1,721,025 research outputs found
Calypso hydrographic data
No full text<p>Data for "3D-intrusions transport active surface microbial assemblages to the dark ocean"</p>
The impact of submesoscales on the stratification dynamics in the Southern Ocean
No full textSubmesoscale dynamics O(1-10 km, hours to days) are considered to strongly affect the stratification of the upper ocean. In the Southern Ocean, studies of submesoscale dynamics are biased to regions preconditioned for strong frontal activity and topographical influence. This dissertation considers the role of submesoscales on the evolution of mixed layer depth and upper ocean stratification in the open-ocean Subantarctic Ocean. First, we present autonomous ocean glider measurements from spring to late-summer to show that transient increases in stratification within the mixed layer during spring result in rapid mixed layer shoaling events. A realistically-forced simulation using a one-dimensional mixed layer model fails to explain these observed stratification events. We show that during this time, baroclinic mixed layer instabilities periodically induce a restratification flux of over 1000 W. m2, suggesting that the unexplained restratification is likely a result of submesoscale flows. Second, we study four separate years of seasonal-length (mid-winter to latesummer) glider experiments to define how submesoscale flows may induce interannual variations in the onset of spring/summer mixed layer restratification. Sustained temporal increases of stratification above the winter mixed layer, which defines the onset of seasonal restratification, can differ by up to 28 days between the four years studied. To explain this discrepancy, equivalent heat fluxes of baroclinic mixed layer instabilities (restratification) and Ekman buoyancy flux (restratification or mixing) are parameterized into a one-dimensional mixed layer model. Simulations including the parameterizations reveal a seasonal evolution of mixed layer stratification which is significantly more comparable to the glider observations than model simulations using heat and freshwater fluxes alone. Furthermore, the parameterization dramatically improves the sub-seasonal variability of mixed layer stratification, particularly during the onset of seasonal restratification when the mixed layer remains deep despite a positive surface heat flux. Following this, we characterize the full seasonal cycle of submesoscale flows using a realistically-forced 1/36 NEMO simulation of the Atlantic Southern Ocean. We show that deep winter mixed layers enhance the upper ocean available potential energy, which through the release of baroclinic mixed layer instabilities drive increased vertical buoyancy flux and potential to kinetic energy. These processes are associated with strong vertical velocities within the mixed layer characterized by large instantaneous upwelling and downwelling fluxes at the location of fronts. The insights from the glider observations propose that baroclinic mixed layer instabilities lead to increased near surface restratification in winter to spring, but are regulated by the synoptic-scale increases in Ekman buoyancy flux, which can keep the mixed layer deep for up to a month after surface warming. We propose the balance between restratification by baroclinic mixed layer instabilities and strong Ekman buoyancy flux driven by the passing of Southern Ocean storms is key in setting the large inter-annual variations of seasonal mixed layer restratification in the Subantarctic Ocean. Finally, we constrain the ability of gliders to represent regional submesoscale dynamics to provide context to current observations and inform future field work operations. Virtual gliders simulated within the 1/36 simulation show that horizontal buoyancy gradients in the Subantarctic are largely isotropic. We show that increasing the number of gliders sampling simultaneously over one month from one to a swarm of six results in improving the representation of the total distribution of horizontal buoyancy gradients across the Subantarctic from 10% to 42%. Similarly, by having a single glider sampling for six consecutive months, the distribution of horizontal buoyancy gradients observed increases to 47% of the total distribution. The insights presented in this dissertation enhance our understanding of submesoscale flows in the open-ocean Southern Ocean. These results are likely to have direct implications for physical and biological processes related to the ocean’s role on climate
Reconstructing the Ocean's Interior from Surface Data
Full text linkA new method is proposed for extrapolating subsurface velocity and density fields from sea surface density and sea surface height (SSH). In this, the surface density is linked to the subsurface fields via the surface quasigeostrophic (SQG) formalism, as proposed in several recent papers. The subsurface field is augmented by the addition of the barotropic and first baroclinic modes, whose amplitudes are determined by matching to the sea surface height (pressure), after subtracting the SQG contribution. An additional constraint is that the bottom pressure anomaly vanishes. The method is tested for three regions in the North Atlantic using data from a high-resolution numerical simulation. The decomposition yields strikingly realistic subsurface fields. It is particularly successful in energetic regions like the Gulf Stream extension and at high latitudes where the mixed layer is deep, but it also works in less energetic eastern subtropics. The demonstration highlights the possibility of reconstructing three-dimensional oceanic flows using a combination of satellite fields, for example, sea surface temperature (SST) and SSH, and sparse (or climatological) estimates of the regional depth-resolved density. The method could be further elaborated to integrate additional subsurface information, such as mooring measurements.United States. National Aeronautics and Space Administration (NNX12AD47G)National Science Foundation (U.S.) (OCE 0928617)National Science Foundation (U.S.) (OCE-0752346
