Towards a revised climatology of summertime dimethylsulfide concentrations and sea–air fluxes in the Southern Ocean

2016 ◽  
Vol 13 (2) ◽  
pp. 364 ◽  
Author(s):  
Tereza Jarníková ◽  
Philippe D. Tortell
Keyword(s):  
High Resolution ◽  
Southern Ocean ◽  
Chlorophyll A ◽  
Mixed Layer ◽  
Mixed Layer Depth ◽  
Cloud Formation ◽  
Layer Depth ◽  
High Resolution Data ◽  
Mean Values ◽  
Data Coverage

Environmental context The trace gas dimethylsulfide (DMS) is emitted from surface ocean waters to the overlying atmosphere, where it forms aerosols that promote cloud formation and influence Earth’s climate. We present an updated climatology of DMS emissions from the vast Southern Ocean, demonstrating how the inclusion of new data yields higher regional sources compared with previously derived values. Our work provides an important step towards better quantifying the oceanic emissions of an important climate-active gas. Abstract The Southern Ocean is a dominant source of the climate-active gas dimethylsulfide (DMS) to the atmosphere. Despite significant improvements in data coverage over the past decade, the most recent global DMS climatology does not include a growing number of high-resolution surface measurements in Southern Ocean waters. Here, we incorporate these high resolution data (~700000 measurements) into an updated Southern Ocean climatology of summertime DMS concentrations and sea–air fluxes. Owing to sparse monthly data coverage, we derive a single summertime climatology based on December through February means. DMS frequency distributions and oceanographic properties (mixed-layer depth and chlorophyll-a) show good general coherence across these months, providing justification for the use of summertime mean values. The revised climatology shows notable differences with the existing global climatology. In particular, we find increased DMS concentrations and sea–air fluxes south of the Polar Frontal zone (between ~60 and 70°S), and increased sea–air fluxes in mid-latitude waters (40–50°S). These changes are attributable to both the inclusion of new data and the use of region-specific parameters (e.g. data cut-off thresholds and interpolation radius) in our objective analysis. DMS concentrations in the Southern Ocean exhibit weak though statistically significant correlations with several oceanographic variables, including ice cover, mixed-layer depth and chlorophyll-a, but no apparent relationship with satellite-derived measures of phytoplankton photophysiology or taxonomic group abundance. Our analysis highlights the importance of using regional parameters in constructing climatological DMS fields, and identifies regions where additional observations are most needed.

scholarly journals Modeling submerged biofouled microplastics and their vertical trajectories

2021 ◽  
Author(s):  
Reint Fischer ◽  
Delphine Lobelle ◽  
Merel Kooi ◽  
Albert Koelmans ◽  
Victor Onink ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Mixed Layer ◽  
Mixed Layer Depth ◽  
Euphotic Zone ◽  
Equatorial Pacific ◽  
Open Ocean ◽  
Subtropical Gyre ◽  
Layer Depth ◽  
High Biological Activity ◽  
Near Surface

Abstract. The fate of (micro)plastic particles in the open ocean is controlled by physical and biological processes. Here, we model the effects of biofouling on the subsurface vertical distribution of spherical, virtual plastic particles with radii of 0.01–1 mm. For the physics, four vertical velocity terms are included: advection, wind-driven mixing, tidally induced mixing, and the sinking velocity of the biofouled particle. For the biology, we simulate the attachment, growth and loss of algae on particles. We track 10,000 particles for one year in three different regions with distinct biological and physical properties: the low productivity region of the North Pacific Subtropical Gyre, the high productivity region of the Equatorial Pacific and the high mixing region of the Southern Ocean. The growth of biofilm mass in the euphotic zone and loss of mass below the euphotic zone result in the oscillatory behaviour of particles, where the larger (0.1–1.0 mm) particles have much shorter average oscillation lengths (< 10 days; 90th percentile) than the smaller (0.01–0.1 mm) particles (up to 130 days; 90th percentile). A subsurface maximum concentration occurs just below the mixed layer depth (around 30 m) in the Equatorial Pacific, which is most pronounced for larger particles (0.1–1.0 mm). This occurs since particles become neutrally buoyant when the processes affecting the settling velocity of the particle and the motion of the ocean are in equilibrium. Seasonal effects in the subtropical gyre result in particles sinking below the mixed layer depth only during spring blooms, but otherwise remaining within the mixed layer. The strong winds and deepest average mixed layer depth in the Southern Ocean (400 m) result in the deepest redistribution of particles (> 5000 m). Our results show that the vertical movement of particles is mainly affected by physical (wind-induced mixing) processes within the mixed layer and biological (biofilm) dynamics below the mixed layer. Furthermore, positively buoyant particles with radii of 0.01–1.0 mm can sink far below the euphotic zone and mixed layer in regions with high near-surface mixing or high biological activity. This work can easily be coupled to other models to simulate open-ocean biofouling dynamics, in order to reach a better understanding of where ocean (micro)plastic ends up.

