Neoichnological Framework of Coastal Habitat Shifts Represented by Bahamian Decapod Burrows

In coastal settings, the cumulative spatial and temporal impacts of burrowing, ichnofabric formation, and biodeposition by large crustaceans have been largely neglected at zoogeomorphic scales. These traces also serve as important (paleo-)environmental and (paleo)hydrologic indicators, both vertical (tidal or groundwater level) and lateral (areal wetland or basin extent). To date, 354 only few studies have addressed the comparative value of decapod ichnites generated by land crabs in carbonate settings. The aim of this paper is to introduce a general conceptual framework for burrows created by three crab species in the Bahama Archipelago, using examples from San Salvador Island

Ecohydrological interactions within “fairy circles” in the Namib Desert: Revisiting the self-organization hypothesis

Vegetation patterns such as rings, bands, and spots are recurrent characteristics of resource-limited arid and semiarid ecosystems. One of the most recognizable vegetation patterns is the millions of circular patches, often referred to as “fairy circles,” within the arid grassland matrix extending over hundreds of kilometers in the Namib Desert. Several modeling studies have highlighted the role of plant-soil interactions in the formation of these fairy circles. However, little is known about the spatial and temporal variabilities of hydrological processes inside a fairy circle. In particular, a detailed field assessment of hydrological and soil properties inside and outside the fairy circles is limited. We conducted extensive measurements of infiltration rate, soil moisture, grass biometric, and sediment grain-size distribution from multiple circles and interspaces in the Namib Desert. Our results indicate that considerable heterogeneity in hydrological processes exists within the fairy circles, resulting from the presence of coarser particles in the inner bare soil areas, whereas concentration of fine soil occurs on the vegetated edges. The trapping of aeolian and water-borne sediments by plants may result in the observed soil textural changes beneath the vegetation, which in turn, explains the heterogeneity in hydrological processes such as infiltration and runoff. Our investigation provides new insights and experimental data on the ecohydrological processes associated with fairy circles, from a less studied location devoid of sand termite activity within the circles. The results seem to provide support to the “self-organization hypothesis” of fairy circle formation attributed to the antiphase spatial biomass-water distributions

Lithological anomalies in a relict coastal dune : geophysical and paleoenvironmental markers

Author Posting. © American Geophysical Union, 2007. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 34 (2007): L09707, doi:10.1029/2007GL029767.Ground exposures of migration surfaces (slipfaces) of a relict Holocene coastal dune along the southeastern Baltic Sea coast provide an ideal opportunity for establishing the causes of prominent reflections on geophysical profiles. High-amplitude reflections on high-resolution ground-penetrating radar (GPR) images correlate well with two major lithological anomalies: 1) paleosols developed on dune slipfaces, and 2) slipfaces consisting of heavy-mineral concentrations (HMCs). Paleosols serve as indicators of dune stability, represent datable chronostratigraphic surfaces, and help reconstruct dune paleo-morphology. HMCs have substantially higher magnetic susceptibility values than background quartz-rich sands and, where they are well-developed, can be also used for spatial correlation. Based on their occurrence at the study site, these enriched horizons likely represent periods of increased wind activity (storminess). Multiple HMCs upwind of paleosol P1 (800–670 cal years BP) likely reflect periods of intensified wind activity along the southeast Baltic region during the Medieval Warm Period.This research was funded by the Ocean and Climate Change Institute and The J. Lamar Worzel Assistant Scientist Fund of the Woods Hole Oceanographic Institution

Coastal impacts due to sea-level rise

Author Posting. © Annual Reviews, 2007. This is the author's version of the work. It is posted here by permission of Annual Reviews for personal use, not for redistribution. The definitive version was published in Annual Review of Earth and Planetary Sciences 36 (2008): 601-647, doi:10.1146/annurev.earth.35.031306.140139.Recent estimates by Intergovermental Panel on Climate Change (2007) are that global sea level will rise from 0.18 to 0.59 m by the end of this century. Rising sea level not only inundates low-lying coastal regions, but it also contributes to the redistribution of sediment along sandy coasts. Over the long-term, sea-level rise (SLR) causes barrier islands to migrate landward while conserving mass through offshore and onshore sediment transport. Under these conditions, coastal systems adjust to SLR dynamically while maintaining a characteristic geometry that is unique to a particular coast. Coastal marshes are susceptible to accelerated SLR because their vertical accretion rates are limited and they may drown. As marshes convert to open water, tidal exchange through inlets increases, which leads to sand sequestration on tidal deltas and erosion of adjacent barrier shorelines

Cylindrical Mega-Voids in Quaternary Aeolianites, Little Exuma Island, The Bahamas: Georadar Response

In addition to karst features, tropical carbonates contain a wide range of smaller cylindrical voids (“pipes”) attributed to bioturbation, tree molds, or dissolution, among others. During geophysical investigation of the Little Exuma Island, The Bahamas, several sites with enigmatic voids were investigated using a high-frequency ground-penetrating radar (GPR) imaging. The aim of the paper is to assess the feasibility of GPR to detect voids within lithified Holocene calcarenites of the Hannah Bay Membe

Complex coastal change in response to autogenic basin infilling: An example from a sub-tropical Holocene strandplain

