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Author Xu, X. ; Chassignet, E.P., Wang, F.
Title On the variability of the Atlantic meridional overturning circulation transports in coupled CMIP5 simulations Type $loc['typeJournal Article']
Year 2018 Publication Climate Dynamics Abbreviated Journal Clim Dyn.
Volume 51
Issue 11
Pages 6511-6531
Keywords NAO-AMOC ; CMIP5 ; NAO index ; AMOC index ; meridional pressure gradient ; magnitude ; structure change of the NAO.
Abstract The Atlantic meridional overturning circulation (AMOC) plays a fundamental role in the climate system, and long-term climate simulations are used to understand the AMOC variability and to assess its impact. This study examines the basic characteristics of the AMOC variability in 44 CMIP5 (Phase 5 of the Coupled Model Inter-comparison Project) simulations, using the 18 atmospherically-forced CORE-II (Phase 2 of the Coordinated Ocean-ice Reference Experiment) simulations as a reference. The analysis shows that on interannual and decadal timescales, the AMOC variability in the CMIP5 exhibits a similar magnitude and meridional coherence as in the CORE-II simulations, indicating that the modeled atmospheric variability responsible for AMOC variability in the CMIP5 is in reasonable agreement with the CORE-II forcing. On multidecadal timescales, however, the AMOC variability is weaker by a factor of more than 2 and meridionally less coherent in the CMIP5 than in the CORE-II simulations. The CMIP5 simulations also exhibit a weaker long-term atmospheric variability in the North Atlantic Oscillation (NAO). However, one cannot fully attribute the weaker AMOC variability to the weaker variability in NAO because, unlike the CORE-II simulations, the CMIP5 simulations do not exhibit a robust NAO-AMOC linkage. While the variability of the wintertime heat flux and mixed layer depth in the western subpolar North Atlantic is strongly linked to the AMOC variability, the NAO variability is not.
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Serial 981
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Author Bruno-Piverger, R.E.
Title Applying Neural Networks to Simulate Visual Inspection of Observational Weather Data Type $loc['typeJournal Article']
Year 2019 Publication Florida State University College of Arts and Sciences, Master's Thesis Abbreviated Journal
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Serial 1090
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Author Wang, S. ; Kranz, S.A. ; Kelly, T.B. ; Song, H. ; Stukel, M.R. ; Cassar, N.
Title Lagrangian Studies of Net Community Production: The Effect of Diel and Multiday Nonsteady State Factors and Vertical Fluxes on O2 /Ar in a Dynamic Upwelling Region Type $loc['typeJournal Article']
Year 2020 Publication Journal of Geophysical Research: Biogeosciences Abbreviated Journal J. Geophys. Res. Biogeosci.
Volume 125
Issue 6
Pages e2019JG005569
Keywords net community production ; O2/Ar ; California Current Ecosystem ; Lagrangian measurements ; vertical fluxes ; nonsteady state
Abstract The ratio of dissolved oxygen to argon in seawater is frequently employed to estimate rates of net community production (NCP) in the oceanic mixed layer. The in situ O2/Ar‐based method accounts for many physical factors that influence oxygen concentrations, permitting isolation of the biological oxygen signal produced by the balance of photosynthesis and respiration. However, this technique traditionally relies upon several assumptions when calculating the mixed‐layer O2/Ar budget, most notably the absence of vertical fluxes of O2/Ar and the principle that the air‐sea gas exchange of biological oxygen closely approximates net productivity rates. Employing a Lagrangian study design and leveraging data outputs from a regional physical oceanographic model, we conducted in situ measurements of O2/Ar in the California Current Ecosystem in spring 2016 and summer 2017 to evaluate these assumptions within a �worst‐case� field environment. Quantifying vertical fluxes, incorporating nonsteady state changes in O2/Ar, and comparing NCP estimates evaluated over several day versus longer timescales, we find differences in NCP metrics calculated over different time intervals to be considerable, also observing significant potential effects from vertical fluxes, particularly advection. Additionally, we observe strong diel variability in O2/Ar and NCP rates at multiple stations. Our results reemphasize the importance of accounting for vertical fluxes when interpreting O2/Ar‐derived NCP data and the potentially large effect of nonsteady state conditions on NCP evaluated over shorter timescales. In addition, diel cycles in surface O2/Ar can also bias interpretation of NCP data based on local productivity and the time of day when measurements were made.
