The radiocarbon analyses of bulk organic matter from sinking particles collected as part of the CARIACO Project over the period of November 1996 to October 1998 showed significant seasonal variation in the &delta14C values. The &delta14C of organic matter (&delta14Corg) ranged from a low of 10.9 ‰ to a high of 70.3 ‰. Although the &delta14Corg showed little correlation with temperature (r22 = 0.22), the &delta14Corg values were significantly higher (average &delta14Corg = 59.2‰) during periods of upwelling than during non upwelling conditions (average &delta14Corg = 29.3‰), when the water column was highly stratified. The increase in the &delta14Corg compositions during upwelling could be due to a slight subsurface maximum of &delta14Cdic that has been observed outside the Caraico Basin (from WOCE data; no samples have been taken in the Cariaco Basin). The mooring in the Cariaco Basin contains four traps at depths of 275 m (which is above the oxic/anoxic boundary), 455, 930 and 1255m (which within an anoxic water column). One vertical profile of &delta14Corg values was measured during the start of the 1996-1997 upwelling season. &delta14Corg values ranged from 20.5 ‰ in the uppermost trap to a high of 38.3 ‰ in the 455m trap, decreasing to a value of 9.1 ‰ at a the deepest trap (1255m). Further profiles need to be analyzed to see if this subsurface maximum in &delta14Corg values is a permanent feature in the sediment trap samples or a signal of a transient event.
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