTD-geostrophy and ADCP-local currents (fluid forcing).

f) Sea-ice characteristics

Methods: Satellite (e.g. SSMI), visual, coring, under-ice observations

g) UV-B radiation

Methods: Spectral radiometer

h) Predator population dynamics

Methods: Age structure methods (e.g. otolith analysis in fishes, tooth analysis in seals, etc.)

i) Predator distribution and abundance

Methods: Fishes & squid: nets, acoustics; Birds & seals: visual observations, aerial surveys, telemetry

j) Predator foraging behavior

Methods: Gut content analysis, behavioral observations, TDR

k) Predator reproduction

Methods: Fishes & squid: larval distribution, abundance; Birds & seals: behavioral observations, egg & pup production

The above measurements and methods are representative of those recommended for application during Southern Ocean GLOBEC time-series surveys. Detailed recommendations of appropriate methods are given in GLOBEC Report No. 5. It is recognised that additional measurements may be required in certain studies, and that not all measurements will be necessarily required in others. Furthermore, certain observations will be more powerful when carried out in conjunction with Process Studies (please see Section 4.3).

4.2.3 Generic Time-Series Survey design

This section describes the generic features of the time-series surveys, based on criteria given in Section 4.2.1. The mesoscale cruise plan, and its integration with Process Studies (Section 4.3), are outlined in Figure 2. The surveys should be planned carefully under consideration of local features pertaining to hydrography (current speeds and directions) and topography and possess the following characteristics:

a) Spatial scales

It is recommended that survey activities be carried out at three spatial scales: macroscale, mesoscale and fine scale. The macroscale (dimensions of order 1000 km) encompasses the mesoscale survey area, and is appropriate for observations of phenomena that impinge on smaller scales. Primary observational tools include satellite imagery, Lagrangian drifters and aerial surveys.

Mesoscale surveys would be accomplished by research vessels. It is recommended that, at the latitude of the Southern Ocean, spacing between grid lines and stations should not exceed 20 km. The area of interest would ideally be about 40,000 km2, or 200 km on a side. However, assuming a station time of 3 h, such a survey would require about 20 days under favorable weather conditions. As this is likely to be too long, a smaller area, e.g. 25,000 km2, or 160 km on a side might well have to be chosen, as this would take about 15 days to survey. Surveys of this extent should be adequate to characterise temporal variability on monthly time scales, which is within the 1-10 week time scale indicated for many key processes.

Fine scale surveys would be carried out before and after the mesoscale survey, using the same research vessel. These surveys would be nested within the mesoscale survey region. The area of interest would be approximately 1000 km2, or 30 km on a side. With spacing of grid lines and stations at 6 km intervals, and assuming a station time of 2 hrs, fine scale surveys could be completed within several days. Surveys of this extent might well be sufficient for characterising small scale variability in the horizontal. However, depending on the species and region under study, it might be more appropriate to choose smaller spacing between grid lines and stations.

b) Temporal scales

Relevant time scales range from min-hr (e.g. foraging behavior) to approximately 6 months (e.g. studies of overwintering strategy), with most falling in the range of 1-10 weeks. The purpose of the time-series surveys is to resolve processes occurring at these time scales. Surveys should be repeated in the area of interest at least once per month. A series of 2-week surveys will, over a 6-month period, provide unprecedented resolution of key processes.

c) Shape of survey areas

It is recommended that the shape of the survey be determined by the area in which it is conducted. Thus, a survey that crosses a broad frontal region might be made rectangular in order to accommodate features on either side of the front (e.g. 400 x 100 km rather than 200 x 200 km), or irregular to accomodate a shoreline. The total survey area should remain constant (i.e. 40,000 km2), in order to (a) retain a total survey period of approximately 2 weeks, and (b) not exceed available logistic resources.

d) Inclusion of survey lines

Traditional transit routes to and from the Antarctic continent provide the opportunity for adjunct studies that would supplement, but not replace, time-series surveys. Common transit routes (Fig. 1) include:

  1. Drake Passage (South America to Antarctic Peninsula)
  2. Indian Ocean (Australia to East Antarctica)
  3. South Atlantic (Capetown to eastern Weddell Sea)
These should be included in cruise plans where possible.

e) Multiple ship participation

Time-series surveys will need to be approximately 6 months long to adequately address key scientific questions. Three different vessels may be required to complete such a survey. Each vessel would commit to a minimum of a 6-week cruise, with the first and last 2-week periods being for time series surveys and the middle 2-week period reserved for process studies.

