Stratified Water Bodies Research Articles

A revised age model for core PG1351 from Lake El’gygytgyn, Chukotka, based on magnetic susceptibility variations tuned to northern hemisphere insolation variations

A combined analysis of magnetic susceptibility, total organic carbon (TOC), biogenic silica (opal), and TiO2 content of the 12.6 m long composite core PG1351 recovered from Lake El’gygytgyn, Chukotka Peninsula, indicate a clear response of the lacustrine sedimentary record to climate variations. The impact is not direct, but through variations in oxygenation of the bottom waters. Mixing of the water body is typical for warmer climates, whereas the development of a stratified water body associated with anoxic conditions at the lake floor appears during cold climates. Oxic conditions lead to a good magnetite preservation and thus to high magnetic susceptibilities, but also to a large-scale degradation of organic matter, as reflected by low TOC (total organic carbon) values. During anoxic conditions, magnetite is severely dissolved yielding very low susceptibility values, whereas organic matter is best preserved, reflected by high TOC values. Hence, in general, neither susceptibility reflects the lithogenic fraction, nor does TOC reflect bioproductivity in case of the studied El’gygytgyn sediments. Based on available infrared stimulated luminescence (IRSL) dating, the obtained susceptibility pattern of core PG1351 shows an obvious correlation to northern hemisphere insolation variations, with a dominating impact of the Earth’s 18 and 23 kyr precessional cycles for the upper half of PG1351, that is, during the past 150 ka. Therefore, the whole susceptibility record, together with biogenic silica (as a proxy for bioproductivity), TOC (as an indicator for redox conditions), and TiO2 (as a proxy for lithogenic input), was systematically tuned to the northern hemisphere insolation yielding an age of about 250 ka for the base of the composite core.

Limnology of Two Antarctic Epishelf Lakes and their Potential to Record Periods of Ice Shelf Loss

George VI Ice Shelf is the largest ice shelf on the western side of the Antarctic Peninsula and its northern margin marks the southern most latitudinal limit of recent ice shelf retreat. As part of a project to reconstruct the long-term (Holocene) history of George VI Ice Shelf we studied two epishelf lakes impounded by the ice shelf at Ablation Point, on the east coast of Alexander Island. These lakes, Moutonnee and Ablation, are stratified water bodies with a lower marine layer and an upper freshwater layer. To determine if their sediment records could be used to detect past changes in the presence or absence of the ice shelf it was necessary to describe their present-day limnology and sedimentology. We measured water column chemistry and sampled the water column and sediments of the lakes along vertical and horizontal transects. We analysed these samples for diatoms, stable isotopes (δ18O, δ2H, δ13CDIC, δ13Corg), geochemistry (TOC, TN, C/N ratios) and physical sedimentology (grain-size). This was supplemented by chemical and biological reference data from the catchments. Results showed that the water columns of both lakes are nutrient limited and deficient in phytoplankton. Benthic productivity is low and decreases with depth. Comparison of water column chemistry with an earlier survey shows a net increase in the thickness of the freshwater layer in Moutonnee Lake between 1973 and 2001, which could indicate that George VI Ice Shelf has thinned during this period. However, a similar trend was not observed in Ablation Lake (5 km to the north) and an alternative explanation is that the changes are a seasonal phenomena. Data from the surface sediment transects identified a number of proxies that respond to the present day stratification of the water column including diatom species composition, stable isotopes and geochemistry, particularly in Moutonnee Lake. Collectively these data have been used to develop a conceptual model for determining past ice shelf configuration in epishelf lakes. Specifically, periods of past ice shelf loss, and the removal of the ice dam, would see the present stratified epishelf lake replaced by a marine embayment. It is suggested that this change would leave a clear signature in the lake sediment record, notably the deposition of an exclusively marine biological assemblage, increased ice rafted debris and δ13Corg values that are indicative of marine derived organic matter.

Ray waves in a pit lake

The special basin shape of Island Copper mine pit‐lake and its sharp salinity stratification make it an ideal place to investigate ray waves, or internal wave beams, as the more recent oceanographic literature tends to name the observed phenomenon. A first‐mode internal seiche oscillates the deep water vertically over the regular bench structure of the sidewalls at a distinct frequency. Theoretical considerations show the disturbances result in internal wave beams traversing the stratified water body at a known angle. Steep sidewalls prevent the ray waves from being trapped in the beach zone. Instead the reflection at the extremely strong pycnocline creates a vertical interference pattern. Here we numerically derive the vertical length scale of this interference to be 0.43 m. This scale is in full agreement with the repeated turbulence pattern discovered underneath the pycnocline.

