Synchroneity of Pliocene planktonic foraminiferal datums in the North Atlantic

Leg 94 of the Deep Sea Drilling Project has provided a unique set of paleomagnetically dated cores, taken along a N-S transect in the North Atlantic. High deposition rates in the sediments, combined with the palaeomagnetic ages, have enabled existing planktonic foraminiferal zonations to be tested and a new zonation for the mid- to high latitudes to be erected. The PL zonation of Berggren (1973, 1977) is shown to be adequate as far north as 41°N, although both the LAD's ofGlobigerina nepenthes andGloborotalia margaritae occur earlier than in tropical regions. North of 41°N these two species have very diachronous LAD's, even though they are common during their range in the northern sites. The new zonation for the mid to high latitude North Atlantic is based on the FAD ofG. margaritae, FAD ofG. puncticulata, LAD ofG. cf. crassula, LAD ofN. atlantica, FAD ofG. inflata and FAD of sinistrally coiled encrustedN. pachyderma.     

Patterns of jellyfish abundance in the North Atlantic

A number of explanations have been advanced to account for the increased frequency and intensity at which jellyfish (pelagic cnidarians and ctenophores) blooms are being observed, most of which have been locally directed. Here, we investigate seasonal and inter-annual patterns in abundance and distribution of jellyfish in the North Atlantic Ocean to determine if there have been any system-wide changes over the period 1946–2005, by analysing records of the presence of coelenterates from the Continuous Plankton Recorder (CPR) survey. Peaks in jellyfish abundance are strongly seasonal in both oceanic and shelf areas: oceanic populations have a mid-year peak that is more closely related to peaks in phyto- and zooplankton, whilst the later peak of shelf populations mirrors changes in SST and reflects processes of advection and aggregation. There have been large amplitude cycles in the abundance of oceanic and shelf jellyfish (although not synchronous) over the last 60 years, with a pronounced synchronous increase in abundance in both areas over the last 10 years. Inter-annual variations in jellyfish abundance in oceanic areas are related to zooplankton abundance and temperature changes, but not to the North Atlantic Oscillation or to a chlorophyll index. The long-term inter-annual abundance of jellyfish on the shelf could not be explained by any environmental variables investigated. As multi-decadal cycles and more recent increase in jellyfish were obvious in both oceanic and shelf areas, we conclude that these are likely to reflect an underlying climatic signal (and bottom-up control) rather than any change in fishing pressure (top-down control). Our results also highlight the role of the CPR data in investigating long-term changes in jellyfish, and suggest that the cnidarians sampled by the CPR are more likely to be holoplanktic hydrozoans and not the much larger meroplanktic scyphozoans as has been suggested previously. Guest editors: K. A. Pitt & J. E. Purcell Jellyfish Blooms: Causes, Consequences, and Recent Advances     

Pollen distribution in the bottom sediments of the western North Atlantic Ocean

An extensive survey of pollen distribution in surficial sediments from the slope and rise between 29° and 72°N, shows patterns which reflect the distribution of vegetation in eastern North America and the effects of aeolian, fluvial, and marine sedimentation. The results of the analysis of 94 core tops show that pollen concentration ranges from 23,000 to 10 grains per gram, and decreases offshore with distance from vegetation sources and northward in relation to lower vegetation density. Maximum concentration occurs in organic-rich, fine-grained lutum deposited off rivers draining the southeastern United States. Low pollen concentrations are associated with high-energy environments, such as the Western Boundary Undercurrent and the Labrador Current. Percentages of dominant pollen types generally correspond with onshore distribution of pollen and vegetation. Oak and other deciduous pollen types are the most abundant in marine sediments off the deciduous forests of eastern United States. Hemlock pollen is essentially restricted to sediments off the hemlock-oak forests of northeastern U.S. and southeastern Canada, and spruce pollen is most abundant adjacent boreal forests and forest-tundra formations. The relative increase in pine pollen seaward reflects the selective effects of marine transport. Synthesis of pollen data by Q-mode factor analysis shows that major vegetation formations of eastern North America produce distinctive, regional marine pollen assemblages.     