Thick bay-fill sequences that often culminate in strandplain development serve as important sedimentary archives of land-ocean interaction, although distinguishing between internal and external forcings is an ongoing challenge. This study employs sediment cores, ground-penetrating radar surveys, radiocarbon dates, palaeogeographic reconstructions and hydrodynamic modelling to explore the role of autogenic processes - notably a reduction in wave energy in response to coastal embayment infilling - in coastal evolution and shoreline morphodynamics. Following a regional 2 to 4m highstand at ca 58ka, the 75km(2) Tijucas Strandplain in southern Brazil built from fluvial sediments deposited into a semi-enclosed bay. Holocene regressive deposits are underlain by fluvial sands and a Pleistocene transgressive-regressive sequence, and backed by a highstand barrier-island. The strandplain is immediately underlain by 5 to 16m of seaward-thickening, fluvially derived, Holocene-age, basin-fill mud. Several trends are observed from the landward (oldest) to the seaward (youngest) sections of the strandplain: (i) the upper shoreface and foreshore become finer and thinner and shift from sand-dominated to mud-dominated; (ii) beachface slopes decrease from \u3e11 degrees to ca 7 degrees; and (iii) progradation rates increase from 04 to 18myr(-1). Hydrodynamic modelling demonstrates a correlation between progressive shoaling of Tijucas Bay driven by sea-level fall and sediment infilling and a decrease in onshore wave-energy transport from 18 to 4kWm(-1). The combination of allogenic (sediment supply, falling relative sea-level and geology) and autogenic (decrease in wave energy due to bay shoaling) processes drove the development of a regressive system with characteristics that are rare, if not unique, in the Holocene and rock records. These findings demonstrate the complexities in architecture styles of highstand and regressive systems tracts. Furthermore, this article highlights the diverse internal and external processes and feedbacks responsible for the development of these intricate marginal marine sedimentary systems

Intense hurricane activity over the past 1500 years at South Andros Island, the Bahamas

© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in E. J., Donnelly, J. P., van Hengstum, P. J., Wiman, C., Sullivan, R. M., Winkler, T. S., d'Entremont, N. E., Toomey, M., & Albury, N. Intense hurricane activity over the past 1500 years at South Andros Island, the Bahamas. Paleoceanography and Paleoclimatology, 34(11), (2019): 1761-1783, doi:10.1029/2019PA003665.Hurricanes cause substantial loss of life and resources in coastal areas. Unfortunately, historical hurricane records are too short and incomplete to capture hurricane‐climate interactions on multi‐decadal and longer timescales. Coarse‐grained, hurricane‐induced deposits preserved in blue holes in the Caribbean can provide records of past hurricane activity extending back thousands of years. Here we present a high resolution record of intense hurricane events over the past 1500 years from a blue hole on South Andros Island on the Great Bahama Bank. This record is corroborated by shorter reconstructions from cores collected at two nearby blue holes. The record contains coarse‐grained event deposits attributable to known historical hurricane strikes within age uncertainties. Over the past 1500 years, South Andros shows evidence of four active periods of hurricane activity. None of these active intervals occurred in the past 163 years. We suggest that Intertropical Convergence Zone position modulates hurricane activity on the island based on a correlation with Cariaco Basin titanium concentrations. An anomalous gap in activity on South Andros Island in the early 13th century corresponds to a period of increased volcanism. The patterns of hurricane activity reconstructed from South Andros Island closely match those from the northeastern Gulf of Mexico but are anti‐phased with records from New England. We suggest that either changes in local environmental conditions (e.g., SSTs) or a northeastward shift in storm tracks can account for the increased activity in the western North Atlantic when the Gulf of Mexico and southeastern Caribbean are less active.This work was funded by the National Science Foundation Graduate Research Fellowship (to E.J.W.), National Science Foundation grant OCE‐1356708 (to J.P.D. and P.J.vH.), the Dalio Explore Foundation and the USGS Land Change Science Program (M.R.T.). We are grateful to members of WHOI Coastal Systems Group, in particular Stephanie Madsen, for their help in the processing core samples. We thank two anonymous reviewers, Matthew Lachniet, Marci Robinson (USGS) and Miriam Jones (USGS) for their helpful feedback on earlier versions of this manuscript. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. The data are available on the National Climatic Data Center (http://www.ncdc.noaa.gov/dataaccess/paleoclimatology‐data) and WHOI Coastal Systems Group (https://web.whoi.edu/coastal‐group/) websites

Subsurface signatures and timing of extreme wave events along the Southeast Indian coast

Written history's limitation becomes apparent when attempting to document the predecessors of extreme coastal events in the Indian Ocean, from 550-700 years in Thailand and 1000 years in Indonesia. Detailed ground-penetrating radar (GPR) surveys in Mahabalipuram, southeast India, complemented with sedimentological analyses, magnetic susceptibility measurements, and optical dating provide strong evidence of extreme wave events during the past 3700 years. The diagnostic event signatures include the extent and elevation of the deposits, as well as morphologic similarity of buried erosional scarps to those reported in northern Sumatra region. Optical ages immediately overlying the imaged discontinuities that coincides with high concentration of heavy minerals date the erosional events to 340 ± 35, 350 ± 20, 490 ± 30, 880 ± 40, 1080 ± 60, 1175 ± 188, 2193 ± 266, 2235 ± 881, 2489 ± 293, 2450 ± 130, 2585 ± 609, 3710 ± 200 years ago. These evidences are crucial in reconstructing paleo extreme wave events and will pave the way for regional correlation of erosional horizons along the northern margin of Indian Ocean