Oceanic–atmospheric modes of variability and their influence on riverine input to coastal Louisiana and Mississippi

The present study examined the individual and combined influences of four oceanic–atmospheric modes of variability on northcentral Gulf of Mexico streamflows. Mississippi River and Pascagoula River mean flows, between phases of long-term modes of variability, were compared using a nonparametric rank-sum test (Mann–Whitney U-test). While the combination of Pacific Decadal Oscillation (PDO), Atlantic Multidecadal Oscillation (AMO), and North Atlantic Oscillation (NAO) determined long-term Mississippi River regimes, the coupling of AMO and NAO determined long-lasting Pascagoula River flow regimes. Mississippi River flow was higher during PDO warm, AMO cold (AMOc), and NAO positive (NAOp) phases than during PDO cold, AMO warm (AMOw), and NAO negative (NAOn) phases. Pascagoula River flow was higher during AMOc and NAOp phases than during AMOw and NAOn phases. During the long-term low Pascagoula River flow regime (AMOw/NAOn phase), fluctuations in river flow were associated with PDO or El Niño Southern Oscillation (ENSO). Pascagoula River flow decreased from PDOw to PDOc phases and from ENSO warm to ENSO neutral to ENSO cold phases.