|
|
The Future of Basic Research in the Ocean Sciences
The Future of Physical Oceanography
The Future of Chemical Oceanography
The Future of Marine Geology and Geophysics
The Future of Biological Oceanography
The Future of Physical Oceanography
Climate
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.
Cross-shelf transports
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. |