Parallel responses of bees to Pleistocene climate change in three isolated archipelagos of the southwestern Pacific

The impacts of glacial cycles on the geographical distribution and size of populations have been explored for numerous terrestrial and marine taxa. However, most studies have focused on high latitudes, with only a few focused on the response of biota to the last glacial maximum (LGM) in equatorial regions. Here, we examine how population sizes of key bee fauna in the southwest Pacific archipelagos of Fiji, Vanuatu and Samoa have fluctuated over the Quaternary. We show that all three island faunas suffered massive population declines, roughly corresponding in time to the LGM, followed by rapid expansion post-LGM. Our data therefore suggest that Pleistocene climate change has had major impacts across a very broad tropical region. While other studies indicate widespread Holarctic effects of the LGM, our data suggest a much wider range of latitudes, extending to the tropics, where these climate change repercussions were important. As key pollinators, the inferred changes in these bee faunas may have been critical in the development of the diverse Pacific island flora. The magnitude of these responses indicates future climate change scenarios may have alarming consequences for Pacific island systems involving pollinator-dependent plant communities and agricultural crops.     

Summer feeding habits of the Pacific pomfret Brama japonica in the transitional and subarctic waters of the central North Pacific

Feeding habits of the Pacific pomfret Brama japonica , ranging from 30 to 40 cm in standard length, were quantitatively evaluated using the index of relative importance and were compared between the transitional domain and subarctic region in the central North Pacific. In the transitional domain (between the subarctic boundary and the subarctic front), this species fed mainly on subarctic and transitional‐water gonatid squids such as Berryteuthis anonychus , Gonatus middendorffi and Gonatopsis borealis , the transitional‐water squid Onychoteuthis borealijaponica , and a subtropical and transitional‐water amphipod, Phronima sedentaria . These prey items accounted for 52·8% by wet mass of total stomach contents. In the subarctic region (north of the subarctic front), Pacific pomfrets preyed primarily on subarctic and transitional‐water squids, such as B. anonychus and G. middendorffi , and secondarily on subarctic amphipods such as Hyperia medusarum and Hyperia glaba . These four prey items comprised 71·6% by mass of total stomach contents. Major transitional domain prey items, such as G. borealis, O. borealijaponica and P. sedentaria , were almost non‐existent in stomachs of fish from the subarctic region. The mean wet stomach content mass expressed as a percentage of body mass was significantly higher in the subarctic region (2·35%) than in the transitional domain (0·75%), suggesting that, for this fish, prey items are more readily available in the subarctic region during summer and their northward migration is a feeding migration. Feeding strategy of the Pacific pomfret was discussed in relation to their seasonal south‐north migration.     

浅谈浮游有孔虫群落海水古温度估算

微体化石组合很早就被用来进行海水古温度估算,近年来利用浮游有孔虫组合来估算古温度的方法有IK TF,MAT,RAM,SIMMAX,ANN和ANND等。本文介绍了这六种方法的主要原理和他们适用的纬度和温度范围,并分别利用FP12E、SIMMAX28及ANN等三类方法来估算冲绳海槽255站位、南海17957站位和ODP1143站位的表层海水古温度,比较计算结果的异同,以验证他们的适用性。     

Kofoidinium, Spatulodinium and other kofoidiniaceans (Noctilucales, Dinophyceae) in the Pacific Ocean

Examples of rarely reported dinoflagellates of the family Kofoidiniaceae F.J.R. Taylor (Noctilucales) from the northwest, equatorial and southeast Pacific Ocean are described and illustrated. Kofoidinium was the most ubiquitous genus with a maximum abundance of 10 cells L(-1). Specimens of this genus were identified to four species: Kofoidinium sp. that showed a pointed extension that emerges from the antero-ventral region and K. velelloides, both of which had diameters that ranged from 40 to 200 microm; Kofoidinium pavillardii which showed a rounded epitheca and a larger size (approximately 300-700 microm in diameter); and another species, tentatively identified as K. splendens, that contained red circular inclusions. Further research is needed to clarify the characteristics that separate K. splendens from the other species. This study is the first to record the genus Spatulodinium in tropical waters and in the southern hemisphere. S. cf. pseudonoctiluca was found in the southeast Pacific Ocean, as well as other smaller specimens with a different shape or disposition of the tentacle that may belong to two other species. In the northwest and equatorial Pacific, specimens of Spatulodinium showed a green pigmentation that suggested the existence of the first species known in the order Noctilucales to contain its own chloroplasts. Immature stages of kofoidiniaceans, some containing symbiotic microalgae, are illustrated, as well as mature stages related to Pomatodinium and to unknown genera of kofoidiniaceans. Kofoidiniaceans are shown to be common and widely distributed in the Pacific, and are probably also frequent in other oceans, but are rarely recognised.     

