Late Oligocene to Recent benthic foraminifers from the northeastern North Atlantic

Deep-sea benthic foraminiferal faunas were studied from Sites 608 (depth 3534 m, 42°50'N, 23°05'W) and 610 (depth 2427 m, 53°13'N, 18°53'W). The sampling interval corresponded to 0.1 to 0.5 m.y. at Site 608 and in the sections of Site 610 from which core recovery was continuous. First and last appearances of benthic foraminiferal taxa are generally not coeval at the two sites, although the faunal patterns are similar and many species occur at both sites. Major periods of changes in the benthic faunas, as indicated by the numbers of first and last appearances and changes in relative abundances, occurred in the early Miocene (19.2-17 Ma), the middle Miocene (15.5-13.5 Ma), the late Miocene (7-5.5 Ma), and the Pliocene-Pleistocene (3.5-0.7 Ma). A period of minor changes in the middle to late Miocene (10-9 Ma) was recognized at Site 608 only. These periods of faunal changes can be correlated with periods of paleoceanographic changes: there was a period of sluggish circulation in the northeastern North Atlantic from 19.2 to 17 Ma, and the deep waters of the oceans probably cooled between 15.5 and 13.5 Ma, as indicated by an increase in delta18O values in benthic foraminiferal tests. The period between 10 and 9 Ma was probably characterized by relatively vigorous bottom-water circulation in the northeastern Atlantic, as indicated by the presence of a widespread reflector. The faunal change at 7 to 5.5 Ma corresponds in time with a worldwide change in delta13C values, and with the Messinian closing of the Mediterranean. The last and largest faunal changes correspond in time with the onset and intensification of Northern Hemisphere glaciation.

Ice rafted debris, planktic foraminifera and reconstructed sea surface temperatures from site GIK23414

Planktic foraminiferal census data, faunal sea surface temperatures (SSTs) and oxygen isotopic and lithic records from a site in the northeast Atlantic were analyzed to study the interglacial dynamics of Marine Isotope Stage (MIS) 11, a period thought to closely resemble the Holocene on the basis of orbital forcing. Interglacial conditions during MIS 11 persisted for approximately 26 ka. After the main deglacial meltwater processes ceased, a 10- to 12-ka-long transitional period marked by significant water mass circulation changes occurred before surface waters finally reached their thermal maximum. This SST peak occurred between 400 and 397 ka, inferred from the abundance of the most thermophilic foraminiferal species and was coincident with lowest sea level according to benthic isotope values. The ensuing stepwise SST decrease characterizes the overall climate deterioration preceding the increase in global ice volume by ab. 3 ka. This cooling trend was followed by a more pronounced cold event that began at 388 ka, and that terminated in the recurrence of icebergs at the site around 382 ka. Because the water mass configuration of early MIS 11 evolved quite differently from that of the early Holocene, there is little evidence that MIS 11 can serve as an appropriate analogue for a future Holocene climate, despite the similarity in some orbital parameters.

Grain size composition of sediment cores from the Weddell Sea, Antarctica

Sedimentary processes in the southeastern Weddell Sea are influenced by glacial-interglacial ice-shelf dynamics and the cyclonic circulation of the Weddell Gyre, which affects all water masses down to the sea floor. Significantly increased sedimentation rates occur during glacial stages, when ice sheets advance to the shelf edge and trigger gravitational sediment transport to the deep sea. Downslope transport on the Crary Fan and off Dronning Maud and Coats Land is channelized into three huge channel systems, which originate on the eastern-, the central and the western Crary Fan. They gradually turn from a northerly direction eastward until they follow a course parallel to the continental slope. All channels show strongly asymmetric cross sections with well-developed levees on their northwestern sides, forming wedge-shaped sediment bodies. They level off very gently. Levees on the southeastern sides are small, if present at all. This characteristic morphology likely results from the process of combined turbidite-contourite deposition. Strong thermohaline currents of the Weddell Gyre entrain particles from turbidity-current suspensions, which flow down the channels, and carry them westward out of the channel where they settle on a surface gently dipping away from the channel. These sediments are intercalated with overbank deposits of high-energy and high-volume turbidity currents, which preferentially flood the left of the channels (looking downchannel) as a result of Coriolis force. In the distal setting of the easternmost channel-levee complex, where thermohaline currents are directed northeastward as a result of a recirculation of water masses from the Enderby Basin, the setting and the internal structures of a wedge-shaped sediment body indicate a contourite drift rather than a channel levee. Dating of the sediments reveals that the levees in their present form started to develop with a late Miocene cooling event, which caused an expansion of the East Antarctic Ice Sheet and an invigoration of thermohaline current activity.

