Showing papers on "Water column published in 1973"

Ecology of Vibrio parahaemolyticus in Chesapeake Bay

Abstract: A study of the ecology of Vibrio parahaemolyticus and related vibrios in the Rhode River area of Chesapeake Bay was carried out over the period December 1970 through August 1971. The incidence of V. parahaemolyticus and related vibrios was found to be correlated with water temperature. The vibrios could not be detected in the water column during the winter months, although they were present in sediment. From late spring to early summer, when water temperatures were 14 ± 1 C, vibrios over-wintering in sediment were released from the bottom communities and attached to zooplankton, proliferating as the temperature rose. The number of vibrios in and on plankton was reflected in the water column bacterial population densities at water temperatures of ca. 19 C. Thus, temperature of the water column in the range of 14 to 19 C was found to be critical in the annual cycle of the vibrios. Interaction between sediment, water, and zooplankton was found to be essential in the natural estuarine ecosystem. Bacterial counts of zooplankton were found to be temperature dependent. The bacterial population associated with zooplankton was found to be predominantly on external surfaces and was specific, differing from that of the sediment. Vibrio spp. and related organisms comprised the total bacterial population associated with zooplankton in summer months. The ecological role of Vibrio spp., including V. parahaemolyticus, was found to be significant, with respect to their property of chitin digestion and in relation to the population dynamics of zooplankton in Chesapeake Bay.

A study of plankton dynamics and nutrient cycling in the central gyre of the north pacific ocean1