Toarcian oceanic anoxic event: An assessment of global causes using belemnite C isotope records

Two hypotheses have been proposed to explain simultaneous large negative excursions (up to 7‰ PeeDee belemnite) in bulk carbonate (δ13Ccarb) and organic carbon isotope records (δ13Corg) from black shales marking the Toarcian oceanic anoxic event (T‐OAE). The first explanation envisions recycling of dissolved inorganic carbon (DIC) with a light isotopic signature into the photic zone from the lower levels of a salinity‐stratified water mass, essentially requiring a regional paleoceanographic driver of the carbon cycle. The second involves the rapid and massive dissociation of methane from gas hydrates that effectively renders the T‐OAE a global perturbation of the carbon cycle. We present C isotope records from belemnites (δ13Cbel) sampled from two localities, calibrated with high‐resolution ammonite biostratigraphy and Sr isotope stratigraphy, in Yorkshire (England) and Dotternhausen (Germany), that can be used to assess which model best explains the observed changes in carbon isotopes. Our records of the δ13C composition of belemnite calcite do not show the large negative C isotope excursions shown by coeval records of δ13C in sedimentary organic matter or bulk sedimentary carbonate. It follows that isotopically light carbon cannot have dominated the ocean‐atmosphere carbon reservoir during the Toarcian OAE, as would be required were the methane release hypothesis correct. On the basis of an evaluation of available carbon isotope records we discuss a model in which the recycling of DIC from the deeper levels of a stratified water body, and shallowing of anoxic conditions into the photic zone, can explain all isotopic profiles. In particular, the model accounts for the higher C isotope values of belemnites that are characteristic of open ocean, well‐mixed conditions, and the lower C isotope values of neritic phytoplankton communities that recorded the degree of density stratification and shallowing of anoxia in the photic zone.

Origin of sulfur rich oils and H 2S in Tertiary lacustrine sections of the Jinxian Sag, Bohai Bay Basin, China

Very high S oils (up to 14.7%) with H 2S contents of up to 92% in the associated gas have been found in the Tertiary in the Jinxian Sag, Bohai Bay Basin, PR China. Several oil samples were analyzed for C and S stable isotopes and biomarkers to try to understand the origin of these unusual oil samples. The high S oils occur in relatively shallow reservoirs in the northern part of the Jinxian Sag in anhydrite-rich reservoirs, and are characteristic of oils derived from S-rich source rocks deposited in an enclosed and productive stratified hypersaline water body. In contrast, low S oils (as low as 0.03%) in the southern part of the Jinxian Sag occur in Tertiary lacustrine reservoirs with minimal anhydrite. These southern oils were probably derived from less S-rich source rocks deposited under a relatively open and freshwater to brackish lake environment that had larger amounts of higher plant inputs. The extremely high S oil samples (>10%) underwent biodegradation of normal alkanes resulting in a degree of concentration of S in the residual petroleum, although isoprenoid alkanes remain showing that biodegradation was not extreme. Interestingly, the high S oils occur in H 2S-rich reservoirs (H 2S up to 92% by volume) where the H 2S was derived from bacterial SO 4 reduction, most likely in the source rock prior to migration. Three oils in the Jinxian Sag have δ 34S values from +0.3‰ to +16.2‰ and the oil with the highest S content shows the lightest δ 34S value. This δ 34S value for that oil is close to the δ 34S value for H 2S (∼0‰). It is possible that H 2S was incorporated into functionalized compounds within the residual petroleum during biodegradation at depth in the reservoir thus accounting for the very high concentrations of S in petroleum.

In situ measurements of dissolved gases (CO 2 and CH 4) in a wide range of concentrations in a tropical reservoir using an equilibrator

An equilibrator system connected to an infrared photo acoustic gas analyzer was used in order to measure directly in situ the concentrations of dissolved CO 2 and CH 4 in waters of a tropical reservoir (Petit Saut, French Guiana). The performance of the system was tested both on a vertical profile in the stratified water body of the reservoir and in the surface waters of the river downstream the dam. Results agreed with conventional GC analysis at ±15% in a wide range of concentrations (CO 2:50–400 μmol l −1 and CH 4:0.5–350 μmol l −1 corresponding to gas partial pressures of respectively 1700–13,000 and 12–8800 μatm). The time needed for in situ measurements was equivalent to water sampling, time for GC analysis in the laboratory being suppressed. The continuous monitoring of gas concentrations for 24 h in the reservoir surface waters revealed rapid changes in concentrations highly significant in the daily emission budget. The system opens new perspectives for the monitoring of gas concentrations in highly dynamic systems like tropical reservoirs.