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ISSN 2169-8953
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Call Number COAPS @ user @
Serial 1114
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Author Laxenaire, R., Speich, S., & Alexandre S
Title Evolution of the thermohaline structure of one Agulhas Ring reconstructed from satellite altimetry and Argo floats. Journal of Geophysical Research Type $loc['typeJournal Article']
Year 2019 Publication Oceans Abbreviated Journal
Volume 124
Issue 12
Pages 8969-9003
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Serial 1096
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Author Xu, X. ; Bower, A. ; Furey, H. ; Chassignet, E.P.
Title Variability of the Iceland-Scotland Overflow Water Transport Through the Charlie-Gibbs Fracture Zone: Results From an Eddying Simulation and Observations Type $loc['typeJournal Article']
Year 2018 Publication Journal of Geophysical Research: Oceans Abbreviated Journal J. Geophys. Res. Oceans
Volume Issue 8
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Abstract Observations show that the westward transport of the Iceland‐Scotland overflow water (ISOW) through the Charlie‐Gibbs Fracture Zone (CGFZ) is highly variable. This study examines (a) where this variability comes from and (b) how it is related to the variability of ISOW transport at upstream locations in the Iceland Basin and other ISOW flow pathways. The analyses are based on a 35‐year 1/12° eddying Atlantic simulation that represents well the main features of the observed ISOW in the area of interest, in particular, the transport variability through the CGFZ. The results show that (a) the variability of the ISOW transport is closely correlated with that of the barotropic transports in the CGFZ associated with the meridional displacement of the North Atlantic Current front and is possibly induced by fluctuations of large‐scale zonal wind stress in the Western European Basin east of the CGFZ; (b) the variability of the ISOW transport is increased by a factor of 3 from the northern part of the Iceland Basin to the CGFZ region and transport time series at these two locations are not correlated, further suggesting that the variability at the CGFZ does not come from the upstream source; and (c) the variability of the ISOW transport at the CGFZ is strongly anticorrelated to that of the southward ISOW transport along the eastern flank of the Mid‐Atlantic Ridge, suggesting an out‐of‐phase covarying transport between these two ISOW pathways.
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Series Editor Series Title Abbreviated Series Title
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ISSN 2169-9275
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Call Number COAPS @ user @
Serial 1023
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Author Roberts, M.J. ; Jackson, L.C. ; Roberts, C.D. ; Meccia, V. ; Docquier, D. ; Koenigk, T. ; Ortega, P. ; Moreno‐ ; Chamarro, E. ; Bellucci, A. ; Coward, A. ; Drijfhout, S. ; Exarchou, E. ; Gutjahr, O. ; Hewitt, H. ; Iovino, D. ; Lohmann, K. ; Putrasahan, D. ; Schiemann, R. ; Seddon, J. ; Terray, L. ; Xu, X. ; Zhang, Q. ; Chang, P. ; Yeager, S.G. ; Castruccio, F.S. ; Zhang. C. ; Wu, L.
Title Sensitivity of the Atlantic Meridional Overturning Circulation to Model Resolution in CMIP6 HighResMIP Simulations and Implications for Future Changes Type $loc['typeJournal Article']
Year 2020 Publication Journal of Advances in Modeling Earth Systems Abbreviated Journal J. Adv. Model. Earth Syst.
Volume Issue Pages Accepted
Keywords
Abstract A multi‐model, multi‐resolution ensemble using CMIP6 HighResMIP coupled experiments is used to assess the performance of key aspects of the North Atlantic circulation. The Atlantic Meridional Overturning Circulation (AMOC), and related heat transport, tends to become stronger as ocean model resolution is enhanced, better agreeing with observations at 26.5°N. However for most models the circulation remains too shallow compared to observations, and has a smaller temperature contrast between the northward and southward limbs of the AMOC. These biases cause the northward heat transport to be systematically too low for a given overturning strength. The higher resolution models also tend to have too much deep mixing in the subpolar gyre.