Abstract: The dynamics of phytoplankton growth in relation to nutrient concentrations were studied in the subtropical central gyre of the North Pacific in November 1971. Rates of excretion of phosphate, ammonium, and urea-N by zooplankton and rates of assimilation of carbon, nitrate, ammonium, and urea-N by phytoplankton were measured. The growth rate of phytoplankton was estimated to be about 0.2-0.3 doublings day-’ in the 70-80-m mixed layer, apparently limited by concentrations of both nitrogen and phosphate. Only nitrogen concentration was so limiting at a station near the western edge of the California Current. No diel changes in concentrations of ambient nutrients were observed. Urea-nitrogen appears to be an important source of nitrogen for phytoplankton growth in these waters and to be an important excretory product of zooplankton. Concentrations of phosphate and ammonium were extremely low, but turnover times were estimated to bc of the order 3-5 days for ammonium and >lO days for urea and phosphate. Biomass of phytoplankton in the mixed layer was also very low, and corresponded approximately to that expected if a laboratory culture were operated as a nitrogenlimited chemostat with a concentration of about 0.48 pg-atom N liter-l in the incoming culture medium and a dilution rate of about 0.13 per day. Physiological differences were noted between the phytoplankton in the mixed layer and that living below the thermocline, as were differences in chemical composition (ratio of C:Chl a and C:N). The central gyre of the North Pacific Ocean is a trans-Pacific body of water extending approximately from 40”N to 15”N and maintained by the surrounding, anticyclonic pattern of surface circulation. Because of the gyre’s size, the effects of land masses and of waters of different origins are buffered in its center, which is therefore an appealing area in which to study plankton-nutrient relationships. As a result of generalized downwelling and mild winters, a thermocline appears to l Supported by U.S. Atomic Energy Commission Contract AT( 11-l )GEN 10, P.A. 20, National Science Foundation Grant No. GA-31167X, ind the Marine Life Research Program. Ship time supported by the National Science Foundation Alpha Helix program. Contribution from Scripps Institution of Oceanography. persist within the euphotic zone over a time measured at least in months, if not in years, and to isolate from deeper waters an environment. which is relatively stable in comparison with equatorial, temperate, and polar seas, or with coastal waters. Hence it is not far-fetched to think of stability in the mixed layer on a time scale rather long in comparison with the expected generation times of phytoplankton ( days) and zooplankton (weeks), notwithstanding seasonal fluctuations in the thickness of the mixed layer2 and in its temperature (Robinson and Bauer 1971). 2 In February 1973 we observed a mixed layer extending to 150 m throughout much of the central gyre, suggesting some mixture of deeper water into the surface layers. LIMNOLOGY AND OCEANOGRAPHY 534 JULY 1973, V. 18(4) NORTH PACWIC PLANKTON DYNAMICS 535 Although concentrations of plant nutrients and organisms are low (Reid 1962; Univ. California 1967, 1970; Sagi 1969; Marumo 1970)) absolute fluctuations in concentrations so far recorded are small in comparison to those in other areas. These variations appear to be of the order twofold to threefold about the mean both areally and seasonally, Sampling problems, for purposes of broad areal representation, would be eased if the apparent uniformity in concentrations of nutrients and organisms persists under careful measurement. The patchiness of diatom species has been compared quantitatively to that found in the subarctic North Pacific (Venrick 1972). All this information suggests that a steady state might pertain with respect to nutrient concentrations, plankton standing stocks, specific growth rates, and grazing. Such a situation would simplify the interpretation of measurements and permit the calculation or prediction of certain stocks and rates not readily measured with existing methods. Dugdale and Goering (1967) and Dugdale (1967) have provided a conceptual framework for the measurement and interpretation of nutrient-phytoplankton-zooplankton relationships in oligotrophic ocean waters with a persistent surface mixed layer. They conceive a two-layered water column: Specific growth rate of phytoplankton would be nutrient-limited in the mixed layer and light-limited below the thermocline. Grazing in the mixed layer would be closely coupled with phytoplankton production, with nitrogenous excretory products of the zooplankton the primary source of the growth rate-limiting nutrient for phytoplankton. Losses of nutrient to deep water, via sinking and migration of zooplankton, would be balanced by vertical turbulent diffusion of nitrate nitrogen from deep water, input of ammonium in rain ( cf. Menzel and Spaeth 1962) or by fixation of molecular nitrogen. This paradigm has many historical sources and seems consistent with present information, including the extensive studies of the Woods Hole group in the Sargasso Sea (Menzel and Ryther 1960, lQ61a,b; Steele and Menzel 1962) and the results of the EASTROPAC program in the eastern tropical Pacific Ocean (Thomas 1970a,b; Thomas and Owen 1971). Usually lacking in such studies have been measures of the degree of coupling between growth of phytoplankton and grazing by herbivores and between rates of excretion by zooplankton and rates of assimilation of nutrients by phytoplankton. Some estimates are available for coastal waters (Harris 1959; Martin 1968; Hargrave and Geen 1968). Pomeroy et al. (1963) presented an estimate for excretion relative to assimilation in the Gulf Stream as well as waters over the continental shelf. There has been no quantitative assessment of the rate of loss of nutrients to deep water, or their rcplaccment via upward diffusion or nitrogen fixation. The deeper water, in which growth of phytoplankton would be light-limited, usually shows a zone of chlorophyll concentrations higher than in the mixed layer above, and this zone may contribute an important fraction of the primary production to the water column (Anderson 1969, 1972; Hobson and Lorenzen 1972; Venrick et al. 1973). The elevated concentration of chlorophyll is due in part to a higher chlorophyll content of each phytoplankton cell ( cf. Steele 1964)) but in some cases the concentration of cells may also be elevated (Anderson 1972). Nitrate as a source of nitrogen for phytoplankton in this layer is relatively more important than in the mixed layer (Goering et al. 1970). We examined the rate of primary production of this deep chlorophyll layer and the physiological adaptations of phytoplankton to the very low light intensities and restricted spectral distribution of energy in hope of achieving a more adequate understanding of production processes in oligo-

Deep maxima of photosynthetic chlorophyll in the Pacific Ocean

Abstract: Data collected on several expeditions through the temperate and tropical Pacific Ocean show that during most of the year the maximum concentrations of chlorophyll occur below the surface, typically in a narrow layer near or below the depth of penetration of 10/0 of the surface light. The layer appears to be continuous across most of the Pacific although the depth and chlorophyll concentration vary regionally. The depth of the layer is more closely related to the depth of the nitrite maximum and to the position of the nutricline than to either light or density regimes. Productivity within the layer is low but positive, and contributes substantially to the total production of the water column. The maximum layer may be a seasonal phenomenon developing in the summer after the stabilization of the water column and mixing to the surface during the winter. Year to year fluctuations of depth and concentration of chlorophyll within the maximum layer may be related to large-scale meteorological fluctuations. Doty and Capurro (1961) have tabulated the position, date, depth, and values of chlorophyll and productivity in the world's oceans. There are several thousands of these measurements in the Pacific. Most are in the Northern Hemi­ sphere, and most are near land masses or is­ lands (e.g., Hawaii, Luzon, Hokkaido, New Cal­ edonia, New Zealand), along the equator, or north of lat 40 0