scholarly journals STUDY OF OCEAN PRIMARY PRODUCTIVITY USING OCEAN COLOR DATA AROUND JAPAN

2010 ◽  
Vol 2 (-) ◽  
Author(s):  
TAKAHIRO OSAWA ◽  
CHAO FANG ZHAO ◽  
I WAYAN Nuarsa ◽  
I Ketut Swardika ◽  
YASUHIRO SUGIMORI
Keyword(s):  
Neural Network ◽  
Chlorophyll A ◽  
Mixed Layer ◽  
Primary Productivity ◽  
Mixed Layer Depth ◽  
Ocean Color ◽  
Sea Surface ◽  
Layer Depth ◽  
Concentration Data ◽  
Gaussian Shape

Ocean primary production is an important factor for determining the ocean's role in global carbon cycle. In recent years, much more chlorophyll-a concentration data in the euphotic layer were derived from the satellite ocean color sensors. The primary productivity algorithms have been proposed based on satellite chlorophyll measurements (Piatt, 1988; Morel, 1991) and other environmental parameters such as sea surface temperature or mixed layer depth (Behrenfeld and Falkowski, 1997; Esaias, 1996; Asanuma, 2002). In order to estimate integrated primary productivity in the whole water column, the vertical distribution of chlorophyll concentration below the sea surface should be reconstructed based on satellite data. In this paper, the vertical profile data of chlorophyll-a (Chl-a) measured around Japan Islands from 1974 to 1994 were reanalyzed based on the shifted-Gaussian shape proposed by Piatt et al (1988). Using this statistical model (neural network) and the photosynthesis irradiance parameters from Asanuma (2002), the distribution of primary productivity and its seasonal variation around Japan islands were estimated from SeaWiFS data, and the results were compared with in situ data and the other two models estimated from VGPM and mixed layer depth model. Keywords: ocean color, primary productivity, chlorophyll profile, artificial neural network

scholarly journals Intra-annual variability of the mixed layer parameters in the Okhotsk Sea

2018 ◽  
Vol 195 ◽  
pp. 170-183 ◽  
Author(s):  
V. A. Luchin
Keyword(s):  
Temperature Distribution ◽  
Mixed Layer ◽  
Mixed Layer Depth ◽  
Kuril Islands ◽  
Water Dynamics ◽  
Positive Temperature ◽  
Okhotsk Sea ◽  
Layer Depth ◽  
Mean Values ◽  
Lower Temperature

All available oceanographic data for the deep-water part of the Okhotsk Sea, in total 111,944 stations collected in 1931–2014, are analyzed after removing the duplicate and lowquality ones. The mixed layer depth is determined on the water temperature profle for each station and monthly mean values of temperature and salinity in the mixed layer are calculated for the 0.5о-size grid. In May-October, the mixed layer depth varies within the range 5–25 m, with the highest values in the areas with active water dynamics. On the contrary, the mixed layer is much deeper in December-April when its thickness exceeds 40–60 meters and even reaches 100–120 m in the central Kuril Straits. Two types of temperature distribution change annually within the mixed layer in the Okhotsk Sea: the winter pattern with higher (positive) temperature at Kuril Islands occurs in December-April and the summer pattern is formed in June-September and is distinguished by spots of lower temperature in the dynamically active  areas with strong tidal and non-tidal currents (Kuril Straits, Kashevarov Bank, entrance to the Shelikhov Bay, Shantar Islands vicinity, northeastern shelf of Sakhalin Island). Transition patterns of the temperature distribution are observed in May, October, and November. Largescale patterns of salinity distribution within the mixed layer are permanent throughout a year and indicate prevailing currents and other processes in the upper layer of the Okhotsk Sea. The maximum salinity is observed in the southern Okhotsk Sea, whereas the lower salinity values are usual for the coastal waters (except the coasts of Kuril Islands) affected to the river runoff.

