Eustatic Sea-level Changes Research Articles

Reply to discussion “Is spreading prolong, episodic or incipient in the Andaman Sea? Evidence from deepwater sedimentation” by J.R. Curray 2015

We consider the presence of thick section in the axial trough indicates that the Pliocene-Recent continuous spreading model proposed by Curray (2015) is not appropriate for the Andaman Sea. The high frequency of eustatic sea level changes during the Plio-Pleistocene is incompatible with large, rapid influxes of sediment, widely separated in time but related to eustacy as proposed by Curray (2015). Instead spreading is probably of Miocene age, and was only renewed recently, if at all. The nature of the crust adjacent to the spreading centre remains uncertain. However, industry seismic data from the East Andaman Basin strongly suggests if the western part of the basin is underlain by oceanic crust it must be Oligocene or older, it is not Early Miocene. This in turn suggests the volcanics dredged from the Alcock rise were extruded onto older crust (whether it is oceanic, island arc or continental), and do not represent the age of oceanic crust formation. Gravity and seismic reflection data point to the East Andaman Basin being dominantly underlain by extended, to hyper extended continental crust and transitional crust. The Alcock and Sewell rises are interpreted as representing the western side of the strongly necked zone of continental crust.

Link between cyclic eustatic sea-level change and continental weathering: Evidence for aquifer-eustasy in the Cretaceous

Cyclic fluctuations in global sea level during epochs of warm greenhouse climate have remained enigmatic, because absence or subordinate presence of polar ice during these periods precludes an explanation by glacio-eustatic forcing. An alternative concept suggests that the water-bearing potential of groundwater aquifers is equal to that of ice caps and that changes in the dynamic balance of aquifer charge versus discharge, as a function of the temperature-related intensity of the hydrological cycle, may have driven eustasy during warm climates. However, this idea has long been neglected for two reasons: 1) the large storage potential of subsurface aquifers was confused with the much smaller capacity of rivers and lakes and 2) empirical data were missing that document past variations in the hydrological cycle in relation to eustasy.In the present study we present the first empirical evidence for changes in precipitation, continental weathering intensity and evaporation that correlate with astronomically (long obliquity) forced sea-level cycles during the warmest period of the Cretaceous (Cenomanian–Turonian). We compare sequence-stratigraphic data with changes in the terrigenous mineral assemblage in a low-latitude marine sedimentary sequence from the equatorial humid belt at the South-Tethyan margin (Levant carbonate platform, Jordan), thereby avoiding uncertainties from land–ocean correlations. Our data indicate covariance between cycles in weathering and sea level: predominantly chemical weathering under wet climate conditions is reflected by dominance of weathering products (clays) in deposits that represent sea-level fall (aquifer charge>discharge). Conversely, preservation of weathering-sensitive minerals (feldspars, epidote and pyroxenes) in transgressive sediments reflects decreased continental weathering due to dryer climate (aquifer discharge>charge). Based on our results we suggest that aquifer-eustasy represents a viable alternative to glacio-eustasy as a driver of cyclic 3rd-order sea-level fluctuations during the middle Cretaceous greenhouse climate, and it may have been a pervasive process throughout Earth history.

Sequence architecture of a Jurassic ramp succession from Gebel Maghara (North Sinai, Egypt): Implications for eustasy

The Jurassic succession at Gebel Maghara, North Sinai, Egypt, represents a mixed carbonate–siliciclastic sequence. Combining information from both fossils and rocks allowed a plausible reconstruction of the depositional environments and of the basin evolution. The Jurassic succession of Gebel Maghara was deposited on a ramp, and the architecture of the ramp facies was strongly controlled not only by sea–level changes but also by extensional tectonics in connection with rifting of the Tethys, North Gondwana. Seven tectonically modified thirdorder sequences (DS 1–DS 7) have been recognized. The first three sequences (DS 1–DS 3), ranging from the Toarcian to the Bajocian, record sea invasion (intertidal to shallow subtidal conditions) across an intracratonic area as a result of eustatic sea–level changes during a quiescent rift stage. The remaining sequences (DS 4–DS 7) reflect open marine mid to outer ramp settings. Non–marine conditions around the Bajocian–Bathonian boundary, documented by caliche, represent the maximum regression of the sea. During an active extensional stage, horsts, which formerly acted as barriers separating the Maghara sub–basin from the main ocean, subsided. Subsequent rejuvenation and reactivation of faults shifted the homoclinal physiography of the ramp to a distally steepened ramp during the early Bathonian, creating a 200–m–thick deltaic wedge. Similar processes during the early Kimmeridgian created a calcirudite–calcarenite succession of slope origin. The diversity and the epifaunal/infaunal percentage of the macrofauna display a cyclic pattern which coincides more or less with the sequence stratigraphic architecture.

