Gulf Of Mexico Sediments Research Articles

Microtextures on quartz grains from the Gulf of Mexico and the Mexican Pacific coastal sediments: Implications for sedimentary processes and depositional environment

Microtexture analyes on quartz from coastal sediments of the Gulf of Mexico and the Mexican Pacific Coast reveal 35 and 30 types of microtextures, respectively, which were grouped into mechanical, mechanical/chemical and chemical categories based on their mode of origin. Microtextures of chemical origin are rarer in the El Carrizal than in the Manzanillo beach sediments of the Mexican Pacific Coast. Microtextures of mechanical origin like straight and curved scratches, pits, broken edges, and V-shaped marks indicate high energy, fluvial to marine depositional environments. The scarcity to absence of chemical features suggest that the energy level was higher at the Mexican Pacific coast than on the Gulf of Mexico coast. V-shaped marks are common in the Gulf of Mexico sediments, whereas they are abundant in the quartz grains from the Mexican Pacific coast. Increased frequency and density of V-shaped marks are produced by exceedingly high wave velocity during storm events or tsunamis. Abundance of V-shaped marks with fresh surfaces of quartz grains from the Mexican Pacific coast indicate an extremely high-energy impact event. Many quartz grains from the El Carrizal beach of the Mexican Pacific coast have abundant closely spaced V-shaped marks with fewer fresh surfaces. Such high frequency of V-shaped marks is mainly linked to grain-to-grain collision, typically associated with high-energy sub-aqueous conditions with a large volume of sedimentary particles in the water column that are produced during a tsunami or storm events. In contrast, many quartz grains from the Gulf of Mexico have large fresh surfaces with moderate percentages of V-shaped marks that might have been produced by high-energy waves with low sediment concentrations during storm events.

The metabolic core of the prokaryotic community from deep-sea sediments of the southern Gulf of Mexico shows different functional signatures between the continental slope and abyssal plain.

Marine sediments harbor an outstanding level of microbial diversity supporting diverse metabolic activities. Sediments in the Gulf of Mexico (GoM) are subjected to anthropic stressors including oil pollution with potential effects on microbial community structure and function that impact biogeochemical cycling. We used metagenomic analyses to provide significant insight into the potential metabolic capacity of the microbial community in Southern GoM deep sediments. We identified genes for hydrocarbon, nitrogen and sulfur metabolism mostly affiliated with Alpha and Betaproteobacteria, Acidobacteria, Chloroflexi and Firmicutes, in relation to the use of alternative carbon and energy sources to thrive under limiting growth conditions, and metabolic strategies to cope with environmental stressors. In addition, results show amino acids metabolism could be associated with sulfur metabolism carried out by Acidobacteria, Chloroflexi and Firmicutes, and may play a crucial role as a central carbon source to favor bacterial growth. We identified the tricarboxylic acid cycle (TCA) and aspartate, glutamate, glyoxylate and leucine degradation pathways, as part of the core carbon metabolism across samples. Further, microbial communities from the continental slope and abyssal plain show differential metabolic capacities to cope with environmental stressors such as oxidative stress and carbon limiting growth conditions, respectively. This research combined taxonomic and functional information of the microbial community from Southern GoM sediments to provide fundamental knowledge that links the prokaryotic structure to its potential function and which can be used as a baseline for future studies to model microbial community responses to environmental perturbations, as well as to develop more accurate mitigation and conservation strategies.

Restoring barrier habitat in Louisiana to compensate for natural resource injuries: Shell Island and Chenier Ronquille Barrier Restoration Projects

