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Appendix 2

ASPECT Antarctic Sea-Ice Processes and Climate

Preliminary Plan

Table of Contents 

  1. Executive Summary
  2. Introduction
  3. Rationale
  4. Overall Objectives of ASPECT
  5. ASPECT Key Scientific Questions
  6. ASPECT Links with the SCAR EASIZ Programme
  7. ASPECT Links with other International Programmes
  8. Implementation Strategy
  9. Other Considerations
  10. Management

Appendices

  1. Contributors to the ASPECT Science Plan
  2. Proposed 1997-98 milestones for ASPECT
  3. Shipboard ice observation protocols
  4. Geochemical and trace metal studies of sea ice in ASPECT
  5. List of Acronyms and abbreviations

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Executive Summary

Despite the growth of activities in global-change research in the Antarctic, both from SCAR programmes and from other international programmes, such as those of IGBP and WCRP, there remain key deficiencies in our understanding and data from the sea ice zone that are not addressed by current or planned research programmes. Important problems not adequately covered by existing Antarctic research programmes include:

  1. The broad climatology of sea ice physical characteristics.
  2. Processes such as ice formation, water mass modification, the maintenance of polynyas, ice edge and coastal fronts, gas exchange, and air-sea interaction.
  3. Modelling sea-ice processes in coupled atmosphere-ice-upper ocean models. Linking scales (local scale to regional scale to global scale models).

There is a special role for the SCAR Global Change Programme in the shelf to ice-edge area (pack ice) that is not being adequately covered by other programmes. Hence SCAR GLOCHANT proposes to establish a programme of multi-disciplinary Antarctic sea ice zone research called Antarctic Sea Ice Processes and Climate (ASPECT).

The broad objectives for ASPECT are:

  1. To establish the distribution of the basic physical properties of sea ice that are important to air-sea interaction and to biological processes within the Antarctic sea-ice zone (ice and snow cover thickness distributions; structural, chemical and thermal properties of the snow and ice; upper ocean hydrography; floe size and lead distribution).
  2. To understand the key sea-ice zone processes necessary for improved parameterisation of these processes in coupled models.

The major focus of the ASPECT programme is physical sea ice processes and ocean-atmosphere interaction in the sea-ice zone. Biological processes and ecology within the Antarctic sea ice zone are addressed by the SCAR EASIZ programme, and ASPECT will also be closely linked with that programme to ensure a broad multidisciplinary approach. As a SCAR programme, ASPECT is focused towards the role of the unique regional environment of the Antarctic sea ice zone, but it is essential that this is closely linked to the international global change research agenda. Hence inter-disciplinary components of ASPECT are designed to contribute to, and extend, international open ocean programmes such as JGOFS.

Many physical elements of ASPECT will contribute to the objectives of the WCRP CLIVAR Programme, a study of Climate Variability and Predictability, which involves investigations of atmosphere, ocean and land at a variety of time scales. ASPECT plans are particularly relevant to the CLIVAR-DecCen component-programme, concerned with decadal to centennial climate variability and predictability. The ASPECT programme will initiate implementation of parts of the sea ice zone research requirements of CLIVAR, and will collaborate closely with CLIVAR and other WCRP programmes to ensure the essential global integration of Antarctic regional research. It may be appropriate for some research elements of ASPECT to eventually become a sub-component of CLIVAR, but because of the unique logistic requirements of work in the Antarctic sea ice zone, ongoing SCAR involvement and sponsorship are important.

The ASPECT programme will build on existing and proposed research programmes, and the shipping activities of National Antarctic operators. The plan includes some components that can be undertaken as part of normal resupply voyages; for example a system of simple but quantified shipboard observations that provide statistical ice and snow thickness distributions. ASPECT will also include a component of data-rescue of valuable historical sea ice zone information. The ASPECT programme will achieve its aims by:

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1. Introduction

ASPECT (Antarctic Sea Ice Processes and Climate) is proposed as a programme of multi-disciplinary Antarctic sea ice zone research within the SCAR Global Change Programme. ASPECT will specifically address key identified deficiencies in our understanding and data from the sea ice zone. The programme is designed to complement and to contribute to the other international programmes in this region, whilst avoiding unnecessary duplication of effort in either programme management or implementation. It will build on existing and proposed research programmes, and the shipping activities of National Antarctic operators, and will also include a component of data-rescue of valuable historical sea ice zone information.

The ASPECT proposal was developed at a joint meeting of the SCAR groups GLOCHANT, EASIZ and GOSSOE in Tokyo in April 1995. These groups met on the recommendation of delegates at SCAR XXIII to review existing programmes and proposals within the Antarctic sea ice zone, and to consider in particular the overlap between the various programmes. The meeting identified gaps in the present research which warranted the development of a specific new programme of multidisciplinary Antarctic sea ice zone research. The ASPECT plan was developed further at a meeting during GLOCHANT IV in Madison in April 1996, and by correspondence.

While the major thrust of the ASPECT programme is physical sea ice processes and ocean-atmosphere interaction in the sea-ice zone, it will be vital to maintain strong links with programmes of ecological research in the sea ice zone, and in particular with SCAR EASIZ. As a SCAR programme, ASPECT is focused towards the role of the unique regional environment of the Antarctic sea ice zone, but it is essential that this is closely linked to the overall international global change research agenda. Hence inter-disciplinary components of ASPECT are designed to contribute to, and extend, international open ocean programmes such as JGOFS.

Many elements of ASPECT will contribute to the objectives of the WCRP CLIVAR Programme, a study of Climate Variability and Predictability, which involves investigations of atmosphere, ocean and land at a variety of time scales. ASPECT plans are particularly relevant to the CLIVAR-DecCen component-programme, concerned with decadal to centennial climate variability and predictability. The ASPECT programme will initiate implementation of parts of the sea ice zone research requirements of CLIVAR, and will collaborate closely with CLIVAR and other WCRP programmes to ensure the essential global integration of Antarctic regional research. It may be appropriate for some research elements of ASPECT to eventually become a sub-component of CLIVAR, but because of the unique logistic requirements of work in the Antarctic sea ice zone, ongoing SCAR involvement and sponsorship are important.

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2. Rationale

The Antarctic sea ice zone remains one of the least known regions of the earth's surface. Apart from satellite derived data on ice extent and concentration, there are few reasonable climatological estimates of ice conditions that can be used for validation of numerical models. What limited information we have, mostly from the Weddell Sea, indicates that the ice characteristics and the dominant processes in the Antarctic are substantially different from those in the central Arctic. The Antarctic sea ice zone acts as a regional boundary between the Antarctic and sub Antarctic, an interface between the upper ocean and the lower atmosphere, and globally, as a region of important interactive physical and biogeochemical processes.

Uncertainties in, and the importance of, the role of sea ice in the climate system are highlighted in a US Global Change Program Report, Forum on Global Change Modeling. On the basis of studies of past climates, which provide evidence for polar amplification of warming it is predicted that under any future global warming scenario, Northern Hemisphere sea ice will probably be reduced, but that projected changes and their timing in the Southern Hemisphere sea ice extent are less certain. Current coupled model studies of an increased carbon dioxide atmosphere are also essentially in conflict in their predicted Southern Hemisphere sea ice response. First simulations with a coupled model even suggested an expansion, but more likely thickening, of the ice cover in particular regions. Other model studies, using different parameter-izations of both fluxes and sea ice processes suggest the opposite effect; that instead sea ice extent and thickness will both be drastically reduced in increased atmospheric carbon dioxide scenarios. Through ice-albedo feedback, these latter simulations also suggest that the sea ice retreat itself accounts for a significant fraction (40%) of the global atmospheric warming that will occur under CO2 doubling, with of course very large increases in the regions more local to the present day ice cover. These projected changes are at present currently impossible to ascertain, because without knowledge of the Antarctic sea ice thickness distribution, it is difficult to provide compelling evidence if and when change occurs. Since the models currently give contradictory results, it suggests that the model parameterizations of sea ice physical processes are different and some, perhaps all, of the models are unrepresentative in some way in their depiction of the sea ice cover. Without present-day knowledge of the ice thickness distribution, models however cannot be verified, so we cannot even ascertain which model physics, if any, are correct.

