Search

Subtidal water level and current variability in Barataria Bay—a microtidal bar‐built estuary within the Mississippi Delta—and its relation to local and remote wind forcings were analyzed using three different methods: (1) statistical analysis of in situ observations, (2) an analytical model with idealized wind field, and (3) a barotropic numerical model. Remote wind effects (i.e., the coastal water levels imposed by Ekman transport) are dominant at forcing currents at the bay mouth and thus control estuary‐shelf exchanges. In contrast, subtidal water level variability, which ranges from 0.35 m at the bay mouth to 0.55 m at the bay head, is mainly associated with local wind effects, especially at the head of the bay. This occurs because the local wind‐induced water level tilting within the bay is larger than the coastal sea level pumping, i.e., the spatially uniform variations in water levels forced by remote winds. This result contrasts with (1) most coastal plain, fjord, and tectonic estuaries and (2) with other bar‐built estuaries in the region, in which remote wind effects dominate water level variability within the estuary. These differences are due to geomorphological features unique to Barataria Bay, such as its limited estuarine‐shelf connectivity and its orientation relative to local shoreline. Plain Language Summary: Water level and current speed in an estuary can be influenced by atmospheric forcing at periods from days to months. These effects can be the major driver of water level variability in estuaries with a small tidal range, such as those located in the southeast and Gulf Coasts of the United States. Thus, understanding these processes is important to predict a variety of processes, including transport of sediment, nutrients, and biota, as well as flooding of coastal areas. This study attempts to illustrate the relative importance of local and remote winds on subtidal water level and currents behavior in Barataria Bay, an estuary in the northern Gulf of Mexico. Results show that estuarine water level variations are largely affected by the passage of cold fronts over the northcentral Gulf of Mexico. The local and remote wind forcings are of about equal importance in controlling the overall water level variations at the bay mouth, whereas the local forcing is the dominant driver inside the bay. On the other hand, remote wind forcing dominates the subtidal currents at the bay mouth thus controlling the exchange between the estuary and the ocean. Key Points: Subtidal water levels are coherent with along‐estuary wind stress over 3‐ to 10‐day periods, consistent with the passage of cold frontsLocal wind forcing dominates over remote wind forcing at controlling water levels and water level slope within the bayRemote winds are dominant at forcing bay mouth currents and estuary‐shelf exchange [ABSTRACT FROM AUTHOR]

Oil seepage is widespread in the Gulf of Mexico, which also applies to the Bay of Campeche in the southern Gulf. The ascension of crude oil and oil-derived hydrocarbons poses a challenge to most seep-dwelling organisms. On the other hand, short- and long-chain hydrocarbons have been shown to be potentially degraded by a range of heterotrophic sulfate-reducing bacteria. Here we present lipid biomarker and carbon isotope data from authigenic carbonates from the Campeche Knolls in the southern Gulf of Mexico and use methane-seep carbonates from the Makran convergent margin (southern Pakistan and Iran) for comparison. The Campeche Knolls and Makran were selected for such comparison as endmember types for oil versus methane seepage in an attempt to identify molecular signatures of oil seepage. The Campeche carbonates yielded on average higher δ13C values (−31.3‰ to −21.9‰) than the Makran methane-seep carbonates (−54.3‰ to −39.8‰) and revealed a particularly high content of ether lipids. The Campeche carbonates revealed a greater variety of alkyl chains in non-isoprenoidal dialkyl glycerol diether lipids (DAGE) and a higher relative proportion of long alkyl chains (DAGEs >C 36) compared with the Makran methane-seep carbonates. Bacterial biomarkers showed an on average distinctively heavier δ13C signature than at the studied methane seeps, indicating bacterial oxidation of oil-derived hydrocarbons. Mixing calculations indicate that up to 73% of the local sulfate reduction is coupled to the oxidation of non-methane hydrocarbons at the oil seeps, contributing as much as 40% to carbonate precipitation. These data imply that oil-seep carbonates can be discriminated from methane-seep carbonates by their respective biomarker inventories in modern and, in cases of moderate to good biomarker preservation, ancient environments, setting the stage for the reconstruction of the influence of fluid composition on the compositions of chemosynthesis-based communities at seeps. • Inventory of dialkyl glycerol diethers (DAGEs) typifies oil seeps • Longer chain lengths in DAGEs are signatures of oil degradation. • Higher diversity of branched chains in DAGEs at oil seeps than at methane seeps • Carbonate minerals and bacterial biomarkers are less 13C depleted at oil seeps. • Bacterial oxidation of oil components contributes to carbonate authigenesis. [ABSTRACT FROM AUTHOR]

Since the 2010 Deepwater Horizon (DWH) oil spill, the Gulf of Mexico Research Initiative (GOMRI) has studied the oil spill from the perspectives of ocean environment, ecosystems, socioeconomics and human health. As GOMRI sunsets in its tenth year after the DWH oil spill, synthesis efforts recently took place to assess the accomplishments of the program. In this paper, we report on DWH modeling as part of GOMRI's Synthesis and Legacy effort. We compile a list of 330 published applications by GOMRI, the Natural Resource Damage Assessment (NRDA), and others studying the DWH oil spill and look at a wide range of subjects, tools, achievements, and integration with field research. We offer highlights and synthesis based on discussions and public webinars held in 2019 and 2020. We synthesize the significant achievements and advancements that have been made in integrating the various disciplines and domains from a modeling perspective. There was a large diversity of tools used, including at least 74 unique modeling systems. Most studies employed circulation models. These hydrodynamic models were often coupled to wave, river, and atmosphere models, as well as representations of high pressure physics and oil chemistry. Several research groups used Lagrangian transport models and statistical inference to track subsurface oil. Some coupled biophysical models were also employed to study oil fate and weathering, larval transport, biological effects, and population dynamics. In a few cases, such biophysical models were linked to marine populations and to humans through socioeconomics effects and ecosystem services. We consider models made for response planning and remediation, damage assessment, and restoration planning. There are relatively few socioeconomic or human health models, although those few examples make good use of biophysical modeling products. Our conclusions offer some insights on how the development of new tools has better prepared us for studying environmental management challenges in the Gulf of Mexico. [ABSTRACT FROM AUTHOR]