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| "But the crowning achievement of TOGA was the development of the Tropical Atmosphere/Ocean (TAO) array of 70 moored buoys. Put in place over eight years, from 1986 to 1994, the array now spans 16,000 km of Pacific Ocean and gathers data on surface winds, sea surface temperatures, surface air temperatures and humidity, and subsurface temperatures at 10 different levels down to 500 m depth." EOS Transactions, American Geophysical Union, 78, 1, January 7, 1997. |
The Tropical Atmosphere-Ocean (TAO) Array, consisting of approximately 70 deep-ocean moorings spanning the equatorial Pacific Ocean between 8N and 8S from 95W to 137E, was maintained at full strength. The purpose of the array is to provide high quality, in-situ, real-time data in the equatorial Pacific Ocean for short-term climate studies, most notably those relating to the El Nino/Southern Oscillation (ENSO) phenomenon. TAO measurements consist primarily of surface winds, sea surface temperature, upper ocean temperature and currents, air temperature, and relative humidity. Data are telemetered in real time via Service Argos, and a subset of these data is placed on the Global Telecommunications System (GTS) for distribution to operational centers for assimilation into weather and climate forecast models. A major step forward in long -term support for the array was the commissioning in FY 96 of the NOAA Ship Ka'imimoana, a research vessel dedicated to servicing TAO moorings between 95W and 165E. Also in FY 96, new Next Generation ATLAS moorings were introduced into the array.
TAO data support research efforts at institutions around the world on the causes and consequences of climate variability originating in the tropical Pacific. Work at PMEL during the past year has focused on describing the evolution of recent ENSO warm events, on analyzing upper ocean heat, salt and momentum balances in the western equatorial Pacific, on investigations of the mean seasonal cycle in the eastern equatorial Pacific cold tongue, on large scale ocean dynamical processes involving equatorial waves and currents, on defining tropical Pacifci surface layer hydrography and ocean mixed layer structure on seasonal to interannual time scales, on the combined use of TOPEX/POSEIDON altimeter and TAO moored measurements to understand large scale sea level and circulation patterns in the tropical Pacific, on assessments of TAO array design and sampling strategies for climate analyses and predictions, and on validation of recent ocean and atmospheric model reanalyses using TAO data. A historical overview of the development of the Tropical Ocean Global Atmosphere (TOGA) observing system was initiated. Specific plans for new measurement programs were advanced: for a Pilot Research Moored Array in the Tropical Atlantic (PIRATA) in collaboration with Brazil and France, for a moored ATLAS array as part of the South China Sea Monsoon Experiment (SCSMEX) in collaboration with Taiwan, and for the Triangle Trans Ocean Buoy Network (TRITON) in collaboration with Japan. The TAO project also established collaborations with the US Department of Energy/Atmospheric Radiation Measurements (DOE/ARM) program to provide long term solar radiation measurements in the western Pacific, with the NASA Scatterometer (NSCAT) program to provide in situ validation data and sensitivity testing of wind forced ocean models, with the NASA Tropical Rainfall Measuring Mission ( TRMM) to provide basin scale in situ rainfall and salinity measurements, and with the NOAA Ocean Atmosphere Carbon Exchange Studies (OACES) program. These efforts all contribute to studies of ocean-atmosphere interaction and climate variability of central interest to PMEL.
The TAO project provides interactive access to TAO data, display software and graphics via the World Wide Web and workstation-based TAO Display Software. The TAO software features a point-and-click interface and a data subscription service providing remote users with automated daily updates to real time and historical TAO data, and is actively used at nearly 50 research institutions throughout the world. This year, time series of data from individual instruments on the TAO moorings have been made available on the World Wide Web. The TAO Project Office has also established a TOGA COARE moored data center, with Web access to nearly all moored time series collected during the COARE experiment.
The importance of Westerly Wind Events (WWEs) in the variability of the western tropical Pacific and the central and eastern equatorial Pacific continues to be investigated, using observations from the Tropical Atmosphere-Ocean (TAO) moorings and ocean model studies. A major effort to determine the x-y-t structure of WWEs was completed. The ability of the TAO array to observe WWEs is marginal, and is being determined.
