The impacts of El Niño-Southern Oscillation (ENSO) on salinity and alkalinity in an equatorial coral reef lagoon (Kanton) are investigated using water samples collected in 1973, 2012, 2015, and 2018. A simple advective-diffusive model is developed to aid in the interpretation of the sparse observations and make estimates of net ecosystem calcification (NEC) rates. Salinity and alkalinity variations in Kanton lagoon are primarily driven by ENSO variations in precipitation. During non-El Niño years (1973, 2012, 2018), salinity increases from the ocean (35.5 psu) to the back of the lagoon (38 psu) because evaporation exceeds precipitation and water resides in the back of the lagoon for ~180 days. At the onset of the 2015-16 El Niño the back of the lagoon is only ~1 psu saltier than the ocean because precipitation had begun to exceed evaporation. The model suggests that during El Niños, when precipitation exceeds evaporation, the back of the lagoon is less salty than the ocean (30 – 32 psu). Alkalinity variations in the lagoon are primarily due to dilution or concentration driven by the ENSO variations in precipitation and NEC that causes an alkalinity deficit of ~250 micromoles/kg in the back of the lagoon. NEC rates in the early stages of the 2015 – 2016 El Niño were ~10% lower (4.7 mmol/day) than in the non-El Niño years (5.2 – 5. 5 mmol/day). The NEC rates and coral cover indicate that Kanton Lagoon has recovered from the complete loss of coral cover during the 2002-03 El Niño.

Analysis of forty years of tide gauge data and reanalysis wind stresses from the Middle Atlantic Bight indicate that along-shelf wind stresses are a dominant driver of coastal dynamic sea level (sea level plus atmospheric pressure) variability at daily to yearly time scales. The sea-level response to along-shelf wind stress varies substantially along the coast and is accurately reproduced by a steady, barotropic, depth-averaged model (Csanady 1978, Arrested Topographic Wave). The model indicates that the sea-level response in the MAB depends primarily on the along-shelf distribution of the along-shelf wind stress, the Coriolis frequency, the bottom drag coefficient, and the cross-shelf bottom slope. The along-shelf wind stress varies along the MAB shelf due primarily to changes in the shelf orientation. The sea-level response depends on both the local and upstream (in the sense of Kelvin wave propagation) along-shelf wind stresses. Consequently, sea-level variability at daily, monthly and yearly time scales along much of the central MAB coast is more strongly driven by upstream winds along the southern New England shelf than by local winds along the central MAB shelf. The residual coastal sea-level variability, after removing the wind-driven response and the trend, is roughly uniform along the MAB coast. The along-coast average of the residual sea level at monthly and yearly time scales is caused by variations in shelf water densities primarily associated with the large annual cycle in water temperature and interannual variations in salinity.