Oceanographic Community Research Articles

Scaling of coastal phytoplankton features by optical remote sensors: comparison with a regional ecosystem model

Different scales of hydrological and biological patterns of the Bay of Biscay are assessed using space‐borne and airborne optical remote sensing data, field measurements and a 3‐dimensional biophysical model. If field measurements provide accurate values on the vertical dimension, ocean colour data offer frequent observations of surface biological patterns at various scales of major importance for the validation of ecosystem modelling. Although the hydro‐biological model of the continental margin reproduces the main seasonal variability of surface biomass, the optical remote sensing data have helped to identify low grid resolution, input inaccuracies and neglect of swell‐induced erosion mechanism as model limitations in shallow waters. Airborne remote sensing is used to show that satellite data and field measurements are unsuitable for comparison in the extreme case of phytoplankton blooms in patches of a few hundred metres. Vertically, the satellite observation is consistent with near surface in situ measurements as the sub‐surface chlorophyll maximum usually encountered in summer is not detected by optical remote sensing. A mean error (δC/C) of 50.5% of the chlorophyll‐a estimate in turbid waters using the SeaWiFS‐OC5 algorithm allows the quantitative use of ocean colour data by the coastal oceanographic community.

On the response of the Aegean Sea to climatic variability: a review

AbstractThe Aegean Sea is a region of special interest for the Mediterranean oceanographic community, as one of the dense‐water formation sites of the Mediterranean, driving its thermohaline circulation. Early oceanographic literature exhibits significantly varying opinions regarding the role of the Aegean as a contributor to the water masses of the eastern Mediterranean. The higher temporal and spatial resolution studies that followed the introduction of Conductivity‐Temperature‐Depth (CTD) profilers in the 1980s, revealed that the various scenarios were within the interannual variability of dense water formation in the region. A peak in this variability was the appearance of the Eastern Mediterranean Transient event in the early 1990s. This phenomenon showed that the Aegean Sea has the potential to function as a source of dense water for the eastern Mediterranean; however, it takes over this role only sporadically, depending on the meteorological conditions over the eastern Mediterranean and, possibly, central/eastern Europe. The North Atlantic oscillation appears to be a contributor to this bimodal behaviour. Palaeoceanographic information has confirmed the large sensitivity of the Aegean Sea to climatic variability. Based on the available information, possible scenarios are examined for the response of the Aegean to the current climatic trends. Copyright © 2004 Royal Meteorological Society

Did the Mediterranean Sea Dry Out During the Miocene? A Reassessment of the Evaporite Evidence from DSDP Legs 13 and 42A Cores

ABSTRACT The idea that the Mediterranean Sea dried out completely during the late Miocene (Messinian, 5-6 Ma) is now widely accepted. This idea, first published in 1972 (Hsu 1972a; Hsu 1972b) grew out of the interpretation by Deep Sea Drilling Project (DSDP) scientists that the evaporites recovered from beneath the floor of the Mediterranean by drilling on DSDP Legs 13 (1970) and 42A (1975) were of shallow-water origin. Since that time, there have been a number of advances in understanding of evaporite depositional processes, and with this in mind, we have reexamined the evidence provided by the DSDP evaporite cores. We show that the case for deposition of the Miocene evaporites of the sub-Mediterranean under shallow-water conditions is based on interpretations that are either equivocal or incorrect. Several features of these evaporites used by the DSDP workers as evidence of shallow-water conditions are more compatible with deposition under deep-water (below wave base) conditions, and others can only be considered as of uncertain origin. In addition, coring has sampled only the upper few tens of meters of the evaporites, a factor that seriously limits any interpretation of the origin of the deposit as a whole. In view of these findings, we suggest that the question of the origin of the Miocene evaporites beneath the floor of the Mediterranean Sea be reexamined by the geologic and oceanographic communities.

A Replacement for the Alvin Submersible

The National Deep Submergence Facility (NDSF) has completed the concept development for a proposed new manned deep submergence vehicle that would replace Alvin. The new vehicle would dive deeper (6,500 meters), have improved observer and pilot viewing, a larger interior volume with improved ergonomics, greater battery capacity with improved endurance, and less reliance on disposable weights and hazardous materials. A proposal based upon the conceptual design has been submitted to the National Science Foundation for consideration in 2004. Should this be approved, a new manned submersible could be available for use by the world's oceanographic community early in 2008.