Coastal Louisiana received significant funds tied to BP penalties as a result of the Deepwater Horizon incident. As it is widely considered that the State of Louisiana sustained most of the damage due to this incident, there has been a firm push to waste no time in implementing habitat restoration projects. Sustaining the land on the coast of Louisiana is vital to our nation’s economy, as several of the nation’s largest ports are located on the Gulf coast in Louisiana. In addition, the ecosystems making up the Louisiana coast are important to sustain some of the largest and most valuable fisheries in the nation. Funded by BP Phase 3 Early Restoration, the goals of the Natural Resource Damage Assessment (NRDA) Outer Coast Restoration Project are to restore beach, dune, and marsh habitats to help compensate spill-related injuries to habitats and species, specifically brown pelicans, terns, skimmers, and gulls. Four island components in Louisiana were funded under this project; Shell Island Barrier Restoration, Chenier Ronquille Barrier Island Restoration, Caillou Lake Headlands Barrier Island Restoration, and North Breton Island Restoration (https://www. gulfspillrestoration.noaa.gov/louisiana-outer-coast-restoration, NOAA 2018). Shell Island and Chenier Ronquille are critical pieces of barrier shoreline within the Barataria Basin in Plaquemines Parish, Louisiana. These large-scale restoration projects were completed in the years following the Deepwater Horizon incident, creating new habitat and reinforcing Louisiana’s Gulf of Mexico shoreline. The Louisiana Coastal Protection and Restoration Authority (CPRA) finished construction of the Shell Island NRDA Restoration Project in 2017, which restored two barrier islands in Plaquemines Parish utilizing sand hydraulically dredged from the Mississippi River and pumped via pipeline over 20 miles over levees and through towns, marinas, and marshes to the coastline. The National Marine Fisheries Service (NMFS) also completed the Plaquemines Parish barrier island restoration at Chenier Ronquille in 2017 utilizing nearshore Gulf of Mexico sediment, restoring wetland, coastal, and nearshore habitat in the Barataria Basin. A design and construction overview is provided herein.

Last interglacial (MIS 5e) and Holocene paleohydrology and paleovegetation of midcontinental North America from Gulf of Mexico sediments

Marine Isotope Stage (MIS) 5e experienced slightly higher insolation and lower global ice volume compared to the pre-industrial climate, however, how climate and vegetation differ regionally during MIS 5e is poorly known. Here, we examined MIS 5e hydrologic and vegetation conditions in the Mississippi River Basin (MRB) in North America (NA) and compared this to the Holocene. To do this, we reconstructed paleohydrology and paleovegetation conditions during the last 150 kyr using plant waxes (n-alkanes) and their carbon (δ13Calk) and hydrogen (δ2Halk) isotopic compositions preserved in ODP 625B core from the northwestern Gulf of Mexico (GOM) near the MRB discharge area. In the early MIS 5e, the jet stream may have been located in its northern most position over the last 150 kyr indicated by the highest δ2Halk values resulting in high warm and moist air mass contribution from the GOM and tropical Atlantic to the MRB. This is likely caused by northern expansion of the Atlantic Warm Pool and a northward shift of the ITCZ with increased warming. The climate may have become drier towards late MIS 5e with precipitation concentrated in summer expanding the C4 grassland distribution, which persisted through the MIS 5b. We speculate that this may be due to prolonged warming and drying from early to mid MIS 5. There were notable increases in plant wax export from western dry grasslands during deglaciation (13.5 ka) and the mid-Holocene (5.3 ka). In contrast, plant wax delivery was low during the MIS 5e without significant source changes. Such contrast between the two interglacials is due to the earlier completion of the LIS retreat in late MIS 6 and an onset of a full interglacial climate during the MIS 5e compared to the Last Glacial and Holocene transition. This study presents timing and mechanisms of precipitation source and vegetation composition changes over the NA as a result of slight changes in insolation and rates of deglaciation. These results provide a baseline for understanding the sensitivity of regional hydrologic and vegetation conditions to slight changes in global climate.

