Climatological Seasonal Cycle of Global Ocean Oxygen, Heat and Apparent Oxygen Utilization Content Anomalies in the Surface Mixed Layer

2020 ◽  
Author(s):  
Zhankun Wang ◽  
Hernan Garcia ◽  
Tim Boyer ◽  
James Reagan ◽  
Just Cebrian
Keyword(s):  
Mixed Layer ◽  
Seasonal Cycle ◽  
Global Ocean ◽  
Surface Mixed Layer ◽  
Oxygen Utilization ◽  
Apparent Oxygen Utilization

scholarly journals Iron stable isotopes track pelagic iron cycling during a subtropical phytoplankton bloom

2014 ◽  
Vol 112 (1) ◽  
pp. E15-E20 ◽  
Author(s):  
Michael J. Ellwood ◽  
David A. Hutchins ◽  
Maeve C. Lohan ◽  
Angela Milne ◽  
Philipp Nasemann ◽  
...  
Keyword(s):  
Stable Isotopes ◽  
Mixed Layer ◽  
Phytoplankton Bloom ◽  
Iron Bioavailability ◽  
Global Ocean ◽  
Minor Role ◽  
Surface Mixed Layer ◽  
Spring Phytoplankton Bloom ◽  
Dissolved Iron ◽  
Particulate Iron

The supply and bioavailability of dissolved iron sets the magnitude of surface productivity for ∼40% of the global ocean. The redox state, organic complexation, and phase (dissolved versus particulate) of iron are key determinants of iron bioavailability in the marine realm, although the mechanisms facilitating exchange between iron species (inorganic and organic) and phases are poorly constrained. Here we use the isotope fingerprint of dissolved and particulate iron to reveal distinct isotopic signatures for biological uptake of iron during a GEOTRACES process study focused on a temperate spring phytoplankton bloom in subtropical waters. At the onset of the bloom, dissolved iron within the mixed layer was isotopically light relative to particulate iron. The isotopically light dissolved iron pool likely results from the reduction of particulate iron via photochemical and (to a lesser extent) biologically mediated reduction processes. As the bloom develops, dissolved iron within the surface mixed layer becomes isotopically heavy, reflecting the dominance of biological processing of iron as it is removed from solution, while scavenging appears to play a minor role. As stable isotopes have shown for major elements like nitrogen, iron isotopes offer a new window into our understanding of the biogeochemical cycling of iron, thereby allowing us to disentangle a suite of concurrent biotic and abiotic transformations of this key biolimiting element.

A New Estimate of Global Ocean Climatology

2021 ◽  
Author(s):  
Kanwal Shahzadi ◽  
Nadia Pinardi ◽  
Marco Zavaterelli ◽  
Simona Simoncelli
Keyword(s):  
Quality Control ◽  
World Ocean ◽  
Global Ocean ◽  
Physical Parameters ◽  
Oxygen Utilization ◽  
Non Linear ◽  
Using Data ◽  
The Impact ◽  
Apparent Oxygen Utilization

