Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
• Data Files
• Parameters
• Instruments
• Deployments
• Project Information
• Funding

This dataset contains core data collected in the Brazos River Plume, TX during three cruises conducted in 2017 and 2018. Cores were analyzed for grain size and mercury content. The sample collection that took place on September 10, 2017 was supported by NSF award OCE-1635893. Award OCE-1829221 supported the rest of the data collection.

Data were collected on three cruises on the Brazos River Plume in the Northern Gulf of Mexico. Cores were collected from: 11 stations on September 10, 2017; 23 stations on October 29, 2017; and 26 stations on July 12, 2018. The September 2017 cruise was conducted on R/V Pelican (PE18-09); the two subsequent cruises were conducted on R/V Trident.

On each cruise, a series of box cores were collected in a grid pattern. From those box cores, a series of sub-cores were collected. Those included: x-radiograph trays, a 3-inch aluminum and/or polycarbonate core, and a 6-inch core. They were stored in a refrigerator at 2 °C and later split into 1 cm sections, x-rayed, and stored in bags until further analysis.

To collect water content, a basic oven was used at 60 °C. They were dried in pre-weighed aluminum tins, and then the water content was calculated after weighing the dry weight.

The grain size was processed in a Malvern Mastersizer 2000 that uses laser diffraction to analyze the grains.

The Mercury content was analyzed in a Milestone DMA-80 that combusts the sample to get a total mercury content.

Data Processing: Most of the data were processed in Excel, Matlab R2020a, or ArcPro 2.6.3. The data were stored in Excel sheets, then graphs and maps were created using Matlab or ArcPro.

BCO-DMO Processing:
- concatenated three separate data files into one dataset;
- added Date column;
- re-named fields to conform with BCO-DMO naming conventions (replaced spaces with underscores);
- rounded Hg_Content and Water_Content columns.

NSF Abstract:

The formation of calcium carbonate (CaCO3) in seawater is a fundamental pathway in the marine carbon cycle. Calcium carbonate formation may occur through biological production (calcification by organisms building shells or skeletal material) or through non-biological (abiotic, or chemical) processes. Although most surface seawater in both open and coastal waters is supersaturated in calcium carbonate, several factors inhibit the abiotic production of calcium carbonate. Therefore the current paradigm is that most calcium carbonate formation in seawater is biological. However, laboratory experiments have demonstrated that addition of solid-phase particles to supersaturated seawater promotes nuclei-induced CaCO3 precipitation (NICP) by providing "seeds" for precipitation. NICP has been demonstrated in the Little Bahama Banks during events of re-suspension of CaCO3-rich sediments. Until very recently, essentially no evidence has shown that NICP occurs in typical marine systems where suspended particles have relatively low CaCO3 content. A recent study by the Israeli partners in this project provides evidence that NICP may play a significant role in the carbon budget in the Red Sea, as a result of an influx of particulate material caused by flash floods and potentially airborne dusts. Such a finding suggests that NICP may be an important CaCO3 formation pathway that has been mostly ignored in the ocean carbon cycle. The goal of this project is to conduct the first comprehensive, in-depth study to evaluate the significance of NICP in the oceans. The project is an international collaboration between U.S. and Israeli scientists, jointly funded by NSF and the U.S.-Israel Binational Science Foundation. A postdoctoral researcher whose Ph.D. work forms the foundation for this study will be supported through this project. An Israeli masters-level student and one U.S. minority undergraduate intern will be advised and trained in this project.

The project will use an integrated approach to assess different mechanisms that may result in NICP, including riverine sediment input, land-derived particle influx via flash floods, bottom sediment resuspension, and atmospheric dust input. Field investigations will be done in a suite of coastal environments: the northern Red Sea, the Mississippi and Sabine River plumes and Galveston Bay in the northern Gulf of Mexico, each of which receive significant quantities of non-carbonate rich sediments. The investigators will also conduct controlled laboratory experiments to verify and extend field observations. If NICP is shown to be significant, this finding could promote a reexamination of important parts of the carbon cycle and the response of the ocean carbon system to ongoing perturbations.

NSF Award Abstract:
The transport and fate of sediment carried by rivers to the coastal ocean is of great ecological and societal importance. River input is the primary source of land-derived sediment to the marine environment. These particles have significant impacts on the health of coastal ecosystems and the geology and bathymetry of coastal oceans and shipping channels. They directly and indirectly affect fisheries and navigation. This research focuses on the movement of sediments carried into the Gulf of Mexico, via the Brazos River, during the unprecedented rainfall and flooding event that occurred during Hurricane Harvey. The Brazos River ranks as the second largest contributor of nutrients and organic matter to the Gulf of Mexico, after the Mississippi River. Unlike the Mississippi, however, most sediment delivered to the Gulf of Mexico from the Brazos is carried during flooding events like that which accompanied Hurricane Harvey. Little is known about the fate of this sediment. It is not clear if it is retained in the coastal zone, where the nutrients and chemicals it carries affect the coastal environment, or is carried offshore and deposited in the deep waters of the Gulf of Mexico. Through intensive sampling of sediments just offshore the mouth of the Brazos River and further offshore in the Gulf of Mexico in what is known as the Texas Mud Blanket, this project will determine the principal repository of sediments delivered to the western Gulf of Mexico by a major Texas river.

The overall goal of this research is to investigate the hypothesis that flood-borne sediment from the Brazos River is initially deposited in the coastal zone and subsequently mobilized and carried offshore with a large fraction of it being deposited in the Texas Mud Blanket. The work builds on the analysis of sea-bottom sediment samples collected in 2017 during flooding associated with Hurricane Harvey. This new program will include two sampling cruises to augment already collected data. The first cruise will entail acquisition of ~25 cores that will indicate sediment deposition and transport in the near-shore region near the Brazos River mouth. Preliminary work indicates that much of the initial deposition of Brazos River sediment occurred east of the original sampling region. The second cruise in will collect additional Brazos region cores and expand sampling into the Texas Mud Blanket, with the goal of documenting changes in Brazos sediment deposition from the Hurricane Harvey flooding. During both cruises, complementary hydrography data will be collected. This includes water column velocities and suspended sediment loads. Provenance of individual layers, within the sediment samples and box cores, will be determined by digital photos and x-radiographs of intact core slabs that show sediment fabric and structures. To differentiate Gulf of Mexico from Brazos River sediments, sub-samples of collected cores will be geochemically analyzed and profiled for short-lived-radioisotope geochronology, water content, grainsize distribution, and mercury and carbonate content. These indicators will help identify the origin of the sediments deposited in the system.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.