Rates of particle scavenging and particulate organic carbon export estimated using 234Th as a tracer in the subtropical and equatorial Atlantic Ocean Academic Article uri icon


  • The export flux of particulate organic carbon and particle scavenging rates were calculated using a super(234)Th-based approach along a transect through the Mid-Atlantic from 35 degree S to 10 degree N during May and June of 1996. The median residence time of dissolved super(234)Th along the transect was 135 days, with intense scavenging from 5 degree N to 6 degree N (\s?\tau\s?\ sub(d) = 86 plus or minus 17 days). Vertical profiles and depth-integrated samples (surface-100 m) of dissolved (53-\s?\mu\s?\m) super(234)Th activities were collected to estimate export fluxes of particulate organic carbon (POC). A steady-state model of the super(234)Th activity balance in the upper 100 m was combined with measurements of the POC super(234)Th ratio on > 53-\s?\mu\s?\m particles. POC export ranged from 3.2 mmol C m super(2) d super(1) in the central South Atlantic to 43 mmol C m super(2) d super(1) at 2.5 degree S. Export production along the Atlantic equator (5 degree S-5 degree N, 25 degree E-5 degree W) is estimated to be 0.29 Gt C yr super(1). The super(234)Th-derived POC export estimates reported here and from other studies are comparable with model simulations of export production from the Princeton General Circulation Model (GCM) for the Atlantic Ocean.

publication date

  • May 1999