Interstadial coral reef terraces and relative sea-level changes during marine oxygen isotope stages 3–4, Kikai Island, central Ryukyus, Japan

Coral reef terraces are one of the best recorders of relative sea-level changes during the last glacial cycle. Thus far, knowledge of relative sea-level record based on coral reefs during the marine Oxygen Isotope Stage (OIS) 3 has been limited to studies of the Huon Peninsula, Papua New Guinea. High-precision a α-spectrometric ²³⁰Th/²³⁴U dating demonstrated an offlapping sequence of five coral reef complexes, ages of which are 66, 64, 62, 55 and 52 ka, in the northern part of Kikai Island, central Ryukyus of Japan. Interstadial reefs, characterized by deepening-upward sequences of coral assemblages, recorded three hemicycles from transgression to highstand at 52, 62, and 66 ka, during which these reefs were drowned. These highstands in the relative sea-level record can be correlated with the eustatic record reconstructed from the Huon reef terraces and with the interstadials 14, 18, and 19 of the GISP 2 oxygen isotope record. This consistency confirms the Huon sea-level record of OIS 3 and implies that the eustatic sea level responded to the millennial-scale climate changes even during the glacial period of OIS 4.     

Comparison of ESR and TIMS U/Th dating of marine isotope stage (MIS) 5e, 5c, and 5a coral from Barbados—implications for palaeo sea-level changes in the Caribbean

Electron spin resonance (ESR) dating of coral has become an efficient geochronological tool in supporting morphostratigraphic studies carried out on Barbados during the last 10 years. The newly developed approach for D_E determination (D_E–D_max plot procedure) improves the precision of ESR dating of Pleistocene coral, and therefore permits differentiation between the main marine isotope stages (MIS) 5, 7, 9 and 11 and also between sub-stages 5e, c and a. This study compares results of ESR and TIMS Uranium series dating (U/Th) of emergent Last Interglacial coral reef terraces from Barbados, and presents some implications for the timing and extent of sea-level changes during marine isotope stages (MIS) 5e, c and a. Both dating methods indicate a distinct formation of up to three coral reef terraces during MIS 5e, at approximately 132 ka (ESR) to 128 ka (U/Th), at c. 128 ka (ESR) and at c. 120 ka (U/Th) to 118 ka (ESR). It is also highly probable that three reef terraces were developed during MIS 5c between c. 103 ka (U/Th) and 105 ka (ESR). The formation of two separate coral reefs during MIS 5a is recognized for the first time on Barbados, with an age estimate for the older MIS 5a-2 reef of 85 ka (ESR) or 84 ka (U/Th), and an age estimate for the younger MIS 5a-1 reef terraces of 74 ka (ESR) or 77 ka (U/Th). Assuming a constant uplift rate of 0.276 m/ka at the south coast of Barbados, sea-level reached its maximum during MIS 5e-3 and MIS 5e-2 between 132 and 128 ka ago. After this, sea-level declined reaching a level of c. −11 m below present sea level approx. 118–120 ka ago (MIS 5e-1). During the substage 5c sea-level was generally lower than in substage 5e. It reached relative maxima at c. −13, −20 and −25 m during MIS 5c (approx. 105 ka) and formed three distinct coral reef terraces probably in relative short time intervals. For the first time, a double sea-level oscillation is recognized on Barbados during MIS 5a: an early MIS 5a-2 (c. 85 ka) with a sea-level places at approx. −21 m, and a late MIS 5a-1 sub-stage (c. 74 or 77 ka) with a sea-level at approx. –19 m below present sea level.     

Sea Level Changes in the Last Several Thousand Years, Penghu Islands, Taiwan Strait

Holocene shore-face and beach-face deposits form plains <5 m above present sea level along Taiwan Strait. We measured the¹⁴C ages of detrital mollusk shells and coral in such deposits at the Penghu Islands. Twelve carbonate samples—mainly from the largest island, Makung—were dated. Age measurements for two coral samples and one mollusk sample from the same outcrop imply that the¹⁴C ages of mollusk shells give the best approximation of depositional age. The highest Holocene relative sea level in the Penghu Islands occurred about 4700 years ago with a height about 2.4 m above the present sea level. Thereafter, relative sea level appreciably fell without detectable fluctuations to its recent position. Our sea level data are consistent with other studies from the central and western Pacific, except for the timing of peak sea level position. This variation may reflect local crustal response to hydroisostatic effects on the continental shelf.     

