Glacial-interglacial Sea Level Changes Research Articles

Sea-level and monsoonal control on the Maldives carbonate platform (Indian Ocean) over the last 1.3 million years

Abstract. The Maldives Archipelago (Indian Ocean), composed of two rows of atolls that enclose an inner sea, offers an excellent study site to explore the forcings of carbonate production at platforms. Glacial–interglacial sea-level changes have been claimed to be the main factor controlling the carbonate platform factories; however, climatic factors may also have an impact. In this work we used geochemical compositional records, obtained by X-ray fluorescence (XRF) core-scanning from the International Ocean Discovery Program (IODP) Site U1467 in the Maldives Inner Sea, to analyze the orbitally driven fluctuations on the carbonate production and export from the neritic environment into the Maldives Inner Sea over the last 1.3 million years. High Sr aragonite-rich carbonates (HSAC) from neritic settings were deposited in the Maldives Inner Sea during sea-level highstand intervals, increasing the Sr/Ca values. In contrast, low Sr/Ca values are observed coincident with sea-level lowstand periods, suggesting that large areas of the atolls were exposed or unable to grow, and therefore, there was a demise in the carbonate production and sediment export to the Maldives Inner Sea. However, comparison of the Sr/Ca values and the sea-level reconstructions for different interglacial periods before and after the mid-Brunhes event (MBE, ∼ 430 ka) indicates that sea level is not the only factor controlling the production of HSAC during sea-level highstands. The study of monsoon and primary productivity proxies (Fe-normalized, Fe/K, and Br-normalized records) from the same site suggests that the intensity of the summer monsoon and the Indian Ocean dipole probably modulated the carbonate production at the atolls. Moreover, Marine Isotope Stage 11 stands out as a period with high sea level and extraordinary carbonate production in the Maldives platform. This outstanding carbonate production in the Maldives atolls (and in other low-latitude carbonate platforms) probably contributed to the mid-Brunhes dissolution event through a strong shelf-to-basin fractionation of carbonate deposition.

Pleistocene sea level changes and crocodile population histories on the Isthmus of Panama: A comment on Avila-Cervantes etal. (2020).

Avila-Cervantes etal. proposed that glacial-interglacial sea level changes played an important role in the evolutionary and demographic histories of the crocodile Crocodylus acutus on the Isthmus of Panama. However, the study used erroneous sea level proxy data that produced flawed paleogeographic reconstructions. We present new paleogeographic reconstructions and review the timing of, and proposed mechanisms behind, the demographic events estimated by Avila-Cervantes etal.. With the data currently available, we find little evidence to support the hypothesis that sea level changes drove population demographic events in crocodiles on the Isthmus. Alternative hypotheses, including changing climate and habitat suitability, are equally valid and should be considered along with well-supported sea level models.

Ostracods reveal the palaeoenvironmental changes in Laizhou Bay, Bohai Sea (eastern China) since the Late Pleistocene

Laizhou Bay is located in the Bohai Sea, eastern China. Since the Late Pleistocene, Laizhou Bay has gone through frequent transgressive and regressive activities and both marine and non-marine sediments have been deposited. In order to further understand the palaeoenvironmental changes since the Late Pleistocene, a core (DK06) was drilled on the coastal plain of Laizhou Bay. From this core, we obtained abundant well-preserved ostracod specimens. After environmental analysis and cluster analysis of these ostracods, four biofacies have been recognised: Biofacies I (shallow marine facies), Biofacies II (estuarine facies), Biofacies III (brackish water facies), Biofacies IV (freshwater facies). The studied ostracod assemblages suggest that the palaeoenvironment of Laizhou Bay went through four transgressions including three well-known marine transgressions during MIS 1, MIS 3 and probably MIS 5 and three regressions since the late Pleistocene, indicating substantial impact of glacial-interglacial sea level changes on the Bohai Sea coastal areas and their biota.

Dominant Role of Sea Level on the Sedimentary Environmental Evolution in the Bohai and Yellow Seas Over the Last 1 Million Years