The role of sea ice in the global climate system has been long recognised and included as a study component of major international weather and climate programmes such as the Polar Sub-Programme of the Global Atmospheric Research Programme, and the World Climate Research Programme. However, whereas in the Arctic a number of multi-national co-operative programmes have advanced our understanding of sea ice processes, there have been few similar programmes implemented in the Antarctic, and none covering the whole of the Antarctic sea ice zone. Organisations such as SCOR-CCCO (1981), WMO-CAS (1982), and the JSC for WCRP Working Group on Sea Ice and Climate (1988), have in general left it to SCAR to provide appropriate co-ordination of scientific initiatives in the Antarctic sea ice zone.

Several factors have restricted implementation of such a co-ordinated Antarctic sea ice zone programme before the present. But changed circumstances, now make it timely to initiate such a programme within SCAR. No other organizations have the experience or expertise for Antarctic research that is contained in the national Antarctic programmes of the SCAR countries. Many of the SCAR countries, tied also through the closely associated Council of Managers of National Antarctic Programmes (COMNAP), are already carrying out, and plan to continue, sea ice zone research in both physical and biological sciences within National programmes: substantial new information is now available, particularly from the Weddell Sea, Amundsen and Bellingshausen Seas, and the Indian Ocean sector. A number of sophisticated, ice-capable research vessels are now working in the Antarctic, and at the same time the increased number of nations working in the Antarctic has seen a growth in all types of shipping activity. And new remote sensing capabilities, particularly active radar systems, have greatly enhanced sea ice observation from space.

A number of other international programmes, for example CLIVAR, JGOFS, and SCAR-EASIZ, have planned activities of direct relevance, but even together do not cover the full scope of the required Antarctic sea ice zone research. The inter-relationship between ASPECT and other relevant international programmes is discussed further below. Important problems that are not being adequately covered by existing Antarctic research programmes include:

  1. Broad climatology of sea ice physical characteristics. Satellite derived data provide large scale estimates of ice extent and concentration, but not of the thickness of ice and snow, which are the primary variables affecting many physical and biological processes, as well as climate processes.
  2. Processes such as ice formation, water mass modification, the maintenance of polynyas, ice edge and coastal fronts, gas exchange, and air-sea interaction.
  3. Modelling sea-ice processes in coupled atmosphere-ice-upper ocean models. Linking scales (local scale to regional scale to global scale models).

There is a special role for the SCAR Global Change Programme in the shelf to ice-edge area (pack ice) that is not being adequately covered by other programmes, and for providing information on the sea ice system for development of coupled models: current models do not include all of the relevant sea ice processes and many important parameters are not available. The role of sea ice (including albedo feedback, ice thickness, flux correction and ice dynamics) has not been well addressed and sea ice should be incorporated into both climate and ecological models. SO-JGOFS would welcome development of models that include sea ice.

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3. Overall Objectives of ASPECT

ASPECT is a multi-disciplinary programme of research within the Antarctic sea ice zone. Its overall aim is to understand and model the role of Antarctic sea ice in the coupled atmosphere-ice-ocean system. This requires an understanding of key processes, and the determination of physical, chemical, and biological properties of the sea ice zone. These are addressed by objectives which are:

  1. To establish the distribution of the basic physical properties of sea ice that are important to air-sea interaction and to biological processes within the Antarctic sea-ice zone (ice and snow cover thickness distributions; structural, chemical and thermal properties of the snow and ice; upper ocean hydrography; floe size and lead distribution). These data are required to derive forcing and validation fields for climate models and to determine factors controlling the biology and ecology of the sea ice-associated biota.
  2. To understand the key sea-ice zone processes necessary for improved parameterization of these processes in coupled models.

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4. ASPECT Key Scientific Questions

Key scientific questions which must be answered to meet the objectives are:

i. What are the broad-scale time-varying distributions of the ice and snow-cover thickness, ice composition and other physical characteristics in the Antarctic sea ice zone

There are currently no systematic, spatially distributed data sets available of the seasonal and regional variability of the ice and snow thickness distribution for the Antarctic sea ice zone. Such data, together with those on ice extent, and concentration, would provide a sensitive and essential test of the performance of numerical atmosphere-ocean models. Similarly, climatic compilations of the main features of ice drift and, in more sophisticated models, the percentage total ice formed by different processes (basal freezing, frazil formation, snow flooding) provide good validation of models. Remote sensing validation and algorithm development are also necessary to use existing and future satellite derived data in a quantitative monitoring mode for sea ice model verification and input fields.

Similar physical data are required to support research into the biology and ecology of the sea-ice-associated biota, and to scale-up from local studies of ecosystems and the biogeochemical system to the whole Antarctic. In particular, the ASPECT and EASIZ programmes together need to quantify the variance spectra of major components of the ice-associated biota and the characteristics of the physical environments with which these are associated.

ii. What are the dominant processes of ice formation, modification, decay and transport which influence and determine ice-thickness, composition and distribution?

Air-ice-ocean interaction effects in the Antarctic are manifested in changes in ice thickness, structure and composition. Flooding of the snow cover followed by refreezing leads to a higher than usual surface salinity, while melting at the base from high ocean heat flux can lower the salinity of the ice from that seen in a bottom freezing condition.

A key early finding about the composition of Antarctic sea ice, and its fundamental difference with Arctic sea ice, is the high percentage of frazil ice structure (typically 40 to 60% of the ice structure) that is observed in much of the seasonal ice cover around Antarctica. The dominant growth regime relating to frazil ice structure is the early interaction of the open ocean wave field with the growing ice cover. This turbulent growth regime causes the frazil ice crystals to form dynamically into pancake ice floes. Ice growth can take place quickly up to some tens of centimetres of ice thickness, but at these thicknesses the ice strongly attenuates the incident wave field, essentially shutting down the driving for further ice growth by the pancake ice growth mechanism. Further modification of these initial ice covers can then proceed thermodynamically either by slow growth beneath the ice cover if the heat flux to the atmosphere is high enough, or by bottom melting in areas of relatively high ocean heat flux.

In areas interior to the pack ice edge, other processes of ice modification that are observed in Antarctica, are ice growth in leads created by ice divergence. Divergence of up to 10% per day has been observed under extreme conditions. Consequently, new open water is frequently exposed within the pack, and much of the total ice mass forms by rapid freezing in these areas. As well as thermodynamic growth, leading primarily to congelation or columnar ice structure, the deformational processes of rafting and ridge-building are also important in the development and distribution of sea ice. Episodic periods of divergence and ice formation in new open water, followed by convergence and thickening by deformation, are related to the passage of synoptic weather systems.