Abundance and opal input of radiolarian species of two sediment cores from the Atlantic sector of the Southern Ocean

Radiolarian-based paleoceanographic reconstructions generally use the abundance of selected radiolarian species. However, the recent focus on the opal flux and the development of isotope measurements in biogenic opal and the organic matter embedded in it demands a better knowledge of the origin of the opal. We present here an estimation of the opal content of the skeleton of 63 radiolarian species from two sites in the Southern Ocean. The skeletons are modelled as associations of simple geometrical shapes, and the volume thus obtained is combined with opal density to obtain the amount of opal. These data are, thus, used to determine the most important opal carriers in the radiolarian assemblage in both cores.

Pleistocene planktonic foraminifera at ODP Site 128-798

ODP Site 798 on the Oki Ridge in the Southern Japan Sea yielded the first continuous and well-preserved record of Pleistocene planktonic foraminifers in the Northwestern Pacific Ocean region. Quantitative analysis of planktonic foraminifers completed for 122 samples from the 200-m-thick Pleistocene section cored at ODP Site 798 provides a proxy record of variations in sea-surface temperature, productivity, and circulation during the past 1.6 m.y. in an area beneath the track of the Tsushima Current. Faunal census data allow recognition of five distinct assemblages: (1) type A assemblages dominated by sinistrally coiling forms of Neogloboquadrina pachyderma representing polar-subpolar surface temperatures, (2) type B assemblages dominated by Globigerina bulloides and thought to represent periods of increased surface productivity and upwelling, (3) type C assemblages marked by significant abundances of dextrally coiling forms of N. pachyderma thought to represent the warm transitional waters of the Tsushima Current, (4) type D assemblages distinguished by relatively high percentages of dextral N. pachyderma and Globorotalia inflata that also represent warmer surface temperatures and increased flow of the Tsushima Current, and (5) type E assemblages marked by relatively large numbers of the delicate species Globigerina quinqueloba and Globigerinita spp., indicative of exceptional preservation conditions and/or episodic high production of these taxa. Early and middle Pleistocene coiling patterns of Neogloboquadrina pachyderma at Site 798 can be correlated with Pleistocene coiling trends and planktonic foraminiferal datums established in the onshore Oga Peninsula sequence of Northern Honshu and open-ocean N. pachyderma coiling dominance shifts in the North Pacific region. A sustained early Pleistocene warm period recognized in both the Oga Peninsula sequence and the Northern Pacific can clearly be recognized at Site 798. In addition, the late Pleistocene planktonic foraminiferal record at Site 798 shows good correlation with glaciation/deglaciation events for the Northern Hemisphere as delineated by oxygen isotopes and represents the first detailed analysis of Pleistocene sea-surface temperature changes in the Northwestern Pacific Ocean region.

Benthic foraminifera and phytodetritus species in sediments from DSDP Leg 85, and ODP Legs 113 and 143

From late middle Eocene through earliest Oligocene, high-latitude regions cooled, and by the end of the period, continental ice sheets existed in Antarctica. Diversity of planktonic microorganisms declined, and modern groups of terrestrial vertebrates originated. Coeval faunal changes in deep-sea benthic foraminifers have been related to cooling of deep waters and increased oxygenation. Cooling, however, occurred globally, whereas species richness declined at high latitudes and not in the tropics. The late Eocene and younger lower-diversity, high-latitude faunas typically contain common Epistominella exigua and Alabaminella weddellensis, opportunistic phytodetritus-exploiting species that indicate a seasonally fluctuating input of organic matter to the sea floor. We speculate that the species-richness gradient and increase in abundance of phytodetritus-exploiting species resulted largely from the onset of a more unpredictable and seasonally fluctuating food supply, especially at high latitudes.