Relationship of surface sediments and benthic foraminiferal distribution patterns in the Norwegian Channel (northern North Sea)

Our study of the distribution of benthic foraminifers in surface sediment samples from the Norwegian Channel has shown that eight species and five different assemblages are important. The assemblages are dominated byUvigerina peregrina, Bolivina skagerrakensis, Cassidulina laevigata, Elphidium excavatum andBulimina marginata, respectively.Hyalinea balthica, Melonis barleeanum andTrifarina angulosa are also abundant. The first four assemblages and their dominant species can be related to certain water masses with known characteristics. Two species are related to certain types of substrate;M. barleeanum seems to prefer a fine-grained substrate, whileT. angulosa occurs most abundantly where the content of silt and clay is low.B. skagerrakensis andH. balthica occur most abundantly in sediments with a high content of organic carbon, whileT. angulosa shows inverse correlation to the organic carbon content.     

Holotypes in the taxonomy of planktonic foraminiferal morphospecies

The claim that holotypes serve as exemplars of morphology is examined in the context of planktonic foraminiferal taxonomy. A review of some species described over the past 90 years suggests that holotypes are selected subjectively, presumably guided by authors' conceptions of diagnostic characters. Evidence of their representative status is never provided. Seldom is the amount of material examined given. That holotypes serve as name-bearers and have no intrinsic status as exemplars is discounted. Although the holotype is rarely described, there is a typological bias in planktonic foraminiferal taxonomy because of the focus on nomenclatural types in accompanying imagery, and on the use of simply applied qualitative definitions. Commonly, type specimens are among the earliest recognized in a taxon and are selected prior to an understanding of its biogeography. Because taxa are distributed in niches within and among water masses in the global ocean, and are quite variable, holotypes are unlikely to be suitable as taxon-wide exemplars. Yet that is their present role. Population variation is under-reported in the literature. Selection of exemplars should be based on species-wide morphometric surveys of populations.     

Calcite dissolution and the modification of planktonic foraminiferal assemblages

The results of an in situ experiment in the Panama Basin allow us to determine the way in which planktonic foraminiferal assemblages are modified by calcite dissolution. Pre-weighed planktonic foraminiferal samples of known species composition were attached to a deep-sea mooring at various water depths between 665 m and 3791 m for a period of 123 days. Weight loss due to dissolution during this period ranged from less than 5% for the shallowest samples to slightly over 30% for the deepest samples. In terms of change in foraminiferal number, this is equivalent to decreases of between 1% and 26%. Only in the samples placed at the two deepest levels (3769 m and 3791 m) was there a significant loss in the total number of foraminifera. The magnitude of change in the abundance of individual species in early related to their different susceptibilities to dissolution. Species such as Hastigerina pelagica, Globigerinella aequilateralis and Candeina nitida, which are very susceptible to dissolution, exhibited the largest decreases in frequency percentage while the more resistent species (Sphaeroidinella dehiscens, Pulleniatina obliquiloculata and Globorotalia truncatulinoides) had minimal changes. From these results a solution-susceptibility ranking for planktonic foraminifera is established that is quite similar to those derived from previous laboratory experiments and sea-floor studies.     

Organic-walled dinoflagellate cysts in western equatorial Atlantic surface sediments: distributions and their relation to environment

In contrast to the wide range of studies carried out in temperate and high-latitude oceanic regions, only a few studies have focused on recent and Holocene organic-walled dinoflagellate cyst assemblages from the tropics. This information is, however, essential for fully understanding the ability of species to adapt to different oceanographic regimes, and ultimately their potential application to local and regional palaeoenvironmental and palaeoceanographic reconstructions. Surface sediment samples of the western equatorial Atlantic Ocean north of Brazil, an area greatly influenced by Amazon River discharge waters, were therefore analysed in detail for their organic-walled dinoflagellate cyst content. A diverse association of 43 taxa was identified, and large differences in cyst distribution were observed. The cyst thanatocoenosis in bottom sediments reflects the seasonal advection of Amazon River discharge water through the Guyana Current and the North Equatorial Countercurrent well into the North Atlantic. To establish potential links between cyst distribution and the environmental conditions of the upper water column, distribution patterns were compared with mean temperature, salinity, density and stratification gradients within the upper water column (0-100m) over different times of the year, using correspondence analysis and canonical correspondence analysis. The analyses show that differences in these parameters only play a subordinate role in determining species distribution. Instead, nutrient availability, or related factors, dominates the distribution pattern. The only possible indicators of slightly reduced salinities are Trinovantedinium applanatum and Lingulodinium machaerophorum. Four assemblage groups of cyst taxa with similar environmental affinities related to specific water masses/currents can be distinguished and have potential for palaeoenvironmental reconstruction.     

