Terrestrially derived dissolved organic matter in the Chesapeake Bay and the Middle Atlantic Blight

Concentrations of lignin-phenols were analyzed in high molecular weight dis solved organic matter (0.2 mu m > HMW DOM > 1 kDa) isolated from surface wa ters of the Chesapeake Bay (C. Bay), and surface and bottom waters of the M iddle Atlantic Eight (MAB). The abundance of lignin-phenols in HMW DOM was higher in the C. Bay (0.128 +/- 0.06 mu g L-1) compared to MAB surface wate rs (0.016 +/- 0.004 mu g L-1) and MAB bottom waters (0.005 +/- 0.003 mu g L -1). On an organic carbon-normalized basis, lignin-phenol abundances in the HMW DOM (i.e., Lambda(6)), were significantly higher (p < 0.05) in bottom waters compared to sediments at some stations in the MAB. Ratios of syringy l to vanillyl phenols (SN) in HMW DOM, indicative of angiosperm-derived lig nin, ranged from 0.165 to 0.422 in C. Bay, 0.100 to 0.314 in MAB surface wa ters, and 0.076 to 0.357 in MAB bottom waters. Ratios of vanillic acid to v anillin (Ad/Al)(V) in HMW DOM, indicative of lignin decay, ranged from 0.61 1 to 1.37 in C. Bay, 0.534 to 2.62 in MAB surface waters, and 0.435 to 1.96 in MAB bottom water. Ratios of SN and (Ad/Al), showed no significant diffe rences between each environment, providing no evidence of any compositional ly distinct input of terrestrial organic matter into each environment. When considering depth profiles of suspended particulate matter in the MAB, wit h C:N ratios, and bulk radiocarbon ages and stable carbon isotopic values i n HMW DOM isolated from these areas, two scenarios present themselves regar ding the sources and transport of terrestrially derived HMW DOM in the MAB. Scenario #1 assumes that a low amount of refractory terrestrial organic ma tter and old DOC are uniformly distributed in the oceans, both in surface a nd bottom waters, and that primary production in surface waters increases D OC with low lignin and younger DOC which degrades easily. In this case, man y of the trends in age and biomarker composition likely reflect general pat terns of Atlantic Ocean surface and bottom water circulation in the area of the MAB. Scenario 2 assumes terrestrial organic matter in bottom waters of the MAB may have originated from weathered shelf and slope sediments in ne arshore areas via a combination of mechanisms (e.g., diffusion, recent resu spension events, and/or desorption of DOM from riverine POM buried deep in these sites) and entered bottom waters offshore in the MAB by diffusion alo ng isopycnal surfaces. These results complement recent work which proposes that transport of DOM across continental shelves may be a significant sourc e of "old" organic matter to the deep ocean. Copyright (C) 2000 Elsevier Sc ience Ltd.