The physical structure and the physical-chemical composition of ice cores also reveal metamorphic changes relating to thermal forcing; the creation of snow ice from surface flooding by sea water; and also formation of superimposed ice from snow melt and refreezing. In areas near ice shelves, significant amounts of bottom accretion of what is called platelet ice, can also occur from the advection of super-cooled water to the surface. Wind and ocean current driving can also contribute to changes by transporting ice from source to sink regions. This ice dynamical effect can produce effects in contradiction to that inferred from a perception of the air temperature fields. In the western Weddell Sea for example, the thickest ice is found in the north, a result of ice deformation and advection effects rather than in the south where the coldest air temperatures are found.

iii. What is the role of coastal polynyas in determining total ice production, heat salt and biogeochemical fluxes, and water mass modification?

Coastal polynyas are a common feature of the perimeter of the Antarctic continent. As opposed to the generally larger deep-water polynyas, such as the Weddell Polynya, the polynyas on the continental shelf are believed to be primarily "latent heat" polynyas: that is, heat loss from the ocean surface is balanced by the latent heat of new ice formation and the polynya is maintained by wind or tidal current removal of the new ice.

The polynyas are regions of intense heat loss from the ocean to the atmosphere, and of rapid and copious ice growth: they may be significant as "ice factories" for the total sea ice zone. Brine rejected during ice growth is concentrated in the polynya areas and can cause localised water mass modification as well as significantly increasing the salinity of Antarctic continental shelf water. In the south west Weddell Sea High Salinity Shelf Water (HSSW) formed through this process is the parent water mass for the production of Ice Shelf Water (ISW) under the Filchner-Ronne Ice Shelf. ISW leaving the continental shelf leads subsequently to the formation of Weddell Sea Bottom Water (WSBW). Adelie bottom water, which occurs on the shelf and shelf slope in the region from 130°E to 150°E, has a recent origin (<5 years ) and appears to be intricately linked to processes in the coastal polynyas of the region. There appear to be significant regional differences in the activity of coastal polynyas.

Ice production in polynyas bordering ice shelves may be enhanced both by an off-shelf wind-field or by an oscillating tidal current. The outgoing tide opens a lead (polynya) where ice production may be very intense, whereas the incoming tide concentrates the newly-formed ice along the ice front. The accumulated production in such latent heat polynyas has been estimated to be as much as 20-30 metres of sea-ice per year.

The ice free polynyas play an important role for Antarctic marine biological systems, and in the control of biogeochemical fluxes. Polynyas have potential importance in biogeochemical cycling in terms of air-sea gas fluxes and vertical convection as a carbon transport mechanism.

Our knowledge of the local wind-fields in the ice-shelf polynya areas is very poor, and the variation in the tidal currents along the edge of the floating ice-shelves is also virtually unknown. Measurements of wind and tidal currents should therefore accompany any measurement programme of ice formation in polynyas.

iv. What are the processes that control the ice-water interactions at the ice-edge, and their seasonal changes

Ice edges, or the zones where the ice cover interacts with the open ocean, have high seasonal and regional variability around Antarctica. Ice edges essentially can be divided into three phases: a growth phase of ice advance, a decay phase where the ice edge retreats; and an intermediate or "equilibrium phase" with small advance and retreat oscillations.

The ice edge growth phase during the fall-winter period, usually proceeds, when open ocean waves are present, by the growth of frazil ice transitioning primarily into pancake ice fields. If shorelines are present or unusually calm conditions exist without ocean waves, the ice edge may advance instead as thin flat sheets of nilas ice. In some regions, the onset of winter conditions allows ice that is advected in from other regions to stay frozen rather than melt, so the ice edge advances by the advection of floes that have been maintained through the summer period. The seasonal cycle of warming air temperature or warm water advection leads to the ice edge retreat. Wave action at the ice edge leads to breaking up of the larger floes. Combined with solar heating of the water in the increased perimeter area of the broken floes, melting is accelerated and the combined mechanical and thermal deterioration of the ice edge proceeds. In some regions, such as the northern Weddell Sea, this decay phase can be considerably delayed or stopped if the ice transport from the south is high enough to keep the ocean water chilled and also shielded from solar heating until the summer season is over. The equilibrium phase occurs when the ice edge is brought to a northern boundary usually corresponding to an ocean frontal structure where warm water exists on the northern side of the front so that the ice transported there is melted as it crosses the front. Variations in the ice advection rate or alternate period of cold air and warm air advection can then cause the oscillations of the ice edge, slightly advancing or retreating after the mean equilibrium position is reached.

The regional variability in the ice edge can be characterised by the period of time that the ice edge exists in these various phases, for example the Weddell Sea undergoes a short advance period, a prolonged equilibrium phase, and a rapid decay phase due to the high transport. In other regions, the ice edge regime is primarily thermodynamically or air temperature controlled, so that the equilibrium phase is very short at the maximum ice edge extent, and the ice advance and retreat are both relatively lengthy and nearly equal in time. The result of these differences in regime can effect the amount, and the position and timing of fresh water flux at the ice edge, and thus impact strongly on the biological regime, and lead to seasonal and regional variations in ice edge blooms around Antarctica.

The seasonal ice zone makes a major contribution to the biological pump of CO2 in the polar region. Every year its northern border moves within a large band of latitude and the ice edge represents a key component of the Southern Ocean dynamics both with regards to the transfer of energy between the atmosphere and the ocean and to the biogeochemical fluxes. Often, but not always, the spring time retreating ice edge is a locus of elevated phytoplankton biomass. There may be a causal link to the sea ice retreat, via increased light availability, surface water stratification, "seeding" by sea-ice algae, or inputs of trace nutrients such as iron from accumulated aerosols. Alternatively, the correlation may largely reflect separate responses to seasonal increases in solar radiation and open water temperatures. Further coherence may occur because, at least in the late stages of melting, the algae can reduce the sea-ice albedo and thus its rate of melting. It has been assumed that the seasonally retreating melting ice can create density structure that increases the stability of the water column in its immediate wake. This environment determines favourable conditions for phytoplankton ice-edge bloom development. Nonetheless field observations conducted in the eastern Weddell Sea and in the Indian sector lead to the conclusion that this conceptual model is not valuable for MIZs submitted to intense transfer of energy from the atmosphere. Availability of realistic description of the ice field and structure will greatly improve coupled physical-biogeochemical models for the ice-edge ecosystem, of major interest for EASIZ and SO-JGOFS.

It is important to understand these links for several reasons. In assessing interannual variations in biological activity, a model able to incorporate changes in physical forcing is desirable, so that trophic structure, predator/prey, and population variations may be better understood. In the context of global climate change, photosynthesis represents the start of the biological transport path which removes atmospheric carbon dioxide to the deep sea and sediments. The ecosystem structure influences what proportion of this fixed carbon reaches the deep sea or is recycled within the upper ocean and returned to the atmosphere.

ASPECT needs to determine:

  1. What are the physical factors controlling the dynamics of the density structure in the MIZ, and how do these impact on the behaviour and timing of MIZ blooms.
  2. Whether changes in the geochemistry of sea ice affect the isotope fractionation of sea ice biota and consequently the isotope ratios of particulate matter in sea-ice and the water column.
  3. Whether sea-ice acts as an accumulator for trace metals, and if so do the elevated concentrations of elements such as Fe or Mn explain qualitative or quantitative changes in the primary production in the surface waters of the MIZ.

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5. ASPECT Links with the SCAR -EASIZ Programme

The SCAR EASIZ (Ecology of the Antarctic Sea-Ice Zone) programme originated as a successor to the SCAR BIOMASS programme. The aim of this programme is to improve understanding of the structure and dynamics of the Antarctic coastal and shelf marine ecosystem. The Antarctic continental shelf is distinctive in being depressed by the weight of continental ice, the proximity or direct contact with shelf ice, the very low riverine input, and the extensive glacial input in the form of bottom water, surface melt and glacial debris. The Antarctic sea-ice zone is also a highly seasonal environment, with large and important differences in biology between summer and winter.