Underwater Measurements of Transmitted Light Spectra in Stratified Water Bodies on the White Sea Coast as a Key to the Understanding of Pigment Composition of Phototrophs in the Chemocline Zone

Underwater Measurements of Transmitted Light Spectra in Stratified Water Bodies on the White Sea Coast as a Key to the Understanding of Pigment Composition of Phototrophs in the Chemocline Zone

Spatial Distribution Patterns of Sulfur Isotopes, Nodular Carbonate, and Ore Textures in the McArthur River (HYC) Zn-Pb-Ag Deposit, Northern Territory, Australia

The HYC Zn-Pb-Ag deposit at McArthur River is the largest known and least deformed Australian sedimenthosted stratiform base metal deposit. A study of mineralogical, geochemical, and isotopic zonation through the deposit reveals concentric distribution patterns in (1) the occurrence of nodular carbonate, (2) the δ34S composition of sphalerite, and (3) microscopic ore textures. The correlation of previously documented lateral metal zonation with these other zonation patterns precludes exclusive postsedimentation mineralization and provides some insight into the mechanisms and controls on synsedimentary to early diagenetic mineralization. This mineralization timing is also supported by new carbon and oxygen isotope analyses, recognition of two stages of texturally and isotopically distinct sphalerite, and reinterpretation of complex sulfide textures. Dolomitic carbonate nodules occur in the south, southwest, northwest, and northern fringes of the deposit and are interpreted to have surrounded the high-grade ore lenses prior to structural and erosive truncation. The carbon and oxygen isotope composition of these carbonate nodules is similar to the sedimentary dolomite within the ore lenses. There is no evidence for incorporation of light carbon derived from oxidation of organic material under closed-system conditions and the nodular carbonate probably formed under open-system conditions in communication with seawater. These nodules displace siltstone laminae and, therefore, likely formed in the very shallow subsea-floor environment. In ore lens 3, the δ34S of laminated early sphalerite (sp1) changes from a mean value of 5 per mil in the deposit center to a mean of 1.7 per mil in the extreme fringes. We interpret this to be the result of sulfide precipitation in a restricted marine basin. Later sphalerite (sp2) associated with nodular carbonate has a mean δ34S value of 9.8 per mil, whereas laminated early sphalerite (sp1) has a mean δ34S value of 3.8 per mil. This isotopic separation of the two paragenetic stages of sphalerite is found in immediately adjacent aggregates. Concentration of 34S in late sphalerite (sp2) is likely the result of closed-system conditions in the sediment pore fluid. Textures of laminated sphalerite change from strongly anastomosing in the central part of the deposit to plane laminar and patchy in the deposit fringes. Mass-balance calculations preclude substantial carbonate dissolution and a stylolitic origin for these textures. Instead we propose that rapidly precipitated sphalerite coagulated and trapped pelagic silt and early pyrite (py1) as it was deposited on the sea floor. In contrast, paragenetically late sphalerite (sp2) and pyrite (py2) must be diagenetic as they overprint and are pseudomorphous after the carbonate nodules. We propose a repeating paragenetic sequence of galena/sphalerite (sp1) → pyrite (py1) → nodular carbonate → sphalerite (sp2) → pyrite (py2), which accounts for all the textural complexity and isotopic disequilibrium between sulfide phases. The data presented in this paper suggest that base metal sulfides formed both in the water column and in the uppermost sediment pile. Biological and thermochemical sulfate reduction probably occurred simultaneously in different parts of a complex physicochemical system in which stratification of the marine environment is seen as the primary control on the lateral distribution of the mineralized facies. We propose a stratified water body in which sharp internal chemical gradients separate a surficial oxic layer, an anoxic layer, and a basal hypersaline brine pool. Asymmetric metal zonation across the deposit reflects individual pulses of metalliferous fluid that were introduced into the basin as a bottom-hugging dense current.