The ability of our present and proposed tropical observing systems to measure the changes that are important for SIP is a continuing assessment activity. A major summary of the space and time scales of thermal variability as measured by the TAO array was completed, and much progress was made on a similar study of the scales of surface wind variability. An ensemble of ocean model experiments was carried out so that detailed sampling studies of the effectiveness of the present observing system can be examined.
Work continues on aspects of longer time scale problems as well. The variability of surface pC02 in the North Pacific was examined with other Ocean Climate Research Division scientists.
A new one dimensional model of the near-surface food web was developed with University of Washington scientists and has been validated against tropical Pacific observations; it is being incorporated into our ocean circulation model. Global studies of the uptake and redistribution of CFCs continued with Department of Energy and National Science Foundation collaborators.
PMEL also participated in the Combined Sensor Program (CSP) which brought together for the first time in a maritime environment a suite of in-situ and remote sensing systems to characterize both air-sea interaction and the radiative balance of the tropical atmosphere, including aerosols and clouds.
Another activity of the PMEL-JISAO Atmospheric Chemistry Program is the chemical sampling and analysis of daily samples from a ground-based aerosol monitoring network. This network has been established in conjunction with NOAA/Climate Monitoring and Diagnostics Laboratory (CMDL) to determine means, variability, and possible trends of key optical, chemical and microphysical properties for a number of important aerosol types.
Predicting global climate change as a consequence of CO2 emissions requires coupled a tmosphere/ocean/biosphere carbon models that realistically estimate the rate of growth of CO2 i n the atmosphere, as well as its removal, redistribution and storage in the oceans and terrestrial b iosphere. The primary objective of NOAA's Ocean Atmosphere Carbon Dioxide Exchange Study ( (OACES) is to quantitatively assess the fate of CO2 in the atmosphere and oceans. In order to accomplish t his goal the natural sources and sinks of carbon dioxide must be determined. During FY 96, the PMEL CO2 group developed a multi-parameter stepwise regression model which quantitatively estimates the amount of anthropogenic CO2 that penetrates into the oceans from changes in d issolved inorganic carbon and other physical and chemical data collected over decadal time s cales. From a comparison of the 1991 C&GC91 cruise data along 152W in the North Pacific wi th the 1973 GEOSECS data, the PMEL scientists determined that the North Pacific accumulated anthropogenic CO2 in the mixed layer at an average rate of 1.3 ± 0.7 µmolk g-1yr-1. T he depth of penetration was approximately 800 m along 152W. These new model results are comparable with previous estimates of anthropogenic CO2 inputs into the North Pacific.
During the past year, the PMEL and AOML CO2 groups also completed a five-month cruise in the South Pacific under the auspices of NOAA's Climate and Global Change (C&GC) Program . The multi-legged cruise, conducted aboard NOAA research vessel Discoverer was a part of t he U.S. JGOFS Program in the Southern Ocean and t he U.S. WOCE Hydrographic Program (WOCE Line P15S), supported jointly by NOAA, NSF, and the Department of Energy. During the experiment, the NOAA scientists determined the concentrations of carbon species and related physical and biological parameters on several south-north transects. Over 4100 samples were collected coll ected and analyzed for dissolved inorganic carbon (DIC), total alkalinity (TAlk), CO2 partial p ressure (pCO2), pH, CFCs, carbontetrachloride, radiocarbon, dissolved organic carbon and nitrogen, dissolved oxygen, nutrients and salinity. Preliminary results from the cruise indicate that the southwestern Pacific region is a large sink for atmospheric CO2. The sink regions are coincident with regions of strong surface water stability induced by a salinity minimum at the surface (Fig. 1). These so-called "barrier layers" prevent CO2 from vertically mixing from below and enhance the invasion of CO2 across the air-sea interface. In the high southern latitudes the barrier layers are maintained by melting ice during the austral summer; whereas, in the tropical and subtropical latitudes the barrier layers are maintained by an excess of precipitation over evaporation, which is common over large regions of the western Pacific. The data collected from this cruise represents the most comprehensive set of chemical and hydrographic measurements of its kind for the southwestern Pacific Ocean. The DIC measurements were accurate to within ± 1. 5 µmol/kg, based upon a nalysis of reference materials and replicate samples. The data from this cruise will be combined with other data sets from the WOCE Hydrographic Program to constrain models of basinwide circulation and carbon distributions in the South Pacific Ocean. We plan to use this data set in combination with CO2 data from the same region in 1973 to determine the amount of anthropogenic CO2 that is stored in t he South Pacific Ocean since the middle of the last century. .
