Lead: Brendan Roark

In collaboration with Texas A&M University: Based on previous experience working with black corals from the Pacific, Gulf of Mexico and the Southeastern United States doing proxy development, we have the capability to develop centennial to millennia long records of changes of trophic dynamics, nutrient source changes and ocean circulation changes. Samples from the west Florida Shelf will fill a gap in the regional reconstruction of environmental changes in the Gulf of Mexico over the last several millennia.

This work supports long term environmental monitoring goals using deep sea corals. Based on previous research (e.g., Roark et al, 2005), we know that these deep-sea proteinaceous corals feed on rapidly exported and sinking particulate organic matter (POM). This means that despite the depth at which the corals are living there is a direct connection to processes operating at the surface of the ocean, such as phytoplankton regime or trophic changes, nutrient source changes or changes in ocean circulation.

Changes in the reservoir age, one of the parameters to be calculated, likely reflect changes in ocean circulation and more specific to the west Florida slope. We can use these reservoir age changes to investigate changes long term changes in the loop current in the Gulf of Mexico.

Disks from each black coral specimen will be soaked in a potassium hydroxide (KOH) solution over 3 days. This soaking dissolves the interstitial glue binding growth layers together. After dissolution, we will separate growth peels, rinse each peel with Milli-Q water, and allow them to dry overnight in a 40 oC oven. This high-resolution sampling allows for hundreds of data points for each coral, depending on the radius of the disk (e.g., approximately 380 individual peels for a disk with 15 mm radius). Note that it is very difficult to sample on an annual resolution because individual layers are exceptionally thin (microns) and easily break apart. Therefore each peel will be comprised of several growth layers still bound together.

Proxy Measurements

The following proxies will be calculated in each black coral specimen: 1) bulk δ13C and bulk δ15N, 2) radiocarbon/14C for age-model determination (by calculating linear growth rates), 3) Iodine counts by scanning electron microprobe (SEM) as a secondary age determination capable of annual resolution, 4) Compound-specific isotope amino acid analysis (CSIA) for δ15N and δ13C. 

250 – 300 μg is required for bulk analysis, and can produce high-resolution bulk isotope records from each black coral (i.e., we can sample aliquots from each peel). After observing major points of interest (excursions, long-term trends) in these high-resolution records, the peels are sampled from these points of interest for compound-specific analysis. This is a much coarser resolution (< 20 samples from an entire record) due to the significant amount of material required for analysis, about 8 mg. Prep time is also much longer, taking several days. Iodine counts with SEM analyses are done over 2-3 days after 2-3 week required to prep thin sections. All the above analyses will be done at the Stable Isotope Geosciences Facility (SIGF) or affiliated laboratories (SEM work) at Texas A&M University. Radiocarbon analysis of selected samples requires ~ 1 mg of material and will be done at the Center for Accelerator Mass Spectrometry (CAMS) at Lawrence Livermore National Laboratory under a long term collaborative agreement Brendan Roark (TAMU) has with CAMS.