Reconstruction of Middle to Late Quaternary sea level using submerged speleothems from the northeastern Yucatán Peninsula

We examined 14 subaerially deposited speleothems retrieved from submerged caves in the northeastern Yucatán Peninsula (Mexico). These speleothems grew during the Middle to Late Quaternary and were dated by ²³⁰Th-U techniques to provide upper depth limits for past sea levels. We report the first relative sea-level limits for Marine Isotope Stages (MIS) 11 and 6, and present new evidence for sea-level oscillations during MIS 5 and early MIS 1. For the latter periods, the origin of growth interruptions is evaluated by combining petrographic methods with trace element analyses. The MIS 5c sea-level highstand probably occurred between 103.94 ± 0.58 ka and 96.82 ± 0.42 ka and must have exceeded -10.8 m (relative to present-day local sea level). The minimum average rate of sea-level fall over a 9.4 ka-long period during the MIS 5e/5d transition is calculated from stalagmite and published coral data at 1.74 ± 0.37 m/ka. For the early Holocene, previous discrepancies with respect to a potential multimetre oscillation of local sea level were found to be challenging to reconcile with the existing speleothem data from the area.     

海南岛南岸全新世珊瑚礁的发育

海南岛南岸的珊瑚礁,是我国全新世珊瑚岸礁最为发育的地区之一,仅次于台湾岛南端的恒春半岛沿岸。前人从生物学^[1-5]、地貌学^[6-8]和地质学^[9-12]角度对海南岛南岸的珊瑚礁进行过较为广泛的研究。作者报道过崖县鹿回头水尾岭剖面珊瑚礁样品的C¹⁴年代测定结果^[13,14]。1979年底至1980年初,作者在海南岛南岸东起小东海沿岸西至西瑁岛西岸地区进行了野外调查与采样。根据野外和室内分析资料,本文公布了一批新测试的C¹⁴年代数据,并进一步讨论了全新世珊瑚礁的发育历史及其与海岸变迁、海面变化和地壳运动的关系等问题。     

Recognition of non-Milankovitch sea-level highstands at 185 and 343 thousand years ago from U–Th dating of Bahamas sediment

Thirty-one new bulk-sediment U–Th dates are presented, together with an improved δ¹⁸O stratigraphy, for ODP Site 1008A on the slopes of the Bahamas Banks. These ages supplement and extend those from previous studies and provide constraints on the timing of sea-level highstands associated with marine isotope stages (MIS) 7 and 9. Ages are screened for reliability based on their initial U and Th isotope ratios, and on the aragonite fraction of the sediment. Twelve ‘reliable’ dates for MIS 7 suggest that its start is concordant with that predicted if climate is forced by northern-hemisphere summer insolation following the theory of Milankovitch. But U–Th and δ¹⁸O data indicate the presence of an additional highstand which post-dates the expected end of MIS 7 by up to 10 ka. This event is also seen in coral reconstructions of sea-level. It suggests that sea-level is not responding in any simple way to northern-hemisphere summer insolation, and that tuned chronologies which make such an assumption are in error by ≈10 ka at this time. U–Th dates for MIS 9 also suggest a potential mismatch between the actual timing of sea-level and that predicted by simple mid-latitude northern-hemisphere forcing. Four dates are earlier than that predicted for the start of MIS 9. Although the most extreme of these dates may not be reliable (based on the low-aragonite content of the sediment) the other three appear robust and suggest that full MIS 9 interglacial conditions were established at 343 ka. This is ≈8 ka prior to the date expected if this warm period were driven by northern-hemisphere summer insolation.     