Transgression and regression deposits from the shallow continental margin provide information on orbital-scale variations in sea level, climate change, and local tectonics. In this study, we conduct a high-resolution chronological and sedimentological analysis of a 125-m core (NHH01) drilled in the southern Yellow Sea. We developed a high-resolution age model at the orbital timescale over the last ∼1 Myr by the astronomical tuning of the sediment grain size. Sedimentological analysis and environmental proxies reveal that the study area is characterized by cyclic alternations of neritic and littoral/fluvial deposits controlled by glacial–interglacial sea-level changes. These results confirm the earlier assumption that sea-level fluctuations play a dominant role in the sedimentary architecture of the southern Yellow Sea. Moreover, only low-frequency sea-level fluctuations (∼100 kyr) were preserved in the NHH01 sequence; however, additional high-frequency (∼40 kyr) sea-level variations were also present in the sediments of the shallower Bohai Sea. Despite the large spatial difference, this finding implies that the sedimentary environment in the eastern marginal seas of China had been influenced by the sea level as a whole over the last 1 Myr. The comparison of the sedimentary environment with other cores from the Bohai Sea, Yellow Sea, and coastal region, as well as records from Indonesia and Japan, reveals that a consistent initiation of large-scale marine transgression occurred at ∼0.8–1 Ma. This phenomenon was likely caused by the long duration of glacio-eustatic high sea-level stands following the Middle Pleistocene transition, which is characterized by a shift in glacial cycles from 40 to 100 kyr.

Magnitudes of sea-level falls at lowstands of the past 900,000 years inferred from gravels underlying the Nobi Plain, central Japan

The Nobi Plain alluvial lowland is drained by the Kiso River system, which discharges large volumes of water and sediment into Ise Bay, Japan. The basin is bounded to the west by the Yoro fault and has been tilted down to the west by repetitive movement on the fault. The basin stratigraphy and its stacking patterns suggest uniform and rapid rates of subsidence and tilting in response to movement on the Yoro fault during the middle and late Quaternary. We used lithostratigraphy, tephrochronological and paleomagnetic data, facies analysis, and diatom assemblage analysis of a 601 m sediment core to identify ten marine transgression–regression sequences, characterized by basal fluvial gravel intervals formed by the Kiso River drainage system, and correlated them with glacial–interglacial sea-level changes during the past 900 ky. We inferred that the mean maximum size of clasts in the basal gravels may be proportional to the magnitude of the fall of sea level inferred from MIS curves since MIS 16; that is, clasts inferred to be deposited during MIS 12 and 16 are largest, and those deposited during MIS 14 are the smallest since MIS 16. These observations suggest that the Kiso River system has adjusted its longitudinal profile to accommodate sea-level changes and that a steeper profile was formed during periods of lower sea level. We also found that the size of gravel clasts in the present-day river is proportional to tractive force on the riverbed, which is controlled mainly by the slope of the river profile. Conversely, the facts that larger gravel clasts were deposited during MIS 20 and that gravel intervals deposited during MIS 22 were thicker than those during MIS 2, suggest that a glacio-eustatic sea-level fall comparable in magnitude to that of the Last Glacial Maximum occurred during MIS 22.

The monsoon and El Niño events during the last glaciation as recorded in core MD98-2182 from the western equatorial Pacific Ocean

Based on an analysis of δ18O and δ13C, the planktonic foraminiferal assemblage, and sedimentary grain size, and the study of multiproxy data such as paleothermocline depth, paleoproductivity, and paleosalinity during the last glaciation in core MD98-2182 from the central equatorial western Pacific warm pool, together with the data from other sites in this region, we found that sedimentary rates, terrestrial sediment grain size distribution, and paleoproductivity were markedly influenced by glacial-interglacial sea level changes in the study area. In late Marine Isotope Stage 3 (MIS3), which was affected by glaciation and southeast summer monsoon action restricted by precession-modulated insolation, sedimentary rates and the coarse grain content of the terrestrial sediment in the study area were the highest in the past ∼38 ka BP, and paleoproductivity was higher during late MIS3 than the Last Glacial Maximum. A La Nina state dominated in the two intervals of late MIS3 and the early Holocene, and the thermocline deepened. Correlated with the strong East Asian winter monsoon in the glacial period, an El Nino state dominated during MIS2, the thermocline shoaled, and the sea surface salinity (SSS) trended lower from the west to the east owing to the precipitation zone as the locus of atmospheric convection shifted eastward.

Effect of glacial-interglacial sea-level changes on the displacement and stress field in the forearc and along the plate interface of subduction zones

Abstract. Combined seismological, space-geodetic and numerical studies have shown that the seismicity at subduction zones may be modulated by tides and glacier fluctuations on timescales of 1–100 a, because these changes in loads on Earth's surface are able to alter the stress field in the upper plate and along the plate interface. Here we use a two-dimensional finite-element model of a subduction zone to investigate how glacial-interglacial sea-level changes affect the forearc region and the plate interface. The model results show that a sea-level fall by 125 m over 100 ka causes up to 0.7 m of vertical displacement, with the maximum uplift occurring between the trench and the coast. The uplift signal induced by the sea-level fall decreases to zero ~20 km landward of the coastline. A subsequent sea-level rise by 125 m over 20 ka causes subsidence, which is again most pronounced in the submarine part of the forearc. The sea-level changes cause horizontal displacements of up to 0.12 m, which are directed seaward during sea-level fall and landward during sea-level rise. With respect to the stress field, the sea-level changes lead to variations in the vertical stress and the shear stress of up to 1.23 MPa and 0.4 MPa, respectively. The shear stress variations are highest beneath the coast, i.e. in the area where the sea-level changes cause the strongest flexure. The resulting Coulomb stress changes on the plate interface are of the order of 0.2–0.5 MPa and indicate that earthquakes are promoted during sea-level fall and delayed during sea-level rise. Our findings imply that eustatic sea-level changes during glacial-interglacial periods may have induced displacements and stress changes that were large enough to affect the seismic cycle of subduction thrusts.

