Studies of nitrogen and phosphorus dynamics in the oligotrophic surface waters of the western North Atlantic Ocean have been constrained because ambient concentrations are typically at or below the detection limits of standard colorometric methods, except during periods of deep vertical mixing. Here we report the application of high-sensitivity analytical methods — determinations of nitrate plus nitrite (N + N) by chemiluminescence and soluble reactive phosphorus (SRP) by the magnesium induced co-precipitation (MAGIC) protocol — to surface waters along a transect from the Sargasso Sea at 26^oN through the Gulf Stream at 37^oN, including sampling at the JGOFS Bermuda Atlantic Time-series Study (BATS) station. The results were compared with data from the BATS program, and the HOT station in the Pacific Ocean, permitting cross-ecosystem comparisons. Microbial populations were analyzed along the transect, and an attempt was made to interpret their distributions in the context of the measured nutrient concentrations.
     Surface concentrations of N + N and SRP during the March 1998 transect separated into 3 distinct regions, with the boundaries corresponding roughly to the locations of the BATS station (~31^oN) and the Gulf Stream (~31^oN). Although N + N and SRP co-varied, the [N + N]:[SRP] molar ratios increased systematically from ~1 to 10 in the southern segment, remained relatively constant at ~40-50 between 31^oN and 37^oN, then decreased again systematically to ratios ≤ 10% north of the Gulf Stream. Dissolved organic N (DON) and P (DOP) dominated (≥ 90%) the total dissolved N (TDN) and P (TDP) pools except in the northern portion of the transect. The [DON]:[DOP] molar ratios were relatively invariant (~30-60) across the entire transect.

© 2001 Elsevier Science