Redeposition of pollen grains in lake sediment

Abstract: Evidence from sediment traps shows that in dimictic Frains Lake pollen grains and the bottom mud in which they are contained are rcsuspendcd during spring and autumn mixing, while in Saylcs Lake, a nonstratificd lake nearby, similar quantities of pollen-bearing sediment are resuspended at irregular intervals throughout the year. In the nonstratified lake resuspended material is poorly mixed in the lake water, while in the dimictic lake, during the seasons of water mixing, resuspended sediment is similar in amount, perccntagc a5 .h weight, and pollen composition at various lcvcls throughout the water column. Rcsuspension occurs without sorting or diffcrcntial movement of individual pollen grains. The pollen content of rcdepositcd scdimcnt serves as a tracer, showing that sediment is moved from the littoral zone to the deeper basin of the lake. In the littoral zone annual stirring may involve the uppermost 6-12 mm of sediment; even in the dccpcr part of the basin, the uppermost millimeter at least is stirred by this process every year. Redeposition of sediment and pollen has been rcportcd from experiments with scdimcnt traps in Frains Lake, a thermally stratified lake in Michigan (Davis 1968); circulating water stirs and rcsuspends scdimcnt during the spring and fall seasons of water mixing. This process is capable of redistributing scdimcnt within the lake basin (Tutin 1955) and thus affecting the Final distribution of pollen grains in sediment, so it has obvious importance for the interpretation of fossil pollen. Seasonal measurcmcnt of redcposi tion has been cxtcnded to a shallow, nonstratified lake for comparison with Frains Lake. The constrast in timing demonstrates that absence of thermal stratification is csscntial for extcnsivc rcdcposition. To evaluate movcmcnt of the scdimcnt and its effect on pollen distribution, scdimcnt traps wcrc set at various depths in various parts of both lakes. With pollen grains serving as a tracer, thcsc traps dcmonstratc the movcmcnt of scdimcnt from one part of the lake basin to another. They serve further to detect any sorting due to differential movement that may occur within the pollen component of the scdimcnt, a phenomenon that had been suspected from the uneven disL Contribution No. 147 from the Great Lakes Restarch Division, The University of Michigan. tribution of different kinds of pollen within lake basins (Davis et al. 1971). The total amount of pollen deposited in traps at diffcrcnt stations scrvcs to assess the thoroughness of water mixing, In addition to information on the dircction of sediment movement, the amount of movcmcnt, and the distribution of pollen within the suspcndcd sediment, the results of the study provide an estimate of the depth to which sediment in lakes is stirred by the action of water currents. Throughout this paper rcferencc is made to “pollen grains.” In fact the refcrcncc is to the waxy exine of the grains, which is identifiable taxonomically and which is rcsistant to decay. Pollen grains filtered from lake water during the flowering season still retain protoplasm, but a few weeks or months later, only the exine remains. Ccrtdn cxccptional types of pollen arc complctcly destroyed soon after entering the lake by bacteria or fungi (Havinga 1967) or benthic organisms (R. Davis 1969). For example poplar pollen was foulld in traps during the flowering season, but was virtually absent from the sediment on the lake floor. However, pollen is not destroyed after it has been incorporated in sediment; this is cstablishcd by the constancy through time of the ratio of pollen grains to silt and clay in the sediment (Davis 1968). It is for LTMNOLOGY AND OCEANOGRAPIIY 44 JANUARY 1973, V. 18( 1) REDEPOSITION OF POLLEN GRAINS 45 this reason that pollen serves as a useful tracer for suspension, movement, and rcdeposition of the scdimcnt as a whole. I gratefully acknowlcdgc the assistance of J, IM. Bciswengcr and L. B. Brubakcr in the design and cxccution of thcsc cxpcrimcnts. W, R. Solomon kindly made available his data on pollen content in the air at Ann Arbor. The George Rcscrvc, The University of Michigan, pcrmittcd the USC of sediment traps on Sayles Lake in 19651966. The work was supported by National Science Foundation Grants G,B 2377, GB 5320, and GB 7727. DESCRIPTION OF SITES Frains Lake (42”20’N, 83”37’W), 12 km northeast of Ann Arbor, Michigan, is about 200 m wide and 500 m long, sloping gradually to a maximum depth of 10 m in the center. There arc no inflowing or outflowing streams. The surrounding topography is nearly flat, (2uitc unprotcctcd from wind, the lake is surrounded by meadows with a relief of only 3-5 m. ICC about 30 cm thick persists for 3-4 months each winter. In summer the water is strongly stratified, with the top of the thermocline at about 4 m. (For more dctailed information on topography, see Davis ct al. 1971.) Saylcs Lake (42”26’N, 84”4’W), near Pinckncy, Michigan, and 35 km west of Frains Lake, is similar in area and shape to Frains Lake and, like Frains Lake, has no major inflowing or outflowing s trcams. Howcvcr, the lakes do differ in two major ways: 1) Saylcs Lake is less than 1 m deep over most of its area and only rcachcs a maximum depth of 3 m in an area just south of the basin’s ccntcr, and 2) Sayles Lake is surrounded by woods on three sides with a steep ridge 20 m high along the south short. ICC cover is similar to Frains Lake, but Saylcs Lake ncvcr develops thermal stratification.