“El Niño” events recorded in dry-forest species of the lowlands of northwest Peru

The northwest coast of Peru (5°S, 80°W) is very sensitive to and impacted by the climate phenomenon El Niño-Southern Oscillation (ENSO). Though mainly desert, this warm, dry region contains an equatorial dry forest. We report the first dendrochronological studies from this region and identify several species that have dendrochronological potential. Short ring-width chronologies of Palo Santo (Bursera graveolens) show a well-developed response to the ENSO signal over the last 50 years and good inter-site correlations. Preliminary isotopic studies in Algarrobo (Prosopis sp.) also show evidence of the 1997–98 El Niño event. ENSO events have a strong effect on the variability in the growth of several species and thereby on the economy of rural communities where the wood is used for housing, cooking, furniture, tools, fodder and medicinal uses. The extensive use of wood in archeological sites also offers the possibility of ultimately developing longer records for some of these species.     

Late neogene biostratigraphy and paleoceanography of DSDP site 310 Central North Pacific and correlation with the Southwest Pacific

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. puncticula — 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.     

Limitation of bacterial growth by dissolved organic matter and iron in the Southern ocean

The importance of resource limitation in controlling bacterial growth in the high-nutrient, low-chlorophyll (HNLC) region of the Southern Ocean was experimentally determined during February and March 1998. Organic- and inorganic-nutrient enrichment experiments were performed between 42 degrees S and 55 degrees S along 141 degrees E. Bacterial abundance, mean cell volume, and [(3)H]thymidine and [(3)H]leucine incorporation were measured during 4- to 5-day incubations. Bacterial biomass, production, and rates of growth all responded to organic enrichments in three of the four experiments. These results indicate that bacterial growth was constrained primarily by the availability of dissolved organic matter. Bacterial growth in the subtropical front, subantarctic zone, and subantarctic front responded most favorably to additions of dissolved free amino acids or glucose plus ammonium. Bacterial growth in these regions may be limited by input of both organic matter and reduced nitrogen. Unlike similar experimental results in other HNLC regions (subarctic and equatorial Pacific), growth stimulation of bacteria in the Southern Ocean resulted in significant biomass accumulation, apparently by stimulating bacterial growth in excess of removal processes. Bacterial growth was relatively unchanged by additions of iron alone; however, additions of glucose plus iron resulted in substantial increases in rates of bacterial growth and biomass accumulation. These results imply that bacterial growth efficiency and nitrogen utilization may be partly constrained by iron availability in the HNLC Southern Ocean.     

Radiolaria as indicators of upwelling processes: The Peruvian connection

In the sediments along the coastal region of Peru, certain radiolarian species have preferences to waters associated with upwelling. Such is the case forPolysolenia murrayana in the upwelling areas “fed” by equatorial water and forCenosphaera (?) sp. in the upwelling areas “fed” by temperate (Subantarctic) water.Cycladophora (?)davisiana appears to “frame” the upwelling centers, suggesting that it prefers regions near thermic fronts.The down-core records of these species, as well as records of quartz and organic carbon, are depicted in three¹⁴C andδ¹⁸O dated cores, located along the Pacific coast of South America, between 11° and 13°S. They suggest that both the eolian and oceanic circulation were more intense during the last glacial stage (approximately between 33,000 and 11,000 years ago) than during the present postglacial. At these latitudes, the intensification in circulation was not only accompanied by an increased coastal upwelling and in turn by an increased primary productivity, but also by a larger supply of Temperate waters to the area.     

