The cores were collected in 1996 from the main channel in the mesohaline part of the bay, near the mouth of the Potomac River and between the Patuxent River and Annapolis. Early results suggest significant periods of seasonal anoxic conditions in the northern part of the Bay between about 1200 and 1500 A.D., as well as increasing overall oxygen depletion since approximately 1700.
Nitrogen isotope profiles from the two cores are broadly similar.
Values become heavier toward the top of the core, peaking at 8.4 permil at a depth of 20 cm. The northern upstream core has a similar 15N profile offset by -1 permil from the southern core profile. Trends of V, Zn, Cr, Ni, and Cu concentrations in the cores are consistent with those of nitrogen isotopes. Higher solid phase concentrations of these metals indicate reducing conditions in the water column and shallow sediments that develop during longer and more intense summer anoxic periods. Vanadium, zinc, and chromium in particular are elevated and fluctuate between 1200 and 1500 A.D. and increase after 1700.