Annual and Seasonal Changes in POC, PON, and Total Particulate Matter in the Gulf of Mexico

The Mississippi River is responsible for draining over 3 million km² area of the North American continent and discharges 240 million metric tons of sediment and 1.35 million metric tons of nutrients annually into the Gulf of Mexico. This occurs primarily in the spring, fueling large algal blooms, which can decrease the amount of dissolved oxygen in subsurface waters as organic matter sinks and decays. Shipboard measurements were made annually in June and August of 2010-2014 on the Texas-Louisiana shelf from Galveston Bay to the Mississippi River. Discrete samples were collected using a CTD Rosette sampler and continuous measurements were made with a towed undulating vehicle and a shipboard flowthrough system. Statistical analyses were used to assess seasonal and annual variability of particulate matter (PM) and particulate organic carbon (POC) and nitrogen (PON). For all seven cruises examined, the concentration of PM, POC, and PON increased with decreasing salinity. Seasonal variability was noticeable but annual variability associated with drought, flood, and normal discharge of the Mississippi-Atchafalaya River system was pronounced. The PM concentration was greater closer to the Mississippi River in the June months and greater near Marsh Island, Louisiana in the August months. POC and PON concentrations do not have a distinct change from June to August as a function of longitude.