Boomeranging around Australia: Historical biogeography and population genomics of the anti‐equatorial fish Microcanthus strigatus (Teleostei: Microcanthidae)

The geographic distributions of marine fishes have been shaped by ancient vicariance and ongoing dispersal events. Some species exhibit anti‐equatorial distributions, inhabiting temperate regions on both sides of the tropics while being absent from equatorial latitudes. The perciform fish Microcanthus strigatus (the stripey) exhibits such a distribution with disjunct populations occurring in East Asia, Hawaii, Western Australia, and the southwest Pacific. Here, we examine the historical biogeography and evolutionary history of M. strigatus, based on more than 80 specimens sampled from the four major populations. We analysed 36 morphological characters, three mitochondrial markers, and two sets of 7,120 and 12,771 single‐nucleotide polymorphisms from the nuclear genome. Our results suggest that M. strigatus represents a cryptic species complex comprising at least two genetically distinct populations worthy of species‐level recognition, with one population exhibiting strong genetic structuring but with intermittent, historical gene flow. We provide evidence for a southwest Pacific origin for the ancestral Microcanthus and explain how past connectivity between these regions might have given rise to the relationships observed in present‐day marine fauna. Our ancestral range reconstructions and molecular‐clock analyses support a southwest Pacific centre of origin for Microcanthus, with subsequent colonization of Western Australia through the Bass Strait followed by transequatorial dispersals to the Northern Hemisphere during the Pleistocene. Our results detail an anti‐tropical dispersal pattern that is highly unusual and previously undocumented, thereby emphasizing the importance of integrative systematics in the evaluation of widespread species.     

“El Niño” events recorded in dry-forest species of the lowlands of northwest Peru

The northwest coast of Peru (5°S, 80°W) is very sensitive to and impacted by the climate phenomenon El Niño-Southern Oscillation (ENSO). Though mainly desert, this warm, dry region contains an equatorial dry forest. We report the first dendrochronological studies from this region and identify several species that have dendrochronological potential. Short ring-width chronologies of Palo Santo (Bursera graveolens) show a well-developed response to the ENSO signal over the last 50 years and good inter-site correlations. Preliminary isotopic studies in Algarrobo (Prosopis sp.) also show evidence of the 1997–98 El Niño event. ENSO events have a strong effect on the variability in the growth of several species and thereby on the economy of rural communities where the wood is used for housing, cooking, furniture, tools, fodder and medicinal uses. The extensive use of wood in archeological sites also offers the possibility of ultimately developing longer records for some of these species.     

Seasonality in Southern Hemisphere freshwater phytoplankton assemblages

Seasonal climatic cycles induce corresponding fluctuations in phytoplankton abundance and productivity at all latitudes, the magnitude of these fluctuations tending to increase with distance from the Equator. In equatorial regions seasonality is dependent on prevailing wind and rainfall patterns while annual temperature fluctuations exert increasing control over seasonal events at higher latitudes. The small annual temperature range of equatorial aquatic systems increases their sensitivity to localized climatic events which can bring about diel changes that exceed normal month-to-month variations. Long-term hydrological cycles with a periodicity greater than one year can also cause dramatic changes in equatorial and tropical aquatic systems leading to greater unpredictability.The factors regulating seasonal patterns of phytoplankton abundance and species composition in equatorial and low-latitude temperate regions of the Southern Hemisphere are examined and compared with similar features in the Northern Hemisphere. Despite the striking diversity of phytoplankton populations and the wide variety of habitats they occupy, seasonal succession follows a common sequence controlled, successively, by physical, chemical and biotic factors. This permits a high degree of predictability in the environmental conditions promoting growth of different taxa.Examination of Southern Hemisphere data indicates that, at class level, phytoplankton successional sequences in Southern Hemisphere aquatic systems are in agreement with the successional paradigm formulated for northern tropical and temperate latitudes. Diatoms characterize early successional episodes and these are followed by chlorophytes, and finally blue-green algae. Extreme habitat modification (e.g. hypertrophy, salinity) tends to lead to dominance of the habitat by a single taxon, often represented by a single species. Predictions of within-taxon species succession in phytoplankton assemblages are far less precise.     