Benthic foraminifera of ODP Leg 104 holes

Benthic foraminifers have been studied in about 900 samples from Sites 642, 643, and 644 (ODP Leg 104, Voring Plateau), ranging in age from Eocene to Holocene. This sequence has been subdivided into seven assemblage zones. The Eocene to middle Miocene deposits are characterized by an agglutinated fauna. This reflects an environment causing dissolution of calcareous tests rather than the original living fauna. The upper Miocene to middle Pliocene deposits contain a diverse benthic foraminiferal fauna dominated by calcareous forms. The uppermost part of the sediment record, deposited during late Pliocene to Holocene, is characterized by many barren intervals and samples containing shallow-water species as well as ice-rafted material indicating glacial periods. Interglacials are reflected in samples containing a true oceanic foraminifer assemblage and no coarse clastic material.

Sedimentology and planktonic foraminiferal dissolution during the latest Cretaceous in the South Atlantic

A high-resolution (10-20 kyr) record of variations in CaCO3 content and dissolution was established for latest Cretaceous (last 0.7 Myr) deep-sea sediments from the South Atlantic Ocean (DSDP Site 516 from the Rio Grande Rise, and sites 525 and 527 from the Walvis Ridge). The degree of fragmentation of planktonic foraminifera (DFP) was used as a measure of calcite dissolution. High negative correlations between DFP and other independent measures of carbonate dissolution (percentage of sand fraction, absolute abundance of planktonic foraminifera, and planktonic/benthic foraminiferal ratio) validate its use as a sensitive index of calcite dissolution in upper Maastrichtian deep-sea sediments. Very high DFP and a significant negative correlation between DFP and CaCO 3 content suggest that Site 516 was located below the foraminiferal lysocline during the entire interval studied. Such a shallow position of the lysocline (paleodepth of Site 516 was 1.2 km) may be explained by "upwelling" of corrosive deep waters along the southern margin of the Rio Grande Rise. Sites 525 and 527 were located above the foraminiferal lysocline; however, three short periods of enhanced dissolution were recognised at Site 525 (paleodepth 1 km) and one interval of strong dissolution was identified at Site 527 (paleodepth 2.7 km). The lack of correspondence between the dissolution regimes at sites from the Walvis Ridge suggests limited deep-water communication across this physiographic barrier. Two of the dissolution maxima recognised at Site 525 correspond to carbonate maxima at Site 527. Variations in "upwelling" intensity along the Walvis Ridge, resulting in fluctuations in primary productivity in this area, may be the proximal cause of both carbonate cycles at Site 527 and dissolution cycles at Site 525. We suggest that development of the bottom Ekman layer between a hypothetical westward geostrophic current and the topographical height of the Rio Grande Rise-Walvis Ridge system may be a plausible hydrodynamical explanation for the proposed "'upwelling" along the southern margin of this topographical structure.

Micropaleontology and stable isotope record of ODP Hole 178-1098C

Detailed study of four Holocene sediment intervals from Ocean Drilling Program Site 1098 (Palmer Deep, Antarctic Peninsula) reveals that in situ dissolution of calcareous foraminifers in the core repository has significantly altered and in some cases eliminated calcareous foraminifers. Despite dissolution, the foraminifer and supporting diatom data show that the most open-ocean and reduced sea-ice conditions occurred in the early Holocene. The influence of Circumpolar Deep Water was greatest during the early Holocene but continued to be important throughout the Holocene. An increase in sea-ice proximal diatoms at 3500 cal. BP documents an expansion in the amount of persistent sea ice. The inferred increase in sea ice corresponds with an overall increase in magnetic susceptibility values. Benthic foraminifers are present in all samples from the Palmer Deep, including the middle Holocene pervasively laminated sediments with low magnetic susceptibility values. The consistent presence of mobile epifaunal benthic foraminifers in the laminated sediments demonstrates that the laminations do not represent anoxic conditions. The uniform composition of the agglutinated foraminifer fauna throughout the late Holocene suggests that the Palmer Deep did not experience bottom-water-mass changes associated with the alternating deposition of bioturbated or laminated sediments.

