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Eric D'Asaro

Senior Principal Oceanographer

Professor, Oceanography

Email

dasaro@apl.washington.edu

Phone

206-685-2982

Research Interests

Physical oceanography, internal waves, air-sea interaction, upper ocean dynamics, Arctic oceanography, ocean instrumentation

Biosketch

Dr. D'Asaro's research spans a wide number of environments from upper ocean mixed layers to nearshore coastal fronts to fjords to deep convection. It retains studies of turbulence and internal waves, but has increasingly moved toward understanding the role of these ocean mixing processes in controlling biochemical processes in the ocean, especially gas exchange and biological productivity. By measuring big signals, like hurricanes or major blooms, it is easier to unravel the underlying processes because the signal to noise is high.

For the past 20 years, D'Asaro has focused on exploiting the unique capabilities of "Lagrangian Floats", a class of instruments that try to accurately follow the three dimensional motion of water parcels particularly in regions of strong mixing. This turns out to be a novel but effective way to measure turbulence in regions of strong mixing.

Lagrangian techniques have not been used very much in measuring mixing and turbulence. Accordingly one of the more exciting aspects of this work is learning how to use Lagrangian floats in the ocean. This understanding draws both upon basic ideas in fluid mechanics and upon understanding of mixing in the ocean. It strongly influences float design, use, and the oceanographic problems studied. The work thus spans a wide range of topics, from fluid mechanics to oceanography to engineering. That makes it particularly fun and interesting.

Chemical species in the ocean and many microbial plants and animals drift with the ocean currents. Floats mimic this behavior, making them excellent platforms for studying aspects of ocean chemistry and biology. There is an ongoing revolution in these fields as electronic sensors become capable of making measurements formerly possible only in the laboratory. Floats equipped with such sensors are potentially very powerful tools. Dr. D'Asaro works to realize this potential, which is especially challenging and interesting as he collaborates with ocean biologists and chemists to design and operate multidisciplinary floats.

Department Affiliation

Ocean Physics

Education

B.A. Physics, Harvard University, 1976

M.S. Applied Physics, Harvard University, 1976

Ph.D. Oceanography, MIT/WHOI, 1980

Projects

Air–Sea Momentum Flux in Tropical Cyclones

The intensity of a tropical cyclone is influenced by two competing physical processes at the air–sea interface. It strengthens by drawing thermal energy from the underlying warm ocean but weakens due to the drag of rough ocean surface. These processes change dramatically as the wind speed increases above 30 m/s.

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30 Mar 2018

The project is driven by the following science questions: (1) How important are equilibrium-range waves in controlling the air-sea momentum flux in tropical cyclones? We hypothesize that for wind speeds higher than 30 m/s the stress on the ocean surface is larger than the equilibrium-range wave breaking stress. (2) How does the wave breaking rate vary with wind speed and the complex surface wave field? At moderate wind speeds the wave breaking rate increases with increasing speed. Does this continue at extreme high winds? (3) Can we detect acoustic signatures of sea spray at high winds? Measurements of sea spray in tropical cyclones are very rare. We will seek for the acoustic signatures of spray droplets impacting the ocean surface. (4) What are the processes controlling the air-sea momentum flux?

Salinity Processes in the Upper Ocean Regional Study — SPURS

The NASA SPURS research effort is actively addressing the essential role of the ocean in the global water cycle by measuring salinity and accumulating other data to improve our basic understanding of the ocean's water cycle and its ties to climate.

15 Apr 2015

Lateral Mixing

Small scale eddies and internal waves in the ocean mix water masses laterally, as well as vertically. This multi-investigator project aims to study the physics of this mixing by combining dye dispersion studies with detailed measurements of the velocity, temperature and salinity field during field experiments in 2011 and 2012.

1 Sep 2012

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Videos

EXPORTS: Export Processes in the Ocean from RemoTe Sensing

The EXPORTS mission is to quantify how much of the atmospheric carbon dioxide fixed during primary production near the ocean surface is pumped to the deep twilight zone by biological processes, where it can be sequestered for months to millennia.

An integrated observation strategy leverages the precise, intense measurements made on ships, the persistent subsurface data collected by swimming and floating robots, and the global surface views provided by satellites.

18 Sep 2018

Lagrangian Submesoscale Experiment — LASER

A science team led by Eric D'Asaro conducted a unique mission to deploy over 1,000 ocean drifters in a small area of the Gulf of Mexico. The real-time data collected from the biodegradable drifters recalibrated understanding of ocean currents.

22 Jan 2018

Eddies Drive Particulate Carbon Deep in the Ocean During the North Atlantic Spring Bloom

The swirling eddies that create patches of stratification to hold phytoplankton near the sunlit surface during the North Atlantic spring bloom, also inject the floating organic carbon particles deep into the ocean. The finding, reported in Science, has important implications for the ocean's role in the carbon cycle on Earth: phytoplankton use carbon dioxide absorbed by the ocean from the atmosphere during the bloom and the resulting organic carbon near the sea surface is sequestered in the deep ocean.

27 Mar 2015

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Publications

2000-present and while at APL-UW

Shear flow instabilities and unstable events over the north Bay of Bengal

Jampana, V., M. Ravichandran, D. Sengupta, E.A. D'Asaro, H. Rahaman, S. Joseph, J. Sreelekha, and D. Chaudhuri, "Shear flow instabilities and unstable events over the north Bay of Bengal," J. Geophys. Res., 123, 8958-8969, doi:10.1029/2017JC013272, 2018.

