Oceanography in the Next Decade Building New Partnerships (1992) / Chapter Skim
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3 Future Directions in Ocean Sciences
3 Future Directions in Ocean Sciences
Pages 47-120
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From page 47... ...
Ocean scientists have made a number of exciting discoveries in the past 30 years that have changed our view of Earth. The discovery of oceanic eddies has been important for an understanding of ocean circulation, propagation of sound in the ocean, fisheries productivity, and other ocean processes.
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From page 48... ...
New partnerships among oceanographers working in different disciplines shouIcl lead to new discoveries about the ocean's role in climate change, the function of micI-ocean ridges, and coastal ocean processes. Aciclitional oceanographic studies in the coming decade will focus on how ecosystems affect global cycles of important chemicals and, conversely, how changes in the global environment affect marine ecosystems.
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From page 49... ...
Primarily planned and executed with National Science Foundation iNSF) support, they focus the work of many scientists on global ocean research.
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From page 50... ...
. One example of the importance of basic research is a 1961 study that is now contributing to the debate about climate change the question of whether ocean circulation has two stable states.
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From page 51... ...
Examples are the growing importance of paTeoceanographic studies that involve geology, geophysics, chemistry, biology, and physical oceanography because of their climate implications. Likewise, the study of ridge crests cuts across geology and geophysics, biology and chemistry, and even slightly, physical oceanography.
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From page 52... ...
The goal of physical oceanography is to develop a quantitative understanding of the ocean's physical processes, including circulation, mixing, waves, and fluxes of energy, momentum, and chemical substances within the ocean and across its boundaries. Addressing such problems will require sustained large-scale observations of the world ocean
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From page 53... ...
Physical oceanographic theories use the equations of fluid dynamics, mollified to account for Earth's rotation and shape E.g., O'Brien, 19851. A goal of physical oceanography is to develop a quantitative understanding of the ocean circulation, including fluxes of energy, momentum, and chemical substances within the ocean and across its boundaries.
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From page 54... ...
Global Ocean Observing System Physical oceanographic observations and modeling are becoming global, but the resources required to deploy and sustain largescaTe observations of the worIc3 ocean are enormous. The exact configuration of a global ocean observing system is unknown, but it would probably include existing observations from satellites, moored open ocean sensors, volunteer observing ships, and the global sea-level network, as well as other observations that are
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From page 55... ...
Ocean Modeling The central focus of numerical modeling of the ocean has been, and continues to be, directed toward fluid dynamics, but the models have importance far beyond physical oceanography. For example, communities of organisms in the upper ocean live in a delicate balance, depending on the stability of the water column, its mixing rates, and its large-scare vertical and horizontal fluid movements.
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From page 56... ...
processes that must be incorporated more accurately into physical oceanographic models fin a manner consistent with observations) include the effects of complex bottom topography on deep-water masses, deep vertical and horizontal mixing, eddies and fronts in the upper ocean, the interaction of water flow and (Effusion of a variety of properties, boundary effects at the seafloor and surface, and the dynamics of shallow and deep boundary currents.
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From page 57... ...
With new observational techniques and a clear measurement strategy, significant progress can be expected in the coming decade in the study of ocean mixing. Surface Mixed Layer The primary production that supports the entire marine food web occurs in the upper sunlit portion of the ocean The euphoric zoner, where photosynthesis occurs.
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From page 58... ...
Deep-reaching convection occurs in the northern North Atlantic Ocean and around Antarctica. These water masses spread throughout the ocean and force deep ocean water, which has been made more buoyant by the downward diffusion of heat, to upwell slowly.
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From page 59... ...
The extreme seasonaTity and rapid spring melting of the Southern Ocean sea ice cover suggest that the heat carried into the surface layer by the upwelling of deep water is a key in understanding the Southern Ocean sea ice budget; the buildup of heat within the mixed layer under the winter ice cover induces melting even before solar radiation melts the ice from above. Ocean heat flux also limits sea ice thickness during the winter to less than 1 meter, in contrast to the 3-meter ice of the more stable Arctic Ocean.
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From page 60... ...
