Physical processes controlling chlorophyll-a variability on the Mid-Atlantic Bight along northeast United States

Abstract

We employed empirical orthogonal function (EOF) analysis to examine the spatial and temporal pattern changes in the surface chlorophyll a distribution (chl-a) on the Mid-Atlantic Bight (MAB) using Moderate Resolution Imaging Spectroradiometer Aqua (MODISA) chl-a data (2003–2016) and Sea-viewing Wide Field-of-view Sensor (SeaWiFS) chl-a data (1998–2007), and interpreted the underlying environmental determinants. A coupled physical-biogeochemical model was used to explore the primary physical factors determining the chl-a variability on the shelf. Model sensitivity studies identified wind mixing, net heat flux, and river discharge as the dominant factors influencing the MAB water column stability and consequent phytoplankton growth. The primary feature of chl-a indicated spring peaks on the outer shelf during the MODISA period, while fall-winter high during the SeaWiFS period in the same area. The observed increase in wind mixing and heat loss during winter and pre-spring were responsible for the delay in the phytoplankton bloom to spring on the outer shelf. The secondary chl-a peak occurred in the fall on the New Jersey shelf during MODISA period, and in the fall-winter in the Delaware Bay estuary for chl-a during SeaWiFS period. The Hudson River discharge was associated with the chl-a anomalies on the New Jersey shelf in the fall and winter during the MODISA period. Both the MODISA and SeaWiFS chl-a concentrations peaked during the fall-winter on the southern part of the MAB (in the EOF mode 3 region), but the MODISA chl-a peak area was north of the SeaWiFS chl-a peak area. The variation of chl-a concentration in the southern region of the MAB was most likely associated with the Chesapeake Bay rivers' discharge. In our study, the regional associations between chl-a and multiple climate-sensitive environmental parameters suggest that basin-scale forcing plays an important role in the underlying chl-a variabilities on the MAB. • The MAB outer shelf experienced more spring chl-a peaks during the MODISA period. • There are high chl-a concentrations in fall-winter during the SeaWiFS period in the outer shelf. • Wind, net heat flux, and river discharge influenced the potential energy anomaly on the MAB. • The outer shelf chl-a patterns were associated with wind mixing and net heat flux. • The inner shelf chl-a patterns were associated with river discharges.