Facies analysis and depositional environments of the Upper Jurassic Jubaila Formation, Central Saudi Arabia

This article deals with the Upper Jurassic carbonates of the Jubaila Formation, exposed throughout the Tuwaiq Mountains, Central Saudi Arabia and discusses the succession of palaeoenvironments resulting from detailed field and lab work. Based on microfacies analysis and sedimentological data, twelve facies are identified within the Upper Jurassic carbonates at Wadi Hanifa, Central Saudi Arabia. These facies are attributed to six main facies belts. Within these facies and facies belts, four distinct biofacies assemblages are recognized. Deposition took place on an extendable ramp, which probably dipped gently eastwards to the sea. A depositional model relates the identified facies and biofacies to a downdip depositional profile of an inner, middle and outer carbonate ramp. The burrowed lime mudstone and bioclastic wackestone–floatstone of facies belt 1 accumulated in a distal middle ramp to outer ramp. The mollusk-coated grains–intraclast rudstone of facies belt 2 were deposited in the distal middle ramp. The branched stromatoporoids Cladocoropsis were deposited in the proximal middle ramp of facies belt 3. The facies of the open lagoon (facies belt 5) and the tidal-flat (facies belt 6) were deposited in the inner ramp behind the ramp crest/shoal facies belt 4. The Early Kimmeridgian Jubaila Formation has been deposited as transgressive and highstand deposits of a third-order depositional sequence, which are mainly controlled by eustatic sea-level changes. During the transgression, an aggradational trend developed, with the construction of a deep subtidal facies of small-scale stacked cycles of mudstones with frequent mottled firm ground and hard ground, storm beds and tempestites. The regressive part has a characteristic progradational trend, with shallow-water carbonate platform deposits arranged into meter-scale coarsening-upward cycles ranged from dolomitic mudstone and wackestone to stromatoporoid packstone and rudstone into bioclastic intraclastic peloidal packstone and grainstone.

Tectono-climatic implications of Eocene Paratethys regression in the Tajik basin of central Asia

Plate tectonics and eustatic sea-level changes have fundamental effects on paleoenvironmental conditions and bio-ecological changes. The Paratethys Sea was a large marine seaway that connected the Mediterranean Neotethys Ocean with Central Asia during early Cenozoic time. Withdrawal of the Paratethys from central Asia impacted the distribution and composition of terrestrial faunas in the region and has been largely associated with changes in global sea level and climate such as cooling associated with the Eocene/Oligocene transition (EOT).Whereas the regression has been dated in the Tarim basin (China), the pattern and timing of regression in the Tajik basin, 400 km to the west, remain unresolved, precluding a test of current paleogeographic models. Here we date the Paratethys regression in Tajikistan at ca. 39 million years ago (Ma), which is several million years older than the EOT (at ca. 34 Ma) marking the greenhouse to icehouse climate transition of the Cenozoic. Our data also show a restricted, evaporitic marine environment since the middle–late Eocene and establishment of desert like environments after ca. 39 Ma. The overall stratigraphic record from the Tajik basin and southern Tien Shan points to deposition in a foreland basin setting by ca. 40 Ma in response to active tectonic growth of the Pamir–Tibet Mountains at the same time. Combined with the northwestward younging trend of the regression in the region, the Tajik basin record is consistent with northward growth of the Pamir and suggests significant tectonic control on Paratethys regression and paleoenvironmental changes in Central Asia.