We need to monitor changes in ocean surface salinity globally. Satellite sensors monitor sea surface temperature and its anomalies, but monitoring sea surface salinity and its anomalies on a global scale is beyond present capabilities, as is determination of the temperature below the very surface.
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From page 61... ...
On the contrary, its integration into a global ocean observing system wouic] provide far greater and more frequent access to the ocean than will ever be possible with research vessels alone.
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From page 62... ...
Surface winds are measured by satellite scatterometers. The sea surface slope can be measured from space by radar altimeters with accuracies adequate for determining many features of ocean circulation.
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From page 63... ...
Coordination of satellite projects with ocean science objectives and in situ ocean measurements is required. The satellite time series of sea surface temperature, winds sea ice, ocean color, and ocean height must be continued without interruption to provide a complete record of their variability.
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From page 64... ...
Significant advances shouIc3 be made during the next decade in physical, biological, and geological oceanography as a result of thoughtful application of acoustic principles and techniques for direct probing and information transfer. Because of its inherent global nature, the acoustic monitoring of ocean climate is a strong candidate for a global ocean observing system.
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From page 65... ...
The aims of marine geochemistry are jlJ to understand the inputs of elements from the continents, mantle, and cosmic sources into the ocean over time; t2J to understand! the process of material removal from the ocean to the sediments and oceanic crust; ;3J to understand the process by which elements and their isotopes are redistributed; t4J to determine the mechanisms of chemical coupling between the ocean and the atmosphere, and interpret the sedimentary record of past oceanic change; and t5J to stucly marine organic compounds both in their relation to the above factors and to the global carbon cycle, and as detectors of oceanographic properties over time.
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From page 66... ...
paleontologic record in special ways. Oxygen and carbon isotopes in marine calcareous shells or tests and organic remains provide insight into ocean surface temperatures, ocean circulation, and the extent of ice storage in past glaciations.
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From page 67... ...
In addition, a significant flux of dissolved material may be expelled from sedimentary wedges and underlying oceanic crust as they clescend into the mantle through subduction zones. Cosmic crust and cosmic ray-producec3 nucTicles are not a major input to the ocean in terms of volume, but are important as tracers and for understanding episodic influxes of significance to the history of our planet.
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From page 68... ...
In addition, photochemical reactions occur in the atmosphere, changing the chemistry of the atmosphere and particle-bound chemicals. Hydrothermal activity in the deep sea is driven by voIcanic processes in the oceanic crust, predominantly at spreading centers.
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From page 69... ...
These particles oxidize rapicITy and appear to scavenge both a large proportion of the hydrothermically transported trace metals and a significant component of elements from ambient seawater. As mixing progresses, ocean circulation is increasingly dominant in dispersing inputs until they cannot be traced directly back to their source.
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From page 70... ...
For geochemical purposes, satellite pictures of ocean productivity must be projected into the vertical dimension to appreciate the fact that strong lateral variations in reactivity occur Reactivity is the intensity of the chemical reactions that are driven by biological activity in the ocean water column)
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From page 71... ...
oceanic crust are its oxidation state and its temperature. Chemical reactions in sediments involving oxidation ant!
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From page 72... ...
Marine Organic Substances The biochemicals that fuel marine organisms are photosynthesized and then respired in the upper ocean on time scales of hours to days. Only about 20 percent of the photosynthetic product escapes from the sunlit surface ocean as sinking particles, and less than 0.5 percent is ultimately preserved in marine sediments.
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From page 73... ...
hux~eyi within +0.5°C and they provided evidence against the idea of diagenetic alteration of the molecular temperature record in the marine water column. The alkenone paTeothermometer has potential applications beyond simple confirmation of stable oxygen isotopic records of sea surface temperatures.
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From page 74... ...
multiple collector thermal ionization mass spectrometers have increased the sensitivity for a wide range of elements and isotopes. High-energy accelerator mass spectrometry allows the measurement of the cosmogenic radioisotopes in the study of a wide range of geochronoTogical questions; it also allows exploitation of the unique properties of these isotopes in a variety of tracer studies.
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From page 75... ...