Biomarker records of phytoplankton productivity and community structure changes in the Japan Sea over the last 166 kyr

Glacial-interglacial sea level changes have caused drastic variations in the surface hydrography, ventilation and ecosystem structure in the Japan Sea. Previous reconstructions using microfossils and geochemical proxies suggested decreased productivity and a more calcareous plankton community during glacial periods. However, the inferred community structure change is not consistent with significantly lower salinity in the Japan Sea during the glacials, which would have had a deleterious effect on calcareous plankton growth. Here, biomarker records of ODP Site 797 are generated to further evaluate phytoplankton productivity and community structure changes in the Japan Sea over the last 166 kyr. Although the contents of the phytoplankton biomarkers changed by two to three orders of magnitude, there were no clear glacial-interglacial patterns as sediment biomarker contents reflected the combined effect of production and water column degradation. The collective assessments of our biomarker records and published records support previous conclusions of decreased productivity in the Japan Sea during the glacials. However, a community structure proxy based on the alkenone/brassicasterol ratio reveals a shift from a diatom-dominated community during the glacials to a coccolithophorid-dominated community during the interglacials, mainly as a result of surface salinity variations in the Japan Sea controlled by sea-level changes. Previous community structure reconstruction using biogenic carbonate/silica ratio could have been complicated by the different environmental factors governing silica and CaCO 3 dissolution in the Japan Sea.

Cyclicity in Pleistocene upper-slope cool-water carbonates: Unravelling sedimentary dynamics in deep-water sediments, Great Australian Bight, Odp Leg 182, Site 1131A

Ocean Drilling Program Site 1131, located in the central Great Australian Bight, recovered an expanded series of Pleistocene cool-water carbonates. Three distinct facies are arranged in repeating sedimentary cycles. Omission intervals form the base of the cycles and are overlain by laminated deposits. The upper part of the cycles consists of bioturbated sediments. Facies cyclicity parallels glacial–interglacial sea-level changes. Firmground/hardground surfaces formed during latest stages of sea-level falls. Laminated sediments were deposited during later sea-level fall and/or early phases of the sea-level lowstand, and the bioturbated intervals are related to interglacial sea-level highstands. Bottom current activity is interpreted to play an important control on facies and cycle development. During the late stages of sea-level fall, upwelling currents winnowed the slope sediments, leading to hardground formation. During latest sea-level falls and early sea-level lowstands, a relative increase in the ramp sediment supply to the slope leading to the formation of the laminated facies was also a response to the continued action of the near-bottom upwelling currents that reworked previously deposited sediments along the slope. During the early sea-level rises, laminated, upwelling-influenced facies were progressively covered by the bioturbated facies. The adopted approach to decipher sedimentary cyclicity, involving the integrated use of wireline logs, geochemical data, FMS images and sedimentological analysis of the lithofacies has allowed to recognise subtle facies changes in upper-slope settings of a distally-steepened carbonate ramp and their relationship with the sea level, as well as to unravel the importance of the oceanic-current regime in the deposition style on the ramp that otherwise would remain unsolved. This integrated method could be applied to study more precisely apparently homogeneous fine-grained calcareous sediment successions of distal-ramp outcrops.

Glacially-influenced late Pleistocene stratigraphy of a passive margin: New Jersey's Record of the North American ice sheet