The biota associated with sea ice includes all those organisms whose distribution is determined by the physical structure of sea-ice cover, and includes organisms ranging in size from microbiota inhabiting the ice fabric to large vertebrates using the ice surface as a resting place or feeding site. Compared with the open ocean, the means of estimating the abundance and distribution of these organisms involves a disparate range of techniques. This implies that building up a picture of the interrelationships within this community is a task closer to the approaches of benthic or terrestrial rather than pelagic ecology. At present, there are major gaps in our understanding of the variability of distribution of organisms, which make a large-scale understanding of the system more or less impossible

Sea ice is a heterogeneous environment. It offers different habitats to a range of organisms, and the physical characteristics of the ice affect the ecology and physiology of those organisms. At small scales, the internal structure of sea ice determines the distribution of microbiota, whilst crystal fabric and ice salinity regulate growth rate through influence on nutrient availability and light climate, including ultra-violet. At larger scales, irregularities in ice topography provide structural diversity for zooplankton, affecting interactions with their predators and prey. At the largest scales, irregularities in ice topography provide structural diversity for zooplankton, affecting interactions with their predators and prey. At the largest scales, the ice-edge zone represents a complex environment where the ecological processes are controlled by the interaction between the biota, the ice and ocean.

An ability adequately to scale up from the relatively local measurements of biological processes in the ice-associated ecosystem to regional estimates of quantities such as carbon cycling or biogenic gas fluxes is a requirement of Southern Ocean global change programmes. To achieve this, we need to be able to use large-scale description of environmental variability to model biogeochemical properties at regional scales. Such an approach would complement studies in the pelagic system, which involve an understanding of the effects of spatial and temporal heterogeneity on ecosystem interactions relevant to ocean biogeochemical cycling.

The EASIZ programme, initiated in the 1995/96 austral summer season, is an integrated study concerned with both benthic and pelagic indicator species (their population structure and dynamics) as influenced by sea ice. Because shallow-water communities are more sensitive to global change, particular attention will be paid to their biology and to understanding seasonal, inter-annual and long-term changes. EASIZ also places special emphasis on the community level. Although ship-borne studies will form an important part of the EASIZ programme, a central role will be played by the network of coastal marine stations around Antarctica. These stations are of great importance in supporting long-term studies, and in allowing work throughout the austral winter.

Key scientific areas for joint attention by ASPECT and EASIZ are:

  1. How does the physical structure of the ice influence the taxonomic composition of the associated biota, and its production?
  2. To what extent are the scales of variability in sea-ice physical structure reflected in those in the associated biota?
  3. To what extent are biological measurements made in areas close to open water (marginal ice- zone or polynyas) representative of the bulk of the sea-ice zone?

The work undertaken within ASPECT will thus complement, rather than overlap, the EASIZ programme. Whereas ASPECT will be undertaking integrated physical and biological work from ships during dedicated cruises at the marginal ice zone (MIZ), or deep within the pack-ice, the main thrust of EASIZ work will be near shore, year-round, and long-term. Work within EASIZ will thus provide important data on temporal variability at a series of sites, to complement the more detailed process studies or data on spatial variability to be obtained within ASPECT. In addition the physical studies proposed under ASPECT will contribute significantly to the overall aims of EASIZ. Close scientific links will be maintained between the two programmes, and the combined results will contribute substantially to our understanding of the Antarctic sea-ice zone.

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6. Links with other International Programmes

ASPECT will complement and contribute to the other international programmes concerned with global change, and with an interest in the Antarctic sea ice zone. Presently active components of other programmes relevant to ASPECT include:

WCRP

The World Climate Research Programme (WCRP) emphasises the physical climate system, while the companion IGBP focuses on biological and chemical processes involved in global change. The Antarctic climate research issues of interest to the WCRP could in principle be construed broadly to include the roles in the global climate of Antarctic sea ice, ocean circulation, ice sheets, and atmosphere, and of course the interactions among these components. The time scales of interest span a great range because of the very long intrinsic time scales of the ice sheets (centuries), although, say, ocean-ice sheet interactions might be much more rapid. Other parts of the system likely have important seasonal to decadal variability, as well as trends.

IPAB and AnITRP

The WCRP has established two programmes which use automatic observing systems to increase meteorological and sea ice related data from the Antarctic region: the International Programme for Antarctic Buoys (IPAB), and the Antarctic Ice Thickness Research Programme (AnITRP). The objective of IPAB is to establish and maintain a network of drifting buoys in the Antarctic sea ice zone in order to support research in the region related to global climate processes, to meet real-time operational meteorological data requirements, and to establish a base for ongoing monitoring. AnITRP aims to principally obtain ice thickness data using upward looking sonar instruments. These instruments, moored to the ocean bottom, record the keel depth of sea ice drifting over their location from sonar ranging measurements made every few minutes. Both programmes are essentially routine observing ones, providing data for initialisation and validation of climate models and for monitoring. The major contributions to both come from national programmes of SCAR members. Data from ASPECT will contribute to, and build on these programmes.

ACSYS

WCRP has also developed the Arctic Climate System Study (ACSYS) for the Northern Hemisphere, but there are no equivalent process studies in the Antarctic sea ice zone. However modelling of Antarctic sea ice, and to some extent of ice-ocean interaction, is presently within the purview of the Sea Ice/Ocean Modelling Panel of ACSYS. A particular emphasis of the ACSYS SIOM Panel has been model development suitable for incorporation into interactive global numerical circulation studies.

CLIVAR

CLIVAR, a study of Climate Variability and Predictability, is a major new initiative of WCRP (since March 1993) which builds on TOGA and WOCE, and aims to determine the extent to which climate can be predicted, and the extent of human influence on climate. CLIVAR involves investigations of atmosphere, ocean and land at a variety of time scales, and is organised into three component programmes: the most relevant of these to Antarctic sea ice zone studies is CLIVAR-DecCen, concerned with decadal to centennial climate variability and predictability. The CLIVAR Science Plan includes consideration of the variability of the ocean's ice cover, and of ocean processes involving sea ice. The ASPECT programme will initiate implementation of some of the sea ice zone research requirements of CLIVAR, and must collaborate closely with CLIVAR and other WCRP programmes to ensure the essential global integration of Antarctic regional research. It may be appropriate for some research elements of ASPECT to eventually become a sub-component of CLIVAR (a 15-year research programme).

WCRP has indicated that discussion of the need for internationally co-ordinated Antarctic climate research should be included in the appropriate workshops being planned under ACSYS and CLIVAR within the next two years, but is unlikely to establish a new Antarctic study group itself in advance of these workshops.

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IGBP
JGOFS

JGOFS is the IGBP core project concerned with the role of the oceans in the global carbon cycle. It has two major goals, set out in its science plan (SCOR 1990). The first goal is to 'determine and understand on a global scale the processes controlling the time-varying fluxes of carbon and associated biogenic elements in the ocean, and to evaluate the related exchanges with the atmosphere, sea floor and continental boundaries'. The second is to 'develop a capability to predict on a global scale the response of oceanic biogeochemical processes to anthropogenic perturbations, in particular those related to climate change'.

The major field components of JGOFS consist of a series of regional studies. The location of these has been determined to study specific phenomena (see JGOFS Implementation Plan - SCOR 1992). The largest regional study in both areal extent and the amount of scientific effort already devoted to it is in the Southern Ocean. This was selected because it is the largest and potentially most significant of the so-called HNLC (high nutrient-low chlorophyll) regions of the world ocean, where annual phytoplankton production is insufficient to utilise fully the dissolved macronutrient pool.