<p>The estimation of climatology is a key element for improving our understanding of the ocean state. Historical data sets available today enables an almost complete reconstruction of global ocean fields. In this study, a new global ocean climatological estimate of basic physical parameters such as temperature, salinity, density, dissolved oxygen, and apparent oxygen utilization is computed using the World Ocean Database (WOD18). The reliability of estimate is closely tied to the quality assurance of the in-situ observations and statistical interpolation schemes of the mapping. Therefore, in this context, WOD18 used for this study has gone through a non-linear quality control procedure developed by Shahzadi (2020) on a global domain. The mapping of resulting data is carried out using Data Interpolating Variational Analysis (DIVA). Sensitivity experiments are carried out to choose the key parameters of DIVA, namely the horizontal correlation lengths, and the Noise to Signal ratio (N/S). Furthermore, two new indices such as roughness index, and root mean square of residuals are designed to show the impact of the correlation length, and N/S ratio choices. For temperature and salinity, two different versions of the climatological estimates are produced: (i) a long-term (1900 to 2017) climatology using multiple platforms in-situ data, and (ii) a shorter time estimate (2003-2017) using data from ocean drifting platforms such as profiling floats. The two versions are intercompared and differences are evaluated.  Similar procedures are applied for global mapping of Density, Oxygen, and Apparent Oxygen utilization. The new climatological estimates are compared with previous estimates such as World Ocean Atlas and World Argo Global Hydrographic climatological estimates, and thereby the differences are analysed.</p><p><strong>Keywords:</strong> WOD18, temperature, salinity, apparent oxygen, DIVA, climatology, non-linear quality control.</p><p>Shahzadi, K., (2020): “A New Global Ocean Climatology”, Ph.D. Thesis (under evaluation), University of Bologna, Italy, pp. (19-35. of pages)</p>

scholarly journals Open-Ocean Submesoscale Motions: A Full Seasonal Cycle of Mixed Layer Instabilities from Gliders

2016 ◽  
Vol 46 (4) ◽  
pp. 1285-1307 ◽  
Author(s):  
Andrew F. Thompson ◽  
Ayah Lazar ◽  
Christian Buckingham ◽  
Alberto C. Naveira Garabato ◽  
Gillian M. Damerell ◽  
...  
Keyword(s):  
Mixed Layer ◽  
Seasonal Cycle ◽  
Gravitational Instability ◽  
Baroclinic Instability ◽  
Open Ocean ◽  
Global Ocean ◽  
Surface Cooling ◽  
Near Surface ◽  
Submesoscale Processes ◽  
Symmetric Instability

AbstractThe importance of submesoscale instabilities, particularly mixed layer baroclinic instability and symmetric instability, on upper-ocean mixing and energetics is well documented in regions of strong, persistent fronts such as the Kuroshio and the Gulf Stream. Less attention has been devoted to studying submesoscale flows in the open ocean, far from long-term, mean geostrophic fronts, characteristic of a large proportion of the global ocean. This study presents a year-long, submesoscale-resolving time series of near-surface buoyancy gradients, potential vorticity, and instability characteristics, collected by ocean gliders, that provides insight into open-ocean submesoscale dynamics over a full annual cycle. The gliders continuously sampled a 225 km2 region in the subtropical northeast Atlantic, measuring temperature, salinity, and pressure along 292 short (~20 km) hydrographic sections. Glider observations show a seasonal cycle in near-surface stratification. Throughout the fall (September–November), the mixed layer deepens, predominantly through gravitational instability, indicating that surface cooling dominates submesoscale restratification processes. During winter (December–March), mixed layer depths are more variable, and estimates of the balanced Richardson number, which measures the relative importance of lateral and vertical buoyancy gradients, depict conditions favorable to symmetric instability. The importance of mixed layer instabilities on the restratification of the mixed layer, as compared with surface heating and cooling, shows that submesoscale processes can reverse the sign of an equivalent heat flux up to 25% of the time during winter. These results demonstrate that the open-ocean mixed layer hosts various forced and unforced instabilities, which become more prevalent during winter, and emphasize that accurate parameterizations of submesoscale processes are needed throughout the ocean.

scholarly journals Characteristics of the seasonal cycle of surface layer salinity in the global ocean

Ocean Science ◽  
2012 ◽  
Vol 8 (5) ◽  
pp. 915-929 ◽  
Author(s):  
F. M. Bingham ◽  
G. R. Foltz ◽  
M. J. McPhaden
Keyword(s):  
Surface Layer ◽  
Mixed Layer ◽  
Seasonal Variability ◽  
Seasonal Cycle ◽  
Arabian Sea ◽  
Mixed Layer Depth ◽  
Bimodal Distribution ◽  
Global Ocean ◽  
Late Winter ◽  
Freshwater Forcing

