Spatial variations of particle scavenging rates within the central and northern Adriatic Sea: use of U--Th disequilibria

Conference · Wed Apr 01 04:00:00 EST 1998

OSTI ID:664596

Dissolved and particlulate Thorium-234 ({sup 234}Th) were measured in near surface waters from the Central and Northern Adriatic Sea in order to gain an insight into the intensity and variability of active scavenging and particle removal processes. Dissolved {sup 234}Th to Uranium-238 ({sup 238}U) activity ratios vary from 0.21 to 0.75 and clearly imply that {sup 234}Th is being actively scavenged from sea water on a timescale of <3 months. The scavenging rate of dissolved {sup 234}Th with respect to scavenging onto particles appears to correlate with primary productivity measurements. Scavenging and rapid removal of particulate {sup 234}Th from the water column is best explained by a mechanism of zooplankton grazing and fecal pellet production. At one sight in the Jabuka Pit, particulate {sup 234}Th residence times below the pycnocline are long (30-40 days) suggesting that particles are being more readily recycled at these depths. By comparison, in a seawater profile collected near the Po outflow region, {sup 234}Th is depleted with respect to {sup 238}U through the entire water column. We conclude from this assessment that particles in waters near the Po River outflow will be more efficiently transported to bottom sediments compared with those in deeper waters over the Jabuka Pit.

• Research Organization: Lawrence Livermore National Lab., CA (United States)
• Sponsoring Organization: USDOE Assistant Secretary for Environment, Safety, and Health, Washington, DC (United States)
• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 664596
• Report Number(s): UCRL-JC--123865-Rev.1; CONF-9604130--; ON: DE98057885; BR: HD2006400
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
ADRIATIC SEA
PARTICULATES
RESIDENCE HALF-TIME
SCAVENGING
SEDIMENTS
THORIUM 234
URANIUM 238