Plankton Tow Samples Research Articles

Calibration of the Mg/Ca of Globorotalia truncatulinoides (R) for the reconstruction of marine temperature gradients

Recent work has provided useful Mg/Ca to water temperature calibrations for shallow‐dwelling planktonic foraminifer species. Globorotalia truncatulinoides (right coiling (R)) is a deep‐dwelling species that can serve as a source of information about the temporal variability in the water characteristics of the thermocline. We present a temperature calibration for the Mg/Ca in the shell of G. truncatulinoides (R) and examine some of the practical issues associated with evaluating the usefulness of the technique. The Mg/Ca in the primary and the secondary calcite of individual G. truncatulinoides (R) correlates exponentially with water column temperatures, showing a change of ∼10% in the Mg/Ca per 1°C (R2 = 0.92). A limited comparison with plankton tow samples demonstrates that the average Mg/Ca temperature was offset +1°C from the average temperature calculated using the δ18O calibration of O'Neil et al. [1969], and the Mg/Ca temperatures have a range similar to the δ18O temperatures. Comparisons of the [Mg] in the core top samples to water depth of deposition indicates that dissolution does not alter the measured value of Mg in the primary calcite.

Temperature:δ 18O relationships of planktonic foraminifera collected from surface waters

Most of the isotopic paleotemperature equations used for paleoceanographic reconstructions have been derived from culture experiments or inorganic precipitates of calcium carbonate. To test these equations in the modern ocean, we measured the oxygen isotope composition of planktonic foraminifera ( Globigerinoides ruber, Globigerinoides sacculifer, Globigerina bulloides and Neogloboquadrina pachyderma) collected from Atlantic and Southern Ocean surface waters, and added published plankton tow data from the Pacific, Indian and Arctic Oceans. The resulting species-specific regression equations of the temperature:δ 18O relationships for G. ruber, G. sacculifer and G. bulloides are statistically indistinguishable. The equations derived for G. sacculifer and G. bulloides agree with relationships obtained from laboratory experiments, in which these species were cultured at pH values close to modern surface waters. The equation derived from N. pachyderma has a significantly lower slope and offset than the other three species but produces a regression equation that is nearly identical to the one for the epifaunal benthic foraminifer Cibicides sp. Our work on plankton tow and pumped samples indicates that culture-derived equations appear to be more appropriate for predicting the absolute δ 18O of the species examined compared to equations derived from inorganic precipitates. However, over the oceanic temperature range, the slopes of the equations we derive for living species agree with the slopes obtained from inorganic precipitates.

Geographic variations in the nitrogen isotope composition of surface particulate nitrogen and new production across the North Atlantic Ocean

Natural 15 N/ 14 N ( δ 15N) was determined in suspended particulate matter (SPM) and plankton tow samples (20- and 233-μm mesh nets) during extensive surveys along E–W transects from Halifax, Nova Scotia, to the Canary Islands in the fall of 1992 and the spring of 1993. This is the first study reporting δ 15N measurements along with NO − 3 and NH + 4 uptake rates in the North Atlantic. During both cruises, the δ 15N of SPM and net-plankton was lower in oligotrophic waters compared with values in eutrophic areas. The lack of correlation between the euphotic zone integrated δ 15N SPM and NH + 4 concentration and NH + 4 uptake rate at both times suggested that the contrast between regions could not be explained by regenerated production, even though NH + 4 was the preferred N substrate in most regions. In fact, based on a correlation analysis, this study suggested that isotope fractionation during nitrate uptake and the residence time of N in SPM ( τ) were the two major factors controlling the δ 15N SPM in 1992. During the fall of 1992, the δ 15N SPM of the oligotrophic region ( τ of 100–170 d) was consistent with the accumulated product equation in closed systems and a δ 15N of new nitrate of 4–5‰. In contrast, in eutrophic regions ( τ of 7–40 d), the δ 15N SPM was consistent with an open system equation. Isotope fractionation ( ε) for growth on nitrate was estimated to be 2.4‰ in the upwelling off Morocco. In 1993, no correlations were observed between δ 15N SPM and nitrate dynamics, probably because of horizontal advection. Based on the low τ of 5–30 d, an open system equation was used with nitrate as the reactant, and it suggested variations of 2–3‰ in either the δ 15N NO3 or ε.