The Southern Ocean regional study (SO-JGOFS) compiled its own science and implementation plan (SCOR 1993). In this it set its own objectives, based on those of the JGOFS science plan but tailored specifically to the circumstances of the Southern Ocean. Two of these relate directly to the areas of interest of the SCAR ASPECT proposal. The first is the question 'What is the effect of sea ice on carbon fluxes in, and to, the Southern Ocean?', and the second is 'What are the major features of spatial and temporal variability in the physical and chemical environment, and in key biotic systems?'.

SO-JGOFS recently evaluated its progress at a symposium examining the first four years of fieldwork. At its meeting following the symposium, the planning group examined progress with respect to specific objectives. It recommended that links with SCAR's global change programme be strengthened, and in particular noted the potential for the ASPECT proposal to promote sea ice research which would be complementary to JGOFS studies. JGOFS interests in the Antarctic sea-ice system include the relative importance of sea ice biota in carbon cycling, the factors governing the location of marginal ice zone phytoplankton blooms, and the physical effects of sea ice in modulating air-sea fluxes of radiatively active gases and solar radiation.

There are some areas where data of fundamental importance to our understanding of the Southern Ocean as a biogeochemical system cannot be obtained within the scope of normal JGOFS process cruises. These relate mainly to the features of variability of the sea ice and its associated biota. SO-JGOFS needs to be able to scale-up small- and meso-scale processes studies to regional estimates. Following the 1995 symposium, three key areas were identified:

GLOBEC

GLOBEC (Global Ocean Ecosystems Dynamics Research) is an IGBP programme concerned with off-shelf (water column) processes, invertebrate and vertebrate indicator species, as well as the physics that influences the population dynamics of animals and predator/prey interactions. The main aim is to understand the linkages between physics and biology on different scales. A Southern Ocean component, SO-GLOBEC will concentrate in three areas: the Antarctic Peninsula, the eastern Weddell Sea and the Indian Ocean sector. Two groups of species will be studied: zooplankton (copepods and krill) and top predators (seals and penguins). There are no direct overlaps between ASPECT and SO-GLOBEC.

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SCAR
APIS

APIS (Antarctic Pack Ice Seals), an initiative of the SCAR Working Group on Biology, is concerned with a census and the population dynamics of marine mammals, primarily crabeater seals, within the sea ice zone. Techniques for the reliable and precise counting of marine mammals are being developed by APIS, and protocols for counting seabirds already exist. Although there are few scientific overlaps with ASPECT there are some possibilities for shared logistic support. ASPECT cruises may provide ships-of-opportunity for some work on seabirds and marine mammals. Regular contact will be maintained between the ASPECT and APIS programmes to ensure that all opportunities for logistical co-operation are taken; and ASPECT data on ice characteristics will be made available to the APIS programme.

SCOR
WG86

The SCOR Working Group 86 on Sea Ice Ecology was established to review the emerging field of sea ice ecology, to determine the existing connections between the within-ice ecology and the physics and chemistry of the sea ice environment, and to co-ordinate, through review publications and conference organization the at-large and emerging research community on this topic, including both Arctic and Antarctic researchers. Participation in ASPECT development, and close interaction with SCOR (along with SO-JGOFS) on ASPECT issues has been a special topic of WG86, and the full endorsement of the development of ASPECT has been given by WG 86. Since the development of a research programme is outside the mandate of SCOR working groups, the ASPECT sea ice ecological component can be regarded as the natural extension of WG86's activities into that realm, and therefore has received its full encouragement and support. Future activities of WG86 that will closely co-ordinate the ASPECT development include the establishment of a series of Gordon Research Conferences on Polar Marine Science, to be held annually beginning in 1997. The first two of these Sea Ice Ecology and Sea Ice Ecology in Globally Changing Environments are of direct relevance to ASPECT ecological studies and will provide important forums for discussion of science results in a timely manner as they develop.

IAnZone

AnZone (Antarctic Zone) has been an affiliation of working-level scientists concerned with the physical marine sciences (primarily physical oceanography, with contributions from sea ice physics, and boundary layer atmospheric sciences) in that region of the Southern Ocean poleward of the Antarctic Circumpolar Current (the Antarctic Zone). Three major experiments in the Southern Ocean have been completed or are underway under AnZone auspices, the Ice Station Weddell (ISW) drift in 1992, the Antarctic Zone Flux Experiment (ANZFLUX) conducted in the eastern Weddell Sea in 1994 and upcoming oceanographic work (1997-99) in the confluence of the Weddell and Scotia Seas near the Antarctic Peninsula on deep ocean ventilation (DOVETAIL).

Significant sea ice work relating to the design of ASPECT has been conducted on these previous AnZone experiments. These efforts provide some historical climatology on the ice thickness distribution for the Weddell Sea region and significant process experiments on the dynamics and thermodynamics of pack ice in the first and second year ice of the eastern and western Weddell Sea. These efforts, when further synthesized and integrated, form a firm foundation for ASPECT studies, and also represent a significant fraction of the ASPECT effort to date. Unlike some regions for example, the climatology of the ice thickness distribution in the Weddell Sea can build on this base, and ASPECT transects are designed to fill gaps there rather than the full seasonal and regional set that are necessary for some other regions.

A broader international group of IAnZone (International Antarctic Zone) has recently been affiliated as a standing committee of SCOR. The goal of IAnZone is to advance knowledge of climate processes within the Antarctic zone through development and co-ordination of observational and modelling programmes, and it will have a primary role in overviewing many of the physical aspects of the oceanography in the Antarctic. It will also conduct process experiments primarily relating to water mass formation processes and the longer-term climatic variability of the ocean, contributing to the CLIVAR program at the decadal to century time scales.

IAnZone and ASPECT have intersecting interests in terms of the role of sea ice in the oceanic and climate systems, and close co-ordination has been established. Joint interaction with CLIVAR between IAnZone and ASPECT has been initiated to ensure the unified Antarctic contribution to the physical side of climate studies will be both adequately considered and presented in that forum. From the operational side, close co-ordination will also be undertaken to, for example, conduct joint cruises to those regions that satisfy the aims of both projects. Co-ordination on the science (e.g. the role of coastal polynyas in water mass modification as well as sea ice formation and air-sea interaction), on the optimal use of limited numbers and schedules of suitable icebreakers, as well as the presentation of the unified air-ice-ocean science to the climate community will be satisfied by this co-operative approach. The approach to ensure this co-ordination has been the direct participation of both ASPECT scientists and IAnZone scientists in each other's meetings and the formulation of science programmes.

GCOS and GOOS

GCOS (Global Climate Observing System) and the climate module of GOOS (Global Ocean Observing System) are proposed operational observing systems sponsored by a consortium of WMO, IOC, UNEP, and ICSU. These programmes are in the planning stage only as yet, but they will address all aspects of the physical climate system, including consideration of sea ice. In their operational form they will not include process studies, nor the same detailed spatial and temporal resolution as many of the present climate-related research programmes, but their implementation will rely on the results from the research programmes, and they will continue some of the research observational programmes as ongoing operational observations.

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7. Implementation Strategy

The ASPECT programme aims to achieve its goals by co-operation within the SCAR community. Some components of this co-operation may involve multi-national process studies, but much will be achieved within individual National Programmes provided that there is a framework of co-ordination, and that common observational protocols are established. Where possible the programme will build on existing and proposed research programmes, and the shipping activities of National Antarctic operators. The implementation plan will include some components that can be undertaken as part of normal resupply voyages; for example a system of simple but quantified shipboard observations that provide statistical ice and snow thickness distributions. ASPECT will also include a component of data-rescue of valuable historical sea ice zone information.