Uncierstanding Redistribution and Removal in the Ocean The general circulation of the global ocean has been relatively well described. From the geochemical point of view, much remains to be learned about the relative importance of the removal of elements at ocean boundaries versus in situ removal by settling particles.
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From page 76... ...
In the upper waters and thermocTine, large horizontal variations in primary productivity and higher levels of food webs have been observed, but little is known about the lateral variability of deep-ocean ecosystems. The effects of ecosystems on the chemistry of particles passing through them are largely unknown.
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From page 77... ...
However, by the 1980s, the focus of the field had shifted toward more process-oriented studies centerec3 around understanding how oceanic crust and lithosphere are created, how these processes are related to the underlying mantle, and the consequences of seafloor spreading on ancient ocean circulation and climate. Four themes currently dominate research in marine geology and geophysics: t1)
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From page 78... ...
Continental margins are the locus of lithospheric deformation, sediment accumulation, and substantial and chemically distinctive magmatism. Subduction and rifting processing at margins determine the size, shape, and distribution of continents and result in complex and dynamic interactions among oceanic crust, continental crust, and mantle systems.
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From page 79... ...
Marine sediments also provide a record of global sea-level changes, sea surface and bottom water temperature variations, changes in ocean current patterns, the volume of water locked in polar ice caps, and the effects of a changing physical and chemical environment on the evolution of marine life. Through drilling and coring, especially in high-latitude regions, paTeoceanographers are poised to make major advances in our understanding of the natural variability in global climate systems in the coming decade.
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From page 80... ...
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From page 81... ...
Two-thirds of the annual heat Toss from Earth's interior occurs through the generation and cooling of the oceanic lithosphere, partially by the circulation of seawater through fractures in the hot oceanic crust. This hydrothermal circulation facilitates a major chemical exchange between seawater and oceanic crustal rocks that acts as an important regulator of the chemistry of the ocean and of the volatile content of Earth's interior.
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From page 82... ...
Magma Transport Beneath Mid- Ocean Ridges Plate spreading and the generation of new oceanic crust and lithosphere along oceanic spreading centers involve a variety of complex and interrelates! geodynamic processes: upwelling and horizontal divergence of the solid mantle beneath spreading centers, pressure-release melting of this upwelling mantle and segregation of the partial melt from the deforming solid matrix, the emplacement and solidification of melt at shallow depths to create the oceanic crust, and the cooling of the crust and mantle to form the oceanic lithosphere.
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From page 83... ...
A major goal for the next decade is to carry out one or more of these studies on the mic3ocean ridge. Processes That Transform Magma into Oceanic Crust The transformation of magma into oceanic crust at spreading centers has fundamental implications for the mechanisms of heat and material transport from creep within Earth to the lithosphere, hydrosphere, ant!
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From page 84... ...
A cletailec! unclerstanding of the individual processes that constitute a hydrothermal system will provide insight into many problems in biological, chemical, geological, and physical oceanography.
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From page 85... ...
In addition, important questions concern changes in the oceanic crust as it ages. The oIcler oceanic crust also contains information concerning mantle convection and composition.
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From page 86... ...
Note that increased volcanic activity in the Cretaceous is associated with eustatic sea levels, high sea surface temperatures, and black shale production. Thus, this may be a link between mantle processes (volcanism and global climate.
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From page 87... ...
Structure arid Composition of Oceanic Crust An understanding of crust formation cannot be achieved in the absence of better knowledge of the composition of the total ocean crust. This information would allow solution of a host of long-standing controversies, including the relationship between crustal structure and spreading rate, the origin of the seismically defined stratigraphy of the oceanic crust, the total magnetization of the crust and how it is distributed with depth, and the depth and nature of hydrothermal interaction in the crust.
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From page 88... ...
Knowledge of continental margin structure and motion has progressed, but understan(ling of the margins is limiter! by the need to understand the basic physical processes that accompany margin formation.
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From page 89... ...
Ocean Basin Sediments Marine sediments provide important records for important Earth processes. For example, marine sediments furnish a history of regional and global volcanic activity, a record of the Tong-term changes in Earth's magnetic field, and a tool for studying largescaTe tectonic processes, such as continental accretion and rifting.