Ecological Stability in a Shallow Equatorial Lake (Lake George, Uganda)

Abstract: The ecological stability of Lake George is illustrated by the relatively small biomass fluctuations that occur in the fauna and flora of the lake. For the phytoplankton it is shown that the gradient of these oscillations is within the range depicted by a specific rate of population increase of +0.05 to -0.05 day$^{-1}$. The relative stability of the phytoplankton community is discussed in the terms of a mathematical model (Talling 1957, 1971) which interrelates the variables, photosynthesis, respiration, biomass and the underwater light climate. Examples of the interrelationship, and the extreme susceptibility of either a positive or a negative increase rate to diurnal environmental changes, are drawn from both long and short term measurements in Lake George. The optical characteristics of the water column are shown to be very dependent upon the mixing regime sustained over the previous 24 h. The occurrence of negative or positive increase rates is dependent not only upon the incident radiation but also upon the wind induced turbulence. It is shown that, given measurements of the rates of photosynthesis and respiration and the other variables included in Talling's model, the biomass at which the Lake George phytoplankton will stabilize is predictable. Although light is likely to limit photosynthesis under all circumstances in Lake George, it is demonstrated that a more favourable photosynthetic response to the light climate may be induced by nutrient enrichment of the nutrient-poor phytoplankton. Because nutrient enrichment can induce increased photosynthetic capacity values, the rates of nutrient supply are thought to be major factors in controlling the ecological stability of the phytoplankton. The mixing regime of the lake is of paramount importance in the decomposition of the sediments and the rate of nutrient release from them. The importance of the nutrient recycling via zooplankton excretion is compared with the total input of nitrogen and phosphorus to the lake. That the ecological stability of the lake is a delicately balanced equilibrium between climate and biota is illustrated by calculations on the oxygen budget of the water column, and by the occurrence of fish-kills. The general characteristics of the lake are discussed in the context of the problems associated with eutrophication.

