* Corresponding author. Tel.: #1-858-822-0591; fax: #1-858-822-3310. E-mail address: mtryon@ucsd.edu (M. Tryon). Deep-Sea Research I 48 (2001) 2121} 2146 Instruments and methods A new benthic aqueous #ux meter for very low to moderate discharge rates Michael Tryon*, Kevin Brown, LeRoy Dorman, Allan Sauter ScrippsInstitutionofOceanography,UniversityofCalifornia,SanDiego,9500GilmanDrive,LaJolla,CA,92093-0244,USA Received 14 August 2000; accepted 1 November 2000 Abstract Signi"cant quantities of #uids and dissolved geochemical components are expelled through the sediment surface in ocean margin and sedimented ridge environments. Recently, signi"cant interest has been generated in constraining hydrological processes in these environments, but direct measurement of #uid #ow in the marine environment has proven to be di$cult and many aspects of marine hydrogeology remain poorly understood. To address the need for a means to make a signi"cant number of direct measurements in a wide range of low to moderate #ow environments, we have developed a new type of benthic aqueous #ux meter that is capable of measuring di!use #uid #ow through the sediment surface on the order of 0.1mmyr}15myr when the #ow is through sediments with permeabilities of less than 10 cm (typical sea#oor sediments). The instrument measures #uid #ow by determining the degree of dilution of a chemical tracer that is injected by an osmotic pump at a known rate into the #uids venting into or out of a collection chamber situated on the sea bed. The pump also withdraws a subsample of this tracer/#uid mix into sample coils allowing a serial record of the #ow rates to be determined. Both upward and downward #ow can be measured and, when #ux rates are high enough to e!ectively #ush the collecting chamber, the instruments also act as geochemical samplers. Three years of laboratory testing and "eld use have constrained the e!ects of (1) temperature, pressure, and deployment duration on osmotic pump performance, (2) disper- sion/di!usion in the sample coils, and (3) de#ection of #ow under a range of sediment permeabilities. Recent deployments on the Kodiak and Cascadia accretionary prisms document the range and capabilities of the instrument in the "eld.  2001 Elsevier Science Ltd. All rights reserved. Keywords: Flow measurement; Fluid #ow; Hydrothermal #ow; Instruments; Seep meter 0967-0637/01/$ - see front matter  2001 Elsevier Science Ltd. All rights reserved. PII:S0967-0637(01)00002-4