HR: 14:15h
AN: OS53B-02    [Abstracts]
TI: Depth Profiles of Stable Nitrogen and Carbon Isotopes and C:N Ratios in Surficial Sediments From the NW Insular Slope of Cuba.
AU: * Soto, L A
EM: lasg@mar.icmyl.unam.mx
AF: Luis A. Soto, Instituto de Ciencias del Mar y Limnología, Universidad Nacional Autónoma de México, Ciudad Universitaria, México, DF 04510, Mexico
AU: de la Lanza, G
EM: gdlle@servidor.unam.mx
AF: Guadalupe de la Lanza, Instituto de Biología, Universidad Nacional Autónoma de México, Ciudad Universitaria, México, DF 04510, Mexico
AU: López-Veneroni, D
EM: dglopez@imp.mx
AF: Diego López-Veneroni, Instituto Mexicano del Petróleo, Eje Central 252 Edificio 24- 111, México, DF 07730, Mexico
AB: The deep sea floor in the studied area remained unexplored for several decades. Recent searching for fossil fuels and gas hydrates in the seabed has renewed interest in studying deep sea processes in the region. Near- surface sediments were recovered with a Reineick box-corer at 3 preselected quadrants located at the channel axis of the Florida Straits and the slope rise off NW Cuba at depths ranging from 1468 to 2094 m. A total of 12- 30 cm long- subcores were sampled for isotopic (¹⁵N/¹⁴N and ¹³C/¹²C) and C:N ratio analyses. Surficial sediment samples exhibited mostly enriched δ¹⁵N values ranging from +3.6 to +6.4‰ with an average of +5.4 ± 0.7. δ¹⁵N values in the deeper quadrants (I and II) near the channel axis were fairly homogeneous in contrast to the shallower one (III) located at the slope rise, which showed a higher variability and significantly depleted values (+3.6‰). Testing of equality of δ¹⁵N values among quadrants was rejected (Friedman's test p<0.368. From the estimated δ¹⁵N average value here recorded a significant input of organic matter from a pelagic source is inferred. The δ¹³C values had a narrow range in all quadrants (-18.5 to -19.13‰) with an average of - 18.71±0.17. A gradient slightly enriched is noted on the seabed from the westernmost quadrants(I and II)towards the slope rise (quadrant III). The average δ¹³C signal in surficial sediments from the Southern Straits approaches that known for the continental shelf of South Florida (-18.5±0.7). Vertical profiles of TOC and TN are highly heterogeneous among quadrants displaying a diminishing trend with depth (0- 18 cm). TOC values are mostly impoverished ranging from 0.16 to 0.67 mmol/g. Slope rise sites concentrated less TOC than locations near the channel axis. The opposite occurred with TN values. Sites near the slope rise attained 0.90 mmol/g whereas in the channel axis, nitrogen was reduced to 0.46mmol/g. C:N ratios ranged from 1.9 to 10.2. An increasing gradient was noted from quadrants located at the channel axis towards the slope rise. The mean molar C:N ratio (5.4) is indicative of marine hemipelagic deposition. δ¹³C vertical profiles indicate episodic OC inputs at 3, 10, and 20 cm. Assuming a conservative sedimentary rate of 2.8 cm/k, such a OC input may have been buried 1000, 3600, and 6200 yr between carbonate layers. Sedimentary organic matter impoverishment in the three quadrants is further supported by the low C and N percentages (0.03-0.15% C; 0.0004-0.005% N). It is postulated that the hydrodynamic conditions may exert an important influence on the vertical and advective fluxes of particulate organic material (POC) which are trapped at the mix layer (700 m) in the Straits, reducing the input of nutrients to bottom dweller communities.
DE: 0400 BIOGEOSCIENCES
DE: 0408 Benthic processes (4804)
DE: 0428 Carbon cycling (4806)
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 0469 Nitrogen cycling
SC: Ocean Sciences [OS]
MN: 2007 Joint Assembly