31 research outputs found
Ocean convergence and the dispersion of flotsam
Floating oil, plastics, and marine organisms are continually redistributed by ocean surface currents. Prediction of their resulting distribution on the surface is a fundamental, long-standing, and practically important problem. The dominant paradigm is dispersion within the dynamical context of a nondivergent flow: objects initially close together will on average spread apart but the area of surface patches of material does not change. Although this paradigm is likely valid at mesoscales, larger than 100 km in horizontal scale, recent theoretical studies of submesoscales (less than ∼10 km) predict strong surface convergences and downwelling associated with horizontal density fronts and cyclonic vortices. Here we show that such structures can dramatically concentrate floating material. More than half of an array of ∼200 surface drifters covering ∼20 × 20 km2 converged into a 60 × 60 m region within a week, a factor of more than 105 decrease in area, before slowly dispersing. As predicted, the convergence occurred at density fronts and with cyclonic vorticity. A zipperlike structure may play an important role. Cyclonic vorticity and vertical velocity reached 0.001 s−1 and 0.01 ms−1, respectively, which is much larger than usually inferred. This suggests a paradigm in which nearby objects form submesoscale clusters, and these clusters then spread apart. Together, these effects set both the overall extent and the finescale texture of a patch of floating material. Material concentrated at submesoscale convergences can create unique communities of organisms, amplify impacts of toxic material, and create opportunities to more efficiently recover such material
Ocean convergence and the dispersion of flotsam
Floating oil, plastics, and marine organisms are continually redistributed by ocean surface currents. Prediction of their resulting distribution on the surface is a fundamental, long-standing, and practically important problem. The dominant paradigm is dispersion within the dynamical context of a nondivergent flow: objects initially close together will on average spread apart but the area of surface patches of material does not change. Although this paradigm is likely valid at mesoscales, larger than 100 km in horizontal scale, recent theoretical studies of submesoscales (less than ∼10 km) predict strong surface convergences and downwelling associated with horizontal density fronts and cyclonic vortices. Here we show that such structures can dramatically concentrate floating material. More than half of an array of ∼200 surface drifters covering ∼20 × 20 km2 converged into a 60 × 60 m region within a week, a factor of more than 105 decrease in area, before slowly dispersing. As predicted, the convergence occurred at density fronts and with cyclonic vorticity. A zipperlike structure may play an important role. Cyclonic vorticity and vertical velocity reached 0.001 s−1 and 0.01 ms−1, respectively, which is much larger than usually inferred. This suggests a paradigm in which nearby objects form submesoscale clusters, and these clusters then spread apart. Together, these effects set both the overall extent and the finescale texture of a patch of floating material. Material concentrated at submesoscale convergences can create unique communities of organisms, amplify impacts of toxic material, and create opportunities to more efficiently recover such material
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Thin ice, deep snow and surface flooding in Kotzebue Sound: landfast ice mass balance during two anomalously warm winters and implications for marine mammals and subsistence hunting
The inaugural data from the first systematic program of sea ice observations in Kotzebue Sound, Alaska, in 2018 coincided with the first winter in living memory when the Sound was not choked with ice. The following winter of 2018-19 was even warmer and characterized by even less ice. Here we discuss the mass balance of landfast ice near Kotzebue (Qikiktagruk) during these two anomalously warm winters. We use in-situ observations and a 1-D thermodynamic model to address three research questions developed in partnership with an Indigenous Advisory Council. In doing so, we improve our understanding of connections between landfast ice mass balance, marine mammals, and subsistence hunting. Specifically, we show: i) Ice growth stopped unusually early due to strong vertical ocean heat flux, which also likely contributed to early start to bearded seal hunting; ii) Unusually thin ice contributed to widespread surface flooding. The associated snow ice formation partly offset the reduced ice growth, but the flooding likely had a negative impact on ringed seal habitat; iii) Sea ice near Kotzebue during the winters of 2017-18 and 2018-19 was likely the thinnest since at least 1945, driven by a combination of warm air temperatures and a persistent ocean heat flux.
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Codes and Data for "The Radiative and Geometric Properties of Melting First-Year Sea Ice", pre-submission
In May 2019, a series of observations of sea ice radiative properties were made over Kotzebue Sound, Alaska during the advanced stages of the Springtime melt. This archive contains the codes and data required to reproduce figures in a manuscript that will be submitted to the Journal of Geophysical Research: Oceans (a pre-submission draft PDF is included within the archive)
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The impact of rain on ocean surface waves and currents: Supporting information
Observational data and MATLAB codes used in the analysis described in "The impact of rain on ocean surface waves and currents" by N. J. M. Laxague & C. J. Zappa, Geophysical Research Letters (2020).
Data contents include time series of wind speed, rain rate, ocean surface wave spectrum, and near-surface current
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Data for: Observations of mean and wave orbital flows in the ocean's upper centimetres (version 1)
Observations of near-surface ocean currents, collected in 2008 in the Santa Barbara Channel. Archive contains a brief 'readme' file and two central MATLAB routines. The routines will grab the included raw data and make use of a small library of additional codes to reproduce key figures in "Observations of mean and wave orbital flows in the ocean's upper centimetres", Laxague & Zappa (2019), Journal of Fluid Mechanics.
See the note below for more information
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Supporting Data: Using Ship-Deployed High-Endurance Unmanned Aerial Vehicles for the Study of Ocean Surface and Atmospheric Boundary Layer Processes
Supporting Data for "Using Ship-Deployed High-Endurance Unmanned Aerial Vehicles for the Study of Ocean Surface and Atmospheric Boundary Layer Processes" Authors: Christopher J. Zappa, Scott M. Brown, Nathan J. M. Laxague, Tejendra Dhakal, Ryan A. Harris, and Ajit Subramaniam. Lamont-Doherty Earth Observatory of Columbia University
Each of the attached files contains the data used to generate the figures for Zappa et al. (2019). For example, 'Fig02_CT_Svalbard.mat' contains the surface brightness temperature time series used in Figure 2 of the aforementioned manuscript
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Data for: The impact of wind gusts on the ocean thermal skin layer
Data used for the analysis described in "The Impact of Wind Gusts on the Ocean Thermal Skin Layer" by Zappa et al. [2019], Geophysical Research Letters (DOI: 10.1002/2019GL083687)
Contents: water surface and sky brightness temperature, wind speed/stress, and mean gust/thermal front propagation speeds. README file within archive provides breakdown of all constituent elements
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Codes and Data for "The Radiative and Geometric Properties of Melting First-Year Sea Ice", v2
In May 2019, a series of observations of sea ice radiative properties were made over Kotzebue Sound, Alaska during the advanced stages of the Springtime melt. This archive contains the codes and data required to reproduce figures in a manuscript that has been accepted at The Cryosphere (EGUSPHERE-2023-2541)
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Data for: The Suppression of Ocean Waves by Spatially Heterogeneous Biogenic Slicks
This dataset includes results obtained from an oceanographic field campaign performed in the East Timor Sea and Western Equatorial Pacific during Autumn 2016. We observed the water surface slope field and surface concentrations of biochemical quantities connected to surface wave damping. The ZIP archive also includes codes for producing graphics from the processed observational data