The continental shelf of Cádiz (SW Spain) has an average width of 40 km, the slope dropping away sharply from a depth of between 150 and 200 m., and receives inputs of particulate matter from the numerous riverine systems located within the Gulf of Cádiz. Sediment cores were collected in two different areas, the Guadalquivir River mouth and the Bay of Cádiz, in order to study sediment accumulation. For this purpose, 210Pb activity profiles were determined in sediment sections by means of gamma spectrometry. Sedimentation rates are 0.01 g yr-1 in Cádiz Bay cores, and varies from 0.09 to 0.11 g yr-1 in cores from the Guadalquivir area. Mass accumulation rates showed a high degree of variability in the Bay of Cádiz when compared to values found in the Guadalquivir area (0.01 – 0.21 and 0.080 and 0.084 g cm-2 yr-1, respectively). These rates fall within ranges reported for several continental shelves and margins, like the northern Iberian margin (0.13–0.50 cm yr-1), the Barcelona continental margin (0.07 – 0.297 cm yr-1 and 0.062 – 0.51 g cm-2 yr-1), the Bay of Biscay (0.04 - > 1.1 cm yr-1 and 0.27 – 0.7 g cm-2 yr-1), and the Gulf of Lions (0.030 – 0.133 cm yr-1 and 0.022 – 0.124 g cm-2 yr-1). The modern sedimentation rates ascertained from 210Pb profiles in this work are consistent with Late Quaternary 14C rates determined in the Gulf of Cádiz continental margin (0.011 – 0.23 cm yr-1), and last century 210Pb sedimentation rates of continental shelf south of Tinto-Odiel estuary (0.08 0.16 cm yr-1). Surface 210Pbxs values range widely from 30.8 to 118 Bq kg-1 on the Cádiz Bay area, and increase up to 147 Bq kg-1 on the Guadalquivir area. Excess 210Pb inventories in the continental shelf of Cádiz are higher in cores taken at depths between 18 and 32 m. The lowest value was recorded in Cádiz Bay area at a depth of 13 m. Overall, sediment 210Pbxs inventory is only a minimum value as 210Pbxs still presents high excesses at the base of the cores in both areas. A general trend can be observed by which surface activity and inventory increase as water column depth increase, according to the findings in the continental shelf of Santa Monica and that of Barcellona.
Sediment accumulation rates in the continental shelf of Cádiz (SW Iberian Peninsula)
GUERRA, ROBERTA;RIGHI, SERENA;
2010
Abstract
The continental shelf of Cádiz (SW Spain) has an average width of 40 km, the slope dropping away sharply from a depth of between 150 and 200 m., and receives inputs of particulate matter from the numerous riverine systems located within the Gulf of Cádiz. Sediment cores were collected in two different areas, the Guadalquivir River mouth and the Bay of Cádiz, in order to study sediment accumulation. For this purpose, 210Pb activity profiles were determined in sediment sections by means of gamma spectrometry. Sedimentation rates are 0.01 g yr-1 in Cádiz Bay cores, and varies from 0.09 to 0.11 g yr-1 in cores from the Guadalquivir area. Mass accumulation rates showed a high degree of variability in the Bay of Cádiz when compared to values found in the Guadalquivir area (0.01 – 0.21 and 0.080 and 0.084 g cm-2 yr-1, respectively). These rates fall within ranges reported for several continental shelves and margins, like the northern Iberian margin (0.13–0.50 cm yr-1), the Barcelona continental margin (0.07 – 0.297 cm yr-1 and 0.062 – 0.51 g cm-2 yr-1), the Bay of Biscay (0.04 - > 1.1 cm yr-1 and 0.27 – 0.7 g cm-2 yr-1), and the Gulf of Lions (0.030 – 0.133 cm yr-1 and 0.022 – 0.124 g cm-2 yr-1). The modern sedimentation rates ascertained from 210Pb profiles in this work are consistent with Late Quaternary 14C rates determined in the Gulf of Cádiz continental margin (0.011 – 0.23 cm yr-1), and last century 210Pb sedimentation rates of continental shelf south of Tinto-Odiel estuary (0.08 0.16 cm yr-1). Surface 210Pbxs values range widely from 30.8 to 118 Bq kg-1 on the Cádiz Bay area, and increase up to 147 Bq kg-1 on the Guadalquivir area. Excess 210Pb inventories in the continental shelf of Cádiz are higher in cores taken at depths between 18 and 32 m. The lowest value was recorded in Cádiz Bay area at a depth of 13 m. Overall, sediment 210Pbxs inventory is only a minimum value as 210Pbxs still presents high excesses at the base of the cores in both areas. A general trend can be observed by which surface activity and inventory increase as water column depth increase, according to the findings in the continental shelf of Santa Monica and that of Barcellona.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
