The Future of Basic Research in the Ocean Sciences
THE FUTURE OF PHYSICAL OCEANOGRAPHY
The economic benefits of understanding the role of the ocean in the climate system are enormous. And accumulating evidence of man-made climate change has brought these issues to the attention of the public. These concerns coincide with recent successes in long-term weather forecasting associated with El Niño, and with advances which enable detailed measurement of climate
variables. (For instance, in the last ten years, the errors in surface heat fluxes obtained from moorings have been reduced by a factor of forty so that the present uncertainty is 5 Watts per square meter.) These factors imply that climate studies will be a significant path for future research in oceanography.
The development of long-term forecasting skill raises challenging scientific problems. These include: understanding and quantifying turbulent mixing, convection, water-mass formation and destruction; the thermohaline circulation and its coupling to the wind-driven circulation; the generation, maintenance, and destruction of climatic anomalies; climatic oscillations and the extratropical coupling of the ocean and atmosphere on seasonal, decadal and interdecadal timescales; the physics of exchange processes between the ocean and the atmosphere. All these problems are of fundamental scientific and practical importance.
Will there be substantial progress on these issues during the next decade? Many physical oceanographers have already begun an enthusiastic frontal assault under the banner of CLIVAR. It is likely that the economic issues which surround global change and climate prediction will motivate continued financial support from society. If people and money are what counts, then we have every reason to be optimistic.
The problem of global climate prediction is the most difficult that our field has encountered. Unlike equatorial oceanography and El Niño, there is not going to be a theory based on linear waveguide dynamics which decisively identifies timescales and
cohesively binds oceanography and meteorology. Further, the decadal timescale of extratropical dynamics means that scientists see only a few realizations of the system within their own lifetime. This is bad for morale, but even worse, we cannot wait to gather enough data to reliably verify the different predictions of climate models. Could meteorologists have developed daily weather prediction models if these scientists saw only three or four independent realizations of the system in a lifetime? The only way around this statistical problem is to expand our data base and frame hypotheses about past climate change and ocean circulation using paleo-oceanographic studies. An important challenge is to test the dynamical consistency of these hypotheses.
The hydrologic cycle
An emerging theme, which is strongly related to climate, is the ocean's role in the hydrologic cycle. New satellite technologies promise to measure sea surface salinity and precipitation. These, coupled with improvements in the computation of evaporation via
indirect methods, will improve our picture of the freshwater flux in the oceans. The freshwater sphere is an encompassing topic that spans oceanography, the atmospheric sciences, polar ice dynamics and hydrology. Our knowledge of the oceanic freshwater source-sink distribution is far poorer than our knowledge of the source-sink distribution of heat. Yet salinity and temperature contend in their joint effect on the density of seawater and in their influence on the ocean circulation, and the climate system. Knowledge of freshwater input from continents, precipitation, and sea-ice is poor. Observational techniques addressing these issues (for example, the use of oxygen isotopes, and tritium/helium to diagnose freshwater sources) herald progress.
Coupled with improved estimates of the freshwater sources at the surface, will be an increased understanding of water-mass dynamics and transformations. We can look for advancement on such fundamental issues as the causes of the temperature-salinity relationship, thermocline maintenance and interhemispheric water-mass exchanges.
Observing the ocean
We will see explosive development of new observational tools, such as those used by the TOPEX/POSEIDON satellite mission which measured the topography of the sea surface to 3 cm accuracy at 7 km spacing for 5 years. Future developments in satellite oceanography promise more of the same at ever-increasing accuracy, coupled with the deployment of new satellite-borne instruments. Yet sea-truth is essential and we envisage in situ observations which will be made by an unprecedented class of autonomous instruments and probes. The ability to manipulate these tools in mid-mission is developing.
A national effort to support sustained high-quality global observations over decades is needed. Measurements of air-sea fluxes of heat, fresh water, and gases, of surface and sub-surface temperature, salinity and velocity, are all necessary to meet new scientific challenges and practical needs. Looking beyond the equatorial TOGA-TAO array, long-term subsurface measurements spanning the global ocean are required.