scholarly journals Characteristics of Mixed Layer Depth and Its Effect on Concentration of Chlorophyll-a (Karakteristik Mixed Layer Depth dan Pengaruhnya Terhadap Konsentrasi Klorofil-a)

2015 ◽  
Vol 19 (4) ◽  
pp. 219 ◽  
Author(s):  
Novita Ayu Ryandhini ◽  
Muhammad Zainuri ◽  
Anastasia Rita Tisiana D. K.
Keyword(s):  
Chlorophyll A ◽  
Mixed Layer ◽  
Mixed Layer Depth ◽  
Vertical Movement ◽  
Water Masses ◽  
Homogeneous Layer ◽  
Indonesian Throughflow ◽  
Layer Depth ◽  
Current Activity ◽  
Chlorophyll A Content

Perairan Selat Badung memiliki karakteristik yang sebagian besar dipengaruhi oleh aktivitas Arus Lintas Indonesia (ARLINDO). Pencampuran massa air akibat pergerakan massa air vertikal menjadikan kondisi lapisan yang homogen, dimana nilai suhu, salinitas dan densitas berada pada nilai yang hampir sama di lapisan tertentu akan membentuk Mixed Layer Depth (MLD). Penelitian dilakukan untuk mengetahui karakteristik MLD dan pengaruhnya terhadap konsentrasi klorofil-a di Perairan Selat Badung, Bali. Metode pengukuran klorofil-a menggunakan spektrofotometri. Hasil penelitian menunjukkan bahwa suhu dan salinitas sebagai parameter MLD, membentuk lapisan yang homogen pada kedalaman yang bervariasi. Sebaran kandungan klorofil-a pada kedalaman MLD 12-23 m, menunjukkan nilai klorofil-a yang cenderung lebih tinggi pada permukaan perairan dibandingkan di perairan yang lebih dalam. Pada MLD kedalaman 12-60 m, menunjukkan bahwa kecenderungan kandungan klorofil-a lebih tinggi pada lapisan di kedalaman tersebut. Namun pada beberapa stasiun menunjukkan bahwa meskipun terdapat lapisan homogen yang cukup dalam, kandungan klorofil-a lebih tinggi di lapisan permukaan dibandingkan pada perairan yang lebih dalam. Kata Kunci: mixed layer depth, klorofil-a, perairan selat Badung Badung Strait characteristics is largely influenced by the ARLINDO (Indonesian Throughflow) current activity. The mixing of water masses due to the vertical movement of water masses, homogenized some range of layer (Mixed Layer Depth), whereas the value of temperature, salinity and density were about on the same range. The study was conducted to determine the characteristics of MLD and its influence on the concentration of chlorophyll-a of Badung Strait, Bali. Chlorophyll-a content was measured by using spectrophotometry method. The results showed that temperature and salinity as the MLD parameters, formed homogeneous layer (MLD) at varying depths. Distribution of MLD at depth of 12-23 m, indicating that chlorophyll-a consentration tends to be higher on the surface than at depth. In conditions at depth of 12-60 m, showed that chlorophyll-a higher on the depth, where a lot of MLD formed on the layer. However, in some stations showed that although there were quite a lot of homogeneous layer, chlorophyll-a consentration was higher on the surface than in the depth. Keywords: Mixed Layer Depth, Chlorophyll-a, Badung Strait

scholarly journals Mesoscale and Submesoscale Effects on Mixed Layer Depth in the Southern Ocean