Microcystin-producing blooms—a serious global public health issue

The investigation on microcystin topics is increasing due to the related ecological and public health risks. Recent investigation confirms a gap in establishing global patterns relating a particular environment to the bloom occurrence of a species and the production of certain microcystin variants. All the results concerning the environmental effects on the microcystin synthesis of one species must be checked in the light of genome diversity. Thus, the poisoning risks of a bloom depend on the strain causing toxicity. To be more effective, specific water treatment methods are required for blooms of different microcystin producing species (such as colonial and filamentous cyanobacteria found in stratified and unstratified water bodies, respectively). With the increasing number of new microcystin variants discovered, the development of new rapid, inexpensive and sensitive enough monitoring methods to promptly screen simultaneously a great diversity of toxins and also check their toxic effects is becoming necessary.

Numerical determination of flushing time for stratified water bodies

It is often advantageous to model a semi-enclosed estuarine or coastal embayment (e.g. fish farms or tidal inlets, or typhoon shelters) as a separate system within a larger water body connected to the outer sea. The water quality of the system depends crucially on its flushing time—the average time of a particle in the system. The flushing time is governed by the barotropic and baroclinic tidal exchanges between the system and the outer sea. We describe herein a general method to determine systematically the flushing time of a stratified water body via a numerical tracer experiment. Numerical solution of the 3D flow and mass transport equations for many practical problems show that the tracer mass removal process depends on the physical topography and bathymetry, tidal range and the degree of stratification in the outer sea. Field application suggests that the tracer mass variation can be well approximated by a double-exponential decay curve that can be described by three flushing coefficients. Using a simple analytical two-segment model, the flushing coefficients can be given a clear physical interpretation, and the flushing time can be easily determined in terms of the coefficients. The method is illustrated by application to a number of tidal inlets in Hong Kong, in both the dry and wet season. The connection between the numerically determined flushing time and the traditional bulk flushing time obtained from salt-balance methods is established.

Microbialite Formation in Seawater of Increased Alkalinity, Satonda Crater Lake, Indonesia: Discussion

Arp et al. (2003) present data which confirm and refine the results of our long-time studies (field campaigns of 1986, 1993, 1996) on Satonda Crater Lake (summarized in Kempe and Kazmierczak 1993). They reiterate the importance of marine stratified water bodies in generating, through sulfate reduction, excess alkalinity, which in turns causes very high CaCO3 supersaturation levels. This geochemical process, called the alkalinity pump (Kempe 1990), was conceptually refined using the quasi-marine Satonda Lake as a geochemical model for some epicratonic marine basins from the geological past (Kempe and Kazmierczak 1994). The concept of an alkalinity pump is important for understanding the abundance of calcified benthic cyanobacterial mats in ancient shallow seas leading to the formation of a variety of marine calcareous microbialitic structures and fine-grained calcareous sediments accumulated on the seafloor (Kempe and Kazmierczak 1990; Kazmierczak et al. 1996). While principally agreeing with Arp et al.'s results, we strongly disagree with two of their major conclusions. The first major objection concerns Arp et al.'s scepticism with respect to the calcification potential of benthic cyanobacterial mats presently living in the lake. On the basis of samples gathered in 1993 and 1996, Arp et al. conclude that these mats calcify very weakly or, in some cases, do not calcify at all. This sharply contradicts our observations showing strong permineralization of the mats both with CaCO3 and silica (e.g., Kempe and Kazmierczak 1993, Pl. 6, figs. 3-6). Mat samples we took at the end of dry season 1986 demonstrate that calcification of the cyanobacteria occurred in vivo. Masses of minute grains of CaCO3 (predominantly Mg-calcite) were observed not only on the mat surface but also within the common mucilage sheaths (glycocalyx) surrounding aggregates of living cyanobacterial coccoid cells (classified as representatives of Pleurocapsales). Minute CaCO3 grains …

Clay sedimentation along the southeastern Neo-Tethys margin during the oceanic convergence stage

The marine sedimentation along the margin of the southeastern Neo-Tethys during the oceanic convergence stage between the Senonian and the Eocene took place on sea-bottom topography formed by the folding of the Syrian arc deformation belt. The clay mineral assemblage within the marine rocks of the synclinal basins of the Syrian arc deformation belt in the southeast of Israel is dominated by smectitic IS (interstratified illite/smectite rich in smectite layers) accompanied by kaolinite, palygorskite and occasional sepiolite. The smectitic IS originated by conversion of the smectite transported from the open marine environment to the synclinal basins. The conversion of the precursor smectite took place due to warm water and the higher salinity resulting from the development of stratified water bodies in the marine synclinal basins. The origin of authigenic palygorskite and occasional sepiolite is related to the conditions of hypersaline bottom waters due to accumulation of residual heavy brines, enriched by Mg. Detrital kaolinite and discrete illite accompanying the smectitic IS in the marine rocks were transported to the Tethyan margin from the continent.