Estimating denitrification in North Atlantic continental shelf sediments

A model of coupled nitrification/denitrification was developed for continental shelf sediments to estimate the spatial distribution of denitrification throughout shelf regions in the North Atlantic basin. Using data from a wide range of continental shelf regions, we found a linear relationship between denitrification and sediment oxygen uptake. This relationship was applied to specific continental shelf regions by combining it with a second regression relating sediment oxygen uptake to primary production in the overlying water. The combined equation was: denitrification (mmol N m^–2 d^–1)=0.019^* phytoplankton production (mmol C m^–2 d^–1). This relationship suggests that approximately 13% of the N incorporated into phytoplankton in shelf waters is eventually denitrified in the sediments via coupled nitrification/denitrification, assuming a C:N ratio of 6.625:1 for phytoplankton. The model calculated denitrification rates compare favorably with rates reported for several shelf regions in the North Atlantic.The model-predicted average denitrification rate for continental shelf sediments in the North Atlantic Basin is 0.69 mmol N m^{– 2} d^–1. Denitrification rates (per unit area) predicted by the model are highest for the continental shelf region in the western North Atlantic between Cape Hatteras and South Florida and lowest for Hudson Bay, the Baffin Island region, and Greenland. Within latitudinal belts, average denitrification rates were lowest in the high latitudes, intermediate in the tropics and highest in the mid-latitudes. Although denitrification rates per unit area are lowest in the high latitudes, the total N removal by denitrification (53 × 10¹⁰ mol N y^–1) is similar to that in the mid-latitudes (60 × 10¹⁰ mol N y^–1) due to the large area of continental shelf in the high latitudes. The Gulf of St. Lawrence/Grand Banks area and the North Sea are responsible for seventy-five percent of the denitrification in the high latitude region. N removal by denitrification in the western North Atlantic (96 × 10¹⁰ mol N y^–1) is two times greater than in the eastern North Atlantic (47 × 10¹⁰ mol N y^–1). This is primarily due to differences in the area of continental shelf in the two regions, as the average denitrification rate per unit area is similar in the western and eastern North Atlantic.We calculate that a total of 143 × 10¹⁰ mol N y^–1 is removed via coupled nitrification/denitrification on the North Atlantic continental shelf. This estimate is expected to underestimate total sediment denitrification because it does not include direct denitrification of nitrate from the overlying water. The rate of coupled nitrification/denitrification calculated is greater than the nitrogen inputs from atmospheric deposition and river sources combined, and suggests that onwelling of nutrient rich slope water is a major source of N for denitrification in shelf regions. For the two regions where N inputs to a shelf region from onwelling have been measured, onwelling appears to be able to balance the denitrification loss.     

Carbonate dissolution and planktonic foraminiferal assemblages observed in three piston cores collected above the lysocline in the western equatorial Pacific

Planktonic foraminiferal assemblages were analyzed in three piston cores recovered from depths above the recent sedimentary lysocline (3.5 km) in the western Pacific Ocean for the purposes of (1) evaluating the effects of carbonate dissolution on fossil assemblages and (2) the impact of dissolution on paleoceanographic reconstructions for the past 300 kyr. We used the perfect test ratio (PTR) of Globorotalia menardii as an indicator of carbonate dissolution. Down-core variations of the PTR indicate that significant dissolution occurred during reglaciation steps represented by isotope stages 7–6, 5–4, and 3–2. The results of principal component analysis (PCA) based on the relative abundances of dominant species of planktonic foraminifera indicate that down-core changes in factor 1 loadings correlate with variations in PTR and with variations in the percentage of coarse fraction (>63 μm) present in the sediments. These correlations indicate that foraminiferal assemblages were apparently altered by dissolution events despite the fact that they were deposited at water depths shallower than the modern lysocline. We also estimated variations in paleo-sea surface temperature (paleo-SST) using the transfer function FP-12E. A negative correlation was found in communality as calculated from PCA and factor 1 loadings; this trend is distinct for the case of communality lower than 0.9. Thus, we conclude that estimated paleo-SST values based upon analysis of planktonic foraminifera are biased by carbonate dissolution.     

