Premium
Role of colloids in upper ocean biogeochemistry in the northeast Pacific Ocean elucidated from 238U‐234Th disequilibria
Author(s) -
-An Huh Chih,
Prahl Fredrick G.
Publication year - 1995
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.1995.40.3.0528
Subject(s) - photic zone , phytoplankton , thermocline , particulates , biogeochemistry , oceanography , water column , chlorophyll a , colloid , environmental chemistry , scavenging , seawater , biogeochemical cycle , geology , deep sea , environmental science , chemistry , mineralogy , nutrient , biochemistry , organic chemistry , antioxidant
Detailed upper ocean profiles of 234 Th in dissolved (<10,000 Daltons), colloidal (10,000 Da–0.45 µ m), and particulate (>0.45 µ m) forms were measured at a station (46°45′N, 126°W) in the northeast Pacific Ocean. On average, dissolved, colloidal, and particulate 234 Th accounted for ∼78, 12, and 10% of the total 234 Th in the euphotic zone (0–100 m). A highly positive correlation exists between colloidal 234 Th and chlorophyll a; both are characterized by higher concentrations in surface waters, a subsurface maximum at 55 m in the seasonal thermocline, and undetectable levels below the euphotic zone. POC: Chl a ratios in the water column suggest phytoplankton as primary producers of the colloidal material. Scavenging residence times of dissolved, colloidal, and particulate 234 Th with respect to their removal processes in the euphotic zone are ∼50, 6, and 8 d. The scavenging rate constant of Th apparently increases with the concentration of colloids.