Coupled uranium isotope and sea-level variations in the oceans

Globally, rivers supply uranium to the oceans with excess ²³⁴U relative to secular equilibrium and ²³⁴U taken-up by corals can be used for dating. In addition, the ²³⁴U abundance in sea water, at the time the coral was growing, can be measured independently. The veracity of U-series ages used in determining past sea-level variations is dependent on selecting pristine corals free from diagenetic alteration. A quantitative test for alteration assumes invariant ²³⁴U abundances in the oceans for at least the past half a million years and results from samples outside of a narrow range in modern ocean ²³⁴U abundance are excluded from data sets. Here, we have used previously published data to show that ²³⁴U in the oceans appears to be variable and directly related to changes in sea-level, not only over long glacial-interglacial timescales but also at very short, centennial timescales. Most of the previously discarded data can be used to provide valuable additional sea-level information. The process permits a unique insight into the interplay between sources and sinks of uranium in the oceans mediated by sea-level changes at rates far faster than previously thought possible. Similar, rapid sea-level, forcing of other trace element abundances in the oceans is likely.     

Submerged upper Holocene beachrock on San Salvador Island,Bahamas: implications for recent sea-level history

Sedimentological, petrographic and radiometric data from a submerged beachrock on San Salvador Island, Bahamas, provide new information about the Late Holocene sea-level history in this area.At French Bay, on the southern shore of the island, samples of beachrock collected at a depth of 1 m below low tide level yielded an average ¹⁴C age of 965 ± 60 years before present. These samples further display a well developed fenestral porosity and present an early generation of low Mg calcite meniscus cement. These features characterize intertidal and supratidal settings; they are not consistent with the present beachrock position and the reported Late Holocene sea-level history in the Bahamas. A 1.5–2m low stand of the sea about 1000 years ago would best explain the observed particularities of the French Bay beachrock.This example from San Salvador shows that the smooth trend of Late Holocene sea-level rise proposed by previous workers might be overprinted by high frequency, low amplitude fluctuations. Recognition of these fluctuations is fundamental when calculating rates of sea-level rise and evaluating the coastal response to a marine transgression. Correspondence to: P. Kindler     

Sea-level estimates during the last deglaciation based on δO and accelerator mass spectrometry C ages measured in Globigerina bulloides

Coupled measurements of δ¹⁸O and accelerator mass spectrometry (AMS) ¹⁴C in a particular species of planktonic foraminifera may be used to calculate sea-level estimates for the last deglaciation. Of critical importance for this type of study is a knowledge of the seasonality of foraminiferal growth, which can be provided by δ¹⁸O measurements of modern shells (core tops, plankton tows). Isotopic (δ¹⁸O, AMS-¹⁴C dating) and faunal records (transfer function sea surface temperature) were obtained from two cores in the North Atlantic at about 37°N. The locations were chosen to obtain high sedimentation rate records removed from the major ice-melt discharge areas of the last deglaciation. Based upon Globigerina bulloides data, four δ¹⁸O-based sea-level estimates were calculated: −67 ± 7 m at 12,200 yr B.P. and −24 ± 8 m at about 8200 yr B.P. for core SU 81-18; −83 ± 10 m at 12,200 yr B.P. and −13 ± 11 m at about 8500 yr B.P. for core SU 81-14. Using a second working hypothesis concerning the seasonability of G. bulloides growth, it is suggested that the sea-level rose by about 40 m during the millennium which followed 14,500 yr B.P.     

Late Pleistocene raised beaches of coastal Estremadura,central Portugal

We present new stratigraphic, sedimentological, and chronological data for a suite of tectonically raised beaches dating to Marine Isotope Stages 5, 4, and 3 along the Estremadura coast of west-central Portugal. The beach deposits are found in association with ancient tidal channels and coastal dunes, pollen bearing mud and peat, and Middle Paleolithic archaeological sites that confirm occupation of the coastal zone by Neanderthal populations. The significance of these deposits is discussed in terms of the archaeological record, the tectonic and geomorphic evolution of the coast, and correlation with reconstructions of global climate and eustatic sea-level change. Direct correlation between the Estremadura beach sections is complicated by the tectonic complexity of the area and the age of the beach deposits (which are near or beyond the limit of radiocarbon dating). Evidence from multiple sites dated by AMS radiocarbon and optical luminescence methods suggests broad synchroneity in relative sea-level changes along this coast during Marine Isotope Stage 3. Two beach complexes with luminescence and radiocarbon age control date to about 35 ka and 42 ka, recording a rise in relative sea level around the time of Heinrich Event 4 at 39 ka. Depending on assumptions about eustatic sea level at the time they were deposited, we estimate that these beaches have been uplifted at rates of 0.4–4.3 mm yr^?1 by the combined effects of tectonic, halokinetic, and isostatic processes. Uplift rates of 1–2 mm yr^?1 are likely if the beaches represent sea level stands at roughly 40 m below modern, as suggested by recent eustatic sea level reconstructions. Evidence from coastal bluffs and the interior of the study area indicates extensive colluvial, fluvial, and aeolian sedimentation beginning around 31 ka and continuing into the Holocene. These geomorphic adjustments are related to concomitant changes in climate and sea level, providing context that improves our understanding of Late Pleistocene landscape change and human occupation on the western Iberian margin.     

