scholarly journals Mixed layer depth over the global ocean: An examination of profile data and a profile-based climatology

2004 ◽  
Vol 109 (C12) ◽  
Author(s):  
Clément de Boyer Montégut
Keyword(s):  
Mixed Layer ◽  
Mixed Layer Depth ◽  
Global Ocean ◽  
Profile Data ◽  
Layer Depth

scholarly journals Global ocean dimethyl sulfide climatology estimated from observations and an artificial neural network

2020 ◽  
Author(s):  
Wei-Lei Wang ◽  
Guisheng Song ◽  
François Primeau ◽  
Eric S. Saltzman ◽  
Thomas G. Bell ◽  
...  
Keyword(s):  
Neural Network ◽  
Artificial Neural Network ◽  
Solar Radiation ◽  
Mixed Layer ◽  
Dimethyl Sulfide ◽  
Mixed Layer Depth ◽  
Environmental Parameters ◽  
Global Scale ◽  
Global Ocean ◽  
Layer Depth

Abstract. Marine dimethyl sulfide (DMS) is important to climate due to the ability of DMS to alter Earth's radiation budget. However, a knowledge of the global-scale distribution, seasonal variability, and sea-to-air flux of DMS is needed in order to understand the factors controlling surface ocean DMS and its impact on climate. Here we examine the use of an artificial neural network (ANN) to extrapolate available DMS measurements to the global ocean and produce a global climatology with monthly temporal resolution. A global database of 57 810 ship-based DMS measurements in surface waters was used along with a suite of environmental parameters consisting of lat-lon coordinates, time-of-day, time-of-year, solar radiation, mixed layer depth, sea surface temperature, salinity, nitrate, phosphate, silicate, and oxygen. Linear regressions of DMS against the environmental parameters show that on a global scale mixed layer depth and solar radiation are the strongest predictors of DMS, however, they capture 14 % and 12 % of the raw DMS data variance, respectively. The multi-linear regression can capture more (∼29 %) of the raw data variance, but strongly underestimates high DMS concentrations. In contrast, the ANN captures ~61 % of the raw data variance in our database. Like prior climatologies our results show a strong seasonal cycle in DMS concentration and sea-to-air flux. The highest concentrations (fluxes) occur in the high-latitude oceans during the summer. We estimate a lower global sea-to-air DMS flux (17.90 ± 0.34 Tg S yr−1) than the prior estimate based on a map interpolation method when the same gas transfer velocity parameterization is used.

Variability of the Oceanic Mixed Layer, 1960–2004

2008 ◽  
Vol 21 (5) ◽  
pp. 1029-1047 ◽  
Author(s):  
James A. Carton ◽  
Semyon A. Grodsky ◽  
Hailong Liu
Keyword(s):  
Mixed Layer ◽  
North Atlantic ◽  
Southern Oscillation ◽  
Mixed Layer Depth ◽  
Global Ocean ◽  
Boreal Summer ◽  
Layer Depth ◽  
The North ◽  
The North Atlantic ◽  
Mixed Layers

Abstract A new monthly uniformly gridded analysis of mixed layer properties based on the World Ocean Atlas 2005 global ocean dataset is used to examine interannual and longer changes in mixed layer properties during the 45-yr period 1960–2004. The analysis reveals substantial variability in the winter–spring depth of the mixed layer in the subtropics and midlatitudes. In the North Pacific an empirical orthogonal function analysis shows a pattern of mixed layer depth variability peaking in the central subtropics. This pattern occurs coincident with intensification of local surface winds and may be responsible for the SST changes associated with the Pacific decadal oscillation. Years with deep winter–spring mixed layers coincide with years in which winter–spring SST is low. In the North Atlantic a pattern of winter–spring mixed layer depth variability occurs that is not so obviously connected to local changes in winds or SST, suggesting that other processes such as advection are more important. Interestingly, at decadal periods the winter–spring mixed layers of both basins show trends, deepening by 10–40 m over the 45-yr period of this analysis. The long-term mixed layer deepening is even stronger (50–100 m) in the North Atlantic subpolar gyre. At tropical latitudes the boreal winter mixed layer varies in phase with the Southern Oscillation index, deepening in the eastern Pacific and shallowing in the western Pacific and eastern Indian Oceans during El Niños. In boreal summer the mixed layer in the Arabian Sea region of the western Indian Ocean varies in response to changes in the strength of the southwest monsoon.

