Integrated Marine Biogeochemistry and Ecosystem Research (IMBER)

End-to-End Food Webs
There is increasing recognition that analyses of biogeochemical cycles, climate impacts and the effects of exploitation in ocean ecosystems requires the development of integrated views of food web operation. With this focus on integration, a new term has appeared – analysing the end-to-end operation of food-webs – encompassing the concept of linking food web operation from microbial systems (that dominate the carbon flows in marine systems) through to the highest trophic level species that may also be subject to exploitation.  Attempts to define the end-to-end food web — or e2e for short — have led to broad definitions that are equivalent to the widely used definition of an ecosystem.  

The term e2e has brought attention to the complexity of the interactions involved in food-webs. Dealing with that complexity was recognised early in the workshop as probably the central challenge we face. The importance of and therefore the need to consider the emergent properties of food webs generated through complex interactions at a wide range of scales. The meeting also demonstrated that many of the major issues faced in e2e analyses are already being tackled by groups working on a range of regional systems. The major scientific task is now one of integration, building on previous and ongoing regional analyses and detailed process studies. Comparative studies between regional systems such as the Arctic-Antarctic and Benguela-Humboldt are also emerging and global comparisons of ecosystem structure and function are being developed. At the same time, generic models (e.g. based on size or simplified functional group representations) are being applied globally or as standard model frameworks parameterised for different regions.  The challenge for IMBER, as GLOBEC comes to an end, is to develop the interdisciplinary integration capacity, linking scientists with interest in biogeochemistry and food web operation, while accounting for the complexity of oceanic ecosystems.   This emphasis on integration requires both a major shift in thinking and a stronger focus on the perennial issues of ensuring iterative links between modelling and observation programmes and maintaining multidisciplinary teams.  Developing a range of analysis and modelling approaches will be crucial, with a requirement for comparison based on both general ecosystem properties (e.g. size structure and patterns of energy flow) as well as specific metrics (e.g. productivity, harvesting yield or stoichiometric balance).

The Mesopelagic Zone
The mesopelagic zone, between depths of about 100 and 1000 m,  is a zone of significant decomposition, recycling, and repackaging of particulate and dissolved organic matter.  The interplay between biological and geochemical processes in this zone has significant effects on the magnitude of the biological pump, which regulates in part atmospheric carbon dioxide and hence can impact climate. While important processes regulating organic matter transformations and remineralization in the mesopelagic zone can be tightly coupled with the euphotic zone, the time and space scales of these processes are different in the mesopelagic zone, which is critical to predicting the ability of the biological pump to sequester carbon in the deep ocean.

The aim of the workshop was to identify the current state of our knowledge about mesopelagic food-web processes, particle flux and dynamics, and biogeochemical cycling, and to identify gaps in our knowledge.  The workshop addressed the following topics: particulate and dissolved organic matter (POM and DOM) distribution, characterization, and flux; planktonic food web controls on vertical transport, cycling, and composition of POM and DOM; linking microbial and metazoan diversity to function; ecological and biogeochemical approaches to estimating remineralization rates; models; methods and new technologies; regional comparisons in food-web structure and biogeochemistry; and potential responses of the mesopelagic zone to environmental change. The workshop participants recommended that future research programmes on the mesopelagic zone should integrate across disciplines (chemistry, microbiology, ecology, physics), and throughout water column (i.e. link with surface processes).  The location of future studies may include time-series sites, places of contrast, sites with strong gradients and where effects of global change are large.  Spatial and temporal variability must be considered.  It was also recommended that species or functional groups should be the focus. In addition to measuring stocks, mechanisms need to be understood to contribute to mechanistic models. Characterization of physical processes (e.g., lateral advection, deep- and mode-water formation) is important for constraining mesopelagic carbon and nutrient budgets. Technological advances to help address future challenges in the mesopelagic zone include:  pressure samplers for measuring in situ respiration, neutrally buoyant sediment trap designs, remotely operated vehicles with sampling capabilities, automated underwater vehicles and floats for increased spatial coverage, and underwater observatories for long-term monitoring.

The Bathypelagic Zone
The bathypelagic zone is one of the great unexplored realms of the global ocean.  The biological pump connects surface processes to the deepest ocean layers, where biological processes occur at very low rates relative to the upper ocean. With deep ocean residence times at centennial to millennial scales in time and global scales in space, the system is only slowly ventilated and circulated.  Biogeochemical signals in the deep ocean are integrative of processes occurring over very long periods. Biological processes in the deepest ocean layers are intimately tied to particle dynamics and microbial food webs, much of which are still only poorly characterized.

The central aim of the workshop was to gather the expertise required to identify what is known about this system, and to identify and pursue outstanding uncertainties. The cross section of disciplines represented included biogeochemistry, organic geochemistry, microbial dynamics, trace element and isotope geochemistry, genomics, particle flux and dynamics, and modeling. Presentations on the biogeochemistry of organic matter covered composition, structure, distribution, fluxes, reactivity, etc., while those on microbial dynamics considered the turnover of the organic matter, processes controlling microbial abundance, as well as deep autotrophic production. Three papers are under development to synthesise our understanding of, (i) deep sea microbial dynamics, (ii) the biogeochemistry of organic matter and (iii) deep ocean metabolism, focusing on the relative roles of autotrophic and heterotrophic processes. The first two syntheses will consider the same deep ocean system, but from the unique perspectives of biogeochemistry and microbes.