The marine oxygen isotope record in Pleistocene coral,Barbados, West Indies

The reef-crest coral Acropora palmata from late Pleistocene reefs on Barbados has recorded the same global variations in oxygen isotopes as planktonic and benthonic foraminifera. Although the record of oxygen isotopes in Acropora palmata is discontinuous, it offers several advantages over the isotope records from deep-sea sediments: (1) the coral grows at water depths of less than 5 m; (2) the samples are unmixed; (3) specimens may be sampled from various elevations of paleo-sea level; and (4) aragonitic corals are suitable for ${}^{230}\text{Th}{}^{234}\text{U}$ and $\text{He}\text{U}$ dating techniques. The latter advantage means that direct dating of the marine oxygen isotope record is possible. Oxygen isotope stage 5e corresponds to Barbados III, dated at 125,000 ± 6000 yr BP. Petrographic and geochemical evidence from five boreholes drilled into the south coast of Barbados indicates a major eustatic lowering (greater than 100 m below present sea level) occurred between 180,000 and 125,000 yr BP. The age and isotopic data suggest correlation of this change in sea level to Emiliani's oxygen isotope stage 6. Acropora palmata deposited at various elevations of sea level during oxygen isotope stage 6 vary by 0.11 ‰ δ¹⁸O for each 10 m of change in sea level. We further hypothesize a minimum drop of 2°C in the average temperature occurred during the regressive phase of oxygen isotope stage 6. These data indicate that temperature lowering of surface water near Barbados lagged behind a major glacial buildup during this time period. Using the δ¹⁸O vs sea level calibration herein derived, we estimate the relative height of sea stands responsible for Barbados coral reef terraces in the time range 80,000 to 220,000 yr BP.     

Detailed documentation of a Holocene sea-level record in the perth region, southern Western Australia

Holocene prograded coastal sequences at Becher/Rockingham, southern Western Australia, contain a detailed record of sea level over the last 6400 yr. Radiocarbon dating and use of a distinct stratigraphic indicator as a sea-level marker permit reconstruction of sea-level history and suggest that the sea was at least 2.5 m above present datum about 6400 yr B.P. before falling to its present level. No evidence was found for eustatic fluctuations of the scale proposed by R. W. Fairbridge [1961, in “Physics and Chemistry of the Earth” (L. H. Ahrens, F. Press, K. Rankema, and S. K. Runcorn, Eds.), Vol. 4, pp. 99–185, Pergamon, Oxford]. The sea-level record preserved on this coast can be explained by hydro-isostasy, tectonism, or eustasy, acting individually or in concert. Without a fixed reference point or analogous data from other locations, a firm conclusion on which mechanism(s) has(have) operated could not be reached. Published sea-level data from this and other coasts are often insufficiently detailed to compare with this study. Application of the techniques of this study to analogous sedimentary sequences elsewhere will provide data of comparable accuracy that would contribute to a more precise understanding of relative sea-level movements in the late Quaternary.     