ANALYSES OF WIND-INDUCED FLOW AND MIXING IN STRATIFIED WATER BODY USING IMAGE PROCESSING AND PIV METHODS

ANALYSES OF WIND-INDUCED FLOW AND MIXING IN STRATIFIED WATER BODY USING IMAGE PROCESSING AND PIV METHODS

A sediment trap flux study for trace metals under seasonal aspects in the stratified Baltic Sea (Gotland Basin; 57°19.20′N; 20°03.00′E)

A seasonal flux study was carried out in the eastern Gotland Basin, a stratified waterbody, to describe the vertical transport of trace metals (Al, Fe, Mn, Cd, Pb, Cu, Zn, Ni, As) in particulate phases through the pycnocline. A sediment trap was deployed between December 1999 and February 2001 in 120-m depth below the pycnocline. The trap was changed quarterly, sampling periods ranged between 6 and 8 days. To characterise the water column, vertical CTD profiles (suspended particulate matter (SPM), salinity, oxygen, hydrogen sulfide) and the determination of trace metals in the dissolved and particulate phases were performed parallel to the trap experiment. The leakage of the sampling bottles was between 9% and 15%. With the exception of nickel, the blank for the investigated metals in the sodium azide poisoned stock solution was in the range between 1% and 16% in relation to the mean trace metal concentrations in the supernatant. The mean resolution (annual average) of trace metals in the supernatant in relation to the total metal concentration in the sample bottle was 53% for Cd, 49% for Mn, 26% for Cu, 14% for Zn, 15% for Ni and 2% for Fe. The vertical distribution of Mn and Fe in the water column was mainly influenced by the seasonal variability of the distance between pycnocline and redoxcline. Concentrations of suspended particulate matter (SPM) in the water column ranged between 0.05 and 0.75 mg/dm 3 with season and depth. During winter, the composition of the trap material is dominated by lithogenic fractions of aluminium and iron, while during summer, particulate organic material (POM) is the main compound with 63% of the total mass flux. Elevated trace metal contents (Zn, As, Fe, Mn, Pb) related to the particle mass were observed in suspended particulate matter (SPM) of the water column in February 2001, which was attributed to the lateral transport of material from the river Memel. A continuous increase of the enrichment factors (EF) in the trap material was noticed from December 1999 to November 2000 with highest values for the time period July 2000–November 2000 for Cd (280), Zn (87) and Ni (13) probably due to the low lithogenic Al content and the enhanced elimination of the metals by degradation products of cyanoblooms. Lead shows decreasing EF during the same time period which we think is a result of the “dilution effect” with particles of mainly biogenic origin. Total mass fluxes ranged between 1 and 200 mg/m 2 day; significant seasonal variations were not observed. This result is discussed in connection with under/overtrapping and in relation to the change of the redox conditions in the depth horizon of the deployed trap. Significant correlation exists between the fluxes of Pb/Al, As/Al, Fe/Al, Cd/C org, Cu/C org, Zn/C org and Ni/C org.

Changes in the photo‐chemistry of Microcystis aeruginosa in response to light and mixing

Summary • Here, variable to maximal chlorophyll fluorescence ratio (Fv : Fm) was used to determine light history of Microcystis aeruginosa colonies in a shallow, stratified lake. • As insolation increased, the lake stratified and M. aeruginosa colonies displayed a depression in Fv : Fm that became less severe with depth. In the afternoon, wind speed increased, entraining colonies and disrupting the discrete depth variable Fv : Fm response. The point where the photochemical response became homogenized allowed determination of the water friction velocity necessary to entrain colonies of M. aeruginosa (u* = 0.003 m s−1). • Rates of Fv : Fm depression were dependent upon the photon flux density, whereas the rate of recovery of Fv : Fm was dependent upon the historical photon density. • A model is presented which models Fv : Fm response to five mixing scenarios: a stratified water body with no motion and no vertical migration; a cell circulating within the surface mixed layer of the Torrens Lake; a nocturnally mixed water column, which stratifies at dawn, allowing vertical migration of positively buoyant M. aeruginosa colonies; organized motion with a Langmuir circulation; and a simulation of turbulent water motion.

