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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.
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A Simple Model for Multiple Equilibria in Ice-Covered Oceans
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.
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- Award ID(s):
- 2211691
- PAR ID:
- 10542690
- Publisher / Repository:
- American Meteorological Society
- Date Published:
- Journal Name:
- Journal of Physical Oceanography
- Volume:
- 54
- Issue:
- 10
- ISSN:
- 0022-3670
- Format(s):
- Medium: X Size: p. 2087-2097
- Size(s):
- p. 2087-2097
- Sponsoring Org:
- National Science Foundation
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