4.3 Process Studies

It will not always be feasible to carry out the relevant process studies for zooplankton and predators simultaneously, which is in contrast to Time Series Surveys where both categories of organisms can and should be monitored during the same cruise. In the following, zooplankton and predators are hence dealt with separately.

4.3.1 Zooplankton

The following key questions which assess the impact of physical processes operating over different temporal and spatial scales on zooplankton population dynamics will be addressed by process studies:

Zooplankton question 3: Factors affecting successful reproduction

Zooplankton question 4: Physical processes influencing larval survival and recruitment to the adult population

Zooplankton question 5: Zooplankton overwintering strategies

Each of these processes will have to be studied in the context of the life history cycle of the various species identified as key organisms. This enables one to break down the processes into elements that can be studied individually.

a) Factors affecting successful reproduction (Question 3)

Assessing the success of reproduction will require study of each of the following aspects which are likely to be constrained by specific physical factors:

  1. Successful mating will depend not only on seasonal and regional changes but also on the small scale availability of mature adults. Such changes should be assessed by changes in sex ratios and timing of maturation in both sexes. Possibly, there are species-specific conditions necessary for mating to be initiated that may depend on the immediate environment (e.g. anecdotal observations indicate that krill require a calm sea for mating to take place).
  2. Assessment of sexual maturation in both females and males will have to be standardised. This can be ascertained by estimating the ratio of somatic versus gonadal tissue using techniques such as histology, dissection and immuno-assay techniques.
  3. Trophic history of reproducing individuals. Gut content, lipid content and composition, and other physiological indicators provide for the assessment of feeding history on different time scales.
  4. Frequency of spawning. Both discrete as well as continuous spawning is known to occur and the relative importance of these strategies needs to be assessed through histological studies and by following egg production under field and laboratory conditions.
  5. Fecundity is considered as the reproductive potential of an animal. In addition, studies to assess egg viability and hatching success should be made.
  6. Egg characteristics. Measurements of volume and density will shed light on positioning strategies (e.g. eggs of Euphausia superba tend to sink whereas copepod eggs hatch in the upper-most layer). Depending on the respective strategy, the effect of ambient temperature and vertical mixing, UV/B exposure (in surface hatchers) and occurrence of egg predators (e.g. phagotrophic dinoflagellates) need to be investigated and modelled.

b) Larval survival and recruitment to the adult population (Question 4)

This is a key process in the life cycle of all organisms that is strongly dependent on environmental conditions but poses considerable difficulties for adequate assessment. There is a pressing need to develop methodology and model simulations to study the following component processes:

  1. Growth rates as a function of food availability in terms of quality and concentration for the various larval and juvenile stages. It is recognised that conventional laboratory studies can sometimes give misleading results. Studies involving field assessments of growth (e.g. using instantaneous growth rates ) and moulting rates should also be utilised. The use of microcosms for such work may also hold considerable promise and has been used successfully in other areas.
  2. Predation on larvae and juveniles. Mortality rates are a key parameter in modelling population dynamics but obtaining accurate estimates is challenging. The CCAMLR Krill working group has had some success assessing krill mortality from length frequency distributions. Such methods should be assessed in more detail and development of new techniques accorded a high priority.
  3. Habitat dependency. Field data indicate that different species require different habitats (e.g. presence or absence of ice cover, ridged vs. flat ice) for successful recruitment. In order to ascertain whether a given population is growing well or in the process of being expatriated into unfavourable conditions (testing larval drift and retention hypotheses) will require knowledge of what constitutes a healthy physiological state. Criteria now in common usage (e.g. length/weight ratios, gut contents, biochemical composition) can be compared with molecular biological and other techniques to determine which is best suited for routine use. Applying these criteria to assess samples of larval and juvenile zooplankton collected on Time Series Surveys will provide information on whether specific regions or hydrographical structures are favorable for or detrimental to larval growth and hence recruitment to the various target populations.
  4. Interrelationship of populations: For widely distributed species such as krill, determining the degree of mixing within and between study areas is particularly important. Further development of genetic techniques to estimate degree of interchange between stocks or populations is required as well as model simulations.