During FY 96, the PMEL CFC Tracer group helped organize and participated in
a multi-institutional oceanographic
expedition in the southwest Pacific on the NOAA Ship Discoverer,
as part of the World Ocean Circulation Experiment (
WOCE). A variety of physical, chemical and biological measurements were
made on this expedition. The CFC
data obtained on this expedition highlight the rapid uptake of atmospheric
gases into the ocean in this region, and the deep CFC signal being carried northward
into the abyssal Pacific Ocean by Antarctic Bottom Waters.
The fourth year of a NOAA Atlantic Climate Change Program (ACCP) supported study to
monitor variability of dense water formation and ventilation processes in the
Greenland-Iceland-Norwegian Seas, using CFCs and helium/tritium as tracers was completed.
These studies have shown that the rate of formation of new Greenland Sea Deep Water (GSDW)
during the 1980s and early 1990s was drastically lower than that in the 1970s. The
near-cessation of the production of this cold, dense water mass by deep convective processes may
be the result of decadal-scale changes in surface conditions in the central Greenland Sea.
Collaborative programs were continued with researchers at the NOAA/ERL Geophysical Fluid Dynamics Laboratory (GFDL) and at the National Center for Atmospheric Research (NCAR) to utilize the CFC datasets in numerical models of ocean circulation. Results of a comparison of CFC observations in the ocean with the results of a coupled ocean-atmosphere numerical model has been published. Such tests are critical if we are to have confidence in the ability of such models to predict possible changes in the earth's climate due to release of greenhouse gases or other anthropogenic activities.
The robust method to determine transfer functions used to remove the geomagnetic induced voltages has been published. This method has been improved and made more robust by using commercial magnetotelluric data contaminated by industrial noise sources such as electrified railways. These data reduction methods have been applied to the voltages collected between Taiwan and Okinawa which greatly improves the accuracy of detecting the motionally induced voltages. The numerical simultaion of the cable voltages using realistic oceanographic and geophysical models has been completed and is being published.
Current moorings and satellite-tracked drifting buoys deployed during spring observed the weakest mean currents ever measured in Shelikof Strait and its sea valley. Flow in the sea valley was dominated by a large, weak clockwise rotation; flow down the strait was 5 cm s-1, in contrast to the more common 15 cm s-1. High concentrations of larvae were observed during the first larval survey. Assimilation of these data into FOCI's biophysical model should provide insight into how pollock larvae survive under such unique conditions.
The research basis for Shelikof Strait FOCI's first decade was documented in a special issue of Fisheries Oceanography (March 1996). Fourteen papers synthesized and presented new results. These included: elucidation of formation and maintenance of dynamics for larval patches, detection of mesoscale biophysical features using novel acoustic techniques, and simulation of pollock life history from egg to late larvae using a coupled physical, individual-based model.
Bering Sea made the first remote measurements of the progression of the spring bloom in the Bering Sea basin using a technologically advanced, moored biophysical platform. During spring 1996, the program augmented its knowledge of phytoplankton dynamics by flying a NOAA P-3 research aircraft equipped with an ocean color scanner over the slope and shelf. Preliminary resultss show higher phytoplankton concentrations where the sea ice is melting in the northern portion of the domain, and a prominent 100 by 200 km patch southeast of the Pribilof Islands with concentrations on the order of ten times background levels. This patch is in a region that has been found to feature a large spawning population of walleye pollock.
