Variability in pigment concentration in warm‐core rings as determined by coastal zone color scanner satellite imagery from the Mid‐Atlantic Bight

Abstract

A time series of coastal zone color scanner (CZCS) derived chlorophyll (CZCS‐chl) and sea surface temperature (SST) satellite imagery was developed for the Mid‐Atlantic Bight (MAB). Warm‐core rings (WCR) were identified by both the warmer SST signal as well as the low pigment concentrations of their cores. The variation in pigment concentrations and SST observed in satellite imagery over the geographic range and life span of four WCRs is investigated. The hypotheses are that pigment concentration increase during the lifetime of the WCR is a response to processes such as convective overturn, upwelling, edge enhancement due to increased vertical mixing, active convergence, or lateral exchange. Empirical orthogonal function analysis (EOF) is used to investigate the relationship between SST and pigment patterns observed in the presence of a WCR. The first two EOF modes explain more than 80% of the variability observed in all four WCRs and in both (SST and pigment) data sets. Temperature and pigment data from a sampling quadrat, 100 × 100 pixels in size and centered on each of the four WCRs (81F, 82B, 82J, and 83E), were extracted from 41 matching pairs of images. The sampling quadrat was moved along the MAB, tracking temperature and pigment concentration in and around the WCRs. The two data sets covary, as shown by the eigenmaps, for same day images when advection of water from the productive shelf region is the source of the variability observed in the CZCS. Advection, determined to be the principal cause of the variability observed, is seen in the imagery as occurring through the north, northeast, southeast, and northwest sides of the rings. Eigenmaps show that the spatial distribution and source of the variability (e.g., shelf/slope or Gulf Stream) was not the same for all four rings examined. The results of this study show that, at the synoptic scales of satellite data, the variability observed in the WCRs is greater at the periphery of the rings. These results show that advective entrainment, rather than processes at ring center (e.g., shoaling of the pycnocline/nutricline in response to frictional decay) or at the periphery due to other processes such as vertical mixing, is the mechanism responsible for the observed variability.