Given the rapid increase in Lagrangian measurements by drifting and profiling floats, and the parallel increase in geochemical tracer data, an intense approach to Lagrangian analysis of advection and diffusion is warranted; our existing base of theoretical tools and concepts is not worthy of the observations which we are about to receive.
Global and regional connections
Many emerging physical oceanographic issues concern connections between large-scale and small-scale motions; for example, the relation between small-scale turbulent mixing and the large-scale meridional overturning circulation. Analogous connections and interactions between scales are arising in issues of societal concern, often centered around the increasing recognition that many issues previously regarded as regional now require a global perspective. Anthropogenic pollutants have reached the open ocean and are known to be transported far from their sources. A better understanding is needed of small-scale processes and small-scale aqueous systems (estuaries, wetlands, coral reefs) and their impacts on global issues. For example, the growth of plankton populations, which affect carbon dioxide levels and thus may be important in global warming scenarios, is dependent on details of circulation at fronts, sea-ice and mixed-layer boundaries.
In most coastal regions, the strongest persistent gradients in properties (for example, salinity, temperature, nutrients or suspended materials) are found in the cross-shelf direction. This is because cross-shelf flow is often inhibited by topography and because
the coastal ocean is the contact zone between terrestrial influences, such as river runoffs, and oceanic influences characterized by nonlinear physical dynamics and oligotrophic biological conditions. Progress has certainly been made on some aspects of the flows that determine cross-shelf transports, especially those related to surface and bottom boundary layer processes. A good deal more has yet to be learned about exchanges that occur in the interior of the water column. The problem is difficult because it often appears that the processes which are relevant for the dominant alongshore flows do not apply to cross-shelf flows. For example, it is likely that instabilities and topographic influences may dominate the exchange process. The exchange itself needs to be understood if we are to address issues such as the control of biological productivity in the coastal ocean, or the removal of contaminants from the near-shore zone.
In addition to cross-shelf exchange processes themselves, there is the question of how the coastal ocean couples to its surroundings on both the landward and seaward sides. Estuarine processes are important for determining the quantity and quality of terrestrial materials that reach the open shelves. The oceanic setting, including eddies, filaments and boundary currents, in turn determines how effectively coastal influences can spread offshore, or how the oceanic reservoir will affect shelf conditions. Consequently, the study of the continental shelf demands consideration of both offshore and near-shore (estuarine and surf zone) dynamics.
Inland waters and environmental fluid dynamics
Our understanding of inland waters, such as estuaries, wetlands, tide flats, and lakes, will be aided the same observational and computational technologies which promise progress on the general circulation problem. This work will afford exciting opportunities for interdisciplinary research blending physical oceanography with biology, geochemistry and ecology. Examples are tidal flushing through the root system of a wetland, and the physical oceanography of coral reefs.
Lakes can be useful analogs of the ocean, with wind and thermally driven circulations, developing coastal fronts, and topographically steered currents. Lakes are important as model ecosystems which are simpler and more accessible than ocean ecosystems. Significant progress can be foreseen in the coming decades in limnology, helped by the tools and ideas developed for the ocean.
The expertise of the physical oceanography community should make possible substantial advances in the understanding of all these shallow systems. Because of the major roles played by turbulence and complex topography, these systems pose impressive and fascinating challenges to physical oceanography.
Turbulent mixing and unexplored scales
Past achievements in quantifying small-scale turbulent mixing in the main thermocline, coupled with exciting recent measurements in the deep ocean, suggest that a description and an understanding of the spatial distribution of turbulent mixing in the global ocean is achievable in the next decade. Unraveling the possible connections between the spatial and temporal distribution of mixing, the large-scale meridional overturning circulation, and climate variability are important aspects of this research.