Using results from the genetic research component, historical surveys, and outside expertise, the project has compiled a draft report on stock structure of walleye pollock in the Bering Sea. Significant variation in mitochondrial DNA allows differentiation of eastern and western Bering Sea pollock and inference of potential gene flow between stocks.
Synthesis from five years of research defined two primary climatic modes for conditions during summer on the Bering Sea shelf. Warm or cold shelf conditions are indicated by the extent of seasonal sea ice in winter/spring and the direction of wind over the shelf in April. Certain higher trophic level species appear to vary in distribution on a multi-annual rather than interannual temporal scale, e.g., the distribution for adult walleye pollock across the shelf did not switch to the outer shelf during every cold year but only during periods when cold conditions persisted for at least three years. The distribution of age-1 pollock also varied with multiple cold or warm years, changing from the outer shelf to the middle and inner shelf as conditions warmed. Consequences of these two scales of variability must be considered when evaluating species interactions on an ecosystem scale.
PMEL was selected to co-manage Southeast Bering Sea Carrying Capacity ( SEBSCC), a 5-year, $1 million Coastal Ocean Program Regional Ecosystem Study. SEBSCC will focus on two elements of the ecosystem: 1) cross-shelf transport and fate of nutrients, and 2) juvenile pollock as a nodal species. A workshop was conducted in November 1995 from which a review document was produced and an announcement of opportunity developed. PMEL is represented on 5 of 15 successful proposals: monitoring and development of biophysical indices, circulation modeling, individual-based modeling of walleye pollock, the role of atmospheric forcing on the "cold pool" and ecosystem dynamics, and the influence of mesoscale eddies on the interaction of lower and higher trophic levels.
During the eruption event response, a novel new experiment was successfully accomplished which made it possible, for the first time, to track and study the evolution of the hot, chemically enriched plumes associated with deep eruptions. This was done using a float which was precisely ballasted to remain within the plume as it was carried by deep ocean currents away from the eruption site. The float, which regularly recorded its position, surfaced after two months of traveling in the plume. Oceanographers were then able to map the movement of the plume and study the plume s chemical and thermal evolution.
Collaborations continued with microbiologists at the University of Washington to determine influences of hydrothermal fluid chemistry and geology on the ecology of a vast, newly discovered subseafloor biosphere as well as the species diversity of its microbial inhabitants. A NOAA initiative is being considered to begin a major research effort to understand and exploit this newly discovered microbial resource.
Major new features of the helium tracer field were discovered and published in Science. These new results, which include the first detailed map of the Loihi seamount helium plume, provide a much clearer map of deep ocean circulation in the north Pacific.
VENTS scientists completed an exhaustive three-year monitoring project of the 1993 Juan de Fuca Ridge seafloor eruption. Among many notable results, this effort yielded the first quantitative determination of heat and mass fluxes from both episodic and quasi-steadystate hydrothermal vent discharge during the entire life cycle of a volcanically-generated hydrothermal system. The effort also resulted in high- resolution, co-registered sidescan sonar and bathymetric maps of the region where the eruption occurred.
In FY 96, the VENTS Program successfully deployed and then later recovered very high-quaity acoustic data from an array of VENTS hydrophones which were designed to augment the acoustic monitoring being conducted using the Navy's SOSUS hydrophone arrays. The VENTS hydrophones are currently deployed in the eastern equatorial Pacific where they are monitoring seismic and volcanic activity along the most active portion of the Earth s seafloor spreading center system.
VENTS physical oceanography studies focused on the central portion of the Juan de Fuca Ridge, revealed the patterns of deep circulation that transport plume water and hydrothermal effluent away from the vent sources and incorporate them into the regional ocean circulation. These studies showed that hydrothermal venting generates unstable eddies that detach from vent plumes and transport plume material up to at least 1000km away from the venting source.
A three-dimensional eddy simulation convection model was completed which is now being used to investigate hydrothermal dispersion processes and the distribution of chemical and thermal constituents in and around hydrothermal plumes in the benthic water column. The model is effective in evaluating methodologies adopted for the analysis of hydrographic field data from hydrothermal venting regions.