Response of reef coral communities to sea-level rise: a Holocene model from Mauritius (Western Indian Ocean)

The fringing reef at Pointe-au-Sable (Mauritius, Indian Ocean) was used to examine the effects of Holocene sea-level rise on coral growth. This reef is about 1000 m wide and comprises a forereef slope (30 m maximum depth), a narrow reef crest and a very shallow backreef (1·5 m maximum depth). Four major coral communities were recognized, which developed within relatively narrow depth ranges: a Pachyseris/Oulophyllia community (deeper than 20 m), an Acropora‘tabulate’Faviid community (20–6 m); a robust branching Acropora community (less than 6 m) and a Pavona community (less than 10m). Three high-recovery cores show the Holocene reef sequence is a maximum of 19·3 m thick and comprises four coral biofacies which are similar to counterparts identified in modern communities: robust branching, tabular-branching, robust branching-domal and foliaceous coral facies. A minimum sea-level curve for the past 7500 years was constructed. Using distribution patterns of coral biofacies and radiocarbon dates from corals, reconstruction of reef growth history indicates that both offshore and onshore reef zones were developing coevally, aggrading at rates of 4·3 mm year^?1 from 6900 years B.P. The reef caught up with sea-level only after sea-level stabilized. Changes in coral community and reef growth rates were driven principally by increasing water agitation due to the decrease in accommodation space. Based on the composition of the successive coral assemblages, the reef appears to have grown through successive equilibrium stages.     

Optically stimulated luminescence age controls on late Pleistocene and Holocene coastal lithosomes, North Carolina, USA

Luminescence ages from a variety of coastal features on the North Carolina Coastal Plain provide age control for shoreline formation and relative sea-level position during the late Pleistocene. A series of paleoshoreline ridges, dating to Marine Isotope Stage (MIS) 5a and MIS 3 have been defined. The Kitty Hawk beach ridges, on the modern Outer Banks, yield ages of 3 to 2 ka. Oxygen-isotope data are used to place these deposits in the context of global climate and sea-level change. The occurrence of MIS 5a and MIS 3 shorelines suggests that glacio-isostatic adjustment (GIA) of the study area is large (ca. 22 to 26 m), as suggested and modeled by other workers, and/or MIS 3 sea level was briefly higher than suggested by some coral reef studies. Correcting the shoreline elevations for GIA brings their elevation in line with other sea-level indicators. The age of the Kitty Hawk beach ridges places the Holocene shoreline well west of its present location at ca. 3 to 2 ka. The age of shoreline progradation is consistent with the ages of other beach ridge complexes in the southeast USA, suggesting some regionally contemporaneous forcing mechanism.     

Carbon isotope chemostratigraphy of a Precambrian/Cambrian boundary section in the Three Gorge area, South China: Prominent global-scale isotope excursions just before the Cambrian Explosion

Carbon isotope chemostratigraphy has been used for worldwide correlation of Precambrian/Cambrian (Pc/C) boundary sections, and has elucidated significant change of the carbon cycle during the rapid diversification of skeletal metazoa (i.e. the Cambrian Explosion). Nevertheless, the standard δ¹³C curve of the Early Cambrian has been poorly established mainly due to the lack of a continuous stratigraphic record. Here we report high-resolution δ¹³C chemostratigraphy of a drill core sample across the Pc/C boundary in the Three Gorge area, South China. This section extends from an uppermost Ediacaran dolostone (Dengying Fm.), through a lowermost Early Cambrian muddy limestone (Yanjiahe Fm.) to a middle Early Cambrian calcareous black shale (Shuijingtuo Fm.). As a result, we have identified two positive and two negative isotope excursions within this interval. Near the Pc/C boundary, the δ¹³C_carb increases moderately from 0 to + 2‰ (positive excursion 1: P1), and then drops dramatically down to − 7‰ (negative excursion 1: N1). Subsequently, the δ¹³C_carb increases continuously up to about + 5‰ at the upper part of the Nemakit–Daldynian stage. After this positive excursion, δ¹³C_carb sharply decreases down to about − 9‰ (N2) just below the basal Tommotian unconformity. These continuous patterns of the δ¹³C shift are irrespective of lithotype, suggesting a primary origin of the record. Moreover, the obtained δ¹³C profile, except for the sharp excursion N2, is comparable to records of other sections within and outside of the Yangtze Platform. Hence, we conclude that the general feature of our δ¹³C profile best represents the global change in seawater chemistry. The minimum δ¹³C of the N1 (− 7‰) is slightly lower than carbon input from the mantle, thus implying an enhanced flux of ¹³C-depleted carbon just across the Pc/C boundary. Hence, the ocean at that time probably became anoxic, which may have affected the survival of sessile or benthic Ediacaran biota. The subsequent δ¹³C rise up to + 5‰ (P2) indicates an increase of primary productivity or an enhanced rate of organic carbon burial, which should have resulted in lowering pCO₂ and following global cooling. This scenario accounts for the cause of the global-scale sea-level fall at the base of the Tommotian stage. The subsequent, very short-term, and exceptionally low δ¹³C (− 9‰) in N2 could have been associated with the release of methane from gas hydrates due to the sea-level fall. The inferred dramatic environmental changes (i.e., ocean anoxia, increasing productivity, global cooling and subsequent sea-level fall with methane release) appear to coincide with or occur just before the Cambrian Explosion. This may indicate synchronism between the environmental changes and rapid diversification of skeletal metazoa.     