Knowledge of the horizontal structure of the ocean on scales between the mesoscale (roughly 50 km) and the microscale (roughly less than 10 m) will be radically advanced and altered. The growing use of towed and autonomous vehicles, in combination with acoustic Doppler current profilers, will revolutionize our view of the ocean by exploring and mapping these almost unvisited scales throughout the global ocean. While this research is driven by interdisciplinary forces (biological processes and variability are active on these relatively small horizontal scales) it is also a new frontier for physical oceanography, and one in which even present technology enables ocean observers to obtain impressive data sets.
Numerical modeling as an integrative tool
Large-scale numerical models of the ocean, and of coupled ocean-atmosphere, are becoming the centerpiece of our science. This is not to say that numerical models dominate our science, but rather that results of theory and observational data are often cast into the form of numerical models. This happens either through data-assimilation or through process-model explorations of theoretical ideas. Yet the fundamental difficulty of computer modeling remains: the ocean has, in its balanced circulation, energy-containing eddies of such small scale (less than 100 km) that explicit resolution of these dominant elements is marginally possible. Compounding this difficulty are the unbalanced, three dimensional turbulent motions which are known to be important in select areas, such as the sites of open ocean convection.
We now have a well-acknowledged list of subregions of general circulation models that are greatly in need of improvement. These include: deep convection; boundary currents and benthic boundary layers; the representation of the dynamics and thermohaline variability of the upper mixed layer; fluxes across the air-sea interface; diapycnal mixing; topographic effects. Progress in all of these areas is likely as our capacity for modeling smaller scale features increases, and as physically-based parameterizations are developed.
Taken from a Report of the APROPOS Workshop, Monterey, California, December 15-17, 1997.
THE FUTURE OF CHEMICAL OCEANOGRAPHY
The medley of questions to which ocean chemistry can contribute calls for some synthesis. We attempted to balance a desire to identify exciting problems, apparent at this time, with the need to provide umbrellas likely to contain the unexpected discoveries of coming decades. The results of our deliberations can be grouped into eight themes.
1. Major and minor plant nutrients - how they are transported to the euphotic zone, affect community structure, and how these processes are influenced by natural and anthropogenic changes. The ocean's ability to support life and the role of life in maintaining the chemical constitution of the ocean are strongly affected by the transport and redistribution of nutrients. Despite exciting progress over many decades, it is clear that unknown processes are controlling the patterns of these mutual controls. Rapid progress will show how subtleties in nutrient dynamics affect end states of great importance, such as fisheries and harmful algal blooms.
2. Land-sea exchange at the ocean margins. Margins influence biogeochemical cycles to an extent much more than their areal extent might imply, while being especially susceptible to anthropogenic influence. Processes that occur disproportionately in margin environments, such as organic matter burial, mineral formation, and denitrification affect the oceanic balances of many elements. Unravelling the highly variable complex of chemical, physical, geological, and biological linkages in margins will provide needed context for human colonization of the coastline.
3. Organic matter assemblies, at molecular to supra-molecular scales, their reactivity and interactions with other materials. Organic matter must be charcterized at scales including, but also greater than, its molecular constituents, to enable understanding its preservation, transport and interactions with inorganic materials. The "micro-architecture" with which constituents are assembled controls reactivity, with important implications for primary and secondary production, photochemical processes, mineral formation and trace metal dynamics.
4. Adjective chemical transport through the ocean ridge system (ridges and flanks), ocean margin sediments, and coastal aquifers. Fluid flow through these environments appears to have greater importance than previously appreciated, and may strongly influence many oceanic chemical cycles. Greater understanding of the magnitude and variability of these advective transports will improve budgeting of chemicals in the oceans and provide explanations for many regional processes affected by the flow, such as mineral formation and nutrient inputs.
5. Forecasting and characterization of anthropogenic changes in ocean chemistry: consequences on local and global scales. Climatic as well as chemical changes to the oceans will affect many different biogeochemical cycles. Assessing natural variability will be critical to determination of anthropogenic effects. Linkage to other oceanographic variables, such as biological and physical processes, will enable better assessment of the role of the oceans in global environmental change.