Nd isotope composition of conodonts: An accurate proxy of sea-level fluctuations

Analyses of the Nd isotope composition of conodonts from the Anti-Atlas (Morocco), the Montagne Noire (France) and the Rhenohercynian domain (Germany) provide insight into the temporal and lateral variations in seawater geochemistry in the western part of the Variscan Sea during the Late Devonian. Most of the isotopic excursions accurately record changes in sea level. The εNd values decreased during regression phases when erosion accelerated supply of unradiogenic Nd from old continental sources. A rise in sea level generated a positive shift in εNd values due to input of more radiogenic oceanic water into the seawater reservoir of the shelf areas. The method has great potential for sea-level research, paleoceanography and correlation because sea-level changes can be precisely recognized even in successions with uniform, monotonous lithologies. However, it has a significant limitation being valid only in epeiric seas and shelf areas. We have used the Nd isotope record to reconstruct the eustatic sea-level changes in late Frasnian–early Famennian time. The onset of the organic-rich Kellwasser units coincides with negative trends in εNd values. This accords with oxygen deficiency at the sea bottom being initiated by short-term regressive events, which in turn would be consistent with cooling periods of glacial origin, as previous authors have suggested.

Constraints on eustatic sea-level changes during the Mid-Pleistocene Climate Transition: Evidence from the Japanese shallow-marine sediment record

During the Middle Pleistocene, the nature of glacial–interglacial fluctuations changed from low-amplitude and a periodicity of 41 ky to high-amplitude and quasi-periodic of 100 ky. The origin of the Mid-Pleistocene Climate Transition (MPT) is an unsolved mystery. At present, there is a debate about whether the initiation of the MPT was a gradual or an abrupt process. This study investigated the process of initiation of the MPT from reconstructions of eustatic sea-level changes, as a proxy for global ice volume, based on a reexamination of lithofacies and fossil occurrences from shallow-marine sediments (Omma Formation) exposed on the west coast of Japan. The Omma Formation comprises 19 depositional sequences spanning marine isotope stages (MIS) 56–21.3, reflecting sedimentation under alluvial plain to offshore conditions. The data indicate that (1) sea-level was lowest during MIS 22 (∼0.9 Ma); (2) sea-level during MIS 34 (∼1.13 Ma) and MIS 26 (∼0.96 Ma) was lower than during any other glacial stage, except for MIS 22; and (3) sea-level during MIS 22 was at most 20 m lower than during MIS 34 and 26. Together, these findings suggest that the initiation of the MPT was a gradual, rather than abrupt, process.

New constraints on late Holocene eustatic sea-level changes from Mahé, Seychelles

This study provides new estimates of globally integrated ice sheet melt during the late Holocene (since 4 ka BP) from Seychelles in the western Indian Ocean, a tectonically stable, far field location where the necessary Glacial-Isostatic Adjustment (GIA) correction is small and is relatively insensitive to predictions using different Earth viscosity profiles. We compare sea level data from Seychelles to estimates of eustasy from two GIA models, ICE-5G and EUST3, which represent end-members in the quantity of global melt during the late Holocene. We use data from a range of coastal environments including fringing reef, present day beaches, fossil plateau and mangrove deposits on the largest island of the Seychelles archipelago, Mahé to reconstruct relative sea-level changes. Our data suggest that extensive coastal deposits of carbonate-rich sands that fringe the west coast formed in the last 2ka and the horizontal nature of their surface topography suggests RSL stability during this period. Mangrove sediments preserved behind these deposits and in river mouths date to c. 2ka and indicate that RSL was between −2 m and present during this interval. Correcting the reconstructed sea level data using a suite of optimal GIA models based on the two ice models mentioned above and a large number (c. 350) of Earth viscosity models gives a result that is consistent with the sedimentological constraints. When uncertainties in both model results and data are considered, it is possible to rule out eustatic sea levels below c. 2m and more than a few decimetres above present during the past two millennia. This uncertainty is dominated by error in the reconstructions rather than the model predictions. We note, however, that our estimates of eustasy are more compatible with the EUST3 model compared to the ICE-5G model during the late Holocene (2–1kaBP). Our evidence from Seychelles shows that the timing of when eustatic sea level first rose close to present is between the predictions of the two end-member GIA models presented here (4kaBP for ICE-5G and 1kaBP for EUST3). Using all lines of evidence currently available from Mahé we suggest that the eustatic contribution during the last 2ka has been less than 2 m . This conclusion is drawn from a tectonically stable, far-field region that is relatively insensitive to earth and ice model uncertainties, and implies that global eustasy has been relatively insensitive to climate fluctuations over the pre-industrial part of the last 2ka.