Optimal Linear Fitting for Objective Determination of Ocean Mixed Layer Depth from Glider Profiles

2010 ◽  
Vol 27 (11) ◽  
pp. 1893-1898 ◽  
Author(s):  
Peter C. Chu ◽  
Chenwu Fan
Keyword(s):  
Mixed Layer ◽  
North Atlantic Ocean ◽  
Mixed Layer Depth ◽  
Maximum Error ◽  
Profile Data ◽  
Layer Depth ◽  
Linear Fitting ◽  
Error Ratio ◽  
Optimal Linear ◽  
Data Points

Abstract A new optimal linear fitting method has been developed to determine mixed layer depth from profile data. This methodology includes three steps: 1) fitting the profile data from the first point near the surface to a depth using a linear polynomial, 2) computing the error ratio of absolute bias of few data points below that depth versus the root-mean-square error of data points from the surface to that depth between observed and fitted data, and 3) finding the depth (i.e., the mixed layer depth) with maximum error ratio. Temperature profiles in the western North Atlantic Ocean over 14 November–5 December 2007, collected from two gliders (Seagliders) deployed by the Naval Oceanographic Office, are used to demonstrate the capability of this method. The mean quality index (1.0 for perfect determination) for determining mixed layer depth is greater than 0.97, which is much higher than the critical value of 0.8 for well-defined mixed layer depth with that index.

scholarly journals Intercomparison and validation of the mixed layer depth fields of global ocean syntheses

2015 ◽  
Vol 49 (3) ◽  
pp. 753-773 ◽  
Author(s):  
Takahiro Toyoda ◽  
Yosuke Fujii ◽  
Tsurane Kuragano ◽  
Masafumi Kamachi ◽  
Yoichi Ishikawa ◽  
...  
Keyword(s):  
Mixed Layer ◽  
Mixed Layer Depth ◽  
Global Ocean ◽  
Layer Depth

scholarly journals Influence of Pycnocline Smoothing and Subgrid-Scale Variability of Density Profiles on the Determination of Mixed Layer Depth

2017 ◽  
Vol 34 (9) ◽  
pp. 2083-2101 ◽  
Author(s):  
Hyejin Ok ◽  
Yign Noh ◽  
Yeonju Choi
Keyword(s):  
Mixed Layer ◽  
General Circulation ◽  
Mixed Layer Depth ◽  
Global Ocean ◽  
Observation Data ◽  
Subgrid Scale ◽  
Layer Depth ◽  
Profile Error ◽  
Density Profiles

AbstractThis study investigates how pycnocline smoothing and subgrid-scale variability of density profiles influence the determination of the mixed layer depth (MLD) in the global ocean, and applies the results of analysis to assess the ability of ocean general circulation models (OGCM) to simulate the MLD. For this purpose, individual, monthly mean, and climatological profiles are analyzed over a horizontal resolution of 1° × 1° for both observation data (Argo) and eddy-resolving OGCM (OFES) results. It is found that the MLDs from averaged profiles are generally smaller than those from individual profiles because of pycnocline smoothing induced by the averaging process. A correlation is found between the decrease in MLD Δh and the increase in pycnocline thickness Δδ of averaged profiles, except during winter in the high-latitude ocean. The relation is estimated as Δh = −αΔδ − β, where α ≃ 0.7 in all cases, but β increases with the subgrid-scale variability of density profiles. A correlation is also found between Δh and the standard deviation of the MLD within a grid. The results are applied to estimate how much of the MLD bias of OFES is due to prediction error and how much is due to profile error, induced by different pycnocline smoothing and the subgrid-scale variability of density profiles. The study also shows how profile error varies with the threshold density difference criterion.

scholarly journals Observed and Modelled Mixed-Layer Properties on the Continental Shelf of Sardinia (Mediterranean Sea)