How the source depth of coastal upwelling relates to stratification and wind
Full text linkAuthor Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 126(12), (2021): e2021JC017621, https://doi.org/10.1029/2021JC017621.Wind-driven coastal upwelling is an important process that transports nutrients from the deep ocean to the surface, fueling biological productivity. To better understand what affects the upward transport of nutrients (and many other properties such as temperature, salinity, oxygen, and carbon), it is necessary to know the depth of source waters (i.e., “source depth”) or the density of source waters (“source density”). Here, we focus on the upwelling driven by offshore Ekman transport and present a scaling relation for the source depth and density by considering a balance between the wind-driven upwelling and eddy-driven restratification processes. The scaling suggests that the source depth varies as (τ/N)1/2, while the source density goes as (τ1/2N3/2), where τ is the wind stress and N is the stratification. We test these relations using numerical simulations of an idealized coastal upwelling front with varying constant wind forcing and initial stratification, and we find good agreement between the theory and numerical experiments. This work highlights the importance of considering stratification in wind-driven upwelling dynamics, especially when thinking about how nutrient transport and primary production of coastal upwelling regions might change with increased ocean warming and stratification.This work was funded by the ONR grant N00014-17-1-2390, and J. He was supported by the NASA FINESST award 80NSSC19K1350.2022-05-2
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Decomposition of vertical velocity for nutrient transport in the upper ocean
Full text linkAuthor Posting. © American Meteorological Society, 2019. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 49(6), (2019): 1561-1575, doi:10.1175/JPO-D-19-0002.1.Within the pycnocline, where diapycnal mixing is suppressed, both the vertical movement (uplift) of isopycnal surfaces and upward motion along sloping isopycnals supply nutrients to the euphotic layer, but the relative importance of each of these mechanisms is unknown. We present a method for decomposing vertical velocity w into two components in a Lagrangian frame: vertical velocity along sloping isopycnal surfaces and the adiabatic vertical velocity of isopycnal surfaces . We show that , where is the isopycnal slope and is the geometric aspect ratio of the flow, and that accounts for 10%–25% of the total vertical velocity w for isopycnal slopes representative of the midlatitude pycnocline. We perform the decomposition of w in a process study model of a midlatitude eddying flow field generated with a range of isopycnal slopes. A spectral decomposition of the velocity components shows that while is the largest contributor to vertical velocity, is of comparable magnitude at horizontal scales less than about 10 km, that is, at submesoscales. Increasing the horizontal grid resolution of models is known to increase vertical velocity; this increase is disproportionately due to better resolution of , as is shown here by comparing 1- and 4-km resolution model runs. Along-isopycnal vertical transport can be an important contributor to the vertical flux of tracers, including oxygen, nutrients, and chlorophyll, although we find weak covariance between vertical velocity and nutrient anomaly in our model.MAF was supported by a National Defense Science and Engineering Graduate Fellowship and AM by NSF OCE-I434788. The authors thank Glenn Flierl and Ruth Curry for helpful conversations, and three anonymous reviewers for comments that improved the manuscript.2020-06-1
Dynamics and variability of the Subantarctic mixed-layer as determined from a high resolution glider dataset
No full textTraditional understanding of mixed-layer (ML) dynamics in the African sector of the Southern Ocean suggests that seasonal summer stratification and subsequent reduction in ML depth (MLD) is determined by the onset of a positive net heat ux. The impact of physical forcing mechanisms on the intra-seasonal variability of the ML is still relatively unknown. Recent research in the North Atlantic has highlighted the role that sub-mesoscale ML eddy dynamics has on ML stratification. It is now understood that large horizontal density gradients drive sub-mesoscale eddy formation which have been shown to result in the early onset of spring phytoplankton blooms at high latitudes. To date these ML eddies have been researched primarily in models with few observational studies available. To test the ML eddy hypothesis in the Subantarctic Zone (SAZ) we use high-resolution (~3km, 4-hourly) glider measurements between austral spring to late summer
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
- …