Trace element trapping in pteropod tests

Abstract: Pteropod tests from the Gulf of Aqaba and the South Atlantic Ocean and “bulk” (soft tissue) plankton samples from Long Island S,ound were analyzed by instrumental neutron aativation analysis (INAA) for 11 trace metals (Fc, Ce, La, Sm, Eu, Th, SC, Cr, Co, Sb, SC) to study the trapping and transport mechanisms for these metals in the oceans and the capability of ptcropods to modify the composition of seawater during this process. The internal correlations among these metals strongly suggest that a finely particulate (

Cariaco Trench: Oxidation of Organic Matter and Residence Time of Anoxic Water

Abstract: THE Cariaco Trench is located on the Caribbean shelf of Venezuela and has a maximum depth of 1,400 m. The surrounding shelf is nowhere deeper than 150 m, thus separating the deep water of the trench from that of the Caribbean. The deep water of the trench is devoid of dissolved oxygen1. Between the sill depth and 500 m both temperature and salinity decrease, resulting in a slight increase in density which stabilizes the water column somewhat precariously. Below 500 m the water is uniform and well mixed. Such anoxic basins are critically dependent on the balance between supply of organic matter and renewal of the deep water. Although the sediments indicate that at least the deep part of the basin has been permanently anoxic for thousands of years2 the relatively small density gradient may facilitate renewal of the deep water on a much shorter time scale. Estimates of the residence time vary between 100 and 2,000 yr (refs. 1,3). Data resulting from a cruise of RV Atlantis II in July 1971 provide a way of assessing the origin and oxidation of organic matter in the trench and the renewal rate of the deep water.

Ecological studies on the deep-water pelagic community of Korsfjorden, western Norway. The topography of the area and its hydrography in 1968–1972, with a summary of the sampling programmes

Abstract: Korsfjorden has a 690 m deep basin separated from the open sea by a sill at 180 m depth and by deeper sills from the inner fjord complex. Seasonal effects of temperature are apparent down to a depth of 300 m, below which temperatures show little variation. The salinity of the deep water is always greater than 35‰, characteristic of oceanic (Atlantic) water. The deep water oxygen content shows evidence in the early months of each year of renewal of the deep water by oceanic water originating, it is presumed, at the surface. Estimates of timing and duration each year are given, based on interpretation of TS diagrams and the oxygen data. The initial sampling programme, 1968–1970, consisted of monthly horizontal transects of the water column with pelagic trawls. The revised programme, 1971 onwards, consists of oblique divided and undivided hauls of the whole water column with a pelagic trawl (mesh size 1 mm) and a smaller net (mesh size 0.5 mm). Preliminary analysis of some copepods and a mysid indic...

Temporal Changes in Some Fresh Water Temperature Structures

Abstract: Microstructure is examined in 61 temperature-depth profiles which were obtained at one location in a fresh water lake. Over the 12 hr of observation, specific features of the microstructure are continuous, but increase in temperature and move up the water column. This temporal behavior is explained by the hypothesis that the microstructure is created by progressive internal waves in which the phase velocity is nearly vertical.

Glucose flux at the sediment-water interface of Toronto Harbour, Lake Ontario, with reference to pollution stress.

Abstract: Cycling of glucose at the sediment–water interface was determined through coupling measurement of natural substrate concentrations with heterotrophic uptake by the natural microbial communities in the sediment and in the water column. The same general pattern was found for both polluted and less polluted parts of Toronto Harbour, so that other labile organic species possibly have similar cycles. Velocity of uptake of glucose (flux) and turnover time showed no relationship to either substrate concentration or total organic matter of the sediments. Activity in the water column could be supported to a major extent by sediment export of substrate by turbulent diffusion. Sediment activity must be supported by particulate sedimentation and hydrolysis of large organic molecules, which may be aided by the macrobenthic community. Pollution stress apparently alters the catabolism of the substrate. The observed substrate concentrations may reflect a minimum of residual concentration, below which the microbial commun...

Radium, thorium, and uranium isotopes in the interstitial water from the Pacific Ocean sediment

Abstract: The Ra, Th, and U isotopic concentrations were determined in the interstitial water expressed from a deep sea core of the eastern equatorial Pacific. The isotopes 226Ra, 228Ra, 230Th, and 228Th are higher by 1 to 3 orders of magnitude than their concentrations in seawater. Radium release from sedimentary phases with migration into the water column is indicated. The results are also compatible with the excess 228Th (relative to 232Th) found in authigenic deep sea minerals.

