Diagenetic state and source characterization of marine sediments from the inner continental shelf of the Gulf of Cadiz (SW Spain), constrained by terrigenous biomarkers

• Surface sediments from the Gulf of Cadiz (GoC) were analyzed by alkaline CuO oxidation, in order to estimate the contribution of terrigenous organic matter (TOM) to the inner continental shelf of the southwest Iberian Peninsula. The parallel analysis of sediment samples from the two most important rivers draining to this coastal area (i.e. Guadiana River and Tinto-Odiel fluvial system) provided fundamental information regarding local terrestrial sources. Relatively constant intensive lignin parameters (S:V= 1.0 +/- 0.1 and C:V= 0.22 +/- 0.04) and high values of the lignin phenol vegetation index (LPVI = 155 +/- 43) indicated that non-woody angiosperm tissues constitute the dominant component of vascular plant material reaching the shelf sediments. The NW to SE decreasing isotopic (C-13) and molecular (As) signatures found among the sediments, coinciding with the Guadiana delivery plume, suggest that this river is the main terrestrial source in the inner GoC shelf Slightly elevated values of degradation indicative ratios ([Ad:Al](v) = 0.41 +/- 0.10: [Ad:Al])(s)=0.34 +/- 0.07; [3,5-Bd:V]=0.14 +/- 0.05; P:[V + S] = 0.24 +/- 0.09) suggested the alteration state of the shelf sediments. The two fold higher ratios of the river sediments (Guadiana: [Ad:Al](v) = 0.82 +/- 0.08: [Ad:Al](s) = 0.84 +/- 0.03; Tinto-Odiel: [Ad:Al](v) = 0.86 +/- 0.12; [Ad:Al](s) = 0.83 +/- 0.013) and the increasing degradation trend observed outward in the shelf, lead us to consider preferential sorption processes, instead of in situ diagenesis, to affect the degradation signature of the shelf sediments. Preferentially solubilized degraded OM is more likely to be sorbed and stabilized prior to transport to the marine system, showing an apparently more advanced degradation state. The use of the 3,5-Bd:V ratio in conjunction with (Ad:Al)(v) revealed a composition continuum of the sedimentary OM ranging from fresh plant materials to highly altered soil humic constituents. Elemental and molecular analyses show a land to sea gradient by a NW to SE decrease of the terrestrial influence, accounting for larger terrestrial inputs (TOM: 71-98%) in those sediments near the Guadiana mouth, and predominantly autochthonous composition (TOM: 42-50%) in those located offshore. This work utilizes lignin derived biomarkers to determine the contribution of terrigenous OM delivered to this poorly described coastal area from regional rivers. Within a context of increasing international efforts to better understand the global C cycling, this study illustrates the relevance of using the alkaline CuO oxidation approach to evaluate C budgets and continental influence in river dominated ocean margins.

Ämnesord

NATURVETENSKAP  -- Kemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences (hsv//eng)

Nyckelord

AMINO-ACIDS

BEAUFORT SHELF

CARBON

GRADIENT

Lead

LIGNIN

NORTHERN GULF

OF-MEXICO

ORGANIC-MATTER

OXIDATION-PRODUCTS

PARTICULATE ORGANIC-MATTER

RIVER

SAMPLES

SEA

Sediment

SEDIMENTS

Soil

SOILS

SORPTION

SURFACE

TRANSPORT

VALUES

Chemistry

Kemi

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