Microatoll record for large century-scale sea-level fluctuations in the mid-Holocene

Coral microatolls have been long used as precise indicators of past sea level, but their use for precise definition of detailed sea-level fluctuations is still rare. Here we report twelve high-precision thermal ionization mass spectrometric ²³⁰Th ages for twelve rims of five mid-Holocene microatolls from an emerged reef terrace at Leizhou Peninsula, northern South China Sea. This is a tectonically stable area, enabling us to reconstruct both the timing and trajectory of local sea-level fluctuations accurately. The elevations of these microatoll rims and cores were accurately determined relative to the surface of modern living microatolls at the same site. The results indicate that the sea level during the period of 7050–6600 yr bp (years before AD 1950) was about 171 to 219 cm above the present, with at least four cycles of fluctuations. Over this 450 yr interval, sea level fluctuated by 20–40 cm on century scales.     

Glacio-isostasy and Glacial Ice Load at Law Dome, Wilkes Land, East Antarctica

The Holocene sea-level high stand or “marine limit” in Wilkes Land, East Antarctica, reached 30 m above present sea level at a few dispersed sites. The most detailed marine limit data have been recorded for the Windmill Islands and Budd Coast at the margin of the Law Dome ice cap, a dome of the East Antarctic Ice Sheet (EAIS). Relative sea-level lowering of 30 m and the associated emergence of the Windmill Islands have occurred since 6900 ¹⁴C (corr.) yr B.P. Numerical modeling of the Earth's rheology is used to determine the glacio-isostatic component of the observed relative sea-level lowering. Glaciological evidence suggests that most of EAIS thickening occurred around its margin, with expansion onto the continental shelf. Consequently, a regional ice history for the last glacial maximum (LGM) was applied in the glacio-isostatic modeling to test whether the observed relative sea-level lowering was primarily produced by regional ice-sheet changes. The results of the modeling indicate that the postglacial (13,000 to 8000 ¹⁴C yr B.P) removal of an ice load of between 770 and 1000 m from around the margin of the Law Dome and adjacent EAIS have produced the observed relative sea-level lowering. Such an additional ice load would have been associated with a 40- to 65-km expansion of the Law Dome to near the continental shelf break, together with a few hundred meters of ice thickening on the adjoining coastal slope of the EAIS up to 2000 m elevation. Whereas the observed changes in relative sea level are shown to be strongly influenced by regional ice sheet changes, the glacio-isostatic response at the Windmill Islands results from a combination of regional and, to a lesser extent, Antarctic-wide effects. The correspondence between the Holocene relative sea-level lowering interpreted at the margin of the Law Dome and the lowering interpreted along the remainder of the Wilkes Land and Oates Land coasts (105°–160° E) suggests that a similar ice load of up to 1000 m existed along the EAIS margin between Wilkes Land and Oates Land.     

Stratigraphic development during the Late Pleistocene and Holocene offshore of the Yellow River delta, Bohai Sea