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1 Dec 2018

A year‐long mooring data are used to study the upper ocean unstable events and instabilities at 18°N 89°E, which is a climatologically important region in the North Bay of Bengal. Near‐surface stability is studied from the context of the buoyancy frequency normalized shear (Vz/N) and reduced shear (S2–4N2) which are convenient measures to quantify flow stability, compared to the more widely used Richardson number (Ri). The analysis is carried out across three contrasting time periods, the monsoon, postmonsoon, and the winter of year 2012. Although it is well known that the flow stability changes from stable to unstable at Ri = Ricr=0.25, the relative importance of the perturbations of shear and buoyancy frequency in driving the unstable events is not well studied over the open oceans and more particularly over the Bay of Bengal. At 18°N, 89°E both higher than average shear and lower than average buoyancy frequency perturbations are crucial in driving the unstable events during the summer and premonsoon period. However, at increasing depths, the influence of shear perturbations becomes more dominant. Invoking the Miles–Howard criteria for flow instability, it is seen that during the postmonsoon period, the buoyancy frequency perturbations are more critical than shear perturbations in driving the unstable events. In winter, the unstable events are influenced by both the buoyancy frequency and shear perturbations.

A gas tension device for the mesopelagic zone

Reed, A., C. McNeil, E. D'Asaro, M. Altabet, A. Bourbonnais, and B. Johnson, "A gas tension device for the mesopelagic zone," Deep Sea Res. 1, 139, 68-78, doi:10.1016/j.dsr.2018.07.007, 2018.

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1 Sep 2018

Highlights

- A new gas tension device (GTD) improves on previous designs of GTDs.

- The new GTD can operate up to 1000 m depth with no pressure dependency.

- Two GTDs successfully measured total dissolved gases in an Oxygen Minimum Zone.

- The GTDs were accurate to ±0.6% compared with independent dissolved gas data.

A multi-method autonomous assessment of primary productivity and export efficiency in the springtime North Atlantic

Briggs, N., K. Guðmundsson, I. Cetinić, E. D'Asaro, E. Rehm, C. Lee, and M.J. Perry, "A multi-method autonomous assessment of primary productivity and export efficiency in the springtime North Atlantic," Biogeiosciences, 15, 4515-4532, doi:10.5194/bg-15-4515-2018, 2018.

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25 Jul 2018

Fixation of organic carbon by phytoplankton is the foundation of nearly all open-ocean ecosystems and a critical part of the global carbon cycle. But the quantification and validation of ocean primary productivity at large scale remains a major challenge due to limited coverage of ship-based measurements and the difficulty of validating diverse measurement techniques. Accurate primary productivity measurements from autonomous platforms would be highly desirable due to much greater potential coverage. In pursuit of this goal we estimate gross primary productivity over 2 months in the springtime North Atlantic from an autonomous Lagrangian float using diel cycles of particulate organic carbon derived from optical beam attenuation. We test method precision and accuracy by comparison against entirely independent estimates from a locally parameterized model based on chlorophyll a and light measurements from the same float. During nutrient-replete conditions (80% of the study period), we obtain strong relative agreement between the independent methods across an order of magnitude of productivities (r2 = 0.97), with slight underestimation by the diel cycle method (–19±5%). At the end of the diatom bloom, this relative difference increases to –58% for a 6-day period, likely a response to SiO4 limitation, which is not included in the model. In addition, we estimate gross oxygen productivity from O2 diel cycles and find strong correlation with diel-cycle-based gross primary productivity over the entire deployment, providing further qualitative support for both methods. Finally, simultaneous estimates of net community productivity, carbon export, and particle size suggest that bloom growth is halted by a combination of reduced productivity due to SiO4 limitation and increased export efficiency due to rapid aggregation. After the diatom bloom, high Chl a-normalized productivity indicates that low net growth during this period is due to increased heterotrophic respiration and not nutrient limitation. These findings represent a significant advance in the accuracy and completeness of upper-ocean carbon cycle measurements from an autonomous platform.

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In The News

NASA, NSF expedition to study ocean carbon embarks in August from Seattle

UW News, Hannah Hickey

Dozens of scientists, as well as underwater drones and other high-tech ocean instruments, will set sail from Seattle in mid-August. Funded by NASA and the National Science Foundation, the team will study the life and death of the small organisms that play a critical role in removing carbon dioxide from the atmosphere, and in the ocean’s carbon cycle.

21 Jun 2018

Scientists watch ocean plastic hotspots form in real time

NewsDeeply, Erica Cirino

Researchers tracked hundreds of buoys deployed in the Gulf of Mexico. Not only did the buoys not spread out – many concentrated into an area the size of a football stadium. The findings may help scientists pinpoint areas for plastic or oil-spill cleanup.

6 Feb 2018

Temporary 'bathtub drains' in the ocean concentrate flotsam

UW News, Hannah Hickey

An experiment featuring the largest flotilla of sensors ever deployed in a single area provides new insights into how marine debris, or flotsam, moves on the surface of the ocean.

18 Jan 2018

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Inventions

Open Water Detection from Beneath Sea Ice

Record of Invention Number: 47655

Eric D'Asaro, Andrey Shcherbina

Disclosure

16 Mar 2016

Acoustics Air-Sea Interaction & Remote Sensing Center for Environmental & Information Systems Center for Industrial & Medical Ultrasound Electronic & Photonic Systems Ocean Engineering Ocean Physics Polar Science Center
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