6. Air-sea exchange rates of gases which directly influence global ecosystems. CO2, other greenhouse gases, halocarbons that affect stratospheric ozone, and sulfur gases that create sulfate aerosol all have important source/sink terms in the oceans. More accurate determination of air-sea fluxes of these gases, of both natural and anthropogenic origin, are critical to assess processes affected by these gases.
7. Relationships among photosynthesis, internal cycling and material export from the upper water column. Most production and remineralization of organic matter occurs in the shallow euphotic zone. Our understanding of processes such as CO2 and N2 sequestration from the atmosphere and pelagic-benthic coupling are thus critically dependent on improving our understanding of euphotic zone recycling.
8. Controls on the accumulation of sedimentary phases and their chemical and isotopic compositions. Further development of paleoenvironmental indicators will enable better understanding of past climatic and carbon cycle variations. Earth historical records provide an invaluable guide to natural variability of the chemistry/climate system, including natural "experiments" in which the whole system has responded to a perturbation.
Taken from the FOCUS: Future of Ocean Chemistry in the U.S. Workshop Report, January 6-9, 1998, Charleston, South Carolina.
THE FUTURE OF MARINE GEOLOGY AND GEOPHYSICS
The societal imperative of making rapid progess in scientific understanding of complicated, non-linear systems. Many of the research topics central to marine geology and geophysics address issues of societal concern, such as changing climate, coastal pollution and erosion, and Earthquake hazards. In some cases, there has been pressure to implement solutions to these problems without a complete understanding of these complicated systems. Even worse, some of these systems are now demonstarted to be highly non-linear, such that input at one frequency can produce a response at very different frequencies. Human forcing may in fact lead to very unpredictable and undesirable consequences. An important area of future research will be in characterizing and modeling systems in which the input forcing function is known or can be measured, and the system response can be inferred from the geologic record (geologic time scales) or from direct observation (human time scales).
The central role of focused fluids in producing volcanic, tectonic, and thermal modification of the planet. Geologic modification of Earth is controlled by its fluids, whether it be water in fault zones, magma erupting on a midocean ridge or island arc, plumes rising from the deep Earth, hydrothermal circulation in ocean crust and sediments, or methane deposits on continental margins. These fluids determine the locus of geologic activity and are the agents for geochemical cycling between the solid Earth and the hydrosphere and atmosphere. Quantitative understanding of the physical and chemical processes which lead to concentrations and focusing of these fluids through the lithosphere, igneous crust, and sediments until their eventual expulsion into the water column or atmosphere, however, is in its infancy. We need to better understand the physical properties of the medium through which the fluids flow, the stresses acting on the systems, and their chemical, mechanical, and thermal interaction with their host rock.
The recognition that the present-day conditions may be unrepresentative of the whole of geologic history. A glance at the recent past shows a climate system principally forced by the eccentricity of Earth's orbit. The present-day nearshore
sequences reflect the flooding of the continental shelves following the melting of large continental ice sheets, and today's seafloor volcanic activity is completely dominated by steady-state formation of new crust at the midocean ridge. However, with the benefit of the geologic record, we see that just one million years ago variations in Earth's tilt were more important than eccentricity in modulating climate. During the prior glacial maxima, sediments bypassed many continental margins through a series of canyons. In the Cretaceous, plume-type volcanism was far more important than it is today in the mass and energy transfer between the deep Earth and the surface. While in some cases, the causes of the changes in the geologic record are easily identified (e.g., rising sea level), in other cases they are not. More emphasis in the future will be directed towards documenting the various different stable states for Earth's systems, discovering what events trigger evolution from one stable state to another, and identifying the linkages between the states of very different systems (e.g., climate and tectonics).
The importance of explicit incorporation of effects of and on the biosphere into marine geology and geophysics. Investigators in MG&G are extremely comfortable with introducing a fair amount of physical and chemical sophistication in their science. Many have their primary professional training in these allied physical sciences. The links to biology, in comparison, are
weaker and must be shored up to make progress on a number of fronts. Just as ocean chemistry cannot be understood using the principles of chemical equilibrium without taking into account biochemical cycling of nutrients, the solid Earth is modified by biologic activity from the scale of bacteria to humans. Submarine ecosystems harbor some of the most unusual and extreme
examples of life on Earth, and the implications of understanding how these systems have adapted to and how they modify their environments have implications for the origin of life itself.