A 61-m-long sediment core (HB-1) and 690 km of high-resolution seismic profiles from offshore of the Yellow River delta, Bohai Sea, were analyzed to document the stratigraphy and sea-level changes during the Late Pleistocene and Holocene. Accelerator mass spectrometry ¹⁴C dating and analyses of benthic foraminifera, ostracods, the mineral composition, and sedimentary characteristics were performed for core HB-1, and seven depositional units (DU 1–DU 7 in descending order) were identified. The seismic reflection data were interpreted in light of the sedimentological data of the core and correlated with other well-studied cores obtained previously in the Bohai Sea area. Seven seismic units (SU 1 to SU 7 in descending order) were distinguished and interpreted as follows: SU 7 corresponds to marine facies in Marine Isotopic Stage (MIS) 5; SU 6, to terrestrial facies in MIS 4; SU 5 and SU 4, to alternating terrestrial and marine facies (DU 7–DU 5) in MIS 3; SU 3, to terrestrial facies (DU 4) in MIS 2; SU 2, to Holocene marine facies (DU 3 and DU 2); and SU 1, to modern Yellow River delta sediments deposited since 1855 (DU 1).The sedimentary facies from DU 7 to DU 5 reflect sea-level fluctuations during MIS 3, and the boundary between DU 5 and DU 6, which coincides with that between SU 4 and SU 5, is a distinctive, laterally continuous, undulating erosion surface, with up to 20 m of relief. This surface reflects subaerial exposure between transgressions during MIS 3. Estimated sea levels during MIS 3 ranged from −35 ± 5 to −60 ± 5 m or lower, with short-term fluctuations of 20 m. Sedimentary environments in the Bohai Sea area were governed mainly by eustatic sea-level changes and the Bohai Strait topography, which controls the entry of sea water into the Bohai Sea area.The mineral composition of the sediment core suggests that the Yellow River did not discharge into the Bohai Sea, or at least did not influence the study area significantly, during parts of MIS 3 and MIS 2 to the early Holocene (11–8.5 cal kyr BP).     

Late Pleistocene (Last Interglacial) terrace deposits, Bahia Coyote, Baja California Sur, México

Late Pleistocene age terrace deposits are exposed in the narrow cliffed coastal plain of Bahia Coyote, Baja California Sur, resting unconformably on the lagoonal-shallow water volcaniclastics of the early Miocene Cerro Colorado Member of the El Cien Formation. The terrace is dissected by widely spaced arroyos and partically covered by alluvial fans in the inner and central areas. The marine deposits vary in thickness from 0.5 to 10 m and were laid down in pre-existing erosional channels and depressions in the Pleistocene landscape. The sequence begins with a cobble conglomerate with oyster shells, overlain by poorly bedded molluscan-rich bioclastic sands and coral rubble, beds of massive Porites in growth position and coral-rhodolith sands and marls. Beach sands and gravels and coastal dunes cap the sequence.Samples of Porites panamensis selected for U/Th dating are well-preserved aragonite (>95%). Preliminary results yield U/Th ages of 109–209 ka but the corals have initial δ ²³⁴U values in excess of modern seawater values. This indicates open-system behavior and uncertainty associated with the ages. A corrected age for the top of the massive Porites unit suggests that the corals grew during the last interglacial, marine isotope stage (MIS) 5e sea level high stand.Assuming global sea level during MIS 5e was ca. 4–5 m above present-day sea level (McCulloch and Esat, 2000) and the growth position of the corals was 1–5 m below sea level, the terraces have been uplifted between 12 and 25 m (12–15 cm/kyr). This is consistent with other terrace-based uplift rates for the central Baja California peninsula, north of the La Paz fault.     

Sea-Level Changes and δO Record for the Past 34,000 yr from Mayotte Reef, Indian Ocean

New sea-level and δ¹⁸O curves for the past 34,000 yr, based on uranium–thorium chronology, are proposed for the southwestern part of the Indian Ocean. The archives include cores drilled from onshore coral reefs and submersed samples from foreslope corals of Mayotte in the Comoro Islands. The Mayotte sea-level curve shows a lowstand of 145 ± 5 m below the present level during the last glacial maximum dated at 18,400 yr. This lowstand is supported by the maximum¹⁸O enrichment in the coral colonies. The residual signal (Δδ¹⁸O), controlled by sea-surface temperature changes, indicates that surface waters 18,400 yr ago were approximately 5°C cooler than present. The deglacial sea-level rise is clearly recorded, with a mean rate of about 1.7 cm yr⁻¹between 18,400 and 10,000 yr ago. The deglaciation phase is characterized by a strong¹⁸O depletion marked by two pulses related to meltwater discharges into the North Atlantic Ocean but also characterized by responses specific to the tropical Indian Ocean.