c) Overwintering strategies (Question 5)

Available information on the different overwintering strategies of the various species suggests that there is a gradient from total diapause of the entire population to active foraging throughout the winter. There also seem to be regional differences in overwintering strategy within the same species for which variation in factors triggering a particular type of winter behaviour may be responsible. In order to assess the gamut of overwintering behaviours the following studies need to be carried out:

  1. Assessment of the life cycle stages which are capable of successful overwintering. This in turn will require studying the physiological state and metabolism of the various stages captured during autumn, early and late winter.
  2. Assessment of the physiological state of overwintering individuals. First there is a requirement to derive condition factors which can be used to characterise the state of individuals in different areas. Such condition factors could utilise assessments of the biochemical composition or possibly the state of the digestive system:

    Biochemical composition: These studies could utilise e.g. dry : wet mass ratios, protein and lipid ratios. In many cases it will be necessary to split the latter into wax esters, triglycerides and polar lipids.

    Digestive system: Activity here could be assessed by, for example, histology and enzyme content or activity studies.

  3. Metabolism of overwintering individuals in relation to environmental conditions should be studied in some detail. Ideally these studies should aim at assessing the energy budget in relation to food resources and storage pools. The measurements should include respiration and excretion rates (e.g. O2 uptake, CO2 and NH3 release) and changes in biochemical composition.
  4. Behaviour. In situ observations using visual, photographic and acoustic techniques are needed to assess the changes in aggregation and feeding behaviour of different stages in different areas in the autumn, winter and spring.
  5. Predation: Estimation of predation rates is necessary because it is a key parameter in modelling studies. Predator avoidance strategies by winter-active species in relation to habitat such as the amount of ice cover should be studied by direct observation (scuba divers), cameras on ROVs, or acoustic techniques and will entail observations of, e.g., flight distance and behavioural strategies (whether organisms seek shelter within ice cavities or flee downward into the water column). Comparisons with strategies in non-ice covered areas should also be made. In diapausing species, population density and location in the water column in relation to predators will need to be assessed.
  6. Mortality by factors other than predation also needs to be considered. Mortality in overwintering populations can be due to intrinsic factors such as old age, but disease, parasites and possibly stage starvation are also likely causes. Dead krill are reported to be an important food source for deep sea benthos of the sea-ice zone. The role of parasites and parasitoids also needs to be elucidated.

4.3.2 Top predators

Process studies will be necessary to address the key questions 2-6 listed above (Section 3.2). Whereas questions 2 and 6 are focussed on performance of predators in relation to sea ice and on overwintering strategies respectively, the questions 3 - 5 encompass various aspects of predator/prey relationships. With regard to the latter questions, it should be pointed out that defining methods and approaches for studying the dynamic interactions between top predators and their prey has received much less attention than, for instance, the population dynamics of either zooplankton prey or top predators taken separately. The development of research programme elements to address each of the key questions will require cooperation by scientists with expertise on sea ice, prey ecology and top predators. Only a small proportion of the necessary research can be carried out from shore-based stations. The variety and complexity of the ship-based research necessitates (a) very careful planning of interactive studies; (b) dedicated time on Time Series Surveys; (c) and Process Study cruises dedicated to predator-prey research.