Hydrocarbon composition and concentrations in the Gulf of Mexico sediments in the 3 years following the Macondo well blowout

In April of 2010, the Macondo well blowout in the northern Gulf of Mexico resulted in an unprecedented release of oil into the water column at a depth of approximately 1500 m. A time series of surface and subsurface sediment samples were collected to the northwest of the well from 2010 to 2013 for molecular biomarker and bulk carbon isotopic analyses. While no clear trend was observed in subsurface sediments, surface sediments (0–3 cm) showed a clear pattern with total concentrations of n-alkanes, unresolved complex mixture (UCM), and petroleum biomarkers (terpanes, hopanes, steranes) increasing from May to September 2010, peaking in late November 2010, and strongly decreasing in the subsequent years. The peak in hydrocarbon concentrations were corroborated by higher organic carbon contents, more depleted Δ14C values and biomarker ratios similar to those of the initial MC252 crude oil reported in the literature. These results indicate that at least part of oil discharged from the accident sedimented to the seafloor in subsequent months, resulting in an apparent accumulation of hydrocarbons on the seabed by the end of 2010. Sediment resuspension and transport or biodegradation may account for the decrease in sedimented oil quantities in the years following the Macondo well spill.

Phosphorus speciation and sedimentary phosphorus release from the Gulf of Mexico sediments: Implication for hypoxia

Phosphorus (P) is an important macronutrient that can limit primary productivity in coastal marine ecosystems. This study provides a quantitative determination of abundance and chemical speciation of P and potential anaerobic P-release rates from northern Gulf of Mexico (GOM) sediments. Seven sediment cores were collected from shelf, slope and deep-sea sediments in the northern GOM. A sequential extraction method was used to operationally separate P pools into readily available-P, Fe/Al–P, alkali extractable organic-P, Ca/Mg–P, and residual-P. Ca/Mg–P was the most abundant form of sediment P (79.0 ± 9.4% of TP). Northern GOM sediments were found to release 0.02–4.4 mg kg−1 d−1 of bioavailable-P under anoxic sediment condition. P-release rate had significant positive correlation (P = 0.001) with the Fe/Al–P fraction, indicating this relatively small pool of TP (∼0.4–10.2%) is primarily releasing available-P to the water column during hypoxia events. The findings of this study suggest that the internal sedimentary P loading contributes substantial bioavailable-P to the P-limited water column which leads to increased primary production in the northern GOM, creating a positive feedback mechanism for hypoxia. Therefore, the action plan to reduce the GOM hypoxia zone needs to take internal sediment P loading into account when managing for watershed nutrient loading.

A 35 Myr North American leaf-wax compound-specific carbon and hydrogen isotope record: Implications for C 4 grasslands and hydrologic cycle dynamics

Hydrology, source region, and timing of precipitation are important controls on the climate of the Great Plains of North America and the composition of terrestrial ecosystems. Moisture delivered to the Great Plains varies seasonally and predominately derives from the Gulf of Mexico/Atlantic Ocean with minor contributions from the Pacific Ocean and Arctic region. For this work, we evaluate long-term relationships for the past ~ 35 million years between North American hydrology, climate, and floral change, using isotopic records and average carbon chain lengths of higher plant n-alkanes from Gulf of Mexico sediments (DSDP Site 94). We find that carbon isotope values (δ 13C) of n-alkanes, corrected for variations in the δ 13C value of atmospheric CO 2, provide minor evidence for contributions of C 4 plants prior to the Middle Miocene. A sharp spike in C 4 input is identified during the Middle Miocene Climatic Optimum, and the influence of C 4 plants steadily increased during the Late Miocene into the Pleistocene — consistent with other North American records. Chain-length distributions of n-alkanes, indicative of the composition of higher plant communities, remained remarkably constant from 33 to 4 Ma. However, a trend toward longer chain lengths occurred during the past 4 million years, concurrent with an increase in δ 13C values, indicating increased C 4 plant influence and potentially aridity. The hydrogen isotope values (δD) of n-alkanes are relatively invariant between 33 and 9 Ma, and then become substantially more negative (75‰) from 9 to 2 Ma. Changes in the plant community and temperature of precipitation can solely account for the observed variations in δD from 33 to 5 Ma, but cannot account for Plio-Pleistocene δD variations and imply substantial changes in the source region of precipitation and seasonality of moisture delivery. We posit that hydrological changes were linked to tectonic and oceanographic processes including the shoaling and closure of the Panamanian Seaway, amplification of North Atlantic Deep Water Production and an associated increase of meridional winds. The southerly movement of the Intertropical Convergence Zone near 4 Ma allowed for the development of a near-modern pressure/storm track system, driving increased aridity and changes in seasonality within the North American interior.