Investigation of sediment core PS2556 from Bellingshausen Sea, Antarctica

Die Rekonstruktion der glaziomarinen Sedimentationsprozesse am antarktischen Kontinentalrand des westlichen Bellingshausenmeeres erfolgte durch die sedimentologische Auswertung eines 962 cm langen Schwerelotkernes aus 3594 m Wassertiefe. Der Kern wurde während des Fahrtabschnittes ANT-XI/3 mit dem FS "Polarstern" vom Scheitel einer Sediment- "Drift" gezogen. An dem Sedimentkern wurde eine lithologische Beschreibung, sowie sedimentologische Untersuchungen und sedimentphysikalische Messungen durchgeführt. Anhand der Ergebnisse konnten signifikante Änderungen in der Zusammensetzung und Struktur der Sedimente erkannt, und drei Faziestypen unterschieden werden. Die Faziestypen charakterisieren jeweils glaziale oder interglaziale Zeiträume. Der größte Teil der Sedimentabfolge gehört der Laminitfazies an. Dabei handelt es sich um feinlaminierte Sedimentabschnitte, die vorwiegend aus feinkörnigen, terrigenen Komponenten zusammengesetzt sind. In die feinlaminierten Abschnitte sind vereinzelte, wenige Milimeter bis Zentimeter mächtige Siltlagen eingeschaltet. Die biogenen Anteile sind gering, Anzeichen für Bodenleben fehlen völlig. Die Manganfazies wird von authigen gebildeten Mangankonkretionen dominiert, die jeweils diskrete Lagen bilden. Dabei handelt es sich zum einen um Mikromanganknollen und -krusten und zum andern um manganhaltige Gangfüllungen. Biogene und terrigene Anteile sind in diesem Faziestyp unbedeutend. Die Biogenfazies ist von strukturlosen und stark bioturbierten Sedimenten gekennzeichnet. In diesen Sedimentabschnitten ist der hohe Anteil an Eisfracht (IRD) und die erhöhten Gehalte an Kalziumkarbonat und Opal in der Sandfraktion markant. Die stratigraphische Einordnung des Sedimentkernes erfolgte über die von Grobe & Mackensen (1992) entwickelte Lithostratigraphie, mit deren Einheiten die Faziestypen des Sedimentkernes korreliert werden konnten. Dabei ergaben sich zwei mögliche Altersmodelle und ein Basisalter von ca. 250.000 Jahren. Anhand der stratigraphischen Fixpunkte wurden Sedimentationsraten des Gesamtsedimentes und Akkumulationsraten des Kalziumkarbonates, des Biogenopals und des organisch gebundenen Kohlenstoffes berechnet. Dabei wurde gezeigt, daß lediglich das Kalziumkarbonat und der Biogenopal als Anzeiger für biologische Produktion dienen können, wobei Lösungsprozesse in der Wassersäule und im Sediment eine große Rolle spielen. Der Gehalt an organisch gebundenem Kohlenstoff ist in dem Sedimentkern nur erhaltungsbedingt zu erklären. Die Sedimentationsprozesse der einzelnen Faziestypen sind von den Eisverhältnissen, der biologischen Produktion, dem gravitativen Transport und der Umlagerung durch Meeresströmungen abhängig. Die Auswirkung der einzelnen Faktoren ist jeweils unterschiedlich ausgeprägt und wirkt sich spezifisch auf die einzelnen Parameter aus. In den Glazialen hatte ein Vorstoß des Schelfeises über die Schelfkante zur Anlieferung großer Sedimentmassen geführt, die über gravitativen Transport den Kontinentalhang hinunter transportiert wurden. Die Feinfracht wurde über parallel zum Kontinentalhang laufende Konturströme westwärts transportiert und in der Larninitfazies der Driftkörper abgelagert. Am Ende der Glaziale kam es zur Sedimentation der Manganfazies. Die geringen Sedimentationsraten am Kamm der Sedimentdrift kamen aufgrund reduzierter Intensität der Konturströme und fehlender Umlagerung von Schelfsedimenten in Folge rückschreitender Schelfeisrnassen zustande. In den Interglazialen kam es durch den aufsteigenden Meeresspiegel zum Aufschwimmen des Schelfeises. Der damit verbundene Abbau der Eisrnassen über dem Schelf, hatte eine hohe Sedimentation von IRD zur Folge. Mit fortschreitendem Interglazial kam es in Zeiten nur saisonaler Meereisbedeckung zu verstärkter biologischer Produktion und zur Sedimentation biogenen Materials.