Stone Age archaeological sites and environmental changes during the Holocene in the NW region of Russia

Abstract The region of NW Russia connecting with the Baltic Sea presents a dynamic ecological system that was sensitive to environmental changes during the Holocene. Certain factors affected environmental changes in the region during the Holocene: deglaciation processes, that finally terminated about 9 cal ka BP; eustatic sea-level changes; and tectonic movements, which are basically considered in the region as isostatic uplift processes. Contextual remains of ancient human occupation sites can be the only evidence of surface stabilization in monotonous sediments, such as aquatic and subaquatic deposits. Prehistoric settlements also mark ancient shorelines. The latter is of great importance for studying the history of water oscillations and coastal-line displacements on the territory of NW Russia. The transgressive–regressive stages of the Baltic Sea (at c. 10.15 cal ka BP, the Ancylus transgression; at c. 7.6–7.0 cal ka BP, the Littorina transgression) have an impact on the positions of prehistorical sites. The complex investigations of the Stone Age archaeological settlements on the Karelian Isthmus and in the Dvina–Lovat’ basin, and their altitudes below sea level, allowed us to reconstruct palaeoenvironmental changes during the Holocene, the chronology of cultural–historical processes and the adaptation strategy of ancient people to environmental conditions in this territory.

Global climate, sea level cycles, and biotic events in the Cambrian Period

The developing high-resolution chronostratigraphy of the Cambrian provides an updated age model for various geologic and biotic events that occurred during this critical period of Earth history. Broad, time-specific patterns of lithofacies, such as organic-rich deposits, and biofacies appear to be consistent across all Cambrian paleocontinents. Records of important evolutionary events including first appearances of certain metazoan taxa, migrations, and extinctions, tend to coincide with changes in eustatic sea level, as do the positions of many Konservat-Lagerstätten, concretion horizons, agnostoid-rich beds, and other sedimentary features. Most of these events or horizons also show a relationship to perturbations in the global carbon cycle. The positions of organic-rich deposits bear strong relationship to both paleogeographic position and sea level history. Cambrian strata show evidence of cyclicity at multiple scales. Synchronous or near-synchronous global cyclicity is inferred to be associated with oceanographic and climatic cycles characteristic of glacial expansion and deglaciation.

Palynostratigraphy and palynofacies of the Upper Triassic Streppenosa Formation (SE Sicily, Italy) and inference on the main controlling factors in the organic rich shale deposition

This paper focuses on the Upper Triassic Streppenosa Formation, penetrated by the Pachino 4 on-shore well, (Southern Sicily, Italy) in order to find stratigraphic age constrains and to reconstruct the paleoenvironmental evolution of this basin within the Upper Triassic palaeogeographic scenario of the western Tethys. Pachino 4 is one of the wells drilled by Eni Exploration and Production in the south-eastern Hyblean plateau with the purpose to better define the time and space distribution of reservoirs and source rocks in an area characterized by considerable subsidence and strong tectonic activity, balanced by high sedimentation rate. The Streppenosa Formation depocenter consists of a thick sequence (>2500m) of organic rich shales, turbiditic limestones and marly limestones, grouped into three members (Lower, Middle and Upper). The well diversified microflora assemblages allow the dating of the upper part of the Lower Member and the Middle Member as Norian and the Upper Member as Rhaetian. The palynofacies variations across the Streppenosa Formation show significative changes in the relative abundances of the organic debris that, associated with the lithological and sedimentological features, allowed a reconstruction of the depositional facies successions and a hypothesis for the forcing mechanisms driving the black shale deposition. We considered that the deposition of the Streppenosa Formation occurred in an epeiric basin, under oxygen-depleted bottom waters, with different depth that varied through time in response to the sedimentation rates, eustatic sea level changes, and basin subsidence. The integration of palynofacies and lithofacies data suggests a crucial role for river runoff, responsible for water stratification and for primary productivity increase in the water column. The process was triggered by warmer and wetter climate conditions as documented in many Upper Triassic successions of the western Tethys realm.