Spatial patterns of modern diatom distribution and multiple paleolimnological records from a small arctic lake on Baffin Island, Arctic Canada

The assumption that within-lake, deep-water sedimentary diatom assemblages are relatively uniform and that a single core is sufficient to depict lake ontogeny was tested for a small tarn on the southwestern Cumberland Peninsula of Baffin Island, Northwest Territories. Diatom transport and deposition were evaluated through analyses of periphytic, planktonic, and epipelic habitats. Diatom stratigraphies of four cores were used to test whether or not trends are comparable in different regions of the lake and throughout the Holocene. Among 12 surface-sediment stations, diatom distributions were alternately highly equitable or variable. Valves of evenly distributed genera (Aulacoseira and Achnanthes) are mixed in the water column prior to deposition. This is supported by plankton tow and periphyton samples, which were respectively dominated by Aulacoseira distans (and varieties) and Achnanthes altaica. Conversely, frequencies of several benthic taxa (e.g., Pinnularia biceps, species of Eunotia) varied up to 30% between stations, in patterns unrelated to water depth, and reflecting habitat specificity and minimal transport prior to burial. Of the four cores (38.0–95.5 cm), analysis of the two longest revealed three distinct zones: (i) a zone dominated by species of Fragilaria (> 9000 BP); (ii) a zone containing benthic acidophilic diatoms indicating natural acidification (9000–7000 BP); and (iii) a zone characterized by numerous species of Aulacoseira ranging from the mid to late Holocene. Clear differentiation of the lower two zones was impossible in the shorter cores, and radiocarbon dates suggest that sediment reworking truncated the earliest records of organic sedimentation at these sites. Correspondence analysis facilitated comparisons of the diatom stratigraphies and enabled the evaluation of core reproducibility. Central cores preserve the most useful paleolimnological records in this environment. Keywords: diatoms, paleolimnology, Arctic Canada, Baffin Island.

High apostome ciliate endoparasite infection rates found in the Bering Sea euphausiid Thysanoessa inermis

Samples of the Bering Sea euphausiid Thysanoessa inerrn~s (Kroyer), collected at 2 stations in the Bering Sea, and consisting primarily of first-year adult females and last-furcilia-stage sub-adults, were studied to determine the percentage infected by the apostome ciliate endoparasite Collinia beringensis (Capriulo & Small). In both groups of krill, infection percentage was found to be extremely high, at 98 and 68 % respectively. The higher rate of 98 % was found in the sample composed of larger and older euphausiids. Such infestation rates suggest that these ciliates may be important modifiers of euphausiid production. Euphausiids (krill) represent a significant proportion of the biomass in the world's oceans and are an important food source for numerous species of whales, fish, seals and birds (Mauchline & Fisher 1969, Mauchline 1980). Given their key ecological role, it is important to identify factors which would negatively impact euphausiid biomass and productivity. Capriulo & Small (1986) reported the discovery of a previously unknown species of apostome ciliate (Collinia berjngensis) living endoparasitically in the haemocoel cavity of the Bering Sea euphausiid Thysanoessa inermis (Krayer). Some of the krill contained extremely high numbers of these ciliates, packed so tightly that normal ciliate cell shapes were altered (Fig. 1). Such high densities of parasites in these planktonic crustaceans suggest the likelihood of physiological impairment to the infected host, perhaps leading to reduced growth, egg production and even death. To begin to assess the impact ot these parasites on krill populations we examined the percentage infection within 2 separate samples of Thysanoessa jnermis collected from the Bering Sea on 2 May (Stn 2012) and 8 May (Stn 2033) 1981, by Dr Sharon Smith and D. Ninivaggi, as part of Brookhaven National Laboratories' involvement in the National Science Foundation funded PROBES project. Samples were taken at night via horizontal tow with a 1 mm mesh plankton net, from surface water (Stn 2012) and 15 m depth (Stn 2033), and fixed in 10 % buffered formalin. The 2 euphausiid samples were characterized with respect to species composition, size, developmental stage and sex (Table 1). Fig. 1. Thysanoessa inermis infected by Collinia beringensis. Photomicrograph shows the protargol-stained ciliate endoparasite (C. beringensis) from the haemocoel fluid of the krill. Note the irregular cell shapes caused by the extremely high ciliate densities found in some hosts O Inter-Research/Printed in Germany 204 Mar. Ecol. Prog. Ser In order to determine the percentage of Thysanoessa inermis infected, 50 individuals were randomly taken (without regard to sex, developmental stage or size) from each sample. Each specimen was rinsed in water, placed under a dissecting microscope on a clean glass slide and cut open in the cephalothorax region. The krill was then removed, leaving the expelled body fluid, which was retrieved with the aid of a Pasteur pipette, on the slide. This fluid was treated with Lugol's solution (iodine-based fixative) to enhance cell contrast for microscope viewing. Slides were then examined under a compound microscope and apostome ciliate presence or absence was recorded. All dissecting instruments were rinsed off between surgical procedures to prevent contamination. Results of this work indicate extreme infection rates in the 2 samples studied of 98 and 68 O/O respectively (Table 2) . The higher rate of 98% occurred in the sample containing the older and larger (mean carapace length 4.52 mm as compared to 3.98 mm, Table 1) krill. Such rates are in marked contrast with those reported elsewhere in the literature for apostome ciliate krill ectoparasites (3 to 16 %; Lindley 1978). The physiological and ecological consequences for the knll harboring Table 1. Thysanoessa mermis and Thysanoessa longipes. Krill population characteristics for nighttime horizontal plankton tow (1 mm mesh net) samples from Stns 2012 (2 May, surface water) and 2033 (8 May, 15 m depth) in 1981 in the Bering Sea. Measurements are based on exammation of 102 and 105 randomly chosen individual knll from Stns 2012 and 2033, respectively. Mean carapace lengths (CL) are presented & SD Species % Pop. n Mean CL Sex (stage)

