Holocene sea-level change and estuary infill in North West Nelson, central New Zealand

The sedimentary sequences found within estuaries in the north west Nelson region of central New Zealand are investigated in order to quantify the timing of the end of the Post Glacial Marine Transgression. This region has been identified as being relatively stable in terms of vertical tectonic movement during the Holocene, but is yet to yield any reconstructions of eustatic sea level. In this study, we investigate the Holocene infill of a barrier estuary (Parapara Inlet) through sedimentological analysis and radiocarbon dating of 18 vibracores up to 4.2 m in length. It is found that the estuary infilled through a combination of lateral flood tide and fluvial delta progradation as well as vertical central basin infill. The central basin infilled at a consistent rate of 0.4 mm/year in both the mid (7.0–6.0 ka) and late-Holocene (2.5–1.5 ka). By the time of early human (Maori) settlement (c. 1 ka), the estuary surface was at low intertidal elevations with sediment being transported from the fluvial to tidal delta. A discernible change in sedimentation rates could not be associated with Maori settlement; however, infill rates increased to at least 12.5 mm/year in the past 150 years due hydraulic sluicing associated with mining. The sedimentary history of Parapara Inlet is compared to nearby Whanganui Inlet, d’Urville Island and Nelson to establish the character of regional Holocene sea level movement. It is found that relative sea level reached modern elevations between 8 and 7 ka in the region. The similarity between sea level curves for the end of the post glacial marine transgression (PMT) to other tectonically stable sites in northern New Zealand suggests that this curve can now be considered a true eustatic signal for the New Zealand archipelago.

Experimental Study of the Dynamic Shear Modulus Ratio and Damping Ratio of the Quaternary Sedimentary Soils in the Offshore Areas of the Yellow Sea

The effects of marine and continental sedimentary environments and geological ages on the dynamic shear modulus ratio and damping ratio of the Quaternary sedimentary soils in the offshore areas of the Yellow Sea were analyzed by using a resonant column device (GCTS, USA). The results show the following: (1) The G max of various marine soils increases with the depth and shows a typical linear relationship. (2) The marine transgression has significantly different effects on the dynamic shear modulus ratio versus the shear strain amplitude curves (i.e., G / G max ~ γ a curves) and the damping ratio versus the shear strain amplitude curves (i.e., λ ~ γ a curves) of the different soil types in the offshore areas of the Yellow Sea. The effects of marine transgression were strong on clays, moderate on silty clays, and minor on silts. (3) The geological ages have noticeable effects on the G / G max ~ γ a curves of the tested marine silty clays, marine silts, and continental silty clays, but the effects of geological ages on the λ ~ γ a curves are minimal. The fitting parameters and recommended empirical equations of the G / G max ~ γ a and λ ~ γ a curves for each type of the tested soils (silty clay, clay, and silt) were obtained mirroring the effects of sedimentary environments and geological ages.

The Shell Midden Sites of Senegambia

There are hundreds of shell midden sites along the Senegambian coastline. The shell middens were first formed during an eustatic event known as the Nouakchottien marine transgression (6,800–4,000 bp). During that marine transgression, the sea shoreline was pushed back hundreds of miles in the interior. This engendered the flourishing of malacological fauna and several fish species. As a result of this, several natural shell midden were formed. From the Late Stone Age to the 2nd millennium ce, populations exploited the aquatic fauna, which resulted in the formation of anthropogenic shell middens. The littoral where these shell middens are found is divided into three archaeological culture areas. Archaeological excavations at some of those sites, such as Khant and Dioron Boumak, have shed light on the nature of the material culture, subsistence activities, and the cultural history in these areas. Research at Soukouta has added new data on iron technology to understanding of the shell middens culture. These findings have also called into question the division of Senegambian prehistory into four distinct cultural areas known as aires culturelles.

The creation of ghost forests is driven by physical, ecological, and disturbance factors but remains a rare phenomenon

Marine transgression and the landward migration of coastlines in response to sea-level rise will determine the future of coastal ecosystems and species worldwide, yet no complete model of these processes exist. Ghost forests, areas where coastal forest has been killed by saltwater inundation, are an attention-grabbing early indicator of marine transgression. Research on marine transgression to date has largely been limited to place-based studies that, due to logistical constraints and foci of expertise, investigate subsets of the potential drivers of marine transgression. Here I take advantage of new open source datasets to provide the first systematic analysis of marine transgression across large scales, focusing on the creation of ghost forests across a region of ecological and scientific importance, the northeast U.S. My analysis provides the first synthesis of the physical, ecological, and disturbance factors that influence marine transgression. It also provides crucial regional context for more intensive studies that have a limited geographic scope. I found that ghost forests are a rare phenomenon in the landscape context: 95% of recent forest loss is concentrated in less than 3.86% of marshes, and between 2000 and 2018, only 0.88% of the entire forested area of the transgression zone experienced loss. As a result of this rarity, regional variation in marine transgression is largely driven by opportunities for rare events, which are more numerous when suitable conditions, such as shallow slopes, cover extensive areas. Quantifying recent trends in the rate of forest loss found little evidence of acceleration, with evidence instead suggesting that fewer ghost forests are being created. I also found that physical, ecological, and disturbance factors, including hurricane impacts, were all important for understanding recent trends in forest loss, suggesting that an interdisciplinary approach is warranted for future analyses and modeling of marine transgression. Such interdisciplinary research is urgently needed, as the current rate of marine transgression points to the likelihood of near-term losses of coastal wetlands, with dire implications for the species that depend on them.