The following consists of an overview of the approaches and methods in use for the study of predator population dynamics and the relevant processes and mechanisms.

a) Population dynamics

  1. Definition of unit populations requires studies using newly developed molecular techniques of genetic variation within and between breeding units of target species. Definition of population units for crabeater seals and fish are particularly important.
  2. Population age structure, fecundity rates, productivity and survival rates for seabirds and seals (both juvenile and adult) are studied basically by annual capture-mark- recapture studies of individually identified animals. Offspring production in relation to breeding population size has been studied widely, but there are few detailed demographic studies of target species and even fewer that have annual data over more than 10 years.
  3. Age structure and vital rates for ice-breeding seals are determined by examination of teeth and reproductive tracts taken from samples of the population. For commercial fish, regular surveys to estimate stock size, population structure, reproductive status and diet are undertaken in support of CCAMLR. Studies on squid are restricted to determining distribution and trophic relationships. In general for fish and squid, age structure and vital rates are determined by examination of otoliths/statoliths and maturity status of the reproductive system taken from samples of the population.
  4. Emigration and immigration: Long-term marking of individuals is not as straightforward in most top predators as it is for flying birds. The use of passive induction transponders offers very significant advantages over flipper tags for penguins but further technological development is required, particularly of recognition systems to detect tagged individuals, to make maximum effective use of this new technology.

b) Foraging ecology

This comprises studies of:

  1. Diet composition - including seasonal, interannual and geographical variations in the nature of the prey, including their size, sex and age, where feasible. Diet research is chiefly based on analysis of stomach (and sometimes faecal) samples (increasingly involving lavage methods for seabirds and seals). Serological techniques can provide important confirmation of visual diet observations in squid. Determination of age, size and sex of prey relies extensively on relationships between structures relatively resistant to digestion (e.g., otoliths, statoliths, beaks, mandibles, eyeballs, carapaces) and whole animals. Better, and standardised, relationships are needed for many taxa. Diet studies other than during the summer months are rare and need to be a particular focus of future work.
  2. Foraging habitat and area, i.e., the physical structure and physical and biological characteristics of the location selected by top predators for feeding activities and how these vary at temporal scales ranging from diel to annual. Once almost entirely dependent either on direct visual observations (seabirds, seals) or net-haul samples with concurrent oceanographic data (fish, squid), data acquisition in this field is now being revolutionised by the use of satellite telemetry, especially for seabirds and seals. Acquisition of congruent data on the nature of the ice and water habitats is essential and, using conventional methods, more difficult for seabirds and seals than for fish and squid.
  3. Foraging behaviour: This comprises all aspects of (a) how predators catch prey, including defining the functional morphology of feeding structures (e.g. squid), the methods used, the conditions and circumstances involved (e.g. in terms of the physical (including optical) properties of their environment); (b) when predators catch prey (time of day, etc.); (c) how often and how much prey is caught. For all except flighted seabirds, relevant quantitative data have only been acquired with the very recent development of archival and satellite-linked instruments on and inside free ranging animals. A range of sensors recording continuously or intermittently data on pressure (= depth), temperature (external and internal), velocity, and light levels, (and often linked to location and physiological data) are permitting unique insights into foraging behaviours, patterns and performance. Requirements for further developing this type of research include smaller and better instruments (i.e., more efficient with respect to power utilisation), better data compression and storage, more accurate sensors to record existing variables (e.g. to collect data on ambient temperature and conductivity in order to determine water body characteristics) and especially better data transfer to satellite. The complementary data on prey distribution and environmental characteristics need to be collected on equivalently fine scales. Laboratory research on sensory competence of predators is also required.

