Sustaining Ocean Observations to Understand Future Changes in Earth's Climate (2017) / Chapter Skim
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2 Collection and Use of Sustained Ocean Climate Observations
2 Collection and Use of Sustained Ocean Climate Observations
Pages 27-58
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From page 27... ...
This chapter describes the ocean observations necessary to close the heat, carbon, and fresh water budgets, drawing on work conducted at the international level to develop specifications for a global network of observing platforms collecting priority ocean data (described further in Chapter 3)
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This section briefly describes the ocean observations that have led to improved understanding of these budgets, illustrates changes based on collected data, and identifies key knowledge gaps where increased observational efforts are required to close the budgets globally. Closing these budgets has been identified as a priority in national and international global ocean observing planning and climate research programs (US CLIVAR, 2013; Benway et al., 2016; GCOS, 2016)
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(pilot) having 1 or more BGC Global sensors Global Ocean Ship- Full ocean depth, 61 lines (54 core, and 19 lines Regional Heat based Hydrographic decadal repeating 7 associated lines NOAA/OOMD funds Global Carbon Investigations Program hydrographic transects with greater sampling NOAA/PMEL and AOML.
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Automated Shipboard Atmospheric profiles No U.S. participation Regional Heat Aerological Programme with balloons launched by about 20 ships, mainly North Atlantic Ship of Opportunity Approximately 15,000 NOAA/AOML and SIO Regional Heat Program (SOOP)
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Many U.S. institutions Fresh water Fixed Platform 103 9 Regional Heat Fresh water Ice Buoy 23 4 Regional Heat Fresh water Metocean Moored Buoy 379 209 Regional Heat Fresh water Tsunameter 35 28 Regional Heat Fresh water Coastal and regional Buoys, tide gauges, 14 GOOS Regional Integrated Ocean Regional Heat GOOS systems radar stations, gliders alliances Observing System (IOOS)
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From page 32... ...
On a regional basis, closure of the heat budget requires observations of ocean heat content, airsea heat exchange, heat transport by ocean currents, and mixing, while the global balance is between the global integrals of heat gain and air-sea flux. The challenge for ocean observing has not been simply that of making accurate temperature measurements (present shipboard instruments can measure to
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From page 33... ...
Although surface drifters and commercial and research ships provide in situ temperature observations near the ocean surface and satellite remote sensing provides spatial coverage by mapping sea surface temperature, the need for temperature observations at depth has been identified as a crucial measurement to account for heat movement and storage in deeper layers of the ocean. Prior to 2004, temperature profiles were collected by ships, either lowering instruments that recorded temperature as a function of depth (CTDs, which measure conductivity, temperature, and depth)
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Other advancements in deep ocean observations include the addition of temperature sensors to existing moorings at depths greater than 2,000 m, which adds high temporal resolution of deep temperature variability to complement the Deep Argo program. To further enhance the value of the Argo program, sampling is planned to be extended into previously unsampled waters, including icecovered and newly ice-free polar regions.
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This research and development feeds into the overall context for sustained ocean observing and may in time demonstrate observing methods suited to sustained use. For now, it is important to work not only toward this but also to build understanding of all contributions to the heat budget.
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. These observations provide strong support for theory and models of CO2 exchange with the ocean and are an essential component to understanding climate change and the global carbon budget.
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, which specifies data quality control standards and provides data access. SOCCOM (Southern Ocean Carbon and Climate Observations and Modeling)
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With these improved capabilities and increased deployments that expand spatial coverage to the entire globe, understanding of the carbon budget will be enhanced and better predictions of how much CO2 will be dissolved into the ocean versus remain in the atmosphere can be made. Significant international coordination and financial resources will be needed to achieve this observational network expansion.
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As with the heat budget, some processes in the carbon budget that influence carbon transport, are not yet routinely observable; and ocean research and process studies are important to build the understanding and capabilities needed to enable sustained observing of these processes. Fresh Water Budget The ocean holds about 97 percent of the water on Earth (Gleick, 1996)
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(d) The climatological mean surface salinity (PSS78)
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Higher density water created at high latitudes, especially in the Antarctic and subpolar North Atlantic, spreads through the deep oceans, returning to the sea surface through both wind-driven upwelling in the Southern Ocean and through downward mixing (diffusion) of heat in the warm low latitudes.