Comment on “New Global Drifter Data Set available”

Stephen Pazan and Peter Niiler (Eos, 13 January 2004, p. 17) ably describe the global drifter data set that has now been assembled, its potential value to the oceanographic community and the locations on the Internet where it can be found.This is indeed an extraordinary resource that can be of immense value to a spectrum of oceanographers. In their enthusiasm to propound the usefulness of the data, they may however, have made one serious error.In illustrating the meandering nature of the Agulhas Return Current with drifter tracks, they state, “New circulation features are also being discovered…In Figure 2 the Agulhas Current can be seen flowing south of the east coast of South Africa; it separates from the coast and meanders northward and southward seven times as it flows to the coast (sic; they mean: to the east). These meanders, which are steadily present from 1979 to 2002, have not been observed before.…”

The seas of Titan

Oceanography may no longer be only an Earth science. Evidence continues to mount that Saturn's giant moon, Titan, may have seas of liquid hydrocarbons that exhibit many phenomena familiar to terrestrial oceanographers, but with an other‐worldly flavor (Figure l ). In less than two years, the Cassini‐Huygens mission, a massive joint undertaking of NASA, the European Space Agency, and the Italian Space Agency will arrive at Saturn and begin exploring the strange world of Titan. Our goal here is to introduce Titan to the oceanographic community, to outline the data to come, and prompt new modeling efforts. We pay particular attention to phenomena observable from Cassini, although we note that many terrestrial phenomena—only now beginning to be surveyed on Earth via moored instrument networks, submersibles, remotely operated vehicles (ROVs), and autonomous underwater vehicles (AUVs), etc.—may have analogues on Titan. We anticipate that Earth will have much to tell us about oceans on Titan, and vice‐versa.

Peter Eric Holloway (1953–2002)

On 27 October 2002, Peter Eric Holloway died suddenly cutting short a highly distinguished career in physical oceanography Holloway was internationally recognized for his contribution to the observation, theory, and numerical modeling of internal waves. The oceanography community sends its sincerest condolences to his family.He had been an AGU member (Ocean Sciences) since 1980.

English

Introduction Strange whales, playful porpoise, out-of-place sailfish and marlin these are just some of the offshore oddities accompanying El Ni~o's dramatic ocean-warming along the Pacific Coast [of California] this year (Stienstra, 1997). How did we get so far so fast as to confidently link changes in tropical climate to marine ecosystem changes thousands of kilometers distant? For many years now the fishery oceanography community has been aware of the long reach and unusual power of the tropical El Nifio-Southern Oscillation (ENSO). Early indications of an E1 Nifio event are now routinely extended into predictions for ecosystem change not only in the equatorial Pacific, but also in the California Current and even into the Gulf of Alaska. Such predictions are largely based on experience developed from past E1 Nifio events, yet in most cases our understanding of cause and effect has failed to keep pace with our observations and expectations. The spectacular late-20 ~ Century decline of cod stocks on the Georges Bank, repeated decades-long boom/bus t cycles for Pacific salmon in the northeast Pacific, and the year-to-year waxing and waning of krill biomass and penguin populations in the Southern Ocean all highlight aspects of dynamic ecosystem variability that beg for an improved scientific understanding. Can these ecosystem changes be linked to ENSO events or other variations in the global climate system? If so, can the pathways of interaction be understood? In the examples listed above, efforts to disentangle natural climate impacts from direct and indirect anthropogenic (e.g. industrial fishing) impacts have been of great interest for fishers, fishery managers, and fishery scientists alike. A growing body of empirical data and analyses have highlighted many environmental and ecosystem changes that appear to be part of much larger scale and sometimes longer term changes playing out in the climate system (e.g. Mysak, 1986; Francis et al., 1998; Dickson and Brander, 1993; Loeb et al., 1997). Thus, an alphabet soup of oscillations and acronyms first introduced in the climate research community-the North Atlantic Oscillation (NAO), E1 Nifio-Southern Oscillation (ENSO), the Pacific Decadal Oscillation (PDO), and the Antarctic Circumpolar Wave (ACW), for example has found a hungry audience in the world of fishery oceanography. To better understand and more skillfully predict climate impacts on marine ecosystems, U.S. GLOBEC scientists are often faced with significant hurdles that come with working across traditional disciplinary boundaries. In this article we discuss some of the challenges in bridging scales of time and space that are required to link large scale climate dynamics to scale marine ecosystem dynamics. First, we review aspects of hemispheric-scale climate variations to provide a broad-spatial and long-temporal context for aiding our understanding of ecosystem dynamics in U.S. GLOBEC regional programs. Second, our perspective shifts to that of the modeling efforts now used to bridge the space-time scales linking local ecosystem processes with hemispheric scale processes in the global climate system. We conclude this article with a brief discussion of the avenues of research that we believe offer promise for advancing our ability to make the climate connections with marine ecosystem dynamics.

