Marine Geology最新文献

Shore platforms, essential for coastal analysis and management, are poorly understood in terms of their long-term evolution, particularly regarding coastal cliff retreat rates and trends, despite their common presence in rocky coastlines. Rock coasts constitute fully erosional environments, yet long-term rates and trends of coastal cliff retreat remain poorly understood. This study adds to the limited number of studies that use cosmogenic isotopes to reconstruct millennial-scale cliff erosion. Cosmogenic ¹⁰Be concentrations were measured in 16 rock samples collected across an active 31 m wide granitic Jangsa shore platform in eastern Korea. A geometry-based inverse numerical model was used to simulate ¹⁰Be concentrations for various cliff retreat modes, relative sea level curves, and platform downwearing models. The model results were combined with measured concentrations to find the most likely scenario for coastal evolution. Our findings reveal that the shore platform has widened through time and is entirely formed during the Holocene, unlike the previous cosmogenic study in western Korea that attributed the formation of shore platforms to former interglacial periods. The results suggest acceleration in cliff retreat rate from 1.4 mm yr⁻¹ at 7.4 kyr BP to 7.0 mm yr⁻¹ at present. Accelerating cliff erosion may pose a threat to coastal communities, particularly in the context of observed and predicted anthropogenic sea level rise.

High-latitude fjords are susceptible to hazardous subaerial and submarine mass movements such as rock avalanches and landslides. Geophysical surveys in the fjords of Baffin Island (Nunavut) have shown widespread evidence of submarine landslides, but their timing and triggers remain relatively unconstrained, limiting our ability to understand the environmental controls on the wide range of landslides occurring in high latitude fjords. Using bathymetric, sub-bottom, and sediment core data, this study seeks to generate a comprehensive understanding of the distribution, morphology, lithology, and timing of submarine landslides in Pangnirtung Fjord (SE Baffin Island, Nunavut). These results are used to evaluate the influence of different environmental controls on the generation of submarine landslides in Arctic fjords. We identified 180 near-surface submarine landslides, most of which are relatively small (∼ 0.13 km²), with elongated depletion zones and wide deposits dispersed along the basin floor of the fjord. Landslide ages, calculated from radiocarbon dating and ²¹⁰Pb/¹³⁷Cs activities, indicate that 8 of the 11 dated landslides occurred in the last 200 years. Four types of environmental controls were identified, which are believed to have preconditioned or triggered the observed landslides: 1) 51% of landslides, by area, are associated with subaerial sources and extend offshore of debris flow channels and fans; 2) 23% are initiated in shallow-water (< 40 m), are non-subaerially influenced, and may have been triggered by nearshore processes and sea-ice loading; 3) 13% are located in deeper waters (>40 m) and associated with sills and moraines, suggesting they are older deposits associated with the retreat of the ice sheet in the fjord; and 4) 13% are offshore of river deltas, likely associated with delta progradation; they form the largest landslide deposits in the fjord. This research suggests that the main triggers for submarine landslides in high-latitude fjords are climatically influenced (rainfall, floods, subaerial debris flows, and sea ice loading). Consequently, the predicted increase in the frequency of subaerial debris flows and river floods due to anthropogenic climate change will likely result in an increase in the recurrence of these types of submarine landslides. Additional monitoring efforts will be then needed to fully evaluate how future climate will impact the submarine landslide hazard across the Arctic.

In recent years, Puerto Rico has been repeatedly hit by drought and hurricane, causing severe damage to the local society and economy. Therefore, understanding the region's climate variability and predicting extreme weather has become an important scientific problem. Cave stalagmites are widely recognized as high-quality terrestrial paleoclimate proxies due to their accurate dating and high resolution. In this study, we present a stalagmite-based multi-proxy reconstruction of hurricane and hydrological changes in Central America from the island of Isla de Mona, Puerto Rico, for the mid-Holocene period (4700–6260 a BP). Our data suggest a significant influence of solar activity on rainfall patterns in Central America via changes in the mean position of the Intertropical Convergence Zone (ITCZ). Our study further shows that El Niño may have played a role in influencing hurricane development at a decadal scale, and also found that the relationship of hurricane activities and El Niño intensity on the decadal and centennial scale is variable. The implications of our findings are crucial for informing contemporary climate models and enhancing our preparedness for potential future climate scenarios in the region.

The sedimentary source-to-sink processes remain under debate in the southwestern Okinawa Trough due to its complex oceanographic context. We employe a multidisciplinary approach combining marine sedimentology and physical oceanography to address the sedimentary source-to-sink processes. This study shows that the East China Sea shelf has been the provenance of the southwestern Okinawa Trough during the past 3000 a, judged from the detrital zircon U-Pb geochronology. Numerical simulations indicated that the bottom currents are the primary drivers that transport sediments from the East China Sea shelf continuously entering the southwestern Okinawa Trough. This study confirms that the source-to-sink system in the southwestern Okinawa Trough is controlled by multiscale ocean processes, and verifies that the sediments are mainly sourced from the East China Sea shelf in the past 3000 a. These arguments greatly improve our understanding on the sediment dispersal and have important implications on the climatic and oceanographic reconstructions.