2016 ◽  
Author(s):  
Reiner Onken
Keyword(s):  
Boundary Conditions ◽  
Mixed Layer ◽  
Initial Conditions ◽  
Mixed Layer Depth ◽  
Vertical Mixing ◽  
Global Ocean ◽  
Surface Boundary ◽  
Regional Ocean Modeling System ◽  
Layer Depth ◽  
Mixed Layer Temperature

Abstract. The Regional Ocean Modeling System (ROMS) has been employed to explore the sensitivity of the forecast skill of mixed-layer properties to the initial conditions, boundary conditions, and vertical mixing parameterisations. The initial and lateral boundary conditions were provided by the Mediterranean Forecasting System (MFS) or by the MERCATOR global ocean circulation model via one-way nesting; the initial conditions were additionally updated by the assimilation of observations. Nowcasts and forecasts from the weather forecast models COSMO-ME and COSMO-IT, partly melded with observations, served as surface boundary conditions. The vertical mixing was parameterised by the GLS (Generic Length Scale) scheme (Umlauf et al. 2003) in four different setups. All ROMS forecasts were validated against observations which were taken during the REP14-MED oceanographic survey to the west of Sardinia. Nesting ROMS in MERCATOR and updating the initial conditions by data assimilation provided the best agreement of the predicted mixed-layer temperature and the mixed-layer depth with time series from a moored thermistor chain. Further improvement was obtained by the usage of COSMO-ME atmospheric forcing which was melded with real observations, and by the application of the k − ε vertical mixing scheme with increased vertical eddy diffusivity. The predicted temporal variability of the mixed-layer temperature was reasonably well correlated with the observed variability in the frequency range above one cycle per day, while the modelled variability of the mixed-layer depth exhibited only agreement with the observations near the diurnal frequency peak. For the forecasted horizontal variability, reasonable agreement was found with observations from a ScanFish section, but only for the mesoscale wavenumber band; the observed sub-mesoscale variability was not reproduced by ROMS.

scholarly journals Observed increase in springtime surface partial pressure of CO<sub>2</sub> in the east equatorial Indian Ocean during 1962–2012

2014 ◽  
Vol 11 (1) ◽  
pp. 521-549
Author(s):  
L. Xue ◽  
W. Yu ◽  
H. Wang ◽  
L. Feng ◽  
Q. Wei ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Partial Pressure ◽  
Mixed Layer ◽  
Mixed Layer Depth ◽  
Equatorial Indian Ocean ◽  
Sea Surface ◽  
Atmospheric Co2 ◽  
Global Ocean ◽  
Layer Depth ◽  
Co2 Sink

Abstract. Rapidly rising atmospheric CO2 and global warming may have been impacting the ocean, and, in contrast, the response of surface CO2 partial pressure (pCO2) in the equatorial Indian Ocean is poorly understood. In this study, we attempted to evaluate the variation of springtime sea surface pCO2 in the east equatorial Indian Ocean (5° N to 5° S along 90° E and 95° E, EIO), which is relatively better occupied, using data collected in May 2012, together with the historical data since 1962 (LDEO_Database_V2012). Results showed that sea surface pCO2 in the investigation area increased from ~308 μatm in April 1963, through ~373 μatm in May 1999, to ~387μatm in May 2012, with a mean increase rate of ~1.7μatm yr−1. Given that the EIO during the study period was almost always a CO2 source to the atmosphere, it was obvious that the observed increase of sea surface pCO2 with time in this region was not due to the local uptake of CO2 via air–sea exchange, although quickly increasing atmospheric CO2 had the potential to increase seawater pCO2. Further, we checked the effects of variations in sea surface temperature, salinity, mixed layer depth and chlorophyll a (as a proxy of biological production) on surface pCO2. We found surface ocean warming partially contributed to sea surface pCO2 increase, whereas the effects of salinity, mixed layer depth, and biological activity were not significant. The pCO2 increase in the equatorial waters (CO2 source to the atmosphere) was probably due to the transport of carbon accumulated in the CO2 sink region (to the atmosphere) towards the CO2 source region on a basin scale via ocean circulation. Additionally, our study showed that more and more release of CO2 from the ocean to the atmosphere and big pH reduction (0.07 pH units) in the past 50 yr (from 1963 to 2012) may have occurred in the EIO. It also demonstrated that ocean acidification may have taken place in the global ocean, not just limited to the CO2 sink region.

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