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The transfer of cold surface water (which absorbs more CO2 than warm surface water) to the deep ocean transfers CO2 absorbed at the surface to the deep ocean, where it is "stored" away from exchange with the atmosphere, as evident in the large inven tory of anthropogenic carbon in the North Atlantic where deep water formation is especially vigorous (Figure 2.3)
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From page 43... ...
Additional studies have challenged the notion of a simple Atlantic "con veyor belt" (e.g., Bower et al., 2009; Mielke et al., 2013; Wunsch and Heimbach, 2013) , including its deficiencies in depicting the global overturning circulation that includes the Southern Ocean (See Figure and Marshall and Speer, 2012; Talley, 2013)
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. Variability in the strength of the overturning circulation influences sea surface temperature and subsequent weather patterns, sea-ice extent, and carbon storage, and is therefore critical for improving our understanding of the climate system and anticipating future changes in Earth's climate.
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. Thus, discussion of sea level and the observations needed to improve our understanding and predictive capabilities for future change provides a complement to the previous discussions of heat, carbon, and fresh water budgets, particularly since ocean heat and mass changes affect sea level.
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FIGURE 2.6 (Black) Monthly averaged global mean sea level observed by satellite altimeters (1993–2016)
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Monitoring the sea surface height, the ocean circulation, changes of land-ice masses and vertical land motion, and air-sea fluxes of heat, fresh water, and momentum all contribute to improved understanding of pro
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Trends were calculated using tide gauge data from the University of Hawaii Sea Level Center Fast-Delivery database, and Ssalto/Duacs altimeter products that were produced and distributed by the E.U. Copernicus Marine and Environment Monitoring Service.
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Remote sensing methods provide incomparable spatial coverage that complements in situ sampling. Key ocean observations made from satellites include sea surface height, surface winds, sea surface temperature, sea surface salinity, ocean bottom pressure, sea state (surface waves and swell)
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. Ocean observations similarly have become essential for constraining the ocean component of these forecast models, for stand-alone systems in operational oceanography (Edwards et al., 2015; Martin et al., 2015)
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Argo profiling floats measure temperature and salinity profiles, which are used to calculate sea water density. Incorporating satellite measurements of sea surface height (altimetry)
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(2005) provides compelling examples on how combined sea surface temperature (SST)
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Future research depends on a healthy and sustained ocean observation system. The data and products from the ocean climate observing system have also enabled services provided by private companies in multiple sectors such as marine forecasts for shipping, seasonal forecasts for agriculture and water resource management, and tailored services based on sea surface temperature and other factors for commercial fisheries operations.
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TECHNOLOGY CHALLENGES OF OCEAN CLIMATE OBSERVING Although great progress in ocean observing has been made, many technological and computational challenges remain and new obstacles are likely to arise as systems expand and new data needs emerge. The observing system deployed to collect in situ ocean climate observations exists in the context of the Earth observing system, which is the combination of in situ and remote sensing observations, and in the context of model-based syntheses and predictions.
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The inherent challenges to sustaining ocean observing in the wideranging and physically harsh environment of the ocean can be overcome with these advances in technology, but ultimately require prioritization and sustained investments in these efforts. FUTURE EVOLUTION OF THE OCEAN CLIMATE OBSERVING SYSTEM Building and improving our understanding of climate requires continued and expanded observations of the ocean that are adaptable over time to address emerging opportunities and data needs.
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In particular, nonphysical sensors that measure nutrients, pH, biomass of oceanic organisms, dissolved oxygen, fluorescence, optical properties, and genetic material have reached or are reaching technical readiness for inclusion in the sustained ocean observing system (Riser et al., 2016)
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National and international research programs have foci on assessing the efficacy of basin-scale observing (e.g., AtlantOS in Europe) and on the ability of the observing system to quantify key processes such as basin-scale meridional overturning in the Atlantic (e.g., AMOC)
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