Table of Contents

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

At each site during the R/V Pelican cruises, a box corer was used to collect surface sediment. The box core was subsampled in triplicate using 40 cm acrylic tubes that were pushed into the sediment to refusal, i.e. 20-30 cm. Cores were extracted in the acrylic tubes, capped on the bottom with an acrylic cap and o-ring, and submerged in a dark incubator filled with bottom water collected at the site. Each core was carefully filled with in situ near bottom water with minimum disturbance to the sediment-water interface and closed to ensure no visible headspace or air bubbles at the top. The submerged cores were allowed to equilibrate with the water in the incubator for 12 hours. A control was included that was an acrylic liner filled with bottom water only. Following this equilibration step, the cores were capped on their tops with an acrylic cap and o-ring. The top caps contained two sampling ports that were opened to collect water samples from the water overlying the sediments in the core tubes. The overlying water was mixed by a slowly turning magnetic stir bar suspended from the top cap. All cores were attached to a reservoir containing bottom water for gravity driven replenishment of water inside the core tubes during sampling. After capping, sampling commenced. 

Samples for DIC were taken every 4-8 hours for up to 23 hours (4-6 time points) from the four cores, i.e. one control core with bottom water only (identified as ‘Control’)  and three cores with sediments and bottom water (identified as ‘Rep1’, ‘Rep2’, and ‘Rep3’).  Dissolved inorganic carbon (DIC) and total alkalinity (TA) concentrations were analyzed in each sample by Wei Jun Cai’s lab at the University of Delaware. For DIC, 1 ml of water sample was measured in triplicate with an infrared CO2 detector-based DIC analyzer (AS-C3 Apollo Scitech). For TA, a 25 ml water sample was measured in duplicate with the open-cell Gran titration method using a temperature-controlled, semi-automated titrator (AS-ALK2 Apollo Scitech). Certified Reference Materials provided by A. G. Dickson, Scripps Institution of Oceanography, were analyzed for DIC and TA for quality control. 

Detailed methods are provided in Wang et al. (2020) and Lehrter et al. (2012).  

Problem report:  Data for a few time points are missing due to lost or broken sample containers.  For 1801 C6, there is missing data, so assumed depths are presented based on the depths similar to the last sampling on cruise 1710 C6-2.  

Sediment-water exchanges, i.e., fluxes, were calculated based on the rate of change in the DIC concentrations over time.  Slopes were calculated for the rate of change for each core with sediments and for the core with bottom water only. The net flux was then calculated as the difference between mean of the sediment core slopes and the control slope.

NSF Award Abstract:
Understanding how extreme events, like hurricanes, impact coastal ecosystems and the cycling of elements like carbon and oxygen, is important for improving our ability to predict how the global carbon cycle will respond to climate. This team of investigators, who have already been working together on understanding the carbon cycle in the Gulf of Mexico continental shelves, have important recent data against which to measure the effects of the passage of Hurricane Harvey in August, 2017. They will sample the waters and sediments of the northwestern Gulf of Mexico in September, October, and January to assess Harvey's impacts on a timescale of weeks to months.

The researchers pose three specific questions: 1. Will the region become a major source of carbon dioxide to the atmosphere, releasing carbon accumulated in the bottom water and sediments, and will this potential impact be faster and greater than during normal fall and winter mixing events? Will this process acidify the surface water and for how long? 2. Will the metabolic balance be substantially pushed toward net heterotrophy as a result of the storm in comparison to other years? 3. Can the amount of material delivered or redeposited across the continental shelf by a tropical cyclone be considerably larger than that related to winter storm systems? The PIs will measure water column nutrients, oxygen, organic carbon, and inorganic carbon system parameters; determine water column and benthic metabolic and nutrient flux rates; and sediment organic matter deposition rates. They will also collect end member river samples. They will compare the immediate (mid-Sept) but limited post-hurricane data and one-month post-hurricane, more detailed data with those collected in July and April to study the impacts of the storms. they will also compare 2017-2018 seasonal data to seasonal data over the same region collected in the past (2006-2008 and 2009-2010). They will also compare the impacts of Hurricane Harvey to those of Hurricanes Katrina and Rita (2005) and Tropical Storm Cindy (June 2017). The project will involve graduate and postdoctoral research and work to communicate results to the public.