Abstract. The seasonal variability of surface layer salinity (SLS), evaporation (E), precipitation (P), E-P, advection and vertical entrainment over the global ocean is examined using in situ salinity data, the National Centers for Environmental Prediction's Climate System Forecast Reanalysis and a number of other ancillary data. Seasonal amplitudes and phases are calculated using harmonic analysis and presented in all areas of the open ocean between 60° S and 60° N. Areas with large amplitude SLS seasonal variations include: the intertropical convergence zone (ITCZ) in the Atlantic, Pacific and Indian Oceans; western marginal seas of the Pacific; and the Arabian Sea. The median amplitude in areas that have statistically significant seasonal cycles of SLS is 0.19. Between about 60° S and 60° N, 37% of the ocean surface has a statistically significant seasonal cycle of SLS and 75% has a seasonal cycle of E-P. Phases of SLS have a bimodal distribution, with most areas in the Northern Hemisphere peaking in SLS in March/April and in the Southern Hemisphere in September/October. The seasonal cycle is also estimated for surface freshwater forcing using a mixed-layer depth climatology. With the exception of areas near the western boundaries of the North Atlantic and North Pacific, seasonal variability is dominated by precipitation. Surface freshwater forcing also has a bimodal distribution, with peaks in January and July, 1–2 months before the peaks of SLS. Seasonal amplitudes and phases calculated for horizontal advection show it to be important in the tropical oceans. Vertical entrainment, estimated from mixed-layer heaving, is largest in mid and high latitudes, with a seasonal cycle that peaks in late winter. The amplitudes and phases of SLS and surface fluxes compare well in a qualitative sense, suggesting that much of the variability in SLS is due to E-P. However, the amplitudes of SLS are somewhat different than would be expected and the peak of SLS comes typically about one month earlier than expected. The differences of the amplitudes of the two quantities is largest in such areas as the Amazon River plume, the Arabian Sea, the ITCZ and the eastern equatorial Pacific and Atlantic.

scholarly journals Spatial and Seasonal Variations of Submesoscale Eddies in the Eastern Tropical Pacific Ocean

2018 ◽  
Vol 48 (1) ◽  
pp. 101-116 ◽  
Author(s):  
Shengpeng Wang ◽  
Zhao Jing ◽  
Hailong Liu ◽  
Lixin Wu
Keyword(s):  
Pacific Ocean ◽  
Kinetic Energy ◽  
Mixed Layer ◽  
Seasonal Variations ◽  
Seasonal Cycle ◽  
Tropical Pacific ◽  
Surface Mixed Layer ◽  
Barotropic Instability ◽  
Tropical Pacific Ocean ◽  
Eastern Tropical Pacific

AbstractThe spatial and seasonal variations of submesoscale eddy activities in the eastern tropical Pacific Ocean (2°–12°N, 95°–165°W) are investigated based on a 1/10° ocean general circulation model (OGCM). In the studied region, it is found that motions shorter than 500 km are subject to submesoscale dynamics with an O(1) Rossby number and Richardson number and a −2 spectral slope for kinetic energy, suggesting that submesoscale eddies there can be well resolved by the model. Enhanced submesoscale eddy kinetic energy (SMKE) is found in the surface mixed layer centered at 5°N. A complete SMKE budget analysis suggests that the submesoscale eddies in the surface mixed layer are generated mainly by the barotropic instability and secondarily by the baroclinic instability. The nonlinear interactions lead to a significant forward energy cascade in the submesoscale range and play an important role in balancing the energy budget. As a response to the change of energy input through barotropic instability, the SMKE exhibits a pronounced seasonal cycle with the largest and smallest values occurring in boreal autumn and spring. Furthermore, the strong seasonal cycle plays an important role in modulating the seasonality of mixed layer depth (MLD). In particular, the restratification induced by the strong submesoscale eddies between July and October makes important contribution to the shoaling of MLD in this season.

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