Some Current‐Directed Movements of Macrobrachium Acanthurus (Wiegmann 1836) (Decapoda, Palaemonidae) Under Laboratory Conditions

Abstract: The larvae of some species of freshwater shrimp of the genus Macrobrachium will develop only in brackish water The increased incidence of these shrimp within estuaries and in the lower reaches of rivers at certain times of the year suggests that regular down—stream migrations are carried out to facilitate the transport of larvae to a brackish estuarine environment Current chamber experiments conducted in the laboratory indicated that gravid individuals tend to swim consistently downstream whereas other adult females tend to swim consistently upstream Other current chamber experiments showed that larval stages, held in brackish water, will drop to a position low in the water column when salinity is reduced (simulating an ebb tide) and revert to swimming higher in the water column when the salinity is increased (simulating a flood tide) These responses are interpreted as a mechanism whereby larvae are prevented from being carried out to sea, thus facilitating their eventual migration upstream to a freshwater environment

Some Observations on the Chlorophyll Maximum and Primary Production in the Eastern North Pacific

Abstract: An oceanographic transect between Central California and the Hawaiian Islands delimited a continuous subsurface chlorophyll maximum associated with an oxygen maximum at 1% to 0.1% light penetration depths. The phytoplankton community consisted primarily of nannoplankton with a prominent diatom component, and was photosynthetically active as measured in „low light level” incubators, contributing an estimated 20–30% to total water column production. Functioning as a nutrient trap blocking the vertical movement of nutrients into the upper euphotic zone, the chlorophyll maximum apparently required an overlying pycnocline for development.

Seasonal Changes in Population Density and Vertical Distribution of prosobranch veligers in offshore Plankton at Plymouth

Abstract: Vertical and horizontal hauls were taken at approximately fortnightly intervals from April 1969 to April 1970 at L 3 (lat. 40° 17.7′ N, long. 4° 11.2′ W) and L 4 (lat. 50° 15′ N, long. 4° 12.5 W). Thirty-two species of prosobranch veliger were present at L 35 these larvae were not as numerous at L 4 and only 26 species were recorded. The number of species was highest in the summer: the number of veligers was highest in February. After mid October both the number of species and the abundance of veligers decreased rapidly and remained low until early February. Veligers of some species occurred later at L 3 and L 4 than in more inshore waters and these were probably individuals carried beyond tidal influences which would normally lead to settlement on the shore. They included Lacuna vincta, Littorina littorea and L. neritoides.Veligers of all ages were found at all depths. At their time of greatest abundance veligers of many species occurred maximally at 5 or 10 m, with a variable decrease towards greater depths and a sudden one towards the surface. This distribution later changed giving a proportionally greater number at greater depth. When numbers were low the larvae scattered through the water column with little or no indication of a preferred depth. An examination of the age composition of veligers of rissoids, Natica alderi, Nassarius reticulatus and Philbertia linearis from certain catches showed that the surface accumulation at the time of abundance was composed of a high percentage of young veligers: in an ageing population there was a higher percentage of larvae, especially the older ones, at greater depths, except for Nassarius reticulatus which consistently showed maximal numbers above 10 m until the larvae became scarce.

Temperature Microstructure in Powell Lake

Abstract: Measurements of the vertical component of the temperature gradient in Powell Lake show phenomena similar to those observed in the ocean. The gradient is an irregular function of depth, with temperature inversions indicating static instability of the water column on the centimeter scale. The lower portion of the lake contains old sea water. Doubly diffusive layers were found only near the very bottom of the lake and another form of thermohaline circulation may exist for 60 m above the layers.

Observations on the limnology and primary production of a small man‐made lake in the West African savanna