Range Expansion Drives Dispersal Evolution In An Equatorial Three-Species Symbiosis

Background

Recurrent climatic oscillations have produced dramatic changes in species distributions. This process has been proposed to be a major evolutionary force, shaping many life history traits of species, and to govern global patterns of biodiversity at different scales. During range expansions selection may favor the evolution of higher dispersal, and symbiotic interactions may be affected. It has been argued that a weakness of climate fluctuation-driven range dynamics at equatorial latitudes has facilitated the persistence there of more specialized species and interactions. However, how much the biology and ecology of species is changed by range dynamics has seldom been investigated, particularly in equatorial regions.

Methodology/Principal Findings

We studied a three-species symbiosis endemic to coastal equatorial rainforests in Cameroon, where the impact of range dynamics is supposed to be limited, comprised of two species-specific obligate mutualists –an ant-plant and its protective ant– and a species-specific ant parasite of this mutualism. We combined analyses of within-species genetic diversity and of phenotypic variation in a transect at the southern range limit of this ant-plant system. All three species present congruent genetic signatures of recent gradual southward expansion, a result compatible with available regional paleoclimatic data. As predicted, this expansion has been accompanied by the evolution of more dispersive traits in the two ant species. In contrast, we detected no evidence of change in lifetime reproductive strategy in the tree, nor in its investment in food resources provided to its symbiotic ants.

Conclusions/Significance

Despite the decreasing investment in protective workers and the increasing investment in dispersing females by both the mutualistic and the parasitic ant species, there was no evidence of destabilization of the symbiosis at the colonization front. To our knowledge, we provide here the first evidence at equatorial latitudes that biological traits associated with dispersal are affected by the range expansion dynamics of a set of interacting species.     

Diatom stratigraphy of the late Pleistocene (Brunhes) subarctic Pacific

Three piston cores in the subarctic region of the North Pacific show consistent changes in relative abundance of diatom species throughout the Brunhes magnetic epoch. These events can be used both as stratigraphic markers to subdivide the interval and as indicators of oceanographic conditions. The stratigraphic record shows an acme forA. ochotensis from about 625-350 Kyr (Isotope Stages 15-10); a marked increase in amplitude of abundance fluctuations forR. hebetata 300-0 Kyr (Stages 8-1), the extinction ofR. curvirostris at 276 Kyr (Stage 8), and abundance fluctuations ofD. seminae roughly in phase with the global oxygen isotope record from 450-0 Kyr (Stages 12-1). In the subarctic Pacific, an abrupt change in species abundance is not a reliable indicator of hiatus occurrence. Although details are not clear, there appears to have been a fundamental change of the subarctic gyre during the middle Brunhes (Stages 10-8 time), with more intense glacial intervals and stronger glacial—interglacial contrast occurring after that time. Coarse clastic detritus is not restricted to glacial intervals, suggesting that ice-rafting has occurred throughout the Brunhes interval; peak levels of ice-rafting may occur during ice-growth and decay, as well as during short intervals within a stage.     

Miocene biochronology and paleoceanography of the North Pacific

Biostratigraphic correlation based on microfossil datum levels, directly or indirectly tied to the paleomagnetic time scale, provides a high resolution time control for the Miocene in the equatorial and middle latitude North Pacific. Faunal changes and abundance fluctuations of planktic foraminiferal species combined with the oxygen Pacific. Faunal changes and abundance fluctuations of planktic foraminiferal species combined with the oxygen isotope record of foraminifers, reveal the paleoclimatic and paleoceanographic history. The planktic foraminiferal assemblage change in the early Miocene, extinction of Oligocene fauna and rise of a highly diverse Neogene fauna, appears to be related to increased water mass stratification in the world oceans presumably resulting from the establishment of circum-Antarctic circulation. An increase in the siliceous productivity in the eastern equatorial Pacific region between 20 and 18 Ma suggests that the vertical and horizontal circulation was intensified at that time. Climates cooled rapidly during the middle Miocene between 14 and 13 Ma suggesting the growth of a major east Antarctic ice sheet. Paleoclimatic conditions remained generally cool, although oscillating, during the late Miocene. In the late early to middle Miocene faunal provincialism developed between low and middle latitudes, and by late Miocene time a distinct provincialism similar to the present was established.     