Sedimentary pigments as markers for environmental change in an Antarctic lake

Fossil pigments were identified in a sediment core from Kirisjes Pond, a small lake in the Larsemann Hills, east Antarctica, using reversed-phase HPLC and LC–MS/MS. Chlorophyll a- and b-derived components indicate the presence of oxygenic primary producers; steryl chlorin esters provide evidence of grazing, while shifts in their esterifying sterol composition record changes in the primary producer community. Bacteriochlorophyll c- and d-derived components, indicative of photic zone anoxia, were identified with structural variations including extensive alkylation in the macrocycle up to C6. The pigment distribution reveals a change from oxygenated freshwater to a stratified water body with development of photic zone anoxia. This coincides with a marine incursion identified from diatom records and is followed by re-isolation and reversion to oxygenated freshwater conditions.

Spatial and temporal heterogeneity in succession of cyanobacterial blooms in a Spanish reservoir

We describe here the limnological characteristics of the Santillana Reservoir (Spain) and study the phytoplankton distribution during a typical growing season (July to November). The reservoir is a eutrophic stratified waterbody in central part of Spain, in which the average phytoplankton biomass in summer is higher than 20 ug chlorophyll a 1-1. Maximum phytoplankton biomass in 1999 occurred between the end of summer and the beginning of autumn (September-October). Cyanobacteria, that were generally prevalent in phytoplankton community, clearly dominated during the peak of phytoplankton biomass. Microcystis wesenbergii was dominant amongst the cyanobacteria and represented almost 100 % of the biomass at the time of maximum phytoplankton value. The importance of environmental variables triggering cyanobacterial bloom events is discussed. Our results indicate that neither temperature nor N/P ratio are related to the bloom development. However, high nutrient concentra­ tion (ammonium in particular) and stability of the watercolumn seems to coincide with the maximum abundance of Microcystis „ wesenbergii.

Periphyton algal communities from the flooded quarry Škalí - species composition, vertical distribution and seasonal changes

The benthic algal community was studied in a flooded quarry situated in Southern Bohemia (Czech Republic), using artificial substrates. The quarry represents a deep, mesotrophic and strongly stratified water body. The variations in species composition and algal biomass observed during one vegetation season are related to depth, temperature, water transparency, and oxygen concentration. Algae typical for the different seasons were distinguished. Bacillariophyceae, Chlorophyceae, Conjugatophyceae and Cyanophyta were dominant almost all the time. Chrysophyceae dominated during a short period in the spring only. Tychonema bornetii, a bluegreen alga known from alpine and Scandinavian regions, was found to be common. This ist the first published record of this species in the Czech Republic. Algal biomass and species composition showed a clear vertical stratification. On the basis of these phenomena, 4 depth zones could be distinguished. During the spring and summer, some species associations from shallower depths moved into deeper zones. In autumn, they moved back into the shallower depth zones.

Closely related Prochlorococcus genotypes show remarkably different depth distributions in two oceanic regions as revealed by in situ hybridization using 16S rRNA-targeted oligonucleotides.

An in situ hybridization method was applied to the identification of marine cyanobacteria assignable to the genus Prochlorococcus using horseradish-peroxidase-labelled 16S rRNA-targeted oligonucleotide probes in combination with tyramide signal amplification (TSA). With this method very bright signals were obtained, in contrast to hybridizations with oligonucleotides monolabelled with fluorochromes, which failed to give positive signals. Genotype-specific oligonucleotides for high light (HL)- and low light (LL)-adapted members of this genus were identified by 16S rRNA sequence analyses and their specificities confirmed in whole-cell hybridizations with cultured strains of Prochlorococcus marinus Chisholm et al., 1992, Prochlorococcus sp. and Synechococcus sp. In situ hybridization of these genotype-specific probes to field samples from stratified water bodies collected in the North Atlantic Ocean and the Red Sea allowed a rapid assessment of the abundance and spatial distribution of HL- and LL-adapted Prochlorococcus. In both oceanic regions the LL-adapted Prochlorococcus populations were localized in deeper water whereas the HL-adapted Prochlorococcus populations were not only distinct in each region but also exhibited strikingly different depth distributions, HLI being confined to shallow water in the North Atlantic, in contrast to HLII, which was present throughout the water column in the Red Sea.

Numerical Modeling of Wind-Induced Flows in Stratified Water Bodies

Two-dimensional (in the vertical plane) wind-induced flows in no-flow-through reservoirs are considered. A numerical algorithm in the flow function–vortex variables is proposed based on the equations of slow stratified flows in the Boussinesq and boundary layer approximations with variable coefficient of vertical turbulent exchange. An analytical solution is given for a simplified problem.