Correlation between wet bulk density and carbonate content from IODP Hole 321-U1338A, 321-U1338B and 321-U1338C

Sediment cores collected from the Eastern Equatorial Pacific Ocean display a clear positive second-order relationship between wet bulk density (WBD) and carbonate content. This has long interested the paleoceanography community because detailed Gamma Ray Attenuation Porosity Evaluator (GRAPE) measurements, which approximate WBD, might be used to determine records of carbonate content at very high temporal resolution. Although general causes for the relationship are known, they have not been presented and discussed systematically on the basis of first principles. In this study, we measure the mass and carbonate content of 50 sediment samples with known WBD from Site U1338, before and after rinsing with de-ionized water; we also determine the mass related proportion of coarse (> 63 µm) material. Samples exhibit clear relationships between WBD, carbonate content, mass loss upon rinsing, and grain size. We develop a series of mathematical expressions to describe these relationships, and solve them numerically. As noted by previous workers, the second-order relationship between WBD and carbonate content results from the mixing of biogenic carbonate and biogenic silica, which have different grain densities and different porosities. However, at high carbonate content, a wide range in WBD occurs because samples with greater amounts of coarse carbonate have higher porosity. Moreover compaction impacts carbonate particles more than biogenic silica particles. As such, a single two-component equation cannot be used to determine carbonate content accurately across depth intervals where both the porosity and type of carbonate vary. Instead, the WBD-carbonate relationship is described by an infinite series of curves, each which represents mixing of multiple sediment components with different densities and porosities. Dissolved ions also precipitate from pore space during sample drying, which adds mass to the sediment. Without rinsing samples, simple empirical relationships between WBD and carbonate content are further skewed by salt dilution.

Benthic foraminiferal assemblage counts from the Gulf of California

Extensive CO2 vents have been discovered in the Wagner Basin, northern Gulf of California, where they create large areas with lowered seawater pH. Such areas are suitable for investigations of long-term biological effects of ocean acidification and effects of CO2 leakage from subsea carbon capture storage. Here, we show responses of benthic foraminifera to seawater pH gradients at 74-207 m water depth. Living (rose Bengal stained) benthic foraminifera included Nonionella basispinata, Epistominella bradyana and Bulimina marginata. Studies on foraminifera at CO2 vents in the Mediterranean and off Papua New Guinea have shown dramatic long-term effects of acidified seawater. We found living calcareous benthic foraminifera in low pH conditions in the northern Gulf of California, although there was an impoverished species assemblage and evidence of post-mortem test dissolution.

Age determinations and stable isotope records of four sediment profiles off Nova Scotia

Continental margin sediments off Nova Scotia accumulate at high rates (up to 360 cm/kyr) and contain a history of millennial-scale environmental changes which are dominated by the proximity of the Laurentide ice sheet during the latest Quaternary. Using stable isotope ratios of oxygen, accelerator mass spectrometer radiocarbon dating, micropaleontology, and sedimentology, we document these changes in six piston cores ranging in water depth from ab. 450 to ab. 4300 m. We find that maximum d18O in N. pachyderma occurred about 15 ka and preceded the maximum abundance of this species in these cores by ab. 1000 years. Between 13 and 14 ka we find a second peak in abundance of N. pachyderma, minimum d18O, and two pulses of ice rafting. The sediment lithology supports terrestrial studies which indicate that there was a general withdrawal of ice beyond the upper Paleozoic and Mesozoic red beds by 14 ka in southeastern Canada, so the ice rafting events between 13 and 14 ka probably reflect ice stream activity in the St. Lawrence valley. The Younger Dryas event is recognized as a peak in abundance of N. pachyderma and ice rafting (dated as ab. 11.3 ka), but meltwater discharge to the Gulf of St. Lawrence was either too small or occurred over too long a time to leave a distinct d18O minimum off Nova Scotia. At 7.1 ka, in the middle of Holocene warming, we find a third peak in abundance of N. pachyderma and another d18O minimum but no ice rafting. We interpret these data as evidence of a late-occurring meltwater event which, if correct, could have originated in the Great Lakes, in the Labrador-Ungava region, or in both. The final millennial-scale phenomenon off Nova Scotia is the onset of "Neoglaciation," marked by increased ice rafting and increased % N. pachyderma beginning about 5 kyr ago.

