Pelagic primary production in the Coral and southern Solomon Seas

1996 ◽  
Vol 47 (5) ◽  
pp. 695 ◽  
Author(s):  
MJ Furnas ◽  
AW Mitchell
Keyword(s):  
Primary Production ◽  
Mixed Layer ◽  
Standing Crop ◽  
Central Basin ◽  
Strong Wind ◽  
Surface Mixed Layer ◽  
Barrier Reef ◽  
Near Surface ◽  
Western Margin ◽  
Coral Sea

Phytoplankton primary production was measured around the periphery of the Coral Sea during October 1985 and in the boundary current systems bordering the northern Australian Great Barrier Reef (GBR) and Papuan Barrier Reef (PBR) during October 1985 and June-July 1988. Under strong wind conditions (mean winds 8-12 m s-1), the north-western Papuan Barrier Reef region was characterized by a shallow surface mixed layer, shallow nutriclines (25-75 m) and shallow subsurface chlorophyll maxima. Under low wind stress conditions (mean winds <5 m s-1), the southern and western Coral Sea were also characterized by a shallow surface mixed layer and stable underlying density profiles but deep (>I00 m) nutriclines and deep (60-125 m) subsurface chlorophyll and primary production maxima. Regardless of location, most primary production occurred above the 20% mid-day isolume surface. Phytoplankton standing crop and primary production in all regions were dominated by picoplankton (<2 μm size fraction). Very high primary production rates (1-3 g C m-2 day-1) were measured at a number of stations adjacent to the western margin of the PBR and within the central basin of the Louisiade Archipelago. Evidence for upwelling along the western margin of the PBR was observed under both north-easterly (normal to the reef axis) and south-easterly (parallel to the reef axis) wind regimes; however, surface outcropping of upwelled water did not occur. Oceanic primary production in the Coral Sea is estimated to be between 100 and 200 g C m-2 year-1. Primary production in and around the Louisiade Archipelago appears to be on the order of 200-300 g C m-2 year-1. Near-surface chlorophyll standing crop was generally better correlated with near-surface primary production than was total chlorophyll with total areal primary production.

scholarly journals Fixed-Point Observation of Mixed Layer Evolution in the Seasonally Ice-Free Chukchi Sea: Turbulent Mixing due to Gale Winds and Internal Gravity Waves

2015 ◽  
Vol 45 (3) ◽  
pp. 836-853 ◽  
Author(s):  
Yusuke Kawaguchi ◽  
Shigeto Nishino ◽  
Jun Inoue
Keyword(s):  
Fixed Point ◽  
Mixed Layer ◽  
Gravity Waves ◽  
Chukchi Sea ◽  
Internal Gravity Waves ◽  
The Arctic ◽  
Strong Wind ◽  
Surface Mixed Layer ◽  
Mixing Processes ◽  
Near Surface

AbstractA fixed-point observation using the R/V Mirai was conducted in the ice-free northern Chukchi Sea of the Arctic Ocean during September of 2013. During the program the authors performed repeated microstructure measurements to reveal the temporal evolution of the surface mixed layer and mixing processes in the upper water column. The shelf region was initially characterized by a distinct two-layer system comprising a warmer/fresher top layer and a colder/saltier bottom layer. During the two-week observation period, the top-layer water showed two types of mixing processes: near-surface turbulence due to strong wind forcing and subsurface mixing due to internal gravity waves. In the first week, when the top layer was stratified with fresh sea ice meltwater, turbulent energy related to internal waves propagated through the subsurface stratification, resulting in a mechanical overturning near the pycnocline, followed by enhanced mixing there. In the second week, gale winds directly stirred up the upper water and then established a deeper homogenous layer. The combination of internal wave mixing and wind-driven turbulence may contribute to releasing the oceanic heat into the atmosphere, consequently promoting the preconditioning of surface water freezing.