Distribution patterns and chorological analysis of fish fauna of the Arctic Region

Chorological structure of ichthyofauna of the Arctic Region is described. Distribution patterns of 504 fish-like vertebrates and fish species are characterized. One hundred and eighty-nine range types are defined, which are combined into eight main categories: 1—Arctic; 2—Atlantic-Arctic; 3—transitional subarctic zone of Atlantic sector; 4—Pacific-Arctic; 5—transitional subarctic subarctic zone of Pacific sector, 6—Pacific-Atlantic (amphiboreal); 7—bipolar; 8—continental (fresh and brackish waters). Arctic and boreal regions are bordered by transitional (subarctic) zones, which are the areas of intermutual penetration of faunas. The distribution of most fish species that penetrate into to the Arctic Region from the southern areas is limited by these transitional zones. The benthic fish species prevail in the group of autochthonous Arctic species (which includes 64 species or 14% of marine fauna). The demersal fauna of the Arctic preudoabyssal is presented by endemic species. Ten variations of amphiboreal distribution patterns are revealed. Three areas may be defined within the Atlantic-subarctic zone in regard to the fish fauna and range types, i.e., Labrador-Greenland region, the Barents Sea region, and Icelandic (transitional) region.     

Synchronous and time-transgressive Neogene radiolarian datum levels in the Equatorial Indian and Pacific Oceans

Fifty radiolarian events of early Pleistocene and Neogene age were identified in an E-W transect of equatorial DSDP sites, extending from the Gulf of Panama to the western Pacific and eastern Indian Oceans. Our objective was to document the degree of synchroneity or time-transgressiveness of stratigraphically-useful datum levels from this geologic time interval. We restricted our study to low latitudes within which morphological variations of individual taxa are minimal, the total assemblage diversity remains high, and stratigraphic continuity is well-documented by an independent set of criteria. Each of the five sites chosen (503, 573, 289/586, 214) was calibrated to an “absolute” time scale, using a multiple of planktonic foraminiferal, nannofossil, and diatom datum levels which have been independently correlated to the paleomagnetic polarity time scale in piston core material. With these correlations we have assigned “absolute” ages to each radiolarian event, with a precision of 0.1–0.2 m.y. and an accuracy of 0.2–0.4 m.y. On this basis we have classified each of the events as either: (a) synchronous (range of ages <0.4 m.y.); (b) time-transgressive (i.e., range of ages > 1.0 m.y.); and (c) not resolvable (range of ages 0.4–1.0 m.y.).Our results show that, among the synchronous datum levels, a large majority (15 out of 19) are last occurrences. Among those events which are clearly time-transgressive, most are first appearances (10 out of 13). In many instances taxa appear to evolve first in the Indian Ocean, and subsequently in the western and eastern Pacific Ocean. This pattern is particularly unexpected in view of the strong east-to-west zonal flow in equatorial latitudes. Three of the time-transgressive events have been used to define zonal boundaries: the first appearances ofSpongaster pentas, Diartus hughesi, andD. petterssoni. Our results suggest that biostratigraphic non-synchroneity may be substantial (i.e., greater than 1 m.y.) within a given latitudinal zone; one would expect this effect to be even more pronounced across oceanographic and climatic gradients.We anticipate that the extent of diachroneity may be comparable for diatom, foraminiferal, and nannofossil datum levels as well. If this proves true, global “time scales” may need to be re-formulated on the basis of a smaller number of demonstrably synchronous events.     