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From page 90... ...
Geologic evidence for the more remote geologic past suggests that atmospheric carbon dioxide may have been as high as four to eight times its present level. Knowledge of these large atmospheric carbon dioxide changes on geologic time scales presents an opportunity to understand global climate change and to test model estimates.
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From page 91... ...
Thus the task is to document the interaction between the oceanic and terrestrial carbon cycle and atmospheric carbon dioxide as well as the pattern of climate change. Instabilities in Ocean-Atmosphere Circulation ire Earth History Evidence strongly suggests that ocean circulation is sensitive to climate change, and changes in ocean circulation in turn influence the nature of the climate equilibrium Bennett, 1977~.
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From page 92... ...
Research Approaches Study of oceanic crust and sediments has been aided over the past 30 years by a number of new techniques, whose application
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From page 93... ...
Continued systematic drilling will be required to obtain a complete picture of the structure of the ocean crust and particularly the chemical composition and hydrothermal alteration processes. Drilling also allows geophysical and geochemical instruments to be placed within the drill holes to measure temperature, chemical fluxes, crustal strain, and other variables important for understanding geological, geochemical, and geophysical processes.
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From page 94... ...
population dynamics of marine organisms. In addition to climate change that may be accelerated by carbon dioxide and other greenhouse gas emissions, overfishing, eutrophication, introcluced species, and other anthropogenic changes affect marine populations, although impacts vary regionally.
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From page 95... ...
The ocean is a carbon sink because some of the organic matter synthesized by organisms in the sunlit upper ocean (the euphoric zone) settles to the seafloor, and some small fraction of that reaching the seafloor is eventually buried in marine sediments, where it may remain for millions of years.
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From page 96... ...
As indicated above, marine food webs affect global biogeochemical cycles, and marine populations, in turn, are affected by changes in global climate and human-induced changes in ocean environments. Some of the best examples of climate effects on marine organisms come from European fisheries, for which long time series exist for fish catch and abundance in relation to key physical and biological variables.
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From page 97... ...
Episodic Export of Material from the Surface The simplest description of the effects of marine food webs on vertical flux involves only the size and species of phytoplLankton and whether the phytoplankton sink before being ingested. For example, the spring diatom bloom in the North Atlantic is thought to sink without significant predation, whereas where cyanobacteria are the dominant primary producers, sinking of organic material from the upper ocean is largely mediated by food-web processes.
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From page 98... ...
Many of these particles are consumed by animals as they sink and are converted into smaller fecal pellets, new animal growth, respired carbon dioxide, and dissolved organic matter. Dissolved Organic Material The measurement of dissolved organic material IDOL is also of great interest to biological oceanographers ant]
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From page 99... ...
This point is cJevelopecl further in "Directions for Coastal Ocean Processes." Biology of Hydrothermal Vent anc] Hydrocarbon Seep Habitats Most oceanic food webs are based on photosynthetic productivity occurring in the upper regions of the ocean.
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From page 100... ...
Support for this work has a broad international base, such as through the RIDGE program, which supports multidisciplinary investigations of the biology, geochemistry, and geophysics of mid-ocean ridge-crest systems. Study of these diverse ecosystems in which chemosynthetic processes replace or complement photosynthetic productivity is necessary to understand the complex nature of marine food webs and the full suite of exchanges and transformations that constitute the global carbon cycle.
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From page 101... ...
In addition, distribution of the wave energy over a wider continental shelf may substantially modify the transport of planktonic organisms to shore, affecting the success of larval recruitment and the transition of organisms from larval to juvenile stages. Other Anthropogenic Influences Other human-induced environmental changes also affect marine populations, although they vary regionally and their extent is disputed.
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From page 102... ...
Research Strategies The complexity of biological systems and their vari time and space pose practical problems for designing programs and setting research priorities. Research based on the theme that fooc3-web variability controls variability in fluxes of biologically important elements in the global ocean could take many forms; efforts must then focus on a subset of key questions and approaches.
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From page 103... ...
