An official website of the United States government
We contend that ocean turbulent fluxes should be included in the list of Essential Ocean Variables (EOVs) created by the Global Ocean Observing System. This list aims to identify variables that are essential to observe to inform policy and maintain a healthy and resilient ocean. Diapycnal turbulent fluxes quantify the rates of exchange of tracers (such as temperature, salinity, density or nutrients, all of which are already EOVs) across a density layer. Measuring them is necessary to close the tracer concentration budgets of these quantities. Measuring turbulent fluxes of buoyancy (Jb), heat (Jq), salinity (JS) or any other tracer requires either synchronous microscale (a few centimeters) measurements of both the vector velocity and the scalar (e.g., temperature) to produce time series of the highly correlated perturbations of the two variables, or microscale measurements of turbulent dissipation rates of kinetic energy (ϵ) and of thermal/salinity/tracer variance (χ), from which fluxes can be derived. Unlike isopycnal turbulent fluxes, which are dominated by the mesoscale (tens of kilometers), microscale diapycnal fluxes cannot be derived as the product of existing EOVs, but rather require observations at the appropriate scales. The instrumentation, standardization of measurement practices, and data coordination of turbulence observations have advanced greatly in the past decade and are becoming increasingly robust. With more routine measurements, we can begin to unravel the relationships between physical mixing processes and ecosystem health. In addition to laying out the scientific relevance of the turbulent diapycnal fluxes, this review also compiles the current developments steering the community toward such routine measurements, strengthening the case for registering the turbulent diapycnal fluxes as an pilot Essential Ocean Variable.
more »
« less
A Refractometer for Measuring Thermohaline Density Microstructure in the Ocean
Abstract Here, we report an optical sensor for measuring millimeter-scale thermohaline density variations in the ocean. The instrument is based on a fiber Fabry–Perot white light interferometer, which can resolve the refractive index of water to better than 2 × 10−8within a sample volume smaller than 1 mm3at a sample rate of 500 Hz. This equates to detectable Absolute Salinity variations of 0.0001 g kg−1, temperature variations smaller than 0.0007°C, and density variations of 0.000 07 kg m−3. Data collected from laboratory characterization and a field deployment suggest the sensor could be useful as a gradiometer for measuring diapycnal mixing down to submillimeter scales. While obtaining high absolute accuracy in refractive index and density was not a primary consideration, the sensor was designed with such an eventual goal in mind, and various aspects of achieving it are discussed. Significance StatementAccurately measuring and modeling ocean salinity at the smallest scales remains an unsolved problem in oceanography. Such measurements would be beneficial to fully understand the vertical transport of heat and salt in the ocean, the effects of melting Arctic ice, and overall oceanic mixing. By achieving very high-resolution refractive index measurements at millimeter spatial scales, the in situ sensor technology reported here could begin to address these challenges.
more »
« less
- Award ID(s):
- 2123241
- PAR ID:
- 10644739
- Publisher / Repository:
- American Meteorological Society
- Date Published:
- Journal Name:
- Journal of Atmospheric and Oceanic Technology
- Volume:
- 42
- Issue:
- 11
- ISSN:
- 0739-0572
- Format(s):
- Medium: X Size: p. 1369-1379
- Size(s):
- p. 1369-1379
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract The Indonesian seas, with their complex passages and vigorous mixing, constitute the only route and are critical in regulating Pacific–Indian Ocean interchange, air–sea interaction, and global climate events. Previous research employing remote sensing and numerical simulations strongly suggested that this mixing is tidally driven and localized in narrow channels and straits, with only a few direct observations to validate it. The current study offers the first comprehensive temporal microstructure observations in the south of Lombok Strait with a radius of 0.05° and centered on 115.54oE and 9.02oS. Fifteen days of tidal mixing observations measured potential temperature and density, salinity, and turbulent energy dissipation rate. The results revealed significant mixing and verified the remotely sensed technique. The south Lombok temporal and depth averaged of the turbulent kinetic energy dissipation rate, and the diapycnal diffusivity from 20 to 250 m are$$\varepsilon$$ = 4.15 ± 15.9) × 10–6W kg–1and$$K\rho$$ = (1.44 ± 10.7) × 10–2m2s–1, respectively. This$$K\rho$$ is up to 104times larger than the Banda Sea [$$K\rho$$ = (9.2 ± 0.55) × 10–6m2s–1] (Alford et al. Geophys Res Lett 26:2741–2744, 1999) or the “open ocean”$$K\rho$$ = 0.03 × 10–4 m2s−1within 2° of the equator to (0.4–0.5) × 10–4m2s−1at 50°–70° (Kunze et al. J Phys Oceanogr 36:1553–1576, 2006). Therefore, nonlinear interactions between internal tides, tidally induced mixing, and ITF plays a critical role regulating water mass transformation and have strong implications to longer-term variations and change of Pacific–Indian Ocean water circulation and climate.more » « less