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Serial 1109
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Author Stukel, M.R. ; Décima, M. ; Landry, M.R. ; Selph, K.E.
Title Nitrogen and isotope flows through the Costa Rica Dome upwelling ecosystem: The crucial mesozooplankton role in export flux Type $loc['typeJournal Article']
Year 2018 Publication Global Biogeochemical Cycles Abbreviated Journal Global Biogeochemical Cycles
Volume 32
Issue 12
Pages 1815–1832.
Keywords Crustaceans ; Diel vertical migration ; Nitrogen cycle ; Biological carbon pump ; Nitrogen isotopes ; Linear inverse ecosystem model
Abstract The Costa Rica Dome (CRD) is an open-ocean upwelling ecosystem, with high biomasses of picophytoplankton (especially Synechococcus), mesozooplankton, and higher trophic levels. To elucidate the food web pathways supporting the trophic structure and carbon export in this unique ecosystem, we used Markov Chain Monte Carlo techniques to assimilate data from four independent realizations of δ15N and planktonic rate measurements from the CRD into steady state, multicompartment ecosystem box models (linear inverse models). Model results present well-constrained snapshots of ecosystem nitrogen and stable isotope fluxes. New production is supported by upwelled nitrate, not nitrogen fixation. Protistivory (rather than herbivory) was the most important feeding mode for mesozooplankton, which rely heavily on microzooplankton prey. Mesozooplankton play a central role in vertical nitrogen export, primarily through active transport of nitrogen consumed in the surface layer and excreted at depth, which comprised an average 36-46% of total export. Detritus or aggregate feeding is also an important mode of resource acquisition by mesozooplankton and regeneration of nutrients within the euphotic zone. As a consequence, the ratio of passively sinking particle export to phytoplankton production is very low in the CRD. Comparisons to similar models constrained with data from the nearby equatorial Pacific demonstrate that the dominant role of vertical migrators to the biological pump is a unique feature of the CRD. However, both regions show efficient nitrogen transfer from mesozooplankton to higher trophic levels (as expected for regions with large fish, cetacean, and seabird populations) despite the dominance of protists as major grazers of phytoplankton.
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Call Number COAPS @ rl18 @
Serial 978
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Author Kranz, S.A. ; Wang, S. ; Kelly, T.B. ; Stukel, M.R. ; Goericke, R. ; Landry, M.R. ; Cassar, N.
Title Lagrangian Studies of Marine Production: A Multimethod Assessment of Productivity Relationships in the California Current Ecosystem Upwelling Region Type $loc['typeJournal Article']
Year 2020 Publication Journal of Geophysical Research: Oceans Abbreviated Journal J. Geophys. Res. Oceans
Volume 125
Issue 6
Pages
Keywords gross primary production ; long‐ ; term ecological research ; equilibrium inlet mass spectrometry ; carbon export ; net community production
Abstract A multimethod process‐oriented investigation of diverse productivity measures in the California Current Ecosystem (CCE) Long‐Term Ecological Research study region, a complex physical environment, is presented. Seven multiday deployments covering a transition region from high to low productivity were conducted over two field expeditions (spring 2016 and summer 2017). Employing a Lagrangian study design, water parcels were followed over several days, comparing 24‐h in situ measurements (14C and 15NO3 ‐uptake, dilution estimates of phytoplankton growth, and microzooplankton grazing) with high‐resolution productivity measurements by fast repetition rate fluorometry (FRRF) and equilibrium inlet mass spectrometry (EIMS), and integrated carbon export measuremnts using sediment traps. Results show the importance of accounting for temporal and fine spatial scale variability when estimating ecosystem production. FRRF and EIMS measurements resolved diel patterns in gross primary and net community production. Diel productivity changes agreed well with comparably more traditional measurements. While differences in productivity metrics calculated over different time intervals were considerable, as those methods rely on different base assumptions, the data can be used to explain ecosystem processes which would otherwise have gone unnoticed. The processes resolved from this method comparison further understanding of temporal and spatial coupling and decoupling of surface productivity and potential carbon burial in a gradient from coastal to offshore ecosystems.