Denitrification in shallow, sublittoral Gulf of Mexico permeable sediments

We examined nitrogen cycling over a 1‐yr period in shallow, sandy sediments at two contrasting sites near a barrier island in the northeastern Gulf of Mexico, and we provide here the direct determination of dinitrogen gas (N2) production at ambient nitrate concentrations in permeable marine sediments. Nitrogen‐stable isotope tracer techniques were used to quantify N2‐production rates and pathways in sediment cores and slurries. To simulate pore‐water advection, the dominant transport process in the upper layer of the permeable sand beds, intact sediment cores were perfused with aerated seawater. This perfusion increased denitrification rates up to 2‐fold in Apalachicola Bay sands and up to 17‐fold in Gulf of Mexico sublittoral sands, respectively, relative to static cores. Seasonal N2‐production rates were highest in spring and fall. Denitrified nitrate originated almost entirely from benthic nitrification at the exposed Gulf site, whereas water‐column nitrate dominated sedimentary denitrification at the sheltered Bay site. Sediment incubations in stirred chambers were used to determine net fluxes of oxygen (O2), N2, nitrate, and ammonium across the sediment‐water interface during varied degrees of continuous pore‐water exchange. Rates of N2 efflux correlated with rates of pore‐water flow increasing from 0.12 mmol N m‐2 d‐1 under diffusion‐limited transport conditions up to 0.87 mmol N m‐2 d‐1 with pore‐water advection. Mineralized nitrogen was completely converted to N2 gas in Gulf of Mexico sediments. Our results demonstrate that advective pore‐water circulation will accelerate benthic N2 production by coupled nitrification‐ denitrification and that substantial nitrogen loss occurs from coastal permeable sediments.

The adsorption of saxitoxin to clays and sediments in fresh and saline waters

The adsorption of saxitoxin to Na- and Ca-montmorillonite, kaolin (crystalline and amorphous), kaolinite, Bread and Butter Creek sediment (an estuarine tidal creek), Gulf of Mexico sediment, and Santa Barbara Basin sediment in deionized water and 32‰ salinity simulated seawater (Instant Ocean™) is reported. Adsorption was partially reversible for all cases and best described using a Freundlich isotherm. The corresponding Freundlich constants ( K F) ranged from 8.83 × 10 3 μmol/kg to 6.76 × 10 4 μmol/kg for freshwater and 4.73 × 10 3 μmol/kg–1.11 × 10 4 μmol/kg for seawater. There is a positive linear correlation seen between the K F values and the cation-exchange capacity of the adsorbents. The release of saxitoxin from previously equilibrated adsorbents was determined in freshwater (0–18%) and seawater (4–53%).

Adsorption of domoic acid to marine sediments and clays

Conditional solid-water distribution coefficients (K(d)) for the adsorption of domoic acid (DA) to a series of complex sediments and clays were determined in artificial seawater. K(d) ranged from 5.11 L g(-1) to 0.97 L g(-1), with a corresponding ranking of: kaolinite > Gulf of Mexico sediment > Santa Barbara Basin sediment > Bread and Butter Creek sediment > poorly crystallized kaolin > Ca-montmorillonite > Na-montmorillonite > well crystallized kaolin > diatomaceous earth. Adsorption correlated with the anion exchange capacity of the clays tested (R(2) = 0.98), but not the more structurally complex sediments. The effect of added transition metals (Fe(iii), Cu(ii), Al(iii)) and terrestrially derived dissolved organic matter (Suwannee River DOM, SRDOM) on DA adsorption to Na-montmorillonite, well crystallized kaolin, and Gulf of Mexico sediment, was also tested. The addition of transition metals led to increased adsorption to all surfaces by a factor of 2-7, presumably by enabling the adsorption of DA-metal complexes. SRDOM enhanced DA adsorption by a factor of approximately 2.5. The release of adsorbed DA from sediments was also examined. Under our conditions, adsorbed DA equilibrated with the overlying aqueous phase within minutes with approximately 50% release.