Melting of Sea Ice Inexplicable for Recent Global Eustatic Sea Level Rise

Global warming and associated sea level rise due to melting of major ice reserves is one of the most important and debated issues of present time. It has unequivocally been proved that mean global surface and ocean temperature is increasing due to anthropogenic input of greenhouse gases like carbon dioxide which has reached its maximum concentration up to 399.35 ppm since last 650,000 years. Due to greenhouse effect global ice caps, sheets and sea ice are melting. But there is an ambiguity of rate of melting of ice and rate of global sea level rise. This can be best exemplified by melting rate of Arctic sea ice with nonequivalent response to the rate of global sea level rise. Conceptual model proposed in this paper differentiates the role of continental glacier, ice sheets and sea ice in the process of global or eustatic sea level rise. It shows that melting of sea ice is not responsible for global or eustatic sea level change. However convoluted effect of melting of continental glaciers and ice sheets and thermal expansion of ocean water due to increasing ocean heat budget is responsible for recent eustatic sea level rise.

Upper Cretaceous sequence stratigraphy of the Galala Plateaux, western side of the Gulf of Suez, Egypt

Based on the study of lithology, biostratigraphy and analysis of facies, this study deduces the occurrence of nine third-order Upper Cretaceous (Cenomanian–Maastrichtian) depositional sequences, which are bounded by eleven sequence boundaries of geographic extent in the Galala Plateaux, situated along the western side of the Gulf of Suez, Egypt. Some of the recorded sequence boundaries (e.g., Cenomanian/Turonian, Turonian/Coniacian, intra Santonian, and Campanian/Maastrichtian sequence boundaries) are not yet confirmed to eustatic sea-level changes. Fourteen main mixed carbonate/siliciclastic facies associations were recognized on a lateral transition between inner to outer ramp settings, with apparent subsidence towards the south. The tectonic position of the Galala Plateaux played an important role in the profound complexity of facies changes and the configuration of depositional sequences representing variable time gaps.

Fusulinids (Foraminifera), lithofacies and biofacies of the Upper Moscovian (Carboniferous) of the southern Moscow Basin and Oka-Tsna Swell

Twenty-nine fusulinid species of 14 genera are determined in the Podolskian and Myachkovian substages (Pennsylvanian) of the southern Moscow Basin. All test sections are determined to genus level, except for the genera Schubertella and Fusiella. Since it is impossible to distinguish between these two genera in oblique test sections, they are identified to the family Schubertellidae. The stratigraphic distribution of fusulinid species put on a new sequence-stratigraphic framework (succession of cyclothems) reveals nonsimultaneous appearance of zonal assemblages in different localities. Sporadical occurrence of index species below and above their designated zones attest for shortage of reliable biostratigraphic markers within the Upper Moscovian interval. The legacy acmezones Fusulinella bocki and Fusulina cylindrica appear to be the most robust divisions in the regional fusulinid zonation. The Podolskian-Myachkovian stratigraphic interval is characterized by progressive decline of Neostaffella, whereas representatives of Fusulina show inverse development. The genus Fusulina changes its facies preference from normal marine subtidal facies in the Podolskian to shoal peloidal-bioclastic grainstones in the upper half of the Myachkovian. Fusulinid genera tend to be distributed patchy and within a broad facies range. It is confirmed that the staffellid genera Reitlingerina and Parastaffelloides are good indicators of shallow-water normal marine euphotic conditions. The genus Hemifusuina occasionally masses in mud-dominated tempestitic limestones of shallowing-upward (regressive) parts of cyclothems. Schubertellids were the most tolerant group as seen from their steady presence in the entire spectrum of marine facies of the studied basin. Five fusulinid biofacies are recognized in the Upper Moscovian: (1) Fusulinella-Ozawainella, (2) Staffellida, (3) Staffellida-Fusulina, (4) impoverished Schubertellidae, and (5) Hemifusulina. These paleo-biofacies are based on mean densities of fusulinids in thin sections (tests per cm2), data departure criteria of these mean densities, the Shannon diversity index H, and Berger-Parker index of dominance d. Degree of differentiation of fusulinid biofacies is notably low, which is explained by unsteady benthic environments affected by frequent storm dispersals of benthic organisms and geologically rapid eustatic sea level changes. The relation of fusulinid, conodont, and general biofacies is discussed. Three general biofacies are recognized: staffellid-syphonean (photozoan and transitional heterophotozoan), bryonoderm extended (heterozoan), and Meekella-Ortonella (assemblages of stressed shallowlagoon to tidal-flat habitats).