-
Abstract Diel variations in oxygen concentration have been extensively used to estimate rates of photosynthesis and respiration in productive freshwater and marine ecosystems. Recent improvements in optical oxygen sensors now enable us to use the same approach to estimate metabolic rates in the oligotrophic waters that cover most of the global ocean and for measurements collected by autonomous underwater vehicles. By building on previous methods, we propose a procedure to estimate photosynthesis and respiration from vertically resolved diel measurements of oxygen concentration. This procedure involves isolating the oxygen variation due to biological processes from the variation due to physical processes, and calculating metabolic rates from biogenic oxygen changes using linear least squares analysis. We tested our method on underwater glider observations from the surface layer of the North Pacific Subtropical Gyre where we estimated rates of gross oxygen production and community respiration both averaging 1.0 mmol O2m−3d−1, consistent with previous estimates from the same environment. Method uncertainty was computed as the standard deviation of the fitted parameters and averaged 0.6 and 0.5 mmol O2m−3d−1for oxygen production and respiration, respectively. The variability of metabolic rates was larger than this uncertainty and we were able to discern covariation in the biological production and consumption of oxygen. The proposed method resolved variability on time scales of approximately 1 week. This resolution can be improved in several ways including by measuring turbulent mixing, increasing the number of measurements in the surface ocean, and adopting a Lagrangian approach during data collection.more » « less
-
Abstract The existence of multiple equilibria (ice-covered and ice-free states) is explored using a set of coupled, nondimensional equations that describe the heat and salt balances in basins, such as the Arctic Ocean, that are subject to atmospheric forcing and two distinct water mass sources. Six nondimensional numbers describe the influences of atmospheric cooling, evaporation minus precipitation, solar radiation, atmospheric temperature, diapycnal mixing, and the temperature contrast between the two water masses. It is shown that multiple equilibria resulting from the dependence of albedo on ice cover exist over a wide range of parameter space, especially so in the weak mixing limit. Multiple equilibria can also occur if diapycnal mixing increases toO(10−4) m2s−1or larger under ice-free conditions due to enhanced upward mixing of warm, salty water from below. Sensitivities to various forcing parameters are discussed. Significance StatementThe purpose of this study is to better understand under what circumstances high-latitude seas, such as the Arctic Ocean, can exist in either an ice-covered or an ice-free state. The temperature and salinity of the ocean, as well as the heat exchange with the atmosphere, are drastically different depending on which state the ocean is in. The theory presented here identifies how forcing from the atmosphere and ocean dynamics determines whether the ocean is ice covered, ice free, or possibly either one.more » « less
-
Abstract The Arctic Ocean is experiencing a net loss of sea ice. Ice-free Septembers are predicted by 2050 with intensified seasonal melt and freshening. Accurate carbon dioxide uptake estimates rely on meticulous assessments of carbonate parameters including total alkalinity. The third largest contributor to oceanic alkalinity is boron (as borate ions). Boron has been shown to be conservative in open ocean systems, and the boron to salinity ratio (boron/salinity) is therefore used to account for boron alkalinity in lieu of in situ boron measurements. Here we report this ratio in the marginal ice zone of the Bering and Chukchi seas during late spring of 2021. We find considerable variation in born/salinity values in ice cores and brine, representing either excesses or deficits of boron relative to salinity. This variability should be considered when accounting for borate contributions to total alkalinity (up to 10 µmol kg−1) in low salinity melt regions.more » « less
