Sub-annual and inter-annual variations of total alkalinity in the northeastern Gulf of Mexico

Abstract

We analyzed sub-annual and inter-annual variations of total alkalinity (TA) distributions in the northeastern Gulf of Mexico using TA data collected in seven cruises from 2012 to 2014, riverine TA records, and surface current and salinity data from Hybrid Coordinate Ocean Model reanalysis. Significant sub-annual and inter-annual TA variations were observed in the upper 150 m of the water column, mainly controlled by riverine TA inputs and ocean currents. Generally, the influence from riverine TA was strongest in the summer, when the influence of freshwater plume extended far from shore and riverine TA was high. Deep-water in the western part of our study area was mainly influenced by the Mississippi-Atchafalaya River plume, and the strength of riverine TA inputs mostly depended on distance from shore. Riverine inputs decreased from the Mississippi-Atchafalaya river-influenced area toward the West Florida Shelf. The riverine TA source for the coastal region near the West Florida Shelf was a composite of multiple local inputs that were highly modulated by both along-shore and offshore currents, and therefore exhibited larger sub-annual and inter-annual variations.