Limitation of Bacterial Growth by Dissolved Organic Matter and Iron in the Southern Ocean

The importance of resource limitation in controlling bacterial growth in the high-nutrient, low-chlorophyll (HNLC) region of the Southern Ocean was experimentally determined during February and March 1998. Organic- and inorganic-nutrient enrichment experiments were performed between 42°S and 55°S along 141°E. Bacterial abundance, mean cell volume, and [³H]thymidine and [³H]leucine incorporation were measured during 4- to 5-day incubations. Bacterial biomass, production, and rates of growth all responded to organic enrichments in three of the four experiments. These results indicate that bacterial growth was constrained primarily by the availability of dissolved organic matter. Bacterial growth in the subtropical front, subantarctic zone, and subantarctic front responded most favorably to additions of dissolved free amino acids or glucose plus ammonium. Bacterial growth in these regions may be limited by input of both organic matter and reduced nitrogen. Unlike similar experimental results in other HNLC regions (subarctic and equatorial Pacific), growth stimulation of bacteria in the Southern Ocean resulted in significant biomass accumulation, apparently by stimulating bacterial growth in excess of removal processes. Bacterial growth was relatively unchanged by additions of iron alone; however, additions of glucose plus iron resulted in substantial increases in rates of bacterial growth and biomass accumulation. These results imply that bacterial growth efficiency and nitrogen utilization may be partly constrained by iron availability in the HNLC Southern Ocean.     

Vertical Profiles of Bacteria in the Tropical and Subarctic Oceans Revealed by Pyrosequencing

Community composition of Bacteria in the surface and deep water layers were examined at three oceanic sites in the Pacific Ocean separated by great distance, i.e., the South China Sea (SCS) in the western tropical Pacific, the Costa Rica Dome (CRD) in the eastern tropical Pacific and the western subarctic North Pacific (SNP), using high throughput DNA pyrosequencing of the 16S rRNA gene. Bioinformatic analysis rendered a total of 143600 high quality sequences with an average 11967 sequences per sample and mean read length of 449 bp. Phylogenetic analysis showed that Proteobacteria dominated in all shallow and deep waters, with Alphaproteobacteria and Gammaproteobacteria the two most abundant components, and SAR11 the most abundant group at family level in all regions. Cyanobacteria occurred mainly in the surface euphotic layer, and the majority of them in the tropical waters belonged to the GpIIa family including Prochlorococcus and Synechococcus, whilst those associated with Cryptophytes and diatoms were common in the subarctic waters. In general, species richness (Chao1) and diversity (Shannon index H′) were higher for the bacterial communities in the intermediate water layers than for those in surface and deep waters. Both NMDS plot and UPGMA clustering demonstrated that bacterial community composition in the deep waters (500 m ∼2000 m) of the three oceanic regions shared a high similarity and were distinct from those in the upper waters (5 m ∼100 m). Our study indicates that bacterial community composition in the DOC-poor deep water in both tropical and subarctic regions were rather stable, contrasting to those in the surface water layers, which could be strongly affected by the fluctuations of environmental factors.     

Late Miocene—early Pliocene planktonic foraminiferal biostratigraphy and paleoceanography of low-latitude marine sequences

Plate reorganization and development of polar glaciation are closely associated with the changing climatic conditions of the Cenozoic. The planktonic foraminiferal fauna in three low-latitude DSDP sites (224, Ninety East Ridge; 317B, Manihiki Plateau; 366A, Sierra Leone Rise) has been examined to determine how these regions responded to the late Miocene climatic cooling that has been previously observed in high-latitude regions. It has been proposed that an expansion of Antarctic glaciation and a resultant eustatic regression are associated with this cooling, with the latter being at least partially responsible for the Messinian “salinity crisis” in the Mediterranean.Only one of the sites, 366A, shows any significant faunal change during the late Miocene and early Pliocene (approximately 8-3 Ma). During the late Miocene, there is a decrease in the abundance of species considered to be tropical-subtropical, suggesting the incursion of a cool water mass into the Sierra Leone Rise region during this time. The lack of any major faunal changes at Sites 214 and 317B indicates that the water masses of the low-latitude regions of the Indo-Pacific were relatively unaffected by this cooling in the late Miocene.The three sites also show no evidence for a change in the level of the CCD between the late Miocene and early Pliocene; however, this is most likely due to their equatorial position and shallow water depth. Higher-latitude sites from both the Atlantic and the Pacific reveal a definite shoaling of the CCD during the late Miocene.