The El Niño/Southern Oscillation (ENSO) system during the Pliocene warm period (PWP; 3-5 million years ago) may have existed in a permanent El Niño state with a sharply reduced zonal sea surface temperature (SST) gradient in the equatorial Pacific Ocean. This suggests that during the PWP, when global mean temperatures and atmospheric carbon dioxide concentrations were similar to those projected for near-term climate change, ENSO variability--and related global climate teleconnections-could have been radically different from that today. Yet, owing to a lack of observational evidence on seasonal and interannual SST variability from crucial low-latitude sites, this fundamental climate characteristic of the PWP remains controversial. Here we show that permanent El Niño conditions did not exist during the PWP. Our spectral analysis of the δ(18)O SST and salinity proxy, extracted from two 35-year, monthly resolved PWP Porites corals in the Philippines, reveals variability that is similar to present ENSO variation. Although our fossil corals cannot be directly compared with modern ENSO records, two lines of evidence suggest that Philippine corals are appropriate ENSO proxies. First, δ(18)O anomalies from a nearby live Porites coral are correlated with modern records of ENSO variability. Second, negative-δ(18)O events in the fossil corals closely resemble the decreases in δ(18)O seen in the live coral during El Niño events. Prior research advocating a permanent El Niño state may have been limited by the coarse resolution of many SST proxies, whereas our coral-based analysis identifies climate variability at the temporal scale required to resolve ENSO structure firmly.

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A well-supported phylogeny of the Neritopsina, a gastropod superorder archaic in origin, radiated ecologically and diverse in morphology, is reconstructed based on partial 28S rRNA sequences. The result (Neritopsidae (Hydrocenidae (Helicinidae ϩ Neritiliidae) (Neritidae ϩ Phenacolepadidae))) is highly congruent with the fossil records and the character distribution of reproductive tracts in extant taxa. We suggest that the Neritopsina originated in subtidal shallow waters, invaded the land and became fully terrestrial at least three times in different clades, by the extinct Dawsonellidae in the Late Palaeozoic and by the Helicinidae and Hydrocenidae in the Mesozoic. Invasion of fresh-and brackish waters is prevalent among the Neritopsina as the Jurassic and freshwater ancestory is most probable for helicinids. The Phenacolepadidae, a group exclusively inhabiting dysoxic environments, colonized deep-sea hydrothermal vents and seeps in the Late Cretaceous or Early Cenozoic. Submarine caves have served as refuges for the archaic Neritopsidae since the Early to Middle Cenozoic, and the marine neritopsine slug Titiscania represents a highly specialized but relatively recent offshoot of this family. The Neritiliidae is another clade to be found utilizing submarine caves as shelter by the Oligocene; once adapted to the completely dark environment, but some neritiliids have immigrated to surface freshwater habitats.

between anchialine cave populations by means of larval dispersal: the case of a new gastropod species Neritilia cavernicola . -Zoologica Scripta, 33 ,[423][424][425][426][427][428][429][430][431][432][433][434][435][436][437] Despite being limited to caves, many anchialine taxa have disjunct insular distributions, which raises questions about their origins and colonization history. This study deals with the new gastropod Neritilia cavernicola sp. n. (Neritopsina: Neritiliidae) from anchialine caves on two islands in the Philippines that are separated by the deep Bohol Strait and situated 200 km apart along the coastline of Cebu Island. Neritilia cavernicola is an obligate stygobiont and most closely resembles Neritilia littoralis , which lives in interstitial waters of the Nansei-shoto Islands, Japan. Its eggs and larval shells are identical to those of other Neritilia species, despite their different adult habitats. This suggests a marine planktotrophic phase (as occurs in amphidromous riverine species of Neritilia ), and consequent migration between islands via ocean currents. Here we present the first genetic structure for anchialine cave organisms; comparisons of 1276 bp sequences from mitochondrial cytochrome oxidase I show no evidence of genetic isolation between the islands. All individuals evidently are part of a panmictic population and the low vagility of adults and their seemingly isolated cave habitats do not limit gene flow in N. cavernicola . This migration model, based on marine larval dispersal, may be widely applicable to anchialine stygobites with insular distributions, as many such organisms (including shrimps, crabs and fishes) are phylogenetically allied to amphidromous species.

A sediment layer (43 cm thick) and surface sediments (5 cm thick) in a submarine limestone cave (31 m water depth) on the fore-reef slope of Ie Island, off Okinawa mainland, Japan, were examined by visual, mineralogical and geochemical means. Oxygen isotope analysis was performed on the cavernicolous micro-bivalve Carditella iejimensis from both cored sediments and surface sediments, and the water temperature within the cave was recorded for nearly one year. These data show that: (1) water temperature within the cave is equal to that at 30 m deep in the open sea; (2) the biotic and non-biotic environments within the cave have persisted for the past 2000 years; (3) mud-size carbonate detritus is a major constituent of the submarine-cave deposit, and may have come mainly from the suspended carbonate mud produced on the emergent Holocene reef flat over the past two millennia; (4) the δ 18 O-derived temperature (T δ 18 O ) of C. iejimensis suggests that the species grows between April and July; (5) the T δ 18 O of C. iejimensis from cored sediments implies that there were two warmer intervals, at AD 340 ± 40 and AD 1000 ± 40, which correspond to the Roman Warm Period and Medieval Warm Period, respectively. These suggest that submarine-cave sediments provide unique information for Holocene reef development. In addition, oxygen isotope records of cavernicolous C. iejimensis are a useful tool to reconstruct century-scale climatic variability for the Okinawa Islands during the Holocene.