Scale formation in selected western North Atlantic flatfishes

Patterns of scale formation (onset, completion and spatial pattern) were examined for five species of flatfishes in four families (Paralichthyidae: summer flounder Paralichthys dentatus, smallmouth flounder Etropus microstomus, Scophthalmidae: windowpane Scophthalmus aquosus, Pleuronectidae: winter flounder Pseudopleuronectes americanus and Soleidae: hogchoker Trinectes maculatus, to determine if the patterns are a useful indicator for the transition from the larval to the juvenile periods. In all species (except T. maculatus in which samples were limited), the ontogenetic pattern was very similar with onset of scale formation occurring on the lateral surface of the caudal peduncle, then spreading anteriorly along the presumptive lateral line, then laterally over the body, on to the head, and eventually on to the median fins. The timing of scale formation, relative to fish size, was late relative to other morphological and behavioural characters (i.e. fin ray formation, eye migration and settlement). The onset of scale formation, across all species, occurred at 9·0–27·0 mm total length (L_T), at the same approximate size as eye migration and settlement. Completion of scale formation on the body occurred at 22–54 mm L_T but completion of scale formation on the fins did not occur until 44–88 mm L_T. Thus completion of scale formation in these flatfishes is apparently the last external morphological change to occur during the larval to juvenile transition and, as a result, is not completed until approximately one third (S. aquosus and P. dentatus) to one fourth (P. americanus) or about the same time (E. microstomus and T. maculatus) as the size at first reproduction. This character may have relevance to defining the end of the larval period and the beginning of the juvenile period in flatfishes and other fishes. In addition, the pattern of scale formation may be useful in enhancing understanding of systematics, functional morphology and habitat use.     

Distribution of recent planktonic foraminifera in surface sediments of the Mediterranean Sea

The Mediterranean Sea is a partillay isolated ocean where excess evaporation over precipitation results in large east to west gradients in temperature and salinity. Recent planktonic foraminiferal distributions have been examined in 66 surface sediment samples from the Mediterranean Sea. In addition to mapping the frequency distribution of 16 species, the faunal data has been subjected to cluster analysis, factor analysis and species diversity analysis. The clustering of species yields assemblages that are clearly temperature related. A warm assemblage contains both tropical and subtropical elements, while the cool assemblage can be subdivided into cool-subtropical, transitional and polar-subpolar groupings. Factor analysis is used to delineate the geographic distribution of four faunal assemblages. Factor 1 is a tropical-subtropical assemblage dominated by Globigerinoiden ruber. It has its highest values in the warmer eastern basin. Transitional species (Globorotalia inflata and Globigerina bulloides) dominate factor 2 with highest values occurring in the cooler western basin. Factor 3 reflects the distribution of Neogloboquadrina dutertrei and is considered to be salinity dependent. Subpolar species dominate factor 4 (Neoglobuquadrina pachyderma and G. bulloides), with highest values occurring in the northern part of the western basin where cold bottom water is presently being formed. The Shannon-Weiner index of species diversity shows that high diversity exists over much of the western basin and immediately east of the Strait of Sicily. This region is marked by equitable environmental conditions and relatively even distribution of individuals among the species. Conversely, in areas where temperature and salinity values are more extreme, diversity values are lower and the assemblages are dominated by one or two species.     