Biodegradation of Synthetic Base Fluid Surrogates in Gulf of Mexico Sediments under Simulated Deep-Sea Conditions

In this study, an anaerobic marine biodegradability test was adapted to study the fate of synthetic base fluid (SBF) surrogates, ethyl oleate and tetradecene, by deep-sea microorganisms. Sediment samples from hundreds of meters deep in the Gulf of Mexico were incubated at low temperatures (4 degrees C) and high hydrostatic pressure in steel vessels. Stimulation of indigenous microbial communities to SBF biodegradation was evident in the fact that the rate of removal of ethyl oleate was greater in sediments that had some previous exposure to SBF (first-order decay coefficient kof -0.22 +/- 0.02 week(-1)) compared to unexposed control sediments (first-order decay coefficient k of -0.11 +/- 0.02 week(-1)). When sulfate-linked tetradecene degradation occurred within the test period, the activity could also be modeled as a first-order decay following an initial lag phase, with an average decay coefficient of k = -0.05 +/- 0.01 week(-1). This study also revealed that the degradation of SBF surrogates by microorganisms collected from deep-sea sediments was not significantly effected by the hydrostatic incubation pressure.

Laurentide Ice Sheet meltwater and abrupt climate change during the last glaciation

A leading hypothesis to explain abrupt climate change during the last glacial cycle calls on fluctuations in the margin of the North American Laurentide Ice Sheet (LIS), which may have routed fresh water between the Gulf of Mexico (GOM) and the North Atlantic, affecting North Atlantic Deep Water variability and regional climate. Paired measurements of δ18O and Mg/Ca of foraminiferal calcite from GOM sediments reveal five episodes of LIS meltwater input from 28 to 45 thousand years ago (ka) that do not match the millennial‐scale Dansgaard‐Oeschger warmings recorded in Greenland ice. We suggest that summer melting of the LIS may occur during Antarctic warming and likely contributed to sea level variability during marine isotope stage 3.

Denitrification in bottom sediment near oil production facilities off the Louisiana Gulf Coast

There is little information on denitrification in Gulf of Mexico bottom sediment. Potential denitrification rates in surface sediment were measured along transects legs extending 0–800 m from two offshore oil production platforms. The average potential denitrification ranged from approximately 50 mg N m−2 d−1 in surface sediment near the platforms to 15 mg N m−2 d−1 in sediment 800 m from the platforms. Measured denitrification rates were correlated to a higher organic matter content in sediment nearer the platforms. This research examined only a small component of nitrogen processing in Gulf of Mexico sediment. Additional research should examine the effect of nitrogen loading and temporal and spatial variability on denitrification rate.

Megaflood erosion and meltwater plumbing changes during last North American deglaciation recorded in Gulf of Mexico sediments: Comment and Reply

Megaflood erosion and meltwater plumbing changes during last North American deglaciation recorded in Gulf of Mexico sediments: Comment and Reply

Megaflood erosion and meltwater plumbing changes during last North American deglaciation recorded in Gulf of Mexico sediments

Submicrometer variations in the median diameter of siliciclastic mud in Orca Basin, northern Gulf of Mexico, sensitively monitor Laurentide ice sheet runoff to the gulf during early stages of the last deglaciation. Grain-size data document a prominent pulse of very fine-grained sediment to the northern Gulf from 12.6 to 12.0 ka, corresponding with the well-known sea-surface meltwater spike in δ 18 O records. Meltwater megafloods at this time eroded and transported large volumes of clay to the Gulf via the Mississippi River system. The nonquartzose megaflood sediments appear to have been derived from clay-rich midcontinental terrace deposits rather than from glacial outwash supplied by the Laurentide ice margin. Sediment grain-size data, in combination with other terrigenous proxies (clay minerals and reworked calcareous nannofossils), indicate substantial variability in deglacial meltwater discharge and associated sediment load of meltwater runoff. This variability reflects changes in continental plumbing consistent with terrestrial records of North American deglaciation.