A numerical investigation of solitary internal waves with trapped cores formed via shoaling

2002 ◽  
Vol 451 ◽  
pp. 109-144 ◽  
Author(s):  
KEVIN G. LAMB
Keyword(s):  
Internal Waves ◽  
Mixed Layer ◽  
Propagation Speed ◽  
Horizontal Velocity ◽  
Buoyancy Frequency ◽  
Surface Mixed Layer ◽  
Near Surface ◽  
Flow Limit ◽  
Wave Propagation Speed ◽  
Solitary Internal Waves

The formation of solitary internal waves with trapped cores via shoaling is investigated numerically. For density fields for which the buoyancy frequency increases monotonically towards the surface, sufficiently large solitary waves break as they shoal and form solitary-like waves with trapped fluid cores. Properties of large-amplitude waves are shown to be sensitive to the near-surface stratification. For the monotonic stratifications considered, waves with open streamlines are limited in amplitude by the breaking limit (maximum horizontal velocity equals wave propagation speed). When an exponential density stratification is modified to include a thin surface mixed layer, wave amplitudes are limited by the conjugate flow limit, in which case waves become long and horizontally uniform in the centre. The maximum horizontal velocity in the limiting wave is much less than the wave's propagation speed and as a consequence, waves with trapped cores are not formed in the presence of the surface mixed layer.

scholarly journals Halocarbon emissions and sources in the equatorial Atlantic Cold Tongue

2015 ◽  
Vol 12 (7) ◽  
pp. 5559-5608 ◽  
Author(s):  
H. Hepach ◽  
B. Quack ◽  
S. Raimund ◽  
T. Fischer ◽  
E. L. Atlas ◽  
...  
Keyword(s):  
Surface Water ◽  
Mixed Layer ◽  
Global Radiation ◽  
Surface Mixed Layer ◽  
Cold Tongue ◽  
Equatorial Atlantic ◽  
Tropical Ocean ◽  
Near Surface ◽  
Biological Source ◽  
Atlantic Cold Tongue

Abstract. Halocarbons from oceanic sources contribute to halogens in the troposphere, and can be transported into the stratosphere where they take part in ozone depletion. This paper presents distribution and sources in the equatorial Atlantic from June and July 2011 of the four compounds bromoform (CHBr3), dibromomethane (CH2Br2), methyl iodide (CH3I) and diiodomethane (CH2I2). Enhanced biological production during the Atlantic Cold Tongue (ACT) season, indicated by phytoplankton pigment concentrations, led to elevated concentrations of CHBr3 of up to 44.7 pmol L−1 and up to 9.2 pmol L−1 for CH2Br2 in surface water, which is comparable to other tropical upwelling systems. While both compounds correlated very well with each other in the surface water,CH2Br2 was often more elevated in greater depth than CHBr3, which showed maxima in the vicinity of the deep chlorophyll maximum. The deeper maximum of CH2Br2 indicates an additional source in comparison to CHBr3 or a slower degradation of CH2Br2. Concentrations of CH3I of up to 12.8 pmol L−1 in the surface water were measured. In contrary to expectations of a predominantly photochemical source in the tropical ocean, its distribution was mostly in agreement with biological parameters, indicating a~biological source. CH2I2 was very low in the near surface water with maximum concentrations of only 3.7 pmol L−1, and the observed anticorrelation with global radiation was likely due to its strong photolysis. CH2I2 showed distinct maxima in deeper waters similar to CH2Br2. For the first time, diapycnal fluxes of the four halocarbons from the upper thermocline into and out of the mixed layer were determined. These fluxes were low in comparison to the halocarbon sea-to-air fluxes. This indicates that despite the observed maximum concentrations at depth, production in the surface mixed layer is the main oceanic source for all four compounds and has an influence on emissions into the atmosphere. The calculated production rates of the compounds yield 34 (CHBr3), 10 (CH2Br2), 21 (CH3I) and 384 (CH2I2) pmol m−3 h−1 in the whole mixed layer.

scholarly journals Halocarbon emissions and sources in the equatorial Atlantic Cold Tongue

2015 ◽  
Vol 12 (21) ◽  
pp. 6369-6387 ◽  
Author(s):  
H. Hepach ◽  
B. Quack ◽  
S. Raimund ◽  
T. Fischer ◽  
E. L. Atlas ◽  
...  
Keyword(s):  
Surface Water ◽  
Mixed Layer ◽  
Surface Mixed Layer ◽  
Cold Tongue ◽  
Equatorial Atlantic ◽  
Tropical Ocean ◽  
Near Surface ◽  
Biological Source ◽  
First Time ◽  
Atlantic Cold Tongue

