A reassessment of the sources and importance of land-anic matter in surface sediments from the Gulf of Mexico.pdf

Geochimica et Cosmochimica Acta, Vol. 62, No. 18, pp. 3055–3075, 1998
Copyright © 1998 Elsevier Science Ltd
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PII S0016-7037(98)00217-8
A reassessment of the sources and importance of land-anic matter in surface
sediments from the Gulf of Mexico
1, 2 2
MIGUEL A. GONI˜, *KATHLEEN C. RUTTENBERG, and TIMOTHY I. EGLINTON
1Department of Geological Sciences, University of South Carolina, Columbia, South Carolina 29208, USA
2Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution,
Woods Hole, Massachusetts 02543, USA
(Received November 12, 1997; accepted in revised form June 8, 1998)
anic matter in surface sediments from two onshore-offshore transects in the northwestern Gulf
of Mexico was characterized by a variety of techniques, including elemental, stable carbon, radiocarbon, and
molecular-level analyses. In spite of the importance of the Mississippi River as a sediment source, there is little
evidence for a significant terrigenous input based on the low carbon:nitrogen ratios (8–5) and the enriched
␦13C values of bulk anic carbon (‰ to ‰). Radiocarbon analyses, on the other
hand, yield depleted ⌬14C values (Ϫ277‰ to Ϫ572‰) which indicate that a significant fraction of the
anic carbon (OC) in all these surface sediments must be relatively old and most likely of
allochthonous origin. CuO oxidations yield relatively low quantities of lignin products (– mg/100 mg
OC) along pounds derived from proteins, harides, and lipids. Syringyl:vanillyl and cin-
namyl:vanillyl ratios (averaging and , respectively) and acid:aldehyde ratios for both vanillyl and
syringyl phenols (averaging and , respectively) indicate that the lignin present in sediments originates
from nonwoody angiosperm sources and is highly degraded. The ␦13C values of lignin phenols in shelf
sediments are relatively depleted in 13C (averag