The prediction of the impact of long-term climate change on tropical cyclone (TC) activity has become a global concern, for which paleotempestology could provide crucial information about TC activity before instrumental archives. The ancient shipwrecks could alternatively be applied to retrieve paleo-TC activity owing to strong TC activity being among the dominant causes of historical shipwrecks. This study presents a preliminary study exploring the potential relationship between the shipwrecks and TC activity based on the compilation of shipwreck relics and chronological assessments of porcelains associated with the shipwrecks in the Xisha Islands, in the northern South China Sea (SCS). The compilation generally spans from the Song Dynasty to the Qing Dynasty (approximately 960 to 1850 CE), showing relatively enhanced shipwreck events during the time interval between 1400 and 1700 CE, consistent with the increased moisture and flood events during this period from other adjacent sedimentary records. Further analysis suggests that paleo-TC activity was controlled by multiple mechanisms concerning the El Niño Southern Oscillation (ENSO), the movement of the Intertropical Convergence Zone (ITCZ), and Asian dust emissions. Frequent ENSO events and the southward retreat of the ITCZ would have contributed to increased moisture in tropical regions promoting TC activity during the Little Ice Age (LIA), while the dust would strengthen TC activity through atmospheric circulations. Additional work combining the archaeological and sedimentary archives should be indispensable to further understand the climatic connections and potential mechanisms of TC processes, under climate change and relevant mitigation measures.

Since the discovery of >570 methane flares on the northern U.S. Atlantic margin between Cape Hatteras and Georges Bank in the last decade, the acquisition of thousands of kilometers of additional water column imaging data has provided greater coverage at water depths between the outer continental shelf and the lower continental slope. The additional high-resolution data reveal >1400 gas flares, but the removal of probable duplicates from the combined database of new flares and those recognized in 2014 yields ∼1139 unique sites. Most of these sites occur in clusters of 5 or more seeps, leaving about 275 unique locations (including 47 clusters) for seepage along the margin. As a function of depth, seep distribution is heavily skewed toward the upper continental slope at water depths shallower than 400 m on the southern New England margin and ∼ 550 m in the Mid-Atlantic Bight, with additional seeps clustered at ∼1100 m and just deeper than ∼1400 m in both sectors. Despite little ongoing tectonic deformation or active faulting on this passive margin, a variety of processes driven from below the seafloor (e.g., migration of fluids along faults or through permeable strata, seepage above diapirs or other pre-existing structures) and from above (e.g., erosion, sapping, unroofing) contribute to the development of seeps in different settings along the margin. In addition, the prevalence of seeps on promontories overlooking shelf-breaking canyons may be directly related to the three-dimensional nature of the hydrate stability zone in these locations. As a function of depth, the parts of the slope at the contemporary landward limit of gas hydrate stability are devoid of seeps, and the upper slope zones with the most concentrated seepage were not within the gas hydrate stability zone even during the Last Glacial Maximum. Thus, if the large number of upper slope seeps is at least partially sourced in gas hydrate degradation, the gas emitted at these seeps must have migrated there from greater depths on the continental slope.

The aim of this paper is to evaluate the position of the Holocene transgression on the coast of the Valencia Gulf. To achieve this goal, a sedimentological and micropaleontological analysis of samples of fossil benthic foraminifera in cores from six boreholes drilled in three different wetlands (Almenara marsh, Moro marsh and Valencia lagoon) was carried out. In order to assess the extent of sea level change, at least three factors must be taken into account: 1) eustatic rise (global scale) 2) neotectonics (regional scale) and 3) the sedimentary factor (local and regional scale). Regarding the first factor, some authors have noted that the Holocene transgression reached +1 m above the current sea level in this area. As for the second factor, while the Valencia lagoon is located on a subsiding coast the northernmost marshes are located on a tectonically stable coast. Finally, sedimentation rates are highly variable depending on the area; whereas in the Valencia lagoon the shoreline generally shifts seawards (progradation) in the northernmost areas the coast is currently undergoing retrogradation, although the anthropic factor clearly interferes with this pattern. One of the main conclusions is that in the Valencian coast the Holocene maximum relative sea level did not exceed the present-day one, except in the case of the subsiding area of the Valencia lagoon. The calculation of sedimentation rates, the relative sea-level curve and the evolution of the water column in the different wetlands seem to corroborate it. Radiocarbon and AAR analyses allowed us to date the maximum extent of the Holocene transgression on the Valencian coast at around 5500 cal yr BP in all cases. Despite the different subsidence the three studied wetlands reflected the predominant marine influence until 5500–5200 BP, which was later followed by a growing fluvial or continental incidence, when glacioeustatic adjustments defined the patterns of coastal progradation.

