Data from: Trends and drivers of hypoxic thickness and volume in the Northern Gulf of Mexico: 1985-2018

Hypoxia is a major environmental issue plaguing the commercially and
ecologically important coastal waters of the northern Gulf of Mexico.
Several modeling studies have explored this phenomenon, but primarily
focus on the areal extent of the mid-summer hypoxic zone. Research into
the variability and drivers of hypoxic volume and thickness is also
important in evaluating the seasonal progression of hypoxia and its impact
on coastal resources. In this study, we compile data from multiple
monitoring programs and develop a geospatial model capable of estimating
hypoxic thickness and volume across the summer season. We adopt a
space-time geostatistical framework and introduce a rank-based inverse
normal transformation to simulate more realistic distributions of hypoxic
layer thickness. Our findings indicate that, on average, there is a
seasonal lag in peak hypoxic volume and thickness compared to hypoxic
area. We assess long-term trends in different hypoxia metrics (area,
thickness, and volume), and while most metrics did not exhibit significant
trends, mid-summer hypoxic thickness is found to have increased at a rate
of 5.9 cm/year (p<0.05) over the past three decades. In addition,
spring nitrogen load is found to be the major driver of all hypoxia
metrics, when considered along with other riverine inputs and
meteorological factors in multiple regression models. Hypoxic volume,
which was also often influenced by east-west wind velocities, was found to
be more predictable than hypoxic thickness.