Glacial isostasy and the sediment supply changes associated with the waxing and waning of ice sheets have dramatic effects on the stratigraphy of adjacent continental shelves. In ancient stratigraphic records, the glacial influences on such deposits could be difficult to recognize because of the removal of coeval terrestrial glacial deposits by erosion. This study illustrates the effects of the Laurentide Ice Sheet on a basin near its maximum limit, the New Jersey continental shelf. Analysis of 1600 km of Geopulse™, Uniboom™, Minisparker™ and airgun profiles reveals four depositional sequences that have a maximum thickness of ∼75 m near the shelf edge. Sequences I and IV correspond to the major glacial–interglacial sea level changes at Marine Isotope Chron (MIC) 6/5e and 2/1, whereas sequences II and III reflect smaller-scale sea-level fluctuations during chrons 4/3c and 3b/3a, respectively. Sequences I and IV are characterized by relatively thick low stand to early transgressive deposits near the shelf edge formed during times of increased sediment supply, but are thin and discontinuous across much of the shelf. Reflection horizons in these units deepen northward in the northern half of the study area due to collapse of a peripheral bulge that formed at the margin of the Laurentide Ice Sheet. The Hudson River moved from a more southerly drainage pattern to the modern Hudson Shelf Valley position, possibly under the influence of the advancing peripheral bulge. Sequences II and III are largely preserved within a broad mid-shelf swale likely created by the migration of an ancestral Hudson River, and their thickness implies much higher sedimentation rates during chrons 4 and 3 than seen today. If the terrestrial glacial record was eroded, the increased rates of sedimentation during the Pleistocene, dominance of sediments derived from northern New England, and northward tilting of strata could be interpreted as a result of uplift of a northern source area. The unusually high frequency of the relative sea-level oscillations (20 kyr), the concentration of sediment supply during low stands and early transgressions, and the correspondence of sea-level change with climatic change could be used to infer their relationship to a nearby ice sheet. Geologists studying deposits formed during times of widespread continental glaciation should consider possible glacial influences on the stratigraphy of mid-latitude deposits, even in the absence of sediments directly deposited by ice.

Late Quaternary Sequence Stratigraphy of a Slowly Subsiding Passive Margin, New Jersey Continental Shelf

High-resolution seismic profiles over a 25,000 km2 area off New Jersey illustrate the effects of high-amplitude, high-frequency eustasy on a slowly subsiding (<0.2 mm/yr) passive margin. Analysis of 1600 km of Geopulse™, Uniboom™, Minisparker™ and air-gun profiles reveals four depositional sequences with a maximum total thickness of 100 m at the shelf edge. Correlation of these sequences to biostratigraphic and aminostratigraphic data from drill sites suggests all of these sequences may be post oxygen isotope stage 6 (~140 ka). Sequences I and IV appear to correspond to the major glacial-interglacial sea level changes (~120 m) during oxygen isotope stages 6/5 and 2/1, respectively. Sequences II and III reflect smaller scale sea level fluctuations. All sequence boundaries are interpreted as type 1, and sequences are predominantly composed of transgressive systems tracts (TST) and lowstand systems tracts (LST). Much of the TST was deposited as incised-valley fills; parasequences in the TST commonly are isolated and fragmented. The low subsidence rate and high-frequency (20 k.y.) eustatic oscillations result in extensive erosion and reworking of previously deposited sediments, both by fluvial incision during lowstands and marine erosion during transgressions and highstands. On continental margins where subsidence rates and sediment supply are low relative to rates of eustasy, sequences are thin, fragmented, and difficult to correlate. Local effects, such as shifting river drainage, salt diapir movements, and glacial isostasy, can significantly influence sequence preservation on such margins.

European research conferences glacial-interglacial sealevel changes in 4 Dimensions

European research conferences glacial-interglacial sealevel changes in 4 Dimensions

Latest Quaternary Outer Shelf and Slope Deposits, Northern Gulf of Mexico, USA: Industry Research Consortium

A consortium of oil companies is undertaking a multiyear shallow coring and high-resolution seismic investigation of the outer shelf-slope deposits of the northern Gulf of Mexico. The program's objective is to reconstruct the depositional, seismic stratigraphic, biostratigraphic, isotopic, and organic geochemical record of the latest Quaternary of a portion of the Gulf margin. Results will serve as an analog to deeper hydrocarbon reservoirs and to help in understanding sedimentation with glacial-interglacial sea-level changes. Nearly continuous cores up to 850 ft long from Main Pass Blocks 303, 242, 288 and Viosca Knoll Block 774 are being described and analyzed. Main Pass 303 core samples Holocene to Oxygen Isotope Stage 6 deposits and as old or older strata are expected to have been penetrated in the other boreholes. Three or four sea level cycles are represented. Seismic acquisition is planned for late 1990. The outer shelf and slope of the northern Gulf is an area of active growth faulting, high sedimentation rate, diapirism, and slumping. Recent work, including this study, shows that near-surface stratigraphy consists of coarse clastics alternating with carbonate-rich mud. Sands and gravels are inferred to have been deposited mostly during lowstands and rising sea level in deltas and valley-fillmore » systems. Delta clinoforms on high-resolution seismic may represent shelf-margin wedges, prograding wedges, or highstand systems tracts. Highstand deposits are characterized largely by thin, continuous intervals of bioturbated muds containing abundant diagenetic carbonate and pyrite. Precise dating and correlation of outer shelf-upper slope facies to magnitude and direction of sea level change is intended during the project.« less