Field work during FY 96 included two oceanographic cruises to recover and redeploy bottom pressure recorders (BPRs) in the tsunami monitoring network. In addition, a coastal and Pacific island tide gauge dataset was collected for each of five small tsunamis generated in FY 96, and a deep ocean BPR time series of the February 17, 1996, Irian Jaya event was acquired off the U.W. west coast.
A report was published on the successful test deployment of a real-time reporting tsunami measurement system off the U.S. west coast.
A report was published on subtidal bottom pressure fluctuations at Axial Seamount, off the West Coast. These fluctuations are part of the background oceanographic signals upon which tsunamis occur, and also provide important information about barotropic processes in the vicinity of the Juan de Fuca Ridge.
Two reports were published that compared in-situ water level measurements, including BPR time series, with satellite altimeter sea level estimates. This work demonstrates the utility of Tsunami Project BPR measurements to studies of low-frequency sea level phenomena.
The Tsunami Hazard Mitigation Implementation Plan was completed in April 1996, and the first year funding of $2.375 million was appropriated to implement the plan as requested.
A proposal to the Defense Advanced Research Projects, entitled the Early Detection and Forecast of Tsunamis, was completed in August, and funding of $500K was approved for the first year tasks.
PMEL's Engineering Development Division supports PMEL research with innovations in elecronics, mechanics, materials, and sofware engineering. PMEL's measurement capabilities in the field and laboratory are enhanced by application of state-of-the-art instruments and systems that integrate observational and measurement technologies.
PMEL complements its research efforts through four cooperative institutes: the Joint Institute for Study of the Atmosphere and Ocean (JISAO), with the University of Washington; the Joint Institute for Marine and Atmospheric Research (JIMAR), with the University of Hawaii; Cooperative Institute for Arctic Research (CIFAR), with the University of Alaska; and the Cooperative Institute for Marine Resources Studies (CIMRS), with Oregon State University.
CO2 fluxes between air and water are poorly constrained because of lack of seasonal and geographic coverage of pCO2 (air-water disequilibrium) values and incomplete understanding of factors controlling the air-sea exchange. In addition to intensive monitoring of carbon parameters and parameters influencing pCO2 levels in surface water on dedicated cruises sponsored by OACES, PMEL, and AOML have outfitted the NOAA Ship Ka'imimoana with a new automated CO2 system to monitor surface water pCO2 on a continuous basis. While this effort has been a success we need more CO2 systems on NOAA ships to obtain the large area coverage. The new shipboard design (Fig. 2), patterned after the systems recently built at AOML and PMEL, uses stop-flow technology to reduce the amount of gas required for analysis by the LICOR detector. It will be improved to facilitate fully autonomous operation. The improvements will include automating draining of water traps, comprehensive self diagnostics by the program running the computer, and automatic rebooting capabilities of the system if errors are detected. The underway system will be an integrated package for measurement of pCO2 in air and water and support sensors necessary to reduce the data (such as equilibrator temperature, location, salinity, sea surface temperature, and barometric pressure). The comprehensive automated package will facilitate operations on ships of opportunity. The NOAA Ship Ka'imimoana, used to maintain the TAO moorings on six month intervals, offers an excellent opportunity to determine seasonal and secular trends in the region.
In addition to this activity, we will continue our pCO2 instrument development activities with the group at MBARI , directed by Francisco Chavez, to provide a suite of chemical and biological sensors deployed on the 155W and 170W TAO morring array in the equatorial Pacific in November of 1996. The work leverages on developmental efforts carried out by MBARI (with support from NOAA, NASA, and PMEL) over the past several years. The primary objectives of this project are: (1) to determine the relationships between physical forcing, primary production and the exchange of carbon dioxide between ocean and atmosphere; (2) to determine the biological and chemical responses to climatic and ocean variability in the equatorial Pacific; (3) to determine the spatial, seasonal and interannual variability in primary production, carbon dioxide, and nutrient distributions; and (4) to determine the spatial, seasonal and interannual variability of sea surface pigment distributions to groundtruth sattelite measurements of ocean color.
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