Radiolarian Indices of Physical and Chemical Oceanographic Phenomena in Recent Sediments of Southern California Continental Borderland: ABSTRACT

The California Current, the eastern limb of the North Pacific gyre, exhibits the following characteristics common to eastern boundary currents: wide, shallow, slow, diffuse boundaries; common upwelling; great seasonal variation; invasions of water masses from outside the system; and cold, low-salinity waters. Studies on plankton tows and Holocene sediments have correlated components of the siliceous microplankton (radiolarians and some diatoms) with several characteristics, such as the main directions of movement of the invading waters, the provenance of these waters, the presence and degree of upwelling, and seasonality and its impact on the underlying sediments. Certain types of radiolarians are potentially useful in determining fossil anoxic and oxic conditions as well as paleodepth. In this study, the authors analyzed box-core sediment and plankton tow samples from the southern California continental borderland, as well as radiolarian density, diversity, taxonomic makeup, and other features related to oceanographic and environmental conditions. Depositional environments were defined for the sediment samples, and radiolarian indicators for paleoenvironmental interpretation were determined. Several borderland environments were identified, and the anoxic nearshore basin was found to have the best preservational qualities for radiolarians and thus the most representative radiolarian biocoenosis.

Application of transfer functions to Indian Ocean planktonic Foraminifera

The distribution and abundance of planktonic Foraminifera from the Indian Ocean are used to illustrate geographic variations in faunal assemblages in the plankton and on the seabed caused by sedimentary and postdepositional processes and to analyze the effect of these variations on paleoecological reconstruction. Principal components analysis of these data describes the composition and distribution of faunal assemblages in plankton-tow samples, low-dissolution core-top samples, and high-dissolution core-top samples. Factor-comparison analysis describes the relationships among these three sets of assemblages: The species composition of low-dissolution faunal assemblages may be accurately described as a simple linear mixing of plankton assemblages. The geographical distributions of the faunal assemblages in the sediments, however, are often displaced equatorward of their counterparts in the plankton. Dissolution causes complex changes in the composition of faunal assemblages and produces an equatorward displacement of several high-dissolution assemblages relative to their counterparts in low-dissolution sediments. Three transfer functions, or equations, are derived using plankton, low-dissolution, and high-dissolution data. Numerical experiments indicate that transfer functions lose accuracy when applied to discordant data sets: The plankton transfer function often underestimates temperatures in core-top sediments, and the low-dissolution transfer function underestimates temperatures in high-dissolution sediments. These systematic differences in temperature estimates are illustrated by applying the three transfer functions to downcore samples representing conditions 18,000 years ago. Other experiments indicate that these distortions can be reduced by using larger size fractions and calibrating transfer functions with both low- and high-dissolution core-top samples.

Coiling Direction Ratios of Foraminifera Globigerina pachyderma (Ehrenberg) in Northeastern Pacific Surface Sediments: ABSTRACT

Coiling direction ratios of Globigerina pachyderma (Ehrenberg) plotted for sediment surface samples from the northeastern Pacific north of 40°N. did not show the consistent relationship which would recommend them as reliable guides for deep-sea core analysis in this region. A generally increasing tendency for sinistral coiling toward the north was noted, from 13 per cent left reported by Parker (1962) from a nearshore sample (40°N.) to a consistent 95-100 per cent left in the northern Gulf of Alaska. Great irregularity in coiling ratios in seaward (east-west) traverses may be related to a nearshore area of warm-water intrusion (Fleming, 1958) affecting the type of plankton supplied to the substrate. Variations from 20-96 per cent left coiling were observed in th se traverses. Dextral coiling percentage usually was higher in samples containing many species and few individuals. The recency of the surface sample also affected the coiling ratios. The problem of distinguishing small Globoquadrina dutertrei (d'Orbigny)--predominantly right coiling--from Globigerina pachyderma (coiling in question) may qualify coiling ratios reported by various authors. Plankton tow samples off Oregon, Washington, and the Aleutian Islands had smaller percentages of G. pachyderma and higher dextral ratios than samples from the underlying sediment surface. End_of_Article - Last_Page 1760------------