Abstract. Halocarbons from oceanic sources contribute to halogens in the troposphere, and can be transported into the stratosphere where they take part in ozone depletion. This paper presents distribution and sources in the equatorial Atlantic from June and July 2011 of the four compounds bromoform (CHBr3), dibromomethane (CH2Br2), methyl iodide (CH3I) and diiodomethane (CH2I2). Enhanced biological production during the Atlantic Cold Tongue (ACT) season, indicated by phytoplankton pigment concentrations, led to elevated concentrations of CHBr3 of up to 44.7 and up to 9.2 pmol L−1 for CH2Br2 in surface water, which is comparable to other tropical upwelling systems. While both compounds correlated very well with each other in the surface water, CH2Br2 was often more elevated in greater depth than CHBr3, which showed maxima in the vicinity of the deep chlorophyll maximum. The deeper maximum of CH2Br2 indicates an additional source in comparison to CHBr3 or a slower degradation of CH2Br2. Concentrations of CH3I of up to 12.8 pmol L−1 in the surface water were measured. In contrary to expectations of a predominantly photochemical source in the tropical ocean, its distribution was mostly in agreement with biological parameters, indicating a biological source. CH2I2 was very low in the near surface water with maximum concentrations of only 3.7 pmol L−1. CH2I2 showed distinct maxima in deeper waters similar to CH2Br2. For the first time, diapycnal fluxes of the four halocarbons from the upper thermocline into and out of the mixed layer were determined. These fluxes were low in comparison to the halocarbon sea-to-air fluxes. This indicates that despite the observed maximum concentrations at depth, production in the surface mixed layer is the main oceanic source for all four compounds and one of the main driving factors of their emissions into the atmosphere in the ACT-region. The calculated production rates of the compounds in the mixed layer are 34 ± 65 pmol m−3 h−1 for CHBr3, 10 ± 12 pmol m−3 h−1 for CH2Br2, 21 ± 24 pmol m−3 h−1 for CH3I and 384 ± 318 pmol m−3 h−1 for CH2I2 determined from 13 depth profiles.

scholarly journals Topographic and Mixed Layer Submesoscale Currents in the Near-Surface Southwestern Tropical Pacific

2017 ◽  
Vol 47 (6) ◽  
pp. 1221-1242 ◽  
Author(s):  
Kaushik Srinivasan ◽  
James C. McWilliams ◽  
Lionel Renault ◽  
Hristina G. Hristova ◽  
Jeroen Molemaker ◽  
...  
Keyword(s):  
Heat Flux ◽  
Surface Layer ◽  
Kinetic Energy ◽  
Wind Stress ◽  
Mixed Layer ◽  
Surface Heat Flux ◽  
Seasonal Cycle ◽  
Surface Heat ◽  
Near Surface ◽  
Coral Sea

AbstractThe distribution and strength of submesoscale (SM) surface layer fronts and filaments generated through mixed layer baroclinic energy conversion and submesoscale coherent vortices (SCVs) generated by topographic drag are analyzed in numerical simulations of the near-surface southwestern Pacific, north of 16°S. In the Coral Sea a strong seasonal cycle in the surface heat flux leads to a winter SM “soup” consisting of baroclinic mixed layer eddies (MLEs), fronts, and filaments similar to those seen in other regions farther away from the equator. However, a strong wind stress seasonal cycle, largely in sync with the surface heat flux cycle, is also a source of SM processes. SM restratification fluxes show distinctive signatures corresponding to both surface cooling and wind stress. The winter peak in SM activity in the Coral Sea is not in phase with the summer dominance of the mesoscale eddy kinetic energy in the region, implying that local surface layer forcing effects are more important for SM generation than the nonlocal eddy deformation field. In the topographically complex Solomon and Bismarck Seas, a combination of equatorial proximity and boundary drag generates SCVs with large-vorticity Rossby numbers (Ro ~ 10). River outflows in the Bismarck and Solomon Seas make a contribution to SM generation, although they are considerably weaker than the topographic effects. Mean to eddy kinetic energy conversions implicate barotropic instability in SM topographic wakes, with the strongest values seen north of the Vitiaz Strait along the coast of Papua New Guinea.

