Seasonal changes in cross-shelf transport of dissolved inorganic carbon across the Louisiana shelf.

The high net primary productivity and overall slow decomposition rate of soil organic matter in Louisiana’s wetlands allow for a great repository for storing organic carbon. Unfortunately, Louisiana’s wetlands are threatened by ongoing high rates of erosion and deterioration that change seasonally, leading to a net loss of terrestrial carbon into the Northern Gulf of Mexico (NGOM). Currently, there exists a lack of understanding about the fate of dissolved inorganic carbon (DIC) as it moves across salinity gradients along the Louisiana shelf. Even less is known about how this DIC transport alters seasonally, with changes in river flow and shelf currents. Quantifying seasonal shifts in carbon transport is critical to comprehending coastal water quality, as dissolved constituents from these terrestrial fresh water sources can change the NGOM’s ability to buffer decreases in pH. The current work is focused specifically around Barataria Bay (BB) and Wax Lake Delta (WLD) outlets, as these regions represent areas of net land loss and net land gain along the Louisiana coast, respectively. The purpose of this study is to understand the distribution and transport of DIC exported from both BB and WLD across the shelf. DIC samples are collected, in conjunction with short-lived radium isotopes ²²³Ra (t_1/2 = 11.43 days) and ²²⁴Ra (t_1/2= 3.66 days) samples for the month of June, July and August in 2019, to quantify cross-shelf transportation processes. Radium behaves as a conservative tracer after it is introduction by river or ground water nearshore, with its dissolved activity decreasing offshore as a function of mixing and decay and has been extensively used in other regions to estimate cross-shelf transport. Preliminary data indicates faster rates of carbon transport during high flow months, slowing down during low flow months, and higher concentrations of DIC and TAlk at BB shelf region compared to WLD region.