Beryllium-7 is a cosmic-ray-produced radioactive nuclide (half-life 53.3 days) that is deposited upon the ocean surface by rainfall. Beryllium-7 profiles were collected and analyzed in May 1991 and March 1992 as part of the ONR SUBDUCTION program. The 7Be activities were homogeneous in the mixed layer and ranged approximately from 100 to 200 dpm/1000 l. The activities dropped off rapidly in the upper thermocline. The 7Be profiles were modeled using a simple seasonal progression of mixed-layer depth, indicating that seasonal changes in the mixed-layer depth control the main features of the profile. The observed temperature, salinity and 7Be profiles from the May 1991 cruise show warm salinity maxima associated with a layer of high 7Be penetrating into the upper seasonal thermocline. The high 7Be concentration suggests that these waters were in relatively thin mixed layers within, approximately, the past month. The model results indicate that in late spring both salinity and 7Be can respond to a shoaling mixed layer on a similar timescale leading to the observed anomalies in the subducted water layer.
|Original language||English (US)|
|Number of pages||28|
|Journal||Deep-Sea Research Part I: Oceanographic Research Papers|
|State||Published - Feb 1996|
ASJC Scopus subject areas
- Aquatic Science