Our study aims at identifying and characterizing tsunami and storm deposits by combining sedimentological, geochemical, and radiocarbon dating analyses. X-ray computed microtomography (micro-CT) is used to characterize the sedimentary fabric of the deposits. The study was conducted on a transect of oriented short sediment cores from a small lagoon at Saint Martin (Lesser Antilles), where both event types could be observed. Using micro-CT data of different event deposits, we were able to derive paleo-flow orientations and directions and compare the dynamics of the events to their environmental setting. The results showed that seven extreme-wave event (EWE) deposits, originating from hurricanes or tsunamis, had the highest Ca/Fe ratios, distinctive for marine input to the lagoon, and were characterized by coarser grains. Some also presented above the sandy part of the event deposit a siliciclastic geochemical signal rich in fine siliciclastic sediment with organic matter, which might correspond to backwash deposits. The thickness and frequency of these sandy EWE deposits in our cores decreased from the proximal to the distal zone in the center of the lagoon, with high lateral and vertical variability in sediment thickness. The youngest EWE deposit relates to the unprecedentedly powerful Category 5 Hurricane Irma, which barely left a fine layer of sand in the lagoon, demonstrating the lagoon's resilience to tropical storms. Five of the six other EWEs, characterized by micro-CT-derived sedimentary fabric, likely originated from tsunamis and occurred over the last 3500 years BP with a recurrence interval of 300–400 years, based on radiocarbon dating. A well-studied tsunami deposit from Pre-Columbian times (∼400 years BP) showed oriented sedimentary fabric, which could be used for paleo-flow reconstruction and EWE-type distinction in the Lesser Antilles, suggesting the use of an additional method for identifying EWE-type deposits in the geological record rather than other methods alone. To develop effective strategies for mitigating the natural hazards faced by communities in the coastal areas of the Lesser Antilles, it will be crucial to examine EWEs in the Caribbean region beyond historic times successfully.

Ancient maritime trading ports along the southern coast of Oman have been the target of archaeological excavations for several decades. Though historical chronologies are well-researched, information from a paleoenvironmental perspective is lacking and can provide a more complete understanding of site development. This study investigates the timing of coastal sand barrier accumulation in the natural harbours at Khor Al Balid and Khor Rori, which had considerable effects on the populations at the ancient cities of al–Balīd and Sumhuram, respectively. Six cores from Khor Al Balid and four cores from Khor Rori were analyzed using sedimentological, microfossil (foraminifera and testate amoebae), geochemical (μXRF), and radiocarbon dating methods. Marine proxies (e.g., Amphistegina spp., C. pseudolobatulus, E. limbatum, Sr, Ca/Si) and lagoon proxies (e.g., T. macrescens, T. inflata, C. constricta and C. aculeata, Ti/Ca, Fe/Ca) were used to identify Marine Sand, Brackish Lagoon/Marsh, and Freshwater facies. Results indicate that the eastern arm of Khor Al Balid closed off from the sea around the 12th century CE and that the western arm closed around the 15th century CE. Siltation of harbours and the formation of sand barriers may have contributed towards site abandonment. Previous archaeological findings suggest that al-Balīd was able to continue with maritime trade activities along the southern seaside edge of the city for several centuries after siltation of Khor Al Balid, possibly with the help of dredging. An extreme overwash event was recorded in almost all cores across both sampling sites, suggesting that a very large cyclone or a tsunami hit the southern Oman coast sometime around the 18th–19th century CE. This event, as well as continuous coastal sand accumulation, may have contributed to the decline and abandonment of Khor Al Balid and highlights the impacts that large storm/wave events have on archaeological site preservation.

There are concerns that intense tropical cyclones (TCs) are expected to become more frequent and powerful in warming climates. However, the long-term trend of TC activities, the spatiotemporal variability of such trends across different latitudes of the Western North Pacific (WNP), and the drives of the variability remain unclear. Here, we present a reconstruction of a 1600-year paleo-TCs activity using a sediment core taken in Li’an Lagoon located in southeastern Hainan Island, South China Sea. We used muti-dating methods (²¹⁰Pb and AMS ¹⁴C dating) for age control and muti-proxy analysis (XRF geochemical element scanning and grain size analysis) for identifying periods of frequent intense TC activities. Based on an updated compilation of basin-wide paleo-TC records, we confirm that there exists a seesaw pattern of intense TC frequency between low and middle latitude in the WNP. Comparing with global and regional paleoclimate proxies, we propose that the basin-wide latitudinal TC activity variation in the WNP can be linked to the migration of Western Pacific Subtropical High (WPSH) and its associated high-latitude forcings (e.g., NAO) and low-latitude internal variability forcings (i.e., El Niño Southern Oscillation, sea surface temperature (SST)). More intense TC will occur at low latitudes in the future, though with less frequency.