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Series Editor Series Title Abbreviated Series Title
Series Volume Series Issue Edition
ISSN 2169-9275
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Call Number COAPS @ user @
Serial 1113
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Author Ali, M. ; Singh, N. ; Kumar, M. ; Zheng, Y. ; Bourassa, M. ; Kishtawal, C. ; Rao, C.
Title Dominant Modes of Upper Ocean Heat Content in the North Indian Ocean Type $loc['typeJournal Article']
Year 2019 Publication Climate Abbreviated Journal Climate
Volume 6
Issue 71
Pages 1 – 8
Keywords
Abstract The thermal energy needed for the development of hurricanes and monsoons as well as any prolonged marine weather event comes from layers in the upper oceans, not just from the thin layer represented by sea surface temperature alone. Ocean layers have different modes of thermal energy variability because of the different time scales of ocean–atmosphere interaction. Although many previous studies have focused on the influence of upper ocean heat content (OHC) on tropical cyclones and monsoons, no study thus far—particularly in the North Indian Ocean (NIO)—has specifically concluded the types of dominant modes in different layers of the ocean. In this study, we examined the dominant modes of variability of OHC of seven layers in the NIO during 1998–2014. We conclude that the thermal variability in the top 50 m of the ocean had statistically significant semiannual and annual modes of variability, while the deeper layers had the annual mode alone. Time series of OHC for the top four layers were analyzed separately for the NIO, Arabian Sea, and Bay of Bengal. For the surface to 50 m layer, the lowest and the highest values of OHC were present in January and May every year, respectively, which was mainly caused by the solar radiation cycle.
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Language Summary Language Original Title
Series Editor Series Title Abbreviated Series Title
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ISSN 2225-1154
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Call Number COAPS @ user @
Serial 1030
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Author Morey, S. ; Wienders, N. ; Dukhovskoy, D. ; Bourassa, M.
Title Measurement Characteristics of Near-Surface Currents from Ultra-Thin Drifters, Drogued Drifters, and HF Radar Type $loc['typeJournal Article']
Year 2018 Publication Remote Sensing Abbreviated Journal Remote Sensing
Volume 10
Issue 10
Pages 1633
Keywords surface drifters ; surface currents ; HF Radar ; STOKES DRIFT ; SEA-SURFACE ; WAVES ; BREAKING ; VALIDATION ; TRANSPORT
Abstract Concurrent measurements by satellite tracked drifters of different hull and drogue configurations and coastal high-frequency radar reveal substantial differences in estimates of the near-surface velocity. These measurements are important for understanding and predicting material transport on the ocean surface as well as the vertical structure of the near-surface currents. These near-surface current observations were obtained during a field experiment in the northern Gulf of Mexico intended to test a new ultra-thin drifter design. During the experiment, thirty small cylindrical drifters with 5 cm height, twenty-eight similar drifters with 10 cm hull height, and fourteen drifters with 91 cm tall drogues centered at 100 cm depth were deployed within the footprint of coastal High-Frequency (HF) radar. Comparison of collocated velocity measurements reveals systematic differences in surface velocity estimates obtained from the different measurement techniques, as well as provides information on properties of the drifter behavior and near-surface shear. Results show that the HF radar velocity estimates had magnitudes significantly lower than the 5 cm and 10 cm drifter velocity of approximately 45% and 35%, respectively. The HF radar velocity magnitudes were similar to the drogued drifter velocity. Analysis of wave directional spectra measurements reveals that surface Stokes drift accounts for much of the velocity difference between the drogued drifters and the thin surface drifters except during times of wave breaking.
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ISSN 2072-4292
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Call Number COAPS @ rl18 @
Serial 985
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