Holocene relative sea-level (RSL) curves for the U.S. Gulf Coast are in mutual confl ict, with some characterized by a smooth RSL rise akin to widely accepted eustatic sea-level curves versus others, including several recent ones, that are characterized by a conspicuous "stair-step" pattern with prolonged (millennium-scale) RSL stillstands alternating with rapid (meterscale) rises. In addition, recent work in Texas and Alabama has revitalized the notion of a middle Holocene RSL highstand, estimated at 2 m above present mean sea level. An extensive sampling program in the Mississippi Delta (Louisiana) focused on the collection of basal peats that accumulated during the initial transgression of the pre-existing, consolidated Pleistocene basement. We used stable carbon isotope ratios to demonstrate that many of these samples accumulated in environments affected by frequent saltwater intrusion in the <30 cm zone between mean spring high water and mean sea level, and we selected plant macrofossils that were subjected to AMS 14 C dating. Nearly 30 sea-level index points from a ~20 km 2 study area on the eastern margin of the delta suggest that RSL rise followed a relatively smooth trend for the time interval 8000-3000 cal yr B.P., thus questioning the occurrence of major RSL stillstands alternating with abrupt rises. Given the narrow error envelope defi ned by our data set, any sea-level fl uctuations, if present, would have amplitudes of <1 m. Although a true middle Holocene highstand never occurred in the Mississippi Delta, the high level of detail of our time series enables a rigorous test of this hypothesis. Correction of our data set for a hypothetical tectonic subsidence rate of 1.1 mm yr-1 (assuming a constant subsidence rate compared to the tectonically relatively stable adjacent coast of Texas) leads to sea levels near 2 m above present during the time interval 6000-4000 cal yr B.P. However, this model also implies a RSL position near-2 m around 8000 cal yr B.P., which is inconsistent both with data of this age from Texas, as well as with widely accepted sea-level data from elsewhere. We therefore conclude that a middle Holocene highstand for the U.S. Gulf Coast is highly unlikely, and that the entire area is still responding glacio-isostatically, by means of forebulge collapse, to the melting of the Laurentide Ice Sheet.
[1] The ever increasing need for accurate predictions of global environmental change under greenhouse conditions has sparked immense interest in an abrupt, century-scale cooling around 8200 years ago, with a focal point in the North Atlantic and with hemispheric teleconnections. Despite considerable progress in the unraveling of this striking feature, including a conceivable driving mechanism (rapid drainage of proglacial Lake Agassiz/Ojibway and a resulting reduced strength of North Atlantic thermohaline circulation), several key questions remain unanswered. One salient aspect concerns the total amount of freshwater released during this catastrophic event, likely echoed by a near-instantaneous eustatic sea-level rise. So far, no attempts have been made to perform high-resolution sealevel studies that explicitly focus on this critical time interval. Here, we present new data from the Mississippi Delta suggestive of abrupt sea-level rise associated with the 8.2 ka event. However, the amount of sea-level rise was likely less than $1.2 m, corresponding to a meltwater volume of less than $4.3 10 14 m 3 ; values lower than estimates used by several recent studies.
Coastal marshes are threatened by relative sea-level (RSL) rise, yet recent studies predict marsh survival even under the high rates of RSL rise expected later in this century. However, because these studies are mostly based on short-term records, uncertainty persists about the longer-term vulnerability of coastal marshes. We present an 8500-year-long marsh record from the Mississippi Delta, showing that at rates of RSL rise exceeding 6 to 9 mm year−1, marsh conversion into open water occurs in about 50 years. At rates of RSL rise exceeding ~3 mm year−1, marsh drowning occurs within a few centuries. Because present-day rates of global sea-level rise already surpass this rate, submergence of the remaining ~15,000 km2 of marshland in coastal Louisiana is probably inevitable. RSL-driven tipping points for marsh drowning vary geographically, and those for the Mississippi Delta may be lower than elsewhere. Nevertheless, our findings highlight the need for consideration of longer time windows in determining the vulnerability of coastal marshes worldwide.
Neuroendocrine secretory products and their interactions with epithelial prostate cells are currently under investigation in order to understand their significance in the pathogenesis, prognosis, and therapy of prostate carcinoma. These neuropeptides have the potential to disrupt the balance between cell death and cell growth in the tumor. Our research was based on the role of bombesin in modulating the mitochondrial membrane potential (#Y m ) in cell death induced by etoposide on PC-3 cells. Cells were cultured and stained with 5,5 ¶,6,6 ¶-tetrachloro-1,1 ¶,3,3 ¶-tetraethylbenzimidazolylcarbocyanine iodide (JC-1). At low membrane potentials, JC-1 produces a green fluorescence, and at high membrane potentials, it forms ''J aggregates'' with red fluorescence. Cells were examined in a confocal microscope. For quantitative analyses, regions of interest were selected. The size, number of pixels, and ratios between fluorescence intensity in the red and green channels in each region of interest were calculated. The loss of #Y m in etoposide-treated PC-3 cells was prevented by bombesin. The quantitative analysis of JC-1 -stained cells revealed a significant decrease in the red (high #Y m ) to green (low #Y m ) ratio in etoposide-treated cells when compared with control cells, which was restored in the presence of bombesin (P < 0.00001). The interaction between treatments and area (P = 0.0002) was highly significant, and confirms that PC-3 cells keep their apoptosis machinery, showing an apoptotic volume decrease in response to etoposide. The protection by bombesin occurs by inhibition of apoptosis and maintenance of mitochondrial integrity. New therapeutic protocols and trials need to be developed to test drugs acting through the neutralization of antiapoptotic intracellular pathways mediated by neuroendocrine hormones. [Mol Cancer Ther 2007;6(4):1292 -9]
The drowning of wetlands and barrier islands in coastal Louisiana has become a widely publicized environmental catastrophe in the wake of hurricanes Katrina and Rita in 2005. The devastation caused by these storms has reenergized the debate about restoring the natural coastal‐defense system and building higher and sturdier levees, in anticipation of future storms. Understanding the contributions of land subsidence and eustatic (global) sea level rise to Louisiana's wetland loss is crucial to the success of any plan designed to protect coastal communities. It is argued here that accelerated sea level rise in the future may pose a larger threat than subsidence for considerable portions of coastal Louisiana.
Xanthomonas axonopodis pv. manihotis (Xam) causes cassava bacterial blight, the most important bacterial disease of cassava. Xam, like other Xanthomonas species, requires type III effectors (T3Es) for maximal virulence. Xam strain CIO151 possesses 17 predicted T3Es belonging to the Xanthomonas outer protein (Xop) class. This work aimed to characterize nine Xop effectors present in Xam CIO151 for their role in virulence and modulation of plant immunity. Our findings demonstrate the importance of XopZ, XopX, XopAO1 and AvrBs2 for full virulence, as well as a redundant function in virulence between XopN and XopQ in susceptible cassava plants. We tested their role in pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI) and effector-triggered immunity (ETI) using heterologous systems. AvrBs2, XopR and XopAO1 are capable of suppressing PTI. ETI suppression activity was only detected for XopE4 and XopAO1. These results demonstrate the overall importance and diversity in functions of major virulence effectors AvrBs2 and XopAO1 in Xam during cassava infection.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.