Late Glacial Marine Transgression and Ecosystem Response in the Landlocked Elefsis Bay (Northern Saronikos Gulf, Greece)

Coastal landscapes are sensitive to changes due to the interplay between surface and submarine geological processes, climate variability, and relative sea level fluctuations. The sedimentary archives of such marginal areas record in detail the complex evolution of the paleoenvironment and the diachronic biota response. The Elefsis Bay is nowadays a landlocked shallow marine basin with restricted communication to the open Saronikos Gulf. A multi-proxy investigation of a high-resolution sediment core recovered from the deepest part of the basin offered a unique opportunity to record the paleoenvironmental and aquatic ecosystem response to climate and glacioeustatic sea level changes since the Late Glacial marine transgression. The retrieved sedimentary deposits, subjected to thorough palynological (pollen, non-pollen palynomorphs, dinoflagellates), micropaleontological (benthic foraminifera, calcareous nannoplankton, ostracods), and mollusc analyses, indicates isolation of the Elefsis Bay from the Saronikos Gulf and the occurrence of a shallow freshwater paleolake since at least 13,500 cal BP, while after 11,3500 cal BP the transition towards lagoon conditions is evidenced. The marine transgression in the Elefsis Bay is dated at 7500 cal BP, marking the establishment of the modern marine realm.

Saline groundwater evolution in Luanhe River Delta, China since Holocene: hydrochemical, isotopic and sedimentary evidence

Since the Quaternary Period, palaeo-seawater intrusions have been suggested to explain the observed saline groundwater that extends far inland in coastal zones. The Luanhe River Delta (northwest coast of Bohai Sea, China) is characterized by the distribution of saline, brine, brackish and fresh groundwater, from coastline to inland, with a wide range of total dissolved solids (TDS) between 0.38–125.9 g L−1. Meanwhile, previous studies have revealed that this area was significantly affected by Holocene marine transgression. In this study, we used hydrochemical, isotopic, and sedimentological methods to investigate groundwater salinization processes in the Luanhe River Delta and its links to the palaeo-environmental settings. The isotopic results (2H, 18O, 14C) show that deep confined groundwater was recharged during the Late Pleistocene cold period, shallow saline and brine groundwater was recharged during the warm Holocene period, and shallow brackish and fresh groundwater was mainly recharged by surface water. The results of hydro-geochemical modeling (PHREEQC) suggest that the salty sources of salinization are seawater and concentrated saline water (formed after evaporation of seawater). The 18O–Cl relationship diagram shows that saline and brine groundwater are formed by three end-member mixings (seawater, concentrated saline water and, fresh groundwater). In contrast, brackish groundwater is formed after the wash-out of saline groundwater by surface water. Using palaeo-environmental data from sediments, we found that palaeo-seawater intrusion during the Holocene marine transgression was the primary cause of groundwater salinization in the study region. Seawater was found to evaporate in the lagoon area during the progradation of the Luanhe River Delta; the resulting concentrated saline water infiltrated into the aquifer, eventually forming brine groundwater due to salinity accumulation. Surface water recharge and irrigation, on the other side, would gradually flush the delta plain's saline groundwater. This study provides a better understanding of saline groundwater evolution in other similar coastal zones.

The impact of tectonic-style on marine transgression and evolution

Plate tectonics drives variation in sea-level, over intervals of approximately107–108years. These variations may have significant effects on the pace of (biological) evolution through the elimination of terrestrial niches and the expansion of shallow-water marine niches. However, within the solar system, only the Earth experiences this kind of tectonism. Venus displays regional tectonism, characterized by rising diapirs within the plastic mantle. Impinging on the lithosphere, these plumes produce a range of structures of varying dimensions; the uplift of which would raise sea-level, were Venus to have oceans. Using Magellan observations of Venus, we model the impact of regional tectonism on sea-level for given areas of Venusian ocean, then compare the effect with terrestrial tectonic processes for similar oceanic area. We show that despite variation in the geographical extent of Venusian-style tectonic processes, the styles of regional tectonism on Venus can produce the same order of magnitude changes in sea-level, for a given area of ocean, as plate tectonics. Consequently, we examine some of the impacts of marine transgression on habitability and the evolution of life.