Marine parameters from synergy of optical and radar satellite data

In 2001 the European Space Agency ESA will launch the earth observation satellite ENVISAT. It will carry several instruments that provide new opportunities to measure oceanographic variables. Together, they represent the main measurement techniques of satellite oceanography, and complement each other in an ideal manner. These instruments are to be used in synergy to: • Improve the analysis of measured wind and ocean wave fields, and thereby improve weather forecasting at weather centers; • Determine the extent and variables of sea ice and develop a five-day sea ice prediction model, to support maritime shipping and offshore activities; • Monitor and map sediment and suspended matter transport in coastal regions, especially in areas with large river estuaries, which greatly affects shipping lanes, harbors, and dredging activities; • Monitor hydrobiological and bio-geochemical variables related to water quality in coastal regions and large inland waters, which affects ecology, coastal development, aquaculture, drinking water supplies, and tourism. To prepare the oceanographic community to make best use of the ENVISAT sensors in the pre-launch phase, existing algorithms to derive marine parameters are used and validated using data from the ERS SAR, the ERS RA, SeaWiFS and IRS MOS sensors now in operation. Derived products are used to address problems that can best be tackled using the synergy of radar and optical data, such as the effect of surface slicks on radar wind measurements, of sea state on ocean color, of wind and waves on the resuspension of suspended matter, and of wind and waves on sea ice variables.

GLOBEC Canada 1996-2000: a sampler

There is increasing evidence that the ocean’s physical environment and its resident biological communities are changing in ways and at time scales that have important consequences for ocean and terrestrial ecosystems and for society. The Global Ocean Ecosystems Dynamics research program (GLOBEC) is an international effort to document and understand these changes, with a specific focus on how marine ecosystems respond to climate variability (both natural and anthropogenic). A Canadian national component of GLOBEC began in 1996, funded jointly by the Department of Fisheries and Oceans (DFO, 1996 to the present) and the Natural Sciences and Engineering Research Council of Canada Research Partnerships program (through March 2000). The program brought together a large number of marine scientists (45) and students and postdoctoral fellows (35) affiliated with both universities (seven) and DFO laboratories (five). The accompanying set of eight papers is a representative cross section of results from GLOBEC Canada. All were initially presented at our final Phase I workshop (May 1999 in Halifax, N.S.). Additional clusters of publications appeared in two previous issues of the Canadian Journal of Fisheries and Aquatic Sciences (56: 2420–2486 and 57: 2488–2546) and individually in a variety of journals (see complete publications list at the GLOBEC Canada Web site ). GLOBEC Canada investigators also contributed to dedicated issues of Fisheries Oceanography and Deep-Sea Research II (cf. Eckman 1994; Wiebe and Beardsley 1996; Coombs et al. 1998; Wiebe et al. 2001) sponsored by GLOBEC International and U.S. GLOBEC. This brief introduction is provided to emphasize the shared themes and approaches that have characterized GLOBEC Canada research. A key motivation for GLOBEC research was a realization, growing within the oceanographic community over the past two decades, that biological “output” variables often covary strongly and for prolonged periods with variables that affect and reflect the physical dynamics of the ocean (for examples, see deYoung et al. 1994). These time series correlations suggest a close association between marine populations and “ocean climate.” Yet, correlative associations also have a disturbing tendency to break down part way through long time series. We need to recognize where, when, and why present and future changes will occur, and ideally, we would like to develop an advance predictive capability. To accomplish this, we need (i) cross-disciplinary collaboration between biologists and physicists to resolve the relative importance of the various paths and circumstances (Fig. 1) under which the physical environmental can affect plankton and fish populations, (ii) a continuing interplay and cross-referencing among three scientific approaches: retrospective analysis of long time series, focussed process studies, and numerical modelling, and (iii) comparisons among different species and regions. Because of the long term nature of some of the changes and interactions, even multiyear bivariate time series at single locations are insufficient to document the full range of system behaviour or to provide sufficient statistical power for tests of associations. The papers in this issue, and those published earlier and elsewhere, provide examples of these synergies.