The role of an ASPECT Scientific Steering Group will be to:

Elements of the ASPECT programme addressing each key scientific questions should include the following:

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i. The broad-scale time-varying characteristics of the ic

Transects involving direct ice sampling by coring is the principal method for determining the dominant variations in growth, metamorphism and decay in various regions. Seasonal sampling is also necessary to determine the evolution of the ice cover. Preliminary work has suggested that in some regions these compositional changes can also vary interannually, and that repeated visits to some regions at the same season but different years can also establish how these changes are related to variability in forcing from the ocean and atmosphere.

Broad scale surveys are required to define a climatology of the time-varying state of the ice thickness distribution and snow cover; structural, chemical and thermal properties of the snow and ice; floe, lead and ridge distribution and upper ocean. A minimum requirement is for autumn, winter, spring and summer measurements along transects perpendicular to the Antarctic coast and spaced at intervals of about 15-30° of longitude. Ice-capable vessels used by an increasing number of national Antarctic programmes are capable of undertaking these surveys in all seasons.

It is not proposed that the surveys be undertaken in any one year, but that a composite climatological picture of the Antarctic sea ice zone be built up over a number of years. The surveys can be achieved by standardised ship-based observations along a series of systematic transects, building on ongoing national efforts (including re-supply voyages) and co-operating with other programmes with survey requirements such as EASIZ and APIS.

Observations during the transects will include both underway measurements and on-site sampling. Underway measurements might include:

On-site sampling, proposed at least every half-degree of latitude along the transects, of

Sampling required for components of the EASIZ programme should be undertaken at the same time, viz:

A fundamental requirement of EASIZ is to devise means of measuring spatial (and temporal) variability of the biological community at the same scales as variability in the physical environment of the sea ice. Studies at some of these scales are well-established, but there is a dearth of information (from the sub-millimetre scale within the ice to the hundreds of kilometres of regional variation), on spatial variability which would allow the linking of different ecosystem components into a coherent structure.

A minimum requirement is to define a sea ice climatology for each of autumn, winter, spring and summer seasons along transects perpendicular to the Antarctic coast and spaced at intervals of about 15-30° of longitude of the time-varying state of the main variables. These include:

ii. The dominant processes of ice formation and modification determining ice-thickness, composition and distribution

iii. The role of coastal polynyas

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iv. The processes at the ice-edge

Specific process studies will be necessary to tackle these problems. In some cases these may be relatively simple and short and might be undertaken as components of the transect programme. In other cases specific multi-disciplinary, and possibly multi-ship, studies will be required.

For example, a small number of selected coastal polynyas should be studied at different seasons in multi-disciplinary studies including elements of meteorology, oceanography, glaciology, marine biology, and remote sensing. A pilot polynya project in one of the Wilkes Land coastal polynyas (ACoPS) has been suggested as a bi-lateral US/Australian effort for late winter 1998. This is being planned as a two-ship operation, with the vessels operating in the polynya for over-lapping periods, thus providing a short period when both are available for components requiring measurements at multiple sites, and also extending the total experimental period from late winter with high ice production (investigation of polynya maintenance, water mass modification, etc.) through to the spring plankton bloom. This pilot study could serve as a precursor to wider circumpolar studies of Antarctic polynyas and sea ice characteristics. Because of the link between coastal polynyas and marine biology, a polynya programme would be complementary to EASIZ.

New research tools that could be used in process studies include Automatic Underwater Vehicles (AUVs) that could be launched under the ice to measure ice thickness; passive and active microwave satellites, synthetic aperture radar (SAR), and the Sea Viewing Wide-Field-of-View Sensor satellite (SeaWIFS).

Ice edge interactions can be addressed by process studies such as a programme of transects perpendicular to the ice edge extending ~100km into the open ocean and penetrating a similar distance into the sea ice. These transects would be repeated several times over the period of ice retreat and during the development of the spring "bloom" to document ice decay, albedo changes, and possible seeding by sea-ice algae.

Within the pack, the ice thickness, radiation budget, melting rate, presence of sea-ice algae, trace element abundances and their transfer to the underlying ocean are all important, and should be measured to support the joint objectives of ASPECT and EASIZ. Coring and sampling of the bottom of the ice, and underway measurements of water column nutrients, fluorescence, pCO2, etc. are also required.

In the open ocean, water column stratification, trace and major nutrient availability, light availability, phytoplankton abundance and productivity, and particle export from the euphotic zone are among the desirable measurements. While most of the activity is likely to be within the top 200 metres, deeper casts to ~1000m are important to look at source strengths for vertical mixing of warmer waters, trace metals and nutrients; to provide baseline values for fluorescence, dissolved organic carbon, suspended particles; and to examine the nature and rate of mesopelagic remineralization via particle C/N/P ratios and dissolved oxygen measurements. Free drifting sediment traps are desirable. It is important to extend the study well out into the open ocean, as increased spring activity can also occur there, so that the ice edge effect can be placed in the context of its surroundings.

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8. Other Considerations

Historical data

Historical data, in the form of ice charts and analogue or narrative reports on ice conditions, exist in the archives of a number of National Programmes. For example the Russian programme has archived data (in hard copy form) of ice observations made from the scientific ships during Antarctic cruises since 1956. ASPECT is investigating the feasibility of analysing and translating such data into a quantitative data base to further contribute to a climatology of the Antarctic Sea Ice Zone. This would permit extension of the most recent (since about 1988) quantitative ship-based ice observations back in time and over a wider region. It may be possible to generate ice thickness distribution information for the period October-November over about 70% of the sea ice zone. This is a sizeable first step in the ASPECT goal to obtain a sea ice climatology, without the necessity of new cruises.

Remote sensing

Remotely sensed data will continue to be a principal tool of sea ice zone research. However there remain uncertainties in the interpretation of even such basic data as that from the SSM/I passive microwave sensors. ASPECT transects offer the opportunity to obtain systematic ground-truth data to improve current passive microwave algorithms, and for the interpretation of the new generation of active radar sounders.

The new generation of radar satellites, such as ERS series and RADARSAT, provide a capability of high resolution imaging regardless of cloud or light conditions. Presently however, no processing capability exists which can perform routine processing of Antarctic radar data to provide geophysical sea ice products. The development of an Antarctic Radarsat Geophysical Processing System would support ASPECT objectives.

Modelling

An important function of ASPECT is to provide modellers with both forcing data (data to initialise the model) and validation data (independent data to verify the model) from a region where there are presently few such data. The physical climate modelling of Antarctic sea ice, and to some extent of ice-ocean interaction, is presently within the purview of the Sea Ice/Ocean Modelling Panel of ACSYS. A particular emphasis of the ACSYS SIOM Panel has been model development suitable for incorporation into interactive global numerical circulation studies, an activity clearly of interest to CLIVAR. ACSYS will continue its involvement in Antarctic sea ice issues, and ASPECT will work though ACSYS and CLIVAR to ensure the essential global integration of Antarctic regional data. ASPECT will also provide the process information necessary to improve sea ice parameterization schemes in coupled climate models.

Both SO-JGOFS and SO-GLOBEC include modelling components. One aim of SO-JGOFS is to model the carbon cycle, and this includes modelling of the impact of sea ice on the development of phytoplankton. JGOFS is especially concerned with developing regional and large-scale models, and would welcome development of models that include sea ice.