2017 ◽  
Vol 47 (9) ◽  
pp. 2173-2188 ◽  
Author(s):  
S. D. Bachman ◽  
J. R. Taylor ◽  
K. A. Adams ◽  
P. J. Hosegood
Keyword(s):  
Southern Ocean ◽  
Mixed Layer ◽  
Large Scale ◽  
Mixed Layer Depth ◽  
Surface Mixed Layer ◽  
Grid Spacing ◽  
Layer Depth ◽  
State Estimate ◽  
Nested Models ◽  
Significant Difference

AbstractSubmesoscale dynamics play a key role in setting the stratification of the ocean surface mixed layer and mediating air–sea exchange, making them especially relevant to anthropogenic carbon uptake and primary productivity in the Southern Ocean. In this paper, a series of offline-nested numerical simulations is used to study submesoscale flow in the Drake Passage and Scotia Sea regions of the Southern Ocean. These simulations are initialized from an ocean state estimate for late April 2015, with the intent to simulate features observed during the Surface Mixed Layer at Submesoscales (SMILES) research cruise, which occurred at that time and location. The nested models are downscaled from the original state estimate resolution of 1/12° and grid spacing of about 8 km, culminating in a submesoscale-resolving model with a resolution of 1/192° and grid spacing of about 500 m. The submesoscale eddy field is found to be highly spatially variable, with pronounced hot spots of submesoscale activity. These areas of high submesoscale activity correspond to a significant difference in the 30-day average mixed layer depth between the 1/12° and 1/192° simulations. Regions of large vertical velocities in the mixed layer correspond with high mesoscale strain rather than large . It is found that is well correlated with the mesoscale density gradient but weakly correlated with both the mesoscale kinetic energy and strain. This has implications for the development of submesoscale eddy parameterizations that are sensitive to the character of the large-scale flow.

scholarly journals Using dissolved oxygen concentrations to determine mixed layer depths in the Bellingshausen Sea

2011 ◽  
Vol 8 (3) ◽  
pp. 1505-1533
Author(s):  
K. Castro-Morales ◽  
J. Kaiser
Keyword(s):  
Southern Ocean ◽  
Mixed Layer ◽  
Mixed Layer Depth ◽  
Potential Temperature ◽  
World Ocean ◽  
Reference Value ◽  
Relative Difference ◽  
Layer Depth ◽  
Biological Production ◽  
World Ocean Atlas

Abstract. Concentrations of oxygen (O2) and other dissolved gases in the oceanic mixed layer are often used to calculate air-sea gas exchange fluxes; for example, in the context of net and gross biological production estimates. The mixed layer depth (zmix) may be defined using criteria based on temperature or density differences to a reference depth near the ocean surface. However, temperature criteria fail in regions with strong haloclines such as the Southern Ocean where heat, freshwater and momentum fluxes interact to establish mixed layers. Moreover, the time scales of air-sea exchange differ for gases and heat, so that zmix defined using O2 may be different to zmix defined using temperature or density. Here, we propose to define an O2-based mixed layer depth, zmix(O2), as the depth where the relative difference between the O2 concentration and a reference value at a depth equivalent to 10 dbar equals 0.5 %. This definition was established by numerical analysis of O2 profiles in coastal areas of the Southern Ocean and corroborated by visual inspection. Comparisons of zmix(O2) with zmix based on potential temperature differences, i.e. zmix(Δθ = 0.2 °C) and zmix(Δθ = 0.5 °C), and potential density differences, i.e. zmix(Δσθ = 0.03 kg m−3) and zmix(Δσθ = 0.125 kg m−3), showed that zmix(O2) closely follows zmix(Δσθ = 0.03 kg m−3). Further comparisons with published zmix climatologies and zmix derived from World Ocean Atlas 2005 data were also performed. To establish zmix for use with biological production estimates in the absence of O2 profiles, we suggest using zmix(Δσθ = 0.03 kg m−3), which is also the basis for the climatology by de Boyer Montégut et al. (2004).

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