Smectite Illitization in Pliocene-Age Gulf of Mexico Mudrocks

AbstractUtilizing high-resolution transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDS) and X-raydiffraction (XRD) techniques, we have studied the transition from shallower smectite-rich mudrocks to deeper illite-rich mudrocks in Pliocene-age turbidite sediments from the northern Gulf of Mexico (GOM). Our objective in this work was to better understand how the smectite-illite transition may affect the onset of geopressuring in GOM sediments. The samples studied were sidewall cores from an offshore Louisiana well. In previous studies of GOM sediments, the smectite-to-illite reaction has mainly been documented in considerably older, Miocene-age sediments.The results of this study elucidate the reaction mechanisms entailed in the transformation of clays in this sediment from smectitic to illitic. We found that illite formed at the expense of smectite in 2 ways: 1) growth of preexisting discrete illite flakes, and 2) creation of new illite layers within mixed-layer illite-smectite. Also, illitization apparently proceeded via a dissolution/precipitation, Al-conserving reaction rather than a solid-state, layer-conserving reaction. Smectite illitization is commonly believed to require input of K from feldspar dissolution. Our XRD results found little correlation between decreases in K-feldsparand increases of illite. However, in 1 instance TEM/EDS analyses indicated the presence of high-charge smectite, which suggests that insufficient K was available for illitization. TEM images also show small packets of authigenic chlorite in illite-rich mudrock. This chlorite may act as a sink for Fe liberated upon smectite illitization.

Sequence Stratigraphy and Structure of Plio-Pleistocene Sediments in Northeast Gulf of Mexico--An Example of Continental Slope Sedimentation: ABSTRACT

Sequence Stratigraphy and Structure of Plio-Pleistocene Sediments in Northeast Gulf of Mexico--An Example of Continental Slope Sedimentation: ABSTRACT

Marine PSSP reflections with a bottom velocity transition zone

Marine shear‐wave reflection methods using the conventional data acquisition system (i.e., source and receiver in water) rely on two mode conversions at the water bottom to produce shear reflections such as PSSP. Some theoretical considerations and the results of a marine check shot survey conducted in the Gulf of Mexico demonstrate that the difficulty in observing PSSP events is attributable to weak P-S and S-P conversion at the bottom in regions with very low shear velocity (a few hundred ft/s or less) sediments at the bottom. For a simple water bottom with a low shear‐wave velocity, water over a uniform half space, the PS conversion factor is proportional to [Formula: see text] and the SP conversion factor is proportional to [Formula: see text], where [Formula: see text] is the bottom shear velocity. For [Formula: see text] their product gives PSSP reflections that can be comparable in amplitude to typical PPPP events. For [Formula: see text], the PSSP events should be about 30 dB weaker and probably not visible. For typical Gulf of Mexico sediments with a shear velocity transition zone several tens of feet thick at the bottom, the situation is even worse, since the velocities start near zero and may not reach 500 ft/s. This condition is common in many areas of recent sedimentations.

Paleobiological Implications of Living Benthic Foraminiferal Distributions in Northern Gulf of Mexico Sediments: ABSTRACT

Twenty-one box cores from the shelf and slope of the northern Gulf of Mexico were sequentially sampled to a sediment depth of 20 cm and stained with Rose Bengal. The water depth of the box-core samples ranged from 52 to 4,510 m. The greater than 63 ..mu..m fraction of each sedimentary interval was examined for the presence of stained (living) benethic foraminifera. The down-core distribution of living specimens are compared between a deltaic and a nondeltaic environment. Forty-four species are epifaunal and 30 species infaunal. However, distinct habitat differences exist between species of the same genus. Contrasting the deltaic and nondeltaic environments, specimens from the deltaic samples occur in greater abundance and to greater sediment depths (up to 20 cm) than those from the nondeltaic environment, which occur to a maximum sediment depth of only 3 cm. These results demonstrate that considerable caution should be used and generalizations avoided with regard to the microhabitat preferences of fossil benthic foraminifera.

Corrigendum: Iridium in Mississippi River suspended matter and Gulf of Mexico sediment

Corrigendum: Iridium in Mississippi River suspended matter and Gulf of Mexico sediment