The Oligocene succession in the eastern North Sea: basin development and depositional systems

AbstractThe Oligocene sedimentary succession in the eastern North Sea is revised and re-interpreted by applying new state-of-the-art reflection seismic data integrated with new bio- and Sr-stratigraphy data from three key wells in the study area. The Oligocene succession in the eastern North Sea is divided into four transgressive–regressive (T-R) sequences, characterized by non-accretional and/or aggradational transgressive systems tracts and prograding regressive systems tracts. Detailed studies of three wells, including biostratigraphy and Sr analysis, constrain the age relationships between the T-R sequences. Internal clinoform geometry indicates that the sediments were sourced from the present southern Norwegian mainland to the north of the depositional area. The direction of progradation shifted from being SE-directed in the earliest Rupelian (early Oligocene) to S- and SW-directed during Chattian time (late Oligocene). Rapid basin subsidence is indicated by the development of non-accretionary transgressive systems tracts, with subsequent progradation into water depths of hundreds of metres. The creation of accommodation space was out of phase relative to eustatic sea-level changes, and mainly controlled by regional-scale differential vertical movements where uplift and exposure of landmasses of the hinterland (southern Norway) occurred concurrently with basin subsidence. Halokinesis had an intra-basinal influence on the main sediment transport direction, but probably did not contribute much in creation of accommodation space.

Tropical tales of polar ice: evidence of Last Interglacial polar ice sheet retreat recorded by fossil reefs of the granitic Seychelles islands

In the search for a record of eustatic sea level change on glacial–interglacial timescales, the Seychelles ranks as one of the best places on the planet to study. Owing to its location with respect to the former margins of Northern Hemisphere ice sheets that wax and wane on orbital cycles, the local—or relative—sea level history is predicted to lie within a few meters of the globally averaged eustatic signal during the Last Interglacial period. We have surveyed and dated Last Interglacial fossil corals to ascertain peak sea level and hence infer maximum retreat of polar ice sheets during this time interval. We observe a pattern of gradually rising sea level in the Seychelles between ∼129 and 125 thousand years ago (ka), with peak eustatic sea level attained after 125 ka at 7.6 ± 1.7 m higher than present. After accounting for thermal expansion and loss of mountain glaciers, this sea-level budget would require ∼5–8 m of polar ice sheet contribution, relative to today's volume, of which only ∼2 m came from the Greenland ice sheet. This result clearly identifies the Antarctic ice sheet as a significant source of melt water, most likely derived from one of the unstable, marine-based sectors in the West and/or East Antarctic ice sheet. Furthermore, the establishment of a +5.9 ± 1.7 m eustatic sea level position by 128.6 ± 0.8 ka would require that partial AIS collapse was coincident with the onset of the sea level highstand.

Chapter 13 Hellenic shelf: late Quaternary tectonics, sea-level changes, sedimentation and geohazards

Abstract The Hellenic shelf lies within and around the Aegean microplate, which is one of the world's most seismically active areas, and has experienced extreme tectonism throughout Quaternary time. This activity, together with eustatic sea-level changes and water-circulation patterns over the same time period, controls the overall configuration of the Hellenic shelf, the rates of uplift and subsidence, and determines the sediment supply and depot centre, as well as the sediment-transfer processes. The above-mentioned geological processes are the causative factors for the frequent occurrence of a variety of geological hazards, such as active faults, submarine gravitational mass movements, tsunami and active gas seeping from the seabed.