Data

ASPECT, in consort with the SCAR Global Change Office, will establish and maintain a sea ice climatology data set based on contributed shipboard observations (in standard format). Other data management policy issues (e.g. centralised or distributed systems) will require further consideration as part of the implementation plan. It will be important to identify any needs for data exchange with other international programmes and problems with restricted access to data.

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9. Management

ASPECT will be managed by a Scientific Steering Group (SSG), composed of scientists working in relevant fields. It is essential that a representative of the EASIZ SSG is one of the members of the ASPECT Group, and vice versa. The SSG will be responsible for developing an ASPECT implementation plan, continually refining and updating the ASPECT science plan, and promoting and co-ordinating ASPECT activities. Much of the work of the SSG will be done by e-mail, but it will be necessary for the SSG to meet once a year. The SSG will maintain close links with, and representation where appropriate on, other relevant international programmes. Workshops with broad international representation should be held when necessary to plan multi-national projects, and to review results and progress.

Close contact should be maintained with the Council of Managers of National Antarctic Programmes (COMNAP) to co-ordinate logistic support requirements.

One member of the ASPECT SSG should be a member of GLOCHANT itself. The SCAR Global Change Office should be responsible for the day-to-day operation of ASPECT and for tasks such as Newsletter production, meeting organisation, and possibly data base management.

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Appendix A

Contributors to the ASPECT Science Plan

Professor S F Ackley
USA CRREL RG
72 Lyme Road
Hanover NH 03755-1290
USA

u2rs9sfa@hanover-crrel.army.mil

Dr I F Allison
Antarctic CRC
University of Tasmania
GPO Box 252-80
Hobart, 7001
Australia

i.allison@antcrc.utas.edu.au

Professor A C Clarke
British Antarctic Survey
High Cross
Madingley Road
Cambridge CB3 OET
United Kingdom

a.clarke@bas.ac.uk

Dr G Dieckmann
Alfred-Wegener-Institute
Postfach 120161
D-27515 Bremerhaven
Germany

gdieckmann@awi-bremerhaven.de

 

Professor A Foldvik
Institutt Universitet i Bergen
Allegaten 70
N-5000 Bergen
Norway

arne.foldvik@uib.nogeofysisk

Professor M Fukuchi
National Institute of Polar Research
9-10 Kaga 1-Chome
Itabashi-Ku
Tokyo 173
Japan

fukuchi@decst.nipr.ac.jp

Dr H Marchant
Australian Antarctic Division
Channel Highway
Kingston 7050
Australia

harvey_mar@antdiv.gov.au

Dr D G M Miller
Sea Fisheries Research Institute
Private Bag X2
Rogge Bay 80112
Cape Town
South Africa

dmiller@sfri.sfri.ac.za

Dr J H Priddle
British Antarctic Survey
High Cross
Madingley Road
Cambridge CB3 0ET
United Kingdom

j.priddle@bas.ac.uk

Professor P Treguer
Universite de Bretagne Occidentale
Institut d'Etudes Marines
Faculte des Sciences
6 avenue Le Gorgeu
29285 Brest Cedex
France

treguer@univ-brest.fr

Dr P Wadhams
Scott Polar Research Institute
University of Cambridge
Lensfield Road
Cambridge CB2 1ER
United Kingdom

pw11@cam.ac.uk

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Appendix B

Proposed 1997-98 milestones for ASPECT

INSERT APP B

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Appendix C

Shipboard ice observation protocols

Using simple, but quantified observations from vessels traversing the sea ice zone, it is possible to derive information on the ice and snow thickness distributions, and their regional and seasonal variability. Underway ship-board observations are able to provide useful information, particularly of the relatively undeformed ice between ridges, because much of the pack area in the Antarctic is composed of floes 0.7 m or less in thickness. Such observations obviously do not compare with instrumentally derived records for precision, but data can be collected over large areas and, provided the data base is large enough, have been show to provide statistically meaningful thickness distributions. The observations are far less reliable in ridged or heavily deformed ice, and proper account must be made for the bias that arises from the vessel's route, particularly for non ice-breaking ships.

The method used for several years by a number of nations, and forming the basis of the ASPECT ice thickness climatology, makes use of three different types of observations. Each type of observation has different strengths and weaknesses, but they can be combined to provide a best-estimate distribution.

A In the first observation, estimates are made of the ice and snow cover thicknesses of individual floes tipped up by the passage of the ship. These measurements are made once per hour on 25 randomly selected floes. A 40 cm diameter buoy, hung on a rope over the side of the ship and approximately 1 m above the ice, provides a scale for the thickness estimates. The data are edited to exclude any observation within 6 nautical miles of the previous observation, to avoid biasing caused by slow progress in heavy ice conditions.

Individual ship-based estimates from overturned floes are accurate to about 0.1 m in thickness, but depend on floes turning sufficiently for their keels become clearly visible. However, the sample may be biased because a high percentage of ridged floes (which represent the thickest ice in the pack) tend to break into their component parts when hit by the ship and are not measured; and in low concentration pack near the ice edge, floes tend to be pushed aside rather than turning over, making such observations impossible.

B For the second observation, an observer, usually on the bridge of the vessel, visually estimates the thickness, concentration, and snow cover of the three dominant ice thickness categories (based on the WMO classification) in the vicinity (~0.5 nautical mile) of the vessel. Thickness estimates are supported by the observations on over-turned floes, as above. The data are entered on log sheets using a code for different classifications

Ice concentration: The fractional ice concentration in each of the 3 dominant ice categories.

Ice type: For each category: based on the WMO classifications, but also including three different new ice types and brash.

Ice and snow thickness: For most thin ice categories ice thickness is a redundant check of ice type estimates.

Floe size: Classified into approximately logarithmic spaced bins.

Topography: Generally only the thickness of level ice is estimated. But the extent (area and sail height) of ridging is also estimated to derive an approximation of total ice mass using a simple model which assumes that the overall pack is in hydrostatic balance, and that ridge sails have a triangular section. The inadequacies of this model are acknowledged, but there is clearly a need for such a correction if realistic average ice thicknesses over large areas of the pack are to be determined from the ship-based observations. The topography code also includes a descriptor for the state of consolidation and weathering of ridges.

Snow Type: A descriptor, used primarily for estimating area-averaged surface albedo.

Open Water: A descriptor. Again the data are edited to exclude any observation within 6 nautical miles of the previous one.

Individually these visual estimates provide the least accurate ice and snow thickness, but they do provide a reasonable estimate of the areal coverage of different ice thickness categories and of their topography. They give a good estimate of the thin ice end of the distribution (since the thickness of new snow-free ice is distinguishable by its albedo) and of the open water fraction within the pack. They also provide (albeit very crudely) an estimate of ridged ice.

C From some vessels direct thickness measurement can be made in situ by drilling, preferably along transects across floes. Such observations are necessarily limited in number, and do not represent very thin or unconsolidated ice which is dangerous to access; nor do they represent very thick, heavily ridged floes which the ship is unable to penetrate (e.g. multi-year ice or very heavy first year ice), and which would be extremely time consuming to sample.

Observational bias is a concern when making sea ice observations from a ship because of the inherent tendency to avoid heavy ice and follow easily navigable routes. On cruises entirely dedicated to sea ice research, the ship's course can be chosen to minimise this bias, but some areas of extreme ridging or multi-year ice may remain unsampled. In practice however the three different methods have been shown to give surprisingly similar thickness distributions over a range of thicknesses from about 0.3 m to 1.2 m, with method B providing a reasonable information on the thinner ice.