scholarly journals Acoustic mapping of mixed layer depth

2018 ◽  
Author(s):  
Christian Stranne ◽  
Larry Mayer ◽  
Martin Jakobsson ◽  
Elizabeth Weidner ◽  
Kevin Jerram ◽  
...  
Keyword(s):  
Mixed Layer ◽  
Mixed Layer Depth ◽  
Chemical Components ◽  
Surface Mixed Layer ◽  
Central Arctic Ocean ◽  
Near Surface ◽  
Direct Observations ◽  
Spatial Coverage ◽  
Major Factors ◽  
Acoustic Mapping

Abstract. The ocean surface mixed layer is a nearly universal feature of the world oceans. The depth of the mixed layer (MLD) influences the exchange of heat and gases between the atmosphere and the ocean and constitutes one of the major factors controlling ocean primary production as it affects the vertical distribution of biological and chemical components in near-surface waters. Direct observations of the MLD are traditionally made by means of conductivity, temperature and depth (CTD) casts. However, CTD instrument deployment limits the observation of temporal and spatial variability of the MLD. Here, we present an alternative method where acoustic mapping of the MLD is done remotely by means of commercially available ship-mounted echosounders. The method is shown to be highly accurate when the MLD is well defined and biological scattering does not dominate the acoustic returns. These prerequisites are often met in the open ocean and it is shown that the method is successful in 95 % of data collected in the central Arctic Ocean. The primary advantages of acoustically mapping the MLD over CTD measurements are: (1) considerably higher temporal and horizontal resolutions and (2) potentially larger spatial coverage.

scholarly journals Cold-Water Events and Dissipation in the Mixed Layer of a Lake

2006 ◽  
Vol 36 (10) ◽  
pp. 1928-1939 ◽  
Author(s):  
B. Ozen ◽  
S. A. Thorpe ◽  
U. Lemmin ◽  
T. R. Osborn
Keyword(s):  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Mixed Layer ◽  
Large Scale ◽  
Cold Water ◽  
Velocity Shear ◽  
Surface Mixed Layer ◽  
Near Surface ◽  
Law Of The Wall ◽  
Upward Direction

Abstract Measurements of temperature, velocity, and microscale velocity shear were made from the research submarine F. A. Forel in the near-surface mixed layer of Lake Geneva under conditions of moderate winds of 6–8 m s−1 and of net heating at the water surface. The submarine carried arrays of thermistors and a turbulence package, including airfoil shear probes. The rate of dissipation of turbulent kinetic energy per unit mass, estimated from the variance of the shear, is found to be lognormally distributed and to vary with depth roughly in accordance with the law of the wall at the measurement depths, 15–20 times the significant wave height. Measurements revealed large-scale structures, coherent over the 2.38-m vertical extent sampled by a vertical array of thermistors, consisting of filaments tilted in the wind direction. They are typically about 1.5 m wide, decreasing in width in the upward direction, and are horizontally separated by about 25 m in the downwind direction. Originating in the upper thermocline, they are characterized in the mixed layer by their relatively low temperature and low rates of dissipation of turbulent kinetic energy and by an upward vertical velocity of a few centimeters per second.

Tropical Cells and a Secondary Circulation near the Northern Front of the Equatorial Pacific Cold Tongue*

2010 ◽  
Vol 40 (9) ◽  
pp. 2091-2106 ◽  
Author(s):  
Renellys C. Perez ◽  
Meghan F. Cronin ◽  
William S. Kessler
Keyword(s):  
Mixed Layer ◽  
Equatorial Pacific ◽  
Secondary Circulation ◽  
Subsurface Water ◽  
Surface Mixed Layer ◽  
Cold Tongue ◽  
Near Surface ◽  
Instability Waves ◽  
Tropical Instability Waves ◽  
The Mean

Abstract Shipboard measurements and a model are used to describe the mean structure of meridional–vertical tropical cells (TCs) in the central equatorial Pacific and a secondary circulation associated with the northern front of the cold tongue. The shape of the front is convoluted by the passage of tropical instability waves (TIWs). When velocities are averaged in a coordinate system centered on the instantaneous position of the northern front, the measurements show a near-surface minimum in northward flow north of the surface front (convergent flow near the front). This convergence and inferred downwelling extend below the surface mixed layer, tilt poleward with depth, and are meridionally bounded by regions of divergence and upwelling. Similarly, the model shows that, on average, surface cold tongue water moves northward toward the frontal region and dives below tilted front, whereas subsurface water north of the front moves southward toward the front, upwells, and then moves northward in the surface mixed layer. The model is used to demonstrate that this mean quasi-adiabatic secondary circulation is not a frozen field that migrates with the front but is instead highly dependent on the phase of the TIWs: southward-upwelling flow on the warm side of the front tends to occur when the front is displaced southward, whereas northward-downwelling flow on the cold side of the front occurs when the front is displaced northward. Consequently, when averaged in geographic coordinates, the observed and simulated TCs appear to be equatorially asymmetric and show little trace of a secondary circulation near the mean front.