Abstract: Summary 1. The results of limnological studies on a small, 35-ha, triangular man-made lake and a small adjacent fish pond in the coastal savanna of Ghana are described. 2. The lake, which has a renewal time of approximately 0.96 years, is subject to large, predictable seasonal changes. Water volume and surface area rapidly reach maximum values in the wet season from April to June despite the low runoff values which average only 1.2% of the precipitation. Minimum values occur in the dry season when up to 76% of the lake area may be exposed. Most of the water is lost by evaporation which may amount to 193 cm annually. 3. The annual cycle in water temperature follows that in solar radiation with peaks towards the end of the dry season in March to April and deep troughs in the wet season from April to June. During the dry season the water column is characterized by greater stability, a higher degree of stratification, and a much higher amplitude of diurnal temperature change (4-5°C) than in the wet season (1°C). Isothermal conditions tend to be approached nocturnally and even during the day in the wet season. 4. The ionic content of the water is low and dominated by bicarbonate, sodium, silica and iron. During the wet season flood water results in a decline in conductivity from 214 to 30 μmhos/cm2, a decrease in pH and transparency, and an increase in oxidizable organic material. Except for the conductivity these values return to normal in about 6 weeks as a result of rapid decomposition of allochthonous materials. 5. The oxygen pulse is strong and photosynthetic activity by phytoplankton high during the dry season whereas in the wet season the converse is true. As a result of the low concentration of organic carbon (0.10–0.35%) in the sediments their oxygen demands are low. Consequently, dissolved oxygen values near the sediment are relatively high and oxygen stratification poorly-developed. Most of the organic carbon appears to be recycled in the water column rather than in the sediments as is generally the case in tropical ecosystems. 6. Rooted vegetation became permanently established in the fish pond but not i n the lake itself. Emergent and floating vegetation which grows profusely in the draw-down area in the wet season is for the most part exported from the system by wind and biological agencies and, therefore, contributes little to the energy and mineral budgets of the lake. Primary production in the water column is mainly by Myxophyceae and Bacillariophyceae and is low during the dry season (1.35 gC/m2/day) and very low in the wet season. Possible reasons for the low level of primary production are discussed.

Characteristics of the nearshore environment off the south coast of rnvers island, antarctic peninsula1

Abstract: Sediment and water samples wcrc taltcn at 17 stations in a nearshore area off the southern coast of Anvers Island, Antarctic Peninsula. The scdimcnts arc diamictons and display great lateral variability. Their organic carbon content falls within the range of values for oceanic sediments; variations can perhaps be cxplainecl in tams of specific local cnvironmcnts of deposition. Silica concentrations in the interstitial water of thcsc sediments seems to bc controlled by biogenic processes of sedimentation. Bacteria. arc prcfcrcntially associated with scdimcnts rich in clay-sized materials and show little or no correlation with organic carbon in these samples; the surface properties of the fine scdimcnt may bc important. Bacterial nmnbcrs in the water column arc similar to those rcportcd for open-ocean arcas below 200 m in lower latitudes. Nutrient values arc high, but many nitrite values arc low rclativc to nitrate as in lower latitudes before the growth season and in the open ocean below the cuphotic zone. Thcsc similarities may indicate that primary proclnctivity at the time and place of investigation was low. A study was carried out in Arthur IIarbor and vicinity, An tactic Peninsula, in Fehruary and March 1967 (Fig. 1), to establish the characteristics of bottom scdimcnts and the overlying water column, to dctcrminc the bacterial numbers in water and scdimcnt samples, to rclatc thcsc qllantitics to scvcral environmental paramctcrs, and to dctcrminc which, if any, of them act as dctcrminnnts of bacterial distribution. In addition, the possibility of bactcrinl liberation of nutrients from the surrounding rock outcrops, and their addition to the ncarshorc nutrient budget, wcrc to bc invcstigatcd. The arca was chosen bccnusc WC felt that in the rclativc abscncc of disturbance by man and his animals, and in the absence of any pcrcnnial streams, the direct influcncc of the landmass on the ncarshore 1 This work was supported by National Scicncc Fonndation Grants GA-264, GA-657, and GA-1320. water mass could best bc evaluated. WC thank K. 0. Emcry and S. Z. El-Saycd for cons tructivc criticism.