Patterns of arthropod abundance and diversity in an Arabian desert

We captured desert arthropods from sand and gravel substrates at five coastal or inland locations m Abu Dhabi around the new moon once every 28 days for two years Three replicated lines of 20 unbaited pitfall traps were used from two hours before dusk until two hours after dawn We examined the data for spatial and temporal variation, especially in relation to climate Around 53 400 arthropods were caught, 97.3% being insects and the rest arachnids Ants were most common (75.4%), followed by the Thysanura (12%), Coleoptera (8.4%), Araneae (1.5%) and Scorpiones (1.1%) Catches differed significantly among sites, substrates and time of year In general, the number of arthropods caught matched the annual temperature cycle Peak catches also followed the annual rains Summer catches were higher at coastal than inland sites Fewer arthropods were caught at gravel sites than on sand, but the number of taxa did not differ consistently between substrates Community composition was generally less similar among sites than between substrates although this was not always the case Inland communities had fewer taxa and generally fewer individuals than those near the coast Isoptera, Tettigonndae and Carabidae occurred less frequently (if at all) inland We suggest that the higher humidity at sites near the coast allows more taxa to occur and to remain active during the extreme heat of summer Further into the Empty Quarter we would expect a decline in the number of taxa and in the total catch     

Diversity and abundance of glycosyl hydrolase family 5 in the North Atlantic Ocean

The diversity and abundance of glycosyl hydrolase family 5 (GH5) were studied in the North Atlantic Ocean. This family was chosen because of the large number of available sequences from cultured bacteria, the variety of substrates it targets, and the high number of similar sequences in the Sargasso Sea environmental genome database. Three clone libraries of a GH5 subcluster were constructed from the Mid-Atlantic Bight and the eastern and western North Atlantic Ocean. The two North Atlantic Ocean libraries did not differ from each other but both were significantly less diverse than the Mid-Atlantic Bight library. The abundance of GH5 genes estimated by quantitative PCR was positively correlated with chlorophyll concentrations in the eastern part of a transect from Fort Pierce, Florida, to the Azores and in a depth profile, suggesting that the supply of labile organic material selects for GH5-bearing bacteria in these waters. However, the data suggest that only <1% of all bacteria harbor the GH5 subcluster. These and other data suggest that the hydrolysis of polysaccharides requires complicated multi-enzyme systems.     

Species composition, abundance distribution and diversity of planktonic Ostracoda in the Beibu Gulf, China

Four cruises of survey were carried out in the Beibu Gulf between Feb 1998 and May 1999. A total of 18 species of planktonic Ostracoda were identified, including Cypridina nana, Cypridina dentata, Cypridina acuminata, Cypridina nami, Euconchoecia aculeata, Euconchoecia elongata, Euconchoecia maima, and other taxa. Planktonic Ostracoda in the gulf were divided into three ecological types: (1) a hyposaline and warm-water group, (2) a eurythermal and eurysaline group, and (3) a hyperthermal and hysaline group. The warm water species such as Euconchoecia aculeate and Cypridina acuminate were the dominant Ostracoda species in the gulf, where the overall Ostracoda density ranged from 0.02 ind./m³ to 51.58 ind./m³ and averaged 1.22 ind./m³. The highest average value (2.73 ind./m³) was found in spring. Fuzzy evaluation measures indicated that the diversity in the gulf remained low (level of class I) during all seasons. Diversity appeared to be relatively higher in some regions in which the water mass was strongly influenced by the open sea and had complex structures. This article also discusses how the species composition, abundance and diversity of planktonic Ostracoda are influenced by environmental factors (e.g., aquatic system, water mass, water temperature and salinity) in the Beibu Gulf.     

Species composition, abundance distribution and diversity of planktonic Ostracoda in the Beibu Gulf, China