c) Energetics and physiology

  1. Energy expenditure: Many changes in the relationship between top predators and their environment are ultimately expressed in terms of changes in energy expenditure, often reflected in physiological condition of the individuals and/or their offspring. Measurement of many activity-specific energy costs of air-breathing, free-living animals can be achieved using isotopic techniques. These techniques require recapture of animals, integration of the cost of activities between consecutive sampling periods, and can only be used over a relatively short period. Recent developments in the use of heart-rate as an index of energy expenditure are promising. However this technique generates large quantities of data (requiring extreme compression of data for storage and/or transmission) and needs accurate calibration studies (e.g. use of respirometric and other techniques on live animals in flumes, wind tunnels, etc.).
  2. Measurements of body mass: For seabirds and seals the most widely used measures of condition are still those of mass, or size-corrected mass. Use of electronic weighing platforms is greatly enhancing (a) the range and quality of such data; (b) the ability to make regular records from individuals with minimum disturbance; (c) the feasibility of estimating body energy stores/reserves; (d) linking such data to simultaneous studies of reproductive performance and survival of both adults and/or offspring.
  3. Other measurements of physiological condition: Sampling populations via collected samples offers a range of additional physiological indices and condition (e.g. blubber thickness, fat and protein reserves, chemical composition, nucleic acid ratios, gonadosomatic and, for fish, hepatosomatic indices). Few of these techniques have been used successfully on a routine basis on animals captured and released alive. Considerable development, both in laboratory and field, in acquisition and interpretation of data using ultrasound, biological impedance and blood chemistry techniques will be required before these techniques can have widespread use.

d) Growth

Various aspects of growth reflect different aspects of interactions between predators and their environment. Growth (in mass and/or morphometrics) of dependent offspring reflects parental performance over the breeding season. Growth rates of juveniles and adults (chiefly accessible via annual or daily growth layers revealed by analysis of sections of teeth, otoliths and statoliths) integrate a range of interactions over daily to annual time scales.

e) Sampling and observation systems

A full definition of the sampling and observation systems required to address the predator-prey interaction element of SO-GLOBEC will need to await the definition of the research programmes required to address the key questions. However, it may be helpful at this stage to summarise some aspects of likely sampling requirements and to note those methods and sampling systems that are being, or will need to be, developed in order to have effective field programmes. GLOBEC Report No. 5 (Table 2) summarises some relevant details and highlights several key requirements in the field of development of new sampling systems.

  1. Electronic systems deployed on and/or in predators need: (a) further miniaturisation; (b) better sensors, especially those collecting oceanographic data; (c) better data compression and storage; and (d) better data transmission systems to satellite. It is likely that further rapid progress will only be achieved via a workshop involving current manufacturers and relevant sensor developers from both predator and oceanographic communities.
  2. Satellites: In the longer term, research relying on satellites will be fully effective only if satellites are dedicated to biological applications.
  3. Measurements of ingestion: The development of systems to record the frequency, amount and nature of prey ingested is essential to attain a thorough understanding of predator-prey interactions. Relatively simple devices and techniques are in use currently; development of more sophisticated systems is a high priority.
  4. ROVs: The use of remote operated vehicles, whether aerial or submersible, is a high priority in this type of research.

4.4 Modelling

4.4.1 Background

At the first Southern Ocean GLOBEC science planning workshop, held in 1991, modelling was identified as a necessary and integral component of the programme. Results from that workshop (U.S. GLOBEC Report No. 5), recommended three essential criteria:

  1. modelling should be undertaken in advance of field programmes;
  2. existing circulation and sea-ice models should be used; and
  3. models developed for the Antarctic marine pelagic system should have a basis in physiology and ecology.

In June 1993 a second workshop was convened to further the development of a science plan; the recommendations from that workshop (GLOBEC Report No. 5) further highlighted the need for modelling as part of a SO GLOBEC programme. Two specific modelling activities were recommended:

  1. a conceptual model of the Antarctic marine pelagic system that could be used as a framework for the development of field and laboratory studies directed at addressing the objectives of SO GLOBEC; and
  2. better integration, via models, of the theory and experimental observations on krill swarming.

These two activities should be emphasised in planning for the SO GLOBEC programme. Models should be developed in advance of field studies and then tested and improved with the incoming data.