The appreciation that we must move beyond steady-state models to study geologic events as they happen. The geologic record contains evidence of many catastrophic events: Earthquakes, landslides, volcanic eruptions, etc. Most of our models, however, smooth these events over time to create steady-state representations for what are really discontinuous processes such as erosion of headlands, creation of oceanic crust, and filling of flexural moats. Such steady-state models distort the true impact of these events on human timescales and are useless for any hazard mitigation. Given the current lack of understanding of the temporal and spatial pattern of most geologic events, we require the technology to install undersea observatories and event-detection systems to catch geologic events in action.
The limitations of present funding structures and technology for problems that span the shoreline. From the standpoint of many problems in geology and geophysics, the division between NSF-OCE and NSF-EAR is somewhat artificial. Although most of the midocean ridge system is under water, sometimes it is easiest to map it where it lies above sealevel (e.g., Iceland).
Fluids vented in the coastal margins may originate from continental aquifers. Ice core data from subaerial drilling can completement deep sea cores. Most efficient use of future resources will require close collaborations between land and marine geoscientists and their corresponding program officers. Even more of an impediment to working across the shoreline is lack of equipment to work near the shoreline, in shallow-water, high-energy environments. No amount of community interest in geologic processes at the continental margins will lead to progress unless the technology is available for imaging, sampling, and monitoring the near-shore region.
Taken from the FUMAGES: Future of Marine Geosciences Workshop Report, December 5-7, 1996, Ashland Hills, Oregon.
THE FUTURE OF BIOLOGICAL OCEANOGRAPHY
- Deep-sea hydrothermal vent communities were discovered that rely on geochemical energy rather than on products of photosynthesis. The new life forms and chemoautotrophic mutualisms at hydrothermal vents fundamentally altered biological classification schemes, known thermal and chemical limits of life, and ongoing searches for origins of life on earth as well as for new life forms on earth, below the earth's surface, and on other planets and moons.
- Humans have fundamentally affected marine ecosystems world-wide via fisheries, aquaculture, introductions of non-native species, modification or destruction of critical habitats, and additions of nutrients and chemical pollutants such as estrogen mimics. No part of the ocean remains unaffected by humans. Human population increases are affecting coastal oceans more profoundly and more rapidly than global climate change, producing urgent need to understand, predict, and mitigate these changes. Ocean ecology can no longer be understood adequately without recognizing these ecosystem-wide perturbations. Examples abound. Harvesting and nutrient input changed the Chesapeake Bay from a bivalve-rich system dominated by benthic production to a more turbid, bivalve-poor system dominated by water-column production -- including harmful algal blooms. Over-fishing caused replacement of coral reefs by seaweed beds throughout the entire island nation of Jamaica. Introduction of non-native bivalves to San Francisco Bay caused local extinctions and drastically altered ecosystem function of the entire bay. Nutrient addition, phytoplankton blooms, and transport of zooplankton in ballast water are implicated in widespread human deaths due to infectious diseases such as cholera that are facilitated and spread by these ecological perturbations.
- Biodiversity of every marine community is vastly greater than previously recognized, and both sampling statistics and molecular tools indicate that the large majority of marine species remains undescribed.
- Phytoplankton smaller than two micrometers and previously largely unknown to science were found to account for up one-half of oceanic productivity. Populations of these small phytoplankton and bacteria are regulated by suspension-feeding protists over vast expanses of the open sea -- making protists responsible for most nutrient regeneration. In these regions, blooms of larger diatoms, capable of exporting carbon and nutrients to deeper communities, can be limited by trace elements such as iron. Spectacular evidence of this limitation came from a large-scale experiment that added dissolved iron to the open ocean. Biotic responses to this addition suggest that production in large regions of the open ocean can be affected by global-scale weather patterns that deliver desert dust to oceanic systems.