These methods, and the results derived from them, are detailed further in Allison and Worby [1994], Worby and Jeffries [in press] and Worby et al., [in press]. The ASPECT SSG will produce and distribute an observational manual, logging sheets, and software for checking and analysing the data.

 

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Appendix D

Geochemical and trace metal studies of sea ice in ASPECT.
(Contributed by G. Dieckmann)

1. Introduction

ASPECT provides an opportunity also to address some of questions asked about the polar oceans, by palaeo-oceanographers, biological oceanographers and modellers. As far as the sea ice zone is concerned, these problems are not covered by other programmes. They will fit well into a multidisciplinary sea ice project, represent a rather novel approach to sea ice research, and could be integrated into ASPECT standard analyses of sea ice cores.

2. Geochemistry of Sea Ice

Question:

Do changes (physical, biological, chemical) in the geochemistry of sea ice affect the isotope fractionation of sea ice biota and consequently the isotope ratios of sequestered particulate matter. i.e. are they likely to be reflected in sediment cores?

Rationale:

Biological removal of CO2 from sea ice (interstitial brine) may have important implications for the 13C/12C isotopic composition of particulate matter derived from sea ice. Photosynthesis limited by CO2 diffusion results in reduced enzymatic 13C discrimination, elevating the ?13C of the organic fraction (?13Corg). Uptake of HCO3, supplementing CO2 diffusion into cells would similarly increase ?13Corg. It is plausible that CO2 (aq) depletion during periods of high primary productivity enhances ice algal ?13Corg to values significantly above those measured in surface water phytoplankton. The ?13Corg in sedimentary records has been proposed as a proxy for past sea surface CO2 (aq) concentrations and there is evidence that sea ice-derived organic carbon contributes significantly to sedimentary Corg. Consequently, the alteration of the sedimentary ?13Corg via input of 13C-enriched organic carbon from sea ice should be considered when reconstructing past sea surface CO2 (aq) concentrations from ?13Corg data in seasonally ice-covered regions of the Polar Oceans.

Neogloboquadrina pachyderma (Ehrenberg, 1861) is the only true subantarctic pelagic foraminifera. It has been found in new ice, congelation ice and the underlying water column of the Weddell Sea. N. pachyderma is incorporated into the ice in large numbers at the time of its formation. An investigation in the Weddell Sea revealed the average number of foraminifera per litre of ice to be 87 with numbers ranging between 0 and 1075. Sea ice there contained 70 times more foraminifera per unit volume than the underlying water column and on an aerial basis the sea ice cover has approximately the same number as 60 m of underlying water column. The foraminifera are usually incorporated into the ice when it is being formed dynamically and are thus subsequently associated mainly with granular ice. Many foraminifera are able to survive and grow in the ice where algal biomass in winter is high compared to the water column, perhaps indicating an overwintering strategy. These observations may have implications for palaeo-oceanographers. N. pachyderma abundance and chemistry have long been used as tools for monitoring polar surface-ocean changes, and for correlating these changes to fluctuations in atmospheric and thermohaline circulation. In polar regions N. pachyderma comprises more than 90% of the marine surface sediment assemblage. Thus this species provides an important ecological and geochemical proxy of past polar ocean temperature, salinity and nutrient conditions.

Gradients in the rate of evaporation and precipitation with latitude result in an approximately linear salinity-?18O relationship (cf. multiple stage distillation). In higher latitudes, linear salinity-?18O relationship is governed primarily by a two component mixing process of glacial meltwaters from the high latitudes with mean ocean water. Therefore, ?18O compositions of sea surface waters can be estimated from salinity. In high latitude surface waters, however, sea-ice formation and meltwater input can locally result in an increase in salinity without an observable change of the water isotopic composition and thus decouple the S-?18O relationship. Consequently, for areas influenced by sea-ice formation or meltwater, independent salinity-?18O relationships must be generated because modern calibration studies show discrepancies between isotopically derived and ecologically derived sea surface temperature estimates.

Objective:

To determine the impact of geochemical changes within sea ice on the isotope relationships of the sea ice biota. Consequences for the sedimentary record past and present?

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3. Trace Metals (Fe, Mn) in Sea Ice

The hypothesis that Antarctic phytoplankton suffers from iron deficiency, thus preventing blooming and the exhaustion of the high concentrations of macronutrients, has not been entirely resolved. The role of sea ice, in particular is little understood. Evidence of high iron concentrations in sea ice indicates that iron may accumulate there and become available upon melting thus possibly contributing to the favourable conditions which lead to the often described localized ice edge blooms. The verification of the role of sea ice, other than its effect of stabilizing the surface water layer, is thus an important goal.

Objective:

To investigate whether sea acts as an accumulator of trace metals and weather elevated concentrations in melting sea ice (e.g. Fe) account for localized enhanced primary productivity in surface waters?

Appendix E

List of Acronyms and abbreviations

ACDP Acoustic Doppler current profiler
ACSYS Arctic Climate System Study (WCRP)
ACSYS-SIOM ACSYS&endash; Sea Ice/Ocean Modelling Panel
AnITRP Antarctic Ice Thickness Research Project (WCRP)
ANZFLUX Antarctic Zone Flux experiment
APIS Antarctic Pack-Ice Seals programme (SCAR)
ASPECT Antarctic Sea-Ice Processes, Ecosystems and Climate (SCAR-GLOCHANT)
AUV Automatic Underwater Vehicle
BIOMASS Biological Investigations of Marine Antarctic Systems and Stocks (SCAR)
BIOTAS Biological Investigations of Terrestrial Antarctic Systems
CCCO SCOR Committee on Climate Change and the Oceans
CLIVAR Climate Variability and Prediction Research (WCRP)
COMNAP Council of Managers of National Antarctic Programmes
EASIZ Ecology of the Antarctic Sea-Ice Zone (SCAR-GoSSOE)
CTD Conductivity Temperature Depth (probe)
DecCen Decadal to Centennial climate variability and predictability (CLIVAR)
ECMWF European Centre for Medium Range Weather Forecasts
ERS Earth Resources Satellite, European Space Agency
GCOS Global Climate Observing System
GLOBEC Global Ocean Ecosystems Dynamics Research (IGBP)
GOOS Global Ocean Observing System
GoSSOE Group of Specialists on Southern Ocean Ecology (SCAR)
HNLC High nutrient-low chlorophyll
HSSW High Salinity Shelf Water
IAnZone International Coordination of Oceanographic Research within the Antarctic Zone
ICSU International Council of Scientific Unions
IGBP International Geosphere-Biosphere Programme
IOC International Oceanographic Commission
IPAB International Programme for Antarctic Buoys (WCRP)
IPCC Intergovernmental Panel on Climate Change
ISW Ice Shelf Water
JGOFS Joint Global Ocean Flux Study (SCOR and IGBP)
JSC Joint Scientific Committee for WCRP
MIZ Marginal Ice Zone
ROV Remote Observational Vehicle
SCAR Scientific Committee on Antarctic Research
SSG Scientific Steering Group
SSM/I Special Sensor Microwave Imager, DMSP Satellite Program
SCOR Scientific Committee on Oceanic Research
SO-JGOFS Southern Ocean - JGOFS
TOGA Tropical Ocean and Global Atmosphere Experiment (WCRP)
UNEP United Nations Environment Programme
UV Ultraviolet Radiation
WCRP World Climate Research Programme
WG Working Group
WMO World Meteorological Organization
WMO-CAS WMO–Commission on Atmospheric Sciences
WOCE World Ocean Circulation Experiment (WCRP)
WSBW Weddell Sea Bottom Water