4.4.2 Conceptual Model

a) Purpose

A conceptual model would provide a framework to (1) formulate, synthesise and address scientific questions, and (2) organise and direct field programmes. Key scientific questions posed in SO GLOBEC have the common goal of understanding the role of physical and biological interactions in determining population variability. The output of field programmes could then be integrated with the conceptual model to answer the central questions.

b) Examples of key questions

  1. Top-down or bottom-up control: A common framework for SO GLOBEC is especially important if the programme is to include multiple sites. It is likely that population and circulation processes vary regionally around the Antarctic. For example, in some regions prey may be controlled by predation (top-down control); whereas, in other regions prey abundance may be controlled by fluctuations in their resources (bottom-up control). Evidence to support either or both mechanisms for the Antarctic marine pelagic ecosystem is inconclusive. The design of a field programme to address this issue could be done more effectively if a conceptual model existed for testing hypotheses relating to different control mechanisms. Moreover, comparison of measurements made in the different regions would be facilitated by the use of a common model.
  2. Experimentally difficult processes: There are areas where measurement techniques are lacking (e.g. . quantitative assessment of mortality from predation). Such processes are difficult to assess experimentally, but can be investigated with models. Hence, the conceptual model should be robust enough to accommodate studies of smaller units as well as studies of the more complete system.

c) Approach

One approach for developing a SO GLOBEC conceptual model is to develop individual modules that describe interactions between the physical environment, food resources, intermediate predators, such as zooplankton and krill, and top predators. These modules represent choices for processes and their mathematical representation. Within each module are submodules that describe specific processes and potentially each module could stand alone. For example, the physical environment module could include large-scale circulation, mixed layer dynamics and sea-ice processes. The food resources module could allow for bio-optical approaches for estimating pelagic primary production and sea-ice algal production as well as pelagic and sea-ice heterotrophic production. The components of the other modules would be expanded similarly to include the needed processes. Within the biological processes modules sufficient detail needs to be allowed so that the important parts of biological life histories are included, i.e. size and stage structured populations. The development of the modules of the conceptual model should help in highlighting processes that are critical and thus need measurement.

d) Implementation

The development of a conceptual model for SO GLOBEC studies would consist of two major phases. First, the basic components of the model must be identified.

The model should then be reviewed, revised and published in the open literature. Through the peer review system a consensus can be reached as to the relevant components for the conceptual model. The second phase is to develop the actual models for the modules of the larger model. It is envisioned that the development of the modules for the conceptual model would be done concurrently by several groups with expertise in a particular area. However, this distributed approach to development of the conceptual model will require that it be done in such a way that the individual components are compatible. Thuis, it is important that the groups involved in the development of the conceptual model recognise that it is part of a larger effort.

4.4.3 Circulation Models

a) Availability

At present a three-dimensional time-dependent circulation model with embedded biology that describes the Antarctic marine pelagic ecosystem does not exist. Most of the few models available for the Antarctic marine system have been designed for circulation studies. The Fine Resolution Antarctic Model (FRAM) provides estimates of the large-scale flow associated with the Antarctic Circumpolar Current (The FRAM Group, 1991). The model was formulated for open ocean thermohaline and geostrophic flows and for the most part the simulated distributions accurately reproduce flow at this scale. However, the accuracy of the simulated circulation in coastal and shelf regions is questionable since shelf circulation dynamics were not explicitly included in FRAM. More relevant, however, is that the spatial resolution of FRAM is not adequate for most of the key biological questions posed in SO GLOBEC.

Finer scale circulation models have been developed for some regions of the Antarctic (e.g. Capella et al., 1992). These models are more amenable to inclusion of shelf circulation processes and can provide simulated circulation distributions at scales that can be matched to many biological processes. An important aspect of these regional models is the inclusion of a sea-ice component.

