Abstract
Vertical profiles of the natural abundances of 15N and 13C in suspended particulate organic materials (POM) were determined together with PON and POC concentrations to the depth of ca 4000 m at five stations in and out of a warm-core ring (WCR). The 15N and 13C profiles showed generally, with one exception for a 15N profile at the northern edge of the ring, the same trend: an increasing abundance of 15N and 13C in the subsurface layer, followed by a decrease with depth. At the northern station, the 15N abundance of PON in the euphotic zone was unexpectedly high (∼20.4‰). PON with high 15N abundance was also observed at 30, 75 and 150 m at the southern periphery of the ring. This was not seen for the 13C of POC. T-S analysis indicated that POM with high 15N content was transported from the northern periphery by the ‘cold streamer’ of the WCR. In the depth zone of 100–500 m, where thermostad appeared in the ring, the 15N of PON increased with depth while the 13C of POC remained constant in the ring; conversely, the 13C of POC decreased with depth while 15N of PON remained constant out of the ring. Temporal variation was noted for the 15N abundance of PON in the thermostad of the WCR, but little variation was observed for the 13C of POC. The spatial and temporal differences between the 15N and the 13C profiles were explained assuming an intensified vertical mixing of the water column in the thermostad of the WCR, and an order of magnitude difference between the abundance of refractory fractions in POC and PON enriched with both 15N and 13C. It is suggested that the POM 15N and 13C isotopie ratios provide complementary information to study particle dynamics in the ocean.
Published Version
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