The three variables are sea surface temperature; sea surface and near-surface ocean color to determine chlorophyll and water clarity; and sea surface wind fields for estimating rates of vertical mixing, air-sea gas exchange rates, and other wind-related processes, such as the seasonal changes in the depth of the surface ocean mixed layer. Numerical Mocking Two clevelopments in modeling should make significant contributions to ecosystem studies in the l990s.
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From page 104... ...
In general, molecular biology will aid the study of marine ecosystems in two ways: it will help to determine the physiological state of organisms, and it will help to identify and characterize the genetic structure of marine populations. Work in these areas will help both to identify the causes of biological variability in the ocean and to understand the implications of this variability for the stability and ecological balance of human-impacted ecosystems.
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From page 105... ...
and highly resolved (minutes to hours time-series measurements, permitting biological oceanographers to study what physical factors control phytoplankton populations. Moorings contribute data on variation over time and depth, whereas satellite sensors provide information on variation over the global ocean surface.
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From page 106... ...
Ideas and technologies are in place to make significant progress cluring the next 10 years in determining the role of marine ecosystems in global ocean biogeochemical cycles and the effects of global change on marine ecosystems. Available technologies range from molecular probes to satellite sensors.
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From page 107... ...
Because of the diversity of coastal ocean regions, significant progress in understanding coastal processes may be achieved in some areas, but it is unlikely that results from all coastal regions can be integrated within the clecacle. Emphasis on toxic algal blooms, ecosystem structure changes, the invasion or dominance of nuisance species, and other human-inducec3 biological effects may well increase.
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From page 108... ...
the thinner oceanic crust, both of which float on the underlying mantle. The continental shelf is essentially the submerged edge of the continental crust.
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From page 109... ...
Lower panel: A trailing-edge margin typical of much of the Atlantic Ocean. The presence of a continental rise, a broad continental shelf, and a coastal plain are characteristic of this type of margin.
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From page 110... ...
The upwelled nutrients fuel marine plant growth, leading to high biomass throughout the food web and some of the worId's greatest fisheries, including those off the West Coast and off the coast of Peru. Upwelling can also intensify the transfer of organic materials from the surface to the seafloor in such areas.
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From page 111... ...
Strong tidal currents intensify near-bottom mixing that can extend to the sea surface in shallow regions such as Georges Bank. This mixing and the resulting circulation enhance nutrient availability in the upper ocean, cause high primary productivity, enrich fisheries, and increase the transfer of organic material to underlying sediments.
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From page 113... ...
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From page 114... ...
Over geological time scales, the fates of sediments can vary widely with sea level; shelf processes can (lifter markedly, clepencling on how much of the shelf Or sloped is exposed above the sea surface. Coastal waters also receive chemicals ant!
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From page 115... ...
An understanding of the effects of water movements on the behavior and distribution of organisms in the ocean will be one of the most challenging aspects of future research, particularly in coastal areas, where both physical processes and organisms are especially diverse and numerous.
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From page 116... ...
Within this broad approach to the coastal ocean, a number of important themes will be common to any detailed study of processes. Air-Sea Interactions The atmosphere is a major driving force of coastal ocean processes, through both its role in driving currents and its direct and indirect controls on biological and chemical processes.
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From page 117... ...
The atmosphere is the basic driving force of many coastal ocean processes. Ocean fluxes, especially heat fluxes, are critical to properties of the atmosphere.
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From page 118... ...
The coastal ocean occupies approximately 20 percent of total ocean area, yet accounts for approximately 50 percent of ocean primary production and approximately 50 percent of global ocean nitrate assimilation by phytoplankton {Walsh 19911.
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From page 119... ...
rates and mechanisms of nutrient delivery and on various it , largely unappreciated characteristics of the species composition and structure of marine food webs in the euphoric zone, deeper in the water column, and in and around the seafloor. Some biogeochemical cycling processes are summarized in Figure 3-7.
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From page 120... ...
To take best advantage of the results of these studies, strong working relationships with the applied science communities need to be forged. Coastal measurements will be an important part of a global ocean observing system because it is at the coasts that most countries, particularly developing nations, will make most of their measurements.
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