Physical Oceanographic Observations in Baffin Bay and Davis Strait

Abstract: During February 1972, scientific personnel operating from the Louis S. St. Laurent obtained the first winter oceanographic temperature and salinity data from Baffin Bay. Six oceanographic stations were occupied: one in central Baffin Bay; a second in eastern Baffin Bay southeast of the first; and a cross-section of 4 stations in southern Davis Strait .... The temperature and salinity data were obtained using discrete samples from Knudsen bottles, equipped with deep-sea reversing thermometers, and an in situ recording salinity/temperature/depth unit (STD). Temperatures and salinities determined from the discrete water samples were used to calibrate the STD and correct it for drift, while the STD was used to detect fine structure in the vertical distributions of temperature and salinity. ... The temperatures presented ... were those obtained from the reversing thermometers. ... they are presented here in comparison with summer data from the same region .... While it is not possible to draw quantitative conclusions from the small amount of available information, it appears that the deep vertical distributions of temperature and salinity in central and southeastern Baffin Bay and Davis Strait may not undergo significant seasonal variation. Observed near-surface variations may be accounted for qualitatively by a combination of winter cooling, freezing and convective mixing and summer meltwater addition. The apparent constancy of flow through Davis Strait is of particular interest. It has been demonstrated that for sufficient heat to be present in the water column for prevention of ice formation in the open lead in northern Baffin Bay known as the North Water, northerly flow of warm water (>0°C) would have to be greater than observed during the summer months. That this does not appear to be the case strengthens the hypothesis... that the open water is due to a southward advection of ice by winds and currents rather than by heat from the water column preventing formation of the ice.

On primary production in the South Bight of the North Sea

Abstract: The area of the North Sea next to the Belgian and Dutch coasts has been surveyed since January 1971. The photosynthetic capacity (potential production) of samples collected at 63 stations and 4 depths has been measured using the 14C technique. The homogeneity of the water column was demonstrated almost everywhere. A general pattern of decrease of the potential production from the coast to the open sea was demonstrated in all seasons. Figures ranged from 3 to 30 mg C m-3 h-1. Primary production was also determined both by calculations, using the Steemann Nielsen (1952) formula, and by in situ measurements. The higher turbidity near the coast has proved to limit considerably the primary production. Figures usually range from 100 to 1500 mg C m-2 day-1. The following topics have also been discussed: relationship between photosynthetic capacity and pigment content, transparency of the water, solar radiation, comparison between production calculated from photosynthetic capacity and production measured in situ,...

Petroleum Derived Hydrocarbons in Gulf of Mexico Waters

Abstract: Petroleum type hydrocarbons occur in waters of the Gulf of Mexico as particulate material floating on the surface of the water (tar balls) or as dissolved components in the water column. Gas chromatographic, mass spectrometric, and carbon isotopic analytical methods have been used to characterize the hydrocarbons in tar balls collected from western Gulf beaches and from Gulf waters. The dissolved hydrocarbon contents of Gulf waters were examined. These included waters taken in the open Gulf, along tanker routes, or near producing platforms. Fingerprint analyses show that a significant portion of the tar balls collected from Texas beaches are probably derived from natural seepages. The water in the northern Gulf of Mexico probably contains less than 0.007 parts per million of dissolved hydrocarbons based on the data examined here. At least three-quarters of this are the heavy hydrocarbons with more than 10 carbon atoms. Hydrocarbon content is significantly less in samples taken below the surface than in surface waters. There are no significant differences in hydrocarbon content between waters taken in the open Gulf, along tanker routes, or near producing platforms. Neither petroleum production operations nor petroleum transport are measurably changing the hydrocarbon content of the nearby water.

Deuterium Distribution in the Gulf of Mexico

Abstract: The variations of the stable isotopes of hydrogen (protium and deuterium) were determined in the various water masses of the Gulf of Mexico. Surface waters of the central Gulf were found to have an average δD=5.6‰ relative to Standard Mean Ocean Water (SMOW), whereThe subsurface water masses, Subtropical Underwater, Antarctic Intermediate Water, and Gulf Basin Water, were found to be characterized by deuterium contents of 5.0–5.5, −0.5 and 0.9‰, respectively. In addition, a high deuterium feature (δD=5.5–6.3‰) was shown in the water column at about 100 m depth just above Subtropical Underwater. The δD values for the fresh water contribution to the Gulf via the Mississippi and Coatzacoalcos Rivers were found to be −42.3 and −19.3‰, respectively. The value for the net fresh water addition to the Gulf was ∼−33‰. The isotopic composition of near-shore waters is consistent with a simple mixing model of fresh water from runoff with ocean water modified by the mixing of sea waters from distinct sources.