Chemical composition of Late Cenozoic volcanic and volcaniclastic deposits from the western Woodlark Basin area, SW Pacific

Tephra fallout layers and volcaniclastic deposits, derived from volcanic sources around and on the Papuan Peninsula, form a substantial part of the Woodlark Basin marine sedimentary succession. Sampling by the Ocean Drilling Program Leg 180 in the western Woodlark Basin provides the opportunity to document the distribution of the volcanically-derived components as well as to evaluate their chronology, chemistry, and isotope compositions in order to gain information on the volcanic sources and original magmatic systems. Glass shards selected from 57 volcanogenic layers within the sampled Pliocene-Pleistocene sedimentary sequence show predominantly rhyolitic compositions, with subordinate basaltic andesites, basaltic trachy-andesites, andesites, trachy-andesites, dacites, and phonolites. It was possible to correlate only a few of the volcanogenic layers between sites using geochemical and age information apparently because of the formation of strongly compartmentalised sedimentary realms on this actively rifting margin. In many cases it was possible to correlate Leg 180 volcanic components with their eruption source areas based on chemical and isotope compositions. Likely sources for a considerable number of the volcanogenic deposits are Moresby and Dawson Strait volcanoes (D'Entrecasteaux Islands region) for high-K calc-alkaline glasses. The Dawson Strait volcanoes appear to represent the source for five peralkaline tephra layers. One basaltic andesitic volcaniclastic layer shows affinities to basaltic andesites from the Woodlark spreading tip and Cheshire Seamount. For other layers, a clear identification of the sources proved impossible, although their isotope and chemical signatures suggest similarities to south-west Pacific subduction volcanism, e.g. New Britain and Tonga- Kermadec island arcs. Volcanic islands in the Trobriand Arc (for example, Woodlark Island Amphlett Islands and/or Egum Atoll) are probable sources for several volcaniclastic layers with ages between 1.5 to 3 Ma. The Lusancay Islands can be excluded as a source for the volcanogenic layers found during Leg 180. Generally, the volcanogenic layers indicate much calc-alkaline rhyolitic volcanism in eastern Papua since 3.8 Ma. Starting at 135 ka, however, peralkaline tephra layers appear. This geochemical change in source characteristics might reflect the onset of a change in geotectonic regime, from crustal subduction to spreading, affecting the D'Entrecasteaux Islands region. Initial 143Nd/144Nd ratios as low as 0.5121 and 0.5127 for two of the tephra layers are interpreted as indicating that D'Entrecasteaux Islands volcanism younger than 2.9 Ma occasionally interacted with the Late Archean basement, possibly reflecting the mobilisation of the deep continental crust during active rift propagation.

Relative abundance of planktonic foraminifera in Pliocene and Pleistocene sediments of DSDP Hole 32-310 from Hess Rise, Central North Pacific (Table II)

Late Neogene planktonic foraminifera have been examined at Site 310 in the Central North Pacific and their stratigraphic ranges and frequencies are presented here. Blow's (1969) zonation developed for tropical regions has been applied where applicable. Where tropical index taxa are rare or absent in this temperate region, Globorotalia crassaformis, and the evolutionary bioseries G. conoidea - G. conomiozea and G. puncticulata - G. inflata have been found useful for zonal subdivisions. A correlation between stratigraphic ranges and frequency distributions of these species at Site 310 in the Central North Pacific, and Site 284 in the Southwest Pacific indicates that these species are relatively consistent biostratigraphic markers in temperate regions of both the North and South Pacific Oceans. An informal zonation for temperate latitudes of the Southwest Pacific has been established by Kennett (1973) and a similar zonal subdivision can be made at Site 310. Paleoclimatic/paleoceanographic interpretations based on coiling ratios, percent abundance, and phenotypic variations of Neogloboquadrina pachyderma indicate four major cold events during early, middle, and late Pliocene, and early Pleistocene. Faunal correlations of these events with similar events elsewhere in the Northeast and Southwest Pacific which have been paleomagnetically dated indicate the following approximate ages for these cold events: 4.7 Ma, 3.0 Ma, 2.6-1.8 Ma, and 1.2 Ma. Faunal assemblages have been divided into three groups representing cool, intermediate, and warmer water assemblages. Cool water assemblages are dominated by ~60% N. pachyderma; intermediate temperature faunas are dominated by species of Globigerina and Globigerinita and contain between 20% and 30% N. pachyderma. Warmer water assemblages are dominated by species of Globorotalia and contain <10% N. pachyderma. Frequency oscillations within these groups, in addition to paleotemperature parameters evident in N. pachyderma, afford refined paleoclimatic/paleoceanographic interpretations.