Much of the biological activity in marine systems occurs in the upper portion of the water column, i.e. the mixed layer. In Antarctic regions, the stability (or lack of stability) of the mixed layer has been suggested as one of the important controls for biological production. Vertical and time-dependent sea ice-mixed layer models exist (e.g., Lemke et al. 1990). However, these have not yet been applied to a wide range of Antarctic environments.

b) Needed models and resources

The paucity of existing circulation models for the Antarctic may be regarded as a handicap to developing a strong modelling effort for SO GLOBEC. However, this is not necessarily the case. Several existing circulation models are generally available that can be adapted for the Antarctic. These include the Semi-spectral Primitive Equation Model (Haidvogel et al. (1991), the S-Coordinate Rutgers University Model (Song and Haidvogel, 1994), the GFDL Ocean Circulation Model (Cox, 1984), the Isopycnal Model (Bleck and Boudra, 1986; Oberhuber, 1986) and the Princeton Ocean Model (Blumberg and Mellor 1987). These models should be adapted to the needs of SO GLOBEC. Two general areas of emphasis are identified:

  1. Site-specific models: Models need to be formulated and implemented for the sites that are selected for SO GLOBEC field programmes. Data sets need to be identified that can be used to formulate, calibrate and verify the models in the various regions. This would include all relevant bathymetry, surface forcing (e.g. wind), hydrographic and sea-ice data sets. Data needs are likely to be the limiting factor in the application and implementation of these models.
  2. Mixed layer and sea-ice dynamics: Models of mixed layer and sea-ice dynamics need to be implemented for various regions and interfaced with coarser scale circulation models.

For the time frame prior to SO GLOBEC field studies, existing computer resources should be sufficient for development of needed circulation models. Limiting factors are likely to be the availability of data sets and human resources to develop and implement the models. The latter limitation could be overcome by making support available for students and researchers to do modelling studies.

4.4.4 Biological Models

a) Availability

The availability of models for any part of the Antarctic marine pelagic system is poor. To date, models that treat primary production processes, pelagic and sea-ice, are unavailable, although some are now in development. Similarly, models for higher trophic levels are few; examples include a modelling study for the early life stages of krill (Hofmann et al., 1992), and another for the population dynamics of Calanoides acutus (Huntley et al., 1994). Models need to be developed for older krill life stages, other zooplankton and top predators.

SO GLOBEC could make a major contribution to modelling and subsequent understanding of the Antarctic system. Many of the key scientific questions can be addressed by modelling studies, perhaps more easily than with field studies. Processes involved in krill overwintering, interactions of salps and krill, and the allocation of food (e.g. krill) among multiple predators, are just some examples of key scientific questions which models could resolve. Process studies and laboratory experiments could provide the inputs for some model parameters and the model could be used to integrate and synthesise observations.

b) Needed models and resources

  1. Modelling of trophic transfers and within-trophic-level processes for the Antarctic marine pelagic ecosystem is a virtually unexplored research area. By fostering research in this area SO GLOBEC can make a significant contribution to understanding of the Antarctic system and to the more general area of theory and development of models for marine ecosystems. Many of the general technical and conceptual issues associated with model development, which also apply to the Southern Ocean, are discussed in GLOBEC Report No. 6.
  2. Swarming and aggregation behavior of krill is one phenomenon, specific to the Antarctic, where there is a strong need for models. This has been identified in previous SO GLOBEC science plans as a critical component of Antarctic modelling studies, and is implicit in many of the key questions. Despite the obvious importance, models of krill swarming behavior have received little attention. This area should receive priority. Interactions between modellers and those doing field and laboratory measurements of krill swarming behavior and the relationship of swarming with top predators should be encouraged. As previously recommended, this may be best accomplished by a workshop sponsored in part by GLOBEC.

4.4.5 Data Assimilation

a) Available techniques

Data assimilation is an area that is rapidly developing and is now being used with ocean circulation models (Brasseur and Nihoul, 1994). First attempts are now being made to use data assimilation with biological models (Lawson et al., 1994). Many of the issues associated with assimilation of data into biological models are discussed in GLOBEC Report No. 6; these issues are also relevant to SO GLOBEC. The development of assimilation methods for biological data should be encouraged and incorporated into SO GLOBEC programmes.

b) Needed models and resources

Assuming that data assimilation techniques for biological data are available, the limiting factor in application of these techniques is adequate data sets. The development of data assimilative models for the Southern Ocean system will require close cooperation between modellers and experimentalists. The importance of this cooperation cannot be overemphasised.