Four cruises of survey were carried out in the Beibu Gulf between Feb 1998 and May 1999. A total of 18 species of planktonic Ostracoda were identified, including Cypridina nana, Cypridina dentata, Cypridina acuminata, Cypridina nami, Euconchoecia aculeata, Euconchoecia elongata, Euconchoecia maima, and other taxa. Planktonic Ostracoda in the gulf were divided into three ecological types: (1) a hyposaline and warm-water group, (2) a eurythermal and eurysaline group, and (3) a hyperthermal and hysaline group. The warm water species such as Euconchoecia aculeate and Cypridina acuminate were the dominant Ostracoda species in the gulf, where the overall Ostracoda density ranged from 0.02 ind./m³ to 51.58 ind./m³ and averaged 1.22 ind./m³. The highest average value (2.73 ind./m³) was found in spring. Fuzzy evaluation measures indicated that the diversity in the gulf remained low (level of class I) during all seasons. Diversity appeared to be relatively higher in some regions in which the water mass was strongly influenced by the open sea and had complex structures. This article also discusses how the species composition, abundance and diversity of planktonic Ostracoda are influenced by environmental factors (e.g., aquatic system, water mass, water temperature and salinity) in the Beibu Gulf.     

Benthic foraminiferal distribution and abundance changes in Skagerrak surface sediments: 1937 (Höglund) and 1992/1993 data compared

Both living (stained) and dead (unstained) foraminiferal assemblages from surface sediments (0–2 cm) in the northwestern part of the Skagerrak have been studied in order to (1) define and characterize the distribution of various modern benthic environments and (2) by comparing these findings with surface samples collected 40–60 years ago, to document possible faunal changes that might have occurred. The investigated area is physiographically divided into the Norwegian slope, the Skagerrak Basin, and the Danish slope. The latter is under the influence of the Jutland Current, while the basin and the investigated parts of the Norwegian slope are bathed in Atlantic water. All areas have bottom waters with a high oxygen concentration. Three living (stained) and three dead (unstained) assemblages occupy the three physiographic areas. Only one assemblage (on the Norwegian slope) is common to both the living and dead assemblages but the boundaries between them lie at comparable depths. The higher standing crops are found on the fertile Danish slope while the lower ones are in the deep basin where the diversity is at a maximum. In the dead assemblages, the relative abundance of agglutinated tests increases with depth. Comparison with data collected 40 to 60 years ago shows increases in absolute numbers of tests, especially in the deep basin. There are changes in assemblage compositions in all areas. The dominant species found in 1937 are different from those of 1992/1993. There is a major change in the basin where one agglutinated species has changed its depth distribution downslope and two present day abundant species are new arrivals. These faunal events are probably linked to environmental changes.     

Evidence for infanticide in bottlenose dolphins of the western North Atlantic

Nine bottlenose dolphin (Tursiops truncatus) calves that stranded in Virginia in 1996 and 1997 died of severe blunt-force trauma. Injuries were concentrated on the head and chest and multiple rib fractures, lung lacerations, and soft tissue contusions were prominent. Skeletal and/or soft tissue trauma occurred bilaterally in all of the calves. One had a bite wound across the left mandible that exhibited deep punctures consistent with the tooth placement in an adult bottlenose dolphin. The lesions were not compatible with predation, boat strike, fisheries interactions, rough-surf injury, or blast injury. However, they were similar to traumatic injuries described in stranded bottlenose dolphin calves and harbor porpoises (Phocoena phocoena) in Great Britain attributed to violent dolphin interactions. The evidence suggests that violent dolphin behavior was the cause of the trauma in the nine calves reported here and that infanticide occurs in bottlenose dolphins of the western North Atlantic.     

A multivariate analysis of phytoplankton assemblages in the western North Atlantic

Principal component analysis (PCA) of a large data set of phytoplanktonrecords, 1111 stations collected in an uneven sampling patternover a 9-year period from the US north-eastern shelf watersis discussed. Year-to-year variation was found to be the largestcomponent of variation in the data and was more important thanseasonal variation and all but the grossest of geographic variation.Strong seasonal and geographic patterns were detected when long-termtemporal variation was removed and it was possible to identifygroups of critical species influencing geographic patterns.In this study PCA techniques were most successful when usedon data collected from a small geographic area or data collectedfrom a narrow spectrum of time (e.g., a single year or a singlemonth) or both. Interpretation of patterns is difficult if severalmajor sources of variation are present. The major sources ofvariation in phytoplankton populations were identified as annualchanges, seasonal changes and geographic patterns. Distincttrends were identified in the geographic pattern with the southernestuaries, the Mid-Atlantic Shelf and offshore versus coastalzones identified as having distinctive fauna] assemblages.