Phototrophic Picoplankton in Lakes Huron and Michigan: Abundance, Distribution, Composition, and Contribution to Biomass and Production

1992 ◽  
Vol 49 (2) ◽  
pp. 379-388 ◽  
Author(s):  
Gary L. Fahnenstiel ◽  
Hunter J. Carrick
Keyword(s):  
Primary Production ◽  
Mixed Layer ◽  
Thermal Stratification ◽  
Size Fraction ◽  
Surface Mixed Layer ◽  
Abundance Distribution ◽  
Size Fractions ◽  
Phototrophic Picoplankton ◽  
Distribution Composition ◽  
Isothermal Mixing

The phototropic picoplankton communities of Lakes Huron and Michigan were studied from 1986 through 1988. Abundances in the surface-mixed layer ranged from 10 000 to 220 000 cells∙mL−1 with a seasonal maximum during the period of thermal stratification. During thermal stratification, maximum abundances were generally found within the metalimnion/hypolimnion at depths corresponding to the 0.6–6.0% isolumes. The picoplankton community was dominated by single phycoerythrin-containing (PE) Synechococcus (59%) with lesser amounts of chlorophyll fluorescing cells (21%), PE colonial Synechococcus-like cells (11%), other PE colonial Chroococcales (6%), and other cells (3%). Single PE Synechococcus was abundant throughout the year whereas chlorophyll-fluorescing and colonial cyanobacteria were more abundant during the periods of spring isothermal mixing and summer stratification, respectively. Picoplankton accounted for an average of 10% (range 0.5–50%) of phototrophic biomass. Phototrophic organisms that passed 1-, 3-, and 10-μm screens were responsible for an average of 17% (range 6–43%), 40% (21–65%), and 70% (52–90%) of primary production. Maximum contributions of < 1, < 3, and < 10 μm size fractions occurred during the period of thermal stratification. Primary production by phototrophic picoplankton was found to equal production in the < 1 μm size fraction.

scholarly journals Acoustic mapping of mixed layer depth

Ocean Science ◽  
2018 ◽  
Vol 14 (3) ◽  
pp. 503-514 ◽  
Author(s):  
Christian Stranne ◽  
Larry Mayer ◽  
Martin Jakobsson ◽  
Elizabeth Weidner ◽  
Kevin Jerram ◽  
...  
Keyword(s):  
Mixed Layer ◽  
Mixed Layer Depth ◽  
Chemical Components ◽  
Surface Mixed Layer ◽  
Central Arctic Ocean ◽  
Near Surface ◽  
Direct Observations ◽  
Spatial Coverage ◽  
Major Factors ◽  
Acoustic Mapping

Abstract. The ocean surface mixed layer is a nearly universal feature of the world oceans. Variations in the depth of the mixed layer (MLD) influences the exchange of heat, fresh water (through evaporation), and gases between the atmosphere and the ocean and constitutes one of the major factors controlling ocean primary production as it affects the vertical distribution of biological and chemical components in near-surface waters. Direct observations of the MLD are traditionally made by means of conductivity, temperature, and depth (CTD) casts. However, CTD instrument deployment limits the observation of temporal and spatial variability in the MLD. Here, we present an alternative method in which acoustic mapping of the MLD is done remotely by means of commercially available ship-mounted echo sounders. The method is shown to be highly accurate when the MLD is well defined and biological scattering does not dominate the acoustic returns. These prerequisites are often met in the open ocean and it is shown that the method is successful in 95 % of data collected in the central Arctic Ocean. The primary advantages of acoustically mapping the MLD over CTD measurements are (1) considerably higher temporal and horizontal resolutions and (2) potentially larger spatial coverage.

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