- Using field experiments, ocean ecologists determined that complex, indirect effects among species can affect food-web interactions profoundly and can structure entire communities over large areas. These indirect effects can cause nonlinear responses of populations or communities to natural or anthropogenic change, resulting in ecosystems rapidly switching from one state to another with little warning of impending change. Indirect effects of humans are pervasive, now including an impact of the salmon enhancement program on the subarctic Pacific; similar indirect effects have been widespread since at least the time of fur trading and commercial whaling, but also can be inferred from middens dating back thousands of years.
- Recent investigations have documented pervasive influences of fluid motions on marine individuals, populations, communities, and ecosystems. They range from turbulence effects on encounter rates between male and female gametes or predator and prey to wide-scale dispersal and short-range settlement behaviors of larvae from deep-sea communities.
The grand challenge is to act with incomplete information but learn deliberately from each action. Given the pace and consequences of coastal ocean degradation, and the rates at which they are accelerating, the need for scientific focus on these issues is urgent. Resolving and understanding anthropogenic versus natural variability and change is one of the greatest problems facing ocean ecologists in the coming decades. Critical issues and promising opportunities include:
- Ocean ecologists must facilitate better stewardship of marine resources and ecosystems by: understanding and predicting which perturbations and food-web alterations will cause collapses of marine communities and the ecosystem services that they provide; predicting and mitigating the effects of harmful algal blooms; understanding and predicting interactions among global climate, marine geochemical processes and marine biota; and, understanding and mitigating outbreaks of microbial pathogens that can decimate important marine populations.
- Meeting these challenges will require better understanding and resolution of the causes and consequences of change on scales from hours to millennia. Recognition that the ocean is not in ecological steady state necessitates extensive time-series data from both remote sensing and in-water systems and better resolution of paleontological patterns. The former will improve dramatically due to emerging molecular, chemical, optical, and acoustical technologies. Prediction will require understanding of the basic ecological mechanisms most affecting marine community structure, while mitigation will require using this understanding to identify especially important interactions or species that can be used as biological fulcrums to leverage ecosystems back to desired states and functions. New methodologies poise ocean ecologists to fill these needs at levels from individual organisms to entire ecosystems. For individuals, adding interactions with chemical cues to effects of flow fields, evaluating chemosensory behaviors of pelagic and benthic organisms, and documenting the consequences for frequencies and outcomes of intra- and interspecific encounters promise significant advances. For ecosystems, the success of iron addition experiments in one ocean at one time encourages analogous experiments elsewhere, notably in nitrogen-poor central gyres where iron may limit nitrogen fixation and where current nitrogen budgets do not balance. As these examples demonstrate, the era of treating organisms as passive particles in the flow or of treating all phytoplankton as ecologically equivalent particles of chlorophyll is well past; mechanistic understanding is required to meet future scientific challenges and to address immediate, and increasing, threats to marine ecosystems.
- In the next two decades, new marine reserves will be started and entire estuaries manipulated within management strategies. It is critical to learn from these manipulations rather than simply to celebrate or bemoan ensuing changes. For marine species with open populations, reserves can help resolve the extent to which particular locations are sources or sinks of larval recruits and the efficacy of reserves having particular sizes. Answers will, in turn, allow design of better reserves. Opportunities must be seized to learn from both intentional and unintentional manipulations, especially those having negative impacts or large spatial scales and therefore limited replication. Compromises between replication and scale are inevitable, but loss of rigor associated with limited replication must be countered by careful attention to making mechanism-based predictions before manipulation and to learning from, and responding to, failures of these predictions.
- Understanding gained in the above efforts must be expeditiously applied to forecast biological change resulting from natural or anthropogenic intrusions, to implement objective measures of forecasting capability, to assess the extent to which undesirable change can be ameliorated, and to facilitate restoration of damaged communities and the ecosystem services that they provide.
Taken from the OEUVRE: Ocean Ecology: Understanding and Visions for Research Workshop Report, March 2-5, 1998, Keystone, Colorado.