High resolution climate and environmental changes of the northern Japan (East) Sea for the last 40 kyr inferred from sedimentary geochemical and pollen data

High-resolution lithological and isotope-geochemical analyses were made on a well age constrained sediment from the northeastern Japan (East) Sea which recorded 10 dark layers (DL) over the last 40kaBP. Pollen analysis of the core allows us to reconstruct the history of surrounding landmass vegetation and to determine pronounced vegetation/climate changes. We found that DL 10 which correlated with a DO/Chinese interstadial 8 was forced by increased East Asian humidity and influx of the nutrient-rich water into the sea. DL 5 formed during the cold Heinrich event 3 (HE), at 30–31kaBP, was most likely to be initiated by the global sea level descent and reduction of seawater exchange with the North Pacific. High resolution of δ18Opf records reflects a unique sensitivity of the Japan (East) Sea to input of the North Pacific water through the shallow Tsushima and Tsugaru Straits. This led us to the important evidence of the eustatic-sea level changes during the last 40kaBP. Since 29kaBP, δ18Opf curve shows a continuous descending sea level interrupted by sharp drops of HE 2 with a following rise of DO interstadial 2. A sharp δ18Opf increase since 18.6kaBP is consistent with coral results which indicate abrupt termination of LGM low stand by a rapid sea level rise initiated at 19.0kaBP.

Pleistocene diversification of the Pomacentrus coelestis species complex (Pisces: Pomacentridae): historical biogeography and species boundaries

Pleistocene eustatic changes in sea level are often invoked to explain genetic divergence among marine organisms. However, molecular phylogenies have revealed relatively few examples of speciation events dating to the Pleistocene. We present a species-level hypothesis of the timing of evolution for the Pomacentrus coelestis species complex (Pomacentridae), based on the nuclear S7 intron and the mitochondrial Cytb gene, and reconstruct ancestral range distributions across the timetree. Ancestral range reconstruction suggests the complex originated in the Coral Triangle and East Indian Ocean, with subsequent range expansion outward from this region. We suggest that land barriers to dispersal (e.g., Indo-Pacific barrier) may be responsible for the divergence between Indian (P. alleni, P. similis, P. caeruleopunctatus, and P. caeruleus) and Pacific (P. micronesicus, P. auriventris, and P. coelestis) species groups, and subsequent isolation by Pleistocene sea-level fluctuations in certain areas of the Coral Triangle (glacial refugia) may play an important role in the diversification of this species complex. Additionally, our analyses show cryptic lineages within P. micronesicus and highlight the need for comprehensive sampling within and among species to reveal recent speciation events.

Evolution at a different pace: distinctive phylogenetic patterns of cone snails from two ancient oceanic archipelagos.

Ancient oceanic archipelagos of similar geological age are expected to accrue comparable numbers of endemic lineages with identical life history strategies, especially if the islands exhibit analogous habitats. We tested this hypothesis using marine snails of the genus Conus from the Atlantic archipelagos of Cape Verde and Canary Islands. Together with Azores and Madeira, these archipelagos comprise the Macaronesia biogeographic region and differ remarkably in the diversity of this group. More than 50 endemic Conus species have been described from Cape Verde, whereas prior to this study, only two nonendemic species, including a putative species complex, were thought to occur in the Canary Islands. We combined molecular phylogenetic data and geometric morphometrics with bathymetric and paleoclimatic reconstructions to understand the contrasting diversification patterns found in these regions. Our results suggest that species diversity is even lower than previously thought in the Canary Islands, with the putative species complex corresponding to a single species, Conus guanche. One explanation for the enormous disparity in Conus diversity is that the amount of available habitat may differ, or may have differed in the past due to eustatic (global) sea level changes. Historical bathymetric data, however, indicated that sea level fluctuations since the Miocene have had a similar impact on the available habitat area in both Cape Verde and Canary archipelagos and therefore do not explain this disparity. We suggest that recurrent gene flow between the Canary Islands and West Africa, habitat losses due to intense volcanic activity in combination with unsuccessful colonization of new Conus species from more diverse regions, were all determinant in shaping diversity patterns within the Canarian archipelago. Worldwide Conus species diversity follows the well-established pattern of latitudinal increase of species richness from the poles towards the tropics. However, the eastern Atlantic revealed a striking pattern with two main peaks of Conus species richness in the subtropical area and decreasing diversities toward the tropical western African coast. A Random Forests model using 12 oceanographic variables suggested that sea surface temperature is the main determinant of Conus diversity either at continental scales (eastern Atlantic coast) or in a broader context (worldwide). Other factors such as availability of suitable habitat and reduced salinity due to the influx of large rivers in the tropical area also play an important role in shaping Conus diversity patterns in the western coast of Africa.