Short-term variation and long-term changes in the oceanographic environment and zooplankton community in the vicinity of a sub-Antarctic archipelago

Mesozooplankton community structure in the vicinity of the Prince Edward Islands (PEIs) was investigated during six surveys conducted in late austral summer (April/May) from 1996 to 1999. Zooplankton samples were collected by oblique tows using a Bongo net fitted with 300-μm mesh. Surface temperature, average temperature and chlorophyll a were measured in conjunction with each net tow. The positions of the Sub-Antarctic Front (SAF) and the Antarctic Polar Front (APF), in relation to the islands, were determined by CTD and/or XBT transects to the west of the islands (upstream). Both fronts were characterized by a high degree of latitudinal variation. Changes in position of the fronts occurred rapidly, the SAF moving up to ∼120 km in a 2-week period. Consequently, the oceanographic environment in the vicinity of the PEIs was subject to a high degree of intra- and inter-survey variation. The positions of the SAF and APF appeared to have a significant impact on phytoplankton biomass in the vicinity of the PEIs, possibly through the alteration of local oceanographic flow dynamics. Water retention over the island shelf in 1996, associated with location of the SAF far to the north of the PEIs, corresponded to enhanced chlorophyll-a concentrations (∼1.54 mg m−3). Conversely, when the fronts were close to the islands, as in 1997 and 1999, higher current velocity limited water retention and chlorophyll-a concentrations in the inter-island region were relatively low (∼0.4 mg m−3). Cluster analyses showed that, in many instances, there was greater similarity among zooplankton communities from different surveys than among communities within surveys, indicating that short-term variability exceeded inter-annual variability. The population structure of the copepod Calanus simillimus indicated that there was inter-annual variation in the timing of the biological season. Differences in the population structure of species, and consequently their contribution to abundance and biomass, may therefore have been an important contributor to inter-annual variation in community structure. Evidence is provided of a long-term southward shift in the position of the SAF. It is postulated that this may affect the PEIs by increasing the proportion of allochthonous energy input, because the PEIs now lie in the path of the front, altering the tropho-dynamics of the island ecosystem. Lower mesozooplankton biomass associated with warmer sub-Antarctic water may have important negative consequences for higher trophic levels that depend on mesozooplankton for food.

Comment on “Operational oceanography: Shall we dance?”

In a Forum article,“Operational Oceanography: Shall We Dance” (Eos Trans., AGU, March 14, 2000) C. Mooers states that “the worldwide oceanographic community is on the brink of operational oceanography” I beg to differ; this community is already immersed in operational oceanography.Mooers also states that the “National Oceanic and Atmospheric Administration (NOAA) has fewer than 100 individuals working in operational oceanography, and they are concentrated at the National Centers for Environmental Prediction (NCEP) of the National Weather Service (NWS).“This is incorrect; NOAA currently has at least 1,317 “full‐time equivalents” (FTEs) working in operational oceanography,some of whom directly trace back to President Jefferson's establishment of the Coast Survey in 1807. And there are hundreds, if not thousands, more in other U.S. agencies at the federal,state, and local levels.

Status of alkenone paleothermometer calibration: Report from Working Group 3

The alkenone unsaturation index, U37K′, has now proven its worth as a tool for paleothermometry. U37K′ measured in most modern sediments throughout the World Ocean can be translated using established calibrations into realistic, seemingly reliable estimates of mean annual temperature at the sea surface (SST). However, it remains mysterious why water temperature estimates based on this biotic index correspond to “mean annual” SST and whether such estimates apply back in geological time. Solving these mysteries is imperative and will require thoughtful, concerted research effort by the biological, chemical, and geological oceanographic community. This report summarizes what is now known about alkenones, in particular, their use in estimating the growth temperature of specific haptophyte algae that synthesize and export these compounds to the marine sediment record. It highlights future field and laboratory research directions that should be taken to clarify and bolster utility of alkenones as a generally valued paleoceanographic tool.

Operational oceanography: Shall we dance?

With the Global Ocean Observing System (GOOS) currently in development, the worldwide oceanographic community is on the brink of “operational oceanography,” which essentially means provision of “operational ocean services” where “operational” means “routine” and “ocean services” means “marine environmental information.” GOOS is a joint campaign of the Intergovernmental Oceanographic Commission, the World Meteorological Organization, the United Nations Environmental Program, and the International Council for Science. GOOS will integrate expanded real‐time in situ and satellite observations with numerical models to form model‐based information products for a multiplicity of societal needs, including scientific research [Stel, 1997].Operational oceanography has become a popular tune without a copyright but with many bandmasters. While Europeans and northeast Asians are moving ahead aggressively with GOOS activities, the United States has been hesitant, lacking in foresight, and awash in planning activities. It is time to ask, What has happened?, What is happening?, and What should happen?

Fashioning a Professional Dialogue in Oceanography: The U.S. Navy and the Ocean Science Community, 1924-1960

Since the Great War of 1914-1918 the relationship between naval officers and ocean scientists in the United States has illustrated well the unpredictable effect of cultural barriers on constructive professional dialogues. The customs and practices attending an academic or industrial laboratory differ dramatically from those absorbed by midshipmen at the United States Naval Academy or officers on board combat ships. Each group lives in a nearly discreet, culturally constructed world. During the course of this century the communication and understanding necessary for these communities to work together toward a common goal required social and political insight as well as extensive entrepreneurship and careful cultural translation. Confronting a poverty of resources after World War One the Navy and the civilian oceanographic community formed a common practice to pool both resources and skill in an effort to perform meaningful ocean research. When the possibility of another war loomed large in the 1930s, they turned to determined cultural translators. The latter, drawn from both communities, converted the primitive common practice and considerable cultural obstacles of the interwar period into a fluid wartime professional dialogue. Fortified by success in World War II, key translators brought the dialogue to maturity after 1945.

Radar imaging of the oceans

Spaceborne radars are able to image ocean surface features, providing useful information on a global basis regardless of the weather conditions (especially clouds), both during the day and at night. This article explains this capability and provides illustrations of some of the results obtained. Mechanisms which allow a radar image of the ocean to be formed are outlined. Then several of the main features that are detected and the inferred parameters that can be measured and used by the oceanographic community are presented.

Exciting, unsettling changes in store for physical oceanography

The U.S. physical oceanographic community is entering a period of change that is both exciting and unsettling. Very critical problems face it, and how they are dealt with could determine if physical oceanography will survive as we know it today.The number of physical oceanographers has increased rapidly. But several large field programs are reaching the end of their data collection phases, and the growth in federal science budgets seems to have stagnated, at least in comparison with the “golden years” still fresh in the memory of many senior scientists. At the same time, technology is providing new tools for making ocean observations and expanding computational capacity. We are progressing from the dark ages, when ocean processes were seen dimly, if at all, into an era where those processes are brilliantly revealed with these new observational and analytical techniques.

Major multidisciplinary ocean project seeks proposals

A major multidisciplinary oceanographic program in the North Atlantic is being put together by the French oceanographic community, and scientists who would like to participate are being asked to submit proposals immediately Field work will begin in September 2000. Known as Programme Océanographique Multidisciplinaire Méso‐Echelle (POMME),the Meso‐scale Multidisciplinary Oceanographic Program, it is supported by several French scientific agencies and will take place between the Azores and the Iberian Peninsula.The program will focus on subduction of mode water in the region, its effect on biological production and the carbon budget in the area, and the fate of organic matter after subduction. More detailed information on the program's framework, rationale, and organization can be found on the Web (http://www.insu.cnrs‐dir.fr).

Even more interdisciplinary future lies ahead for ocean chemistry

Ocean chemistry is among the most interdisciplinary of marine sciences, but even greater linkage to other oceanographic and materials science disciplines is recommended in a new report by the chemical oceanography community. The field has advanced dramatically during the past 20 years and is poised to make fundamental new contributions in the coming decades, the report emphasizes.Chemical and biogeochemical processes in the ocean have profound implications for atmospheric chemistry ocean biology, and (via hydrothermal processes) the evolution of the ocean crust. Chemical tracer studies underlie much of our understanding of ocean circulation, while the chemical and isotopic composition of microfossils provides a record of past ocean circulation, temperature, and climate. Chemical processes in the marine realm thus have a profound impact on key aspects of the environment while providing the tools to study other fundamental oceanic processes.

SAMI: a low-frequency prototype for mapping and imaging of the seabed by means of synthetic aperture

The objective of the Synthetic Aperture Mapping and Imaging (SAMI) project was to develop and to test at sea a wide-band synthetic aperture sonar prototype, capable of providing high-resolution seafloor images together with bathymetry maps. This system used the motion of a physically small array in order to synthesize a longer array, providing images with an across-track resolution independent of both range and transmit frequency. Such systems are clearly very relevant to the high-precision long-range (low-frequency) imaging of the sea bottom. The project has led to the construction of a prototype tested at sea on several well-known areas for comparison with existing images and maps. These areas included several types of sea bottom, depths, and geological structures. The results obtained in real time, on-board ship, have shown the relevance of the proposed wide-band techniques. The many profiles produced have provided high-resolution images and maps of various seafloors. Interpretation by geologists showed that the system was capable of providing the same or finer detail than a deep-sea short-range, high-frequency system and maintained a higher resolution over a wider swath. The sea data processed have shown that the system provided maps with a cubic meter voxel. The resolution cell is constant over the whole range (50 to 2500 m) thanks to the dynamic focusing of the synthetic aperture. Postprocessing of a part of the data stored during the experiments has been carried out in the laboratory. This work has shown that techniques such as autofocusing can give an increase in resolution (i.e., gain in contrast and resolution of about 3 dB). The results displayed in the paper show the relevance of the techniques developed to the provision of a complete high-performance imaging tool for the oceanographic community.